Crop production responses to soil amelioration treatments on an infertile sand over clay in South Australia

Abstract

An important proportion of crop production in South Australia is carried out on neutral-alkaline soils comprising infertile siliceous sands overlaying sodic subsoils. Crop growth is limited by the infertile nature of the non-wetting, rapidly draining upper soil horizons and also by the lower soil horizons which are generally dense sandy clays, often sodic and with poor physical structure. A replicated experiment was established at Stansbury, SA in 2004 to compare production under best district practice management with that from several ‘once off’ soil amelioration treatments; surface applied organic matter (composted pig bedding litter), three subsoil treatments involving deep ripping to 0.4 m and addition of an ameliorant (either liquid nutrients, gypsum or organic matter as lupin grain), and a treatment that combined the surface and all the subsoil treatments together. Treatments were designed to improve soil chemical and physical properties and enhance root and crop growth. Of the treatments tested, deep ripping (0.4 m) and associated placement of nutrients in fluid form provided the most consistent crop responses, with the response being greater where the clay was closer to the surface. Some crop responses to the once off subsoil amelioration were still evident after 4 crops. Differences in crop water use (evapotranspiration) were not apparent from gravimetric measurements at sowing and harvest suggesting that other soil chemical and physical properties may be responsible for the yield responses, or there may have been undetected differences in the partitioning of water use between evaporation and transpiration within seasons. Among the crops studied, wheat was the most responsive to amelioration treatments and canola slightly less so, whereas lupin was generally unresponsive to soil amelioration strategies at this site.