Study On Methane Uptake By Paddy Soils And Its Controlling Factors

The activity of methane uptake and its controlling factors (temperature, soil moisture et al.) by paddy soils, which were collected from Zhejiang University farm (loamy soil) and Jinhua area(red soil), were investigated under laboratory conditions.The results showed that the soil samples collected from Zhejiang University farm had the abilities of uptaking atmospheric methane slowly, whereas the red soil paddies from Jinhua area had not. There were no uptake of methane after the soil samples were sterilized for both two soils, showing that the uptake processe was a biologically-mediated process entirely.Both two paddy soils could uptake methane when its initial concentration was higher than 10Ml~', and the uptake rate of methane increased with its initial concentration increased. High methane concentration (> 1000Ml籐~') could stimulate the soils which could not uptake atmospheric methane to be able to uptake it.Methane uptake by paddy soils didn't follow the first-order-kinetics, its rate increased in the early stage of incubation, then decreased after reaching its maximum, and the process was similar to pesticide degradation in the soils. Therefore, the model that Liu and Zhang (1987) developed to simulate pesticide degradation in soils could be employed to simulate the process of methane uptake by paddy soils. The goodness of model-fitting showed that the model employed was one of the best to simulate the process of methane uptake by the paddy soils in a closed system.Ranged from 5"C to 50 , the optimum temperatures for methane uptake by two studied paddy soils were about 30.5 for loamy soils (from Zhejiang University farm) and 32.1'C for red paddies (from Jinhua area), respectively. Methane uptake was nearly almost inhibited at temperatures above 50癈 or below 5癈 (10癈).Ranged from 5g*kg~' (air-dried) to TSOg'kg"1, the optimum water content for methane uptake were 306 gg~' for loamy soils and 402 g*kg~l for red soils, respectively, and the air-dried soils showed no capabilities of methane uptake at all. The uptake of methane by the two paddy soils tested decreased with the soil water content decreased while it was below its optimum level, and also decreased with the soil water content increased while it was above its optimum level.The results also showed that the loamy soils had a higher potential for methane uptake than red soils.