Studies On Effects Of Different Water And Fertilizer Management On Greenhouse Gas Emissions And Mechanism In Rice-Pepper Rotation System In Tropical Regions,China

Greenhouse gas emissions are widely considered as the main reason for global warming.Rice and vegetable fields are the main sources of methane（CH₄）and Nitrous oxide（N₂O）emissions,respectively.Irrigation and fertilization are two key factors affecting greenhouse gas emissions in agricultural fields.Rice-vegetable rotation is a common agricultural planting mode in Hainan province,China,which is characterized by high multiple cropping index and high fertilization rate.The selection of the typical early rice-late rice-pepper rotation system in Hainan region to study the greenhouse gas emission characteristics of rice-vegetable rotation system under different water and fertilizer management conditions,which is a great significance to supplement the lack of research on greenhouse gas emission of rice-vegetable rotation system in tropical China and guide the agricultural production to reduce weight,stabilize yield and reduce emission.There were eight treatments in rice season which were 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）.There were four treatments in pepper season that are conventional irrigation-PK fertilizer（D-PK）,conventional irrigation-NPK fertilizer（D-NPK）,conventional irrigation-NPK+organic fertilizer（D-NPK+M）and conventional irrigation-organic fertilizer（D-M）.CH₄,N₂O and CO₂emissions in rice-vegetable 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）Compared with the soil background value before planting,soil p H decreased by0.21-0.67 and 0.41-0.83 after rice and pepper harvest,respectively,the decrease of p H obviousiy was in N fertilizer application.After rice-vegetable rotation,soil organic matter increased by 6.3%-38.0%,NPK+M and M treatments significantly increased soil organic matter content.The contents of soil available P and available K decreased by 2.1%-45.0%and 27.3%-65.1%respectively after rice harvest and increased by 182.3%-606.4%and653.3%-869.3%respectively after pepper harvest.（2）The cumulative CH₄emissions were 10.3-78.9 kg·hm^-2,84.6-185.5 kg·hm^-2and1.8-5.4 kg·hm^-2in early rice season,late rice season and pepper season respectively.CH₄emission in continuous flooding treatment was slightly higher than that in conventional irrigation management in late rice season and pepper season,and CH₄emission in organic fertilizer treatment was higher than that in other treatments.CH₄emissions from rice-vegetable rotation system were mainly concentrated in the rice season and higher in the late rice season than in the early rice season.CH₄emissions in early rice season were mainly concentrated in the middle and late planting stage,while CH₄emissions in late rice season were mainly concentrated in the middle and early planting stage.（3）The cumulative N₂O emissions were 0.18-0.76 kg·hm^-2,0.15-0.58 kg·hm^-2and0.32-9.10 kg·hm^-2in early rice season,late rice season and hot pepper season respectively.N₂O emission was higher in conventional irrigation treatment than in continuous flooding treatment.The N₂O emission was higher when chemical nitrogen fertilizer was applied,and the combined application of organic and inorganic fertilizer could reduce the N₂O emission.N₂O emission from rice-vegetable rotation system was mainly concentrated in pepper season.The N₂O emission factor in rice-vegetable rotation system were as follows:early rice season>late rice season>pepper season.N₂O emission in rice season was negatively correlated with AOA,AOB,nirK and nirS gene copy numbers,and positively correlated with nosZ gene copy numbers.N₂O emission in pepper season was negatively correlated with AOA,AOB,nirK and nosZ gene copy numbers,and significantly negatively correlated with nirS gene copy numbers.（4）The irrigation and fertilization significantly affected CH₄emission,N₂O emission,yield,GWP and GHGI.Soil CH₄emission was negatively correlated with N₂O emission.Soil NH₄⁺-N contents were negatively correlated with CH₄emission,and negatively correlated with N₂O emission in rice fields,and positively correlated with N₂O emission in pepper season.Soil NO₃^--N contents were negatively correlated with N₂O emission,negatively correlated with CH₄emission in rice field,and positively correlated with CH₄emission in pepper field.There was a significant negative correlation between CH₄emission and soil temperature at 5 cm in paddy field.Soil p H was significantly positively correlated with CH₄emission,and negatively correlated with N₂O emission.（5）Soil enzyme acitivities were closely related to soil nutrient transformation.Cellulase,urease and hydroxylamine reductase were significantly positively correlated with the contents of soil organic carbon,available phosphorus and available potassium,and significantly negatively correlated with total nitrogen and alkali-hydrolyzable nitrogen.Ammonooxygenase was significantly negatively correlated with the contents of soil organic matter,available phosphorus and available potassium,and positively correlated with alkaline hydrolyzable nitrogen.Soil enzymes indirectly affect soil greenhouse gas emissions by affecting soil nutrients.（6）The yield of early and late rice were 7310-9402 kg·hm^-2and 3902-7354 kg·hm^-2respectively,and the yield of pepper was 2222-4285 kg·hm^-2,There was no significant difference in yield among the treatments except PK treatments.The GWP of early rice season,late rice season and pepper season were 13255-21859 kg·hm^-2,8927-16820kg·hm^-2and 4188-11802 kg·hm^-2,respectively,There was no significant difference in GWP among the treatments except PK treatments.The GHGI were 1.82-2.58 kg·kg^-1,2.14-2.79 kg·kg^-1and 1.88-3.05 kg·kg^-1in early rice season,late rice season and pepper season,respectively,There was no significant difference in Ghgi among all treatments.Given crop yield,GWP and GHGI,conventional irrigation and with the combined applicaiton of chemical and organic fertilizers（D-NPK+M）,conventional irrigation and inorganic fertilizer（D-NPK）and and organic fertilizer（D-NPK+M）are recommended for early rice,late rice and pepper plantation respectively,in tropical regions,Hainan,China...