Abstract
A field experiment was conducted on Rasulpur soil series (Typic Camborthids) to determine P requirement of wheat for obtaining 95 % relative yield. Site selection criteria were calcareousness and P deficiency. Phosphorus sorption isotherms were constructed to study the behavior of soil to phosphate application by adding 0, 5, 10, 15, 20, 40, 60 and 80 IJg P mL-1 and modified Freundlich equation was constructed. The parameters a (amount adsorbed in IJg g -1) and b (buffer capacity in mL g -1) were estimated by regression of the logarithmic form of the data obtained from the adsorption isotherms Theoretical doses of P (mg kg1 soil) were calculated from this equation to develop P levels in the soil solution under field conditions which were 001, 002, 003, 004, 005, o 10, 0 15, 020, 0.25, 0.30, OAO and 0.50 with native solution P level as control with and without Nand K Wheat crop was grown in the randomized complete block design with three replications. Maximum wheat grain and straw yield of 3.37 and 3.50 Mg na', respectively was recorded at solution P level of 0.20 mg P L 1 Phosphorus concentration in wheat grain and straw was OA10 and 0 138 % which was found at solution P level of OAO mg P L-1, respectively. External solution P requirement was 0.146 mg P L 1 and internal P requirement was found 0289 % for obtaining 95 % relative yield of wheat. Key words: Phosphorus sorption isotherms, modified Freundlich model, wheat yield, P concentration, external and internal P requirement
