RESPONSE OF RICE TO SOIL FERTILITY CONSTRAINTS AND BIO-FERTILIZERS IN

COASTAL ALLUVIAL SOIL OF KARNATAKA

Thesis submitted to the University of Agricultural Sciences, Dharwad

in partial fulfillment of the requirements for the

Degree of

Master of Science (Agriculture) in

SOIL SCIENCE AND AGRICULTURAL CHEMISTRY

By

DHANYA V. MATHEWS

DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY

COLLEGE OF AGRICULTURE, DHARWAD UNIVERSITY OF AGRICULTURAL SCIENCES,

DHARWAD - 580 005

AUGUST, 2005

ADVISORY COMMITTEE

DHARWAD ( P. L. PATIL ) AUGUST, 2005 MAJOR ADVISOR

Approved by :

Chairman : ____________________________

(P. L. PATIL)

Members : 1. __________________________

(G. S. DASOG)

2. __________________________

(H. T. CHANNAL)

3. __________________________

(V. V. ANGADI)

C O N T E N T S

Chapter No.

Title Page No.

I INTRODUCTION 1

II REVIEW OF LITERATURE 5

III MATERIAL AND METHODS 40

IV EXPERIMENTAL RESULTS 56

V DISCUSSION 108

VI SUMMARY 128

VII REFERENCES 131

APPENDICES 159

LIST OF TABLES

Table No.

Title Page No.

1. Location of soil samples of Mirjan village 42

2. Physical and chemical properties of experimental site 46

3. pH, EC, organic carbon and available N content of 100 soil samples of Mirjan village

58

4. Available P, K and Zn content of 100 soil samples of Mirjan village

64

5. Area indicating available nutrient status of Mirjan village 69

6. Effect of nutrients and biofertilizers on plant height (cm) 71

7. Effect of nutrients and biofertilizers on number of tillers per hill

72

8. Influence of nutrients and biofertilizers on number of leaves per hill

74

9. Leaf area (cm²) as influenced by nutrients and biofertilizers 76

10. Leaf area index as influenced by nutrients and biofertilizers 77

11. Effect of nutrients and biofertilizers on dry matter accumulation (q/ha)

79

12. Effect of nutrients and biofertilizers on yield components 81

13. Effect of nutrients and biofertilizers on grain yield (q/ha), straw yield (q/ha) and harvest index

83

14. Concentration of nitrogen (%) in rice as influenced by nutrients and biofertilizers

84

Contd…..

Table No.

Title Page No.

15. Concentration of phosphorus (%) in rice as influenced by nutrients and biofertilizers

86

16. Concentration of potassium (%) in rice as influenced by nutrients and biofertilizers

88

17. Concentration of zinc (µg/g) in rice as influenced by nutrients and biofertilizers

91

18. Nitrogen uptake (kg/ha) of rice at different stages of crop growth as influenced by nutrients and biofertilizers

93

19. Phosphorus uptake (kg/ha) of rice at different stages of crop growth as influenced by nutrients and biofertilizers

95

20. Potassium uptake (kg/ha) of rice at different stages of crop growth as influenced by nutrients and biofertilizers

97

21. Zinc uptake (g/ha) of rice at different stages of crop growth as influenced by nutrients and biofertilizers

99

22. Nutrient use efficiency (NUE) of nitrogen, phosphorus, potassium and zinc

102

23. Apparent nutrient recovery (%) of nitrogen, phosphorus, potassium and zinc

103

24. Effect of nutrients and biofertilizers on available nitrogen,

phosphorus, potassium (kg/ha) and zinc (µg/g) at post harvest stage

105

25. Economics of rice as influenced by nutrients and biofertilizers

107

LIST OF FIGURES

Figure No.

Title Between pages

1. Location of the study area 40-41

2. Plan of layout 47-48

3. Available Nitrogen status of Mirjan village 108-109

4. Available Phosphorus status of Mirjan village 109-110

5. Available Potassium status of Mirjan village 110-111

6. Available Zinc status of Mirjan village 110-111

7. Effect of nutrients and biofertilizers on grain yield (q/ha) and straw yield (q/ha)

120-121

8. Response curve for nitrogen, phosphorus and potassium

120-121

9. Effect of nutrients and biofertilizers on total nitrogen, phosphorus and potassium uptake at harvest stage

124-125

10. Effect of nutrients and biofertilizers on zinc (g/ha) uptake at harvest stage

125-126

LIST OF PLATES

Plate No.

Title Between pages

1. Overall view of the experimental site 45-46

2. Comparison of RDF and no nutrients 118-119

3. Combined application of biofertilizers and ZnSO4 with RDF and 150% RDF

118-119

LIST OF APPENDICES

Appendix No.

Title Page No.

I. Monthly meteorological data for the experimental year (2004-05) and average of past 54 years (1950-2003) of experimental site at Mirjan of Kumta taluk

159

II Price of inputs and outputs used in calculatory cost of cultivation and returns per ha

160

INTRODUCTION

India has a coastline of 8129 km. This ecosystem constitutes 5.5 per cent of the total

geographical area of the country. Rice is the predominant crop in coastal region which is the staple food of India.

Among the rice growing countries of the world, India ranks first in area and second in production. The average productivity of rice in India is 2 t ha

-1. Accounting for over 20 per cent

of the total rice area of the country, the coastal region represents nearly all rice ecologies namely; irrigated, rainfed, shallowland, rainfed semideep, deepwater and upland.

Karnataka has a coastline of 310 km on the Arabian sea, which accounts for 6.09 per cent of the area of the state.

Rice is the principal cereal crop of Karnataka. The productivity of rice in coastal Karnataka is low due to heavy rainfall, inadequate and improper time of application of nutrients. The heavy rainfall results in leaching of nutrients like nitrogen and potassium which leads to poor fertility condition of soil, low pH, iron and aluminium toxicity causing the main constraints for the low productivity of rice.

Nitrogen is known as the key nutrient of rice production. It is one of the most important and essential nutrient which directly influences the growth, development, yield and quality of rice. Nitrogen applied in low land rice is lost from soil through leaching and denitrification.

The next limiting nutrient which reduces the productivity of rice is phosphorus as it is required for cell division, seed formation, crop maturation and also stimulates root growth and development. Majority of the coastal rice soils are low to medium in phosphorus. Acidic reaction and high content of Fe and Al oxides leading to fixation causes phosphorus deficiency in these soils. Therefore the rice crop may respond to phosphorus application. The phenomena of grain filling is influenced by potassium fertilization. But most of the coastal soils are low to medium in potassium due to heavy leaching.

Among the micronutrients zinc is the most important essential plant nutrient, whose widespread deficiency has become serious nutritional problem in rice, limiting its yield in coastal areas. Zinc deficiency in rice appears right from seedling stage in nursery and three weeks after transplanting in transplanted plot, if the soil is deficient in Zn. This micronutrient is an important constituent of a number of enzymes and co-enzymes, hence its deficiency adversely affects photosynthesis and auxin concentration, thereby affecting growth, flower setting and development of fruits (Chatterjee and Maiti, 1981).

Though the productivity of rice in coastal ecosystem is low, proper and judicious use of fertilizers containing major and micronutrients can increase its productivity. But the increasing cost of fertilizers particularly nitrogenous and phosphatic poses severe constraints to our farmers particularly on small and marginal farmers. Therefore it became imperative to search for alternative low cost resources to relieve the pressure on nitrogenous and phosphatic fertilizers. In this context, an alternative low cost resources like biofertilizers have gained prime importance in the recent decades.

Biofertilizers include selective microorganisms like bacteria, fungi and algae which are capable of fixing atmospheric nitrogen or convert insoluble phosphate in the soil into forms available to plants. They are cost effective, eco-friendly and renewable sources of plant nutrients to supplement chemical fertilizers. Biofertilizers also play a vital role in maintaining long term soil fertility and sustainability.

The efficient biological nitrogen fixers in rice field are Azospirillum, Blue Green Algae (BGA), Rhizobium, Azotobacter. Azospirillum has been recognized as an important diazotroph colonising root environment of cereal crops. It can, not only fix atmospheric N2, but also can enhance uptake of nutrients from soil and can produce plant growth promoting substances. The N2 fixing ability of Azospirillum is 25 to 30 kg N ha

-1 season

-1. Thus it can

save 25 per cent of fertilizer nitrogen. Phosphatic biofertilizers solubilize fixed insoluble forms of phosphorus already

present in the soil and make it available for use of plants. It can be applied for lowland and upland rice. Bacteria like Bacillus megatherium var Phosphaticum, Pseudomonas fluorescens, fungi like Penicillium digitatum and Aspergillus niger are found to have a strong phosphate dissolving ability.

In view of the above, the present investigation was taken up with the following objectives.

1. To study nutrient status of soils of a pilot site in coastal agro-ecosystem of North Karnataka and mapping nutrient status by GIS technique for identifying soil fertility constraints

2. To study the response of rice to identified soil fertility constraints and biofertilizers and

3. To study nutrient uptake by rice and residual soil fertility as influenced by nutrient levels and biofertilizers

II. REVIEW OF LITERATURE

The nutrient status of soils have a great role in influencing the yield and quality of

crop in an agro ecological region. Keeping this in view, literature pertaining to nutrient status of coastal soils, response of rice to nutrients and biofertilizers, nutrient uptake by rice and residual soil fertility are reviewed here under the following headings. 2.1 Nutrient status of coastal soils 2.2 Response of paddy to nutrients and biofertilizers 2.3 Nutrient uptake of paddy as influenced by nutrient levels and biofertilizers 2.4 Residual soil fertility as influenced by nutrients and biofertilizers

2.1 Nutrient status of coastal soils The coastal zone of Karnataka is subjected to heavy rainfall resulting in leaching of

nutrients particularly nitrogen and potassium leading to poor soil fertility, low pH, high Al and Fe content, low available phosphorus and low to medium available potassium. ‘Zn’ deficiency is another important problem in these soils. Rice is the main crop in this ecosystem and the low fertility status of these soils results in low production of rice. Considering the very low efficiency of nitrogeneous and phosphatic fertilizers it has become a necessity to integrate the use of biofertilizers and inorganic fertilizers for higher yield and higher soil fertility.

Gopal Rao and Rajashekhar (1965) reported that high rainfall areas of coastal belt of Mysore state have high organic carbon content and low potassium.

Viswanath et al. (1978) evaluated the fertility status of soils of heavy rainfall coastal mountainous region of Karnataka and found that the soils were generally acidic with low available P and K.

Sandy coastal alluvium of Tamil Nadu is low in total P2O5 and lime and fair in total K2O and organic carbon (Ratnam et al., 1969). Ramamoorthy and Bajaj (1969) reported that soils of Mysore are mainly medium in N and K and low in P.

Ananthanarayana et al. (1986) reported that soils of the coastal Malnad and Southern Maidan region of Karnataka are formed from acidic parent material granite or peninsular gneiss and are inherently low in Ca. Badrinath et al. (1986) reported that coastal soils of Karnataka are acidic non saline with relatively high organic carbon content.

Heavy intensity of rains coupled with hill slopes and percolate soils as exist in Konkan may result in soil erosion and removal of major part of nutrients through sufficient runoff and leaching. Organic carbon content of surface soil was in the range of 1.12 to 2.13 per cent while it ranged from 0.48 to 1.32 per cent in the lower depth (Pereira et al., 1989).

Adhikari and Ghosh (1991) studied seasonal influence on electrochemical properties of soils of West Bengal and observed a decrease in EC during monsoon and high organic carbon content in pre-monsoon season.

Joplin et al. (1993) evaluated the fertility status of some Alfisols and found that the soils were high in organic carbon, low in available phosphorus and only a small portion were deficient in available potassium.

Girisha and Badrinath (1996) observed that soils of Dakshina Kannada district were highly acidic and medium in organic carbon and available potassium.

Usha and Jose (1983) suggested that the excessively inflated C/available N ratio in soils of high organic C content may be due to the fact that the soils could retain only a limited quantity of mineralised N and therefore loss of N due to leaching and denitrification became pronounced in soils where large amount of N was released by minerailization.

Dongale and Patil (1989) studied the organic carbon, total and available nitrogen content in laterite, soils of Konkan and they found that available nitrogen contributed 12.91 per cent of total nitrogen in the profile. Organic carbon ranged from 0.6 to 2.12 per cent.

The available P2O5 of the surface soil ranged between 1.97 and 3.95 kg/ha while in sub surface samples it ranged between 0.98 to 3.95 kg/ha indicating that soils were deficient in available P2O5. Soils were well supplied with K2O (Pereira et al., 1989).

Balasubramanian and Raj (1969) from their studies on different forms of phosphate on laterite soils claimed that Fe and Al phosphate occupied major portion than Ca phosphate in those soil.

Chihba and Sekhon (1985) observed that available nitrogen and K decreased with depth, but available phosphorus did not show any definite trend with depth. In laterite soils the presence of sesquioxides is responsible for the strong bonding of P (Krishnakumari et al., 1985).

Tomar and Chand (1992) found that available phosphorus increased with pH and decreased with organic carbon.

Dongale (1993) studied the depth distribution of P in laterite soils of coastal region. Results showed that soils derived from granite and gneiss contained less P than those form basalt. Total P varied in the range of 250-800 ppm. P content on surface layer decreased with depth.

Roy and Bagchi (1973) studied different forms of K in West Bengal soils and they identified that water soluble K had positive correlation with exchangeable, total and available form. From their studies on various forms of K in red, black, laterite and alluvial soils of Karnataka, Ranganathan and Sathynarayana (1980) reported that water soluble K ranged from 0.05 to 0.08 me per litre. In sub-soluble 0.03 to 0.08 me per lit in 30-60 cm and 0.02 to 0.07 me per lit in depth below 60 cm.

Bandyopadhyay et al. (1985) concluded that coastal soils of Orissa and West Bengal were rich in water soluble, exchangeable, non exchangeable and available K. Available K ranged from 280 kg per ha to 1309 kg per ha.

Parkar et al. (1989) obtained high amount of total K in Atlantic coastal plains. This was attributed to the K-rich parent material and relatively young age of the soils.

Adhikari and Ghosh (1991) observed that water soluble, exchangeable and non-exchangeable K ranged from 0.03 to 0.104, 0.1 to 0.365 and 0.64 to 3.86 me per 100 g, respectively and the amounts of all these forms of potassium were found much greater in alluvial and coastal saline soils than in the lateritic soils. Ano (1991) reported that K status of coastal plain sands are affected by pH and organic matter. The soils were found to be very low in K.

Mohta et al. (1964) and Kanwar and Randhawa (1967) observed that available zinc was maximum at the surface and decreased with depth.

Chatterjee and Das (1964) found that there was more ammonium acetate extractable zinc in soils with pH below 6.0 and its content decreased as pH rose above 7.0.

Eswarappa et al. (1969) and Balasundaram et al. (1973) observed significant positive correlation between available zinc and organic matter in soils of Mysore and Tamil Nadu respectively.

Praseedom and Koshy (1975) observed that surface soils contained 0.3 to 7.7 ppm of available zinc and 0.8 to 7.7 and 1.3 to 8.00 ppm of available zinc was observed in second and third layer respectively.

Badrinath et al. (1986) reported that soils of coastal Karnataka are low in available Zn ranging from 0.2 to 0.6 ppm.

2.2 Response of paddy to nutrients and biofertilizers As the coastal soils are poor in fertility, proper and judicious application of fertilizers

containing major and micronutrients along with biofertilizers can increase the growth and yield of rice.

2.2.1 Effect of N, P, K and Zn on growth components of rice Nitrogen

Maske et al. (1993) reported that application of nitrogen at different levels (at 0, 40, 80 and 120 kg/ha) results in difference in height, number of functional leaves per hill, leaf area and dry matter per hill. They observed that with increase in nitrogen content all the above parameters will increase. Rao et al. (1996) reported that application of 100 kg N/ha in three splits (25% basal + 50% tillering stage + 25% panicle initiation stage) recorded maximum plant height, LAI, number of tillers per hill and dry matter. Rao and Moorthy (1997) reported that with the increase in N application from 0-90 kg/ha, plant height showed a significant increase.

Devasenamma et al. (1999) reported that nitrogen application caused significant variation in total dry matter production over control at all the crop growth stages. There was significant increase in total dry matter production with successive increase in levels of nitrogen up to 180 kg at all stages of crop growth.

Kumari et al. (2000) conducted a field experiment to study the effect of different levels of nitrogen on growth of rice. They observed taller plants at higher level of nitrogen application i.e. 120 kg/ha. Dry matter production also increases with increased level of nitrogen.

Somasundaram et al. (2002) observed significant increase in plant height, leaf area index and dry matter accumulation with each successive increase in N level form 0 to 150 kg/ha. Addition of N from 100 to 150 kg/ha did not significantly improve the above parameters. However maximum values for growth parameters were recorded at 125 kg N/ha.

Phosphorus Reddy et al. (1984) and Alam and Azmi (1984) reported that dry matter, plant height

and number of tillers increased significantly with increasing phosphorus. Pawar and Chavan (1996) studied the response of rice to different sources of

complex phosphatic fertilizers in lateritic soils and reported that the treatment nitrophosphate produced significantly higher number of tillers/hill. Urea ammonium phosphate and urea + single super phosphate were next in performance and at par with each other.

Singh et al. (1999) reported that plant height increased significantly up to 30 kg P2O5/ha and difference between 30 and 60 kg P2O5/ha were non-significant but were significantly superior over control (P0). Potassium

Vijayan and Sreedharan (1972) reported that there was a significant increase in plant height by the higher levels of potassium.

Hati and Misra (1982) studied the effect of levels of potash on dry matter of rice. They used 4 levels of K (0, 30, 60, 90 and 120 kg/ha) as muriate of potash. They reported that potash treatments effected significant variations in the dry matter at 60 days and at harvest. The dry matter increased significantly with increase in level of potash up to 60 kg K/ha. A decline in the dry matter was observed at 120 kg K/ha.

Ravi and Rao (1992) conducted a field experiment to study the effect of graded levels of potassium and times of application, with three levels of potassium (0, 60 and 120 kg/ha) and four schedules of application (All basal, half as basal + half at 30 DAT, half as basal + half at PI stage and 1/3 equally as basal, at 30 DAT and at PI stage). They observed that dry matter production significantly increased at 90 DAP and at harvest due to levels of potassium only. A significant superior LAI was obtained.

Bohra and Doerffling (1993) revealed that increasing levels of K application improved plant height, tiller number and shoot dry weight at flowering. However significant difference were observed only in the sensitive variety IR-28, whereas K50 and K75 treatments produced significantly higher value than the K0 treatment. Zinc

Sriramachandrasekharan and Mathan (1988) conducted a field experiment to study the influence of zinc sources on the growth characters viz., plant height, number of tillers/hill and root characters. Application of zinc increased plant height, number of tillers, root length root volume and root weight and root length density. Application of zincated urea alone or in combination with zincated suphala were on par in regard to character studied.

Maji and Bandyopadhyay (1990) studied the response of rice to zinc in coastal saline soils. They used two levels of zinc (6.8 and 13.6 kg/ha) and reported that a decreasing trend in dry matter was observed with higher doses of zinc.

2.2.2 Yield components and yield as influenced by N, P, K and Zn Nitrogen

Murthy and Murthy (1978) observed significant increase in the yield when nitrogen rate increased from 60 to 120 kg ha

-1. Increase in the grain yield was due to increase in total

dry matter hill-1

, panicle m-2

, spikelets m-2

and high leaf area index. Biswas and Bhattacharya (1987) conducted field experiments in both wet and dry

seasons for two consecutive years to study the optimisation of nitrogen supply vis-à-vis spacing for higher yielding rice in coastal saline soils and reported that medium spacing (15 x 15 cm) is the most favourable for better elaboration of yield attributing characters and for higher response to applied nitrogen resulting in economic usage of fertilizer. The most optimum level of nitrogen per hectare was 99 kg N in wet and 98 kg N in dry season.

Patra and Padhi (1989) reported that nitrogen application significantly increased the grain yield. Yield increased with each increment of nitrogen irrespective of source and method of application.

Anil et al. (1989) reported that grain yield significantly increased with increasing nitrogen levels up to 120 kg N/ha. Whereas, Singundhupe and Rajput (1989) indicated that application of nitrogen significantly increased both grain and straw yields up to 150 kg N/ha compared with unfertilised treatment.

Machhi et al. (1989) conducted a field experiment to find out the optimum dose of nitrogen and method of application of nitrogen in paddy variety Masuri. He reported that the treatment of pellets method application gave the highest yield but it was at par with that due to broadcasting method. He also reported that the effect of two different levels of nitrogen (80 and 120 kg/ha) on paddy yield was not significant.

Panda (1993) conducted field experiments to study the comparative performance of prilled urea (PU), urea super granule (USG) and large granule urea (LGU) at two nitrogen (40 and 60 kg N/ha) levels on wet land rice in coastal soils of Orissa and reported that application of fertilizer nitrogen in general increased the grain yield of rice over the control (no nitrogen) treatment. Among the sources of nitrogen, USG proved superior to PU and LGU in terms of grain yield and N-use efficiency.

Pandey and Tripathi (1994) reported that the grain yield was significantly higher at 120 kg N/ha than at lower levels owing to significant increase in panicles/m

2 and panicle

weight. Krishnan et al. (1994) revealed a linear rice response with increasing N levels through

the grain yield continued to increase up to 240 kg N/ha. The yield increase per kg of N was the highest from 0-60 kg N/ha (31.3 kg.kg N

-1) followed by 60-120 kg N/ha (21.51 kg.kg N

-1).

Beyond 180 kg N/ha, the yield increase was not significant and registered only 0.5 kg increase for each kg of N applied.

Mutanal et al. (1997) reported that the application of nitrogen through nimin coated urea proved superior than through prilled urea, tar coated urea and large urea granules. The optimum dose was 75 kg N/ha, which recorded higher return compared with 50 and 100 kg N/ha.

Patil et al. (1999) conducted an experiment to study nitrogen use efficiency in coastal saline soils. Rice variety Jaya was grown with slow release modified urea material, i.e., blending urea with 40 per cent neem and farmyard manures with three levels of N (100, 75, 50 kg/ha) through urea. Blending urea with 40 per cent FYM @ 100 kg N/ha applied in three splits gave significantly highest yield over the rest of the treatments.

Rajarathinam and Balasubramaniyan (1999) conducted a field experiment to study the response of hybrid (CORH 2) rice to different plant populations (50, 33 and 25 hills/m

2)

and N levels (150, 200, 250 kg/ha) under low land condition. The yield parameters were more with the population of 50 hills/m

2. Yield parameters and yield were higher with 200 and 150 kg

N/ha. However the treatment combination of 50 hills/m2 and application of 150 kg N/ha was

found economically feasible agronomic practice for rice hybrid CORH 2. Rammohan et al. (2000) studied the influence of different levels of nitrogen on growth

and yield of rice in coastal saline soils and reported that increase in nitrogen level increased the growth parameters and yield of rice. Phosphorus

Nair and Pisharody (1970) reported that paddy yield was not increased due to application of 22.4 to 56 kg P2O5/ha alone or with various rates of nitrogen and potash. It was concluded that phosphatic requirement of rice could be met from the native fixed phosphorus present in the soil. Banga et al. (1990) reported that application of P2O5 significantly increased the yield in soils testing low and medium in available P2O5.

Latchanna et al. (1989) reported that number of panicles per m2 increased by 9.5, 15,

18 and 20 per cent with 20, 40, 60 and 80 kg P2O5/ha application over control. Application of phosphorus also resulted in increased number of filled grains per panicle, 1000 grain weight, grain and straw yields, however the increase was marked up to 40 kg P2O5/ha only.

Annadurai and Palaniappan (1994) reported that application of graded level of phosphorus (0, 9.5, 19 and 38 kg P2O5/ha) significantly improved the number of productive tillers and 1000 grain weight which in turn increased the yield of IR-20 rice variety.

Singh et al. (2000) conducted field experiments to study the response of rice to 4 levels of P2O5, viz., 0, 30, 60 and 90 kg P2O5/ha. They found that both rice grain and straw yields increased with graded levels of P2O5 applications. There was significant response to applied P up to 60 kg P2O5/ha. Potassium

Singh et al. (1976) working with traditional varieties reported that application of K2O at 120 kg/ha all the transplanting gave the highest straw yield, but split application viz., at transplanting, tillering and panicle initiation gave the highest grain yield.

Hati and Misra (1982) conducted field experiments on a sandy clay loam soil with graded levels of K (0, 30, 60, 90 and 120 kg/ha) as muriate of potash and applied in four different splits full at planting, 50 per cent each at planting and tillering, 25 per cent each at planting and panicle initiation and 50 per cent at tillering and 50 per cent at planting and 25 per cent each at tillering and panicle initiation stage. They observed that the yield increased significantly with increase in potash level up to 60 kg K/ha and a decline in the yield was

observed at 120 kg K/ha. they also observed that split application of potash failed to produce significant yield difference.

Mandal and Mahapatra (1983) quoted that grain yield of rice was positively correlated with leaf area duration from flowering to maturity and number of spikelets/m

2, per cent filled

grains and test weight of grain. The leaf area duration was improved by the application of 160 kg N + 120 kg K2O/ha during dry season and 120 kg N + 80 kg K2O/ha during wet season with adequate phosphorus (60 kg P2O5/ha).

Bhargava et al. (1985) reported a progressive increase in response to K2O. At 60 kg K2O/ha, the increase in yield was about 6-8 kg grain/kg in rice. The yield response in most soils was significant at 40 to 60 kg K2O/ha.

Yield responded significantly to split application of 50 kg K2O/ha (½ at transplanting + ½ at active tillering). Application of 100 kg K2O/ha at transplanting was as efficient as split application. Potassium helped to increase the panicle bearing tillers and grain weight (Kolar and Grewal, 1989).

Cox and Uribe (1992) concluded that K fertilization (0 to 120 kg/ha) always increased the grain yields and higher level resulted in K fixation.

Ravi and Rao (1992) conducted a field experiment to study the effect of graded levels of potassium and times of application with three levels of potassium (0, 60, 120 kg/ha) and four schedules of applications (all basal, half as basal + half at 30 DAT, half as basal + half at PI stage and 1/3 equally as basal, at 30 DAT and at PI stage). They reported that maximum test weight, number of filled grains/panicle and yield were obtained due to application of potassium in two equal splits as basal and at PI stage.

Raju et al. (1999) reported that rice yield and its attributing characters responded favourably to higher dose (60 kg K2O/ha) of K, but not at lower doses (40 kg/ha) except when the entire dose was applied at panicle initiation stage. In general, K fertilization showed beneficial effect on grain tillering and harvest index and reduced the duration of crop. Zinc

Gill and Hardeep (1978) reported that application of zinc sulphate at 20 kg/ha increased the productive tillers, panicle lengths and number of grains per panicle in rice. Whereas, Patel (1979) observed that application of 0-25 kg ZnSO4/ha increased 1000 grain weight, number of effective tillers per plant, fertile spikelets per panicle and panicle lengths.

Uddin et al. (1981) found that with increase in the levels of ZnSO4 application number of effective tillers, plant height, panicle length, number of grains per panicle and 1000 grain weight was increased. Saravanan and Ramanathan (1986) reported that 25 kg ZnSO4/ha is the optimum rate for rice grown on Cauvery delta clay loam soils.

Reddy et al. (1984) conducted field experiments for two kharif and rabi seasons to study the direct and residual effect of micronutrients on rice. They reported that the residual effect of micronutrients on rabi rice was higher compared with direct application to kharif rice. Application of zinc, manganese and molybdenum over and above NPK favourably influenced all yield attributes and finally grain yields in both the years. Application of zinc alone resulted in higher grain yield both by direct application to kharif rice and as residual effect to rabi crop.

Ilangovan and Palaniappan (1987) reported that soil application of six per cent Zn-DAP enhanced the grain yield significantly over no Zn (control). Four, five and six per cent Zn-DAP recorded higher yield over soil application of ZnSO4 @ 25 kg/ha, foliar application of ZnSO4 @ 0.5 per cent sprayed on 30 and 45 days after planting and seedling root dipping in two per cent ZnO suspension.

Sriramachandrasekharan and Mathan (1988) reported that combined application of Zincated suphala and zincated urea and zincated urea alone gave highest value in the case of number of panicles/m

2, 1000 grain weight, dry mater production and yield. Panicle length,

number of filled grains/panicle, harvest index was not influenced by zinc sources. Ingle et al. (1997) reported that application of 15 kg Zn/ha through zinc sulphate with

N, P, K (100:50:50) fertilizers gave the highest grain and straw yields of paddy and was found significantly superior over control and other treatments.

Kumar et al. (1998) studied the effect of Zn application on yield attributing characters and yield of rice. Application of 25 kg ZnSO4/ha in transplanted field or spraying standing crop with 0.5 per cent ZnSO4 solution three weeks after transplanting or dipping seedling roots in 2 per cent ZnO suspension were equally effective in correcting zinc deficiency. Zinc application in transplanted field in general improved yield attributes like number of panicles, test weight, panicle length and fertile spikelets significantly.

Katyal and Gangwar (2000) conducted an experiment to study the effect of micronutrients on rice productivity and reported that application of ZnSO4 as basal @ 10 kg/ha during kharif in alternate years with recommended dose of NPK gave yield at par with application in every year. Interaction effect of NPK and Zn

Sikdar and Gupta (1979) observed that spikelet sterility was higher at 100 kg N + 50 kg P2O5 + 50 kg K2O ha

-1 as compared to 50 kg N + 25 kg P2O5 + 25 kg K2O ha

-1. But, the

spikelets panicle-1

, grain yield and 1000 grain weight were higher with higher dose of fertilizers.

Venkateswarlu and Singh (1980) observed higher grain yield with 120 kg N + 60 kg P2O5 + 45 kg K2O ha

-1 followed by 80 kg N + 40 kg P2O5 + 30 kg K2O ha

-1. Yield attributes like

number of effective tillers m-2

, panicle weight, grains panicle-1

and test weight were increased with increase in the fertility level.

Chandrasekarappa (1985) reported that application of 100 kg N, 100 kg P2O5 and 50 kg K2O ha

-1 gave the highest grain yield. This was on par with 100 kg N, 50 kg P2O5 and 50

kg K2O ha-1

. The increase in yield was due to increased dry matter production, plant height, leaf area index, leaf area duration, number of tillers hill

-1 and to some extent panicle length

and 1000 grain weight. Moula et al. (1988) conducted field experiments with rice variety Sona Mahsuri in

black clayey soils for 3 consecutive kharif seasons revealed that the rice crop responded well to soil application of fertilizer N up to 150 kg/ha, P2O5 up to 150 kg/ha and K2O up to 50 kg/ha under different soil fertility levels. 150 kg N + 50 kg P2O5 + 50 kg K2O per ha in soils of low available N and P, 100 kg N + 50 kg K2O per ha in soils high and very high in available N and P were found to be ideal fertilizer schedules. Sharma and Mittra (1989) reported that grain yield of rice increased significantly with increase in the levels of N and P.

Upadhyay (1994) conducted a field experiment to study the effect of different levels of potash viz., 0, 25, 50, 75 and 100 kg K2O/ha under four NP levels (kg/ha) viz., N0P0, N50P25 (low), N100P50 (medium) and N150P75 (high) on rice (GR11). The results revealed that potential production and profit from kharif low land rice can be secured by fertilizing the crop with 100 kg N + 50 kg P2O5/ha. Low land kharif rice is not responding to potash application.

Rao and Shukla (1996) conducted a field experiment during kharif seasons at BHU, Varanasi revealed that highest grain yield of rice was obtained with ammonium polyphosphate (APP) applied at 90 kg P2O5 ha

-1 in combination with 30 kg ZnSO4 ha

-1.

Among the sources of phosphorus tested, APP followed by UNP recorded the highest grain yield over DAP. Increasing the doses of phosphorus significantly increased the grain yield. Increasing the zinc sulphate up to 30 kg/ha significantly improved the grain yield. Similar trend was observed in respect of all the growth characters studied.

2.2.3 Effect of biofertilizers on crop growth Biofertilizers are inputs containing microorganisms which are capable of mobilizing nutritive elements from non-usable form to usable form through biological processes. Azospirillum is an important nitrogen fixing biofertilizer, whose application increases grain yield of cereals by 5-20 per cent. Phosphorus solubilizing bcteria solubilize insoluble/fixed forms of phosphorus into forms which are readily taken by the plants. 2.2.3.1 Effect of Azospirillum on crop growth Tien et al. (1979) reported the excretion of auxins particularly IAA, gibberellins and cytokinins of Azospirillum brasilense.

Nayak et al. (1986) reported that inocultion of rice with Azospirillum increased the production of tillers, plant height and early reproductive stage. Purushothaman et al. (1987) reported that inoculation of Azospirillum brazilense strain sp. 7 increased the germination, seed vigour index of cv. IR50 and cv. Co-40. It also increased the shoot and root length, number of primary roots and dry weight of seedlings.

Singh et al. (1989) reported that two strains of Azospirillum in maize showed at 35°C a better growth of both plant and bacteria above which reduced plant height. Stancheva and Dinev (1992) reported that the interaction between Azospirillum brasilense and the maize root system increased the plant biomass. 2.2.3.2 Effect of PSB on crop growth

Gaur and Singh (1982) observed that inoculation of Bacillus polymyxa along with rock phosphate increased the dry matter of rice plants.

Datta et al. (1982) reported that there was an increase in dry matter of rice (Jaya and IR-8) due to inoculation with phytohormone producing P solubilizing bacteria Bacillus firmis inoculated along with rock phosphate and superphosphate.

Taha et al. (1969) observed that inoculation of soils with phosphate solubilizers like Bacillus megatherium, Pseudomonas increased the dry matter of barley plants.

Gowda (1980) reported that dry matter of maize plant increased on application of rock phosphate with phosphorus solubilizing bacteria and fungi.

Prabhakar (1989) reported that the N and P content of shoot and dry weight of shoot and root increased significantly by the inoculation of maize crop with phosphorus solubilizing Pseudomonas sp. in presence of both superphoshate and rock phosphate as compared to respective uninoculated control.

Raj et al. (1981) in a green house experiment observed that ragi plant showed increased plant height by inoculation with Bacillus circulans.

Patil et al. (1979) reported that dry matter of cowpea was highest with inoculation of phosphate soluiblizing microorganism.

Jones and Srinivasa (1992) observed significant increase in plant height and dry biomass of sunflower inoculated with Glomus faciculatum and Pseudomonas striata.

2.2.4 Effect of biofertilizers on yield and yield components 2.2.4.1 Effect of Azospirillum

Rao et al. (1979) reported that Azospirillum inoculation significantly increased the grain yield of rice variety Pusa 2-21 at 0, 40 and 60 kg N/ha.

Rao et al. (1983) observed a statistically significant positive yield response to inoculation with Azospirillm sp. at different levels of N fertility over three consecutive seasons. The response of Azospirillum was more pronounced at 30 and 40 kg N/ha of fertilizer N than at a higher level. Although the mean yields of both grain and straw were increased by inoculation with Azospirilum, the interaction between N fertilizers and inoculation was not statistically significant.

Prasad and Singh (1984) reported the combined effect of inoculation of Azospirillum and incorporation of Azolla in rice in pot culture. Incorporation of Azolla as a green manure, inoculation of seedlings with Azospirillum and or application of N increased the yield of rice.

Azospirillum inoculation significantly increased the filling rate of grains and grain yield per plant in rice (Watanabe and Lin, 1984).

Field experiments carried out in Tamil Nadu with rice (ADT 36) revealed that inoculation with Azospirillum brasilense increased grain yield upto 22 per cent and straw yield by 8 to 41 per cent (Gopalaswamy and Vidhyasekaran, 1987). The number of productive tillers, grain yield and straw yield in rice cultivars ADT 36, IR50 and ADT37 were also increased by inoculation of Azospirillum (Gopalaswamy and Vidhyasekaran, 1988).

Rao et al. (1987) revealed that data on the effect of inoculation with N2 fixing bacteria on rice yield and concluded that yield response to inoculation is most pronounced at moderate levels of (30-60 kg N/ha) fertilizer nitrogen. Thus inoculation with N2 fixing bacteria combined with fertilizer N could increase yields.

Mahapatra and Sharma (1988) reported that dipping roots of rice seedlings in 2 per cent solution of Azospirillum increased the yield of 200 kg/ha over uninoculated treatment.

Azospirillum inoculation was found to be beneficial for upland rice (Purushothaman, 1988). The grain and straw yield of direct sown rice were increased by seed treatment and soil application of Azospirillum (Gopalaswamy et al., 1989).

Kumar and Balasubramanian (1989) reported that 25 to 50 kg N/ha can be saved by Azospirillum inoculation in rice cultivation.

Jayaraman (1990) studied the comparative efficiency of different biofertilizers viz., Azospirillum, Azolla and blue green algae with and without sub-optimal levels of N (0, 15, 75 kg/ha) and recommended level of N revealed that the application of 75 kg N/ha supplemented by Azospirillum or Azolla or bluegreen algae was found to be more efficient in influencing the grain yield. It showed a significant increase in kharif rice and the increased yield was statistically on par in rabi rice as compared to the application of recommended level of 100 kg N alone/ha.

Farmers can obtain higher yield in direct seeded rice that can later be converted into wet land rice by applying irrigation water at 45 days after sowing, Azospirillum inoculation and split application of potassium fertilizer (Govindaswamy et al., 1992).

Govindan and Bagyaraj (1995) studied the field response of wetland ice to Azospirillum inoculation and reported that Azospirillum inoculation enhanced shoot and root

growth, grain and straw yield. Recommended dose of fertilizer N + inoculation gave maximum grain yield. At 75 per cent N and 50 per cent N level inoculation resulted in significant increase in straw yield. At 25 per cent and 0 N, the effect of inoculation on straw yield was not significantly difference from their respective uninoculated controls.

Tien et al. (1979) proposed that changes in root morphology are caused by plant growth factors produced by Azospirillum. They found that inoculation of pearl millet greatly increased proliferation of lateral roots and root hairs. 2.2.4.2 Effect of PSB

Gerretson (1948) for the first time reported that inoculation of seedlings with P soubilizing microorganisms increased the crop yields. After this the beneficial influence of artificial inoculation with P soluibilizers along with soluble or insoluble phosphatic sources has been reported with different crops including cereals viz., rice, maize, wheat, sorghum, barley etc. by different workers (Sundara Rao and Sinha, 1963; Bajpai and Sundara Rao, 1971; Gaur and Ostwal, 1972).

Sharma and Singh (1971) reported that inoculation with phosphobacteria and application of bone meal to soil increased the grain yield of rice.

Datta et al. (1982) reported that there was increase in grain yield of rice (jaya and IR-8) due to inoculation with phytohormone producing P solubilizing bacteria Bacillus firmis inoculated along with rock phosphate and superphosphate.

Gaur and Singh (1982) obtained increased yield of rice by inoculation of seedling roots with Bacillus polymyxa along with rock phosphate. The yield with 60 kg rock phosphate with the above culture was as good as super phosphate applied at 60 kg P2O5/ha.

Mohod et al. (1991) reported that the P-solubilizing cultures (Pseudomonas striata and Bacillus polymyxa) significantly increased the number of grains/panicle, weight of 1000 grains, grain weight/panicle, grain yield and straw yield of rice variety KJP-184. The cultures were more efficient with rockphosphate than with super phosphate.

Gaur and Ostwal (1972) reported inoculation of wheat with Bacillus polymyxa significantly increased the grain and straw yield of wheat.

Taha et al. (1969) observed that inoculation of soils with phosphate solubilizers like Bacillus megatherium, Pseudomonas increased the yield of barley plants.

Gowda (1980) reported that inoculation of phosphate solubilizing microorganisms along with insoluble phosphate sources increased the yield of maize plants under pot culture conditions.

Mehta et al. (1996) in their experiment on integrated nutrient management of sugarcane recorded an increased cane yield upto 6.6 per cent and sugar yield upto 10.2 per cent when inoculated with Pseudomonas over uninoculated control with recommended dose of inorganic fertilizers. 2.2.4.3 Effect of dual inoculations

Kundu and Gaur (1984) in a green house eperiment observed thatby inoculating rice seedlings with mixed cultures of azotobacter chrococcum, Pseudomonas striata and Aspergilus awamori increased the grain yield with and without chemical fertilizers over the control. The response due to mixed culture inoculation was more than single cultures showing the synergistic effect of two types of organisms. The results indicate that the mixed culture inoculation can be used safely for better yields and is superior over single culture inoculations.

Arangarasan et al. (1998) studied the field response to inoculation with diazotrophic bacteria viz., Azospirillum lipoferum, Herbaspirillum seropedicae and phosphorus solubilizing bacteria Bacillusmegatherium var. Phosphaticum in rice. In inoculated treatments with the two bacteria cultures, increase in shoot and root length, 1000 grain weight and grain yield were recorded over uninoculated control. Coinoculation resulted in increased grain yield by 9-14 per cent over control.

Kundu and Gaur (1980) reported an increased wheat yield due to inoculation of Azotobacter chroococcum, Bacillus polymyxa and Pseudomonas striata as combined inoculum over their single inoculations.

Bolimov et al. (1995) in their study on interaction effects of nitrogen fixing and phosphate soluiblizing bacteria, observed a significant positive effect on grain yield of barley cultivars when inoculated with mixtures of Azospirillum lipoferum 137 with Agrobacterium radiobacter 10 and Agrobacterium mysorens 7.

Field trials conducted by Alagawadi and Gaur (1992) to study the effect of combined inoculation of Azospirillum brasilense and Pseudomonas striata or Bacillus polymyxa

indicated a significant increase in the dry matter and yield of sorghum over inoculation of individual organisms.

Prathibha et al. (1996) reported an increased dry matter yield of cotton due to dual inoculation of Azospirillum and Pseudomonas striata over single inoculations and also improvement of other beneficial microflora in the cotton rhizosphere.

2.3 Nutrient uptake by paddy as influenced by nutrient levels and biofertilizers

A knowledge of uptake and concentration of nutrients in plant parts at different stages of crop growth will help in arriving at the optimum requirement of the nutrients for the crop plants.

2.3.1 Nutrient uptake as influenced by nutrients N, P, K and Zn Nitrogen

Padmaja (1977) reported that nitrogen concentration in both grain and straw increased with increasing concentration of nitrogen in the root medium.

Dubey and Bisen (1989) reported that nitrogen uptake increased significantly with increased levels of nitrogen in grain and straw. Increase in N uptake by grain and straw was observed with increasing level of nitrogen.

Sagar and Reddy (1995) reported that the uptake of phosphorus and potassium in grain and straw of rice was significantly increased with the split application of higher levels of nitrogen. Phosphorus

Rao et al. (1988) reported that application of 60 kg P2O5 ha-1

significantly increased the nitrogen, phosphorus and potassium in grain and straw over 30 kg P2O5 ha

-1.

Subbaiah (1991) indicated consistent increase in N, P and K uptake with increased levels of P which was attributed due to effective absorption and higher dry matter accumulation brought out by P nutrition.

Mongia et al. (1998) conducted a green house experiment to study the effect of phosphatic fertilizers and liming on rice in acid sulphate soils. They concluded that phosphate application resulted in both increased P content and uptake but at each P level, application of lime further increased P content and uptake. P application reduced the Al and Fe content of both grain and straw, but increased the Mn content.

Reddy and Rao (1984) reported that application of 60 kg P2O5 ha-1

recorded a total uptake of 119.4 kg nitrogen and 46.9 kg P2O5 ha

-1. The increase in uptake was attributed to

increased root growth due to P application in a sandy loam soil with 30 kg available P2O5 ha-1

. Potassium

Vijayan and Sreedharan (1972) conducted a field experiment to study the effect of levels and times of application of potash on IR-8. They reported that the content of K in the grain and straw were highest at the maximum level of 80 kg/ha of K applied and the best time of application of K was found to be half at planting and the other half at the active tillering stage.

Singh and Patiram (1987) opined that uptake of K increased with increasing level of K.

Velayutham et al. (1992) reported that the split application of potassium increased the NPK uptake and the yield of low land rice. The uptake of potassium and grain yield were found to be maximum under the treatments receiving 125 kg K2O/ha in three equal splits at basal, maximum tillering and panicle primordium initiation stages.

Upadhyay (1994) reported that N, P and K content and uptake in both grain and straw were not appreciably influenced due to various levels of potash. P uptake (52.8 kg/ha) by rice crop increased significantly upto 25 kg K2O/ha over control.

Panda et al. (1999) reported that application of K at 40 kg/ha recorded significantly the N, P and K uptake over that of no K. The additional increase in N, P and K uptake over control was 1, 0.4 and 2.21 kg respectively.

Pal et al. (2000) reported that significant differences were recorded in K uptake by rice grain due to splitting of K levels over basal and these follow the same trend as in the case of rice yield. Effect of NPK

Reddy and Murthy (1988) reported that the phosphorus uptake by rice increased with increase in levels of N, P and K fertilizer. Differences in P uptake due to varieties and fertilizer levels were significant.

Sharma and Mittra (1989) reported that uptake of N, P and K increased significantly with increasing N levels. Application of P resulted in marginal increase in nutrient uptake.

Rajkhowa and Baroova (1991) reported that the highest grain yield and N, P and K uptake were recorded in treatment with 100 per cent recommended fertilizer than fifty or seventy five per cent.

Bellakki et al. (1997) observed that increase in RDF (recommended dose of fertilizer) level from 50 to 125 per cent resulted in increase of N uptake from 42.00 to 71.51 kg/ha by grain and from 29.49 to 50.77 kg/ha by straw during kharif 1992-93. similarly uptake of P and K also increased significantly upto 125 per cent NPK dose over control.

Rao et al. (1998) reported that there was an increase of 16.9 per cent and 15.6 per cent of N-uptake by straw and grain respectively in a direct seeded rice over a transplanted rice. Phosphorus and potassium uptake by rice grain was not influenced significantly by methods of planting. But P and K uptake by straw of direct seeded crop was significantly higher than transplanted rice. Zinc

Kaur et al. (1985) opined that zinc concentration in all the plant parts increased up to 30 days after transplanting and decreases thereafter with rate of decrease being much faster from 30 to 45 days than from 45 to 60 days.

Ilangovan and Palaniappan (1987) reported that application of Zn significantly increased the NPK uptake and Zn uptake in rice. Soil application of Zn-DAP, especially 6 per cent grade, was efficient and economic in meeting the Zn nutrition of rice in a Zn deficient low land rice soil.

Saravanan and Ramanathan (1988) conducted a field experiment with seven levels of ZnSO4 (0, 12.5, 25.0, 37.5, 50.0, 62.5 and 75 kg/ha) to study the effect of zinc application on its availability and yield of rice. They observed that the uptake of Zn by rice increased with the increased level of Zn application. Similar observations were made by Ingle et al. (1997).

Verma and Tripathi (1981) studied the effect of interactions of P-Zn and P-Cu on dry matter yield and micronutrient availability to rice in water logged Alfisols and reported that addition of P alone or in combination with Zn decreased the concentration of Zn, Cu, Fe and Mn in rice plants however addition of Zn alone increased its concentration in the plant.

Kumar and Singh (1979) conducted a field experiment to study the effect of different doses and methods of zinc application on zinc status of rice plants. Maximum zinc content under all the treatments was observed at active tillering stage. With advancement in age, the zinc concentration in plant declined. Zinc application in nursery gave maximum concentration of zinc in the treatment of root dipping in ZnO suspension irrespective of zinc application in transplanted field at all the stages. Under transplanted condition, the similar trends were observed with little variations.

2.3.2 Effect of biofertilizers on nutrient uptake 2.3.2.1 Effect of Azospirillum

Prasad and Singh (1984) reported the combined effect of inoculation of Azospirillum and incorporation of azolla in rice in pot culture. Incorporation of azolla as a green manure, inoculation of seedlings with Azospirillum and or application of N increased growth, nutrient uptake and yield of rice.

Azospirillum inoculation enhanced proliferation of the root system which increased mineral uptake (N, P and K) and consequently increased the dry matter accumulation (Lin et al., 1983; Okon and Kapulnik, 1986).

In a hydroponic system under greenhouse condition, inoculation of rice seedlings with Azospirillum resulted in enhanced PO4

- ion uptakes of the plants in 4 of the 7 samples tested

(Murthy and Ladha, 1988). Govindan and Bagyaraj (1995) conducted an experiment to study the response of

rice to Azospirillum inoculation at graded levels of nitrogen fertilizers and found that Azospirilum enhanced grain yield, straw yield and N uptake of field grown wet land rice.

Saha et al. (1985) reported that mustard crop at maturity recorded significant increase in total N of shoot due to Azospirillum inoculation. The magnitude of increase being 7.5 to 16.7 per cent over uninoculated control. 2.3.2.2 Effect of PSB

Sharma and Singh (1971) reported that the incorporation of phosphobacterium culture along with superphosphate + ammonium sulphate increased the uptake of N and P2O5 in grain as compared to the application of superphosphate + ammonium sulphate.

Gaur and Ostwal (1972) reported inoculation of wheat with Bacillus polymyxa significantly increased the P uptake in the grain. The inoculation along with rock phosphate was found to be more efficient.

Increase in yield and P uptake by gram due to inoculation with Bacillus magatherium and Bacillus circulans was noticed in an acid red loam soil (Ahmad and Jha, 1977).

Datta et al. (1982) reported that phosphobacteria in combination with rock phosphate and super phosphate increased the uptake of phosphorus by rice.

Mohod et al. (1989) reported that P solubilizing culture alone or in combination with phosphatic fertilizers increased the P uptake in rice plant. The beneficial effects of culture was greater with rock phosphate than single superphosphate.

Mohod et al. (1991) reported that the phosphorus solubilizing culture significantly increased the N uptake in rice cv. KJT-184. The beneficial effects of culture was greater with rockphosphate than single super phosphate. 2.3.2.3 Combined effect of Azospirillum and PSB

Kundu and Gaur (1984) in a green house experiment observed that inoculating rice seedlings with mixed cultures of Azotobacter chrococcum, Pseudomonas striata and Azpergillus awamori increased the N and P uptake in rice.

Alagawadi and Gaur (1992) reported that combined inoculation of Azospirillum brasilense and Pseudomonas striata or Bacillus polymyxa resulted in a significant increase in the nutrient uptake of sorghum over inoculation of individual organisms.

Prathibha et al. (1996) reported an increased nutrient uptake in cotton due to dual inoculation of Azospirillum and Pseudomonas striata over single inoculations.

2.4 Residual soil fertility as influenced by nutrient and biofertilizers Soil fertility can be enhanced by balanced nutrition. Application of fertilizers

containing major and micronutrients results in balanced nutrition, which results in good soil fertility. 2.4.1 Available NPK and Zn as influenced by nutrients

Velu and Ramanathan (1999) conducted field experiments during summer, Kuruvai and Thaladi seasons with different source of N applied at 153 kg N/ha to study the available N in soil. They reported that available N was higher during thaladi than the other two seasons. Application of urea super granule increased the available N in soil over prilled urea in all the crop seasons. While coal tar coated urea, neem cake coated urea, lac coated urea and ammonium chloride proved next best in order in increasing the available N content of the soil.

Pandian and Perumal (2000) reported that application of fertilizer N alone showed the depletion of primary nutrient status of the rice soil, while in combination with the organic manures, the nutrient status were improved.

Mahajan et al. (1992) conducted field experiments during kharif season of 1985, 1986 and 1987 to study the yield, nutrient uptake and available nutrient status in rice soil as influenced by complex fertilizers. They reported that the nitrogen fertility status was significantly improved with fertilizer application in all the three years compared to unfertilized soil. The effect of complexes and straight fertilizers on N fertility was at par with each other in the first two years, whereas in the third year APP and DAP recorded significant increase. The available P2O5 status was also increased with fertilizer use.

Velu et al. (1986) conducted two fields experiments to study the effect of NPK fertilizers on the nutrient content of soil in a wet land rice. They reported that application of both N and P enhanced the N availability in the soil. Application of urea increased the available N of the soil. The available P and K status of the soil was improved by P and K application, respectively.

Velayutham et al. (1992) reported that soil available nitrogen and potassium were influenced by the application of potassium in both rabi and kharif seasons. Potassium application did not change the status of available phosphorus. Available nitrogen was maximum (1356.0 and 120.2 kg N/ha in rabi and kharif respectively) where 62.5 kg of K was applied as basal. Soil available potassium was maximum (146 and 158 kg K2O/ha in rabi and kharif respectively) where 125 kg K2O was applied as basal.

Tyagi and Bharadwaj (1994) studied soil samples of six depths from a long term fertilizer experiment site. They reported that the status of available N, P and K was maximum in surface layer and minimum in lower most layer. The graded levels of applied NPK and fallowing significantly increased available N, P and K in soil over control. Also the effect of biofertilizer and FYM was positive. Addition of potassium (100% NPK vs 100% NP) increased available potassium status.

Singh et al. (2002) reported that continuous sorghum-wheat cropped over a period of 15 years depleted available K in loamy sand soils to almost half of its initial level. Higher doses of potassium could maintain available K status of soil. Continuous application of optimum and heavy doses of nitrogen to crops could not increase KMnO4 extractable N status in soil. Long term use of phosphatic fertilizer resulted in phosphorus build up in soil.

Ingle et al. (1997) reported that applications of increasing levels of Zn through ZnSO4.7H2O or ZnO did not influence significantly the availability of NPK. However, the levels and sources of Zn increased the availability of Zn and particularly by the appliation of 15 kg Zn/ha. Similar results were recorded by Turambekar and Daftardar (1992).

2.4.2 Available nutrients as influenced by biofertilizers Shankaraiah and Nagaraju (1997) reported that, inoculation of Azotobacter and

Azospirillum resulted in 20-25 per cent economy of fertilizer N requirement besides improving the residual nitrogen content of sugarcane soils.

Mandhare et al. (1997) observed the positive influence of Azotobacter on cane yield, available nitrogen and organic carbon content of soil after harvest. These parameters were more pronounced when the biofertilizers were combined with 100 per cent N fertilizer.

Mohod et al. (1989) reported that the use of P-solubilizing culture alone or in combination with phosphatic fertilizers increased the root cation exchange capacity (CEC) and available phosphours in soil. The beneficial effects of P solubilizing organisms on P availability was greater with rock phosphate than single super phosphate. The culture increased the P release efficiency of rock phosphate (RP) and made it equivalent to single superphosphate (SSP) in respect of available phosphorus in soil.

Selvalakshmi and Devarajan (2001) conducted two field experiments on a low P available soil to evaluate the efficiency of coated DAP in rice variety (ADT 36 (Kuruvai season) and Nimin coated urea in rice variety IR 20 (Samba season). Phosphorus was applied at levels 100, 80 and 60 per cent of recommended P as coated and uncoated DAP and recommended dose of N was coated with Nimin. The treatments receiving coated DAP in first experiment, coated DAP along with Nimin coated urea in second experiment recorded the higher availability of P than uncoated fertilizers.

III. MATERIAL AND METHODS

The particulars relating to the geographical set up of the study area, collection and preparation of the soil samples and the analytical methods adopted in the investigation are briefly presented in this chapter. Under this investigation rice was taken as the test crop.

3.1 Location of the study area The study area belongs to the Mirjan village of Kumta taluk. The Mirjan village is

located between 14°29’ 33.8” N latitude and 74°25’ 27.6” E longitude. It is representative of the agro-ecological sub-region 19.3 covering Karnataka coast of around 350 km (Sehgal et al., 1992). Fig. 1 represents the location of the study area.

3.2 Climate The climate of study area is characterized by high humidity nearly all the year round

(Appendix I). The rainfall is plentiful. The year may be divided into four seasons. 1) The summer from March to May has rising temperature with the maximum

temperature of the year occurring in April or May. 2) The south-west monsoon season, from June to September, which lasts for four

months from the beginning of June characterized by heavy rainfall. 3) October and November constitute the retreating monsoon or post monsoon season

and 4) The period from December to February is generally dry with low humidity and low

temperature and very little rainfall.

3.3 Identification of soil fertility constraints 3.3.1 Collection of soil samples

For identification of soil fertility constraints in the study area hundred (100) soil samples (surface and subsurface) at random locations were collected under different land uses in the study area. The exact sample location was recorded using a Global Positioning System (GPS). Locations of the soil samples were given in Table 1.

3.3.2 Preparation and storing of soil samples Soil samples collected were dried in shade. The air dried samples were ground with a

wooden pestle and mortar and passed through 2 mm sieve to separate the coarse fragments (>2 mm). The fine earth samples were stored in separate containers and used for various analysis.

3.3.3 Methods of soil analysis 3.3.3.1 Soil reaction

Soil pH was determined in 1:2.5 soil-water suspension and 1:2.5 soil-1N KCl solution by potentiometric method (Jackson, 1967). 3.3.3.2 Electrical conductivity

Electrical conductivity was determined in 1:2.5 soil-water extract using conductivity bridge and expressed as dSm

-1 (Jackson, 1973).

3.3.3.3 Organic carbon The organic carbon content of a finely ground soil sample was determined by Walkely

and Black’s wet oxidation method as described by Jackson (1967) and expressed in g kg-1

soil. 3.3.3.4 Available nitrogen

Available nitrogen content of the soil was determined by following modified Subbaiah and Asija method (Sahrawat and Burford, 1982). The modification includes distillation as in standard method, then addition of Devarda’s alloy followed by further distillation. 3.3.3.5 Available phosphorus

Available phosphorus in soil was extracted by Bray and Kurtz No.1 extracting solution (0.03 N NH4F in 0.025 N HCl) (Bray and Kurtz, 1945). In the extract phosphorus was determined by chlorostannous reduced molybdophosphoric method using spectrophotometer at 660 nm (Jackson, 1975). 3.3.3.6 Available potassium

Available potassium in soil was extracted by neutral normal ammonium acetate and subsequent estimation was by flame photometry (Jackson, 1973). 3.3.3.7 Available zinc

Fig. 1. Location map of the study area

Table 1. Location of soil samples of Mirjan village

Sample No. Latitude Longitude

1. 14029ι 19.9"N 74025ι 27.1"E 2. 14029ι 22.1"N 74025ι 19.8"E 3. 14029ι 18.8"N 74025ι 30.1"E 4. 14029ι 11.8"N 74025ι 25.6"E 5. 14029ι 17.1"N 74025ι 25.6"E 6. 14029ι 18.3"N 74025ι 9.8"E 7. 14029ι 17.6"N 74025ι 27.8"E 8. 14029ι 21.3"N 74025ι 32.0"E 9. 14029ι 15.6"N 74025ι 43.3"E

10. 14029ι 22.1"N 74025ι 43.7"E 11. 14029ι 19.9"N 74025ι 41.0"E 12. 14029ι 18.0"N 74025ι 37.7"E 13. 14029ι 14.2"N 74025ι 39.1"E 14. 14028ι 35.4"N 74026ι 15.6"E 15. 14028ι 31.6"N 74026ι 12.5"E 16. 14028ι 27.1"N 74026ι 10.0"E 17. 14028ι 23.3"N 74026ι 13.2"E 18. 14028ι 20.7"N 74026ι 7.5"E 19. 14028ι 18.1"N 74026ι 12.4"E 20. 14028ι 32.6"N 74026ι 9.4"E 21. 14028ι 41.1"N 74026ι 11.0"E 22. 14028ι 41.0"N 74026ι 15.0"E 23. 14028ι 42.3"N 74025ι 57.1"E 24. 14028ι 38.4"N 74025ι 59.0"E 25. 14028ι 33.8"N 74026ι 01.0"E 26. 14028ι 33.9"N 74026ι 5.4"E 27. 14028ι 40.3"N 74026ι 8.4"E 28. 14028ι 36.2"N 74026ι 03.6"E 29. 14028ι 43.5"N 74026ι 4.9"E 30. 14028ι 51.9"N 74026ι 17.7"E 31. 14029ι 01.2"N 74025ι 20.6"E 32. 14029ι 02.3"N 74025ι 19.4"E 33. 14029ι 16.6"N 74025ι 34.2"E 34. 14029ι 48.0"N 74025ι 43.0"E 35. 14029ι 52.1"N 74025ι 45.2"E 36. 14029ι 53.5"N 74025ι 42.8"E 37. 14028ι 34.68"N 74026ι 13.56"E 38. 14028ι 36.12"N 74025ι 59.16"E 39. 14029ι 18.96"N 74025ι 41.52"E 40. 14029ι 16.44"N 74025ι 30.72"E 41. 14029ι 50.28"N 74025ι 42.96"E 42. 14029ι 23.4"N 74025ι 27.1"E 43. 14029ι 24.2"N 74025ι 27.8"E 44. 14029ι 21.0"N 74025ι 23.9"E 45. 14029ι 17.7"N 74025ι 12.9"E 46. 14029ι 18.1"N 74025ι 30.8"E 47. 14029ι 19.9"N 74025ι 31.6"E 48. 14029ι 23.7"N 74025ι 43.3"E 49. 14029ι 21.9"N 74025ι 40.8"E 50. 14029ι 11.8"N 74025ι 38.8"E

Table 1. Contd…..

Sample No. Latitude Longitude

51. 14029ι 15.9"N 74025ι 39.7"E 52. 14029ι 8.3"N 74025ι 43.6"E 53. 14028ι 38.4"N 74025ι 18.8"E 54. 14028ι 43.2"N 74025ι 58.5"E 55. 14028ι 32.7"N 74025ι 58.4"E 56. 14028ι 35.9"N 74026ι 07.0"E 57. 14028ι 44.5"N 74026ι 05.3"E 58. 14028ι 51.6"N 74026ι 13.9"E 59. 14028ι 54.0"N 74026ι 22.4"E 60. 14028ι 41.1"N 74025ι 47.1"E 61. 14028ι 38.8"N 74026ι 17.5"E 62. 14028ι 27.6"N 74026ι 16.7"E 63. 14028ι 54.8"N 74025ι 29.9"E 64. 14028ι 49.2"N 74025ι 31.7"E 65. 14029ι 4.6"N 74025ι 22.6"E 66. 14029ι 55.3"N 74025ι 47.1"E 67. 14029ι 51.6"N 74025ι 37.6"E 68. 14028ι 38.64"N 74026ι 14.64"E 69. 14029ι 26.1"N 74025ι 19.3"E 70. 14029ι 27.3"N 74025ι 25.9"E 71. 14029ι 20.0"N 74025ι 10.1"E 72. 14028ι 42.9"N 74026ι 03.1"E 73. 14028ι 43.5"N 74025ι 59.5"E 74. 14028ι 52.9"N 74026ι 22.3"E 75. 14028ι 49.8"N 74025ι 46.3"E 76. 14028ι 01.6"N 74025ι 25.0"E 77. 14028ι 59.4"N 74025ι 22.3"E 78. 14028ι 58.5"N 74025ι 19.9"E 79. 14029ι 46.8"N 74025ι 36.6"E 80. 14029ι 48.2"N 74025ι 45.1"E 81. 14029ι 55.2"N 74025ι 49.2"E 82. 14029ι 9.1"N 74025ι 34.5"E 83. 14029ι 12.84"N 74025ι 55.56"E 84. 14029ι 39.12"N 74025ι 45.84"E 85. 14029ι 27.96"N 74025ι 15.60"E 86. 14029ι 6.72"N 74025ι 19.2"E 87. 14028ι 35.76"N 74026ι 20.76"E 88. 14029ι 51.72"N 74025ι 33.96"E 89. 14029ι 22.92"N 74025ι 21.36"E 90. 14029ι 32.28"N 74025ι 16.68"E 91. 14029ι 21.12"N 74025ι 9.84"E 92. 14029ι 33.00"N 74029ι 40.2"E 93. 14029ι 40.2"N 74025ι 17.4"E 94. 14029ι 47.4"N 74025ι 10.92"E 95. 14029ι 49.2"N 74025ι 19.2"E 96. 14030ι 8.28"N 74025ι 15.24"E 97. 14029ι 44.88"N 74025ι 34.32"E 98. 14029ι 0.6"N 74025ι 37.2"E 99. 14029ι 1.68"N 74025ι 44.4"E 100. 14029ι 24.72"N 74025ι 15.96"E

Available zinc, was extracted by using DTPA extractant as explained by Lindsay and Norvell (1978). The concentration of zinc in the extract was estimated using atomic absorption spectrophotometer (AAS Shimadzu model).

3.3.4 Preparation of soil fertility maps using GIS A dbf consisting of data for X and Y coordinates in respect of sampling site location

was created. A shape file (vector data) showing the outline of Mirjan area was created in Arc view 3.1.

The dbf file was openend in the project window and in X-field, X-coordinates were selected and in Y-field, Y-co-ordinates were selected. The Z field was used for different nutrients. The Mirjan shape file was also opened and from the surface menu of Arc view spatial analyst “Interpolate grid option” was selected.

On the output “grid specification dialogues”, output grid extend chosen was same as Mirjan. Shp and the interpolation method employed was spline. Then map was reclassified based on ratings of respective nutrients.

3.4 Field experiment As a part of the present investigation a field experiment was carried out in the farmers

field at Mirjan village to study the response of paddy to identified nutrient constraints and biofertilizers over all view of the field is given in Plate 1. Table 2 represents the physical and chemical properties of the experimental site.

3.4.1 Physical properties 3.4.1.1 Particle size analysis

Particle size distribution of soil samples was estimated by International Pipette Method as described by Piper (1966) using sodium hydroxide as dispersing agent. From the dispersed suspension, an aliquot of clay plus silt and clay were pipetted out from specified depth at specific time intervals depending on the suspension temperature. The total sand obtained by repeated decantation of silt and clay was passed through 0.05 mm sieve. The fraction that was finer than 0.05 mm was added to silt determined initially by pipetting to have particle size classes as per USDA systems.

3.4.2 Chemical properties Soil pH, electrical conductivity, organic carbon, available nitrogen, available

phosphorus and available potassium were estimated as described in section 3.3.3.1 to 3.3.3.6.

3.4.3 Treatment details The following treatments were designed based on the identified soil fertility constraints to study the response of rice. Fig. 2 represents the layout of the experimental site.

T1 = Control T2 = Azospirillum + PSB T3 = RDF T4 = RDF + Azospirillum + PSB T5 = RDF + 25 kg ZnSO4/ha T6 = RDF + 25 kg ZnSO4/ha + Azospirillum + PSB T7 = 150% RDF T8 = 150% RDF + Azospirillum + PSB T9 = 150% RDF + ZnSO4 25 kg /ha T10 = 150% RDF + ZnSO4 25 kg /ha + Azospirillum + PSB

3.4.4 Experiment details Crop : Rice Variety : MTU-1001 Spacing : 20 cm x 10 cm RDF : 75:75:90 kg N, P2O5 and K2O/ha Design : RBD Replication : 3

3.4.5 Cultural operations Seedlings were raised in the nursery bed. One month old seedlings were

transplanted in the main field on 4th July 2004 with 2-3 seedlings per hill. Seedlings of

respective treatments were inoculated with biofertilizers slurry. After inoculation, the inoculated and uninoculated seedlings were transplanted. A fertilizer dose of N:P2O5:K2O, 75:75:90 kg/ha was given in 2 split doses as per the recommendation. Fertilizers were given

Plate 1. Overall view of the experimental site

Table 2. Physical and chemical properties of experimental site

Sl. No. Particulars Value

A. Physical properties

Particle size distribution

1 Sand (%) 80.2

2 Silt (%) 7.0

3 Clay (%) 12.8

4 Textural class Loamy sand

B. Chemical properties

1 Soil reaction (1:2.5) 4.55

2 Electrical conductivity (dS/m) 0.18

3 Organic carbon (g/kg) 6.9

4 Available nitrogen (kg/ha) 281

5 Available phosphorus (kg/ha) 8.2

6 Available potassium (kg/ha) 79

7 Available zinc (µg/g) 0.48

R I

R II R III

T1 T10 T8

T2 T9 T7

T3 T8 T10

T4 T7 T9

T5 T6 T4

T6 T5 T3

T7 T4 T2

T8 T3 T1

T9 T2 T6

T10 T1 T5

Fig 2. Plan of layout

LEGEND

T1 = Control T2 = Biofertilizers T3 = RDF T4 = RDF + Biofertilizers T5 = RDF + ZnSO4 @ 25 kg/ha T6 = RDF + ZnSO4 @ 25 kg/ha + Biofertilizers T7 = 150% RDF T8 = 150% RDF + Biofertilizers T9 = 150% RDF + ZnSO4 @ 25 kg /ha T10 = 150% RDF+ZnSO4 @ 25 kg /ha + Biofertilizers

Treatments – 10 Replication – 3

Spacing 20 cm x 10 cm

in the form of urea, diammonium phosphate and muriate of potash as per the recommendation, ZnSO4 @ 25 kg/ha was applied in the respective treatments.

Plant protection measures were also taken as per recommendation. The crop was harvested on 21

st October 2004, on attaining physiological maturity and kept separately for

drying. Hand threshing and winnowing was done to separate the grains. After thorough sun drying weight was recorded treatment wise for grain and straw respectively.

3.5 Collection of experimental data Five hills per plot were selected randomly in the net plot and tagged for recording

observations at four stages (30th, 60

th, 90

th day after transplanting and at harvest).

3.5.1 Observations on growth components 3.5.1.1 Plant height

The plant height of five hills were measured from the ground level to tip of the top most leaf at early stages (30, 60, 90 DAT), up to the tip of main panicle at maturity and the average height was expressed in centimetres. 3.5.1.2 Number of tillers per hill

Total number of tillers were counted in each hill and averaged for five hills. 3.5.1.3 Number of leaves per hill

Total number of leaves were recorded per hill separately and averaged for five hills. 3.5.1.4 Leaf area per hill

For computing leaf area, number of tillers per hill were counted. The length and maximum width of each leaf on the middle tiller was measured and leaf area of each leaf was computed as follows.

Leaf area = K x L x W Where,

K = Constant factor L = Length of leaf (cm) W = Width of leaf (cm) The value of constant K was taken as 0.7 at all other stages of growth and 0.67

during maturity stage (Gomez, 1972). The leaf area per hill was then calculated as follows. Leaf area per hill (sq.cm) = Total leaf area of middle tiller x total number of tillers per

hill It was recorded for five hills separately and averaged to get leaf area per hill.

3.5.1.5 Leaf area index (LAI) Leaf area index is defined as the leaf area per unit land area, it was calculated by

dividing the leaf area per hill by the land area occupied by a single hill.

P

A LAI =

Where, LAI = Leaf area index P = Unit land area A = Leaf area

3.5.1.6 Dry matter production Dry matter production in the above ground portion of plants were recorded at the four

crop growth stages viz., 30, 60, 90 DAT and at harvest. The plant samples were first washed and then dried in shade for 24 to 36 hours. After that they were dried in an oven at 65-70°C to constant weight and the oven dry weight was recorded. The average of five hills were taken as the dry matter production per hill and it expressed in quintals per hectare.

3.5.2 Observations on yield and yield components The panicles from the randomly selected and tagged five hills for taking biometric

observations at harvest were used and the following observations on yield components and yield were recorded. 3.5.2.1 Panicle length

Panicle length from five tillers selected from randomly labelled plants in each plot was recorded from base to the tip of the panicle. The mean value was calculated and expressed in centimetres. 3.5.2.2 Number of grains per panicle

Ten panicles were selected randomly from five labelled hills and their grains were separated and counted. The mean value was worked out and recorded as number of grains per panicle. 3.5.2.3 Test weight (1000 grain weight)

One thousand grains were counted from randomly selected five hills per each treatment and their weight was recorded and expressed in grams. 3.5.2.4 Grain yield

The grains were separated by threshing separately from each net plot and were dried under sun for three days. Later winnowed and cleaned and then weight of the grains per net plot was recorded. From the net plot values, the grain yield per hectare was computed and expressed in quintals per hectare. 3.5.2.5 Straw yield

Straw from each net plot was dried under sun for ten days, weight was recorded on complete drying and expressed in quintals per hectare. 3.5.2.6 Harvest index (HI)

Harvest index is defined as the ratio of economic yield to the biological yield and it was calculated by using the formulae given by Donald (1962).

(q/ha) dstraw yiel(q/ha) yieldGrain

(q/ha) yieldGrain

(q/ha) yieldBiological

(q/ha) ieldEconomic yHI

+==

3.6 Economic analysis The cost of cultivation for each treatment was worked out by taking into consideration the price of inputs prevailing in the market. The grain/seed and straw yield of crops were considered to work out the gross returns from each treatment. Benefit cost ratio was calculated using the formulae.

Gross returns

B:C ratio = ———————————

Cost of cultivation

The prices of inputs and outputs are given in Appendix II.

3.7 CHEMICAL ANALYSIS OF PLANT SAMPLES 3.7.1 Preparation of plant sample

The five plants sampled for estimating the dry mater production and nutrient uptake from each field at 30, 60, 90 DAT and harvest were thoroughly washed with distilled water and dried in hot air oven at 65°C. Dried samples were powdered in a Willey mill to considerable fineness before storing them in polythene bags for further analysis.

3.7.2 Digestion of plant samples Powdered whole plant samples were separately treated with concentrated HNO3 for

twelve hours for pre digestion. Then the pre digested samples were treated with diacid (HNO3:HClO4) mixture (10:4 ratio) and digested on sand bath at low temperature till colourless white precipitate was obtained. The residue was dissolved in 6N HCl, filtered then the content was made to known volume by using 6N HCl. This was used for further nutrient analysis.

The following analysis were carried out from the diacid digested samples of whole plant. 3.7.2.1 Phosphorus

Phosphorus in digested samples was determined by Vanadomolybdophosphoric yellow colour method (Jackson, 1967) by using spectrophotometer at 420 nm wavelength. 3.7.2.2 Potassium

Potassium in the aliquot was estimated with the help of flame photometer after appropriate dilution (Jackson, 1967). 3.7.2.3 Zinc

Zinc was estimated in the aliquot of plant extract using atomic absorption spectrophotometer (Shimodzu model). 3.7.2.4 Nitrogen estimation of whole plant samples

For the estimation of nitrogen in plant samples, 0.5 g of powdered samples were digested with concentrated sulphuric acid in the presence of digestion mixture (CuSO4 + K2SO4 + Selenium powder) till it turned colourless. The digested sample was further diluted

with distilled water to a known volume. Nitrogen was estimated in a Microkjeldhal unit as described by Black (1965).

3.8 Nutrient studies 3.8.1 Nutrient uptake (kg/ha)

The nutrient uptake by rice at 30, 60, 90 DAT and at harvest was worked out using the following equation.

(kg/ha) yieldmatterxDry 100

(%) content Nutrient(kg/ha) uptake Nutrient =

3.8.2 Nutrient use efficiency (kg yield/kg nutrient) Nutrient use efficiency was computed by the following formula.

added nutrient

plot control in yieldGrain -plot treated in yieldGrain NUE =

3.8.3 Apparent nutrient recovery (%) Apparent nutrient recovery was computed by the following formula.

x100added Nutrient

plot control in Uptake - plot treated in UptakeANR =

3.9 Chemical analysis of post harvest soils After harvest soil samples were collected from the field and processed and analysed

for available nitrogen, phosphorus, potassium and zinc. They were determined using the same procedures as described in section 3.3.3.4 to 3.3.3.7.

3.10 Statistical analysis The experimental data obtained was subjected to statistical analysis adopting

Fischers method of analysis of variance as outlined by Gomez and Gomez (1984). The level of significance used in F-test was 5 per cent. Critical Difference (C.D.) values are given in the table at 5 per cent level of significance, whenever the F test was significant at 5 per cent level.

IV. EXPERIMENTAL RESULTS

A study was undertaken during kharif 2004 to identify the nutrient constraints of a

pilot site of coastal agro-ecosystem of north Karnataka and the response of paddy to nutrients and biofertilizers. The study area was Mirjan village of Kumta taluk.

Fertility status of the study area, growth and yield parameters nutrient content and uptake of rice, available nitrogen, phosphorus, potassium and zinc in soil at harvest stage were studied and the results are presented in this chapter under the following headings. 4.1 Identification of soil fertility constraints 4.2 Response of paddy to nutrients and biofertilizers 4.3 Nutrient content of rice at different growth stages 4.4 Nutrient uptake of rice at different growth stages 4.5 Nutrient use efficiency 4.6 Apparent nutrient recovery 4.7 Available N, P, K and Zn status in soil at post harvest stage and 4.8 Economic analysis

4.1 Identification of soil fertility constraints The results of the investigations carried out to identify the soil fertility constraints in

Mirjan village are presented in this chapter. The cultivated land of study area was grouped into three different land uses namely,

1. Paddy 2. Mixed plantation (coconut, arecanut and banana) and 3. Cashew

4.1.1 Soil reaction (pH) The data on the pH of the soil samples is presented in the Table 3. The pH of the soil samples at the surface ranged from 3.92 to 5.91 with a mean of 4.70 and standard deviation of 0.43. The pH values varied from 4.01 to 5.75 at the subsurface. Mean and standard deviation recorded were 4.82 and 0.42 respectively. There was an increase in pH with depth in most of the samples. The pH of the soil samples under paddy ranged from 3.92 to 5.91 with a mean of 4.64 and standard deviation of 0.44. It ranged from 4.01 to 5.54 at the subsurface. Mean and standard deviation recorded were 4.68 and 0.38 respectively.

Soil samples under plantations showed a variation in pH in the range of 4.18 to 5.80 at the surface with a mean of 4.93 and standard deviation of 0.44. In the subsurface it ranged from 4.25 to 5.75 with a mean of 5.06 and standard deviation of 0.38.

Soil samples categorised under cashew showed pH values in the range of 4.10 to 5.35 at the surface with a mean of 4.59 and standard deviation of 0.34. At the subsurface pH was in the range of 4.10 to 5.47 with a mean of 4.82 and standard deviation of 0.41.

4.1.2 Electrical conductivity (dS m-1) The data on electrical conductivity of soil samples are presented in Table 3. The EC

of the soil samples ranged from 0.011 to 0.520 dS m-1

at the surface. Mean and standard deviation were 0.071 dS m

-1 and 0.068 respectively. In the lower depth it ranged from 0.010 to

0.258 dS m-1

with a mean of 0.063 dS m-1

and standard deviation of 0.050. There was a decrease in EC with depth.

The EC of the samples under paddy ranged from 0.011 to 0.520 dS m-1

the surface with a mean of 0.077 dS m

-1 and standard deviation of 0.089, whereas in the subsurface, the

EC ranged between 0.010 and 0.258 dS m-1

with a mean of 0.071 dS m-1

and standard deviation of 0.061.

The EC values of the samples under plantations were in the range of 0.020 to 0.170 dS m

-1 with a mean of 0.061 dS m

-1 and standard deviation of 0.036. The conductivity values

at the subsurface showed a variation from 0.017 to 0.161 dS m-1

with a mean of 0.054 dS m-1

and standard deviation of 0.033. The EC of the samples under cashew ranged from 0.017 to 0.297 dS m

-1 with a mean

of 0.072 dS m-1

and standard deviation of 0.058 at the surface, whereas in the subsurface it ranged between 0.010 and 0.247 dS m

-1 with a mean of 0.061 dS m

-1 and standard deviation

of 0.047.

Table 3. pH, EC, organic carbon and available N content of 100 soil samples of Mirjan village

pH EC (dS/m) Organic carbon

(g/kg) Available N

(kg/ha) Sl. No.

Surface Sub-

surface Surface

Sub-surface

Surface Sub-

surface Surface

Sub-surface

Paddy 1 5.08 4.92 0.026 0.018 17.6 13.2 448 378 2 4.52 5.11 0.011 0.010 14.3 10.2 321 285 3 5.08 4.61 0.082 0.072 14.7 4.3 392 235 4 4.35 4.38 0.047 0.025 13.8 5.0 392 287 5 4.94 4.75 0.020 0.023 15.9 5.5 325 224 6 4.45 4.17 0.047 0.014 18.7 13.2 395 320 7 4.52 5.54 0.130 0.061 18.0 14.1 365 294 8 5.91 5.32 0.091 0.055 12.0 9.7 336 220 9 4.12 4.15 0.042 0.052 13.0 10.5 276 307

10 4.12 4.35 0.052 0.080 9.0 9.0 294 222 11 5.34 5.40 0.011 0.055 6.0 5.7 261 245 12 4.26 4.62 0.063 0.168 10.3 6.0 255 230 13 5.23 5.02 0.121 0.145 13.5 6.1 331 301 14 4.98 4.88 0.054 0.041 19.2 11.1 361 308 15