Sulphur and phosphorus in balanced pasture nutrition

Abstract

Clover-based pastures frequently require both sulphur (S) and phosphorus (P) fertilisers for nearmaximum growth. Fertilisers with a wide range of S:P ratios are commercially available. Selection of fertilisers to provide well-balanced pasture nutrition requires criteria to judge nutritional balance. In the work described in this paper, the effects of various combinations of S and P fertilisers on clover growth and herbage chemical composition were investigated in a field trial. There were large clover dry matter responses to both nutrients and a large positive interaction between them, emphasising that balanced nutrition is essential for efficient use of both nutrients. The ratio of S:P in clover herbage appeared to be a useful indicator of nutritional balance. For data combined over the experimental period (16 months), treatments more deficient in S than in P had clover S:P ratios less than 0.72 and vice versa. However, because S fertiliser costs much less than P fertiliser, a higher S:P ratio in clover, approximately 0.76, corresponded to an -economically optimal balance of S:P in fertiliser. - Keywords: clover, fertiliser, nutrient ratios, pasture, plant analysis, phosphorus, sulphur