Effect of a wide range of nitrogen applications on herbage nitrate content in long-term fertilizer trials on all-grass swards

Abstract

In three long-term nitrogen fertilization experiments with total applications of up to 1120 kg N per ha per year and cutting at a DM yield of 2 to 2.5 t per ha, the herbage nitrate content of all-grass swards was studied for each cut. At applications of 60 kg N per ha per cut, with a maximum of 360 kg N per ha per year, there was little or no increase in nitrate content. At applications of 80 kg N per ha per cut, totalling 400–560 kg N per ha per year, 3% of the samples had nitrate contents higher than 0.75% N03. At applications of 120 and 160 kg N per ha per cut, totalling 600–1120 kg N per ha per year, 61 and 67% of the samples exceeded 0.75% N03, respectively. The excess nitrate did not occur in the spring cuts, but for the most part in the summer cuts and seldom in the autumn cuts. This may explained by a positive relationship between temperature and herbage nitrate content, under favourable moisture conditions. In warm but dry periods there was no relationship and nitrate contents were low.