Effects of Different Nitrogen Types on Nitrogen Use Efficiency, Field Water Quality, and Soil Microbial Community in the Rice–Crayfish Co-Culture System

Purpose The rice–crayfish co-culture system (RCS) has developed rapidly in recent years due to its highly comprehensive benefits in China. A 2-year RCS experiment was carried out to assess the N types suitable. Methods The following four treatments were implemented in a paddy field: (1) no N fertilizer (CK), (2) base fertilizer as compound fertilizer and topdressing urea (CF), (3) slow-release compound fertilizer (CRF), and (4) base fertilizer as organic–inorganic compound fertilizer and topdressing urea (OF), and rice growth, soil conditions, and field surface water quality were measured. Results The yield, N fertilizer agronomic efficiency, N partial production efficiency, and N use efficiency of rice in CRF significantly increased by 8.8%–14.3%, 44.2%–64.9%, 13.6%–15.0%, and 30.8%–39.2%, respectively compared with CF. Meanwhile, CRF improved the N accumulation of rice and the soil NH 4 + -N content in the full heading stage, while OF improved soil urease and catalase activities in the rice growth period compared with CF and CRF. No significant differences were found in the bacterial diversity under different N varieties. CRF had the best effect in terms of reducing NH 4 + -N and NO 3 - -N concentrations at the lowest level. Conclusions Even though the cost of CRF was significantly higher, CRF still had the highest net income, and CRF and OF had higher net income compared with CF. A comprehensive analysis of rice yield, surface water quality, and NUE found that CRF was the best choice in RCS, and eco-friendly controlled-release fertilizer should be encouraged.