Responses of Soil Bacterial Communities and Enzyme Activities to Straw Return and Potassium Fertilization with Two Soils Under Soil Potassium Balance Condition in Rice–Wheat System

Long-term imbalance in fertilization has resulted in a serious decline in potassium (K) fertility in the Yangtze River Delta region of China. Understanding of the complex responses of soil microbial communities and enzyme activities to different K fertilizer measures while maintaining soil K balance can provide a scientific basis for rational application of K fertilizer. Two field experiment sites (JY, loam soil with high pH and K fertility; GD, silty loam soil with low pH and K fertility) were selected to study the effects of K fertilizer management on enzyme activities and bacterial communities under soil K balance condition. K fertilizer treatments included no K fertilizer (K0), straw return combined with K fertilizer (SRK), and inorganic K fertilizer only (IK). Soil bacterial communities were examined using MiSeq sequencing. Wheat yield, soil nutrient contents, and enzyme activities were higher in the SRK than in the IK and K0 treatments. Available K was the most important factor affecting wheat yield. The SRK and IK treatments significantly altered bacterial communities and enzyme activities, which in turn affected the cycling of soil nutrients. The positive effect of the SRK treatment on wheat yield, enzyme activities, and potential bacterial functions in silty loam soil was greater than that in loam soil, which was closely related to soil texture, pH, and K fertility. The SRK measure is a promising approach to maintain crop yield and soil fertility and more necessary to be adopted in silty loam soil with low pH and K fertility.