Get reliable rangeland science

The interrelationships between the nitrate?N and nitrogen content and dry matter yield of Midmar ryegrass (Lolium multiflorum cv. Midmar) were investigated. Data were collected from N fertility trials, from two seasons (1985 and 1987) on four soil sites (Metz, Griffin, Clovelly and Katspruit) with N fertilizer rates ranging from 0 to 1 080 kg N/ha/yr, but varying on different sites. The data showed little accumulation of nitrate?N with increasing nitrogen levels up to 3,2?3,5% nitrogen, followed by a sharp increase in nitrate?N with little further increase in nitrogen content. Dry matter yields approached a maximum between 3,2 and 3,5% nitrogen and between 0,15 and 0,25% nitrate?N, thereafter an accumulation of nitrogen or nitrate?N occurred with little increase in dry matter yield. Above these limits, applied N fertilizer appeared to be in excess of the growth requirements of the plant and potentially toxic to ruminants. This indicated a wasteful use of N fertilizer. The data are reviewed in terms of potential toxicity to ruminants.