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

Abstract

ABSTRACT 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. Fed 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.