The relationship between the nitrogen and nitrate content and nitrate toxicity potential of Lolium multiflorum

Abstract

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.