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EXTERNAL AND INTERNAL PHOSPHORUS REQUIREMENT OF WHEAT IN BHALIKE SOIL SERIES OF PAKISTAN

M. SARFRAZ, S. M. MEHDI^*, M. ABID AND MUHAMMAD AKRAM

Abstract: A field experiment was conducted during Rabi 2004-05 in Bhalike soil series (Typic Camborthid) to determine the phosphorus (P) requirement of wheat for obtaining 95 % relative yield. Site selection was based on 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 µg P mL^-1 and were examined by the modified Freundlich equation. The parameters a (amount adsorbed ug g ^-1) and b (buffer capacity mL g ^-1) were estimated by regression of the logarithmic form of the data obtained from the adsorption isotherms. Theoretical doses of P (mg kg^-1 soil) were calculated from this equation to develop P levels in the soil solution under field conditions which were 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.40, 0.50 and 1.00 mg L^-1 with native solution P level as control with and without nitrogen and potash. Maximum wheat grain (4.36 Mg ha^-1) and straw yield (4.45 Mg ha^-1) was recorded with 0.30 mg P L^-1 developed by adding 54.10 mg P kg^-1. The maximum phosphorus concentration in wheat grain and straw was 0.318 and 0.118 % with P level of 0.50 mg L^-1, respectively. External soil solution P requirement was 0.273 mg P L^-1 and internal P requirement was found 0.276 % for obtaining 95 % relative yield of wheat.

University College of Agriculture and Department of Statistics, Bahauddin Zakariya University, Multan, Pakistan.

^*Director, Soil Salinity Research Institute, Pindi Bhattian, Distt. Hafizabad, Pakistan.