Studies on competition for sulfur between subterranean clover and annual ryegrass. I. Effect of nitrogen and sulfur supply

Abstract

The effects of nitrogen and sulfur supply on growth and competition between subterranean clover (Trifolium subterraneum cv. Trikkala) and ryegrass (Lohum rigidum cv. Wimmera) were examined in a glasshouse experiment over a period of 45 days and in a field experiment over one growing season by using the de Wit model. Sulfur supply had no effect on competition between the species. Yield and sulfur content of both species in mixtures were at least equal to those in monoculture, irrespective of nitrogen and sulfur supply. In swards which were severely deficient in nitrogen, subterranean clover was more responsive to increasing sulfur supply than was ryegrass, but this did not cause interspecific competition. Under field conditions during spring, there was some indication that ryegrass was the superior competitor in sulfur-deficient swards which had received nitrogen fertilizer. Nitrogen application reduced the percentage of subterranean clover in the sward at all levels of sulfur supply, because it had a much greater effect on yield of ryegrass relative to the yield of subterranean clover. Sulfur application increased the percentage of subterranean clover in the mixed swards at each level of nitrogen supply.