Effect of addition of N, P and K fertilizers on the pH of alkaline alluvial soil on incubation*

An incubation experiment was done to study the effect of eight N, P and K fertilizers on the pH of alkaline alluvial soil. pH was measured periodically (6 hours, 1, 2, 3, 4, 6, 8, 10, 17, 40 and 80 days) after adding normal rates of fertilizers and soil incubation at 50% water holding capacity at room temperature. Within 6–8 days, ammonium sulphate and ammonium chloride progressively reduced pH from 7.6 to 5.9 which remained almost unchanged upto 40 days of incubation but it increased to 6.6. and 6.4 at 80 days of incubation. Calcium ammonium nitrate decreased pH slowly and kept it reduced from 7.6 to 6.8 during 4 to 80 days of incubation. Urea did not affect pH upto 3 days after which it also reduced pH to 6.7. Diammonium phosphate and single superphosphate reduced pH by 0.3 unit whereas muriate of potash and sulphate of potash reduced it by 0.2 to 0.3 unit in 80 days of incubation.