# Mitigating gaseous nitrogen emissions in cotton fields through green manure and reduced nitrogen fertilization

## TL;DR

Using green manure and reducing nitrogen fertilization can cut harmful gas emissions in cotton fields while improving soil health.

## Contribution

The study reveals how green manure with reduced nitrogen fertilization mitigates gaseous nitrogen emissions and alters soil microbial communities.

## Key findings

- OVG with 25% N reduction reduced total gaseous N emissions by 36.07%.
- OVG increased Proteobacteria abundance and microbial network complexity.
- Reducing N by ≥50% lowered emissions and changed bacterial assembly processes.

## Abstract

Integrating green manure with reduced nitrogen (N) fertilization is a promising strategy to mitigate N emissions in intensive cotton cultivation, however, the underlying mechanisms remain poorly understood. This study investigated the effects of three green manure incorporation patterns—no green manure (NG), Orychophragmus violaceus (OVG), and Vicia villosa (VVG)—combined with four N reduction levels (100, 50, 25%, and conventional) on gaseous N emissions (NH3 and N2O), soil physicochemical properties, and bacterial community characteristics using a cotton field experiment in the Yellow River Basin. Results showed that OVG incorporation with 25% N reduction (N2 treatment) significantly reduced total gaseous N emissions by 36.07% on average during the cotton growth period, reducing NH3 and N2O emissions by 13.31–54.11% and 32.25–68.77%, respectively, compared with N2 application without OVG. OVG application also increased the relative abundance of Proteobacteria (28.10%), enhanced heterogeneous selection in bacterial community assembly (200%), and increased the complexity of co-occurrence networks, compared with NG. Compared with conventional N fertilization (N3 treatment), ≥50% N reduction significantly lowered NH3 (>25.51%) and N2O (>32.76%) emissions, reduced the relative abundance of Acidobacteria (−20.23%), simplified co-occurrence networks, and increased homogeneous selection in bacterial assembly (50.00%). Integrating green manure with 25% N reduction substantially reduced gaseous N emissions, which was associated with the enhanced microbial biomass carbon (MBC) and facilitated recruitment of key bacterial taxa (e.g., Sphingosinicella, Azohydromonas, Phototrophicus) within the microbial co-occurrence network. These findings provide insight into how green manure application coupled with N reduction can mitigate gaseous N losses and reshape soil microbial ecology, offering a theoretical basis for sustainable nutrient management during cotton production.