The response of pastures in Northern Ireland to N, P and K fertilizers and to animal slurries: I. Effects on dry-matter yield

Abstract

SUMMARY: Sixteen factorial experiments made from 1969 to 1971 on Northern Ireland pastures measured effects on yield of 0, 180 or 360 kg of N, 0, 30 or 60 kg of P and 0, 150 or 300 kg of K/ha/year both with and without 138,000 1 of slurry/ha.Without slurry, pasture yield was almost always substantially increased by nitrogen, slightly by potassium and hardly at all by phosphorus. There was a slight positive interaction between nitrogen and potassium, but no other interactions. Response to nitrogen was not linear and therefore was lower than has been obtained in many British trials.Slurry sharply reduced response to nitrogen and virtually eliminated response to phosphorus and potassium. The NH₄-nitrogen content of slurry gave an adequate measure of its effect on pasture yield. The nitrogen, phosphorus and potassium contents of the most concentrated slurries were 15, 29 and 36 times respectively those of the most dilute batches. Hence considerable imprecision is brought into a fertilizer programme when slurry is applied.As manuring on individual fields can never be precise, the fertilizer phosphorus and potassium needed for grassland is best assessed by considering the farm as a whole. A nutrient balance can show if the farming system is gaining or losing phosphorus and potassium. The amounts of fertilizer phosphorus and potassium needed are those which cover any deficits on the farm as a whole.