CALIBRATION OF SOIL TEST METHODS FOR AVAILABLE PHOSPHORUS IN SWELL–SHRINK SOILS FOR WHEAT

Abstract

Eighteen surface soil samples (alkaline, calcareous clay, low to high in Olsen P) belonging to Inceptiosls, Vertisols, and Entisols were collected in bulk. Five kg soil (<2 mm) was placed in plastic pots. Four levels of P2O5 (0, 50, 100 and 150 kgha−1) with constant rates of N and K2O @ 200 and 100 kgha−1 respectively were applied. Wheat (cv. HD 2189) was grown keeping four plants in each pot with factorial CRD and three replications. Wheat yields were recorded and grain and straw samples analyzed for P. Soil available P was estimated with six extractants viz. 0.5 M NaHCO3 pH 8.5 (Olsen P), 10% NaOAc pH 4.8 (Morgan P), 0.03 N NH4F+0.025 N HCl (Bray P), 1 M NH4HCO3+0.005 M DTPA pH 6 (Soltanpour P), 0.002 N H2SO4 pH 3, (Truog P) and 0.05 N HCl+0.0025 N H2SO4 (Nelson P). Critical limits using scatter diagram and percent yield and P uptake were calculated. Soils containing low Olsen P recorded lower percent grain yield indicating efficient utilization of applied P than in soils with medium and high Olsen P. Percent wheat yield showed significant relationship with estimates of Olsen, Morgan, Soltanpour and Bray extractable P in soils. The highest correlation coefficient values were observed between Olsen P and percent wheat grain yield (r=0.915* *) and Olsen P and percent P uptake by wheat (r=0.894* *). The scatter diagram showed that critical limit of soil P was 29 kgha−1 according to Olsen's method. Thus, Olsen's method was found to be most suitable for estimating available P in swell–shrink (Inceptisols) soils of Western India.