Sorption and Availability of Fertilizer Phosphorus to Soybean-Wheat on a Typic Haplustert

Field experiments were conducted for three years on a fine smectitic Hyperthermic Typic Haplustert low in Olsen-P (5.4 mg kg⁻¹ soil) to evaluate the Prequirement of a soybeanwheat cropping sequence. Phosphate was applied at the rates of 0, 9, 18, 27, 36 and 45 kg ha⁻¹ to the first soybean crop and thereafter to each of the subsequent crops in amounts equivalent to P depleted by the preceding crop. Laboratory studies indicated that the soil sorbed 87 per cent of the added Pin 0.01M CaCl₂ medium. Optimum P dose worked out over three year period was found tobe 19 kg and 23 kg P ha⁻¹ for soybean and wheat, respectively.