Effects of withholding phosphate and potash fertilizer on grain yield of cereals and on plant-available phosphorus and potassium in calcareous soils

abonos fosfatados abonos potasicos angleterre application rates calcareous soils cereal crops crop yield cultivos de cereales disponibilidad de nutrientes dose d'application england engrais potassique field experimentation inglaterra nutrient availability phosphate fertilizers potash fertilizers rendement des cultures rendimiento de cultivos rotation culturale rotational cropping sol calcaire