Studies on competition for sulfur between subterranean clover and annual ryegrass. II. Interrelation of nitrogen supply and soil temperature

Abstract

The effects of soil temperature (7, 13, 19 and 25¦C) end supplies of nitrogen and sulfur on growth and competition between subterranean clover ( Triticum subterraneum cv. Trikkala) and ryegrass (Lolium rigidum cv. Wimmera) were examined in a glasshouse experiment over a period of 62 days. Soil temperature influenced competition for sulfur in mixtures of species supplied with nitrogen fertilizer. When the sulfur supply was low, there was no competition between the species at temperatures of 7 and 13¦C. However, at 19 and 25¦C ryegrass suppressed the yield and sulfur content of subterranean clover. When sulfur was applied to the mixture, nitrogen application did not result in competition at any temperature. When nitrogen supply was low, the yield and sulfur content of ryegrass were poor compared with those of subterranean clover. However, this did not result in competition between the species at low or high levels of sulfur supply. In both species, yield and sulfur content increased, and sulfur concentration decreased with increasing soil temperature. Hence there were severe symptoms of sulfur deficiency in plants grown with added nitrogen at 19 and 25'C, and no symptoms in plants grown at lower temperatures. While both species had the same optimum temperature range for growth (between 19 and 25¦C), ryegrass grew relatively better than subterranean clover at lower temperatures.