**6.5 Effects of field management (fertilization, water management, farming operations) on methane production**

In the rice paddy filed, organic fertilizer application (such as animal manure, sewage sludge, crop residues) significantly enhances soil nutrient availability, microbial biodiversity and their activity [60]. Consequently, the increased availability of carbon after the application of organic fertilizer increases CH4 emissions and leads to a clear shift in the dominant methanogens in paddy soil [2, 61]. The CH4 emission and soil fertility both were significantly increased by multiyear organic fertilization in paddy soil [62]. The **Figure 6** shows the effects of organic fertilizer on the pathway of CH4 production from rice soil. In the rice production, water management and nitrogen (N) fertilizers are the two main driving factors of greenhouse gas emissions [63]. N application can increase the production of CH4 in paddy fields. The level of the microbial community and NH+4 stimulates the growth and activity of CH4 oxidation bacteria, reducing CH4 efflux [64]. N fertilizers might also affect CH4 production at the level of the microbial community [65]. In terms of water management, controlled irrigation can reduce CH4 production compared to flood irrigation. Flooding conditions in the fields cause limited oxygen and other gasses such as sulfates in that soil environment. This condition promotes methanogenesis activities that release more CH4 emission to the atmosphere [66]. Field burning of agricultural residues also results in release of CH4, nitrous oxide and other minor GHGs. Rice straw is a perspicuous type of organic matter to apply in terms of the carbon cycle in paddy field. The rice straw increased CH4 emission significantly [67].

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**Figure 6.**

*Methane Cycling in Paddy Field: A Global Warming Issue*

**7. Oxidation process of methane in the paddy field soil**

*Effects of organic fertilizer on the pathway of CH4 production from rice soil [12].*

In paddy fields, CH4 production and oxidation happen simultaneously, so it is difficult to directly determine CH4 production and oxidation separately. CH4 oxidation may occur in aerobic and anaerobic ways. Previously CH4 oxidation was usually determined by comparing CH4 fluxes from flooded soils under aerobic and anaerobic incubation conditions [68]. By using this approach, CH4 oxidation accounted for up to >90% of CH4 production [52]. With the development of CH4 oxidation inhibitors and isotopic methods, CH4 oxidation is now widely measured using these approaches and shows relatively low ratio (less than 70%) to CH4 production [69]. Generally, CH4 emission is extremely influenced by the balance between CH4 production and CH4 oxidation in paddy fields [70]. Oxidation of CH4 reduces the emission of CH4 in the soil of rice field to the atmosphere. CH4 is relatively inert in anoxic environments, but is oxidized by methanotrophic bacteria as soon as oxygen becomes available [71]. Aerobic methanotrophic bacteria are present in the oxic surface layer of the submerged paddy soil and in the rhizosphere where oxygen is available in a shallow layer around the rice roots. The most distinctly possible sites for CH4 oxidation in rice fields are the water–soil interface and the rhizosphere. It has been shown that CH4 oxidation is taking place within these zones of the paddy soil so that part of the produced CH4, does not reach the atmosphere [72]. The increase of CH4 production may, in turn, stimulate methanotrophic growth and CH4 oxidation [73], but methanotrophic growth can be limited by low oxygen concentrations [74, 75]. Because larger rice

*DOI: http://dx.doi.org/10.5772/intechopen.94200*

*Methane Cycling in Paddy Field: A Global Warming Issue DOI: http://dx.doi.org/10.5772/intechopen.94200*

**Figure 6.** *Effects of organic fertilizer on the pathway of CH4 production from rice soil [12].*
