Different forms of potassium and their contributions toward potassium uptake under long-term maize (Zea mays L.)-wheat (Triticum aestivum L.)-cowpea (Vigna unguiculata L.) rotation on an inceptisol.

摘要

In a long-term fertilizer experiment at the Indian Agricultural Research Institute, New Delhi, with maize, wheat, and cowpea, various forms of potassium (K) and their contribution toward K uptake were found to be affected by fertilizer use and intensive cropping. The treatments included for the study were a control, 100% nitrogen (N), 100% N-phosphorus (P), 50% NPK, 100% NPK, 100% NPK+farmyard manure (FYM at 15 t ha-1 to maize only), and 150% NPK. The concentration of nonexchangeable K was greatest, followed by exchangeable K and water-soluble K. The study revealed no significant change in water-soluble K concentration in surface soil compared to N, NP, and control, indicating existence of an equilibrium between different K forms. Application of 100% NPK significantly increased water-soluble K concentration in surface soil compared to N, NP, and control treatments after maize, wheat, and cowpea. Application of NPK+FYM and 150% NPK resulted in greater quantities of all the K forms as compared to other treatments. Among the three forms, water-soluble K contributed predominantly to K uptake by maize and wheat; however, nonexchangeable K contributed significantly to K uptake by cowpea.