AGFACTSAGFACTSAGFACTS

www.agric.nsw.gov.au

ORDER NO.P1.21. AGDEX 100/510

Cropping onraised beds insouthern NSW

Agfact P1.2.1, first edition 1997H.G.Beecher, J.A. Thompson,D.W. McCaffery and J.S. Muir*

(Revised June 2003)

INTRODUCTIONIrrigation in southern NSW has developed on soilsthat can have severe limitations to crop growth underirrigated conditions. These limitations includephysical problems such as:

• poor tilth

• inadequate infiltration

• shallow hard-setting surface horizons

• crusting surface soils

• dense subsoils

• waterlogging

• soil compaction.

Chemical problems such as sodicity, salinity, and lownutrient status also occur in most soils.

Soil conditions that are conducive to high cropproduction are shown in Figure 1. The surface soil isaggregated and does not disperse or slake. Thesubsoil is not dense, and is permeable, well-aeratedand does not disperse.

Most irrigated land is devoted to rice, pasture andwinter cereal production on contour or border checkstyle layouts. The current farming system based onflood irrigation, with poor grades and rigid, limitedcrop rotations, can lead to the following problems:

• soil degradation

• poor water management

• waterlogging

• low yields

• reduced economic returns.

If irrigation farming in southern NSW is to besustainable, existing soil management techniques mustbe improved. Irrigation systems can be significantlyimproved by incorporating raised bed furrow irrigationtechniques into a whole farm system.

Furrow irrigation provides the advantages of:

• greater flexibility in crop rotations

• more efficient water management

• improved soil structure.

This Agfact provides an overview of the importantproperties and problems of soils used for broadacrecropping under irrigation in southern NSW. Itdiscusses how the use of innovative irrigationtechniques can improve the productivity of irrigatedcrops, and how raised bed irrigation technology canprovide the basis for improved crop production.

MAJOR IRRIGATED SOIL TYPESThere are three main soil types used for broadacreirrigation farming in southern NSW. They areself-mulching clay soils, red-brown earth soils and claysoils that are not self-mulching.

Self-mulching claysThe self-mulching clays (e.g. Yooroobla clay,Wunnamurra clay and Niemur clay) occur as extensive

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Figure 2. Major irrigation company areas insouthern NSW

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plains throughout the region. They are characterisedby a heavy texture, with a uniform clay profile. Thesurface horizon, in the dry state, is self-mulching,being composed of easily disturbed small aggregatesresulting from extensive cracking. The self-mulchingsoils are generally associated with gilgai formationsand frequently occur in association with transitionalred-brown earths. However, toward the west of theregion the gilgai formations may not be present. Theself-mulching clays vary in colour from reddish brownto grey. They also vary in the degree of gilgaidevelopment and in the presence of free lime (calciumcarbonate) in the surface soil. Initial water infiltrationinto dry self-mulching soils is rapid (most of theirrigation water enters in the first 30 minutes). Afterthis, swelling closes the large cracks, and infiltrationrates are significantly lower. The self-mulching surfacecondition is favourable for seedling establishment.Traffic tends to compact these soils when they arewet.

Red-brown earths and transitionalred-brown earthsThese soils (e.g. Cobram loam, Birganbigal loam andDeniboota loam) are red-brown to grey-brown,weakly structured to massive surface horizons, and

feature an abrupt boundary between topsoil andsubsoil horizons. The subsoils have usually brighterbrown to red clay horizons with well-developed blockyaggregates. The soil typically becomes yellow brown toyellow grey, with lime concretions present below 60cm.

Transitional red-brown earths (e.g. Wilbriggieclay loam and Marah clay loam) are a sub-group of thered-brown earths. Transitional red-brown earths haveshallow surface horizons 5–10 cm thick, with aclay-loam texture, whereas red-brown earths haveloam or sandy loam textured surface horizons,typically 15–30 cm deep.

Topsoils can contain a high proportion of fine sandand silt. When the surface soil is exposed to floodirrigation or heavy rainfall, the soil aggregates (beinglow in clay and/or organic matter to bind them) slaketo form microaggregates. Dispersion is likely if thesoil is sodic (exchangeable sodium percentage [ESP]greater than 6) and non-saline. Both slaking anddispersion increase the soil bulk density, causing poorcrop emergence, increased waterlogging and poorinfiltration.

The subsoils are generally high in clay content andhave high bulk density. The high bulk density of the

Raised beds improve drainage and aeration of the rootzone following irrigation, leading to good rootdevelopment of crops on grey self mulching clay (left), transitional red-brown earths (top right) and brownclay soils (lower right).

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subsoil impedes root growth. Zones of low hydraulicconductivity (‘throttles’) can occur at the interfacebetween the topsoil and subsoil horizons, limitingwater and air movement.

The pH (CaCl2) of the topsoil is normally 5.5 to 6.5,and the subsoil is frequently alkaline and sodic.

Clays that are not self-mulchingThe non self-mulching clays (e.g. Billabong clay andRiverina clay) occur in areas of very low grade andhave the following features:

• a shallow surface crust over a blocky clay subsoil

• relatively uniform clay content throughout theprofile

• low amounts of lime

• moderate amounts of gypsum (calcium sulfate)below 60 cm

• grey or brown colour

• sodicity throughout the profile.

The sodicity leads to dispersion upon irrigation, sowater movement and aeration tend to be very poor.The alkaline and saline conditions that occur,particularly in the subsoil, can also restrict plantdevelopment.

FAVOURABLE SOIL CONDITIONSIrrigated crops require a stable topsoil that provides afavourable environment for emerging seedlings andwater entry, and a subsoil that transmits water and aireasily, allowing unimpeded root penetration. Only thencan the growth potential of the plant be achieved. Themost productive soils around the world have severalfeatures in common:

• well-aggregated surface soil that does not slake ordisperse

• high calcium content

• high organic matter content

• high biological activity

• low density (degree of compaction)

• a silty clay loam texture

• permeable and well-aerated subsoil

• non-sodic subsoil resulting in minimal swelling.

Most irrigation soils in southern NSW, by comparison,possess numerous limitations for plant growth. Thephysical (structural) nature of the soil directly affectsplant growth through its influence on:

• soil resistance to root penetration

• soil water content and movement

• soil aeration

• soil temperature.

The closest soil we have to the ideal is the self-mulching clay.

WHAT ARE RAISED BEDS?Raised bed farming is a system where the crop zoneand the traffic lanes (wheel tracks or furrows) aredistinctly and permanently separated. Soil is movedfrom the traffic lanes (or furrows) and added to thecrop zone, slightly raising the surface level of the cropzone. Raised bed technology is an adaptation of thetraditional hill and furrow row cropping design.Irrigation water moves laterally from the furrow

AVOID FLOODING

When irrigating on contour or border checklayouts with grades of 1:1500 to 1:2500, themajor concerns are slaking and dispersionresulting from flooding the entire soil surface.This is especially the case with red-brown earths,transitional red-brown earths and nonself-mulching clays. Slaking and dispersion affectcrop emergence by prolonging waterloggedconditions. Crop emergence may also be affectedby the formation of crusts as the slaked and/ordispersed soil surface dries.

Potential soil structural problems can be identifiedquickly and easily using slaking and dispersion testsin the field.

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through the bed by ‘subbing’ (soaking up from thefurrow to the top and middle of the bed againstgravity).

ADVANTAGES OF RAISED BEDSImproved surface and internal drainage ofthe soil, because the entire soil surface is notflooded. The soil wets up by subbing, so the raisedbed layout reduces waterlogging in both winter andsummer crops. More favourable root-zone conditionsexist for plant growth since there is a greater depth ofsurface soil, and the furrows act as drains, so rapid re-aeration of the root-zone occurs following irrigationor rainfall. Wetting of the soil by subbing reduces theincidence of surface crusting, which providesimproved seed bed conditions and allows improvedcrop emergence.

Improved soil structure of the cropzone, because most machinery wheel compaction isconfined to the furrows. Crop growth is improved, assoil conditions are maintained within favourablelimits. Minimum tillage and direct drilling techniquesallow soil structure to be improved through increasedorganic matter levels and root activity, even wherestubbles are burnt.

Reduced tillage requirements, because the cropzone is not compacted by wheeled traffic. This resultsin reduced mechanical inputs and costs, and smallertractors can be used for cultivating. The use of thefurrows for traffic is more likely to allow culturaloperations to be undertaken at the optimum time,unlike border check and contour layouts, where delaysare experienced, and where the soil is looser andpotentially more boggy.

Increased range of crops and pastures thatcan be grown in rotation. The grower can easilychange crop sequences to benefit from favourablemarket prices. The opportunity exists to water-upsome winter crops with less risk of poorestablishment caused by seed burst, dispersion andcrusting of the surface soil. This increases thepossibility for double cropping, offering improvedflexibility in crop choice and better land utilisation.

Improved financial returns. The ability tooperate in a double cropping crop sequence—combined with improved root-zone conditions andfewer and more timely cultural operations—makesbetter profits likely.

OPTION OF PERMANENT RAISED BEDSThe conventional practice for row cropping has beento cultivate and reform hills or raised beds after theharvest of each crop. If the raised beds are

adequately constructed initially, they can be left inplace over a long period—at least five years.Construction of raised beds in a permanent formatsignificantly reduces operating costs by removing theneed for annual construction of the beds. It also aidsthe potential for double cropping since successivecrops can be sown close to optimum sowing dates,avoiding delays by cultivation requirements of othersystems. Reduced cultivation contributes toimprovements in soil structure by maintaining orimproving levels of soil organic matter.

PADDOCK SELECTIONSoilRaised beds have been constructed by farmers on eachof the three main soil types, and have performedsatisfactorily. You will need to carefully assess thesuitability of the soil for this technique, becauseincreased levels of management input are required.Self-mulching soils are the most easily managed whenusing the raised bed system because cracking clay soilsregenerate their structure by shrinking and swelling.When using red-brown earths and non self-mulchingclay soils, you need to pay attention to issues such as:• moisture content at the time of cultivation• sodicity levels and gypsum requirements• soil aggregate sizes• soil crusting at seedling emergence• water entry during irrigations.

Gypsum, if necessary, should be incorporated beforethe first crop after bedding up, as later incorporationmay destroy soil structural improvements.

Field gradesRaised beds are most suited to flatter grades of about1 in 1000 to 1 in 2500. Where possible, use the mosteven natural grades, without big cut and fillrequirements, and run lengths of up to 800 m. Thisreduces the number of structures required to water apaddock. Flatter paddocks should have shorter runlengths.

Landforming, preferably laser-guided, isrecommended. When paddocks that have not beenlaser-graded are laid out to raised beds, they are likelyto develop problems including over-topping of thebeds and waterlogging. This in turn causes soilcrusting and seedling emergence problems.

Recirculation systemsFlow rates are usually adjusted to allow 8–12 hourchangeover intervals. A recirculation system isessential to allow reuse of drainage water from thefurrows and harvesting of rainfall runoff.

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Even on slaking and dispersive soils, crops can grow well using raised beds and appropriate management.

Wheat double cropped into burnt maize stubble. Raised beds provide increased possibilities for doublecropping, allowing winter cereals to be sown directly after harvest of summer crops.

A cross-section of a raised bed showing itsdimensions and its seed bed. Wider flat beds suitwell-structured soils which allow good subbing.Higher, narrower beds are best where subbing ispoor or where better drainage is needed.

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Recirculation systems should also help to retain andmanage any pesticide residues on-farm.

WeedsPermanent raised beds should be constructed inpaddocks where the weed population is minimal, sincethe beds are intended to remain in place withminimum cultivation for some time. Use of cultivationto control weeds is not advocated, because improvedsoil physical condition is an objective of the use ofbeds. Frequent cultivation may destroy theseconditions, particularly when carried out atinappropriate soil moisture contents. However,strategic cultivation may be necessary where perennialweeds cannot be adequately controlled by herbicides.

SalinitySaline soils and shallow watertable areas can result insalt concentrating on the surface of the beds. Theseareas should be avoided for raised bed systems. Theexisting watertables and soil salinity levels should bemeasured at the outset and monitored over time.

Soil pHAcid soil conditions should be avoided or ameliorated,as the potential range of crops may be limited by soilacidity. Lime, if necessary, should be incorporatedbefore bedding up for the initial crop. Laterincorporation requires knocking down of the beds,which may destroy soil structural improvements.

PADDOCK PREPARATIONHeavy machinery used for landforming can causesevere subsoil compaction if undertaken whensubsoils are wet. Soil moisture content should be closeto the lower plastic limit (see ‘Glossary’) whenlandforming. Growing a winter crop beforelandforming can assist in drying the subsoil.Landforming often leaves the soil pulverised, with finedust particles overlying large compacted aggregates.

Permanent raised beds are intended to be in place forseveral crops, so good initial paddock preparation isessential.

CONSTRUCTION OF RAISED BEDSBed dimensionsBed width varies with the soil type and theequipment to be used to grow the crop. Raised bedirrigation requires the water to sub up. The beds arenormally 1.5–2.0 m wide, allowing a bed top width of1.0–1.5 m (see Figure 3). This contrasts withconventional hills which are traditionally spaced at 75–100 cm centres. Favourably structured soils (e.g.self-mulching clays) are usually able to wet up well,enabling the use of a wider bed configuration of 1.8–2.0 m. Red-brown earth soils and non self-mulchingclays may need narrower (1.0–1.5 m) bedconfigurations to ensure adequate water entry.

For summer cropping alone there is no majoradvantage of wider flat-topped beds over hills.However, if the crop sequence is to include wintercropping, then the use of wider flat-topped beds ismore appropriate, because more rows can be placedon the bed.

Bed height can be 15–20 cm. Uniformity of bedheights allows the use of fixed rather than floatingrow crop equipment.

Bed height depends on soil type and paddock grade.For the flatter grades and longer runs, bed heightsneed to be greater to reduce waterlogging. Forred-brown earths and non self-mulching clays whichdo not sub easily, the bed height needs to be moreshallow.

Hilling upThe soil should be cross-worked with deep tillagebefore hilling up, so that the soil is loose to below theanticipated furrow depth. This depth of cultivated soilallows accurate and straight furrowing and hilling.

Two techniques are most commonly used to constructbeds:

• removing every second lister from a toolbar andconnecting the remaining pairs of lister shanks with

Figure 3. Irrigated raised beds showing the dimensions of segregated traffic and crop areas

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heavy bed-forming chains

• listing up hills as for normal furrow irrigation, andthen placing a bed shaper over two adjacent hills toform a bed.

In some cases, rotary hoes are used in association withlisters and bed shapers to form the raised beds.

Once the beds have been constructed they may have arough appearance, with a mixture of fine powdery soiland large clods. It is better to leave them in thiscondition than to try to work them down to a finercondition wetting by rain and drying will usually allowweathering of the larger clods. Pre-watering andfurther cultivations (during herbicide incorporationand sowing) accelerate the weathering process andassist seedbed preparation.

Red-brown earths, transitional red-brown earths andnon self-mulching clay soils have sodic horizons andare generally low in organic matter. Raised beds onthese soils require special management and a narrowerbed width (1.0–1.5 m) to help with subbing, especiallyafter excessive working or landforming. More time andpatience is often required to allow these soils toimprove their structure, in order to improve subbing.This may require a number of crops to successfullyimprove soil structure. Beds on these soils are oftenfallowed over winter before a summer crop, or,alternatively, winter cereals can be grown. The wintercereal crop can be established after rainfall, and it hasa fibrous root system that improves the soil structureof the beds before more expensive summer croppingis attempted.

The approach developed at Tatura, Victoria, tomanage the problem of poor water entry—especially

in red-brown earth soils—has been to hill up the bedsand then cultivate the soil to a good tilth. Thiscultivation, referred to as ‘aggresizing’, involves tillingthe bed at close to the lower plastic limit, using aspring-tined cultivator. The loam surface soil of ared-brown earth forms aggregates 0.1–0.4 cm indiameter—which, once dried, are stable to rewetting.By cultivating at this moisture content there is verylittle dust formed, reducing the hard-setting soilcondition. Substantial improvements in waterinfiltration have been achieved using the aggresizingtechnique.

Where initial subbing is anticipated to be a majorproblem due to soil type and condition, some growershave opted to construct narrower hills. These hills,half the size of the planned final bed-width, are usedto grow the first crop in the problem soil. When thesoil structure has improved, the hills are converted tothe wider bed format (0.9-1.8 m) after harvest.

With the raised bed system, productivity can bemaintained at a high level on the better soil types, anddramatically improved on poorer soil types,particularly if attention is paid to soil structure.

Time of bed constructionRaised beds can be constructed at any time, providedsoil conditions are suitable. If the paddock is to belandformed before permanent bed construction, it ispreferable to grow a winter crop to dry the soil profile.This will reduce the chance of landforming equipmentcontributing to subsoil compaction.

Autumn construction of raised beds allows a choiceof:

• Fallowing the beds during winter. This allows thebeds to consolidate, and may improve soil structure.

The height and width of raised beds is influenced by soil type, and available tillage and sowing equipment.

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It can also increase your chances of sowing on timein spring, if rainfall is high during the winter.

• Sowing the beds immediately with a winter cerealcrop. This is usually done under conditions createdby rainfall, without irrigation, and allows thedevelopment of fibrous root systems to bind thesoil aggregates.

In the rice farming system, if the paddock has beenpreviously levelled, raised beds can be prepared afterremoval of the rice stubble, allowing a summer cropto be grown. In this case, most of the soil preparationwould occur in late winter and early spring, provided itis not too wet.

Run lengthsThe length of run depends upon the soil type and theslope of the land used. On lighter soils, shorter runlengths are preferred so that the top end is not over-watered. On heavy soils, run lengths of up to 800 mhave been successfully used in southern NSW,providing that satisfactory laser grading has beenachieved.

Cut areasAreas of fields heavily cut by landforming arefrequently characterised by the exposure of sodicsubsoil horizons which are low in plant nutrients andwhich frequently have higher soil pH levels that affectplant nutrient availability. Cut areas require specialattention in regard to fertiliser and gypsumapplications. (Animal manures are also being appliedby growers as a soil amendment to cut areas.)

It is important that the permanent raised beds areconstructed in good condition, as there may not bethe opportunity for later cultivation to rectify anyproblems. The furrows should be as straight aspossible, otherwise later cultivation operations willmodify bed dimensions.

MAINTENANCE OF PERMANENT BEDSMajor maintenanceThe paddocks may require additional landformingevery three to seven years. Possible reasons for thisinclude:

• poor initial landforming

• soil movement due to soil swelling and gilgai effects

• wet harvesting, particularly of late summer crops,damaging bed dimensions and soil condition.

Minor maintenanceFurrow spinners are used to repair the furrow andreshape the edge of the beds. Soil and stubble materialis removed from the furrow and moved to the sowing

line on the top of the raised bed. Once beds are upand subbing, there are usually no further problems,other than furrow tyre compaction on the edge of thebed which may need cultivating occasionally. This canbe achieved by using cultivating knives at theappropriate moisture content (lower plastic limit)followed by re-furrowing with listers.

IRRIGATION MANAGEMENTIrrigation methodsSmall hand syphons (5.0–7.5 cm), with one or two perfurrow, are the most flexible way to irrigate. Controlof water in individual furrows is possible, regulatingthe rate of advance down each furrow. Some furrows,especially trafficked furrows, tend to water quickly andfinish before untrafficked furrows. Irrigation of thesequick watering furrows needs to be cut off earlier,unless the recirculation system can handle the drainageflows.

Alternative systems of pipes through the channelbanks, or large moveable syphons over the bank, havebeen used to irrigate several furrows at once. No flowcontrol within the group of furrows is then possible,so recirculation systems must be available to handleincreased drainage flows. These systems are moreexpensive but reduce labour requirements, as watercontrol is then managed in groups of furrows.

Pre-wateringPre-watering (irrigating before sowing) is the preferredtechnique on unconsolidated beds, or where the soilsare prone to crusting or hard setting. It is particularlyuseful for summer crops, as sowing intounconsolidated beds and watering up can result inpoor crop emergence due to bed and seed subsidenceduring irrigation. Prewatering avoids suddenreductions in soil temperatures and subsequent effectson seed germination that may result when watering up.In addition, the survival of seed inoculant for legumecrops (such as soybeans) is enhanced, as the inoculantis placed directly into moist soil.

Pre-watering for winter crops can also be carried outconfidently later in the season than on flat layouts dueto better general field drainage.

Watering upSummer crops should only be watered up on well-consolidated beds (e.g. double cropped beds). Whereunconsolidated beds are being used, pre-irrigation ispreferable to help consolidate the beds.

Raised beds should be uniformly high so that all ofthe seed line is above the furrow water levels,especially for soybeans.

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Hilling up conventional hills for later conversion to raised beds.

Rotary hoes can be used after listing, to form beds.

Raised bed shapers can be placed over two adjacent conventional hills to form raised beds.

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Watering up of raised beds presents a much lower riskof waterlogging than with flat layouts, due to betterfield drainage down the furrows.

Therefore, most crops can be watered up on time,avoiding the need to wait for rain, as is the case on theflat.

Watering durationCrops grown in furrow irrigation are more tolerant ofexcessive watering duration than those irrigated on flatlayouts, due to the better re-aeration of the soil in thebeds after drainage of the furrow.

However, watering times should be kept to 12 hoursor less for most crops, as waterlogging can still occurin the raised beds with long watering times. Longwatering times have significantly reduced yields insome grain legume crops grown on hills (e.g. mungbeans).

Raised beds on red-brown earth soils can presentproblems in maintaining adequate infiltration, due toslaking and dispersion of soil in the furrow. In thiscase, water may not sub entirely across the width ofthe permanent beds, leaving a dry ‘bone’ section in thecentre of the bed. Irrigation and stubble managementmay need to be modified to allow adequate moistureto infiltrate the beds. Methods of overcoming thisproblem include:

• run water at a high level in the furrows (withoutflooding the beds) to increase the wetted surface ofthe furrow

• leave stubble in the furrow to slow the rate ofwetting of the soil surface, hence decreasing the rateof slaking and dispersion

• establish a continuous flow down the furrows usingsmall-diameter syphons (saturated soil culture).

Saturated soil cultureFor some hard-setting soils the use of saturated soilculture (continuous flow furrows) may be necessary.In this system, small diameter syphons (e.g. 2.0 cm)may be used in each alternate furrow to reduce thepotential for moisture stress affecting yield. Theapproach is suitable for soils which have very poorinfiltration and subbing characteristics. Soybean is theonly crop with which it can be successfully used. Inthese situations good weed control is necessary at theoutset.

Need for recycling facilitiesThe use of furrow irrigation requires that a drainagerecirculation and storage facility be available to reusetail water and rainfall runoff.

Irrigation schedulingMoisture stress at critical times can significantly affectgrain yield in all irrigated crops. Growers need to beable to predict when irrigation of a crop is necessary.Irrigation can be scheduled by using neutron probesto estimate soil water content, or with climate-basedscheduling services such as Water Watch provided byNSW Agriculture. Details of the service are availablefrom district agronomists.

Listers with heavy connecting chains can be used to form raised beds.

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FERTILISER REQUIREMENTS

Soil testingSoil physical and chemical testing is recommended onall fields before contemplating the use of raised beds.

Soil pH. Measuring soil pH is important, as bothalkaline (high pH) or acidic (low pH) soils can result innutrient deficiencies.

Subsoils exposed during landforming frequently havea pH greater than 7.0 (CaCl2) and are usually deficientin zinc. Crops vary in their tolerance to acidic soilconditions. Where acid soil conditions exist, applyinglime to raise the soil pH to 5.5 allows the full range ofcrops to be grown. Molybdenum, essential forsuccessful nodulation of legume crops, is less availablebelow pH 5.5 and should be applied if soil conditionsare acidic.

Landformed cut areas are likely to require extraphosphorus (P) (40-50 kg/ha), and zinc (Zn) (l0 kg/ha. A soil test before bedding up will indicate whetherthere are any nutrient deficiencies. Furtherrecommendations on liming are available in AgfactAC. 19 Soil acidity and liming.

Gypsum requirement. Sodic surfaces, eithernaturally occurring or exposed by landforming, aredifficult to manage, and gypsum application will berequired. Application rates of 2.5-5.0 t/ha arecommonly used and applications can be targetedtoward the exposed subsoil areas in the paddock.

Fertiliser type and placementFertiliser application and placement varies betweencrops. Details are provided in Agfacts about specificcrops.

Strategies for permanent raised beds. Onpermanent raised beds, particularly in the doublecropped or minimum tillage situations, fertilisermanagement needs to be considered in a longer timeframe, particularly for less mobile nutrients such asphosphorus. It is preferable to apply nutrients such asphosphorus, sulfur, zinc and molybdenum insufficient quantities to provide for the requirementsof a number of successive crops. This avoids majorsoil disturbance often associated with deep fertiliserplacement in the bed, and subsequent poor seed bedcondition.

CROP ESTABLISHMENTThe first crop is usually planted into a conventionallyprepared seed bed following construction of the bed.Depending on the time of construction, either awinter or summer crop can be grown.

Row spacingA range of row spacings can be used on raised beds.

Summer crops are usually established with two rowsper bed top, with each row next to the furrow. Thisposition generally waters up well and reducesestablishment problems especially where infiltrationinto the middle of the bed is considered to be poor.

For some crops (e.g. soybeans or mung beans), threeto six rows can be spaced across the bed. Theincreased number of plant rows allows earlier closureof the crop canopy and better suppression of weeds.This configuration is only appropriate where goodsubbing to the bed centre occurs. Narrower rowspacings are also preferred where sowing is delayedbeyond the optimum date.

Winter crops can be established on the bed tops with15–18 cm spacing, as for conventional combinespacings. In some cases, small-seeded crops (e.g.canola) may be broadcast and then lightly harrowedfor seed burial.

Sowing ratesThe sowing rates used for raised beds are the same asthose used for conventional layouts. Sowing rates mayneed to be increased to compensate for reducedseedling emergence when using direct drilling orminimum tillage practices.

HARVESTCompaction should be minimised by the harvesterwheels tracking in the furrows. Header wheelconfigurations do not generally fit with furrowspacings, so you will need to consider modifyingthe header wheel spacings.

Winter crops are usually harvested when soils are dry,and compaction will be minimal. However, harvestingof summer crops is more likely to coincide with wetsoil conditions, and harvester wheels will compact soilwithin the bed. Where possible, avoid harvestingunder wet soil conditions.

If the harvest must proceed under these conditions,use narrow harvester tyres to minimise soilcompaction. Harvester grain bins should be emptiedas often as possible, reducing axle loads andconsequent soil compaction. Similarly, it is preferableto keep tractors and field bin traffic on the paddockmargins.

STUBBLE MANAGEMENTWinter cropThe stubble residue of irrigated winter cereal cropscan be bulky and can hamper the establishment of

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following double cropped summer crops, because thestubble may be too thick to handle with existingsowing equipment. Summer crops can be successfullyestablished into either slashed or standing cerealstubble by use of a fluted disc coulter in front of thesowing tine to cut through the cereal straw.

Other options include burning the stubble or slashingthe stubble and directing the slashed residue towardthe centre of the beds away from the summer cropsowing lines at the bed edge.

The stubble of winter legume and oilseed crops doesnot impede the sowing of following summer crops.

Summer cropAlthough less bulky than winter cereal stubble, thestubble residue of summer crops can pose a problemfor double cropping. The most common approach toremoving this stubble is raking and burning.

All cropsAlternative methods of removing stubble includeslashing and mulching, incorporation and grazing bylivestock. In double cropped situations, retainingstubble often reduces dry matter production and grainyields (see Figure 4) and delays maturity of succeedingcrops. Delayed maturity may lead to delayed sowing ofany following crop. Also, more fertiliser is neededwhen stubble is retained, rather than removed.

Overall, to achieve high yields, the best managementapproach is to remove crop stubble wherever possible.

The most suitable method has been burning,especially in the double crop system. Burning stubblealso plays a significant role in improving crop hygieneby reducing the population of weeds, crop insect pestsand potential disease sources.

WEED CONTROLWeeds reduce crop yields by competing for moisture,nutrients and light and can result in reduced grainprices due to dockage for contamination. They canalso act as an alternative host for diseases, and causeharvesting and machinery problems.

Ideally, new beds should be constructed on land with alow weed burden. Crop selection should be based inpart on an assessment of the weeds in the paddock.Growing crops with different seasonal or herbiciderequirements is a technique that can be used toeffectively manage weed infestations.

Annual grass weedsPre-emergent herbicides can be incorporated beforesowing the first crop that follows bedding up (e.g.control of barnyard grass in soybeans and maize; andcontrol of ryegrass, wild oats or phalaris in wheat orbarley).

Perennial weedsA build-up of perennial weeds (e.g. dock and Johnsongrass) is a significant potential problem with directdrilled permanent beds. Perennial weed populationsshould be monitored and controlled while infestationsare small.

Appropriate crop sequences should be used to give arange of weed control options.

Cultivation methodsWeeds can be cultivated in the furrows. Shallowinter-row cultivation is possible between the widelyspaced rows of summer crops.

HerbicidesIn direct drilled and double cropped situations,herbicides are an essential tool in controlling weedinfestations on raised beds. In-crop herbicides tocontrol weeds are necessary, as is the use ofpre-emergent knockdown herbicides.

The use of soil residual herbicides needs to berecorded so that plant-back periods are observed.Some herbicides may restrict the range of crops thatcan be sown for 12 months or more following theiruse (e.g. Glean® or trifluralin).

Further information on plant-back recommendationsis available in the NSW Agriculture publications Weedcontrol in winter crops and Weed control in summer crops.

Figure 4. The effect of stubble managementtreatments on the yields of crops in an irrigateddouble cropping trial at Leeton Field Station

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CROP ROTATIONSA healthy crop rotation is a sequence of crops thatallows the grower to maintain control of themanagement options available for efficient cropproduction through the following aspects:

Weed control. The three main considerations inchemical weed control are to:

• maintain the range of effective herbicides that arecurrently available, by minimising the risk ofherbicide resistance developing in weed populations

• minimise the potential for chemical pollution due toexcessive use of herbicides

• reduce waste due to the poor use of herbicides.

Alternating between cereal and broadleaf types ofcrops allows more effective post-emergence weedcontrol. Alternating between chemical groups,integration with preemergent herbicides and strategiccultivation can help to avoid or delay development ofweed resistance.

Nutritional benefits. Legume crops or pasturesmay build up residual nitrogen in the soil that willreduce the nitrogen fertiliser requirements for the nextphase of the crop sequence.

Disease control. Growing crops with differentdisease susceptibilities reduces the build-up of diseaselevels. Table indicates those plant diseases that affectparticular crops. Recommendations on host-freeperiods (crop and/or weed) to reduce the incidence ofplant disease may be obtained from Agfacts onspecific crops. Good crop husbandry and rotationpractices are necessary for disease control, especiallywhen double cropping (using short rotations).

The raised bed system is ideally suited to a flexible,alternating crop sequence. Raised beds can be used inseveral cropping sequences—either for a single annualcrop each year or in a double cropped situation, or in acombination of the two. Double cropping is asatisfactory cropping option; however, it can delaysowing from the optimum dates, particularly for thesummer crop phase. Attention needs to be focussedon the appropriate crop type and cultivar to be sownat any particular time, and on weed and diseaseproblems. A wide choice and selection of crops andpasture can be grown successfully on such a system.

The choice of crop or pasture depends on thepaddock history; markets; disease, weed and insectburdens; and future rotation requirements for thepaddock. If the optimum dates are used for sowing,

the harvest dates can be predicted. With adequatewater, machinery and labour available, the mostprofitable of the available crops can be slotted intotime frames over a given period, weather permitting.

Raised beds allow growers to successfully grow cropsin sequence, if the crop rotation principles previouslyoutlined are observed.

EQUIPMENT REQUIREMENTSWith the raised bed farming system, the tractor andheavy machinery requirements are reduced comparedto conventional farming practices. Once the initialdevelopment stage of levelling and hilling up has beenundertaken, reduced soil compaction, improved soilstructure and better furrow trafficability decrease thedraft requirement of tillage implements by up to 60%.As a result, tillage operations can be undertaken withsmaller and narrower wheeled row crop tractors (range50–150 kW), which fit the 1.5–2.0 m bedconfiguration. This can reduce the capitalrequirements for farm machinery and the variablecosts of tractor use.

Hilling up (listing up)Hills or beds are hilled up from the flat using toolbarmounted listers or shovels at appropriate spacings. Seethe section in this Agfact on construction of beds.

PlantingConventional combines can be adapted to the raisedbeds. Combines wide enough to straddle three bedsare usually selected. The normal undercarriage can beused to sow small-seeded crops at row spacings of15 cm. Those boots sowing to the furrows can beexcluded or seed can be allowed to fall into the furrow.When sowing soybeans and other crops, the combineundercarriage can be modified to allow the sowingtines to be altered to the desired row spacing.

Sowing equipment needs to handle as much trash aspossible and be able to sow all kinds of seed sizes andrates. Individual sowing tines or discs with floatingdepth control, such as a parallelogram, are ideal tohandle uneven bed heights. The ability to sow intomoisture, with press wheels, is ideal but not essential.

Specialised summer crop planters are required forcrops such as maize or sunflowers where the spacingbetween plants within rows is important.

FertilisingMost growers use ‘fertiliser rigs’ to band nitrogen andphosphorus fertiliser. Fertiliser rigs consist of fertiliserboxes mounted on toolbars with delivery tubes to discopeners or narrow shanks. Metering devices vary in

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their degree of complexity; some are ground driven,others are driven from the tractor.

Deep application of anhydrous ammonia gas requiresspecialised equipment and high powered tractors.

Inter-row cultivationInter-row cultivation is carried out using a toolbar onwhich a range of implements can be attachedincluding knives, discs, tines or shovels. Frequently thetool bars are set up with the implements mounted intandem, with sweeps at the rear to clean the furrow.

Furrow cleaningFurrow cleaning can be successfully undertaken usingAlabama sweeps or furrow spinners. Frequently,knives are used to loosen soil at the bed edge andfurrow base before furrow cleaning.

Bed maintenanceSignificant work is needed only when beds aredamaged during wet harvests. Deeper tines or discsare needed to disrupt the compaction zones andreshape and/or re-form the beds. Where damage iscaused by header wheels during a wet harvest, raisedbeds can be repaired by using minimal strategic tillagewith tined implements.

Techniques, for example middle busting (atappropriate soil moisture contents), are becomingavailable to repair beds damaged by compactionwithout knocking them down. Where beds are middlebusted, a toolbar-mounted shank with a pyramidalfoot is used down the centre of the bed. Subsequentcultivation with rolling cultivators or power harrowsmay be necessary.

Stubble managementA stubble mulcher and/or slasher is also helpful toassist in burning or incorporating stubble.

Pesticide applicationInsecticides and fungicides. Insecticides andfungicides are usually applied aerially. The use of bandbooms is also an option. It reduces costs by reducingthe amount of pesticide used, and can significantlyreduce pesticide drift.

Herbicides. Herbicide application is normally madewith a boom spray and a range of machinery used forincorporation. On raised beds, incorporation can beachieved effectively by several implements includingpower harrows, rotary hoes, tines or rolling cultivatorsand prickle chain harrows.

If band spraying is required, the boom spray is usuallymounted on a toolbar on which spray shields may alsobe fitted.

HarvestingConventional harvesting equipment is used. Whereverpossible, the header wheels should travel in thefurrows, to reduce soil compaction.

ACKNOWLEDGMENTSThe data in Table 1 was provided by Mr AndrewWatson, Plant Pathologist (Vegetables), NationalVegetable Industry Centre. Comments on the draftmanuscript by Mr David McKenzie and Mr GeoffMcLeod were also appreciated.

FURTHER INFORMATIONFurther information is available from NSWAgriculture’s web site www.agric.nsw.gov.au

Power harrows can be used to renovate raised beds.

DISCLAIMERThe information contained in this publication is based onknowledge and understanding at the time of review (June2003.) However, because of advances in knowledge, users arereminded of the need to ensure that information upon whichthey rely is up to date and to check currency of theinformation with the appropriate officer of New SouthWales Department of Agriculture or the user’s independentadviser.

Artwork by John Hoye and E. RobertsPhotographs by staff of NSW AgricultureProduced by staff of NSW Agriculture, Orange January, 1998

Shielded sprayers can be used for spraying furrowsor between plant rows on raised beds.

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