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

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 of 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.Keywords: dry matter; dry matter yield; fertility; fertilization; fertilizer; growth requirements; lolium multiflorum; nitrate; nitrogen; nitrogen levels; protein toxicity; ryegrass; toxicity; yiel