The effect of wet season land treatment and nitrogen fertilizer on safflower, linseed, and wheat in the Ord River valley. 3. Wheat

Abstract

Gabo wheat was grown under irrigation at Kimberley Research Station in the 1964 dry season following 6 months and 18 months clean and weedy fallows. Four levels of nitrogen fertilizer, as ammonium sulphate and urea, were superimposed. After 6 months clean fallow and 6 and 18 months weedy fallows, grain and dry-matter yield responded to up to 160 lb N an acre. Grain and dry-matter yield after 6 months clean fallow were greater than those after weedy fallows at the same nitrogen fertilizer level. After 18 months clean fallow no significant responses to nitrogen fertilizer were obtained. Mitscherlich curves were fitted to the total dry-matter and grain yield responses to nitrogen fertilizer after the four fallowing treatments. The analysis indicated that 1 part of nitrogen as ammonium sulphate was equivalent to 1.61 (dry matter) or 1.72 (grain) parts of nitrogen as urea. There were strong correlations (r = 0.956 for dry matter; r = 0.917 for grain) between the Mitscherlich constants for individual replicates of the fallow treatments and soil nitrate-nitrogen measured in the 0-3 foot profile before sowing. Soil nitrate-nitrogen, mineralized and accumulated during a summer clean fallow, appears to be almost three times as effective in producing a grain yield response as nitrogen applied as ammonium sulphate at sowing, and almost five times as effective as urea nitrogen at sowing.