Fertilization regimes and the nitrification process in paddy soils: Lessons for agricultural sustainability from a meta-analysis

Abstract

Increasing evidence shows that fertilization plays a key role in improving nitrogen (N) storage and increasing N supply capacity in paddy soils. How fertilizer regimes (N application rate, substitution rate, and fertilizer type) and environmental variables (soil pH and SOM) affect N pools, nitrification processes (abundance of nitrifying microorganisms, nitrification rate), and N losses (NH3 volatilization and N2O emission) in paddy soils is still unclear. Here, we conducted a meta-analysis by compiling a total of 1307 individual experimental observations from 64 peer-reviewed publications to evaluate the impacts of N fertilization with other amendments (manure, biochar, or nitrification inhibitors) on the abovementioned paddy soil N sequestration and turnover. Overall, fertilization increased N pools (total N, NH4+-N, and NO3−-N content) and the abundance of main nitrifying microorganisms (AOA and AOB) by 7.3 % to 51.4 % and 70.3 % to 146.9 % in paddy soil, respectively, while stimulating NH3 volatilization and N2O emissions by 277.3 % and 149.7 %, respectively. The increased N losses following fertilization were positively correlated with the expansion of paddy soil N pools. In particular, the substitution of organic fertilizer for chemical fertilizer at 30 % to 70 % had a better effect on elevating soil N sequestration, while a substitution rate of >70 % reduced N losses. Moreover, the application of biochar and nitrification inhibitors was conducive to increasing total N, NH4+-N, and NH3 volatilization and reducing N2O emissions in fertilized paddy soils. Our findings indicated that fertilization regimes substantially stimulated N pools and N losses in paddy ecosystems. Thus, to avoid environmental and economic consequences, the optimization of N management and adjusting soil properties should be considered to increase N use efficiency and suppress N losses.