Ground Cover Supplement : GC Supplement - Water use efficiency
GROUND COVER WATER USE EFFICIENCY 16 STORE MORE Moisture probe Soil moisture probes are providing practical information for management and marketing decisions By Greg Butler HOW MUCH WATER is available for crop growth is pivotal to yield, but few growers can do more than know whether their soil is wet or dry. While soil characterisation provides information on the water-holding capacity, soil probes can provide details of how stored water is changing over time. For the past two years. the South Australian No-Till Farmers Association (SANTFA) has been trialling electronic soil moisture probes. Located in key soil types in commercial paddocks, the probes gather soil moisture data at 10, 20, 30, 50, 70 and 100-centimetre intervals every 15 minutes. Using solar power and telemetry, the data is automatically transferred to an internet server via the mobile phone network. The probes effectively track wetting fronts as they move down the profile and crop water use at various rooting depths. The objective of measuring soil moisture down the soil profile was to provide growers with better information on availability of soil moisture when making decisions about in-crop nitrogen and grain marketing in relation to potential yield, protein and screenings. Growers involved in the trials report having successfully used the data for both of these management decisions. Deep water might not be reached if root growth is slow or there is a physical or chemical barrier between the surface and subsoil. Conversely, if deep water is reached later in the growing season it can help sustain grain fill, even if there is little rainfall. Changes in levels throughout the shape of the graph (Figure 1) indicate which profile is full, filling or being drawn down by the crop roots. While each trace is on a separate scale, it is the degree of change in the trace that is of interest. The chart is from a dry year and the small rainfall events are not reaching the subsoil. Lack of change in the 20 and 30cm traces suggests the soil is dry and moisture is not being removed or added. Fortunately, the profile contained deep stored moisture and this is being extracted in spring. Small steps in the line show the diurnal pattern of water removal during the day but not during the night. By tracking moisture throughout the year, the impact of stubble cover and summer weeds on water holding can also be monitored. In a new project being led by CSIRO's Dr Phil Ward, moisture probes will be used to evaluate the role of stubble cover on infiltration and soil water-holding capacity. In these trials subsurface probes will be used that are completely buried, so the surface area directly above the probe will be representative of the treatment area. These subsurface probes can be sown and harvested over. Probes are located at a low-rainfall site on Eyre Peninsula, a medium-rainfall site on central Yorke Peninsula and a high-rainfall site in the Mid North of SA. Four probes have been placed at each site and stubble will be removed from two plots. At each site there is an automated rain gauge, so rain events can be matched to trends in soil moisture. The subsurface probes will also record soil temperature. Data will be gathered for at least the next three years. □ GRDC Research Code CSP00110 More information: Greg Butler, research and development manager, SANTFA, 08 8842 4278, firstname.lastname@example.org SUBSURFACE PROBES CAN BE SOWN AND HARVESTED OVER. FIGURE 1 A stacked graph of soil water status by depth Soil water content 30 Jul 6 Aug 13 Aug 20 Aug 27 Aug 3 Sep 10 Sep 17 Sep 24 Sep 1 Oct 8 Oct 15 Oct 2007 Each trace is on an independent scale but the change in the shape of the trace indicates if water is being used (descending) or added (ascending) to the profile, and how fast this is occurring. 10cm 20cm 30cm 50cm 70cm 100cm Diffuse rainfall Deep root activity. Hold off on nitrogen input. Root activity retracting to 100cm South Australian grower Kym I'Anson has been using soil moisture probes to assist with in-crop nutrient decisions for the past two years and has been pleased with the results.
GC Supplement - Wheat breeding
GC Supplement - Agronomy