Chondrilla juncea in Australia. 2. Preplanting weed control and wheat production

Abstract

The response of wheat to nitrogen fertilization and to the time and mode of skeleton weed control was determined at three locations in southern New South Wales. Nitrogen fertilization was found to increase grain yield significantly in most situations. But nitrogen reduced total grain yield where adverse seasonal conditions caused severe water stress after flowering. Added nitrogen exaggerated the water stress and reduced grain weight. Temporary removal of skeleton weed, obtained by spraying the fallow with 2,4-D four to six weeks before seeding, increased grain yield by an average of nearly 5 bushels an acre. The magnitude of the response was modified by rainfall incidence, weed cover, and time of spray application relative to seeding. The effects of chemical weed control, followed by crop competition, were apparent in stubble sown crops 12 to 18 months later in the form of reduced weed populations and increased grain yield. Preplanting sprays reduced the response to nitrogen fertilizer but the interaction, generally, was not significant. Spraying the fallow with a contact herbicide, or substituting an additional cultivation for the 2,4-D fallow spray, also increased grain yield. These results emphasize the importance of suppressing skeleton weed, by the most appropriate means available, in the period before sowing.