Skeleton weed (Chondrilla juncea) in the Victorian Mallee. 2. Effect of legumes on soil fertility, subsequent wheat crop and weed population

Abstract

Following two to three years of competition between lucerne, annual medics, or field peas with skeleton weed at six sites in the Mallee, Victoria, a wheat crop was grown on fallow at each site between 1966 and 1968 to determine the effect on the weed populations and to measure the relative ability of the legumes to improve the nitrogen content of the soil. Skeleton weed populations declined throughout both the fallow and cropping periods on all treatments, and the possible mechanisms involved are discussed. All legumes increased the nitrogen status of the soil at the different sites, which led to higher wheat yield and grain protein content. There was limited response to applied nitrogen fertilizer, except on the volunteer pasture treatments. Lucerne and the annual medics were similar in their effects on soil nitrogen. However, moisture conservation during the fallow period was more effective following lucerne in some years, owing to the lower skeleton weed populations, and resulted in much higher grain yields in the drought year of 1967.