Determination of suitable equilibrium P concentration for phosphate requirement of wheat under greenhouse condition and its relationships with some soil properties
2011
Shabazi, Karim | Majidi, Aziz
Phosphorus sorption in soils is a key process in determining of its availability for plants. Extensive research has shown that recommended phosphorus can be improved based on soil characteristics. In this study, P sorption isotherms for different soils under wheat cultivation had been drawn. Equilibrium conditions were: 25°C, 0.01 M CaCl2, and 48h Shaker. Curves of adsorption isotherm used to add phosphorus fertilizer based on phosphorus equilibrium concentration. Equilibrium P concentration range of 0.02 to 1.2 was selected. Wheat plants were grown for six weeks. Yield approached more than 85% maximum in most soils when phosphate in solution was adjusted to 0.3 mgL-1.The standard phosphorous requirement was varied from 19 to 157 mgkg-1. There was significant correlation between isotherm parameters and cation exchange capacity (CEC) and there was no correlation with other soil properties. There was linear relation between added P and bicarbonate extractable P(Olsen P) in all soils(R2=0.96-0.99 by mean 0.98) and the slope of this linear equation (by plotting P added against Olsen P)varied from 0.23 to 0.47 and averaged 0.23. This mean that 63% added P was unavailable. There was no significant different in P recovery between soil P treatments. The phosphorus critical level for sodium bicarbonate extractant (Olsen P) based on Cate _ Nelson procedure was determined 13 mgP kg-1. In West Azerbaijan province experiment; the phosphate adsorption maximum as calculated by the Longmuir equation was used to predict the fertilizer P requirement of wheat(Triticum aestiviom, cv. Zarin) on a sandy loam soil. For this soil 25% saturation of the adsorption maximum gave the optimum dry mater yield.
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