[Effect of Different Fertilization Treatments on Methane and Nitrous Oxide Emissions from Rice-Vegetable Rotation in a Tropical Region, China].

The study of the effects of different fertilization treatments on soil methane (CH4) and nitrous oxide (N2O) emissions in rice-vegetable rotation systems is of great significance to supplement the research gap on greenhouse gas emissions in tropical regions of China. In this study, four fertilization treatments were set up during the pepper season:phosphorus and potassium fertilizer application (PK); nitrogen, phosphorus, and potassium (NPK) application; half application of nitrogen, phosphorus, and potassium plus half application of organic fertilizer (NPK+M); and application of organic fertilizer (M). There was no fertilizer application during the following early rice season. The objective of our study was to investigate the rules of CH4 and N2O emissions under different fertilization treatments in the pepper growth season, and the effects of different fertilization treatments in the pepper growth season on rice yield, and CH4 and N2O emissions in the following early rice growth season. The close static chamber-gas chromatography method was applied to determine soil CH4 and N2O emissions. We measured crop yield, estimated global warming potential (GWP), and calculated greenhouse gas emission intensity (GHGI). Our results showed that:① the cumulative CH4 emission under the four fertilization treatments ranged between 0.9 kg·hm-2 to 2.7 kg·hm-2 during the pepper growth season and between 5.5 kg·hm-2 to 8.4 kg·hm-2 during the early rice growth season. Compared with NPK, NPK+M and M reduced the cumulative CH4 emission in the pepper growth season by 35.3% and 7.6%, respectively; however, NPK+M and M increased the cumulative CH4 emission in the early rice season by 37.5% and 55.1%, respectively. There was a significant difference in cumulative CH4 emission between M and NPK in the early rice growth season. ② The cumulative N2O emission under the four fertilization treatments varied from 0.5 kg·hm-2 to 3.0 kg·hm-2 in the pepper growth season and from 0.3 kg·hm-2 to 0.5 kg·hm-2 in the early rice growth season. The cumulative N2O emission was significantly decreased by 33.7% in NPK+M and by 16.0% in M, compared with that in NPK. In the early rice growth season, the cumulative N2O emission was decreased by 23.5% by NPK+M but was increased by 9.1% by M. There was no significant difference in the cumulative N2O emission among the four fertilization treatments. ③ The yields of pepper and early rice under the four fertilization treatments were 3055.6-37722.5 kg·hm-2 and 5850.9-6994.4 kg·hm-2, respectively. Compared with that in NPK, NPK+M and M significantly increased pepper yield. The GWP under the four fertilization treatments in the pepper-early rice rotation system varied from 508.0 kg·hm-2 to 1864.4 kg·hm-2. Compared with NPK, NPK+M significantly decreased GWP by 25.7% and M insignificantly decreased GWP by 5.7%. The pepper growth season with the four fertilization treatments contributed to 69.2%-78.1% of the total GWP, and N2O contributed to 77.3%-85.3% of the total GWP. The GHGI ranged between 0.03 kg·kg-1 and 0.09 kg·kg-1 in the pepper growth season and between 0.04 kg·kg-1 and 0.24 kg·kg-1 in the early rice growth season. Compared with that in NPK, both M and NPK+M significantly reduced the GHGI by 71.5% and 54.7%, respectively, in the pepper growth season. In the early rice season, NPK+M significantly decreased the GHGI by 44.0%, but M non-significantly decreased the GHGI by 20.8%. The peak in N2O emission in the tropical pepper-early rice rotation system appeared after fertilization, and N2O emissions primarily occurred in the pepper growth season. However, CH4 emission was mainly concentrated in the early rice season. Considering the overall enhancing effects on crop yield and mitigation of greenhouse gas emissions, the co-application of chemical and organic fertilizers (NPK+M) can be recommended as an optimal fertilization practice to mitigate greenhouse gas emissions and maintain crop yield in pepper-rice rotation systems of Hainan, China.

[Effects of Water and Fertilization Management on CH4 and N2O Emissions in Double-rice Paddy Fields in Tropical Regions].

Paddy soils are widely considered a main source of methane (CH4) and nitrous oxide (N2O). Comprehensively evaluating CH4 and N2O emissions from double-rice systems in tropical regions with different water irrigation and fertilizer applications is of great significance for addressing greenhouse gas emissions from such systems in China. In this study, eight treatments were evaluated:conventional irrigation-PK fertilizer (D-PK), conventional irrigation-NPK fertilizer (D-NPK), conventional irrigation-NPK+organic fertilizer (D-NPK+M), conventional irrigation-organic fertilizer (D-M), continuous flooding-PK fertilizer (F-PK), continuous flooding-NPK fertilizer (F-NPK), continuous flooding-NPK+organic fertilizer (F-NPK+M), and continuous flooding-organic fertilizer (F-M). CH4 and N2O emissions in double-rice fields in tropical region of china were monitored in situ by closed static chamber-chromatography method and crop yields as well as global warming potential (GWP) and greenhouse gas intensity (GHGI) were determined. The results show that:① The cumulative CH4 emissions from early rice and late rice are 10.3-78.9 kg·hm-2and 84.6-185.5 kg·hm-2, respectively. Compared with F-PK and F-NPK treatments, F-NPK+M and F-M treatments significantly increased the cumulative emissions of CH4 from early rice season. Under the same fertilizer conditions, the cumulative CH4 emissions under continuous flooding condition were significantly higher than that under conventional irrigation condition. Irrigation and fertilization had extremely significant effects on CH4 emission in the early rice season. ② The cumulative N2O emissions across all treatments were 0.18-0.76 kg·hm-2 in early rice season and 0.15-0.58 kg·hm-2in late rice season, respectively. During early rice season, compared with F-PK, F-NPK significantly increased the cumulative N2O emission; however, compared with D-PK, D-NPK, D-NPK+M, and D-M treatments significantly increased the cumulative N2O emissions. Compared with F-PK, other three treatments under continuous flooding condition significantly increased N2O cumulative emission in late rice season; compared with D-PK, D-NPK, and D-M treatment significantly increased the cumulative N2O emission. Irrigation and fertilization had significant impacts on N2O emissions in late rice season, and fertilization had significant impacts on N2O emission in early rice season. ③ Early and late rice yields were 7310.7-9402.4 kg·hm-2 and 3902.8-7354.6 kg·hm-2, respectively. Early rice yields in both F-NPK and F-M treatments were significantly higher than those in F-PK, D-PK, and D-NPK treatments. Compared with PK, the other three fertilization treatments under the same irrigation condition significantly increased late rice yield. The GWP and GHGI in early rice season were 580.8-2818.5 kg·hm-2and 0.08-0.30 kg·kg-1, respectively. There was no significant difference in GWP among four fertilizer treatments under conventional irrigation condition in the early rice season. However, F-NPK+M and F-M treatments had a significant increase in GWP compared with F-PK. The GHGI in F-NPK+M and F-M treatments were significantly higher than that in other treatments. The GWP and GHGI in late rice season were 3091.6-6334.2 kg·hm-2 and 0.50-1.23 kg·kg-1, respectively. Irrigation significantly affected GWP and GHGI in both early and late rice seasons but fertilization had no significant impact on GWP and GHGI in late rice season. ④ Correlation analysis results showed that soil NH4+-N content and soil temperature below 5 cm soil layer had an extremely significant negative correlation with CH4 emissions. Soil pH was extremely significant positive correlated with CH4 emissions but significantly negatively correlated with N2O emission. Soil NH4+-N and NO3--N concentrations were extremely significantly negatively correlated with N2O emission. Given crop yield, GWP, GHGI, and D-NPK+M can be recommended for local water and fertilizer management to reduce greenhouse gas emissions while maintaining rice yields.