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

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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.