[Effects of Biochar Addition Under Different Water Management Conditions on N2O Emission From Paddy Soils in Northern Hainan].

Abstract

Alternating dry and wet conditions affect the main processes of N2O production, such as nitrification and denitrification. Such conditions are very common in tropical rice-growing areas, such as Hainan. As a type of soil amendment, biochar is widely used to improve physical and chemical properties of soil and to reduce soil greenhouse gas emissions. However, there is a lack of existing in-depth research on the emission reductions of biochar when used in tropical soils that undergo frequently alternating dry and wet conditions. In this experiment, typical paddy soil from northern Hainan was used as the test soil, and corn stalk biochar, carbonized under anaerobic conditions at 400℃, was used as the test biochar. This experiment explored the effects of adding biochar on soil greenhouse gas emissions and microbial-related functional genes under different water management conditions. The experiment comprised a 30 d culture, kept in the dark at 25℃, and a total of six treatments:alternating dry-wet conditions without adding biochar (AWD1), alternating dry-wet conditions with 2% biochar (AWD2), alternating dry-wet conditions with 4% biochar (AWD3), continuous flooding without adding biochar (CF1), continuous flooding with 2% biochar (CF2), and continuous flooding with 4% biochar (CF3). The results showed that:① the addition of biochar under different moisture conditions can reduce N2O emissions in acidic paddy soil (P<0.05, the same below), as the total N2O emissions with the AWD3 treatment were 0.43 mg ·kg-1, which indicates an approximate reduction of 68%, relative to the AWD1 treatment; ② Corn stalk biochar can significantly increase the soil pH under different water management conditions. Compared to the no-biochar treatment, the soil pH increased by 0.5 units on average after cultivation with the addition of biochar, and as the soil NH4+-N content increased, it led to a decrease in Eh. ③ Corn stalk biochar significantly reduces the abundance of ammonia oxidizing bacteria and significantly increases the nosZ gene abundance. However, it decreases the ratio of (nirK+nirS)/nosZ, inhibits the nitrification process, and promotes the reduction of N2O in the denitrification process. Thereby, the addition of corn stalk biochar can reduce N2O emissions. These results show that alternating dry-wet conditions, combined with the addition of corn stalk biochar, are beneficial for reducing N2O emissions in paddy soil, which may have further application in the reduction of agricultural greenhouse gas emissions in northern Hainan.