Uptake of nitrogen by pasture legumes and associated ryegrass at three sites in Otago

Abstract

Ryegrass was sown alone and in combination with white, red, subterranean, or alsike clovers in small plots at 3 sites in Otago. At 2 sites lucerne was also sown. Plots were cut regularly over a 3-year period, and all herbage was removed. Nitrogen yields were measured in harvested herbage separated into ryegrass and sown legume components. Relative to other species, and in terms of N uptake, white clover performed well at all sites, especially at Berwick, a moist cool site; alsike clover performed well at Berwick and moderately well at Invermay (intermediate climatic conditions) and Dunback (dry mild site); red clover was poor at Berwick but good at Invermay and Dunback; and subterranean clover was very poor at Berwick and Invermay, but moderately good at Dunback. Highest N yields in clover herbage over the last 2 years were 237 and 123 kg/ha/year from white clover at Invermay and Berwick and 231 kg/ha/year from red clover at Dunback. Lucerne N uptake averaged 630 kg/ha/year over the last 2 years at Invermay. %N content of all legumes was consistently depressed by dry conditions. Subterranean clover consistently had lower %N than the other species. Initially, ryegrass N uptake was depressed by clover, but in the final year there was evidence from %N and N uptake measurements that ryegrass benefited marginally from association with clovers at Invermay and Dunback, but not at Berwick. However, this benefit could not with certainty be ascribed to N transfer from clovers to ryegrass.