Some factors affecting grass-clover relationships.

Abstract

A study has been made on the Southern Tableland of New South Wales of factors influencing grass-clover balance in a pasture of two annuals, Wimmera ryegrass and subterranean clover. It was found that the decrease in the proportion of the grass commonly experienced under farm conditions was not due to increasing soil compaction or to scarcity of grass seedlings. It was due almost wholly to imperfect nutrition involving both nitrogen and phosphorus. Greatest yields of dry matter, nitrogen, and phosphorus were given by grass-dominant pastures rather than by clover-dominant pastures. A factor of which the field significance has not been appreciated is the competitive ability of clover for soil nitrogen. Results showed that under appropriate conditions grass development may be considerably reduced by competition for nitrogen by the associated clover. It is suggested that the faculty of legumes to use combined nitrogen has been contributed to the soil by prior legume growth offers the basic reason for the advantages to be derived from ley farming. Periodic cropping of pasture land reduces soil nitrogen to a level a t which the legumes again make an effective contribution of nitrogen by fixation of increased quantities from the atmosphere.