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Ammonia (NH3) emissions should be mitigated to improve environmental quality. Croplands are one of the largest NH3sources, they must be managed properly to reduce their emissions while achieving the target yields. Herein, we report the NH3emissions, crop yield and changes in soil fertility in a long-term trial with various fertilization regimes, to explore whether NH3emissions can be significantly reduced using the 4R nutrient stewardship (4Rs), and its interaction with the organic amendments (i.e., manure and straw) in a wheat–maize rotation. Implementing the 4Rs significantly reduced NH3emissions to 6 kg N ha–1yr–1and the emission factor to 1.72%, without compromising grain yield (12.37 Mg ha–1yr–1) and soil fertility (soil organic carbon of 7.58 g kg–1) compared to the conventional chemical N management. When using the 4R plus manure, NH3emissions (7 kg N ha–1yr–1) and the emission factor (1.74%) were as low as 4Rs, and grain yield and soil organic carbon increased to 14.79 Mg ha–1yr–1and 10.09 g kg–1, respectively. Partial manure substitution not only significantly reduced NH3emissions but also increased crop yields and improved soil fertility, compared to conventional chemical N management. Straw return exerted a minor effect on NH3emissions. These results highlight that 4R plus manure, which couples nitrogen and carbon management can help achieve both high yields and low environmental costs.

The research examined the chloroplast genome structure and evolutionary relationships of Allium guanxianense. The cp genome spans 152,480 bp and comprises a large single copy region (82,305 bp, 53.98% length ratio), a small single copy region (18,353 bp, 12.04%), and two inverted repeat sequences (25,911 bp, 16.99%). A total of 132 genes were identified within the cp genome of A. guanxianense, including 86 protein-coding genes (PCGs), 38 tRNAs, and 8 rRNAs. Its cp genome structure is basically consistent with other species of the sect. Bromatorrhiza, with the only difference being the distributions of ndhFand rpl22at the IR region. The codon usage bias analysis for PCGs revealed that mutation pressure drives the preference for codon usage in Alliumspecies. Phylogenetic analysis of 35 Alliumspecies showed that the genus can be divided into three major lineages, with A. guanxianensepositioned at the top of the sect. Bromatorrhizain first lineage, forming a well-supported sister clade with A. omeiense. Our study presents, for the first time, the morphological characteristics and chloroplast genome features of A. guanxianense, and analyzes its relationship with closely related species. This is of significant importance for the classification, phylogeny, and conservation of this narrowly distributed endemic species.