Optimal substitution of inorganic fertilizer with organic amendment sustains rainfed maize production and decreases soil N2O emissions by modifying denitrifying bacterial communities in Northern China

Abstract

Aims

The current study aims to investigate the optimal substitution rate of inorganic fertilizer with organic fertilization practices to reduce N₂O emission without yield penalty in rainfed maize and to explore its denitrifier regulating mechanisms. Methods A field study started in 2016 was continued in 2020 and 2021 by using five organic nitrogen (N) fertilizer substitution treatments, including 0 % (T1), 50.0 % (T2), 37.5 % (T3), 25.0 % (T4), 12.5 % (T5), and no fertilizer control (T6). In addition to these organic fertilizer substitution rates, the maize's remaining N and phosphorus requirements were fulfilled by applying chemical fertilizer up to 200 kg N ha^–1 and 150 kg P₂O₅ ha^–1. Results The application of organic fertilizer in treatments T2, T3, and T4 reduces the total N₂O emission by 38.19 %, 24.48 %, and 22.22 %, respectively, compared with T1. Different substitution rates did not significantly affect biomass but significantly (P<0.05) affected grain yield. Treatments T1, T3, and T5 had the highest grain yield, with no significant difference. The total N and NO₃⁻−N contents were lower, but the soil moisture was higher in treatment T3 compared to T1. Based on the bioinformatics analysis, key OTUs of nifH N fixing bacteria, nirK, and nirS denitrifiers are subordinate to the generic levels of Azospirillum, Cronobacter, Devosia, and Sulfuricaulis, respectively. Conclusions In the current study, a substitution rate of 37.5 % organic fertilizer sustains maize yield by neutralizing soil pH, improving soil moisture, and nitrate-N, and abundance of nifH N fixing bacteria and nirK denitrifiers to reduce N₂O emission in rainfed maize fields in Northern China.