The effects of a wide range of nitrogen rates on some chemical constituents of the herbage from perennial ryegrass swards with and without white clover

Abstract

Summary: Selected herbage samples from a 6-year experiment in which nitrogen rates between 0 and 897 kg/ha were applied annually on perennial ryegrass swards were analysed for nitrate-nitrogen, true-protein and non-protein nitrogen, water-soluble carbohydrate, potassium and sodium content and for amino acid composition. The nitrate-nitrogen content of the herbage increased with increasing nitrogen rate from 224 kg/ha upwards, but the potentially toxic level of 220 mg/100 g dry matter was not reached until the annual nitrogen rate was about 560 kg/ha. On average, at the 897 kg nitrogen/ha rate the non-protein nitrogen content had increased to 27·5% of the total nitrogen yield, and 40·3% of the non-protein nitrogen yield consisted of nitrate nitrogen. Nitrate content was shown to be a sensitive indicator of the level of nitrogen nutrition of the herbage, the optimum nitrogen rate for dry-matter production coinciding with a nitrate-nitrogen content of approximately 100 mg/100g dry matter. The amino acid composition of the herbage varied little with either the rate of nitrogen or the date of cutting. It was demonstrated that, on average, a 1% unit increase in the crude-protein content of the herbage was accompanied by a 1% unit decrease in the carbohydrate content. The sodium content of the herbage increased with increasing nitrogen rate up to between 448 and 560 kg/ha, but the potassium content showed little variation.