Availability of N P K in Soil in Relation to Growth of three Rice Varieties Grown with Different Combinations of these Nutrients

A pot culture experiment was conducted with 4 levels of nitrogen, two levels each of phosphorus and potassium. Three high yielding paddy varieties were raised and planted. Soil samples collected from the pots during various stages of plant growth were analysed for available nitrogen, phosphorus and potassium. The available nitrogen varied markedly from stage to stage. It was high 15 days after transplantation and sharply decreased to very low value at 30 days, with gradual increase thereafter. Values for available phosphorus were low at the initial stage and high at later stages. Application of 80 kg. P₂O₅ per hectare increased the available phosphorus content of the soil over 40 kg. P₂O₅ application. Available potassium content of the soils was highest at 15 days and lowest 30 days after transplanting the crop. Application of 80 kg. K₂O per hectare increased the availability of potassium in the soil over 40 kg K₂O application.