Division of Soil, Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi, 110012.
In a long-term fertilizer experiment on a Typic Ustochrept, inclusion of potassium in fertilizer schedule has helped in maintaining higher step-K and constant rate K (CR-K) in both surface (0–0.15 m) and sub-surface (0.15–0.30 m) soils. However, application of NP and/or N alone has resulted in minimum values of step-K and CR-K in both the soil depths after 25 years of intensive cropping of three crops (two grain crops + a fodder) a year. Major portion of total extractable step-K appeared in the first two extractions. Almost similar values of step-K have been observed in both the soil depths under all fertilizer treatments but CR-K values were slightly higher in surface than in sub-soil. Based on the critical levels set for step-K and CR-K in soils, all the plots showed sufficiently higher values indicating the ability l)f the experimental soil to supply sufficient potassium to crops even after 25 years of intensive cropping without K-fertilizers.
Potassium dynamics, constant rate K, long-term experiment, intensive cropping
