Division of Soil and Crop Management, Central Soil Salinity Research Institute, Kamal, Haryana, 132001.
Present address: 1Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi, 110012.
A long-term fertilizer experiment, over 10 years, studied the effect of NPK fertilizers alone and in combination with green manuring (Sesbania aculeata) or farmyard manure (FYM) on potassium (K) balance and release properties in rice-wheat cropping sequence on Aquic Natrustalfs. The treatments consisted of control, 100% nitrogen (100% N), 100% nitrogen and phosphorus (100% NP), 100% nitrogen, phosphorus and potassium (100% NPK), 100% NPK + green manuring (GM), 100% NPK + farmyard manure (FYM) and 150% NPK. In all the fertilizer and manure treatments removal of K in the crop exceeded K addition and the total soil K balance was negative. Apparent potassium use efficiency of applied K in the 100% NPK treated plot was lower as compared to 100% NPK + GM and 100% NPK + FYM treated plots. The distribution pattern of the water soluble, exchangeable and non-exchangeable K, at various depths of soil profile indicated that a major portion of the applied K remained in the top 30 cm soil and moved in successively decreasing amounts down the profile to a depth of 60 cm in the plots receiving K fertilizer. The neutral 1 N ammonium acetate-extractable K in the surface soil (0–15 cm) ranged from 187 to 324 kg ha−1 in different treatments. The highest and lowest values were obtained in 150% NPK and 100% NP treatments, respectively. It was observed that in plots receiving fertilizer K, the contribution of nonexchangeable K to plant uptake was lower as compared to without K fertilization (control, 100% N and 100% NP). The results suggest that sub-soil layers are also stressed for K and the continuous mining of soil reserve K may affect crop yields adversely in long-term.
Exchangeable K, long-term fertilization, potassium balance
