An experiment begun in 1958 measuring effects of N, P and K fertilizers on yield and N, P and K contents of grass:1. Effects during 1964–7

Abstract

SUMMARYThe effects of N, P and K fertilizers on the yield and N, P and K contents of grass cut for conservation, measured during 1958–63, were again measured during 1964–7. Grass given 38 kg N/ha per cut needed 31 kg K/ha per cut for full yield, grass given 75 or 113 kg N/ha per cut needed twice as much K. With sufficient K, at least 75 kg N/ha per cut was justified. The grass responded little to P.Percentage N in the grass, though greatly increased by N fertilizer, was little altered by K fertilizer. Percentage K, whilst greatly increased by K fertilizer, was decreased by N unless 62 kg K/ha per cut also was given. Percentage P in the grass was little increased by P fertilizer.Exchangeable K in the surface soil (0–20 cm) was maintained with time where the grass was given either 38 kg N plus 31 kg K or 75 kg N plus 62 kg K/ha per cut, corresponding to an N:K ratio of 1:0·82. Percentage K in the grass decreased with time throughout. Whereas a N:K ratio of 1:1·66 best maintained % K in grass during 1958–63 it was no better than an N:K ratio of 1:0·82 during 1964–7.Although exchangeable Mg in the surface soil decreased markedly between 1958 and 1967 (Mg fertilizer was not applied), % Mg in the grass did not. Mg in the grass was increased by N, but decreased by K fertilizer, and exceeded 0·2% (in dry matter) only in 1967 and then only where 75 or 113 kg N/ha per cut was applied.