Effects of Different Soil Moisture Conditions and Zinc Sulfate and Monocalcium Phosphate Fertilizers on the Extractable-P in a Calcareous Soil

For evaluating effects of different soil moisture conditions, zinc (Zn) and phosphorus (P) on extractability of P in a calcareous soil, two experiments were conducted as factorial on the basis of a completely randomized design with two replications under laboratory conditions in 2012. The first experiment was arranged with four factors, including Zn at two levels (0 and 20 mg Zn per kg of soil as ZnSO₄.7H₂O), P at two levels (0 and 60 mg P per kg of soil as Ca(H₂PO₄)₂.H₂O), soil moisture at two levels (0.6FC and FC) and incubation time at four levels (1, 10, 30, and 60 days) and the second experiment was accomplished with three factors of Zn and phosphorus at the above mentioned levels, and wetting-drying cycles at three levels (1, 10 and 20 cycles). The extractable soil- P values were measured at the end of each incubation period or wetting-drying cycle by Soltanpour and Schwab method. The results showed that application of P increased the extractable P in both soil moisture conditions. The extractable P significantly decreased with increasing duration of incubation, especially in the first 10 days and then remained constant for the rest of the period. The Zn supply decreased extractable P and this reduction was more pronounced with increasing incubation time. Increase in soil water content from 0.6FC to FC increased the extractable-P. The effects of wetting-drying cycles on the extractable-P were different with and without application of 60 mg P per kg of soil. Under no P supplying condition, wetting-drying cycles exhibited higher amounts of extractable P compared with incubation at constant moisture condition; while  under  P applied condition, imposing wetting-drying cycles led to a decrease in amounts of extractable P compared to incubation under constant moisture condition.