Methane gas flux measurement and its control in Paddy Field

二氧化碳和/或甲烷的通量被认为对全球环境变化有影响。气室法一般用于测量气体特别是甲烷的生物圈/大气通量。然而，测量值在空间上变化很大。场地的空间变异性使得很难估计来自农田或生态系统的气体通量。微气象学方法整合了大的表面积，从而减少了空间变异性问题。涡动相关法是估算大气通量最可靠的方法。然而，该方法需要快速测量的气体浓度考虑通量短于5 Hz，这几乎是不可能的大多数气体使用现有的传感器。最近，理论上提出了涡动积累方法，用于测量条件气体采样的标量通量。涡流累积法忽略了快速测量气体浓度的需要。我们根据这一理论研制了一套新的系统，并对系统的可靠性进行了检验，在不同的稻田小区中，用不同的稻草或堆肥量，测定了水稻的生长、土壤Eh甲烷浓度和稻田甲烷排放速率。分蘖的水稻植株的数量增加，在6月在不同的速度取决于地块。施用稻草的小区，即使在移栽后不久，土壤气体中的甲烷浓度也超过40%。在分蘖期，几乎所有小区的浓度都在30%以上。移栽后不久甲烷排放速率很低，到最大分蘖期显著增加。说明水稻生长发育的差异影响稻田土壤环境，进而影响甲烷排放速率。

The fluxes of carbon dioxide and/or methane are considered to have influences upon global environmental change. The chamber methods are genrally used to measure the biosphere/atmosphere fluxes of the gases, especially of methane. The measured values, however, widely varies spatially. The site spatial variability makes it difficult to estimate gases fluxes from a field or ecosystem. The micrometeorological methods integrate large surface area thereby reducing the spatial variability problem. The eddy correlation method is most reliable one to estimate tha gas fluxes. However, the method requiers fast measurements of the gas concentration considered for flux shorter than 5Hz, which are almost impossible for most gases using the sensors presently existing. Recently, the eddy accumulation method was theoretically proposed to measure scalar fluxes using conditional gas sampling. The eddy accumulation method by passes the need for fast measurements of gas concentration. We have developed a new system based on this theory, checked its reliability, and measured methane flux in the paddy filed.In various plots of rice paddy fields supplied with different amounts of rice straw or compost, growth of rice plants, soil Eh methane concentrations in soil gas, and methane emission rates measured over the cultivation perriod. The number of tiller of rice plants increased during June at different rates depending on the plots. The methane concentration in the soil gas were more than 40% in the plots applied with rice straw even soon after the transplanting. At the tillering stage the concentrations were more than 30% in almost all the plots. The methane emission rates were very low soon after the transplanting and markedly increased at the maximum tiller stage. It was suggested that the difference of growth of rice plants affects the soil environment of paddy filed and also the methane emission rate.