Potassium supply and adsorption capacity changes in a Chinese subtropical paddy soil chronosequence

An accurate assessment of the effect of long-term rice cultivation on K-supplying capacity and adsorption characteristics of paddy soils has theoretical and practical significance for rational application of K fertilizers. We measured changes in basic soil properties and K adsorption isotherms in a representative subtropical paddy soil chronosequence in Southern China. Results showed that mean water dissolvable K and non-exchangeable K contents of paddy soils (27.0 and 184.8 mg kg(-1)) were higher than those of original soils (15.5 and 169.5 mg kg(-1)), but the mean exchangeable K contents showed the opposite trend (paddy soils, 37.1 mg kg(-1); original soils, 52.5 mg kg(-1)). Long-term paddy cultivation caused reduced K-supplying capacity and K+ adsorption capacity of paddy soils in the red soil regions, which was attributed to the rapid loss of sorbents (e.g. Fe-d and clay) by leaching and the competitive occupation of sorption sites by the accumulated soil organic matter. The promotion of sustainable and balanced K fertilizer inputs and appropriate increase in short-term applications of K fertilizer (K fertilizer input > K output from harvest) during application of N and P fertilizers to paddy soils were necessary to maintain the K-supplying capacity of soils and the crop yield.