External and internal phosphorus requirement of wheat in Bhalike soil series of Pakistan.

摘要

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 micro g 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.