Methane production potential of soil profile in organic paddy field

Abstract

The use of organic fertilizers in the organic paddy/rice field can increase methane (CH<sub>4</sub>) production, which leads to environmental problems. In this study, we aimed to determine the CH<sub>4</sub> production potential (CH<sub>4</sub>-PP) by a soil profile from samples using flood incubation. Soil properties (chemical, physical, and biological) were analyzed from soil samples of three different paddy farming systems (organic, semi-organic, and conventional), whilst soil from teak forest was used as the control. A significant relationship was determined between soil properties and CH<sub>4</sub>-PP. The average amount of CH<sub>4</sub>-PP in the organic rice field profile was the highest among all the samples (1.36 µg CH<sub>4</sub>/kg soil/day). However, the CH<sub>4</sub> oxidation potential (CH<sub>4</sub>-OP) is high as well, as this was a chance of mitigation options should focus on increasing the methanotrophic activity which might reduce CH<sub>4</sub> emissions to the atmosphere. The factor most influencing CH<sub>4</sub>-PP is soil C-organic (C<sub>org</sub>). C<sub>org</sub> and CH<sub>4</sub>-PP of the top soil of organic rice fields were 2.09% and 1.81 µg CH<sub>4</sub>/kg soil/day, respectively. As a consequence, here the mitigation options require more efforts than in the other farming systems. Soil with various amounts of C<sub>org</sub> reached a maximum point of CH<sub>4</sub>-PP at various time after incubation (20, 15, and 10 days for the highest, medium, and the lowest amounts of C<sub>org</sub>, respectively). A high amount of C<sub>org</sub> provided enough C substrate for producing a higher amount of CH<sub>4</sub> and reaching its longer peak production than the low amount of C<sub>org</sub>. These findings also provide guidance that mitigation option reduces CH<sub>4 </sub>emissions from organic rice fields and leads to drainage every10–20 days before reaching the maximum CH<sub>4</sub>-PP.