Abstract
Fertilizer P availability indices (F) are required to initialize soil and plant P model. The developed F were related with soil characteristics (CaC01, Al20,, Fe20„ clay, silt, sand, organic matter, pH) including labile-P (P,), Olsen-P (OP), P„/OP ratio, and plant yield and P-uptake. Correlation coefficient and stepwise multiple regression were employed to relate F, developed at two incubation period (a 7-day and a 6-month) using labile-P (V) and Olsen-P ('F) test values of 19 alkaline calcareous soils (0-30 cm layer) treated with 0, 30, 60 and 90 mg P soil. The 'F, developed at a 7-day incubation correlated significanrly with relative yield at all P rates (r = 0.48 to 0.57) and soil P,,/OP ratio at higher P rates (r = -0.45 to 0.69), but not with P-uptake (r = 0.19 to 0.37). The "F, correlated significantly with relative yield at 60 mg P kg-' soil (r = 0.629") and P-uptake at 90 mg P kg-' soil (r = 0.541.). Employing stepwise multiple regression, 'F, increased significantly with a decrease in both Al20, and Fe203 and increase in P,I0p ratio with low P addition (R2 = 0.67"). At higher P levels, "F, increased significantly with a decrease in surface area (SA) and organic matter (OM) and increase in P, test values (R2 = 0.71 to 0.72"). With 'F,„ OM and OP test values were related mostly under different P status (R2 = 0.78 to 0.93"). At moderate applied P, 'F, increased with a decrease in CaCO, and P,, test values (112 = 0.91"). With higher P addition, 'F. increased with an increase in OP and decrease in OM and P„/OP ratio explaining 93 percent of variation. It indicated the need of different equations required to predict F under different soil P status. Partitioning of the soils based upon Al20, and Feu(), contents may be helpful for further studies and testing under field conditions.
A. Rashid, T. Hussain , A. Razzaq. (2000) Fertilizer phosphorus availability indices in relation to soil characteristics under wheat crop, The Journal Soil & Environment , Volume 18, Issue (1-4).
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