Ground Cover Supplement : GC Supplement - Subsoil constraints
GROUND COVER SUBSOIL CONSTRAINTS 13 PROJECT UPDATES Identifying constraints on the south coast sandplain of WA PROJECT: IDENTIFYING SOIL CONSTRAINTS TO CROP PRODUCTION ON THE SOUTH COAST SANDPLAIN. DAVID HALL, JEREMY LEMON, BRENDAN NICHOLAS, TANIA BUTLER, NICK MIDDLETON AND YVETTE OLIVER THE WESTERN AUSTRALIAN south coast sandplain covers just over 1.5 million hectares. Reliable rainfall (420 to more than 600 millimetres) and innovative farming practices have seen a shift in production from predominantly grazing to mixed-farming enterprises. This shift has seen the sandplain develop into a diversi- fied cropping region that has become a major producer of canola, lupin and barley. However, farmers are concerned that the physi- cal, chemical and biological fertility of soils may not be improving at the rate required to be sustainable. Consequently, a project initiated by farmers was funded to investigate what soil factors limit crop production and how they can be remedied. The approach taken in this project has been to identify whether farmers are achieving their rainfall-limited potential yields, what soil factors are enhancing or limiting crop yields and investigating specific issues including non-wetting, compaction and subsoil acidity. ARE FARMERS ACHIEVING THEIR RAINFALL-LIMITED POTENTIAL YIELDS? Crop and soil measurements were collected during the 2004 and 2005 growing seasons in poorly perform- ing paddocks. The measurements were used to predict potential yields and compared with actual growth rates and grain yields. An example is given in Figure 1 (next page). The analysis shows that the gap between farmer canola yields and potential yields ranged from 0.2 to 1.4 tonnes per hectare in 2004. In addition, removing nitrogen stress during the growing season would have resulted in a further 0.1 to 0.8t/ha. It is clear that soil and nutrient limitations are key constraints to crop production on sandplain soils. WHAT SOIL PROPERTIES ARE LIMITING CROP PRODUCTION? Detailed surveys of paddocks that farmers believe have underperformed in the past have shown that there are several key soil constraints to crop production. These include: 1. Non-wetting. The organically stained layers of sand- plain soils (0 to 15 centimetres) are often water-resistant, depth to which crop roots can grow and the presence of barriers to root growth was vital to their understand- ing of how to manage crops and inputs accordingly. Surprisingly, many growers in the high-rainfall zone felt that their crops were lacking the ability to access all the soil moisture. By combining the knowledge gained from soil pits, the information in the soils database and our current knowledge of subsoil constraints, the research team has been able to map and determine the extent of the major subsoil constraints for WA (see Figure 2). It has been determined that about a quarter (five million hectares) of the state’s agricultural soils are highly susceptible to compaction and nearly a third (5.3 million hectares) are highly susceptible to, or currently have, subsurface acidity. The soil pit workshop interaction, with more than 300 farmers, 70 agribusiness people and other research staff, exceeded our expectations and has created demand for more information and further visits. When the soil pit information was combined with grower surveys and individual farmer interviews it became apparent that grower awareness of the subsoil and its constraints was low.More workshops are being planned for 2006 with a number of farmer groups already booked in for August. In addition, two on-farm research sites are being developed with our Grower Group Alliance partners, the Mingenew Irwin Group (MIG) and Corrigin Farm Improvement Group (CFIG). Chris Gazey is a senior research officer, Alison Slade a development officer and Dr Stephen Davies a research officer at the Department of Agriculture, Western Australia. GRDC Research Code UWA00081 More information: Chris Gazey, 08 9690 2000, firstname.lastname@example.org THE WORKSHOPS SERVED A DUAL PURPOSE: 1 Onsite identification of the constraints -- this information has been added to the WA Department of Agriculture's Soil Map Unit Database. 2 An educational experience for both farmers and project staff.
GC Supplement - Pastures
GC Supplement - Farm safety