| Methane (CH4) and nitrous oxide (N2O) are two important greenhouse gases. For the reason of human activities the concentrations of CH4 & N2O have been increasing clearly since the industrial revolution. A study indicates that rice paddy fields are one of the most important biology sources of CH4 & N2O. Therefore, in recent years CH4 & N2O emissions from rice fields are given more attentions in the field of global climate change.In this paper an experiment study of CH4 & N2O emissions were carried out by using static chambers in rice-rice rotation system in Qingyuan region of Guangdong province. The experiment data were analyzed. Beside the measurements of CH4 & N2O fluxes, the biogeochemical model-DNDC (Denitrification and Decomposition) was used to simulate CH4 & N2O emissions from the early and later rice. The simulations were compared with observations. On the basis of control-experiment a series of sensitive experiment about the factors affecting CH4 & N2O emissions were conducted. Many reasonable mitigation methods were brought out according to the sensitive experiments. In the end, total amount of CH4 & N2O emissions from rice fields of Guangdong province was preliminary estimated by using DNDC model.The seasonal variation of CH4 emission flux from the early rice fields is three-peak model. Three peak values appear respectively in the phase of regreening, tillering and fruiting. The two peak values in tillering and fruiting term are very obvious. The average CH4 emission flux of the whole early rice growing season is 4.38mg/m2 h In the growing season of the later rice there are three clear CH4 emission peaks. In the beginning (tillering term) of the later rice there is a high emission flux, and in the middle term (tasseling) there is a low methane emission flux. The highest peak value appears in the phase of tillering. The seasonal average CH4 emission flux of the whole later rice is 6.09mg/m2 h Water level and the Eh value have obvious effects on CH4 emission. When the water level is about 2cm, there is often a corresponding peak of CH4 flux. We should avoid shallow water level of about 2cm or choose intermittent irrigation in order to decrease CH4 emission from rice fields. When Eh<-100mv, there are a lot of CHU production from the early rice. The Eh value of later rice(-60mv--150mv) is higher than that of early rice. CH4 emission and the yield have a large difference for different rice cultivar. Jinyou 99 has not only little CH4 emission but also a large yield comparing Qisijian.So, we should choice the rice variety which has little CH4 emission and large yield.The processes of CH4 emission are discussed in detail by comparing the DNDC model outputs with the results from field measurements. Results show that DNDC model can elucidate well the seasonal change of CHU emission and most of CH4 emission pulses in the region. On the basis of these sensitive experiments are carried out. Sensitive experiments indicate that: CD There is a positive correlation between temperature and CH4 & N2O emissions from rice paddy fields. Temperature increasing can arouse CH4 & N2O emissions fluxes increasing. CHU & N2O emissions fluxes increasing can result in the greenhouse effect enhancing. Therefore, the temperature increases. (2) when soil organic carbon increases, CH4 & N2O emissions fluxes will increases. Soil pH has different effect on CHU & N2O emissions. The highest value of CH4 emission appears in the environment of alkalescence, but N2O appears in acidity. Soil pH and soil organic carbon lie on the characteristic of soil. Therefore, reducing CH4 & N2O emissions through controlling SOC and pH is not impossible. (3) In order to reducing CH4 & N2O emissions water management and fertilization are necessary methods. According to the trait of CHU & N2O emissions and sensitive experiments, the following advices are brought out. If soil organic matter is abundance at the beginning, the rice field should be in the station of dry-wet alternating. The mid-season draining which can reduce CH4 emission is use... |
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