Grains Research and Development

Introduction

Problems in cropping systems

In the rain-fed cropping systems of southern Australia crops are sown either into dry topsoil (dry sowing) shortly before the opening seasonal rains, or into moist topsoil following the opening rains.

Water repellent soils wet-up unevenly via preferred pathways thereby inducing patches of dry topsoil. It can take considerable time and multiple rainfall events before the appearance of uniform wetting in the topsoil. Seeds sown into non-wetting soils germinate at different rates and emergence is often patchy and delayed. In the case of severe water repellence parts of the soil may never wet-up over the growing season and in these ‘dry patch’ areas the crop fails to emerge.

Alternatively, in cases of severe repellence establishment might be poor over the majority of the soil with good patches where the water has infiltrated better. Corresponding delays of emergence of weeds also occur possibly complicating the timing and efficacy of herbicides.

Patchy and delayed crop emergence often results in poor soil cover, increased erosion risk, poor competition with weeds, low yield potential and inefficient use of fertilisers and pesticides. Timing of herbicide and fertiliser operations is often compromised as the crop developmental stage varies widely depending on the uniformity of crop emergence.  

Despite water repellence being typically a feature of soils with a sandy surface, even before they were cleared for agriculture, there is a perception that the severity of water repellence is increasing in some cropping systems in southern Australia. The following factors are likely to contribute to more severe symptoms of soil water repellence:

  1. Minimum tillage

    The practice of minimum tillage and stubble retention is well established in many cropping systems and has numerous benefits. Minimal soil mixing in minimum tillage systems results in a soil profile which is highly stratified, with a high concentration of residues and organic matter in the soil surface. The increased concentration of organic matter, including the waxes that cause repellence can increase the severity of repellence in sandy-textured soils.

  2. Furrow sowing

    Furrow sowing with narrow knife points and press wheels is one of the most common seeding systems for broadacre cropping in southern Australia. It is efficient, simple, relatively cheap and very effective on many soil types. Furrow sowing originally using winged points or sweep points was introduced to water repellent sands to improve crop establishment by moving repellent sand to the ridges, which could then harvest water into the furrow where the seed was sown. This harvesting of water improves the wetting-up of the sown seedbed.

    However, with some knife points and press wheel systems in water repellent sand it has been noted by growers and researchers that sometimes the furrow remains dry while the ridges are wet. It appears that the dry repellent sandy topsoil falls into the slot opened behind the knife point and is being concentrated around the seed and the fertiliser. The impact of water repellence is therefore exacerbated and crop emergence is poor.

    This may be even more pronounced with dry sowing, which has been increasingly adopted as grain growers attempt to get the benefits of early crop establishment and efficiency of the seeding operation.

  3. Climate

    A drying climate and climate variability can also exacerbate the problem of water repellence. Smaller and less frequent rainfall events at the start of the season lowers the probability of the seedbed wetting-up evenly over time and exacerbates the expression of water repellence, especially later in the season as the soil cools and repellence is increased at lower temperatures.

    In repellent sands the crop often undergoes several germinations at different times coinciding with each seasonal rainfall event. If the rainfall events become less frequent then so do the opportunities for germination.

    A map of southern Western Australian wheatbelt demonstrating rainfall trends from 1976 to 2008. 

    Western Australian wheatbelt - rainfall trend since 1976

  4. Biomass production 

    Increased biomass production with better agronomy can increase the wax inputs returning to the soil in residues.

Research

Research to improve productivity and profitability from non-wetting soils is underway with the Grains Research and Development Corporation funding two key projects in Western Australia.

The research projects Novel solutions for managing non-wetting soils and Delivering agronomic strategies for water repellent soils aim to increase knowledge about soil amelioration techniques and explore management techniques promoting better strategies for water repellent soils.

Management options which increase water infiltration uniformity and reduce erosion will protect surface soils and retain soil carbon, while increasing grain production and profitability from improved soil water infiltration will be to the benefit of the grower, the environment and the industry as a whole.

A yield increase of 10 per cent across two million hectares in southern Australian could result in an extra four million tonnes of grain production worth approximately $800 million per year.

  1. Novel solutions for managing non-wetting soils

    Novel solutions for managing non-wetting soils builds on previous research which found water repellence in acid sandy soils in southern cropping areas of WA disappeared under zero-till and stubble retention systems. The research is carried out as part of the CSIRO Sustainable Agriculture Flagship portfolio.

    The main focus of this project is to explore management techniques that promote water infiltration into non-wetting soils.

    The aim is to:

    1. Review existing knowledge of management systems and identify gaps in that knowledge.
    2. Explore management practices that increase water infiltration and identify mechanisms and strategies that can be applid to non-wetting soils elsewhere in WA and South Austral
    3. Evaluate repellency at the plant scale, identify causes and test remedial strategies.

    The project, led by Margaret Roper (CSIRO), will continue carrying out trials in acid sandy soils in the southern cropping region of WA. Management mechanisms and strategies that are found can then be applied to non-wetting soils elsewhere in WA and also on alkaline soil trials in South Australia.

    Preliminary studies have shown that severity of water repellence as measured in the laboratory increases under zero-till and stubble retention and this increase is closely linked with soil organic carbon content. However, field measurements of soil water content indicate consistently higher soil moisture throughout the year under zero-till and stubble retention, despite the more severe soil water repellency. This project will investigate this unexpected finding in trials on the south coast to determine how it can be used in other farming systems.

  2. Delivering agronomic strategies for water repellent soils

    Existing agronomic options are available to manage water repellent soils, including furrow sowing, spreading and incorporating clay-rich subsoil, use of soil wetting agents and alternative land use options. In addition, emerging agronomic options such as the use of deep cultivation or soil inversion are being investigated by researchers and growers.

    Delivering agronomic strategies for water repellents soils, led by Stephen Davies at the Department of Agriculture and Food WA, is investigating each of the management practices and their impacts on soil water repellence and crop productivity as well as the drivers and barriers to grower adoption.

    Improving grower understanding of which management practice is most suited to their circumstance and giving them confidence about how to implement the practice to maximise success is a key objective.

    In collaboration with a number of WA grower groups, research into each of the agronomic strategies will continue over a number of crops and seasons to provide an opportunity to conduct an economic analysis, including rotational gross margin analysis. New research will also be established to address barriers to adoption of potential management practices and will define factors that determine the efficacy of each management strategy.

    The results of this research will be extended to grower groups through a series of interactive workshops over the life of the project, which will include review and evaluation components. In addition, the project will support on-farm demonstrations and deliver grower case studies, in-field workshops, field walks, presentations and publications to further extend the management information.

Grower Group participation 

Water repellent management types

Tools for managing non-wetting soils range from short to long-term mitigation, medium and long-term amelioration and alternative land use. Decision making will be influenced by factors such as soil type, cost, timing and longevity of benefits. The following tables give an overview of each management tool and their cost benefit analysis.

A number of the mitigation tools such as improved furrow sowing and banded surfactants can be used cheaply across a wide range of soil types and landscapes. Amelioration options such as clay spreading or one-off soil renovation with soil inversion or rotary spading are more costly and complex, but are longer lasting. The best approach may be for growers to utilise mitigation tools over their entire seeding program and where strong water repellence occurs, or where there is the potential for the biggest productivity gains, implement the longer lasting amelioration techniques.          

Information about the processes and techniques which aim to raise the clay content of sands should be read in conjunction with the resource Spread, delve, spade, invert — a best practice guide to the addition of clay to sandy soils. The 52-page publication draws on 30 years of research and features eight case studies on the experiences of growers who have used clay to improve their soils and productivity. The resource is available from Ground Cover Direct http://www.grdc.com.au/Resources/Bookshop 

Table 1: Short-term mitigation tools

Management tool Water repellent management type Soil type Operating cost (excluding capital) Timing Longevity of benefits Problems/issues with the management tool Other major benefits
Improved furrow sowing MitigationA All repellent soils Cost of winged points or boots versus standard knife points Sowing 1-5 months1
  • furrow infill
  • repellent soil around seed
  • herbicide damage
  • variable efficacy
  • water harvesting maximises capture and use by crops of small rainfall events
  • repellent soil in inter-row may act as a mulch reducing evaporation
Furrow sowing with banded-applied wetting agents MitigationA All repellent soils $10-12/ha/year Sowing 2-3 months
  • cost (ongoing)
  • lack of industry expertise
  • incompatible machinery
  • unstable furrows
  • variable efficacy
  • wetting agent could be used as a carrier for cheap and efficient delivery of other beneficial inputs such as micro-nutrients or fungicides
Blanket-applied wetting agents MitigationA Loamy gravels & Loamy sands $25-50/ha/year depending on rate required Pre-sowing 2 years
  • cost (ongoing)
  • lack of industry expertise
  • efficacy soil type specific
  • some weed control benefits if blanket wetting agent improves synchronous germination of weeds

A Mitigation – minimisation of the effects of water repellence but repellence remains

1 Longevity of furrow benefits for harvesting water will depend on furrow stability which will depend on soil type and cover etc.

 

Table 2: Long-term mitigation tools

Management tool Water repellent management type Soil type Operating cost (excluding capital) Timing Longevity of benefits Problems/issues with the management tool Other major benefits
Zero till and full stubble retention MitigationA All — except rocky and stony soils Predominantly capital cost Sowing Ongoing
  • suitability for a wide range of soil types and landscapes
  • root disease
  • poor herbicide incorporation
  • residue management
  • concentration of nutrients at surface
  • ‘thatching’ effect reduces soil water from low rainfall events
  • reduced risk of wind erosion
  • increased microbial activity
  • water retention via mulching
Liming MitigationA All acidic and repellent sandy soils ~$75/ha for 2t/ha, but varies depending on transport distance Usually pre-sowing Ongoing — provided optimum pH is maintained
  • may require high lime rates
  • severity of soil repellence reduced but not eliminated
  • some nutrients become less available
  • improved availability of some nutrients
  • prevention and/or amelioration of aluminium toxicity
  • improved weed control
On-row vs inter-row sowing MitigationA All repellent soils Predominantly capital cost Sowing 1-2 months
  • stubble handling
  • increased risk of stubble and root borne pests and disease associated with previous crop row
  • lack of 2cm accuracy with autosteer
  • zones of enhanced fertility created as nutrients and organic matter and associated biology concentrated in same row each year

A Mitigation – minimisation of the effects of water repellence but repellence remains

 

Table 3: Medium and long-term amelioration tools

Management tool Water repellent management type Soil type Operating cost (excluding capital) Timing Longevity of benefits Problems/issues with the management tool Other major benefits
Soil inversion (mouldboard ploughing) AmeliorationB
  • deep sands
  • loamy sands
  • loose gravels
  • deep sand over gravel/clay
$100-120/haD
  • One-off inversion
  • Pre-sowing
  • end of seeding
  • late-winter early spring
5-10+ years
  • wind erosion risk on sands until cover crop is established
  • seeding depth difficult to control in loosened soil
  • loss of soil moisture during cultivation
  • poor inversion can reduce efficacy
  • unknown impact of buried water repellent layer on soil water
  • weed control
  • reduced subsoil compaction
  • reduced stubble borne disease
  • enhanced water and possibly nutrient holding in the subsurface soil in the root zone (particularly in pale sands)
  • nutrient, lime and organic matter incorporation into the profile
Rotary spading Partial ameliorationC
  • deep sands
  • loamy sands
  • deep sand over gravel/clay
$150/haD Pre or end of sowing Unknown but likely to be 3-7 years
  • high cost
  • wind erosion risk on sands until cover crop is established
  • seeding depth control in loosened soil
  • loss of soil moisture during cultivation
  • some control of certain weeds
  • reduced subsoil compaction
  • nutrient, lime and organic matter incorporation into the profile
Clay delving AmeliorationB Shallow duplex (suitable clay within delving depth) ~$300-600/haD Pre-sowing 15 years or more
  • high cost
  • soil type suitability
  • subsoil incorporation
  • higher biomass can enhance haying-off risk
  • lack of industry providers
  • clay-rich subsoil may contain toxic levels of salt or boron or extreme pH
  • difficult to control rate of clay at the surface
  • moderate (indirect) benefit in controlling weeds
  • increased soil pHif alkaline subsoil is applied
  • reduced subsoil compaction
  • nutrient addition — often K, S and B from some clay-rich subsoil
  • increase in nutrient and water holding capacity of the topsoil
Clay spreading AmeliorationB
  • sands
  • deep sandy duplex (suitable clay source in paddock)
$500-900/haD Pre-sowing 15 years or more
  • high cost
  • subsoil incorporation
  • higher biomass can enhance haying-off risk
  • clay availability
  • soil compaction
  • clay-rich subsoil may contain toxic levels of salt or boron
  • difficult to control rate of clay at the surface
  • moderate (indirect) benefit in controlling weeds
  • increased soil pHif alkaline subsoil is applied
  • nutrient addition - often K, S and B from some clay-rich subsoil
  • increase in nutrient and water holding capacity

B Amelioration – correction or removal of topsoil water repellence for three or more years  

C Partial amelioration – some pockets of repellent soil may be left near the surface

D Estimated cost based on contractor rates

 

Table 4: Adaptation and alternative land use

Management tool Water repellent management type Soil type Operating cost (excluding capital) Timing Longevity of benefits Problems/issues with the management tool Other major benefits
Trees tagasaste, permanent pasture Adaptation

Deep sands (inherently poor crop productivity)

N/A System change Ongoing
  • system change
  • high cost
  • profitability
  • mitigated subsoil compaction
  • increased water and nutrient use efficiency on high leaching soils

Acknowledgement:

Kondinin Group would like to thank Stephen Davies (DAFWA) and Margaret Roper (CSIRO) for their contribution in developing content for this website.