The effect of cropping after medic and non-medic pastures on total soil nitrogen, and on the grain yield and nitrogen content of wheat

Abstract

The effect of medic and non-medic pastures on grain yield and nitrogen content of wheat was studied over 15 seasons on a friable grey clay in the Wimmera. The effects of length and type of pasture ley on grain yield and nitrogen content were closely related to the effects of these treatments on total soil nitrogen. Grain yield was not increased in any season by increasing total soil nitrogen beyond 0.1 10%. The grain yield response to increased total soil nitrogen varied markedly with seasons and most of the variation could be accounted for by variation in November rainfall; grain yield response was greater in years of higher November rainfall. Grain nitrogen content increased with increasing total soil nitrogen over the range studied (0.078% to 0.1 28%). Seasonal variation in grain nitrogen response to total soil nitrogen was mainly associated with variation in September and November rainfall. Higher September rainfall increased the response and higher November rainfall decreased it. The decline in total soil nitrogen that occurred with cropping was strongly correlated with the level of total soil nitrogen before cropping.