Fertilization changes nitrogen and carbon concentrations in saline-alkali paddy soil and their relationship with gas emissions: An analysis from the perspective of functional genes

Abstract

Rice cultivation in saline-alkali land fully utilizes marginal land resources to increase yield, but it brings environmental problems like ammonia (NH₃) and greenhouse gas (GHG) emissions. However, the correlation between soil nitrogen (N) and carbon (C) concentrations and gas emissions, along with the microbial mechanisms, remains unclear in actual saline-alkali rice fields. A 147-day saline-alkali rice field experiment was conducted with five different N-fertilizer applications: NF1 (urea), NF2 (C-based slow-release fertilizer), NF3 (organic-inorganic compound fertilizer), NF4 (microbial fertilizer), and NF5 (inorganic compound fertilizer). The NH₃ volatilization rate had significant positive correlations with carbon dioxide emission flux and soil ammonia-N (p < 0.05). Methane emission flux was significantly (p < 0.05) positively correlated with total organic-C in soil, but was negatively correlated with all N forms. The nirS gene abundance was significantly (p < 0.05) higher than nirK gene by more than 285.65 times, and nitrous oxide emission flux was increased with nirS gene abundance. Two-way analysis of variance indicates that N-fertilizer types can significantly (p < 0.01) affect gas emissions. Weighted average NH₃ volatilization rates were 14.46 % – 27.51 % lower in NF1 and NF3 treatments compared to the other N-fertilizer treatments. The global warming potentials were significantly (p < 0.05) lower in NF1 and NF2 treatments by 17.21 % – 35.93 % compared to CK and the other N-fertilizer treatments. Overall, NH₃ volatilization can be effectively reduced by the NF1 and NF3 applications in saline-alkali rice fields, and NF1 and NF2 are suitable fertilizers to apply for the control of GHG emissions.