The introduction of high-yielding varieties of seeds and the increase in cropping intensity has resulted in a significant rise in the extent of phosphorus removal by crops. Fertiliser phosphorus is, therefore, important in order to meet the crop requirements at various stages of growth. Though maintenance of a high level of phosphorus in the soil solution is difficult, fertiliser phosphorus is retained in the soil except by run-off or erosion. This residual fertiliser helps in building up the phosphorus level in the soil, a part of which becomes available to succeeding crops ( Fertiliser News , ISSN 0015-0266).