Improvement method and classification system for evaluating soil available K and plant K status for rice and winter wheat K fertilization

Scarcity and unbalanced application of potash in China has resulted in a widespread exhaustion of K reserves in cropland soils during recent decades. The most common soil K fertility index used is soil available K, measured using the 1 mol L^-1 ammonium acetate (NH₄OAc) method. However, the NH₄OAc method was only suitable for evaluating K availability in soils of the same type or with similar K buffering capacities, but not in soils with variable K buffer capacities or in which the non-exchangeable K contribution to plant K uptake varied. So, establishing a better method to present real K availability in various soils to crops and the precise diagnostic indexes of plant K and a stable uniform fertilizer recommendation indexes are substantial important for improving K utilization efficiency.