The effect of nitrogen on Cashew in North Queensland

A report for the Rural Industries Research and Development Corporation by Patrick O’Farrell, John Armour and David Reid

February 2000 RIRDC Publication No 00/24 RIRDC Project No DAQ 145A

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© 2000 Rural Industries Research and Development Corporation. All rights reserved. ISBN 0 642 58054 5 ISSN 1440-6845 ‘The effect of nitrogen on cashew in North Queensland’ Publication No. 00/24 Project No. DAQ 145A The views expressed and the conclusions reached in this publication are those of the authors and not necessarily those of persons consulted. RIRDC shall not be responsible in any way whatsoever to any person who relies in whole or in part on the contents of this report. This publication is copyright. However, RIRDC encourages wide dissemination of its research, providing the Corporation is clearly acknowledged. For any other enquiries concerning reproduction, contact the Communications Manager on phone 02 6272 3186. Researcher Contact Details Patrick O’Farrell Queensland Department of Primary Industries PO Box 1054 MAREEBA QLD 4880 Phone: 07 4092 8555 Fax: 07 4092 3593 Email: ofarrep@dpi.qld.gov.au Website: http://www.dpi.qld.gov.au

RIRDC Contact Details Rural Industries Research and Development Corporation Level 1, AMA House 42 Macquarie Street BARTON ACT 2600 PO Box 4776 KINGSTON ACT 2604 Phone: 02 6272 4539 Fax: 02 6272 5877 Email: rirdc@rirdc.gov.au Website: http://www.rirdc.gov.au Published in February 2000 Printed on environmentally friendly paper by Canprint

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Foreword The aim of this project was to develop, by using nitrogen (N) to modify vegetative and reproductive growth, techniques to regulate growth and achieve a phenological growth cycle best correlated with high nut yield for the Australian cashew industry. The level of imports of cashew kernel into Australia and the current shortfall in world production of raw cashew nut indicate that cashew production in Australia has good potential. Extensive land areas with climate suitable for cashew production exist in northern Australia. Countries with processing facilities are willing to either purchase or shell Australian nut-in-shell (NIS) production, providing Australian producers with a range of marketing options: NIS, kernel or valued added sales. Economic NIS yields for cashew have been defined and these will be achieved by a combination of high-yielding varieties and efficient and sustainable crop management practices that support the realisation of genetic potential. These practices relevant to Australia production systems are not well defined. Nitrogen is an important component of crop management programs because of this nutrient’s scope to modify growth and yield. This report describes work undertaken from 1993 to 1997 at Dimbulah, North Queensland, that investigated the effect of N on cashew vegetative and reproductive growth. In conducting this research, methodology and standards for expressing NIS and kernel yield were developed, and nutrient concentration in leachate was monitored. This report, a new addition the RIRDC’s diverse range of over 450 research titles, forms part of our New Plant Products R&D Program which aims to facilitate the development of new industries based on plants or plant products that have commercial potential for Australia. Most of our publications are available for viewing, downloading or purchasing online through our website at www.rirdc.gov.au/pub/cat/contents.html • downloads at www.rirdc.gov.au/reports/Index.htm • purchases at www.rirdc.gov.au/pub/cat/contents.html Peter Core Managing Director Rural Industries Research and Development Corporation

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Acknowledgments The authors gratefully acknowledge and thank: Noel Grundon (CSIRO Land and Water), Sam Blaikie (CSIRO Plant Industry) and Norm Butler (Manager, Cashews Australia) for their advice and assistance in the conduct and interpretation of this work. Staff of Analytical Chemistry, Department of Natural Resources, Mareeba, for soil, leaf and water analyses. Andrew Hinton (QDPI Rural Industry Business Services) for assistance and advice in assessing the economic benefit of the Project technology. Melissa Andresen for tirelessly typing and formatting this report. Peter Shearer Pty Ltd for providing the experimental site and in-kind support for the Project. RIRDC for financial support of the Project. QDPI for institutional and financial support of the Project.

About The Authors Mr PJ O’Farrell is a Senior Experimentalist with the Queensland Horticultural Institute, Department of Primary Industries at Mareeba. He has work in horticultural research and development for over 30 years mainly in banana. Since 1991 he has worked in cashew plant improvement, nitrogen nutrition and general crop agronomy. Dr JD Armour is a Senior Soil Scientist with Analytical Chemistry, Department of Natural Resources at Mareeba. Since 1995 he has collaborated with the DPI cashew research team studying plant nutrition for sustainable high yields. He has 21 years experience in soil chemistry and plant nutrition for a wide range of agricultural systems including bananas, potatoes, peanuts, pastures and tobacco. Mr DJ Reid is a Senior Biometrician with the Queensland Beef Industry Institute, Department of Primary Industries at Rockhampton (formerly at Mareeba 1993–1996). He has worked as a biometrician for 13 years with experience in a range of industries including horticulture, field crops, beef cattle, fisheries and forestry. Since 1993 he has been part of the DPI cashew research team providing advice on statistical design, data analysis and interpretation.

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Contents Foreword .................................................................................................................................. iii Acknowledgments.....................................................................................................................iv About The Authors ...................................................................................................................iv Contents .....................................................................................................................................v Tables.......................................................................................................................................vii Figures.......................................................................................................................................ix Executive Summary ...................................................................................................................x Industry Summary....................................................................................................................xv

1. Introduction ......................................................................................................................1

2. Objectives ..........................................................................................................................2

3. Methodology......................................................................................................................2 3.1 Site description ..........................................................................................................2 3.2 Tree selection and trial design...................................................................................3 3.3 Nitrogen treatments ...................................................................................................5 3.4 Tree management ......................................................................................................6 3.5 Growth and yield data collected................................................................................6 3.6 Chemical analyses of soil ..........................................................................................8 3.7 Chemical analyses of leaves......................................................................................9 3.8 Monitoring nutrient movement in leachate ...............................................................9 3.9 Statistical procedures...............................................................................................10

4. Results..............................................................................................................................10 4.1 Pre-trial soil fertility and tree nutritional status.......................................................10 4.2 Fertility changes 1995 to 1997 ................................................................................11 4.3 Canopy growth and pruning ....................................................................................12 4.4 Shoot and panicle growth ........................................................................................14 4.5 Nut-in-shell (NIS) yield at 9% WC, and kernel yield (at 5% WC).........................18 4.6 Leaf nutrient levels..................................................................................................24 4.7 Nitrogen movement in leachate...............................................................................28

5. Discussion ........................................................................................................................30 5.1 Nut-in-shell and kernel moisture standards and assessment methodology .............30 5.2 Effects of nitrogen on vegetative and reproductive growth ....................................31 5.3 Optimum leaf sampling time...................................................................................32 5.4 Soil fertility and leaching ........................................................................................33 5.5 The ‘ideal’ phenological cycle and a crop management program...........................34

6. Implications.....................................................................................................................38 6.1 Impact of N management practices on the Australian cashew industry..................38 6.2 Benefit-cost analysis of the research expenditure ...................................................38

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7. Recommendations ..........................................................................................................41 7.1 Development of industry standards for NIS/kernel moisture and assessment

methodology............................................................................................................41 7.2 Further work to confirm N effects and to develop a calibration system for N

applications..............................................................................................................41 7.3 Selection of varieties with early season nut drop tendency.....................................42 7.4 Development of fertigation technology...................................................................42 7.5 Development of sophisticated farm management systems......................................42

8. Intellectual Property ......................................................................................................43

9. Communication Strategy ...............................................................................................43

10. Appendices ......................................................................................................................44 Appendix 1. Statistical summaries of descriptors analysed in uniformity trials

in 1993 and 1994. ....................................................................................................44 Appendix 2. Dates of treatment applications from 1995 to 1997. ................................47 Appendix 3. Leaf types sampled and leaf N concentrations from 1995 to 1997. .........48

11. References .......................................................................................................................53

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Tables

Table 3.1 Nitrogen timing treatments of the N timing trial..................................................3

Table 3.2 Tree and yield characteristics measured in the uniformity trials in 1993 and 1994. .....................................................................................................4

Table 3.3 Nitrogen timing treatments of the N rates-by-timing trial. ..................................5

Table 3.4 Nitrogen rates (kg/ha) applied in 1995, 1996 and 1997. ......................................6

Table 4.1 Selected soil chemical properties prior to the commencement of treatments (10.1.95) and after the start of reproductive N applications in 1997 (18.6.97). Data for individual depths are means for all treatments.................................................................................................10

Table 4.2 Nutrient levels in mature pre-floral vegetative flush leaves (MFF) and immature pigmented leaves (IP) sampled prior to the commencement of treatments.............................................................................11

Table 4.3 Nitrogen treatment effects on canopy surface area (m²) from 1994 to 1997. Means not followed by a common letter differ significantly, (P<0.05)..............................................................................................................12

Table 4.4 Nitrogen treatment effects on canopy height and diameter from 1994 to 1997. Means not followed by a common letter differ significantly, (P<0.05)..............................................................................................................13

Table 4.5 Nitrogen treatments effects on dry weight (kg) of pruning removal. Means not followed by a common letter differ significantly, (P<0.05)..............................................................................................................14

Table 4.6 Nitrogen treatment effects on shoot length (mm) of 10 branches. Means are square root transformed with backtransformed means in parenthesis. Means not followed by a common letter differ significantly, (P<0.05)........................................................................................15

Table 4.7 Nitrogen treatment effects on panicle number of 10 branches. Means not followed by a common letter differ significantly, (P<0.05).........................17

Table 4.8 Nitrogen treatment effects on total NIS production. Means not followed by a common letter differ significantly, (P<0.05)...............................18

Table 4.9 Nitrogen treatment effects on commercial NIS production. Means not followed by a common letter differ significantly, (P<0.05).........................19

Table 4.10 Nitrogen treatment effects on panicle growth. Means not followed by a common letter differ significantly, (P<0.05). .............................................20

Table 4.11 Nitrogen treatment effects on tree canopy productivity. Means not followed by a common letter differ significantly, (P<0.05)...............................21

Table 4.12 Distribution (%) of commercial NIS weight across time in the 1995, 1996 and 1997 harvest seasons. Means not followed by a common letter differ significantly, (P<0.05).....................................................................22

Table 4.13 Nitrogen treatment effects on kernel weight and quality. Means not followed by a common letter differ significantly, (P<0.05)...............................23

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Table 4.14 Effect of the largest mature pre-floral vegetative flush leaf (LMFF) and the mature terminal leaf (internal position) (MI) on N concentrations (%) on three sampling dates in 1995. Means not followed by a common letter differ significantly, (P<0.05)...............................25

Table 4.15 Concentrations of non-treatment nutrients in mature external (ME) and largest mature pre-floral vegetative flush (LMFF) leaves from 1995 to 1997.......................................................................................................28

Table 6.1 Canopy productivity and canopy surface area (CSA) data used to define Project benefits. .......................................................................................39

Table 6.2 Potential incremental profit†. .............................................................................39

Table 6.3 Project benefits. ..................................................................................................40

Table 6.4 Annual Project costs ($). ....................................................................................40

Table 6.5 Summary of investment criteria. ........................................................................40

Table A1.1 Statistical summaries of the 10 descriptors for Port Douglas and K160 evaluated by cluster analysis techniques. .................................................44

Table A1.2 Statistical summaries of the 10 descriptors for Port Douglas and K160 trees selected by cluster analysis and subjected to analysis of variance. .............................................................................................................45

Table A1.3: Statistical summaries of the nine descriptors of cv 9/14 (n=30) evaluated by cluster analysis techniques. ...........................................................45

Table A1.4 Statistical summaries of the nine descriptors of cv 9/14 (n=24) for trees selected by cluster analysis and subjected to analysis of variance. .............................................................................................................46

Table A2.1 Dates of treatment applications during vegetative and reproductive growth from 1995 to 1997..................................................................................47

Table A3.1 Availability (3) of leaf types from 1995 to 1997. ..............................................48

Table A3.2 Nitrogen treatment effects on N concentration (%) in largest pigmented leaves (LP) from 1995 to 1997. Means not followed by a common letter differ significantly, (P<0.05)......................................................49

Table A3.3 Nitrogen treatment effects on N concentration (%) in mature external leaves (ME) and largest mature pre-floral vegetative flush leaves (LMFF) in 1995. Means not followed by a common letter differ significantly, (P<0.05). .............................................................................50

Table A3.4 Nitrogen treatment effects on N concentration (%) in mature external leaves (ME) and largest mature pre-floral vegetative flush leaves (LMFF) in 1996. Means not followed by a common letter differ significantly, (P<0.05). .............................................................................51

Table A3.5 Nitrogen treatment effects on N concentration (%) in mature external (ME) and largest mature pre-floral vegetative flush leaves (LMFF) in 1997. Means not followed by a common letter differ significantly, (P<0.05)........................................................................................52

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Figures

Figure 4.1 Phenological development of 100% vegetative (•) and 100% reproductive N (o) timings from 1995 to 1997 and their relationship with temperature and rainfall. Horizontal bars in (a) represent timing of treatment applications. ...................................................................................16

Figure 4.2 Nitrogen concentration in (a) mature external (ME) and (b) largest mature pre-floral vegetative flush (LMFF) leaves for times of N application. Horizontal bars indicate period of treatment application. (σ-100% Veg.; λ-Veg./Rep.; υ-100% Rep.). * Denotes P<0.05........................26

Figure 4.3 Nitrogen concentration in (a) mature external (ME) and (b) largest mature pre-floral vegetative flush (LMFF) leaves for rate of N application. (υ-low; λ-medium; σ-high). * Denotes P<0.05..............................27

Figure 4.4 (a) Leachate nitrate-N concentrations. (υ-Medium. Veg./Rep.; λ-Medium Veg.; σ-inter-row) and (b) precipitation under cashew trees in 1997................................................................................................................29

Figure 5.1 A crop management program based on the ‘ideal’ phenological cycle of cv 9/14 in the Dimbulah area of North Queensland. .......................................37

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Executive Summary Introduction Cashew is a tropical evergreen tree species valued for its nutritious kernel which is consumed either raw or in processed products. Cashew nut-in-shell (NIS) production, in terms of world production of edible nuts, ranks third at about 700 000 t. Based on current international and domestic demand for cashew kernel considerable potential exists for expanding the Australian cashew industry beyond its current size of 300 ha. Australia imported almost 5000 t of cashew kernel in 1995, valued at AUD33.4 million. About 4000 ha are required to supply the Australian market, and it is reasonable to expect that an efficient industry would be interested in supplying export markets. Climate and land with adequate water supply do not limit expansion. Countries with processing facilities are willing to either purchase or shell Australian NIS production providing Australian producers a range of marketing options: NIS, kernel or valued added sales. Economic NIS yields of 2.8–5 t/ha have been defined. High-yielding varieties as well as efficient and sustainable crop management practices will be required to achieve these yield levels. However, crop management practices are not highly developed in Australia or overseas. Nitrogen (N) fertilisation is an important component of crop management programs. Because of the dramatic impact of N on plant growth, N management offers possibilities for achieving desirable growth and nut production responses. This report describes work undertaken from 1993 to 1997 at Dimbulah, North Queensland, that investigated the effect of N on cashew vegetative and reproductive growth. In conducting this research, methodology and standards for expressing NIS and kernel yield were developed, and nutrient concentration in leachate was monitored. Objectives The objective of the Project was to gain, by using N to modify vegetative and reproductive growth, understandings of the relationship between shoot, floral and nut development to develop techniques to regulate growth and achieve a phenological growth cycle (the ‘ideal’ cycle) best correlated with high nut yield. From this work it was intended to define: 1. A phenological cycle and aspects of vegetative and reproductive growth best correlated

with high nut yield; 2. The influence of N on vegetative and reproductive growth; and 3. Tree N assessment procedures based on leaf analysis to guide N applications to achieve

the ‘ideal’ phenological cycle. The practical benefits for the cashew industry anticipated from this work were: 1. An annual crop management program based on the ‘ideal’ phenological cycle for the

Dimbulah region; 2. Nitrogen application recommendations that promote the ‘ideal’ phenological cycle; and 3. Procedures for assessing tree N requirement (an index leaf, leaf sampling time and leaf N

standards) to achieve the ‘ideal’ phenological cycle.

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Methodology The project objectives were achieved through a trial in which N was applied at two rates and at three times during the phenological cycle. The times were, 100% of the annual rate applied during the vegetative growth phase (100% Veg.) viz December–April, 100% during the reproductive growth phase (100% Rep.) viz June–October, and 50% during each phase (Veg./Rep.). Nitrogen treatments were designed to modify vegetative and reproductive growth to provide understandings of the relationship between these growth phases and nut production. The trial utilised 24 cv 9/14 trees which were three and one-half years old when the trial was started in 1995. Results and Outcomes Nut-in-shell/kernel moisture standards and assessment procedures. We recommend that NIS and kernel yield and kernel recovery be stated at standard water contents (WC). This is convention in other crop research (macadamia, peanuts, grain) where, like cashew, product moisture influences product weight. We recommend the following standard water contents: NIS at 9%, kernel at 5% and kernel recovery based on NIS and kernel weight at their respective moisture contents. Further, for the cultivar under study we established standards for defining commercial and non-commercial NIS yield. A minimum commercial nut weight (3.03 g at 9% WC) was defined, derived in part from the smallest kernel weight defined by the International Organisation for Standardisation (ISO) for raw kernel trade. While nuts below this standard yield kernels that are defined as too small for raw kernel sale, they may have use in value added products. The kernel yield of non-commercial nut was not assessed in this study. Research workers in Australia have not previously addressed these aspects of cashew research methodology. Nitrogen effects on vegetative and reproductive growth. In two out of the three years of the study commercial NIS and kernel yield was greatest and the proportion of nut drop by November highest in treatments receiving N during the vegetative growth phase. The high N 100% Veg. timing produced the highest commercial NIS yield in 1996 (15.2 kg/tree) and 1997 (11.5 kg/tree). As a result, our recommended minimum N rates are 120 kg/ha for four-year-old trees and 180 kg/ha for five and six-year-old trees. Higher rates of N may further increase NIS yield but may reduce mean nut weight. The use of higher N rates will thus be a compromise between NIS yield, mean nut weight and possible excessive canopy growth. Improved levels of nut drop by November (the recommended time for the completion of nut drop because of possible crop loss from monsoon rain after this month) in treatments receiving N during the vegetative growth phase, was due to higher levels of pre-July shoot and panicle growth. Optimum leaf sampling time. Two index leaves were identified for assessing tree nutritional status, a mature terminal leaf from a quiescent vegetative shoot (ME) and the largest mature pre-floral vegetative flush leaf of a floral shoot (LMFF). Each is of value for commercial use being easily recognisable, predicably available and displaying sensitivity to N application over their periods of availability.

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Assessment of tree nutritional status could be done twice a year using ME leaves in early winter (April–May) before floral development and LMFF leaves (November–December) before the vegetative growth season. Nitrogen application during the vegetative growth phase was shown in this study to be important for NIS and kernel yield and timing of nut drop and therefore the pre-vegetative assessment would be the more important of the two assessment times. Further, attempts to correct N deficiency following the pre-floral assessment would risk post-November nut drop. The pre-floral assessment should be used as a check that N concentrations are adequate and to make small adjustments to N level if necessary. Based on the range of leaf N concentrations recorded for the high N rate 100% Veg. timing, ‘optimum’ levels for ME and LMFF leaves are 2.26 to 2.34% and 1.35 to 1.82%, respectively. Optimum concentrations in LMFF leaves indicate that the normal N application regime should be applied during the vegetative growth period. If however, N concentration were lower than the optimum, additional N to the normal regime would be applied. Soil fertility and leaching. We have assessed the potential environmental consequences of the fertiliser treatments on sustainable long-term nut production. High nitrate concentrations in leachate (up to 128 mg N/L) at a depth of 1 m were recorded during periods of high precipitation. This, and the low soil N recorded in June and July (subsequent to the monsoon season), demonstrates the challenge of keeping N within the tree’s root zone. Nitrogen treatments were applied in five equal applications to provide maximum opportunity for uptake of N by the root system and minimal opportunity for leaching during heavy rainfall. This application strategy would not be viable in a commercial operation because of the high application costs. The application of N by fertigation is a cost-effective alternative as frequent and very precise applications can be made. Nitrate data as well as that of other nutrients (e.g. K, Ca, Mg) require further interpretation and the modelling of water movement. This information will be readily transferable as generic information for tree crops on well-drained soils. The ‘ideal’ phenological cycle and a crop management program. The timing of N application can influence the phenological development of cashew at Dimbulah. Two contrasting growth patterns were observed in two of the three years of the study. In 1995 and 1996 vegetative N applications (December–April) promoted higher levels of pre-July shoot and panicle development and nut drop by November compared with when 100% of the annual N was applied during the reproductive phase (June–October). The latter N timing resulted in higher levels of post-November nut drop, 47% of the commercial NIS weight in 1995 and 24% in 1996. Completion of nut drop by the end of November in the Dimbulah area is an important criterion by which the suitability of a particular phenological cycle for this area is judged. A cycle based on N applied entirely during the vegetative growth phase is therefore accepted as the ‘ideal’ for this area. The important cultural operations (e.g. nutrition, irrigation, insect and weed control) were superimposed on the cycle.

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Implications The impact of the Project’s outcomes on the Australian cashew industry was assessed. In 1998 Cashews Australia implemented N timing recommendations from this study. This followed a complete crop loss (96 t NIS valued at $167 000) in the previous year due in part to ill-timed N application. A total NIS yield for the farm of 150 t and valued at $261 000 was harvested in 1998. Harvesting was completed in December and the total harvest was estimated at 95% of the potential crop. The benefit:cost ratio of the Project benefits was conservatively calculated at 4.7, that is, for every dollar invested in the Project there is expected to be $4.70 worth of benefits to industry. The analysis was based on the existing planted area (300 ha) and it was assumed that over the term of this analysis, 1998 to 2017, the area would remain unchanged. This is unlikely to be the case. Given the potential for cashew production in Australia, expansion of the current area by current and new investors is a strong possibility. Recommendations A number of recommendations to further develop the outcomes of this Project are outlined below. Development of industry standards for NIS/kernel moisture and assessment methodology. For valid comparison of NIS and kernel yield, moisture standards for expressing NIS and kernel yield need to be accepted by the cashew industry. To initiate discussion of this, we recommend that NIS be expressed at 9% WC, kernel at 5% WC and kernel recovery based on NIS and kernel yield at their respective water contents. Commercial NIS yield standards also need discussion. Under research conditions and in commercial practice estimates of NIS yield may include different ranges of nut weights. We have defined a minimum commercial nut weight for the cultivar used in this study and recommend that NIS yield be stated in commercial terms and that this be reconciled according to ISO standards as done in this study. Further work to confirm N effects and to develop a calibration system for N applications. The results of this study must be confirmed over at least two more growth seasons. While the weight of evidence from the study states that N applied during the vegetative growth phase will promote NIS yield and early season nut drop, conflicting responses were observed during the three years of the work. The study resolved three basic issues for developing a calibration system for N applications. These were, N timing requirement, two index leaves and sampling times for assessing tree N status, and ‘optimum’ ranges for leaf N concentration. To develop the system further will require work to define response curves for a larger range of N rates applied during the vegetative growth phase. Selection of varieties with early season nut drop tendency in plant improvement programs. Nut drop by the end of November is critical for economic cashew production in the Dimbulah area. While N management will be important for achieving early season nut drop, the benefits of this technology will be enhanced by varieties with early season tendencies.

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Early season nut drop must therefore be a criterion for assessing the suitability of a particular variety in evaluations of genetic material. Development of fertigation technology. High concentrations of nitrate-N were measured in leachate at a depth of 1 m during uncontrolled soil drainage that is frequent during the monsoon season. This season coincides with the vegetative growth phase when N applications are recommended. Small and regular N applications will therefore be required to minimise leaching of N. Regular surface applications of solid N forms are likely to be prohibitively expensive on cashew plantations of the size (500 ha) envisaged for Australian production. Fertigation will therefore provide a cost-effective solution and this technology and its application to cashew culture must be developed. Development of sophisticated crop management systems. Successful cashew development in Australia will depend in part on production systems that feature highly organised personnel and plantation management, well-timed nutrient and water applications, and integrated pest management. This study has defined a crop management program based on a phenological cycle conditioned by vegetative N application. Considerable scope exists for developing the management model beyond its present rudimentary form into a sophisticated system similar to that developed for avocados. This should be the vision of cashew research workers in Australia, and research in this country should be coordinated toward collating data supportive of its development.

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Industry Summary The background to the Project The profitability of cashew growing in Australia will depend very much on a combination of high yielding varieties and efficient crop management practices. Crop management practices cover the whole range of cultural practices (nutrition, irrigation, pruning, pest control, etc) required for commercial production of cashew nut. Little research has been done in Australia to develop efficient cultural practices or to organise them according to the seasonal growth cycle of the tree to maximise nut production. The aim of the Project The aim of the Project was to study the effect of nitrogen (N) on cashew growth and nut yield to develop: 1. An annual crop management program based on the ‘ideal’ annual growth cycle for the

Dimbulah region; 2. Nitrogen application recommendations that promote the ‘ideal’ annual growth cycle; and 3. Leaf sampling procedures for assessing tree N requirement to achieve the ‘ideal’ annual

growth cycle. The Project work undertaken The project objectives were achieved through a trial in which N was applied at two rates and at three times during the annual growth cycle of the tree. The times were: 1. 100% of the annual rate applied during the vegetative growth phase viz December–April, 2. 100% of the annual rate applied during the reproductive growth phase viz June–October, and 3. 50% of the annual rate applied during each phase. The cashew variety 9/14 was used in the trial. The trees were three and one-half years old when the trial was started in 1995. Tree growth and nut yield was recorded during the three years of the trial. Nut-in-shell (NIS) yield was assessed according to two criteria: (a) what nut would yield a commercial size kernel (called commercial NIS yield); and (b) a time by which nut drop should be completed. This time was defined as the end of November because of the increased incidence of rain and associated risk of crop loss after this time. The major findings of the Project The five major findings of the Project were:

Nitrogen applied from December to April gave the highest commercial NIS yield and the highest proportion of nut drop by the end of November;

Nitrogen applied from June to October gave the highest proportion of nut drop after

November;

Two sample leaves and adequate leaf N levels were defined for assessing tree N health;

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High concentrations of nitrogen were leached through the soil during heavy rain; and

A crop management program covering all the cultural operations required to grow cashew commercially was developed. This program was scheduled on an annual growth cycle produced by applying nitrogen from December to April. The program is described on page 37 of this report.

Implications of the Project’s findings for Industry

Strong vegetative growth is required during the period December to April for high nut yield and early nut drop. Depending on tree N health, which can be assessed using the procedures described on pages 32 and 33 of this report, N applications may be required over the period December to April for vegetative growth. If N is applied during this period small and regular applications should be considered to minimise leaching during the monsoon season. The application of N by irrigation may be a cost effective application method of achieving this.

Application of N after June should be done with caution because of the risk of late nut drop.

Further work on N management in cashew is required particularly to refine the method of

assessing tree N health for determining N application rates. Industry support is required to do this work.

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1. Introduction Cashew (Anacardium occidentale L.) is a tropical evergreen tree generally considered to be native to the northern part of South America (Ohler, 1979). The tree is valued for its nutritious kernel and, in terms of world production of edible nuts, it ranks third at about 700 000 t (Chacko et al. 1998). Based on current international and domestic demand for cashew kernel, considerable potential exists for expanding the Australian cashew industry beyond its current size of 300 ha. Australia imported almost 5000 t of cashew kernel in 1995 valued at AUD33.4 million (Agtrans Research, 1996). This quantity of kernel is equivalent to 20 000 t of nut-in-shell (NIS) (calculated on 25% kernel recovery). At a yield of 5 t/ha, 4 000 ha would be required to meet Australia’s domestic demand. In addition to the area required to supply the Australian market, it is reasonable to expect that an efficient industry producing high-quality kernel would be interested in export opportunities. According to reports, these opportunities exist due to a shortfall in world production that is expected to continue (Chacko et al. 1990). Climate and the availability of land with an adequate water supply do not limit expansion, as many thousands of hectares of suitable land exist in northern Australia (Chacko et al. 1990). Furthermore, countries with processing facilities are willing to either purchase or shell Australian NIS production, providing Australian producers with a range of marketing options: NIS, kernel or value added sales (P. Shearer, pers. comm). Economic NIS yields have been variously reported at 2.8 to 5 t/ha NIS (Cann et al. 1987; Oliver et al. 1992; Hinton 1998). A major financial commitment by research organisations, funding agencies and industry has been invested to develop/select varieties that produce economic yields. However, profitability will not only depend on high-yielding varieties, but also on efficient and sustainable crop management programs which maximise cultural efficiency and nut production. Annual crop management programs have been developed for a number of crops in Australia, an excellent example being the program developed for avocado by Whiley et al. (1988). These programs cover the whole range of field practices (nutrition, irrigation, crop protection) required to culture the crop and are designed to manage crop growth and input resources to maximise productivity. Such programs do not exist for cashew Australia or overseas. This is due to the young nature of the Australian industry and associated research, and to a lack of clear information from overseas research that can be applied to the local industry. Crop management programs are developed by determining the ‘ideal’ phenological cycle, that is the cycle which correlates best with highest productivity, and reliable treatments (nutrition, irrigation, growth regulators) which maintain the crop close to the ‘ideal’ cycle (B Cull, pers. comm). Nitrogen (N) fertilisation is of particular interest in determining reliable treatments because, of the range of nutrients required by plants for growth, it is believed that N and to lesser extent K are the only real manipulators of growth (Cull 1986). Nitrogen management therefore offers possibilities for achieving desirable growth and nut production responses. The influence of N on cashew vegetative and reproductive growth has been reported in a number of studies including Sawke et al. (1985) and Ghosh (1989). However, these papers present limited understanding of the relationship between these

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growth phases and nut production. Such an understanding is fundamental for developing techniques to manipulate these growth phases to control growth and enhance nut production. This report describes work undertaken from 1993 to 1997 at Dimbulah, North Queensland, that investigated the effect of N on cashew vegetative and reproductive growth. In conducting this research methodology and standards for expressing NIS and kernel yield were developed, and nutrient concentration in leachate was monitored. 2. Objectives The objective of the Project was to gain, by using N to modify vegetative and reproductive growth, understandings of the relationship between shoot, floral and nut development so as to develop techniques to regulate growth and achieve a phenological growth cycle (the ‘ideal’ cycle) best correlated with high nut yield. From this work it was intended to define: 1. A phenological cycle and aspects of vegetative and reproductive growth best correlated

with high nut yield; 2. The influence of N on vegetative and reproductive growth; and 3. Tree N assessment procedures based on leaf analysis to guide N applications to achieve

the ‘ideal’ phenological cycle. The practical benefits for the cashew industry anticipated from this work were: 1. An annual crop management program based on the ‘ideal’ phenological cycle for the

Dimbulah region; 2. Nitrogen application recommendations that promote the ‘ideal’ phenological cycle; and 3. Procedures for assessing tree N requirement (an index leaf, leaf sampling time and leaf N

standards) to achieve the ‘ideal’ phenological cycle. 3. Methodology 3.1 Site description This study was conducted at a cashew plantation known as ‘Cashews Australia’ located at Dimbulah, North Queensland. Dimbulah (17° 10’S, 145° 05’E, elevation 460 m) has an average annual rainfall of 780 mm, 81% falling in the months December to March (Bureau of Meteorology). Mean maximum and minimum temperatures during the study ranged from 24.5°C in July to 31.3°C in December and from 13.9°C in July to 21.5°C in February, respectively. The site of the N rates-by-timing trial was situated on a gently inclined 3–5% slope facing south-east. Tree and row spacings were 6 m and 8 m, respectively, and tree rows were orientated north-east/south-west. The soil is a haplic, mesotrophic, red, chromosol with a Principal Profile Form of Dr4.62 (Northcote, 1971; Neil Enderlin, DNR Mareeba, pers. comm.).

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3.2 Tree selection and trial design Initial methodology proposed. The project objectives were to be achieved through a study of the effect of N application timing on growth and nut production. Sufficiently mature clonal trees were not available for the work in 1993 and it was proposed to use seedling trees of two seedlines known locally as Port Douglas and K160. Morphological variation covering a range of vegetative and reproductive features (growth habit, leaf, panicle, nut, and apple characteristics) was obvious within each seedline. Uniformity trials were planned on each seedline to select uniform trees for the N timing trial. The planned N timing trial was a randomised complete block (RCB) design with three N timings using uniform trees of the two seedlines (Table 3.1). Treatments were to be applied to single tree plots with replicate number determined from the results of the uniformity trials. Nitrogen application timings were designed to modify shoot and reproductive growth to provide insights into vegetative and reproductive growth relationships. From these results it was intended to develop N nutrition practices which manage growth and achieve high nut production. At the same time an ‘ideal’ phenological cycle on which to order crop management practices, and the optimum sampling time for leaf nutrient analysis were to be defined. Table 3.1 Nitrogen timing treatments of the N timing trial.

Proportion (%) of the annual N rate applied during: Treatment Vegetative growth phase

January–April Reproductive growth phase

August–November

1 100 0 2 0 100 3 50 50 4† 50 50

† Annual rate of N is ¼ of the annual rate of treatments 1, 2 and 3. Duration and level of vegetative flushing, panicle emergence, flowering, fruit set, premature and mature nut drop were to be used to describe the phenological cycle. Relationships between vegetative growth, reproductive growth, N applications and leaf N levels were to be examined to determine factors that influence nut production. Leaf N standards, and a system to calibrate N applications based on leaf N were to be developed. Leaf nutrient levels (N, P, K, Ca, Mg, Zn, B, Cu, Fe, Mn, and S) were to be monitored monthly from Treatment 3 of the N timing trial to determine a leaf sampling time. Uniformity trials of seedlines Port Douglas and K160. Eighteen morphological characters (Table 3.2) were recorded in 1993 from 95 Port Douglas and 96 K160 trees. From these characters, 10 descriptors (Table A1.1) were selected for statistical analysis because of their possible or documented influence on nut yield. These data were analysed by cluster analysis techniques to group trees of similar characteristics. From the analysis, four groups (replicates) of four similar trees from each seedline were selected for the N timing trial (Table A1.2).

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Table 3.2 Tree and yield characteristics measured in the uniformity trials in 1993 and 1994.

Character Assessed Port Douglas and K160 cv 9/14 ( -recorded; -not recorded) Vegetative canopy height canopy diameter canopy skirt height trunk circumference number of terminals/m² Inflorescence number of panicles/m² panicle size (length, width) Apple mature apple colour overall shape size (length, width) average weight Nut progressive and total NIS weight total number of nuts mature nut colour overall shape average weight size (length, width, breadth) kernel recovery (%)

The expected experimental variation and the treatment responses needed to detect significant differences between the selected trees were assessed. For each seedline, trees within each group were randomly allocated to the four treatments of the N timing trial, and the 10 descriptors for each subjected to analysis of variance. This analysis indicated that, for these variables, treatment responses needed to be about 25% to detect significant differences at the 5% level. It was unlikely that the planned treatments would produce a difference of this magnitude and therefore the use of the K160 and Port Douglas trees for the N timing trial was abandoned. Uniformity trial of cv 9/14. Following the abandonment of the K160 and Port Douglas seedlines in 1994, 30 three and one-half-year-old clonal trees of cv 9/14 were assessed for suitability for the N timing trial. This cultivar, referred to as R9T14 in the Northern Territory Department of Primary Industries and Fisheries’ varietal assessments, had shown high yield performance (Richards et al., 1988).

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Ten morphological characters were recorded (Table 3.2), nine being subjected to cluster analysis to determine uniform groups of trees (Table A1.3). From this analysis, four groups of six similar trees were identified (Table A1.4). As six trees were available per replicate, the trial design was improved to a rates-by-timing trial with two N rates and three N application times. This design gave the opportunity, not afforded by the previous design, to study the possible interaction of rate and timing. To determine the likely experimental variation and treatment responses required to detect significant differences with the new design, trees within each group were randomly allocated to the six treatments and the nine descriptors for each subjected to analysis of variance. This analysis indicated that, for these variables, treatment responses needed to be about 10–12% to detect significant differences at the 5% level. This was considered achievable. Nitrogen rates-by-timing trial. The revised trial design was a two N rates by three N timing factorial in a RCB design (Table 3.3). The four replicates were defined by the four groupings from the uniformity trial, replicates consisting of single tree plots. To improve the opportunity to study the possible interaction of rate and timing, three additional trees, which had been assessed in the uniformity trial, were selected to receive a low rate (half the medium rate) of nitrogen. The low N trees were not included in the statistical design. Growth and nut and kernel yield responses from the low N treatment did not appear to contribute to the understanding of N rate and timing. Only leaf N data for the low N rate trees are therefore presented in this report. Table 3.3 Nitrogen timing treatments of the N rates-by-timing trial. N timing treatment Proportion of the annual N applied during: Vegetative growth

December–April Reproductive growth

June–October 100% Veg. 100 0 Veg./Rep. 50 50 100% Rep. 0 100

3.3 Nitrogen treatments Nitrogen source and application method were designed to limit N loss from volatilisation and leaching, and thereby maximise the availability of applied N to the tree. Nitrogen treatments were applied as ammonium nitrate (34% N) in five equal monthly dressings during the vegetative (December–April) and reproductive (June–October) growth phases in 1995–1997 (Table A2.1). Treatments were applied to the irrigation zone under the trees and watered in the absence of following rain. Nitrogen rates (Table 3.4) were guided by the cashew nutrition work of Richards (1993) and rates used for mango in the Mareeba–Dimbulah area. Vegetative growth was considered excessive in treatments receiving vegetative N (100% Veg. and Veg./Rep.) in 1996. The 1997 rates were therefore kept the same as the 1996 rates. The tree density of the trial was 208 trees/ha and this was used to calculate N rate per tree.

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Table 3.4 Nitrogen rates (kg/ha) applied in 1995, 1996 and 1997.

1995 1996 & 1997 Treatment Veg. phase Feb–Apr

Rep. phase June–Oct

Total

Veg. phase Dec–Apr

Rep. phase June–Oct

Total

Med. 100% Veg. 27 0 27 120 0 120 Med. Veg./Rep 14 40 54 60 60 120 Med. 100% Rep. 0 80 80 0 120 120 High 100% Veg. 41 0 41 180 0 180 High Veg./Rep. 20 60 80 90 90 180 High 100% Rep. 0 120 120 0 180 180

Vegetative N treatments were started in February 1995, halfway through the vegetative growth phase. As a result, the 100% Veg. and Veg./Rep. treatments received a lower annual N rate in 1995 compared with 100% Rep. which received the full annual N rate. The amount applied to the vegetative N treatments during the vegetative growth phase was proportional to the length of the remaining vegetative growth phase. 3.4 Tree management Applications of P, K, Ca, and Mg were made annually in February 1995 and 1996 and April 1997 as surface dressings to the area within the irrigation zone under the tree. Micronutrients (Zn, Cu, Fe, Mn and Mo) were applied as foliar sprays, surface dressings or fertigation. Rates were guided by soil and leaf analyses, and local experience with other crops on similar low fertility soils. Soil moisture was monitored with a neutron moisture meter to a depth of 1.2 m in two replicates each of the Med. 100% Veg. and Med. 100% Rep. treatments. In the absence of rainfall, irrigation was applied at weekly intervals at rates to achieve drainage to 0.7–1 m depth. Insects and weeds were controlled as required: insects by insecticide sprays and weeds by chemical sprays under the tree canopy and slashing of inter-rows. Trees were pruned immediately following the completion of nut drop. The 100% Veg. and Veg./Rep. treatments were pruned in December 1995, 1996 and 1997. The 100% Rep. treatments were pruned in March 1996, March 1997 and December 1997. Foliage outside an area defined by a 45° angle from the base of the tree and a perpendicular 2 m from the trunk was removed. 3.5 Growth and yield data collected Canopy size and pruning. Canopy height, canopy diameter and skirt height were measured in November 1994 and in December 1995, 1996 and 1997. Canopy diameter was defined as the mean of two diameter measurements taken perpendicular to each other. The skirt height was the distance from the ground to the bottom of the canopy. The canopy shape approximated half a sphere, the radius (r) of which was taken to be the mean of half the two diameter measurements and the tree height less skirt height. Hence canopy surface area (CSA) was determined by CSA = (4 * π * r²) / 2

7

The total wet weight of prunings removed from each tree (W1) and the weight of a sub-sample of the total wet prunings (W2) was recorded at the time of pruning. The wet sub-sample was dried to constant weight at 60°C (D1) and the total dry weight of prunings removed per tree (D2) was determined by D2 = W1 * (D1 / W2) Shoot and panicle growth. Shoot length and panicle number was recorded monthly for 10 branches per tree. Mean monthly shoot length and panicle number was expressed as a proportion of the annual total for each during 1995, 1996 and 1997. The mean monthly NIS weight was also expressed as a proportion of the annual total NIS weight. These data were used to describe the phenological cycle. Shoot length and panicle number was recorded for 10 branches per tree in June (1995 and 1997) and July (1996) and December annually to develop indices for vegetative and reproductive growth. The total for the 10 branches in June or July and in December, and the increase from June or July to December was calculated. Panicle density was recorded in December 1996 and 1997. The number of panicles covered by a 0.5 m square quadrant was counted at the four cardinal points around the canopy. The total number of panicles per tree was calculated from the mean of the four counts and the CSA. Nut-in-shell yield. All nuts, including very small nuts, were harvested monthly. Nut-in-shell weight and number of nuts were recorded from monthly harvests. Nuts were weighed after equilibrating to ambient relative humidity. Samples from each treatment were oven dried at 65 °C to constant weight (7 days, 0.1% weight loss per day) and assumed to be at 1% water content (WC). Nut-in-shell weight was then expressed at 9% WC. The commercial value of the very small nuts was questionable as many were void, that is lacking a kernel. The 1995 and 1996 post-harvest nut assessments were done together and assessment methodology and standards for defining non-commercial nuts had not been resolved at this time. An assessment of the number and weight of very small nuts in the 1995 harvest, subjectively defined as non-commercial (maximum weight 1.68 g; mean weight 1.39 g at 9% WC), had previously been made in an attempt to determine a procedure for separating non-commercial nuts. The procedure was not developed further and all nut sizes for each of the 1995 and 1996 harvests were bulked for assessment of NIS and kernel yield. In 1997 a minimum commercial nut weight was defined. This was 3.03 g (9% WC) and was derived from the mean 1996 kernel recovery (31.36%) and the smallest kernel weight defined by the International Organisation for Standardisation for raw kernel trade (0.909 g for W500 count, ISO 1988). Nuts of this weight were approximately 25 mm in length. This standard was used to separate non-commercial (<25 mm, maximum weight 3.89 g, mean weight 1.42 g) and commercial nuts (≥25 mm) for the 1997 harvest. A sample of nuts from one replicate of each treatment was assessed to determine the level of non-commercial nuts remaining with the commercial nuts following separation. This assessment showed that nuts graded as commercial had an average of 14% by number and 5% by weight of non-commercial nuts.

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For comparison of the 1997 harvest with the 1995 and 1996 harvests, it was necessary to derive commercial NIS weights for 1995 and 1996 from the available information. The small nuts of 1995 were assumed to represent the non-commercial nuts and their weight was expressed at 9% WC. The commercial NIS weight (9% WC) for 1995 was then determined as the total NIS weight (9% WC) less the non-commercial NIS weight (9% WC). Less information on non-commercial nuts was available in 1996. An estimate of the number of non-commercial nuts in 1996 was obtained by assuming that the proportion of void nuts recorded for each treatment at kernel extraction was equivalent to the proportion of non-commercial nuts and that this proportion was constant across time. This would probably have overestimated the number of non-commercial nuts. The weight of non-commercial nuts at 9% WC was determined as the product of the number of void nuts and the average non-commercial nut weight at 9% WC from 1995 (1.39 g). Commercial NIS weight (9% WC) was then calculated as total NIS weight (9% WC) less non-commercial NIS weight (9% WC). Commercial nut number was calculated as the total nut number less the number of non-commercial nuts. Mean nut weight (9% WC) of commercial nuts was calculated from the commercial NIS weight (9% WC) and the number of commercial nuts. Commercial NIS weight/m² of canopy was calculated from the commercial NIS weight (9% WC) and CSA. Distribution of nut drop across the harvest period was assessed by analysis of the proportion of the commercial NIS weight harvested by August, November and January. The number of nuts per panicle was calculated from the number of commercial nuts and the number of panicles per tree. Kernel yield. A sub-sample of NIS from each treatment was soaked in water for 4–6 days to soften the shells before the kernels were extracted with testa attached. The number of defective nuts was recorded. These nuts were either void (lacking a kernel), had a kernel size that occupied less than 25% of the internal shell cavity, or the kernel was rotted or insect infested. Defective kernels would occur in a commercial harvest and so were included in the assessment of kernel weight and kernel recovery. The extracted kernel with testa was oven dried at 65 °C to constant weight (4 days, 0.1% weight loss per day) and assumed to be at 0% WC. Dried kernel plus testa weight (KT) was reduced to kernel weight (K) using a regression equation developed from measurements of kernel and testa weight of the cultivar under study. The equation was: K = -0.0149 + 0.9647 * KT (R² = 0.9993) Kernel weight of the sub-sample was adjusted to 5% WC. Kernel recovery was calculated as the ratio of kernel weight (5% WC) of the sub-sample to commercial NIS weight (9% WC) of the sub-sample. Total kernel weight was calculated by multiplying the total commercial NIS weight (9% WC) by the kernel recovery derived from the sub-sample. 3.6 Chemical analyses of soil Pre-trial assessment and annual monitoring of fertility changes. Soil samples were collected prior to the start of the experiment and then annually (June or July) at the end of vegetative N treatments and prior to reproductive N treatments. Cored samples were taken with a 75 mm auger within the fertiliser treatment and irrigation zone. One core per tree was collected and individual depths were kept separate. Additional samples were collected from

9

four locations in the inter-row area which had not received either N treatments or basal nutrients. Depths of sampling were 0–10, 10–20, 20–30, 30–45, 45–60, 60–90 and 90+ cm on 10.1.95, 18.7.95, 30.7.96 and 18.6.97. The samples were air dried, ground to <2 mm and analysed for pH (1:5 water); electrical conductivity (1:5 water); Colwell extractable P (Colwell, 1963); ammonium- and nitrate-N; organic carbon (Walkley and Black, 1934); exchangeable Na, K, Ca and Mg; DTPA extractable Cu, Zn, Mn and Fe. All methods were the standard methods described by Rayment and Higginson, 1992. 3.7 Chemical analyses of leaves Pre-trial assessment and monthly monitoring of tree nutritional status. Pre-treatment samples were taken from all replicates of the trial on 25 January 1995. Two leaf types were sampled: mature leaves of the previous season’s pre-floral vegetative flush (MFF) and immature pigmented leaves (IP). The terminal pair immediately before the apex was sampled from four shoots, one shoot at each cardinal point around the tree. During the trial, leaves were sampled monthly to identify an index leaf to measure tree N status, and to monitor tree N level in response to treatments. Four leaf types were sampled which were: • The largest immature pigmented leaf of a shoot in vegetative flush or pre-floral vegetative

flush (LP). The largest leaf was 1–6 leaves from the apex. • A mature terminal leaf from a quiescent vegetative shoot. Leaves of this type were

sampled from two shoot positions: (a) shoots existing in shaded positions within the canopy (MI); and (b) shoots on the periphery of the canopy (ME). Both leaf types were of current season’s growth. The sampled leaf was 1–4 leaves from the apex. The ME type approximated that of Richards (1993).

• The largest mature pre-floral vegetative flush leaf (LMFF). The sampled leaf was 3–9 leaves from the apex and was taken from floral shoots with panicles at various stages of maturity (flowering, nut development or ‘spent’).

The criteria for judging suitability of a leaf type as an index for tree N assessment were sensitivity to N treatments, ease of recognition and predicably available. Analytical procedures. Samples were dried at 65 °C in a forced draft oven and ground to <1 mm before analysis. Nitrogen and P content were determined by colorimetric procedures after Kjeldahl digestion. Calcium, K and Mg (Kjeldahl digestion) and Cu, Zn, Mn and Fe (nitric-perchloric digestion) were determined by atomic absorption spectrophotometry. Leaf samples were not washed prior to analysis because of the likelihood that spray residues would not to be completely removed and soluble nutrients could be leached from the leaves (Arkley et al., 1960). 3.8 Monitoring nutrient movement in leachate Ceramic cups were installed in December 1996 to compare nutrient movement in the fertilised and unfertilised zones. Three cups (79 x 39 mm) were located at a depth of 1 m under the canopy drip-line of two trees receiving the medium N rate, one as 100% Veg. and the other as Veg./Rep. Two additional cups were installed at a similar depth in the unfertilised inter-row. Water was extracted from the soil profile via the ceramic cup at a negative pressure equivalent to natural drainage. The pressure was generated by a falling head of water that was maintained between fixed heights by a pump. The cups were

10

connected to individual 5 L water traps also located at a depth of 1 m. The traps were emptied at sampling times. Samples were collected at a minimum of weekly intervals, after being stored at soil temperature in the light-proof water traps, and more frequently as drainage events dictated. The samples were chilled after extraction and then frozen on delivery to the laboratory until the time of analysis. Volumes of water extracted were calculated from the height of the water in the calibrated external sampler. Water samples were analysed for pH; electrical conductivity; ammonium- and nitrate-N, Na, K, Ca and Mg (Rayment and Higginson, 1992). Ammonium- and nitrate-N data are presented in this report. 3.9 Statistical procedures Data were analysed by standard analysis of variance to determine the effects of N rate and timing on vegetative and reproductive growth. Normality and variance assumptions were checked and transformations were applied where necessary. Shoot length data were square-root transformed (√ (x+1)) prior to analysis in order to stabilise the variance. Means were tested using a protected least significant difference (lsd) test at the 5% level. 4. Results 4.1 Pre-trial soil fertility and tree nutritional status Soil fertility status. The soil fertility at the start of the experiment (Table 4.1) was consistent with the inherent low fertility of the soil and prior limited levels of fertiliser inputs. Available N (NH4 and NO3) was low, while P and K were of medium levels. Copper was low (0.1 mg/kg; 0–10 cm) and Zn marginal (0.5 mg/kg; 0–10 cm). Organic carbon was 0.39%. Table 4.1 Selected soil chemical properties prior to the commencement of treatments

(10.1.95) and after the start of reproductive N applications in 1997 (18.6.97). Data for individual depths are means for all treatments.

Depth pH E.C. NH4-N NO3-N Bicarb P Ex. Cations (m.e./100g) (cm) (1:5

water) (dS/m) (mg/kg) (mg/kg) (mg/kg) Na K Ca Mg ECEC

10.1.95

0–10 6.19 0.05 3.2 3.0 27 0.09 0.45 1.17 0.35 2.1 10–20 6.31 0.04 1.4 <1 13 0.09 0.36 0.95 0.22 1.6 20–30 6.38 0.03 <1 <1 0.09 0.31 0.73 0.20 1.3 30–45 6.39 0.03 <1 <1 0.10 0.24 0.76 0.45 1.5 45–60 6.41 0.03 <1 <1 0.10 0.22 0.77 0.45 1.5 60–90 6.38 0.03 <1 <1 0.10 0.21 0.90 0.74 1.9

18.6.97

0–10 5.44 0.03 2.4 1.3 101 0.04 0.05 1.04 0.17 1.30 10–20 5.21 0.03 1.3 1.2 83 0.05 0.05 0.52 0.08 0.70 20–30 5.08 0.04 1.3 <1 0.04 0.07 0.43 0.08 0.62 30–45 5.03 0.06 1.1 1.1 0.03 0.12 0.37 0.13 0.65 45–60 5.20 0.07 1.1 3.1 0.04 0.21 0.63 0.24 1.12

E.C. = electrical conductivity Bicarb P = bicarbonate extractable P m.e./100g = milliequivalents/100g ECEC = effective cation exchange capacity

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Tree nutritional status. Levels of N, P and K were similar for all trees when replicates were assessed in terms of proposed treatments (Table 4.2). Phosphorus and K were low in the MFF leaves and adequate in the IP leaves when compared with ranges described by Robinson et al. (1997). Nitrogen was low in both leaf types and reflected the low N status of trees before the commencement of the trial. Table 4.2 Nutrient levels in mature pre-floral vegetative flush leaves (MFF) and

immature pigmented leaves (IP) sampled prior to the commencement of treatments.

Nitrogen (%) Phosphorus (%) Potassium (%) MFF IP MFF IP MFF IP N rate n.s. n.s. n.s. n.s. n.s. n.s. Medium 1.021 1.698 0.090 0.199 0.452 1.324 High 1.015 1.724 0.089 0.199 0.443 1.324 5 lsd 0.116 0.154 0.010 0.016 0.058 0.068 N Timing n.s. n.s. n.s. P=0.073 n.s. ** 100% Veg. 0.960 1.687 0.087 0.199 0.421 1.319 ab Veg./Rep. 1.061 1.652 0.090 0.188 0.491 1.254 b 100% Rep. 1.034 1.794 0.092 0.211 0.430 1.400 a 5% lsd 0.142 0.189 0.013 0.019 0.071 0.083 Rate x Timing n.s. n.s. n.s. n.s. n.s. n.s. Med. Veg. 0.966 1.671 0.084 0.197 0.408 1.313 Med. Veg./Rep. 1.072 1.566 0.087 0.187 0.528 1.273 Med. Rep. 1.024 1.856 0.100 0.214 0.420 1.388 High Veg. 0.954 1.703 0.090 0.201 0.435 1.325 High Veg./Rep. 1.050 1.738 0.093 0.188 0.455 1.235 High Rep. 1.043 1.732 0.084 0.207 0.440 1.413 5% lsd 0.201 0.267 0.018 0.027 0.101 0.177 Adequate levels† 2.40-2.58 0.16-0.20 1.10-1.20

n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001 † Robinson et al. (1997) 4.2 Fertility changes 1995 to 1997 Soil mineral N concentrations were very low at the start of the experiment (Table 4.1) and generally remained so at each sampling. The exception was in 1996 when samples were collected after the start of the reproductive N treatments. For this sampling, some high concentrations of NH4 (up to 33 mg/kg) and NO3-N (up to 29 mg/kg) were detected under some trees of the medium N rate 100% Rep. and the high N rate 100% Rep. and Veg./Rep. treatments. The concentrations in the inter-row remained very low. Soil pH under the trees, but not the inter-row area decreased during the trial. The initial soil pH was near neutral throughout the profile (6.19–6.41, Table 4.1). After six months, the pH of soil under the tree canopy receiving basal fertiliser (and N treatments for medium and high N rates of 100% Veg. and Veg./Rep.) had decreased by a mean value of 0.37. The decrease was not related to the rate or timing of N application. Further decreases in pH were recorded in 1996 and 1997. The pH of the inter-row, which was not fertilised, was unchanged.

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Bicarbonate extractable P concentrations under the trees increased from 27 and 13 mg/kg in 1995 to 101 and 83 mg/kg in 1997 for 0–10 cm and 10–20 cm depths, respectively (Table 4.1). However, the concentrations of P were variable at each sampling with standard deviations of between 17 and 30 mg/kg. This reflects the difficulty of monitoring changes in the soil nutrient status for a slowly mobile nutrient under conditions of surface application in the absence of cultivation. The exchangeable cations, Na, Ca and Mg were reasonably consistent throughout the experiment, despite annual applications of Ca and Mg. In contrast, K concentrations decreased from the initial concentrations of 0.21 to 0.45 m.e./100g to between 0.05 and 0.21 m.e./100g in 1997 (Table 4.1). Concentrations of Cu and Zn increased in the top 0–10 cm of soil from very low concentrations in 1995 (0.1 and 0.5 mg/kg, respectively) to high concentrations in 1997 (4.6 and 2.8 mg/kg, respectively). The increase reflects the applications made to the soil in 1995 and 1996, the absence of cultivation and the very low mobility of these nutrients through the soil profile. 4.3 Canopy growth and pruning Canopy growth. Canopy surface area (CSA) was measured in November 1994, before the commencement of the trial (Table 4.3). All treatments had similar CSA (P>0.10) at this time because the two canopy attributes used to calculate this variable, height and diameter, were also similar (P>0.10) (Table 4.4). Table 4.3 Nitrogen treatment effects on canopy surface area (m²) from 1994 to 1997.

Means not followed by a common letter differ significantly, (P<0.05). Nov

1994 Dec 1995

Increase1994-95

Dec 1996

Increase1995-96

Dec 1997

Increase1996-97

N rate n.s. n.s. n.s. * P=0.088 n.s. n.s. Medium 12.34 23.42 11.08 37.61 b 14.19 48.48 10.87 High 12.69 25.05 12.35 42.27 a 17.22 51.78 9.50 5% lsd 1.50 2.12 1.62 4.29 3.54 4.37 2.58 N Timing n.s. n.s. n.s. *** *** *** n.s. 100% Veg. 12.99 25.40 12.41 46.55 a 21.15 a 56.42 a 9.87 Veg./Rep. 12.47 23.89 11.42 41.64 a 17.75 a 52.09 a 10.45 100% Rep. 12.09 23.42 11.32 31.64 b 8.22 b 41.87 b 10.23 5% lsd 1.83 2.60 1.98 5.25 4.33 5.35 3.16 Rate x Timing n.s. n.s. n.s. n.s. P=0.088 n.s. n.s. Med. Veg. 12.47 23.51 11.05 42.81 19.30 53.59 10.78 Med. Veg./Rep. 12.25 24.06 11.81 38.04 13.98 49.26 11.22 Med. Rep. 12.30 22.70 10.40 31.99 9.30 42.59 10.59 High Veg. 13.51 27.29 13.78 50.29 23.00 59.25 8.96 High Veg./Rep. 12.69 23.72 11.04 45.23 21.61 54.91 9.68 High Rep. 11.89 24.14 12.25 31.29 7.15 41.16 9.87 5% lsd 2.59 3.68 2.80 7.43 6.12 7.57 4.47

n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

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Table 4.4 Nitrogen treatment effects on canopy height and diameter from 1994 to 1997. Means not followed by a common letter differ significantly, (P<0.05).

Nov

1994 Dec 1995

Increase1994-95

Dec 1996

Increase1995-96

Dec 1997

Increase1996-97

Canopy height (m) N rate n.s. *** n.s. * n.s. * n.s. Medium 2.66 3.43 b 0.77 4.19 b 0.76 4.57 b 0.38 High 2.75 3.61 a 0.86 4.38 a 0.78 4.73 a 0.35 5% lsd 0.16 0.11 0.13 0.17 0.18 0.15 0.11 N Timing n.s. *** n.s. *** * *** * 100% Veg. 2.79 3.64 a 0.85 4.55 a 0.91 a 4.84 a 0.29 b Veg./Rep. 2.72 3.56 a 0.84 4.39 a 0.83 a 4.70 a 0.31 b 100% Rep. 2.60 3.36 b 0.76 3.92 b 0.56 b 4.41 b 0.49 a 5% lsd 0.20 0.14 0.16 0.21 0.22 0.18 0.13 Rate x Timing n.s. n.s. n.s. n.s. n.s. n.s. n.s. Med. Veg. 2.70 3.54 0.84 4.38 0.84 4.68 0.30 Med. Veg./Rep. 2.68 3.49 0.81 4.28 0.79 4.60 0.33 Med. Rep. 2.61 3.26 0.65 3.91 0.65 4.43 0.51 High Veg. 2.89 3.75 0.86 4.73 0.98 5.01 0.29 High Veg./Rep. 2.76 3.63 0.86 4.50 0.88 4.80 0.30 High Rep. 2.59 3.45 0.86 3.93 0.48 4.39 0.46 5% lsd 0.28 0.20 0.23 0.30 0.31 0.26 0.18 Canopy diameter (m) N rate n.s. n.s. n.s. P=0.075 n.s. n.s. n.s. Medium 2.67 3.46 0.79 4.49 1.03 5.19 0.70 High 2.68 3.52 0.84 4.70 1.19 5.34 0.64 5% lsd 0.16 0.14 0.13 0.24 0.21 0.22 0.15 N Timing n.s. n.s. n.s. *** *** *** n.s. 100% Veg. 2.70 3.51 0.81 4.89 a 1.38 a 5.58 a 0.69 Veg./Rep. 2.62 3.42 0.81 4.66 a 1.24 a 5.38 a 0.71 100% Rep. 2.69 3.53 0.84 4.24 b 0.70 b 4.85 b 0.61 5% lsd 0.20 0.17 0.16 0.30 0.26 0.27 0.19 Rate x Timing n.s. n.s. n.s. n.s. P=0.056 n.s. n.s. Med. Veg. 2.69 3.40 0.72 4.75 1.35 5.48 0.73 Med. Veg./Rep. 2.64 3.48 0.85 4.46 0.98 5.24 0.78 Med. Rep. 2.68 3.50 0.82 4.25 0.75 4.86 0.61 High Veg. 2.71 3.62 0.90 5.03 1.41 5.68 0.65 High Veg./Rep. 2.60 3.37 0.77 4.86 1.50 5.51 0.65 High Rep. 2.71 3.57 0.86 4.23 0.66 4.84 0.61 5% lsd 0.28 0.24 0.23 0.42 0.36 0.38 0.27

n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001 Differences (P<0.001) among N timings in CSA were not evident until December 1996, at which time the vegetative N timings had a larger CSA compared with the 100% Rep. timing. Canopy height and diameter were greater (P<0.05) in the vegetative N timings in December 1996, compared with 100% Rep. timing, due to a greater (P<0.05) increase in both attributes in the vegetative N timings between December 1995 and December 1996. The relative ranking in CSA existing in December 1996 among the N timings (100% Veg. and Veg./Rep. > 100% Rep.) was maintained through to December 1997. Between December 1996 and

14

December 1997 there was a greater (P<0.05) increase in canopy height in the 100% Rep. timing compared with the vegetative N timings. This was insufficient however to effect a change in the relative ranking in CSA among the N timings because all timings had similar (P>0.10) increases in canopy diameter. The high N rate produced a greater (P<0.05) CSA at December 1996 compared with the medium rate, but by December 1997 there was no difference (P>0.10) between the N rates. Dry weight of pruning removal. In 1995, pruning removal in the vegetative N timings was lower (P<0.05) compared with the 100% Rep. timing (Table 4.5). In contrast, the 100% Veg. timing had greater (P<0.05) pruning removal in 1996 and 1997 compared with the reproductive N timings (Veg./Rep. and 100% Rep.). Cumulative pruning removal for the period 1995 to 1997 was also greater (P<0.05) in the 100% Veg. timing compared with the reproductive N timings. Table 4.5 Nitrogen treatments effects on dry weight (kg) of pruning removal. Means

not followed by a common letter differ significantly, (P<0.05). 1995 1996 1997 Cumulative

1995-97 N rate n.s. P=0.076 n.s. n.s. Medium 6.64 7.20 8.49 22.32 High 7.52 8.19 8.83 24.54 5% lsd 1.27 1.11 1.83 2.70 N Timing * * *** *** 100% Veg. 6.36 b 8.95 a 12.05 a 27.36 a Veg./Rep. 6.31 b 6.94 b 9.23 b 22.48 b 100% Rep. 8.56 a 7.20 b 4.70 c 20.45 b 5% lsd 1.56 1.36 2.25 3.30 Rate x Timing P=0.073 * n.s. P=0.053 Med. Veg. 5.07 7.51 b 11.30 23.87 Med. Veg./Rep. 6.84 6.15 b 9.38 22.36 Med. Rep. 8.01 7.95 b 4.78 20.73 High Veg. 7.66 10.40 a 12.80 30.86 High Veg./Rep. 5.79 7.74 b 9.07 22.59 High Rep. 9.11 6.44 b 4.61 20.16 5% lsd 2.21 1.92 3.18 4.67

n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001 4.4 Shoot and panicle growth Shoot growth. The 100% Veg. timing had greater (P<0.05) pre-July shoot growth compared with the 100% Rep. timing in 1995 (Table 4.6, Figure 4.1c). In 1996 the vegetative N timings (100% Veg. and Veg./Rep.) had greater (P<0.05) pre-July shoot growth compared with the 100% Rep. timing. In both these years shoot growth was similar (P>0.10) for all N timings by December because of greater (P<0.05) post-July shoot growth in the 100% Rep. timing compared with the vegetative N timings. Nitrogen timing did not affect shoot growth in 1997.

15

Table 4.6 Nitrogen treatment effects on shoot length (mm) of 10 branches. Means are square root transformed with backtransformed means in parenthesis. Means not followed by a common letter differ significantly, (P<0.05).

June–July Dec Increase June–July to Dec 1995 N rate n.s. n.s. n.s. Medium 36.55 (1335) 40.98 (1679) 16.22 (262) High 34.51 (1190) 38.64 (1492) 15.05 (225) 5% lsd 4.97 4.87 3.89 N Timing * n.s. *** 100% Veg. 39.15 a (1532) 40.08 (1605) 7.54 c (56) Veg./Rep. 36.45 ab (1328) 40.08 (1605) 15.45 b (238) 100% Rep. 31.00 b (960) 39.28 (1542) 23.90 a (570) 5% lsd 6.08 5.96 4.76 Rate x Timing n.s. n.s. P=0.085 Med. Veg. 42.12 (1773) 42.66 (1819) 6.29 (39) Med. Veg./Rep. 34.26 (1173) 39.71 (1576) 19.14 (366) Med. Rep. 33.28 (1107) 40.59 (1646) 23.23 (539) High Veg. 36.18 (1308) 37.50 (1405) 8.80 (76) High Veg./Rep. 38.64 (1492) 40.45 (1635) 11.77 (137) High Rep. 28.72 (824) 37.98 (1442) 24.58 (603) 5% lsd 8.60 8.43 6.74 1996 N rate n.s. n.s. *** Medium 34.43 (1184) 38.04 (1446) 15.07 a (226) High 36.23 (1311) 38.21 (1459) 10.80 b (116) 5% lsd 7.21 6.94 2.28 N Timing * n.s. ** 100% Veg. 38.54 a (1484) 39.96 (1596) 10.30 b (105) Veg./Rep. 39.04 a (1523) 41.48 (1720) 12.35 b (152) 100% Rep. 28.40 b (806) 32.93 (1083) 16.16 a (260) 5% lsd 8.83 8.50 2.79 Rate x Timing P=0.062 n.s. * Med. Veg. 43.06 (1853) 44.59 (1987) 11.28 b (126) Med. Veg./Rep. 32.82 (1076) 36.96 (1365) 16.74 a (279) Med. Rep. 27.40 (750) 32.56 (1059) 17.20 a (295) High Veg. 34.01 (1156) 35.33 (1247) 9.32 b (86) High Veg./Rep. 45.27 (2048) 46.01 (2116) 7.95 b (62) High Rep. 29.40 (864) 33.29 (1108) 15.12 a (228) 5% lsd 12.49 12.02 3.95 1997 N rate n.s. n.s. * Medium 24.38 (593) 26.86 (721) 10.95 a (119) High 27.38 (749) 28.77 (827) 8.44 b (70) 5% lsd 4.14 3.94 2.49 N Timing n.s. n.s. n.s. 100% Veg. 26.09 (679) 27.76 (770) 9.10 (82) Veg./Rep. 25.20 (634) 27.40 (750) 10.02 (99) 100% Rep. 26.36 (694) 28.29 (799) 9.97 (98) 5% lsd 5.07 4.83 3.05 Rate x Timing n.s. n.s. n.s. Med. Veg. 22.95 (526) 25.31 (640) 10.48 (109) Med. Veg./Rep. 24.50 (599) 27.51 (756) 11.91 (141) Med. Rep. 25.69 (659) 27.77 (770) 10.46 (108) High Veg. 29.22 (853) 30.21 (912) 7.71 (58) High Veg./Rep. 25.89 (669) 27.30 (744) 8.14 (65) High Rep. 27.03 (730) 28.81 (829) 9.48 (89) 5% lsd 7.16 6.83 4.32

n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

16

Figure 4.1 Phenological development of 100% vegetative (•) and 100% reproductive N (o) timings from 1995 to 1997 and their relationship with temperature and rainfall. Horizontal bars in (a) represent timing of treatment applications.

Panicle growth. Pre-July panicle number was greater (P<0.05) in the vegetative N timings compared with the 100% Rep. timing in 1995 and 1996 (Table 4.7, Figure 4.1b). This panicle growth of the vegetative N timings was associated with high pre-July shoot growth in 1995 and 1996 (Table 4.6). By December 1995 and 1996 there was no difference (P>0.10) in panicle number among N timings. Nitrogen timing had no effect (P>0.10) on panicle number in 1997. While the high N rate produced a greater (P<0.05) level of pre-July panicle growth compared with the medium N rate in 1997 only, this trend was evident in previous years.

17

Table 4.7 Nitrogen treatment effects on panicle number of 10 branches. Means not followed by a common letter differ significantly, (P<0.05).

1995 1996 1997 June Dec Increase

June–DecJuly Dec Increase

July–DecJune Dec Increase

June–Dec N rate n.s. n.s. n.s. n.s. n.s. P=0.070 * n.s. n.s. Medium 9.3 43.7 34.3 10.2 36.1 25.9 12.5 b 29.8 17.3 High 12.3 41.9 29.7 11.4 31.4 20.0 18.5 a 33.2 14.7 5% lsd 4.0 13.4 12.1 5.5 9.7 6.5 5.0 8.3 6.6 N Timing ** n.s. n.s. * n.s. n.s. n.s. n.s. n.s. 100% Veg. 14.3 a 42.0 27.8 15.5 a 34.0 18.5 18.6 35.9 17.3 Veg./Rep. 12.1 a 39.9 27.8 12.1 a 37.0 24.9 13.9 32.6 18.8 100% Rep. 6.0 b 46.5 40.5 4.8 b 30.3 25.5 14.0 25.9 11.9 5% lsd 4.9 16.4 14.8 6.7 11.9 7.9 6.1 10.2 8.1 Rate x Timing n.s. n.s. n.s. * n.s. n.s. n.s. n.s. n.s. Med. Veg. 13.5 42.5 29.0 20.0 a 41.0 21.0 15.5 33.8 18.3 Med. Veg./Rep. 9.0 43.0 34.0 6.3 b 35.5 29.3 10.3 33.0 22.8 Med. Rep. 5.5 45.5 40.0 4.3 b 31.8 27.5 11.8 22.5 10.8 High Veg. 15.0 41.5 26.5 11.0 ab 27.0 16.0 21.8 38.0 16.3 High Veg./Rep. 15.3 36.8 21.5 18.0 a 38.5 20.5 17.5 32.3 14.8 High Rep. 6.5 47.5 41.0 5.3 b 28.8 23.5 16.3 29.3 13.0 5% lsd 7.0 23.2 20.9 9.5 16.8 11.2 8.7 14.4 11.4 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

18

4.5 Nut-in-shell (NIS) yield at 9% WC, and kernel yield (at 5% WC) Total NIS yield. Total NIS weight included non-commercial nut. In 1995, total NIS weight and number of nuts was greater (P<0.05) in the 100% Rep. timing compared with the 100% Veg. timing (Table 4.8). In 1996 and 1997 the reverse response occurred, both variables being greatest (P<0.05) in the 100% Veg. timing. Treatments did not affect the proportion of non-commercial nut by weight or by number in any year, however, levels were higher in 1997. Levels were on average 10.2, 8.9, and 32.2% by number in 1995, 1996 and 1997, respectively. Table 4.8 Nitrogen treatment effects on total NIS production. Means not followed by

a common letter differ significantly, (P<0.05).

1995 1996 1997 NIS wt.

(g) Number of nuts

NIS wt. (g)

Number of nuts

NIS wt. (g)

Number of nuts

N rate n.s. * * ** * n.s. Medium 7370 1404 b 11903 b 2530 b 10913 b 3201 High 7902 1722 a 13224 a 2982 a 12038 a 3429 5% lsd 1325 280 1074 250 985 329 N Timing *** *** *** *** *** ** 100% Veg. 5992 b 1164 b 14529 a 3213 a 13105 a 3692 a Veg./Rep. 6903 b 1465 b 12379 b 2649 b 11628 b 3398 a 100% Rep. 10014 a 2060 a 10783 c 2407 b 9694 c 2855 b 5% lsd 1623 343 1316 307 1206 403 Rate x Timing n.s. n.s. n.s. n.s. n.s. n.s. Med. Veg. 5150 944 13414 2823 12399 3535 Med. Veg./Rep. 6855 1349 11483 2423 10722 3200 Med. Rep. 10105 1919 10811 2345 9618 2869 High Veg. 6833 1384 15645 3602 13811 3850 High Veg./Rep. 6950 1580 13274 2876 12534 3596 High Rep. 9923 2202 10754 2470 9770 2841 5% lsd 2295 485 1861 434 1706 570 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001 Commercial NIS yield. Future references to NIS yield parameters are understood to mean commercial yield. In 1995, NIS weight was greater (P<0.05) in the 100% Rep. timing compared with the 100% Veg. timing (Table 4.9). Of the two nut characteristics likely to influence NIS weight (nut number and mean nut weight), number was responsible for the greater NIS weight of the 100% Rep. timing. In 1996 and 1997, NIS weight was greatest (P<0.05) in the vegetative N timings (100% Veg. >Veg./Rep.). Greater NIS weight of the 100% Veg. timing compared with the 100% Rep. timing was due to greater (P<0.05) nut number in 1996 and both number and mean nut weight in 1997.

19

Table 4.9 Nitrogen treatment effects on commercial NIS production. Means not followed by a common letter differ significantly, (P<0.05).

1995 1996 1997 NIS wt.

(g) Number of

nuts Mean nut

wt. (g) NIS wt.

(g) Number of nuts

Mean nut wt. (g)

NIS wt. (g)

Number of nuts

Mean nut wt. (g)

N rate n.s. * *** * *** * * ** n.s. Medium 7177 1257 b 5.69 a 11594 b 2308 b 5.02 a 9363 b 2083 b 4.49 High 7680 1560 a 4.96 b 12850 a 2713 a 4.75 b 10662 a 2416 a 4.41 5% lsd 1301 254 0.26 1035 220 0.22 1133 237 0.12 N Timing *** *** ** *** *** n.s. *** ** * 100% Veg. 5819 b 1041 b 5.63 a 14111 a 2912 a 4.88 11503 a 2513 a 4.58 a Veg./Rep. 6659 b 1286 b 5.23 b 12033 b 2400 b 5.03 10069 b 2297 a 4.39 b 100% Rep. 9806 a 1898 a 5.11 b 10521 c 2219 b 4.75 8466 c 1937 b 4.37 b 5% lsd 1594 312 0.32 1268 270 0.27 1388 290 0.14 Rate x Timing n.s. n.s. n.s. n.s. * n.s. n.s. n.s. n.s. Med. Veg. 5020 852 5.89 13038 2553 bc 5.11 10696 2309 4.63 Med. Veg./Rep. 6588 1156 5.70 11130 2169 c 5.14 9061 2046 4.43 Med. Rep. 9922 1762 5.46 10613 2202 c 4.82 8322 1893 4.40 High Veg. 6619 1231 5.36 15185 3271 a 4.64 12309 2717 4.53 High Veg./Rep. 6729 1415 4.76 12935 2632 b 4.93 11067 2549 4.34 High Rep. 9691 2034 4.76 10429 2236 c 4.68 8611 1981 4.34 5% lsd 2254 441 0.45 1793 382 0.39 1962 411 0.20 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

20

Nut-in-shell weight was greater (P<0.05) at the high N rate in 1996 and 1997 due to greater (P<0.05) nut number. The two floral characteristics likely to influence NIS weight, number of panicles/m² of canopy and number of nuts per panicle, were unaffected (P>0.10) by treatments (Table 4.10). The number of panicles per tree was, however, greater (P<0.05) in the 100% Veg. timing compared with the 100% Rep. timing in both 1996 and 1997. This was probably a factor of greater CSA in the 100% Veg. timing (Table 4.3) which led to greater nut number in this N timing compared with the 100% Rep. (Table 4.9). Table 4.10 Nitrogen treatment effects on panicle growth. Means not followed by a

common letter differ significantly, (P<0.05).

Number of panicles /m² of canopy

Number of panicles per

tree

Number of commercial nuts

per panicle 1996 1997 1996 1997 1996 1997

N rate n.s. n.s. n.s. n.s. n.s. n.s. Medium 15.7 24.8 585 1220 4.18 1.87 High 14.8 23.3 625 1195 4.63 2.05 5% lsd 3.4 4.1 150 201 1.20 0.38 N Timing n.s. n.s. P=0.056 ** n.s. n.s. 100% Veg. 15.1 25.1 712 1401 a 4.48 1.89 Veg./Rep. 15.1 24.5 618 1279 a 3.95 1.84 100% Rep. 15.4 22.6 485 942 b 4.78 2.16 5% lsd 4.1 5.0 183 246 1.47 0.46 Rate x Timing n.s. n.s. n.s. n.s. n.s. n.s. Med. Veg. 14.5 28.5 622 1533 4.33 1.59 Med. Veg./Rep. 16.5 25.3 624 1246 3.56 1.70 Med. Rep. 16.0 20.8 510 879 4.65 2.32 High Veg. 15.8 21.8 803 1269 4.63 2.19 High Veg./Rep. 13.8 23.8 612 1312 4.35 1.98 High Rep. 14.8 24.5 461 1004 4.91 1.99 5% lsd 5.9 7.1 259 348 2.10 0.65 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001 Nut-in-shell weight/m² of canopy was greater (P<0.05) in the 100% Rep. timing compared with the 100% Veg. timing in 1995, but was unaffected (P>0.10) by treatments in 1996 and 1997 (Table 4.11). The proportion of early season (August) nut harvest in 1995 and 1996 was greater (P<0.05) in the vegetative N timings compared with the 100% Rep. timing (Table 4.12, Figure 4.1a). Early season nut harvest of the vegetative N timings in these years was associated with greater levels of pre-July panicle development compared with the 100% Rep. timing (Table 4.7). In 1995 and 1996 the proportion of nut harvest by November was greater (P<0.05) in 100% Veg. timing compared with the 100% Rep. timing. Greater (P<0.05) levels of post-

21

November nut harvest occurred in the reproductive N timings in 1995 (100% Rep.) and 1996 (Veg./Rep. and 100% Rep.). Treatments did not affect the distribution of nut harvest in 1997. Table 4.11 Nitrogen treatment effects on tree canopy productivity. Means not

followed by a common letter differ significantly, (P<0.05).

Commercial NIS weight (g) per m² of canopy 1995 1996 1997

N rate n.s. n.s. n.s. Medium 307.0 310.4 194.1 High 307.4 309.2 206.0 5% lsd 38.4 34.5 15.3 N Timing *** n.s. n.s. 100% Veg. 227.0 c 305.8 204.3 Veg./Rep. 279.5 b 292.1 193.1 100% Rep. 415.6 a 331.5 202.9 5% lsd 47.0 42.2 18.7 Rate x Timing n.s. n.s. n.s. Med. Veg. 212.8 307.2 201.4 Med. Veg./Rep. 274.4 295.3 184.2 Med. Rep. 433.9 328.8 196.7 High Veg. 241.2 304.5 207.2 High Veg./Rep. 284.7 288.9 201.9 High Rep. 397.3 334.2 209.0 5% lsd 66.4 59.7 26.5 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001 The level of early season nut harvest was greater (P<0.05) at the high N rate compared with the medium rate in 1996 and 1997. A similar trend was observed in 1995. This response was associated with greater levels of pre-July panicle development with the high N rate compared with the medium rate in these years (Table 4.7). Kernel yield. Kernel weight was greater (P<0.05) in the 100% Rep. timing compared with the 100% Veg. timing in 1995 (Table 4.13) and was due to both determinants of kernel weight, NIS weight and kernel recovery (Tables 4.9 and 4.13). Conversely, in 1996 and 1997 the 100% Veg. timing produced greater (P<0.05) kernel weight compared with the 100% Rep. timing. Kernel recovery was lower in the 100% Veg. timing in 1995 (P<0.05), 1996 (P<0.05) and 1997 (P=0.057) compared with the 100% Rep. timing. Kernel weight of the 100% Veg. timing was sustained, however, by greater (P<0.05) NIS weight compared with the 100% Rep timing in these years (Table 4.9). Lower kernel recovery of the 100% Veg timing compared with the 100% Rep. timing in 1997 was associated with higher (P<0.05) levels of defective nut. This trend was also apparent in 1996.

22

Table 4.12 Distribution (%) of commercial NIS weight across time in the 1995, 1996 and 1997 harvest seasons. Means not followed by a common letter differ significantly, (P<0.05).

1995 1996 1997 August November Jan 1996 August November Jan 1997 August November Jan 1998

N rate n.s. ** n.s. * n.s. n.s. ** * Medium 6.9 73.8 b 84.5 13.1 b 86.3 94.5 11.9 b 92.9 b 100.0 High 9.9 80.4 a 86.3 18.4 a 82.7 93.5 21.5 a 95.1 a 100.0 5% lsd 4.4 4.7 5.0 4.3 6.3 5.1 5.8 2.0 N Timing *** *** *** *** *** *** n.s. n.s. 100% Veg. 15.5 a 91.2 a 99.2 a 26.5 a 94.8 a 100.0 a 20.2 93.6 100.0 Veg./Rep. 8.5 b 87.0 a 90.3 b 16.6 b 83.1 b 95.5 a 15.7 94.4 100.0 100% Rep. 1.3 c 53.1 b 66.7 c 4.2 c 75.7 b 86.6 b 14.1 94.0 100.0 5% lsd 5.3 5.8 6.1 5.2 7.7 6.2 7.2 2.5 Rate x Timing n.s. n.s. n.s. * n.s. * n.s. n.s. Med. Veg. 14.5 89.4 99.4 26.8 a 95.5 100.0 16.5 92.1 100.0 Med. Veg./Rep. 5.9 80.6 86.1 9.1 b 81.9 91.6 9.9 93.0 100.0 Med. Rep. 0.4 51.5 68.2 3.5 b 81.7 91.9 9.2 93.5 100.0 High Veg. 16.5 92.9 99.0 26.2 a 94.1 100.0 23.9 95.1 100.0 High Veg./Rep. 11.0 93.3 94.6 24.2 a 84.4 99.3 21.5 95.7 100.0 High Rep. 2.2 54.8 65.3 4.8 b 69.8 81.3 19.0 94.5 100.0 5% lsd 7.6 8.2 8.7 7.4 10.9 8.8 10.1 3.5 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

23

Table 4.13 Nitrogen treatment effects on kernel weight and quality. Means not followed by a common letter differ significantly, (P<0.05).

1995 1996 1997 Kernel

weight (g)

Kernel recovery

(%)

Defective nuts (%)

Kernel weight

(g)

Kernel recovery

(%)

Defective nuts (%)

Kernel weight

(g)

Kernel recovery

(%)

Defective nuts (%)

N rate n.s. n.s. n.s. * n.s. n.s. * n.s n.s. Medium 2162 29.7 14.2 3725 b 32.2 9.7 2763 b 29.6 6.48 High 2256 29.3 16.0 4146 a 32.3 9.9 3154 a 29.6 6.70 5% lsd 410 0.7 4.0 344 0.4 2.9 348 0.5 1.5 N Timing *** ** n.s. *** ** n.s. ** P=0.057 * 100% Veg. 1659 b 28.6 b 13.9 4477 a 31.7 b 10.4 3370 a 29.2 8.26 a Veg./Rep. 1978 b 29.7 a 17.5 3898 b 32.4 a 9.9 2964 ab 29.5 6.15 b 100% Rep. 2989 a 30.3 a 13.9 3431 c 32.6 a 9.1 2541 b 30.0 5.36 b 5% lsd 520 0.8 4.9 421 0.5 3.6 427 0.6 1.8 Rate x Timing n.s. n.s. P=0.087 n.s. n.s. n.s. n.s. n.s. n.s. Med. Veg. 1431 28.6 13.1 4107 31.5 10.9 3088 28.9 8.25 Med. Veg./Rep. 1966 29.8 19.3 3618 32.5 11.2 2696 29.7 6.34 Med. Rep. 3088 30.8 10.3 3449 32.5 7.2 2505 30.1 4.84 High Veg. 1888 28.7 14.8 4847 31.9 9.9 3652 29.6 8.27 High Veg./Rep. 1990 29.6 15.7 4178 32.3 8.7 3232 29.3 5.95 High Rep. 2891 29.7 17.6 3413 32.7 11.0 2578 29.9 5.89 5% lsd 710 1.1 6.9 595 0.8 5.1 603 0.9 2.6 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

24

The high N rate produced greater (P<0.05) kernel weight in 1996 and 1997 compared with the medium rate. This was due to higher (P<0.05) NIS weight (Table 4.9) as kernel recovery and the proportion of defective nuts was not affected by N rate. 4.6 Leaf nutrient levels Two leaf types, the largest mature pre-floral vegetative flush leaf (LMFF) and the mature internal leaf (MI), were sampled concurrently on three occasions during the reproductive N applications of 1995 (Table A3.1). The leaf N of each was compared (Table 4.14) to determine which of the two types was most responsive to N applications. On two of the three sampling occasions, a significant (P<0.001) interaction between leaf type and N timing was observed. This was due to a greater increase in leaf N in the LMFF leaves compared with the MI leaves suggesting that the LMFF leaf is the more responsive of the two types to N applications. The largest pigmented (LP) and mature external (ME) leaves were generally available during the summer–autumn months (corresponding to the vegetative N treatment applications), and the LMFF leaves over the winter–spring months (corresponding to reproductive N treatment applications) (Table A3.1). Availability of LP leaves tended to be less predictable and their N concentration less responsive to N timing compared with ME leaves (Tables A3.2-5). Leaf N reflected N timing in ME in 1996 and 1997, and in LMFF leaves in all years of the study (Figure 4.2, Tables A3.3-5). During the vegetative N applications of 1996 and 1997, leaf N in ME leaves was higher (P<0.05) in the 100% Veg. timing compared with the 100% Rep. timing. This response carried through to July in 1996 and to June in 1997. These were the months of high panicle emergence of the 100% Veg. timing (Figure 4.1b) suggesting remobilisation of N to floral development. Leaf N in LMFF leaves was higher (P<0.05) in the 100% Rep. timing compared with 100% Veg. timing in all years after September (the latter part of the reproductive N applications). Leaf N in ME and LMFF leaves in the Veg./Rep. N timing was generally intermediate between the 100% Veg. and the 100% Rep. timings throughout the year in each year of the study (Figure 4.2, Tables A3.3-5). Leaf N was generally higher in the vegetative N timings (100% Veg. and Veg./Rep.) in 1996 and 1997 compared with 1995 reflecting the combined influence of low tree N at the start of the trial (Table 4.2) and low vegetative N applications in 1995 (Table 3.4). In ME and LMFF leaves, leaf N was frequently higher (P<0.05) at the high N rate compared with the medium rate in 1995, 1996 and 1997 (Figure 4.3, Tables A3.2-5). While no statistical comparisons were made between the low and the medium and high N rates, leaf N was usually lowest at the low N rate. Leaf N in ME and LMFF leaves ranged from 1.47 to 2.07% and 1.70 to 2.25% at the high N rate in 1996 and 1997, respectively. This N rate produced the highest NIS yield in these years (Table 4.9).

25

Table 4.14 Effect of the largest mature pre-floral vegetative flush leaf (LMFF) and the mature terminal leaf (internal position) (MI) on N concentrations (%) on three sampling dates in 1995. Means not followed by a common letter differ significantly, (P<0.05).

28.7.95 7.9.95 5.10.95

Rate (R) P=0.076 * * Medium 1.520 1.585 a 1.585 a High 1.609 1.749 b 1.781 b 5% lsd 0.099 0.124 0.180 Timing (T) n.s. *** *** 100% Veg. 1.592 1.424 a 1.196 a Veg./Rep. 1.604 1.791 b 1.645 b 100% Rep. 1.497 1.786 b 2.209 c 5% lsd 0.121 0.152 0.220 R x T n.s. n.s. n.s. Leaf type (L) *** *** ** LMFF 1.246 a 1.451 a 1.588 a MI 1.883 b 1.883 b 1.778 b 5% lsd 0.065 0.087 0.118 L x R n.s. n.s. n.s. L x T n.s. *** *** LMFF – 100% Veg. 1.250 1.067 a 0.908 a LMFF – Veg./Rep. 1.311 1.577 b 1.581 bc LMFF – 100% Rep. 1.177 1.707 bc 2.275 d MI-100% Veg. 1.934 1.780 c 1.484 b MI-Veg./Rep. 1.898 2.004 d 1.709 c MI-100% Rep. 1.817 1.865 cd 2.142 d 5% lsd 0.144 0.186 0.262 L x R x T n.s. n.s. n.s. n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

26

Figure 4.2 Nitrogen concentration in (a) mature external (ME) and (b) largest mature pre-floral vegetative flush (LMFF) leaves for times of N application. Horizontal bars indicate period of treatment application. (σ-100% Veg.; λ-Veg./Rep.; υ-100% Rep.). * Denotes P<0.05.

(a) ME

1.30

1.50

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27

Figure 4.3 Nitrogen concentration in (a) mature external (ME) and (b) largest mature pre-floral vegetative flush (LMFF) leaves for rate of N application. (υ-low; λ-medium; σ-high). * Denotes P<0.05.

(a) ME

1.30

1.50

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28

Leaf nutrient concentrations other than N. Concentrations of P, K, Ca, Mg, Cu, Zn, Mn and Fe were monitored in ME and LMFF leaves. There were generally no consistent statistical differences in the concentrations of these nutrients among N treatments. The ‘optimum’ leaf concentrations were derived from ranges for these elements over the three years of the study (Table 4.15). In defining ‘optimum’ levels, it was assumed that adequate levels of the various nutrients had been applied in fertiliser applications and that uptake and utilisation by the tree was not limited. The application of foliar nutrients invalidated some analyses of Cu, Zn and Mn because of spray residues on the leaves. Table 4.15 Concentrations of non-treatment nutrients in mature external (ME) and

largest mature pre-floral vegetative flush (LMFF) leaves from 1995 to 1997.

Nutrient ME LMFF Range ‘Optimum’ Comments Range ‘Optimum’ Comments

P (%)

0.09–0.18 0.14 Concentrations increased slightly with soil P levels over time

0.07–0.14 0.10

K (%) 0.59–1.1 0.78 0.28–1.15 0.72

Ca (%) 0.17–0.36 0.26 0.19–0.72 0.37

Mg (%) 0.17–0.27 0.21 0.14–0.31 0.21

Cu (mg/kg) 3.2–20.6 NA† Foliar spray residues detected on leaves

2.3–5.3 4.0

Zn (mg/kg) 8.9–254 NA Foliar spray residues detected on leaves

8.6–254 NA Foliar spray residues detected on leaves

Mn (mg/kg) 93–461 93 – 189 Foliar spray residues detected on leaves in 1995 and 1996

92–451 NA Foliar spray residues detected on leaves in 1995 and 1996

Fe (mg/kg) 23–64 45 35–64 52

† not available 4.7 Nitrogen movement in leachate Nitrogen concentrations sampled at 1 m depth under trees of the medium N rate 100% Veg. and Veg./Rep. timings during major drainage events of 1997 are presented in Figure 4.4a. Leachate N sampled is consistent with the rates of N applied and coincides well with precipitation (Figure 4.4b). Leachate N was highest for the 100% Veg. timing at most sampling times during March and April 1997. Over this period twice the quantity of elemental N was applied to the 100% Veg. timing compared with the Veg./Rep. timing. Maximum concentrations in both timings were 128 and 65 mg N/L for the 100% Veg. and Veg./Rep. timings, respectively. Leachate N decreased sharply in the 100% Veg. timing following the final vegetative N application on 23 April. The concentrations of nitrate in the inter-row averaged 9 mg N/L and it appears that there was lateral movement of N from the treatment trees approximately 3 m away. Ammonium concentrations were generally low (mean 1.1–2.9 mg/L) with occasional spikes as high as 21 mg/L. These generally occurred shortly after the application of ammonium nitrate.

29

Figure 4.4 (a) Leachate nitrate-N concentrations. (υ-Medium. Veg./Rep.; λ-Medium Veg.; σ-inter-row) and (b) precipitation under cashew trees in 1997.

0

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30

5. Discussion 5.1 Nut-in-shell and kernel moisture standards and assessment

methodology Moisture standards. Nut-in-shell and kernel weight should be reported at a stated water content (WC) to allow valid comparison of yield parameters. This is convention in other crop research (macadamia, peanuts, grain) where, like cashew, product moisture influences product weight. In this study we have reported NIS and kernel yield and kernel recovery at ‘specified’ water contents viz, NIS at 9%, kernel at 5% and kernel recovery as kernel weight at 5% as a proportion of NIS at 9%. Nut-in-shell at 9% WC is derived from the work of Okwelogu and Mackay (1969), who calculated the maximum safe water content for storage of raw cashew nut at 8.9 to 9.1%. A moisture content of 9% or lower is recommended for storage in India (Russell, 1969) and in Brazil the recommendation for storage is not greater than 9% (Franca, 1988). Kernel at 5% WC is the maximum specified by the International Organisation for Standardisation for packaging following processing of the nut (ISO, 1988). The actual water contents of NIS and kernel in this study were not known. The raw cashew nut (meaning NIS) contains volatile constituents that are driven off with the moisture when the nut is dried in a conventional oven (Okwelogu and Mackay, 1969). To overcome this, these workers determined the moisture content of the raw nut by distillation using toluene as the entraining solvent. The method prescribed by the International Organisation for Standardisation for determining the moisture content of cashew kernel is drying at 70 °C under pressure of about 3 kPa (ISO, 1982 and 1988). Both these procedures have major drawbacks. There are health risks associated with the use of toluene, while drying under pressure requires a vacuum oven that may not be readily available (certainly not for this study). For these reasons, neither of these methods was used in this study but a more practical approach was sought. Nut-in-shell and kernel was dried in a conventional oven at 65 °C to constant weight and assumed to be at 1% and 0% WC, respectively. The actual water content of NIS and kernel dried by this method needs to be determined. Commercial NIS yield. All nuts including very small nuts were harvested for assessment of NIS and kernel yield in this study. In commercial practice however, various numbers of small nuts are not ‘captured’ by harvesting machinery and post-harvest cleaning equipment. In addition, some of the small nuts are intentionally removed on the assumption that they have no kernel and hence no commercial value. Commercial NIS and kernel yield is therefore influence by the level of these nuts surviving post-harvest treatment. In this study we have attempted to reconcile commercial and non-commercial NIS yield an aspect not previously examined by research workers in Australia. A minimum commercial nut weight (3.03 g at 9% WC) was defined in 1997, derived in part from the smallest kernel weight defined by the ISO for raw kernel trade. While nuts below this standard yield kernels that are defined as too small for raw kernel sale, they may have use in value added products. The kernel yield of non-commercial nut was not assessed in this study. Non-commercial NIS weight was estimated for 1995 and 1996. It is not known how these estimates compare with weights had the 1997 standard been used to determine non-commercial NIS weight. The maximum weight of small nuts averaged across all treatments in 1995 (1.68 g)

31

was less than the same figure for 1997 (2.37 g). Commercial NIS for 1995 therefore is likely to have been overestimated when it was calculated by subtraction of the non-commercial nut weight from the total NIS weight. The 1996 non-commercial nut weight was calculated from the mean weight of the small nuts of 1995 (1.39 g) and the proportion by number of void nuts of 1996 recorded during kernel extraction. It was noted during kernel extraction that the void nuts were mostly the smaller nuts, but void nuts sometimes occurred with larger nuts. It is likely that the proportion of void nuts would have tended to overestimate the weight of non-commercial nuts. This may have been balanced by the mean weight of the 1995 small nuts (1.39 g) which was lower than the mean weight of 1997 non-commercial nuts (1.42 g). 5.2 Effects of nitrogen on vegetative and reproductive growth Contrasting responses of NIS and kernel yield and timing of nut drop to N rate and N timing were evident in the three years of the study. This highlights the challenge of confirming treatment responses in short-term studies of perennial tree species, the growth of which can be affected by previous and current season’s environmental influences. Rate-by-timing interactions were almost non-existent and it may be that the range of the two N rates used was insufficient to produce rate-by-timing interactions. In two out of the three years of the study NIS and kernel yields were greatest, and the proportion of nut drop by November highest in treatments receiving N during the vegetative growth phase. The high N 100% Veg. timing produced the highest NIS yield in 1996 (15.2 kg/tree) and 1997 (11.5 kg/tree). As a result, our recommended minimum N rates are 120 kg/ha for four-year-old trees and 180 kg/ha for five and six-year-old trees. Higher rates of N may further increase NIS yield but may also continue to reduce mean nut weight. The use of higher N rates will thus be a compromise between NIS yield, mean nut weight and possible excessive canopy growth. In 1995 vegetative N treatments were started mid-way through the vegetative growth phase, and the resulting range of N rates applied, appears to have confounded treatment responses and favoured the reproductive N timings (Veg./Rep. and 100% Rep.). Lower N rates were applied during the vegetative growth phase compared with those applied during the reproductive phase. The 100% Veg. timing was affected the most, receiving only 34% of the total annual rate that was applied to the 100% Rep. timing. Treatment responses, for example NIS weight and canopy productivity, reflect this difference. Nut-in-shell weight of the 100% Rep. timing was 70% greater than the 100% Veg. timing in 1995 while in the following two years NIS weight of the 100% Veg. timing was 25% greater than the 100% Rep. timing. Furthermore, the 100% Rep. timing’s canopy productivity was 80% greater than the 100% Veg. timing in 1995, while in 1996 and 1997 all timings had similar productivity levels. Commercial NIS weight increased from 1995 to 1996 in all timing treatments but decreased from 1996 to 1997. The proportion of non-commercial nuts by number in 1995 and 1996 was 10.2 and 8.9%, respectively, while in 1997 it was 32.2%. Total number of nuts (which includes non-commercial nuts) increased from 1996 to 1997. Accepting the limitations of our estimates of non-commercial nut weight for 1995 and 1996, it still reasonable to expect that commercial NIS weight in 1997 would have been greater if the proportion of non-commercial nuts was similar to 1995 and 1996. Potential commercial NIS weight for 1997 could simply

32

be calculated by multiplying the mean commercial nut weight for each timing treatment in 1997 by the total number of nuts for each timing in 1997 adjusted to a commercial number using the proportion of commercial nuts in 1996 (91.1%). This results in potential yields in 1997 of 15 408 and 11 366 g/tree for 100% Veg. and 100% Rep. timings, respectively. The potential NIS yield represents an increase in commercial NIS weight from 1996 to 1997 for the two timings of 25%. Potential NIS and kernel yield is dependent not only on aspects of tree productivity that affect total weight and quality, but also on aspects that affect the timing of nut drop. Nut drop should be completed by the end of November in the Dimbulah area as the risk of crop loss becomes greater after this month because of the increasing incidence of rainfall. Fallen nuts germinate and harvesting machinery cannot operate efficiently under wet conditions. Further, harvesting activities after November conflict with other priorities such as pruning, fertilising and insect control. Improved levels of nut drop by November in 1995 and 1996 in treatments receiving N during the vegetative growth phase was due to higher levels of pre-July shoot and panicle growth. The opposite trend occurred when N was applied during the reproductive growth phase, higher levels of post-July vegetative and panicle growth leading to higher levels of post-November nut drop. This was particularly evident in 1995 when almost 50% of the commercial NIS yield for the 100% Rep. timing occurred post-November. When cumulative NIS weight over the period of the study are compared assuming total nut loss after November, yields of the 100% Veg. timing are 30% higher than the 100% Rep. timing. 5.3 Optimum leaf sampling time Two index leaves were identified for assessing tree nutritional status, a mature terminal leaf from a quiescent vegetative shoot (ME) and the largest mature pre-floral vegetative flush leaf of a floral shoot (LMFF). Both types are from current season’s growth. Each is of value for commercial use being easily recognisable, predicably available and displaying sensitivity to N application over their periods of availability. Further, each precede a major growth event, the ME prior to flowering and nut development and the LMFF prior to the main period of vegetative growth. They are therefore well placed to assess and adjust tree nutritional status before these important growth phases begin. Assessment of tree N status could be done twice a year by using the ME leaf in early winter (April–May) before floral development and the LMFF leaf (November–December) before the vegetative growth season. Nitrogen application during the vegetative growth phase was shown to be important for NIS and kernel yield and timing of nut drop and therefore the pre-vegetative assessment would be the more important of the two assessment times. Further, attempts to correct N deficiency following the pre-floral assessment would risk post-November nut drop. The pre-floral assessment should be used as a check that N concentrations are adequate and to make small adjustments to N level if necessary. The limited number of suitable trees available for this study restricted the number of N rates that could be evaluated to two. Therefore, it was not possible to develop a response curve over the rates of N. The ‘optimum’ leaf N concentrations were derived from the high N rate 100% Veg. timing, the treatment which achieved the highest NIS and kernel yield and maximised nut drop by November. Based on the range of leaf N concentrations recorded for this treatment during the recommended sampling times stated previously, the ‘optimum’

33

levels for ME and LMFF leaves would be 2.26 to 2.34% and 1.35 to 1.82%, respectively. The range for ME is similar to that reported by Robinson et al. (1997) for a similar leaf type, which was 2.40 to 2.58% for the ‘most recently hardened leaf on an actively growing shoot’. The range for the LMFF leaf is lower than the reported study and also lower than that of the ME leaf. The LMFF leaf is positioned adjacent to a developing panicle and the recommended sampling time coincides with the completion of nut development. It is possible that nutrient is being drawn from this and other pre-floral leaves to support nut growth. The ‘optimum’ concentrations represent current tree N status, leaf N level reflecting the previous N fertiliser program and the impact of factors influencing N uptake by the roots, N metabolism and N off-take in biological materials. They have little value in defining future N requirement. ‘Optimum’ concentrations in LMFF leaves therefore indicate that the normal N application regime should be applied during the vegetative growth period. However, if N concentration is lower than the ‘optimum’, additional N to the normal regime would be applied. The study resolved three basic issues for developing a calibration system for N applications. These were, N timing requirement, two index leaves and sampling times for assessing tree N status, and ‘optimum’ ranges for leaf N concentration. To develop the system further will require work to define response curves for a larger range of N rates applied during the vegetative growth phase. Assessment of tree nutritional status for other nutrients (P, K, Ca, Mg, Cu, Zn, Mn and Fe) could be undertaken at the same time as samples are taken for N. The LMFF leaves offer the most convenient opportunity for diagnosis as fertiliser applications can then be made prior to the monsoon season. Insoluble fertiliser forms are applied in December prior to the monsoon rains to facilitate nutrient movement to the roots. This timing will also reduce the amount of insoluble fertiliser residues present during the harvesting season and the risk of harvesting equipment relocating it from the application area under the tree to the centre of the inter-row. The ‘optimum’ concentrations for P, Ca and Mg derived from this work are similar to the values reported by Robinson et al. (1997). Potassium concentrations are however, lower than their adequate range of 1.10–1.20%. 5.4 Soil fertility and leaching Annual soil samples collected in June or July were analysed to monitor changes in soil fertility. Soil N concentrations were very low at this time and it would appear that, in this soil type and at this time, soil sampling as an aid for determining N application rate would be of little value. Applied N was either taken up by the plant or leached below the depth of sampling. However, this sampling is useful for monitoring the status of other nutrients. Additional work was undertaken to assess the potential environmental consequences of the fertiliser treatments on sustainable long-term nut production. High nitrate concentrations in leachate (up to 128 mg N/L) at a depth of 1 m were recorded during periods of high precipitation. This, together with low soil N recorded in June or July (subsequent to the monsoon season), demonstrates the challenge of keeping N within the tree’s root zone.

34

Nitrogen treatments were applied in five equal applications to provide maximum opportunity for uptake of N by the root system and minimal opportunity for leaching during heavy rainfall. This application strategy would not be viable in a commercial operation because of the high application cost. The application of N by fertigation is a cost-effective alternative as frequent and very precise applications can be made. Irrigation management must however, be of a high standard to avoid undesirable effects from off-site movement of nutrients and potential acidification of the irrigated zone. The nitrate data as well as that of other nutrients (e.g. K, Ca, Mg) require further interpretation and the modelling of water movement. The water fluxes, together with the concentration data recorded so far, will provide an outstanding insight into nutritional management of cashew on soils with low nutrient and water holding capacity. This information will be readily transferable as generic information for tree crops on well-drained soils. Investigations into the rapid changes in soil pH after commencement of the fertiliser treatments could not be completed in time for this report. The increase in available P concentrations between 1995 and 1997 indicates that the rate of application (40 kg/ha in 1995 and 1996, 20 kg/ha in 1997) was in excess of removal by the crop, leaching and reaction with the soil. A reduction in extractable soil K concentrations in the top 60 cm is not reflected in leaf K concentrations in either the ME or LMFF leaves. The reason for this is unknown and may be understood when leachate data is studied further. Because of the known low levels of available Cu and Zn in this soil type, foliar applications were made in early 1995. Soil applications were also made in April 1996. Despite these applications, Zn concentration in ME leaves between June and August 1996 was as low as 8.9 mg/kg. This demonstrates the limitation in plant availability associated with the surface application of non-mobile nutrients such as Cu and Zn. Because the rates of leaching are extremely low due to reactions of the nutrients with soil organic matter and clay, the nutrients remain in the top few centimetres of soil (Brennan and McGrath, 1988). This area dries out rapidly so that root activity and the ability of the plants to absorb the nutrients will be greatly reduced. The effect of soil applications on extractable Cu and Zn concentrations were readily detected in the 0–10 cm samples collected after the application of the fertilisers to the soil. Foliar application is the most reliable method of application of these nutrients because cultivation cannot be used to physically improve the distribution through the root zone. 5.5 The ‘ideal’ phenological cycle and a crop management program Phenology is the relationship between climate and periodic biological phenomena (Wolstenholme and Whiley, 1989). Cashew shows distinct developmental phases (pheno-phases), for example vegetative flushing, flowering, and nut maturation, which predominate at particular times during the year. The overall seasonal pattern of development can be modelled by relating the different pheno-phases and identifying critical growth phases that influence productivity. Once critical phases are identified and understood, management decisions can be made which are most likely to increase tree productivity (Whiley et al., 1988).

35

An Australia industry must be competitive at world market prices. Nut-in-shell yields, which have not been demonstrated under commercial culture to this time, ranging from 2.8 to 5 t/ha (Cann et al., 1987; Oliver et al., 1992; Hinton, 1998), are required to be economically viable. Cashew plantations of 500 ha are envisaged as necessary for Australian production (Chacko et al., 1998). Successful cashew production in Australia will therefore depend on cultivars with relevant growth and nut production specifications and production systems that support the realisation of genetic potential. These production systems will feature highly organised personnel and plantation management, well-timed nutrient and water applications, and integrated pest management. This study has demonstrated that N timing can influence the phenological development of cashew at Dimbulah. Two contrasting growth patterns were observed in two of the three years of the study. In 1995 and 1996 vegetative N applications (December–April) promoted higher levels of pre-July shoot and panicle development and nut drop by November compared with when 100% of the annual N was applied during the reproductive phase (June–October). The latter N timing resulted in higher levels of post-November nut drop, 47% of the commercial NIS weight in 1995 and 24% in 1996. Completion of nut drop by the end of November in the Dimbulah area is an important criterion by which the suitability of a particular phenological cycle for this area is judged. A cycle based on N applied entirely during the vegetative growth phase is therefore accepted as the ‘ideal’ for this area (Figure 5.1). The important cultural operations have been superimposed on the cycle. The placement of each operation in relation to the phenological development of the tree, and the important elements of each is explained as follows. 1. Nutrition • Tree nutritional status is assessed prior to vegetative and reproductive development. • Nitrogen is applied during the vegetative growth phase to promote vegetative growth for

high NIS and kernel yields and nut drop by November. • Insoluble fertiliser forms are applied in December prior to the monsoon rain to facilitate

movement of nutrient to the roots. This timing will also reduce the amount of insoluble fertiliser residues present during the harvesting season and the risk of harvesting equipment relocating it from the application area under the tree to the centre of the inter-row.

• Foliar Zn in particular, and other micronutrients as required are applied at times of vegetative flushing to maximise uptake by the tree.

2. Irrigation • Irrigation system checks prior to the irrigation season. • Irrigation most important during flowering and nut development. Only applied during

vegetative growth phase if soil moisture becomes limiting to growth. 3. Insect control • Seasonal pests most active during the vegetative growth phase. • Important to protect both vegetative and floral growth. • Protection during flowering and early nut development critical for NIS yield. • Avoid insecticide applications during pollination.

36

4. Weed control • Important for reducing weed competition for nutrient and water, harbourages for

invertebrate pests, fire hazard and facilitating pre-harvest field preparations. • Avoid chemical sprays to fallen nuts. 5. Pre-harvest field preparations • Previous season’s nuts, trash and rocks removed from rows. Ground surface levelled and

inter-row grass slashed to aid sweeping and pick-up of nuts. Minor pruning to raise canopy skirts to reduce obstruction to sweepers and operator vision.

6. Harvesting • Completed by the end of November to avoid conflict with pruning and fertilising. 7. Pruning • Hedging of canopy sides, topping and raising of canopy skirts in December following

harvest and before the major vegetative growth season.

37

Figure 5.1 A crop management program based on the ‘ideal’ phenological cycle of cv 9/14 in the Dimbulah area of North Queensland. Dec Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Rainfall (mm) 185 210 139 29 15 14 5 5 6 18 54 100 Deficit (mm) — — — -95 -99 -90 -109 -127 -158 -183 -144 -91 Number of wet days 13 14 10 4 2 2 1 1 1 2 5 8 ‘Ideal’ phenological cycle Flowering and nut set Wet season Nut drop vegetative flush Pre-floral veg. flush and

panicle emergence Nut maturation

Cultural operations† Nutrition Leaf samples Leaf samples Nitrogen Foliar Zn sprays Foliar Zn sprays

N, P, K, Ca, Mg, B

Irrigation maintenance Irrigation (Low, Medium, High) L L-M M-H H H M Insect control‡ Mango shoot caterpillar

Leaf miner, Leaf roller

Spotting bug, Tea mosquito, Passion vine bug, Pink wax scale, Red-banded thrips Weed control Pre-harvest field preparations Harvesting Pruning

† Noel Grundon, Sam Blaikie, Norm Butler (pers. comm.) ‡ denotes time of activity

38

6. Implications 6.1 Impact of N management practices on the Australian cashew industry The total area of the Australian cashew industry is 300 ha existing as two holdings, ‘Cashews Australia’ at Dimbulah in North Queensland with an area of 240 ha and ‘Cashews NT’ at Wildman River in the Northern Territory with an area of 60 ha. In 1997, Cashews Australia suffered a total crop loss of 96 t NIS, valued at $167 000 (P. Shearer, pers. comm.). Peak nut drop occurred post-November coinciding with early monsoon rains in mid-December. The 1997 fertiliser program began in June and based on the results of this study late N timing was considered a major factor responsible for the late season nut drop. In 1998 Cashews Australia implemented N timing recommendations drawn from this Project. A total NIS yield for the farm of 150 t and valued at $261 000 was harvested in 1998. Harvesting was completed in December and the total harvest was estimated at 95% of the potential crop. 6.2 Benefit-cost analysis of the research expenditure A benefit:cost analysis was performed using the Grains Research and Development Corporation guidelines for economic evaluation as a guide (GRDC, 1992). Project benefits. The Project demonstrated that, by N rate and timing, NIS yields above levels produced by current industry fertiliser practices could be achieved. The Project has also defined a crop management program that will, in conjunction with N management technology, improve farm efficiency and result in cost savings. The Project’s benefits to industry have been quantified on the basis of industry’s adoption of N management technology only. The unit benefit. To quantify the unit benefit from the Project, ‘without Project technology’ (i.e. current industry practice) and ‘with Project technology’ (i.e. the application of Project technology) for mature trees were compared by gross margin analyses. Reliable industry NIS yields for mature size trees were not available. Available industry data were for trees that had not reached a mature canopy size, and were of a different size and variety to the Project trees. To compare ‘without Project technology’ and ‘with Project technology’ for mature size trees, NIS yields per hectare were calculated from canopy productivity and canopy surface area data (Table 6.1). A number of assumptions were made for this comparison: • the inherent capacity for canopy productivity of the industry cultivar (cv NDR2) was the

same as the Project cultivar (cv 9/14); • canopy productivity was constant irrespective of canopy size; • industry nutrition practices described by Grundon (1998), that is ‘with Project

Technology’, would achieve the same level of nut drop by November as the medium N rate 100% Rep. treatment of the Project (87.6%, mean of 1996 and 1997), while the level achievable ‘with Project technology’ was equivalent to the high N rate 100% Veg. treatment (94.6%);

39

• the productivity of the industry cultivar reflected the productivity of the range of genotypes grown by industry; and

• the actual contribution of Project technology (N rate and timing) was 47.5% of the productivity improvement.

The latter assumption was based on the estimated contribution of other elements (P and K) to NIS yield from Richards (1993). Tree population was 208 per hectare and this was derived from the tree spacing (8 x 6m) most commonly used in industry. Table 6.1 Canopy productivity and canopy surface area (CSA) data used to define

Project benefits.

Canopy productivity (g/m² of canopy) Industry† Project‡

CSA (m²) for a tree spacing 8 x 6m

112.6 165.2 56.27

† cv NDR 2 (mean of 1996 and 1997) (Grundon, 1998) ‡ cv 9/14 (mean of 1996 and 1997) for high N rate of 100% Veg. treatment Based on Project NIS yield improvements, the potential Project benefit was $952/ha (Table 6.2). Table 6.2 Potential incremental profit†. ‘without Project

technology’ ‘with Project technology’

Yield per hectare (t) 1.31 1.93 Gross income ($/ha) 2142 3162 Total variable costs ($/ha) 1241 1309 Gross margin ($/ha) 901 1853 Incremental profit ($/ha) — 952

† Data were drawn from ‘Cashew production in North Queensland – estimating profitability’ (Hinton, 1998) and rounded to the nearest dollar. Potential area affected. Project technology was first applied by industry in 1998. The potential industry area affected by the project was based on the total area of mature size trees at Cashews Australia and Cashews NT in 1998 and reaching mature size from this year to 2017. This was 220 ha in 1998 and increased to a maximum of 300 in 2000 (P. Shearer, pers. comm.) and assumed to remain at this maximum area to 2017 (Table 6.3). The probability of success. This benefit:cost analysis has been assessed retrospectively of the Project developing technology which will improve NIS yield above current industry estimates. The probability of success (that is the Project achieving this) which has been used in this assessment of the Project benefit has therefore been taken at 100%.

40

Transferability of research results and adoption rates. It was assumed that 100% of industry would adopt Project technology in year 1998. Actual benefit realised however, would be limited by the level of efficiency of a number of cultural practices including irrigation, nutrition and insect management. It was assumed that 60% of the benefit would be realised by industry in 1998 and this would increase to 70% in 2001 and remain at this level until 2017. Table 6.3 Project benefits. 1998 1999 2000 2001-2017 Potential project benefits Incremental Profit ($/ha) 952.00 952.00 952.00 952.00 Potential area affected (ha) 220 220 220 300 Potential net benefits ($ 000) 209.44 209.44 209.44 286.60 Dilution factors Probability of success (%) 100 100 100 100 Transferability of research results (%) 100 100 100 100 Adoption rates (%) 60 60 60 70 Expected net benefits ($ 000) 125.67 125.67 125.67 199.92 Project costs. The project was funded from 1 July 1993 to 30 June 1998. Table 6.4 shows the costs for each financial year of the Project’s term. Table 6.4 Annual Project costs ($).

Year RIRDC QDPI Industry Total 1993–94 22 503 32 011 1 700 56 214 1994–95 17 761 48 855 1 000 67 616 1995–96 25 121 51 297 1 000 77 418 1996–97 27 157 53 862 1 000 82 019 1997–98 16 939 56 555 500 73 994 Total 109 481 242 580 5 200 357 261

Investment criteria. A summary of the investment criteria is presented in Table 6.5. The net present value was calculated at the 8% discount rate. The analysis of the Project shows a positive return on investment with a benefit:cost ratio of 4.7. That is, for every dollar invested in the Project there is expected to be $4.70 worth of benefits to industry. Table 6.5 Summary of investment criteria.

Present value of costs ($ 000) 267 Present value of benefits ($ 000) 1257 Net present value ($ 000) 989 Benefit:cost ratio 4.70 Internal rate of return (%) 33.8

41

The benefit:cost ratio calculated in this analysis is a conservative estimate. The analysis was based on the existing planted area (300 ha) and it was assumed that over the term of this analysis, 1998 to 2017, this area would remain unchanged. This is unlikely to be the case. Given the potential for cashew production in Australia, expansion of the current area by new investors is a strong possibility. Further, preparations are in progress for additional plantings totalling 750 ha at Cashews Australia, Dimbulah, North Queensland (P. Shearer, pers. comm.). 7. Recommendations 7.1 Development of industry standards for NIS/kernel moisture and

assessment methodology So that the results from various studies can be compared, standards for expressing NIS and kernel yield need to be accepted by the cashew industry. To initiate discussion of this within the industry, we recommend that NIS be expressed at 9% WC, kernel at 5% WC and kernel recovery based on NIS and kernel yield at their respective water contents. Furthermore, commercial NIS yield standards need to be discussed. Under research conditions all nuts are usually harvested (total yield) while in commercial practice many small nuts are discarded during harvesting and post-harvest cleaning (commercial yield). We have defined a minimum commercial nut weight for the cultivar used in this study and recommend that NIS yield be stated in commercial terms and that this be reconciled according to ISO standards as done in this study. 7.2 Further work to confirm N effects and to develop a calibration system

for N applications The results of this study must be confirmed over at least two more growth seasons. While the weight of evidence from the study states that N applied during the vegetative growth phase will promote NIS yield and early season nut drop, conflicting responses were observed over the three years of the work. Of note were: 1. Nut-in-shell and kernel yield responses in 1995 were inconsistent with responses in 1996

and 1997. 2. In 1997 all timing treatments had similar proportions of nut drop by November whereas

in the previous two years of the study, higher levels of post-November nut drop were associated with reproductive N applications.

The study resolved three basic issues for developing a calibration system for N applications. These were, N timing requirement, two index leaves and sampling times for assessing tree N status, and ‘optimum’ ranges for leaf N concentration. To develop the system further will require definition of response curves for a larger range of N rates applied during the vegetative growth phase.

42

7.3 Selection of varieties with early season nut drop tendency Nut drop by the end of November is critical for economic cashew production in the Dimbulah area. The risk of crop loss from wet conditions after this month increases because of the increased incidence of rainfall. This study showed that crop losses of 15–30% (nut drop post-January) may occur from miss-timed N application. Losses of 25–50% could potentially be sustained from nut drop post-November. While N management will be important for achieving early season nut drop, the benefits of this technology will be enhanced by varieties with early season tendencies. Early season nut drop must therefore be a criterion for assessing the suitability of a particular variety in evaluations of genetic material. 7.4 Development of fertigation technology High concentrations of nitrate-N were measured in leachate at a depth of 1 m. This occurred during uncontrolled soil drainage flow that is frequent during the monsoon season. The monsoon season coincides with the vegetative growth phase when N applications are recommended. While the fate of leached nitrate was not determined, as samples were only taken at 1m depth, it is possible that in this soil type nitrate could be lost from the tree’s root zone. In addition to detrimental effects on soil chemical properties, this loss could potentially mean a reduction in nut yield and wastage of fertiliser and application outlays. Small and regular N applications will be required to supply N during this important growth phase and to minimise nitrate leaching. Regular surface applications of solid N forms are likely to be prohibitively expensive on cashew plantations of the size envisaged as necessary for Australian production (500 ha, Chacko et al., 1998). Fertigation will therefore provide a cost-effective solution and this technology and its application to cashew culture must be developed. 7.5 Development of sophisticated farm management systems Successful cashew development in Australia will depend in part on farm management systems that feature highly organised personnel and plantation management, well-timed nutrient and water application, and integrated pest management. This study has defined a crop management program based on a phenological cycle conditioned by vegetative N application. Considerable scope exists for developing the program beyond its present rudimentary form into a sophisticated system similar to that developed for avocados by Kernot et al., (1998). This software system, with linkages to a farm record-keeping facility, has the capacity to generate management recommendations aimed at improving production, quality and profitability. It would be eminently suitable for the management of large-scale cashew plantations. It could be argued that the size of the industry at this time does not warrant a sophisticated system of this type and that there is probably insufficient data available to develop such a system for cashew. Nevertheless, this should be the vision of cashew research workers in Australia and research should be coordinated toward collating data supportive of its development.

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8. Intellectual Property In two out of the three years of the study, N applied during the vegetative growth phase of cashew promoted NIS and kernel yield and early season nut drop. This is essential technology for successful commercial cashew nut production in the Dimbulah area, where cool winter temperatures slow the seasonal development of the tree. Floral growth and nut maturation occurs later in the year compared with warmer areas, such as the Northern Territory, increasing the risk of crop loss from monsoon rain. The information cannot be protected by patent for commercial advantage. It has been extended to industry during the course of the Project and has also been used to define N fertiliser recommendations in the Cashew information kit (Grundon et al., 1999). In all communications of the information to date, and those intended (publication in scientific journals), due recognition has and will be given to contributing parties. Copyright restrictions will ensure appropriate acknowledgment of contributors. 9. Communication Strategy The results of this study have been extended to industry, agri-business and cashew research workers by personal communication, site walks, and reporting at the Eighth Cashew Research and Development Workshop (O’Farrell et al., 1996). The trial has served as an on-farm demonstration of a ‘whole systems best practice’ management of cashew incorporating not only nitrogen (and other nutrient) management but also, fertigation, soil water monitoring and irrigation, insect control and pruning. Canopy productivity levels of the trial are double that reported for industry by Grundon (1998). The results of this work have been used to define N nutrition practices in the Cashew information kit (Grundon et al., 1999). This publication will provide information to students, research and extension workers, agri-business, current growers and potential investors. The results will also be published in scientific journals.

44

10. Appendices Appendix 1. Statistical summaries of descriptors analysed in uniformity trials

in 1993 and 1994. Table A1.1 Statistical summaries of the 10 descriptors for Port Douglas and K160

evaluated by cluster analysis techniques. Descriptor Minimum Maximum Median Mean Port Douglas (n=95) total NIS weight (g/tree) 534 7456 3486 3607 mean nut weight (g) 2.90 11.00 5.29 5.62 kernel recovery (%) 22.2 36.9 30.4 30.1 nut drop by the end of Nov (%) 4.3 100.0 71.2 64.7 canopy surface area (m²) 22.68 56.55 36.19 37.02 number of terminals/m² 10.0 47.0 21.0 22.7 number of panicles/m² 6.0 39.2 16.0 16.4 number of nuts per panicle 0.42 7.91 2.03 2.44 trunk circumference (cm) 39.0 65.0 51.0 51.0 apple weight (g) 17.9 113.3 47.2 49.5 K160 (n=96) total NIS weight (g/tree) 645 11359 4539 4704 mean nut weight (g) 3.23 11.07 6.02 5.96 kernel recovery (%) 21.6 40.2 32.8 32.4 nut drop by the end of Nov (%) 0.0 100.0 44.2 48.8 canopy surface area (m²) 21.50 55.30 39.27 39.03 number of terminals/m² 13.0 52.0 24.0 25.1 number of panicles/m² 6.0 46.0 17.2 18.0 number of nuts per panicle 0.46 10.45 2.10 2.79 trunk circumference (cm) 37.5 63.0 51.0 51.0 apple weight (g) 19.6 104.5 50.8 53.9

45

Table A1.2 Statistical summaries of the 10 descriptors for Port Douglas and K160 trees selected by cluster analysis and subjected to analysis of variance.

Descriptor Minimum Maximum Median Mean Port Douglas (n=16) total NIS weight (g/tree) 2383 7158 3386 3932 mean nut weight (g) 3.25 5.96 4.73 4.72 kernel recovery (%) 27.8 34.2 32.4 32.0 nut drop by the end of Nov (%) 7.2 100.0 70.9 61.1 canopy surface area (m²) 28.15 48.68 37.98 38.24 number of terminals/m² 11.0 28.0 21.5 21.3 number of panicles/m² 6.0 20.0 14.0 14.4 number of nuts per panicle 1.20 6.72 3.08 3.27 trunk circumference (cm) 44.0 57.0 50.0 50.0 apple weight (g) 25.9 55.0 43.3 40.7 K160 (n=16) total NIS weight (g/tree) 1775 6425 3081 3579 mean nut weight (g) 5.24 7.28 6.27 6.38 kernel recovery (%) 28.3 34.1 31.7 31.6 nut drop by the end of Nov (%) 18.5 57.5 37.0 35.6 canopy surface area (m²) 35.69 51.04 40.86 42.19 number of terminals/m² 14.0 28.0 22.5 21.4 number of panicles/m² 7.2 23.2 14.4 14.0 number of nuts per panicle 0.83 3.07 1.91 1.97 trunk circumference (cm) 49.0 59.0 54.5 54.8 apple weight (g) 41.4 87.3 66.8 65.8

Table A1.3: Statistical summaries of the nine descriptors of cv 9/14 (n=30) evaluated by

cluster analysis techniques. Descriptor Minimum Maximum Median Mean total NIS weight (g/tree) 1666 3476 2294 2283 mean nut weight (g) 5.21 6.43 5.65 5.71 kernel recovery (%) 30.9 34.7 32.9 32.7 nut drop by the end of Nov (%) 59.8 86.4 75.1 74.7 canopy surface area (m²) 9.82 16.42 12.32 12.48 number of panicles/m² 12.0 34.0 20.6 21.2 number of nuts per panicle 1.83 5.70 2.93 3.28 trunk circumference (cm) 34.0 44.0 39.0 39.2 apple weight (g) 39.1 51.5 47.0 46.2

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Table A1.4 Statistical summaries of the nine descriptors of cv 9/14 (n=24) for trees selected by cluster analysis and subjected to analysis of variance.

Descriptor Minimum Maximum Median Mean total NIS weight (g/tree) 1666 2772 2316 2274 mean nut weight (g) 5.21 6.43 5.63 5.72 kernel recovery (%) 30.9 34.7 32.7 32.7 nut drop by the end of Nov (%) 60.4 86.4 74.9 74.9 canopy surface area (m²) 9.82 16.42 12.32 12.52 number of panicles/m² 13.0 34.0 21.0 21.6 number of nuts per panicle 1.83 5.36 2.93 3.17 trunk circumference (cm) 34.0 43.0 39.0 39.2 apple weight (g) 39.1 51.5 47.0 46.3

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Appendix 2. Dates of treatment applications from 1995 to 1997. Table A2.1 Dates of treatment applications during vegetative and

reproductive growth from 1995 to 1997.

Vegetative growth December to April

Reproductive growth June to October

1995 23.06.95 26.07.95

28.02.95 31.08.95 27.03.95 26.09.95 03.05.95 25.10.95

1996 19.12.96 26.06.96 23.01.96 31.07.96 14.03.96 26.08.96 09.04.96 25.09.96 29.04.96 29.10.96

1997 17.12.96 18.06.97 20.01.97 23.07.97 19.02.97 25.08.97 17.03.97 23.09.97 23.04.97 22.10.97

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Appendix 3. Leaf types sampled and leaf N concentrations from 1995 to 1997. Table A3.1 Availability (3) of leaf types from 1995 to 1997.

Sample date

Largest immature

terminal leaf

Mature terminal leaf (internal

position)

Mature terminal leaf (external

position)

Largest mature pre-floral

vegetative flush leaf

(LP) (MI) (ME) (LMFF)

25.01.95 3 29.03.95 3 3 02.05.95 3 3 24.05.95 3 05.07.95 3 28.07.95 3 3 3 07.09.95 3 3 05.10.95 3 3 07.11.95 3 29.11.95 3 19.12.95 3 05.02.96 3 3 13.03.96 3 3 24.04.96 3 3 03.06.96 3 3 3 02.07.96 3 3 30.07.96 3 02.09.96 3 25.09.96 3 30.10.96 3 27.11.96 3 02.01.97 3 20.01.97 3 20.02.97 3 17.03.97 3 3 23.04.97 3 3 20.05.97 3 3 16.06.97 3 3 23.07.97 3 25.08.97 3 24.09.97 3 22.10.97 3 21.11.97 3 14.12.97 3

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Table A3.2 Nitrogen treatment effects on N concentration (%) in largest pigmented leaves (LP) from 1995 to 1997. Means not followed by a common letter differ significantly, (P<0.05).

Vegetative N treatments

28.2.95-3.5.95 Vegetative N treatments

19.12.95-29.4.96 Vegetative N treatments

17.12.96-23.4.97

29.3.95 2.5.95 5.2.96 13.3.96 24.4.96 3.6.96 20.1.97 17.3.97 23.4.97 20.5.97 16.6.97

N rate n.s. n.s. ** * P=0.086 n.s. ** * n.s. *** n.s. Medium 1.589 1.647 1.904 b 1.692 b 2.243 1.619 2.291 b 2.204 b 1.674 1.789 b 1.829 High 1.610 1.743 2.381 a 1.876 a 2.383 1.759 2.494 a 2.393 a 1.712 2.001 a 1.918 5% lsd 0.168 0.164 0.324 0.143 0.162 0.183 0.143 0.140 0.149 0.087 0.130 N Timing * ** *** n.s. *** *** n.s. * P=0.072 *** n.s. 100% Veg. 1.781 a 1.883 a 2.617 a 1.851 2.631 a 1.991 a 2.321 2.407 a 1.816 2.044 a 1.902 Veg./Rep. 1.551 b 1.723 a 2.349 a 1.716 2.369 b 1.703 b 2.418 2.310 ab 1.650 1.880 b 1.867 100% Rep. 1.468 b 1.479 b 1.461 b 1.784 1.938 c 1.373 c 2.439 2.180 b 1.614 1.761 c 1.852 5% lsd 0.205 0.201 0.396 0.175 0.199 0.244 0.175 0.171 0.183 0.107 0.159 Rate x Timing * n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. P=0.093 n.s. Med. Veg. 1.603 bc 1.761 2.419 1.738 2.520 1.995 2.256 2.278 1.884 1.897 1.842 Med. Veg./Rep. 1.701 ab 1.692 2.069 1.647 2.237 1.541 2.296 2.238 1.570 1.748 1.821 Med. Rep. 1.464 bc 1.488 1.223 1.690 1.971 1.320 2.322 2.097 1.570 1.723 1.825 High Veg. 1.958 a 2.005 2.815 1.964 2.743 1.987 2.386 2.535 1.748 2.192 1.962 High Veg./Rep. 1.401 c 1.754 2.630 1.786 2.500 1.865 2.540 2.382 1.731 2.013 1.914 High Rep. 1.471 bc 1.470 1.699 1.877 1.906 1.426 2.555 2.263 1.658 1.799 1.879 5% lsd 0.290 0.285 0.560 0.248 0.281 0.317 0.247 0.242 0.258 0.151 0.225 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

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Table A3.3 Nitrogen treatment effects on N concentration (%) in mature external leaves (ME) and largest mature pre-floral vegetative flush leaves (LMFF) in 1995. Means not followed by a common letter differ significantly, (P<0.05).

ME LMFF Vegetative N treatments

28.2.95-3.5.95 Reproductive N treatments

23.6.95-25.10.95 Veg. N trts.

started 19.12.95

29.3.95 2.5.95 24.5.95 5.7.95 28.7.95 28.7.95 7.9.95 5.10.95 7.11.95 29.11.95 19.12.95

N rate n.s. n.s. n.s. n.s. n.s. P=0.089 ** n.s. n.s. n.s. * Medium 1.758 1.875 1.530 1.486 1.855 1.186 1.345 b 1.502 1.417 1.320 1.399 b High 1.754 1.874 1.627 1.571 1.908 1.307 1.557 a 1.672 1.459 1.195 1.531 a 5% lsd 0.169 0.194 0.161 0.205 0.095 0.142 0.150 0.244 0.204 0.305 0.115 N Timing n.s. P=0.060 n.s. * n.s. n.s. *** *** *** * *** 100% Veg. 1.749 1.982 1.633 1.727 a 1.932 1.251 1.068 b 0.907 c 0.893 c 0.949 b 1.030 c Veg./Rep. 1.791 1.932 1.580 1.491 ab 1.897 1.311 1.578 a 1.580 b 1.487 b 1.339 a 1.446 b 100% Rep. 1.728 1.710 1.522 1.367 b 1.816 1.177 1.708 a 2.274 a 1.934 a 1.485 a 1.920 a 5% lsd 0.207 0.237 0.198 0.251 0.116 0.174 0.183 0.298 0.250 0.373 0.141 Rate x Timing n.s. n.s. P=0.068 n.s. P=0.095 n.s. n.s. n.s. P=0.061 n.s. n.s. Med. Veg. 1.734 1.978 1.525 1.673 1.840 1.194 0.994 0.892 1.034 0.957 0.991 Med. Veg./Rep. 1.814 1.914 1.455 1.482 1.872 1.197 1.453 1.442 1.326 1.289 1.372 Med. Rep. 1.725 1.733 1.609 1.303 1.853 1.167 1.589 2.173 1.891 1.715 1.834 High Veg. 1.764 1.987 1.741 1.781 2.024 1.307 1.142 0.922 0.752 0.941 1.068 High Veg./Rep. 1.768 1.949 1.705 1.501 1.921 1.426 1.703 1.718 1.649 1.390 1.520 High Rep. 1.730 1.686 1.434 1.430 1.779 1.188 1.828 2.375 1.978 1.255 2.006 5% lsd 0.293 0.335 0.279 0.355 0.164 0.246 0.259 0.422 0.353 0.527 0.199

n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

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Table A3.4 Nitrogen treatment effects on N concentration (%) in mature external leaves (ME) and largest mature pre-floral vegetative flush leaves (LMFF) in 1996. Means not followed by a common letter differ significantly, (P<0.05).

ME LMFF Vegetative N treatments

19.12.95-29.4.96 Reproductive N treatments

26.6.96-29.10.96 Veg. N trts.

started 17.12.96

5.2.96 13.3.96 24.4.96 3.6.96 2.7.96 3.6.97 2.7.96 30.7.96 2.9.96 25.9.96 30.10.96 27.11.96 2.1.97

N rate * ** *** n.s. n.s. n.s. n.s. * * * * * P=0.088 Medium 1.762 a 1.445 a 1.831 b 1.936 1.720 1.922 1.674 1.544 b 1.596 b 1.617 b 1.544 b 1.294 b 1.429 High 2.036 b 1.711 b 2.044 a 2.010 1.709 2.073 1.752 1.685 a 1.793 a 1.758 a 1.774 a 1.465 a 1.590 5% lsd 0.254 0.154 0.114 0.192 0.149 0.206 0.196 0.124 0.159 0.134 0.184 0.162 0.188 N Timing n.s. *** *** *** *** *** *** ** * *** P=0.095 * n.s. 100% Veg. 2.043 1.805 a 2.184 a 2.348 a 1.947 a 2.430 a 2.043 a 1.705 a 1.593 b 1.522 b 1.542 1.248 b 1.451 Veg./Rep. 1.852 1.410 b 1.965 b 1.963 b 1.669 b 2.070 b 1.698 b 1.688 a 1.647 b 1.621 b 1.645 1.385 ab 1.465 100% Rep. 1.801 1.520 b 1.663 c 1.608 c 1.529 b 1.493 c 1.399 c 1.451 b 1.845 a 1.920 a 1.790 1.505 a 1.613 5% lsd 0.311 0.189 0.139 0.235 0.183 0.252 0.240 0.152 0.195 0.164 0.225 0.198 0.230 Rate x Timing n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. P=0.073 n.s. n.s. n.s. n.s. Med Veg. 1.951 1.627 2.033 2.423 1.924 2.271 2.013 1.605 1.521 1.416 1.445 1.147 1.401 Med Veg./Rep. 1.676 1.297 1.917 1.813 1.647 1.929 1.683 1.588 1.423 1.571 1.500 1.318 1.327 Med Rep. 1.657 1.413 1.544 1.573 1.590 1.565 1.323 1.440 1.845 1.863 1.686 1.417 1.559 High Veg. 2.135 1.983 2.336 2.274 1.969 2.588 2.073 1.806 1.664 1.628 1.639 1.349 1.501 High Veg./Rep. 2.028 1.523 2.013 2.113 1.690 2.211 1.713 1.788 1.871 1.671 1.789 1.452 1.603 High Rep. 1.944 1.625 1.783 1.643 1.469 1.421 1.470 1.461 1.845 1.976 1.894 1.593 1.667 5% lsd 0.440 0.267 0.197 0.333 0.259 0.357 0.339 0.215 0.276 0.232 0.319 0.280 0.326 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

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Table A3.5 Nitrogen treatment effects on N concentration (%) in mature external (ME) and largest mature pre-floral vegetative flush leaves (LMFF) in 1997. Means not followed by a common letter differ significantly, (P<0.05).

ME LMFF Vegetative N treatments

17.12.96-23.4.97 Reproductive N treatments

18.6.97-22.10.97

20.2.97 17.3.97 23.4.97 20.5.97 16.6.97 23.7.97 25.8.97 24.9.97 22.10.97 21.11.97 14.12.97

N rate *** *** *** *** * n.s. * * ** *** *** Medium 1.764 b 1.923 b 1.625 b 1.692 b 1.495 b 1.610 1.731 b 1.838 b 1.899 b 1.659 b 1.618 b High 2.122 a 2.247 a 1.892 a 2.004 a 1.699 a 1.735 1.934 a 2.018 a 2.067 a 1.869 a 1.863 a 5% lsd 0.101 0.103 0.096 0.126 0.169 0.160 0.150 0.178 0.115 0.110 0.108 N Timing ** ** *** *** ** n.s. n.s. n.s. ** * * 100% Veg. 2.064 a 2.211 a 1.893 a 2.017 a 1.835 a 1.711 1.876 1.921 1.863 b 1.641 b 1.653 b Veg./Rep. 1.902 b 2.051 b 1.755 b 1.864 a 1.534 b 1.731 1.796 1.896 1.965 b 1.807 a 1.742 ab 100% Rep. 1.864 b 1.993 b 1.628 c 1.665 b 1.423 b 1.575 1.825 1.968 2.122 a 1.843 a 1.827 a 5% lsd 0.123 0.126 0.117 0.155 0.207 0.196 0.184 0.218 0.141 0.135 0.132 Rate x Timing P=0.074 n.s. n.s. * n.s. n.s. n.s. n.s. n.s. n.s. n.s. Med. Veg. 1.802 2.020 1.703 1.774 b 1.664 1.667 1.772 1.744 1.765 1.514 1.489 Med. Veg./Rep. 1.766 1.913 1.637 1.681 b 1.457 1.665 1.762 1.872 1.873 1.725 1.626 Med. Rep. 1.725 1.836 1.536 1.622 b 1.365 1.497 1.659 1.899 2.059 1.738 1.738 High Veg. 2.326 2.402 2.083 2.259 a 2.005 1.756 1.980 2.099 1.960 1.769 1.816 High Veg./Rep. 2.038 2.188 1.873 2.046 a 1.610 1.796 1.829 1.920 2.057 1.890 1.858 High Rep. 2.002 2.150 1.721 1.707 b 1.481 1.652 1.902 2.037 2.185 1.947 1.916 5% lsd 0.174 0.179 0.166 0.219 0.293 0.277 0.260 0.309 0.199 0.190 0.186 n.s. = not significant (P>0.10); * P<0.05; ** P<0.01; *** P<0.001

53

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