Mineral fertilizer substitution and application of Bacillus velezensis SQR9 reduced nitrogen-oxide emissions in tropical vegetable fields

Abstract

Substituting mineral fertilizer with organic fertilizer and plant growth-promoting microbes (PGPM) inoculation have been well documented as two possible mitigation options for soil nitrogen (N)-oxide (N₂O and NO) emissions in cropland. However, whether the combined application of the two measures can have an additive, antagonistic or no effect in reducing N-oxide emissions is unknown, especially in tropical-intensive vegetable fields. Utilizing a field experiment in typical tropical continuous and rotational vegetable cultivation systems, we examined how organic fertilizer substitution for mineral fertilizer accompanied by Bacillus velezensis SQR9 inoculation influenced N-oxide emissions, vegetable yields, and successive cropping obstacles. Partial substitution with organic fertilizer accompanied by Bacillus velezensis SQR9 inoculation increased vegetable yields based on alleviating the incidence of plant wilt and decreased N-oxide emissions by 11 % compared to the partial substitution and by 35 % compared to conventional mineral fertilizer. These inhibitory effects on soil N-oxide emissions may be mainly attributed to the increased abundance of nosZ genes and the key species enrichment in the bacterial co-occurrence networks related to N₂O reduction (Desulfobacteroata and Verrucomicrobiota), and decreased in nirS genes. The stimulation of vegetable yield and the incidence of plant wilt suppression following organic substitution accompanied by Bacillus velezensis SQR9 inoculation was probably due to the promoted efficiency of N uptake and utilization by vegetables. Although the increased amount of organic fertilizer application was another strategy for stimulating vegetable yields and reducing the incidence of plant wilt, it also obviously stimulated soil N-oxide emissions. Rotational cropping improved vegetable yields while decreasing soil N-oxide emissions by 10 % when compared to the continuous cropping system. Overall, the work suggested that the combined application of organic fertilizers and PGPM may be an environment-friendly strategy for ensuring food security while mitigating N-oxide emissions in tropical-intensive vegetable fields.