Controlling variables and emission factors of methane from global rice fields

Abstract

Abstract. Rice cultivation has long been known as one of the dominant anthropogenic contributors to methane (CH 4 ) emissions, yet there is still uncertainty when estimating its emissions at the global or regional scale. An increasing number of rice field measurements have been conducted globally, which allow us to reassess the major variables controlling CH 4 emissions and develop region-and countryspecific emission factors (EFs). The results of our statistical analysis show that the CH 4 flux from rice fields was closely related to organic amendments, the water regime during and before the rice-growing season, soil properties and agroecological conditions. The average CH 4 fluxes from fields with single and multiple drainage were 71 % and 55 % that of continuously flooded rice fields. The CH 4 flux from fields that were flooded in the previous season were 2.4 and 2.7 times that of fields previously drained for a short and long season, respectively. Rice straw applied at 6 t ha −1 in the preseason can decrease CH 4 emissions by half when compared to that applied shortly before rice transplanting. The global default EF was estimated to be 1.19 kg CH 4 ha −1 day −1 with a 95 % confidence interval of 0.80 to 1.76 kg CH 4 ha −1 day −1 for continuously flooded rice fields without organic amendment and with a preseason water status of short drainage. The lower EFs were found in countries from South Asia (0.85 kg CH 4 ha −1 day −1 ) and North America (0.65 kg CH 4 ha −1 day −1 ) relative to other regions, indicative of geographical variations at sub-regional and country levels. In conclusion, these findings can provide a sound basis for developing national inventories and mitigation strategies of CH 4 emission from rice fields.

Soil carbon dioxide venting through rice roots

“…Hence, CO 2 will enter the roots by diffusion and mass flow in the transpiration stream and be vented to the shoots and atmosphere by diffusion through the aerenchyma (Higuchi, Yoda, & Tensho, ). There has been much research on this pathway for CH 4 emission from ricefields (Butterbach‐Bahl, Papen, & Rennenberg, ; Nouchi, Mariko, & Aoki, ; Schütz, Seiler, & Conrad, ; Wang, Akiyama, Yagi, & Yan, ), but CO 2 —which is >20 times less volatile than CH 4 —has received little attention. High CO 2 concentrations and associated HCO 3 − can be toxic to root cells, and therefore, some degree of venting is necessary for healthy growth (Greenway et al, ).…”

Methane Cycling in Paddy Field: A Global Warming Issue

“…The rates of CH 4 production also increased Methane Cycling in Paddy Field: A Global Warming Issue DOI: http://dx.doi.org/10.5772/intechopen.94200 with incubation time, those of roots grown on LL soil after a prolonged lag phase, but in a late phase, arbitrarily chosen after 17-28 days, reached a similar value in all different root samples assayed (Figure 4b) [41]. The root morphophysiological traits were positively and significantly correlated with grain yield, whereas root length, specific root length, root oxidation activity, root total and active absorbing surface area were negatively and significantly correlated with total CH 4 emission [10]. However, rice plants can enhance CH 4 production by providing substrates for methanogenesis through the production of root litter and root exudates that contain carbohydrates and amino acids [50].…”

“…Atmospheric CH 4 mixing ratio has increased by 6.8 ppb y −1 over the last decade [5]. Paddy field is the dominant anthropogenic source of CH 4 [6][7][8][9][10], accounting for approximately 10% of global CH 4 emissions [11]. Emissions of CH 4 from paddy soils are concentrated in irrigated areas; irrigated paddy soils account for 60% of the total rice harvesting area worldwide, but produce 78% of CH 4 emissions in rice-producing areas [12].…”

Soil carbon flux research in the Asian region: Review and future perspectives

“…We removed studies in which the exact sampling year from calculations for each decade that were difficult to obtain. Flux data were derived from Wang et al 2018 . warming.…”