Keywords: Phosphorus, Potassium, Calcium, Decreasing inputs, Soil depletion, Arable crops, Yields, Nitrogen use efficiency.
Sufficient readily available amounts of phosphorus (P) and potassium (K) in soil, and a satisfactory soil pH status, are important factors in maintaining soil fertility and crop production. In most UK arable soils, readily plant-available P and K reserves have been built up to satisfactory levels due to past fertiliser and organic manuring practice, so that only maintenance fertiliser dressings are needed to replace the P and K removed by crops. Survey data show, however, that farmers have decreased P and K fertiliser inputs in the last few years by applying these nutrients to a smaller proportion of the arable cropped area, as a strategy for reducing production costs under difficult economic circumstances. Omission of P and K fertilisers for a few years, should not adversely affect yields and/or quality of cereal and oilseed rape crops in the rotation, unless the soil PK status is already low. However, long term experiments in England show that the continuation of such a policy will lead to yield losses once available soil P and/or K reserves have declined below the critical level appropriate for the soil and cropping system. This will also result in less efficient use of fertiliser N and other crop husbandry inputs, which is both economically and environmentally undesirable. Soil pH effects on crop yield and composition emphasise the need for regular liming to replace losses of calcium from agricultural land.
A E Johnston, K W T Goulding and P R Poulton, IACR Rothamsted, Harpenden, UK.
A G Chalmers, ADAS Bridgets, Winchester, UK.
44 pages, 12 Figures, 26 Tables, 60 Refs.