Ground Cover Supplement : GC Supplement - Managing Subsoils 2004
MANAGING SUBSOILS 8 By DAVID HALL and JEREMY LEMONOver the past 15 years, there has been a shift from grazing to grain production on the south coast sandplain of Western Australia, particularly in areas which receive rainfall of less than 600 millimetres a year. The sandplain, which covers 1.6 million hectares, incorporating the area from Albany to Condingup (more than 500 kilometres) and extending inland from the coast about 60km, was traditionally an area where grazing enterprises predominated. Initial yields in the mid-1990s clearly showed that in the absence of waterlogging and non-wetting, crop yields on sandplain soils were among the highest in the nation. Commercial canola yields of 3.5 tonnes per hectare and experimental barley yields greater than 7t/ha have been produced on south coast sandplain soils. However, farmers believe their yields have not been sustained despite technological advances. Graingrowers along the south coast believe the limitations to crop production are soil-based and are related to the three key aspects of soil fertility -- physical, chemical and biological. There is little current information to identify the relative importance of these factors or their interactions. Through the subsoil constraints initiative the GRDC, in partnership with the Department of Agriculture WA, CSIRO and the WA State Chemistry Centre, is investigating key soil management issues. The principal issue of concern is that technology aimed at improving soil conditions has not always resulted in yield improvements. For instance, claying, which reduces non-wetting in sands, has in some instances resulted in yield declines. While there is some evidence to suggest that the yield declines are associated with compaction (Figures 1 and 2) resulting from claying operations, there is further evidence to suggest that other soil factors (hardsetting, crusting, nutrient deficiency, EC (salinity), pH, boron toxicity), poor clay incorporation and inadequate nutrition may be responsible. Many growers have also observed that the root systems of crops grown on sandplain soils are often highly dimorphic -- prolific roots within the organically stained portions of the A horizon, but sparse elsewhere in the soil profile. This also applies to perennial pastures and trees. Taprooted crops (for example, canola) often develop fibrous root systems with primary roots failing to extend beyond the organically stained layers. The root systems may reflect the nutritional status of the soils, but the symptoms may also be attributed to mechanical compaction, toxicities or pathogens. The extent to which these unusual root systems affect crop production is unknown. The interactions between crop production, soil biology, organic matter and crop nutrition are poorly understood. Within most sandplain paddocks there is considerable variability in crop growth. Areas with diverging yields can be identified by remote sensing, yield maps and grower observations over time (Figure 3). Sites have been selected for detailed investigations within this SIP08 project from Condingup to Wellstead. Within each site several points with differing crop growth -- on what appear to be identical soils -- will be analysed in detail. At each point physical, chemical, and biological properties of soil (plant growth and nutrient status, root growth, soil organic fractions, plant pathogens) will be analysed and compared in detail. The information from the survey will be compared between the sites and related to specific limits from the literature. Crop yields will be compared with predicted/potential yields for each site using the APSIM (Agricultural Production Systems sIMulator) and PyCal (Potential Yield Calculator) crop growth and production models. Further to the survey information, key soil parameters will be investigated as a part of this project. These include aluminium toxicity and declining soil pH, optimum claying rates and management, and studying root morphology and soil biology. The project aims to: n develop relationships between aluminium and soil pH for sandplain soils of the south coast. Soil samples ranging in pH from 3 to 5 have been collected for this component of the project. This research will enable farmers to determine at what point along the pH continuum lime should be applied in order to optimise profitability and production; n define optimum claying management for ameliorating non-wetting. Laboratory and field experiments will be used to investigate optimal levels of clay addition and incorporation to non-wetting soils. Properties of clays and their effects on water entry, hardsetting, crusting, compaction and crop nutrition will be investigated. Where claying has been unsuccessful, clay types, application rates, the extent of mixing of the clay into the topsoil and the water distribution in the soil profile will be characterised. Sites where claying has been unsuccessful will be studied in detail with the intent of preventing future application problems; and n root morphology will be measured at sites used in benchmarking. Specific experiments will be established to identify treatments to rectify yield and root growth limitations in sandplain subsoils. Treatments are likely to include rotations with perennial species, mechanical decompaction (ie deep ripping) and deep nutrient/lime placement. Tramline farming will be an essential component of retaining the benefits of ripping. The south coast of WA has enormous potential for grain production. In recent years, 10 percent of the nation's crop has been delivered to the Esperance port zone. It is clear from sandplain farmers that improving their soil management is their next major step to improving crop yields. While specific issues are being targeted in this project, the information on soil management and the physical, chemical and biological aspects of soil fertility will provide a basis for managing sandplain soils now and into the future. GRDC RESEARCH CODE DAW 00093 For more information: David Hall, 08 9083 1111, firstname.lastname@example.org Improving yields on the sandplain Figure 1 (above): Soil strength measured in mega pascals (Cone Penetrometer) for neighbouring sites which had been clayed or left unclayed. Figure 2 (left): Carry grader used in the claying operation. Figure 3 (above): Remotely sensed image of 'greeness' from a site at Jerdacuttup WA. Sites with contrasting production levels, as indicated by differing colours, will be sampled intensively to identify how soil conditions affect crop production. Figure 4 (right): Poorly developed canola root system found on a sandplain soil. Majority of the roots are within 15cm of the surface. Soil compaction is not an obvious problem at this site.
GC Supplement - Precision Agriculture 2004
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