Crop and pasture rotations at Coonalpyn, South Australia: effects on soil-borne diseases, soil nitrogen and cereal production

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Abstract
A crop rotation experiment was conducted at Coonalpyn, South Australia from 1976 to 1979 on a deep, red duplex soil. The experiment compared the productivity of grain legumes and of volunteer and sown annual pastures, and assessed their effects on the mineral nitrogen supply for subsequent wheat and barley crops, and their capabilities for preventing the root diseases of wheat cereal cyst nematode (Heterodera avenae), bare patch (Rhizoctonia solani) and Haydie (Gaeumannomyces graminis). Satisfactory legume dominance of the annual pastures was achieved only in 1979, while the grain legumes grew well and produced more dry matter than the pastures in each season. Wheat and barley yields averaged (1977- 1979) 2.0 t/ha after volunteer and sown pastures, and 2.8 t/ha after grain legumes, with the greatest response in 1979. In that year, wheat produced 11 kg grain/mm of growing season rainfall after grain legumes, but only 6 kg after pastures. The numbers of lesions on the nodal roots caused by R. solani and on the seminal roots by G. graminis varied with the season but both were less after grain legumes than after pasture. Gaeumannomyces graminis had the greatest effect on grain yield and, with soil nitrate at seeding, explained up to 68% of the variation in yield in 1979.