Potassium Fractions in Acid Soil Continuously Fertilized with Mineral Fertilizers and Amendments under Maize-Wheat Cropping System

After thirty-one years of continuous cropping of maize-wheat in an acid Alfisol, the effect of different mineral fertilizers with or without amendments was studied on different forms of potassium. Continuous application of chemical fertilizers and amendments improved all the potassium fractions in soil over control. Integrated use of balanced dose of chemical fertilizer, with FYM or lime sustained higher yields of maize in comparison to inorganic fertilizers alone. Accordingly, potassium uptake was also higher when FYM or lime was applied with 100% NPK. Continuous application of urea (100% N) alone resulted in zero yield. Significant positive relationship amongst the different forms of soil potassium in 0–0.15 m depth indicated the existence of equilibrium among themselves. At lower depths, however, non-exchangeable K was not significantly correlated with HCl-K. All the potassium fractions exhibited significant positive relationship with yield and potassium uptake by maize except the non-exchangeable K.