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 nitratenitrogen 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/100 g 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.
INTRODUCTIONs t a g e o f 8 r o w t h o n e a c h occasion > and t h e yields of herbage dry matter and crude protein were deterThe yield results have been reported (Reid, 1970(Reid, , mined. 1972) for a 6-year experiment designed to obtain Herbage samples were analysed for nitratedetailed information on the response curves relating nitrogen, water-soluble carbohydrate, potassium herbage dry-matter and crude-protein yields to and sodium content from all replicates of nine nitrogen application rate on perennial ryegrass nitrogen treatments (0, 112...897 kg nitrogen/ha) swards with and without white clover. To supple-on both the grass and clover and the pure-grass ment this information selected herbage samples swards at all cuts in the first, third and sixth years, from the experiment were analysed for nitrate-True-protein and non-protein nitrogen analyses nitrogen, true protein and non-protein nitrogen,' were made on samples from all replicates of five water-soluble carbohydrate, potassium and sodium nitrogen treatments (0, 224...897 kg nitrogen/ha) content, and amino acid composition.on the pure-grass sward only at all cuts in the 3 EXPERIMENTAL PROCEDURE y e a r S ' ^nd amino-acid analyses on samples from one replicate of the same five nitrogen treatments The treatments, design and methods were de-on the pure-grass sward at all cuts in the third year scribed in an earlier paper (Reid, 1970). Briefly, a only. series of 21 nitrogen rates ranging from 0 to For the nitrate-nitrogen analysis 1 g of dried 897 kg/ha was applied in five equal dressings each sample was extracted with 80 ml boiling water for yea...