Effects of repeated phosphorus fertilisation on field crops in Finland 1.Yield responses on clay and loam soils relation to soil test P values

Abstract

In order to update phosphorus (P) fertiliser recommendations for the Finnish clay and loam soils enriched with applied P, the effects of repeated P fertilisation on the yields of cereal and other crops were measured at eight sites over a period of 12-18 years. Yield results of some earlier field studies were also used in calibrating the soil test P values determined by the Finnish acid ammonium acetate method (PAc). Significant yield responses to P fertilisation were obtained on soils which had low PAc values or medium levels of PAc and too low or too high pH values (< 6.0 or 7.5 in water suspension). The mean relative control yield (RCY, yield without applied P divided by yield with sufficient P multiplied by 100) of the eight sites was 94.6% (n = 128, mean PAc 15.5 mg dm-3) varying from 87% at PAc 2.8 mg dm-3 to 100% at high PAc. A PAc level of 5-7 mg dm-3 was adequate for cereals, grasses and oilseed rape on the basis of the RCY value of 95% at optimal pH. At this PAc replacing the amounts of P in the crops (14 kg in 4 t grain) and the fixation of extractable P (about 6 kg ha-1 a-1) produced almost maximum yields in favourable seasons and were considered optimal.;