Effect of poor-quality irrigation water on potassium release from soils under long-term fertilization

Different irrigation and fertilization managements can greatly affect plant potassium (K) uptake in soils. A continuous extraction experiment was used to analyze the influence of poor-quality irrigation water on K release from soils under long-term copping with different fertilizations. The results demonstrated that K release kinetics included a rapid stage and a subsequent slow one. K leached in the solution with Ca:Mg ratio 75:25 and sodium adsorption ratio (SAR) 45 was minimum (146 mg kg(-1)), while K leached in the solution with Ca:Mg ratio 25:75 and SAR 5 was maximum (212 mg kg(-1)). Due to the specific ion effect, Mg2+ played a more important role in the release of K than Ca2+. The K release rates and quantities of released K in the soils without K fertilizers were lower than others. Long-term planting without K fertilizers results in the decrease of K fertility. Power equation and parabolic equation fully simulated the process of K release, suggesting a diffusion-controlled process. The K extracted by saline water may be more available to plants or be leached down below root zone. Therefore, much K will be leached by saline water in the long run, especially by water containing large numbers of Mg2+. Without any K input, K fertility of soils will decrease under long-term cropping. Thus, there is an urgent need for the improvement of irrigation and K fertilization managements in soils.