Long-term effects of fertilizers on herbage production: II. Chemical composition

The effects of Nitro-chalk, superphosphate and potassium fertilizers on the chemical composition of grassland herbage and the removal of major plant nutrients have been traced over 14 years. Without fertilizer N, but with adequate K, clover supplied a yearly average of up to 87 lb Nsol;acre. With an annual application of 348 lb N and adequate K, 237 lb of N was recovered annually. Without applied P, herbage P concentration fell with time especially under heavy N treatment. When P was applied, herbage P concentration did not fall, irrespective of N treatment: K depressed P concentration irrespective of P application. Maximum removal of P occurred with annual applications of 348 lb N, 43 lb P and 280 lb K: at these rates gain and loss of P approximately balanced. Herbage K concentration was greatly increased by K fertilizer. It was reduced by N when no K was applied but applying K counteracted this effect. Removal of K slightly exceeded the 280 lb of K applied when 348 lb N was also applied.