Ground Cover Supplement : GC Supplement - Managing Subsoils 2004
MANAGING SUBSOILS &5 ing subsoil issues in the Mallee one, problems lie beneath the surface rmers and regional agronomists and advisers oncerning subsoil constraints; current or past practices applied to tackling ubsoil management (successes, hopes and ilures); and yield histories and rainfall for some target addocks. eview This will comprise a region-wide review of existing soil information (state government atasets and regional agronomists' experience) us a literature review of past studies on subsoil anagement. A broad overview of the distribution of major soil types across the GRDC Southern Zone will be compiled from Victorian, South Australian and NSW government sources. The cropping areas in this zone that have above-500 millimetres average annual rainfall will be the study areas for review of subsoil properties. The study will concentrate on regions that already have a high level of farmer engagement and progressive farming practices. Soil investigations Soil investigations will involve limited local, intensive surveys on selected paddocks (including any opportunity to use pre-existing paddock scale survey and yield data). Fieldwork will be carried out at a paddock scale for at least one site with each group. We will deploy farm quad-bike mounted sensors (Electromagnetic Induction, EMI and Gamma Radio Spectroscopy, GRS) to determine the variability of some soil properties. Survey and sampling will be carried out as close to harvest as possible (ripe grain and no further soil water use). Selected soil samples will be analysed using traditional laboratory testing methods and it is anticipated that all samples will be subject to mid infra-red (MIR) spectral analysis to provide surrogate estimates for a number of physical and chemical properties. Reference pits will be excavated and sampled to provide more robust soil profile data than that collected with narrow soil cores. These will also be used as a focus for farmer group engagement. Priority-setting Analysis of the issues to develop research priorities for GRDC will be based on consultation and some basic spatial and seasonal modelling. The remotely sensed data and available grower paddock records will be used together with field data to analyse the seasonal effects of weather, and compare with theoretical potential yields and estimated subsoil restrictions to crop yields. The priority constraints for further investment will be assessed on a spatial area basis, seasonal factors and potential for improved returns based on a rating of the likely effectiveness of any future management solutions generated by future research investment. The results of this analysis will be presented back through the farmer groups to review and validate priorities for submission to the GRDC. GRDC RESEARCH CODE DAV 00056 For more information: Richard MacEwan, 03 5430 4326, Richard.MacEwan@dpi.vic.gov.au rchers have found g EM38, an apparatus il salinity through induction, can help detect eas of fields. e EM38 measures the soil tivity and this is strongly l water, salt and clay y to sense water allows determine areas within subsoil constraints limit al soil compaction that with ripping, there is tical option to remove constraints. Improved hese soils will rely on location of the problem k; ariable production potential across the paddock; and n devising variable fertiliser rate strategies to match that variable production potential. EM mapping What is better than an EM map? Two EM maps! Researchers are experimenting with using two EM maps, one around sowing time and the other after harvest. Two maps allow more precise calculation of crop water-use and therefore more accurate estimates of yield potential. Figure 1 shows average soil water content from the 0.4 to 1.6m soil layer determined at sowing and harvest at the Loxton site. CSIRO's soil water-content maps are determined by on-site calibration of EM38 readings with measured soil water contents. The calibration relationship is not perfect because of the interference of salt and clay content, with a mean error of around 15 to 20mm water for a 1-metre soil profile. The research team views this error as acceptable for defining different management zones within the paddock, provided the management history is similar. Yield and gross margin maps In addition to soil EM38 mapping, yield or biomass (derived from satellite imagery) maps can also provide a measurement of paddock variability. The more consistency there is between the variability identified on an EM map and a yield map, the more confidence there is that it is subsoil issues driving yield variability. Conversely, where there is little consistency between the two maps, then other significant yield limiting factors are involved. A collection of yield or biomass maps over the years from the same paddock will reveal consistently poor areas as well as the areas that behave differently in wet and dry years. While a set of several yield or biomass maps for the paddock helps in interpreting the causes of yield variation, its management requires consideration of the economics of production. One way this can be considered is to map the gross margin. The question, however, remains -- can higher profits be achieved at such sites from, say, the reduction of inputs in the salt-affected areas or can some agronomic treatment boost profits in these areas? EM with no yield maps While a collection of yield or biomass maps provide useful information on the likely subsoil constraints where no -- or a limited collection of -- yield maps exist, two EM maps offer alternative information, particularly on the high and low water-use areas. At the Loxton field site, the water-use map was compared to the yield map (Figure 2). Subtracting the soil water content measured by EM38 at harvest from the soil water content measured at sowing, and adding seasonal rainfall, gives us a good estimate of crop water use. A strong resemblance between crop water use and yield is seen (Figure 2). Note the mid-slope areas showing high water use (dark blue) and yield (blue), conversely, the low water use and yield areas are coloured red. Therefore, management plans based on the potential water supply can be developed and tested. Basing management on water supply should be more reliable than using other single factors since water supply is the major determinant of grain yield in Australia. CSIRO is testing the value of knowing where the subsoil constraints are by developing site-specific fertiliser plans for a number of the focus paddocks in the Mallee Sustainable Farming network across the Murray Mallee. Fertiliser is one of the high-cost items for Mallee farmers and if cost savings and more efficient fertiliser use can be achieved, then some of the losses attributed to subsoil constraints may be clawed back. EM mapping offers new ways to detect the extent and severity of subsoil constraints in Mallee soils that should help develop more precise and profitable farming strategies in areas with often- unseen subsoil constraints. EM mapping should also be useful in the higher rainfall areas. GRDC RESEARCH CODE CSO 216 For more information: Garry O'Leary, 03 5091 7200, fax 03 5091 7210, firstname.lastname@example.org ater content (0.4 to 1.6 m) determined from (vertical mode) measured at sowing and n during 2003. Note the significantly drier (lighter shade). Figure 2: Water use and yield map of wheat grown at Loxton during 2003. Note that the water-use map is very different to a single water-content map (Figure 1) and the greater resemblance of the water-use map to the yield map. Deeper issue: changing land practices are overcoming the problem of waterlogging, but there are hidden problems in the subsoil.
GC Supplement - Precision Agriculture 2004
GC Supplement - Value Chain