Albert Rovira*, Gupta, V.V.S.R.** and David Roget***
*Formerly CSIRO and CRC for Soil & Land Management
**CSIRO Division of Entomology, Glen Osmond, SA
***Honorary Research Fellow, CSIRO Division of Entomology; Formerly CSIRO Sustainable Ecosystems, Glen Osmond, SA
Fourteen soil fumigation field trials conducted in Victoria and South Australia between 1971 and 1976 demonstrated that one of the major constraints to production by cereals was root disease (Rovira, 1988). Soil fumigation gave yield increases ranging from 0.3 to 2.65 tonnes per hectare – the highest responses were obtained in calcareous sandy soils of the Mallee in Victoria and Streaky Bay in South Australia. Control of soil borne root diseases such as Take-all (Gaeumannomyces graminis var.tritici), cereal cyst nematode (Heterodera avenae) and rhizoctonia root rot ( Rhizoctonia solani) was mainly responsible for the yield increases but the release of mineral nitrogen from the soil biomass also contributed.
At this stage no rotation trials had been conducted in Australia to study the effects of rotation on these three diseases. In the early 1970’s a knock down herbicide, “Sprayseed” (ICI, paraquat + diquat) was being tested as a tool to enable the direct drilling of crops which offered a promising strategy to protect fragile and erosion prone soils. At this stage we decided to set up trials at Avon and Kapunda in South Australia to study the impacts of rotation and tillage on root diseases of wheat in two environments representing the major wheat growing regions of southern Australia. When these two trials were completed, another was set up at Waikerie where the rainfall and soil type is typical of the Mallee region in South Australia, Victoria and New South Wales.