Soil aggregate stability helps construct a stable nitrogen fixation system in lignite-based amendment-driven saline-sodic soil remediation

Abstract

Lignite−based amendments are promising soil conditioners for improving crop yield and nitrogen use efficiency, but there is limited knowledge regarding the potential effects of lignite−based amendment on nitrogen cycling−related microbial communities and their impacts on NH3 volatilization and crop nitrogen uptake in saline−sodic farmland. Here, we investigated the influences of lignite bioorganic fertilizer (LBF) on NH3 volatilization, nitrogen uptake, and microbial communities containing nifH, amoA, and nirS genes through a two−year field experiment. Three treatments were considered in the experiment, i.e., a control treatment with no organic fertilizer application (CK), a farmyard manure treatment (FYM) involving the application of sheep manure at a rate of 21 t ha−1, and a LBF treatment with optimal application rates of 3.0 and 4.5 t ha−1. Results showed that compared with the control treatment (CK), the LBF treatment reduced the total NH3 volatilization by 22.3% and 13.5% in 2019 and 2020, respectively. In addition, the LBF treatment significantly increased sunflower nitrogen uptake by 52.5% and 114.2% in 2019 and 2020, respectively, in comparison with the CK treatment. Moreover, the LBF treatment not only increased the absolute abundance of the nifH gene by 111.5% and altered the core microbes in the nifH−containing community, but it also enhanced the complexity, stability, and cooperation of co−occurrence network of the nifH−containing community, which were positively related to the sunflower nitrogen uptake. The LBF and FYM treatments reduced NH3 volatilization by improving the soil aggregate stability and saturate hydraulic conductivity. These results indicated that LBF may offer a feasible measure to improve the sunflower nitrogen uptake by constructing a complex, stable, and cooperative nitrogen fixation system, without the risk of NH3 volatilization in saline−sodic farmland.