Efficiency of Ammonium Polyphosphate and Diammonium Orthophosphate for Wheat on a Typic Ustochrept Varying in Available Phosphorus

Efficiency of ammonium polyphosphate and diammonium orthophosphate was evaluated in a greenhouse experiment conducted on a Typic Ustochrept. Both the sources of P were equally effective in increasing drymatter yield, while shoot P uptake was higher with DAP than with APP applied at 20 and 40 mg kg⁻¹ soil having 3.0 and 6.4 mg available P kg⁻¹, but reverse trend was observed at higher levels andavailable P contents. Available P content of the soils after the harvest of wheat crop was generally higher with APP than DAP treatment. The amount of fertilizer - P (P_f) required to produce maximum yield at different available P content of soil (P_s) was described by the equation: P_f = 63.65 -3.05 P_s (r = 0.95).