Changes in Potassium Forms, Clay and Silt Mineralogy Brought About by Intensive Cropping

Potassium management in Indian agriculture has been traditionally overlooked because of high fertilizer cost and anomalous crop response to potassium fertilizers in majority of Indian soils. Suspecting that this could have an adverse effect on potassium nutrition of crops and affect soil health and Indian agriculture, a study was undertaken to simulate short term heavy removal of potassium by repeated harvesting of Panicum maximum (Jacq.) grown with or without fertilization on three major soil groups of India viz., Inceptisol, Alfisol and Vertisol. Fertilization increased cumulative crop yield and potassium uptake in Alfisol followed by Inceptisol and Vertisol. The quantity of water soluble, exchangeable, non exchangeable K decreased during the crop growing cycle both in the fertilized and unfertilized treatments in all the soils. Exchangeable K in the Inceptisol and non exchangeable K in the Vertisol decreased more significantly in the fertilized plots as compared to control. A decrease in 10 Å peak and consequent increase in vermiculite/montmorillonite-interstratified minerals in Inceptisol and kaolinite in Alfisol suggests degradation of mica whereas transformation of vermiculite to montmorillonite-interstatified minerals was taking place in the clay fraction of the soils under study. A general decrease of 10 Å peak was also observed in the silt fraction of Inceptisol and Alfisol suggesting degradation of micas. Thus intensive cropping without K fertilization will lead to all forms of potassium depletion and subsequent degradation of clay and silt minerals that may constraint profitable crop production in the post green revolution era.