Prediction of plant response to fertilisers by means of soil tests

Abstract

Abstract Ryegrass grown in pots was used to measure the phosphate status and response to phosphate of 35 recent, gley recent, and gley soils of the South Island. Yields of dry matter, phosphorus uptake, and relative yields or responses were used as plant growth parameters for correlation with chemical methods of assessing soil phosphorus status. Plant growth was found to depend on the level of surface‐bound iron and aluminium phosphate in these soils. The high level of calcium‐bound (apatite) phosphate was not related to yield or uptake. The soil extraction methods gave correlations in the decreasing order: ion exchange membrane, Olsen, Egner‐Riehm, Bray No. 1, Bray No. 2, and Truog. The order is in line with the ability of the extractants to remove the iron and aluminium phosphates from the surface of soil particles.