A novel composting system for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer

Ammonia emissions not only lead to environmental pollution but also reduce the quality of compost products. Here, a novel composting system (condensation return composting system, CRCS) was designed for mitigating ammonia emissions. The results showed that the CRCS reduced ammonia emissions by 59.3% and increased the total nitrogen content by 19.4% compared with the control. By integrating the results of nitrogen fraction conversion, ammonia-assimilating enzyme activity, and structural equation modeling, it was found that the CRCS facilitated the conversion of ammonia to organic nitrogen by stimulating ammonia-assimilating enzyme activity and ultimately retained nitrogen in the compost product. Moreover, the pot experiment confirmed that nitrogen-rich organic fertilizer produced by the CRCS significantly increased the fresh weight (45.0%), root length (49.2%), and chlorophyll content (11.7%) of pakchoi. This study provides a promising strategy for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer with high agronomic value.