Effect of Fertilizer Reduction Combined with Straw Return on phoC Gene Under Corn–Soybean Rotation in Northeast China

In Northeast China, long-term large-scale monoculture farming has caused a decrease in soil nutrients. To maintain crop yields, excessive amounts of chemical fertilizers are frequently used, resulting in multiple problems. In recent years, diversified cropping systems (such as corn–soybean rotation) have been increasingly introduced into Northeast China to help preserve soil nutrients. Additionally, conservation tillage methods (such as straw return) have been widely adopted in Chinese agriculture to enhance soil fertility and reduce chemical fertilizer application. However, the characteristics of soil phosphorus cycling under combined agricultural practices are yet to be fully clarified, not to mention the mechanism of P cycling enzyme changes driven by soil functional microorganisms. Therefore, this study investigated the impact of straw return combined with fertilizer reduction from a field experiment on soil phosphatase activity and the phoC gene characteristics. The results of the field experiment show that straw return combined with fertilizer reduction based on the maize–soybean rotation system exhibited no significant effects on the contents of soil organic matter, total phosphorus and other nutrients (with declines of less than 10%), indicating that soil nutrient status was well maintained. Organic material addition also increased soil phosphatase activity and phosphatase functional gene abundance, significantly improving their diversity and community structure. Linear regression results show that the variation in phoC gene abundance is an important molecular mechanism driving the differences in soil phosphatase activity under various agronomic methods. Our results offer important guidance for implementing effective strategies to reduce fertilizer use in agricultural practices in Northeast China.