Effects of the lignite bioorganic fertilizer on greenhouse gas emissions and pathways of nitrogen and carbon cycling in saline-sodic farmlands at Northwest China

Mitigating climate change and improving food production are major challenges worldwide. Applications of lignite-based bioorganic products (or lignite-based fertilizer) can improve soil physicochemical properties and crop production in saline-sodic farmland. However, little is known about the effects of lignite bioorganic fertilizer (LBF) on greenhouse gas (GHG) emissions and climate change mitigation. Thus, a two-year field experiment was conducted in saline-sodic farmlands in the upper Yellow River basin, Northwest China. The field experiment comprised six treatments, including a negative control without any organic fertilizer (CK), a positive control amended with sheep manure (FYM), and four treatments amended with 1.5 (LBF1), 3 (LBF2), 4.5 (LBF3), and 7.5 t ha−1 (LBF4) LBF. The results showed that the LBF treatments decreased the emissions of CH4 and CO2 while increasing N2O emissions when the application rate was over 3 t ha−1. Additionally, FYM treatment acted as a CH4 source, while LBF2 and LBF3 treatments were both CH4 sinks. The LBF3 treatment had the highest net ecosystem carbon budget (NECB) and the lowest net ecosystem global warming potential (NGWP), which were 6.04 and 4.82 t ha−1 and -22.09 and −17.39 t ha−1 higher than those of the CK treatment in 2019 and 2020, respectively. Moreover, the net ecosystem economic budget (NEEB) of the LBF2 and LBF3 treatments was higher than that of the other treatments. Compared with the CK treatment, the FYM treatment increased the NCEB and decreased NGWP but it also decreased the NEEB. For nitrogen and carbon cycling, the LBF3 treatment increased almost all gene families involved in nitrogen cycling, except for nirA and hao, while the FYM treatment reduced the nirKS, norBC, nosZ, and hao gene families. The modules for carbohydrate metabolism and methanogenesis were also reduced by the LBF treatments. In conclusion, the LBF2 and LBF3 treatments had higher NECB, NGWP, and NEEB, indicating that the application of lignite bioorganic fertilizer at 3.0–4.5 t ha−1 is appropriate for climate change mitigation in saline-sodic farmlands in the upper Yellow River basin, Northwest China.