Enhanced remediation of paddy soils contaminated with butachlor through the application of nitrogen-fixing cyanobacteria as a nitrogen fertilizer substitute

Butachlor, a widely used herbicide in paddy fields, exhibits persistent environmental residues, posing significant ecological concerns. Nitrogen-fixing cyanobacteria (NFC), as a biofertilizer, not only enhance soil fertility and crop growth but also show potential in influencing the environmental fate of herbicides. However, the specific effects of NFC as a nitrogen fertilizer substitute on butachlor remediation in paddy soils remains unexplored. To address this, a 105-day outdoor pot experiment was conducted to evaluate the impact of NFC on soil properties, microbial community dynamics, and butachlor removal efficiency. The results showed that NFC application increased soil carbon and nitrogen content, enhanced enzyme activities (e.g., urease), and reshaped the microbial community structure compared with conventional fertilization. Co-occurrence network analysis further showed that NFC increased the complexity of soil microbial ecological networks, leading to closer species interactions and favoring the aggregation and proliferation of microorganisms that mediate butachlor degradation (e.g., Sphingomonas). As a result, the extinction of butachlor was accelerated, and the amount of butachlor residue at harvesting stage was reduced by 35.81–57.06% relative to conventional fertilization. This study provides a theoretical foundation for the application of NFC in paddy soils, highlighting its potential to improve soil health and sustainability in the context of butachlor use.