The incorporation of aquaculture feed within a rice–crayfish coculture system significantly enhances nitrogen cycling, thereby diminishing the reliance on chemical fertilizers. However, this benefit is often overlooked in practice, and farmers continue to use large quantities of chemical fertilizers to maximize production, resulting in excessive soil fertility and water nitrogen pollution. Thus, avoiding nitrogen pollution in rice–crayfish coculture systems has become a pressing issue. In this study, we conducted a two-year experiment with two rice cultivars, and a 33.3% reduction in nitrogen fertilizer in a rice–crayfish coculture system (RC), to systematically analyze the overall nitrogen balance, rice nitrogen nutrition, and soil fertility, as compared with a rice monoculture system (RM). Our findings revealed the following: (1) Under the 33.3% reduction in nitrogen fertilizer, the nitrogen surplus in the rice–crayfish coculture system was comparable to that in the rice monoculture, and was controlled at an environmental safety level. (2) Nitrogen utilization efficiency and the accumulation of nitrogen in the rice–crayfish coculture were comparable to those in the rice monoculture. The nitrogen cycle in this system was able to provide the nitrogen required for rice growth after nitrogen fertilizer reduction. (3) The rice–crayfish coculture significantly improved the overall soil fertility and the effectiveness of soil nitrogen nutrition. Furthermore, cutting off the application of nitrogen fertilizer after the mid-tillering stage effectively controlled the total nitrogen content in soil after rice maturity. In conclusion, reducing nitrogen fertilizer in a rice–crayfish coculture system is feasible and beneficial. It ensures rice production, reduces the risk of excessive nitrogen surplus and surface pollution, and promotes a greener, more environmentally friendly paddy field ecosystem.

Organic fertilizer is utilized to improve the organic carbon levels in arable soils, which is helpful for soil quality improvement and crop yield increase. However, the after-effect of organic fertilizer varies among regions with different temperature and precipitation conditions, and the extent of the impact remains unknown. This study aimed to investigate the impact of varying temperature and rainfall conditions on the accumulation of soil organic carbon after organic fertilizer application. A meta-analysis of 168 peer-reviewed studies published between 2005 and 2022 involving a total of 464 trials was conducted. The following was discovered: (1) In the major grain-producing areas of China, there was a significant positive correlation (p < 0.01) between latitude and soil organic carbon content. Meanwhile, temperature and precipitation had a significant negative correlation (p < 0.01) with soil organic carbon content. (2) The increase in temperature inhibited the increase in soil organic carbon storage. The improvement effect of organic fertilizer application in the low-temperature areas was significantly increased by 60.93% compared with the mid-temperature areas, and by 69.85% compared with the high-temperature areas. The average annual precipitation affected the after-effect of organic fertilizer as follows: 400–800 mm > 400 mm > more than 800 mm. (3) The influence of climatic conditions on the after-effect of organic fertilizer was more significant depending on the specific tillage practice. To increase organic fertilizer use efficiency and eliminate greenhouse gas emissions, liquid organic fertilizers with abundant trace nutrients and amino acids, which take advantage of releasing nutrients more swiftly and have a better fertilization effect, could be an alternative to traditional organic fertilizers.