Study On Methane Emission From The Double-Cropping Rice In Hunan Red Soil Under Different Long-Term Fertilizing Systems

It is well known that greenhouse gase emission result in global warming and its reaction product affect human's healthy directly Rice ecosystem is one of major sources of atmospheric methane(CH₄),its influence on greenhouse effect has been given attention by global researchers.Since China is the largest producer of rice grain and double-cropping rice system is typical planting pattern,it plays an important role in the increase of atmospheric methane.To study the effect of long-term fertilization treatment on the seasonal variation of CH₄ emission and the effect of soil physical and chemical property changes result from long-term fertilization on methane emission under different long-term fertilizing systems(including CK,NP,NK,NPK,OM and JF),methane emission fluxes from the double-cropping paddy field in Hunan red soil were monitored by using the method of static chamber-gas chromatographic techniques.This paper discussed the effect of environmental and crop factors on methane emission and produced a forecast model to simulate methane fluxes to estimate contribution of CH₄ emission on GWP under long-term different fertilizing systems.The results showed that:Methane emission from double cropping paddy field under long-term different fertilizing systems exhibited similar seasonal variation.During the early rice growth period, there were three peaks of methane emission at transplanting stage,tillering stage and maturing stage,respectively.CH₄ emission s dominantly occurred at the middle growth stage and methane accumulation emission occupied 70%of total emission.CH₄ emission of the late rice field had only one peak and reached the highest fluxes one week after transplanting,with little emission during the late growth period.CH₄ emission mainly occurred at one month after transplanting of the late rice,during the period of transplanting and tillering,CH₄ accumulation fluxes occupied 60%of total fluxes.Fertilization plays an important role in CH₄ flux.The rank of CH₄ emission in different fertilization treatments in early rice field was OM＞JF＞NPK＞NP＞NK＞CK,but in late rice field it was OM＞JF＞NPK＞NK＞NP＞CK.Methane fluxes in organic manure amendment treatments were significantly higher than other treatments.Methane fluxes in single chemical fertilizer treatments were higher than in unbalanced nutrient treatments.Studies on the effect of different long-term fertilizing systems on soil organic matter,total N and pH showed that,there was a significantly positive correlation between CH₄ fluxes and soil organic matter and total N,and a significantly negative correlation between CH₄ fluxes and soil pH.No significant correlation was found between CH4 flux and soil NH₄⁺-N and NO₃^--N concentration.The environmental factors of different long-term fertilizing systems affecting methane emission from double cropping paddy fields were discussed,including temperature,soil Eh, soil pH,water depth.Under different long-term fertilizing systems,the results showed that, there was a significantly positive correlation between CH₄ emission flux and air temperature in the late rice field and comparatively weak correlation in the early rice field. This trend is same with the effect of soil Eh on CH₄ flux.There was a significant positive correlation between CH₄ flUX and soil temperature in double cropping paddy field.No significant correlation was found between CH₄ flUX and water depth.CH4 flUX peaks mostly appeared around pH 5.0.There was a significant positive correlation between CH₄ flux and soil pH in the late rice field.The crop factors of different long-term fertilizing systems affecting methane emission from double cropping paddy fields were discussed,including plant height,above-ground biomass,root biomass,leaf area,biomass and yields of rice grain.The results showed that, there was a significantly positive correlation between CH₄ flux and plant height, above-ground biomass and root biomass of paddy fields.No significant correlation was found between CH₄ flux and leaf area.The biomass and yields of rice grain were higher with CH₄ accumulation emission fluxes.Based on principal component analysis of the effect factors of CH₄ emission,six forecast equations of different long-term fertilizing systems were established.The simulated greenhouse gases fluxes based on these models roughly corresponded with the measured values in the same order of magnitude and the same dynamic characteristics. Furthermore,the contribution of CH₄ emission under long-term different fertilizing systems on GWP was estimated,its ranks on the time scale of 20 years to 500 years were organic manure amendment treatment＞chemical fertilizer treatment＞single nutrient treatment＞control.