Comparative responses to applied fertilizer phosphorus on manured and unmanured soils

Abstract

The response to fertilizer phosphorus (P) was investigated in a field experiment. On a manured area the omission of fertilizer P did not reduce herbage dry matter (DM) yield over a 6 year period, and herbage P concentration was not affected by fertilizer P and did not decline in the absence of P fertilizer. On an unmanured area, the omission of P fertilizer for the first 3 years depressed yields by 6%, but this increased to 15% during the subsequent 3 years. Significant linear regressions were obtained between ammonium acetate extractable P (NH₄OAc-P) in the soil and the various fertilizer rates, and the application of 31.7 kg P ha^-1 yr^-1 to the unmanured soil would have left NH₄OAc-P at 0–5 cm unchanged.