Journal of the Indian Society of Soil Science

Laboratory and field experiments were conducted for two years (1990 and 1991) to find out the extent of constraint of phosphorus and sulphur in Islamnagar 3 and 4 soil series (Vertic Ustochrepts), to evaluate crop response to applied P and S and to establish the critical limits of P and S for soybean. About 87 per cent samples of Islamnagar 4 and 72 per cent in Islamnagar 3 series were found to be low in available P and about 25 per cent samples in the two soil series were low in available's. In nine field experiments with graded rates of 0, 30, 60 and 90 kg P₂P₅ ha⁻¹ and 0, 20, 40 and 60 kg S ha⁻¹ optimum response to P was noted at 60 kg P₂O₅ ha⁻¹ and that of Sat 40 kg S ha^−l. Using data obtained from 30 field experiments and employing scatter plot and statistical procedures, critical limits of 7.25 and 6.95 mg P kg⁻¹ and 1l.25 and 1l.15 mg S kg⁻¹, respectively, were established to isolate P and S responsive soils from those of non-responsive soils