Abstract

Potassium balance and non-exchangeable potassium release in 0.01 M CaCl₂ medium in a Typic Haplustert were studied in a 7-year-old soybean–wheat rotational experiment involving 4 levels of cattle manure along with the recommended dose of K (66 kg/ha.year). Continuous cropping without returning crop residues to the soil led to a negative balance of 66–107 kg K/ha.year. Manuring at the rate of 4 and 8 t/ha did not significantly change the negative balance, but application of 16 t/ha manure reduced the negative K balance. Continuous cropping without cattle manure reduced cumulative K release from 236 mg/kg (initial) to 195 mg/kg. Application of manure at 4, 8, and 16 t/ha kept K release at 229, 245, and 246 mg/kg soil, respectively. A parabolic diffusion equation was the best fit to describe K release. Cropping under the present level of K input resulted in a decline in non-exchangeable K whatever the addition of manure. Manuring at 4 and 8 t/ha has accelerated the mining of native K, which increased the unsustainability of the system.