Continuous Cropping,Fertilization, and Organic Manure Application Effects on Potassium in an Alfisol under Arid Conditions

Effects of continuous cropping and addition of organic manures (farmyard manure, FYM, and groundnut shells, GNS) along with inorganic fertilizers on nonexchangeable potassium (K) release kinetics in a K-deficient Alfisol were studied in a 20-year manurial experiment under arid conditions. There was a depletion in available K under continuous cropping without K input (control) as compared to other treatments such as 100% nitrogen–phosphorus–potassium (NPK), 50% NPK + 4 metric tons (MT) groundnut shells ha^?1, 50% NPK + 4 MT FYM ha^?1, and 100% organic (i.e., 5 MT FYM ha^?1). Over 20 years of cropping without K input, available K was reduced from 155 kg ha^?1 (in 1985) to 82 kg ha^?1 (in 2005), showing a negative balance of 73 kg ha^?1. Soil in control plots showed available K in the deficient range (<50 mg kg^?1), whereas four other fertilizer and manurial treatments were greater than the critical limit. Considerable improvements in nonexchangeable K-release parameters such as step K and cumulative K release were observed in manured plots over control. Parabolic diffusion and first-order kinetic equations explained K release from soils. Potassium-release rates were drastically reduced in control plots, and there were increased release rates with continuous addition of manures. Results suggest that soils with groundnut shells or FYM (4 MT ha^?1) along with 50% inorganic fertilizer additions could maintain greater K release rates after 20 years of cropping as compared to cropping without K input.