Continuous potassium fertilization combined with straw return increased soil potassium availability and risk of potassium loss in rice-upland rotation systems

Crop residues perform an essential role in the material cycling and energy exchange processes and are commonly used as an organic soil amendment and potassium (K) substitute to enhance field productivity in rice-upland rotation systems. Elucidating the effects of continuous K fertilization combined with straw return on the fate of soil K is of great significance to the scientific application of K fertilization and the sustainable development of the ecological environment. A short-(5 years) and a long-term (38 years) field experiments at the Wuxue (WX) and Wangcheng (WC) sites respectively were conducted to study the effects of continuous K fertilization combined with straw return on soil potassium (K) fertility and loss. Results showed that K fertilization and straw return improved soil K supply capacity significantly. K fertilization (NPK) and straw return (NPK + ST) at WX and WC sites significantly increased soil exchangeable K content (KE) by 27.7%–102.1% and 36.6%–100.0%, respectively, compared with that of the treatment without K (NP). K release kinetics showed that most K+ was released in soil of the NPK+ST treatment, indicating a stronger soil K+ supplying capacity. Long-term K deficit resulted in the conversion of illite to interlayer minerals and kaolinite, which were not detected at the short-term experiment site. Integrated K fertilizer and straw return reduced soil bulk density (BD) and degree of anisotropy (DA), increased fractal dimension (FD) and optimized soil pore structure distribution. Nonetheless, continuous sufficient K input raised the amount of total K loss through runoff and leaching. Compared with that of NP treatment, the total K loss of NPK and NPK + ST treatments were increased by 160.3% and 227.5%, respectively. This strategy contributed to the conversion of bio-waste into resources, sustainable soil K management and scientific K fertilizer application for agricultural production.