Greenhouse Gas Mitigation Potential of Alternate Wetting and Drying for Rice Production at National Scale—A Modeling Case Study for the Philippines

Abstract

Worldwide, rice production contributes about 10% of total greenhouse gas (GHG) emissions from the agricultural sector, mainly due to CH4 emissions from continuously flooded fields. Alternate Wetting and Drying (AWD) is a promising crop technology for mitigating CH4 emissions and reducing the irrigation water currently being applied in many of the world's top rice‐producing countries. However, decreased emissions of CH4 may be partially counterbalanced by increased N2O emissions. In this case study for the Philippines, the national mitigation potential of AWD is explored using the process‐based biogeochemical model LandscapeDNDC. Simulated mean annual CH4 emissions under conventional rice production for the time period 2000–2011 are estimated as 1,180 ± 163 Gg CH4 yr−1. During the cropping season, this is about +16% higher than a former estimate using emission factors. Scenario simulations of nationwide introduction of AWD in irrigated landscapes suggest a considerable decrease in CH4 emissions by −23%, while N2O emissions are only increased by +8%. Irrespective of field management, at national scale, the radiative forcing of irrigated rice production is always dominated by CH4 (>95%). The reduction potential of GHG emissions depends on, for example, number of crops per year, residue management, amount of applied irrigation water, and sand content. Seasonal weather conditions also play an important role since the mitigation potential of AWD is almost double as high in dry as compared to wet seasons. Furthermore, this study demonstrates the importance of temporal continuity, considering off‐season emissions and the long‐term development of GHG emissions across multiple years.

Activity data on crop management define uncertainty of CH4 and N2O emission estimates from rice: A case study of Vietnam

“…Such a huge range of emissions can be explained by the number of days a field is flooded, and, thus, if rice is cropped in one or two or three seasons per year, and on the availability of irrigation water. Similar findings, regarding the range and the driving factors of the variability, were recently reported as well in a study for the Philippines (1–940 kg CH 4 ‐C ha –1 year –1 ; Kraus et al., 2022). As discussed earlier in the Kraus et al.…”

“…As discussed earlier in the Kraus et al. (2022) study, major factors affecting the magnitude of seasonal emissions are mostly related to the stimulating effect of residue incorporation on CH 4 emissions (see also Wassmann et al., [2000]), and the tremendous importance of water management related to fields experiencing multiple drainage events for stimulating root growth, due to shortage in irrigation water or in the frame of AWD management schemes, significantly reducing CH 4 emissions by 35% (Yagi et al., 2020).…”

“…and N 2 O emissions from rice systems at the national scale of Vietnam. et al, 2016), effects of field management such as residue management (Weller et al, 2016), or alternative wetting and drying (AWD) on GHG fluxes (Kraus et al, 2022). The latter study also describes the use of…”

“…(2015) described the development and implementation of a new biogeochemistry module, called MeTr x for rice systems in the LandscapeDNDC framework, and tested its performance for simulating soil N 2 O and CH 4 emissions as well as crop yields for rice–rice and rice–maize systems on the Philippines. Further developments included testing of the model framework for simulating short‐term and decadal changes in soil organic C stocks (Kraus et al., 2016), effects of field management such as residue management (Weller et al., 2016), or alternative wetting and drying (AWD) on GHG fluxes (Kraus et al., 2022). The latter study also describes the use of LandscapeDNDC to assess the mitigation potential of AWD at the scale of the Philippines.…”

“…More recently, toward Tier 3 approach, biogeochemical models have been increasingly used to help fill these data gaps, as once calibrated, they allow for multiannual simulations, and, for example, to test the effects of changing land management on emissions (Fitton et al., 2017; Kraus et al., 2022). In this study, we applied the biogeochemical LandscapeDNDC model (Kraus et al., 2015) to rice systems of Vietnam to (1) calculating a national soil N 2 O and CH 4 inventory, (2) to identify regional hotspots of emissions, and (3) to test a new approach to address and limit uncertainties of the inventory due to uncertainties in water, residue, and fertilizer management.…”