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。室法通常用于测量气体的生物圈/大气通量，特别是甲烷通量。然而，测量值在空间上差异很大。场地的空间变异性使得很难估计来自一个场地或生态系统的气体通量。微气象方法整合了大表面积，从而减少了空间变异性问题。涡流相关法是估算气体通量最可靠的方法。然而，该方法需要快速测量通量小于5Hz的气体浓度，这对于使用现有传感器的大多数气体来说几乎是不可能的。近年来，从理论上提出了涡流积累法，利用条件气体采样测量标量通量。涡流积累法解决了快速测量气体浓度的需要。在此基础上研制了一套新的系统，对其可靠性进行了检验，并对稻田甲烷通量进行了测量。在提供不同数量秸秆或堆肥的稻田中，水稻植株的生长，土壤气体中Eh甲烷浓度，以及在耕作期间测量的甲烷排放量。水稻分蘖数在6月份随地块的不同有不同的增加速率。在水稻移栽后不久，施用秸秆的地块土壤气体中甲烷浓度均在40%以上。在分蘖期，几乎所有地块的浓度都在30%以上。甲烷排放速率在移栽后不久很低，在最大分蘖期显著增加。结果表明，水稻植株的生长差异影响了稻田土壤环境，同时也影响了甲烷的排放速率。

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.