Editing IPCC:AR6/WGIII/Chapter-7 (section)

==== 7.4.3.5 Improve Rice Management ====

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'''Activities, co-benefits, risks and implementation opportunities and barriers.''' Emissions from rice cultivation mainly concern CH 4 associated with anaerobic conditions, although N 2 O emission also occur via nitrification and denitrification processes. Measures to reduce CH 4 and N 2 O emissions include (i) improved water management (e.g., single drainage and multiple drainage practices), (ii) improved residue management, (iii) improved fertiliser application (e.g., using slow release fertiliser and nutrient specific application), and (iv) soil amendments (including biochar and organic amendments) ( [[#Pandey--2014|Pandey et al. 2014]] ; [[#Kim--2017b|Kim et al. 2017b]] ; [[#Yagi--2020|Yagi et al. 2020]] ; [[#Sriphirom--2020|Sriphirom et al. 2020]] ). These measures not only have mitigation potential but can improve water use efficiency, reduce overall water use, enhance drought adaptation and overall system resilience, improve yield, reduce production costs from seed, pesticide, pumping and labour, increase farm income, and promote sustainable development ( [[#Quynh--2015|Quynh and Sander 2015]] ; [[#Yamaguchi--2017|Yamaguchi et al. 2017]] ; [[#Tran--2018|Tran et al. 2018]] ; [[#Sriphirom--2019|Sriphirom et al. 2019]] ). However, in terms of mitigation of CH 4 and N 2 O, antagonistic effects can occur, whereby water management can enhance N 2 O emissions due to creation of alternate wet and dry conditions ( [[#Sriphirom--2019|Sriphirom et al. 2019]] ), with trade-offs between CH 4 and N 2 O during the drying period potentially offsetting some mitigation benefits. Barriers to adoption may include site-specific limitations regarding soil type, percolation and seepage rates or fluctuations in precipitation, water canal or irrigation infrastructure, paddy surface level and rice field size, and social factors including farmer perceptions, pump ownership, and challenges in synchronising water management between neighbours and pumping stations ( [[#Quynh--2015|Quynh and Sander 2015]] ; [[#Yamaguchi--2017|Yamaguchi et al. 2017]] ; [[#Yamaguchi--2019|Yamaguchi et al. 2019]] ).

'''Conclusions from AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL); mitigation potential, costs, and pathways.''' The AR5 outlined emissions from rice cultivation of 0.49–0.723 GtCO 2 -eq yr –1 in 2010 with an average annual growth of 0.4% yr –1 . The SRCCL estimated a global mitigation potential from improved rice cultivation of 0.08–0.87 GtCO 2 -eq yr –1 between 2020 and 2050, with the range representing the difference between technical and economic constraints, types of activities included (e.g., improved water management and straw residue management) and GHGs considered ( [[#Dickie--2014a|Dickie et al. 2014a]] ; [[#Beach--2015|Beach et al. 2015]] ; [[#Paustian--2016|Paustian et al. 2016]] ; [[#Griscom--2017|Griscom et al. 2017]] ; [[#Hawken--2017|Hawken 2017]] ) (SRCCL, Chapter 2).

'''Developments since AR5 and IPCC Special Reports (SR1.5, SROCC and SRCCL).''' Since AR5 and the SRCCL, studies on mitigation have principally focused on water and nutrient management practices with the aim of improving overall sustainability as well as measurements of site-specific emissions to help improve the resolution of regional estimates. Intensity of emissions show considerable spatial and temporal variation, dependent on site specific factors including degradation of soil organic matter, management of water levels in the field, the types and amount of fertilisers applied, rice variety and local cultivation practices. Variation in CH 4 emissions have been found to range from 0.5–41.8 mg m 2 hr –1 in South-East Asia ( [[#Sander--2014|Sander et al. 2014]] ; [[#Chidthaisong--2018|Chidthaisong et al. 2018]] ; [[#Setyanto--2018|Setyanto et al. 2018]] ; [[#Sibayan--2018|Sibayan et al. 2018]] ; J. [[#Wang--2018|Wang et al. 2018]] ; [[#Maneepitak--2019|Maneepitak et al. 2019]] ), 0.5–37.0 mg m 2 hr –1 in Southern and Eastern Asia ( [[#Zhang--2010|Zhang et al. 2010]] ; [[#Wang--2012|Wang et al. 2012]] ; [[#Oo--2018|Oo et al. 2018]] ; J. [[#Wang--2018|Wang et al. 2018]] ; [[#Takakai--2020|Takakai et al. 2020]] ) ''',''' and 0.5–10.4 mg m 2 hr –1 in North America (J. [[#Wang--2018|Wang et al. 2018]] ). Current studies on emissions of N 2 O also showed high variation in the range of 0.13–654 ug/m 2 /hr ( [[#Akiyama--2005|Akiyama et al. 2005]] ; [[#Islam--2018|Islam et al. 2018]] ; [[#Kritee--2018|Kritee et al. 2018]] ; [[#Zschornack--2018|Zschornack et al. 2018]] ; [[#Oo--2018|Oo et al. 2018]] ).

Recent studies on water management have highlighted the potential to mitigate GHG emissions, while also enhancing water use efficiency ( [[#Tran--2018|Tran et al. 2018]] ). A meta-analysis on multiple drainage systems found that Alternative Wetting and Drying (AWD) with irrigation management, can reduce CH 4 emissions by 20–30% and water use by 25.7%, though this resulted in a slight yield reduction (5.4%) ( [[#Carrijo--2017|Carrijo et al. 2017]] ). Other studies have described improved yields associated with AWD ( [[#Tran--2018|Tran et al. 2018]] ). Water management for both single and multiple drainage can (most likely ) reduce methane emissions by about 35% but increase N 2 O emissions by about 20% ( [[#Yagi--2020|Yagi et al. 2020]] ). However, N 2 O emissions occur only under dry conditions, therefore total reduction in terms of net GWP is approximately 30%. Emissions of N 2 O are higher during dry seasons ( [[#Yagi--2020|Yagi et al. 2020]] ) and depend on site specific factors as well as the quantity of fertiliser and organic matter inputs into the paddy rice system. Variability of N 2 O emissions from single and multiple drainage can range from 0.06–33 kg/ha ( [[#Hussain--2015|Hussain et al. 2015]] ; [[#Kritee--2018|Kritee et al. 2018]] ). AWD in Vietnam was found to reduce both CH 4 and N 2 O emissions by 29–30 and 26–27% respectively with the combination of net GWP about 30% as compared to continuous flooding ( [[#Tran--2018|Tran et al. 2018]] ). Overall, greatest average economic mitigation potential (up to USD100 tCO 2 -eq –1 ) between 2020 and 2050 is estimated to be in Asia and the Pacific (147.2 MtCO 2 -eq yr –1 ) followed by Latin America and the Caribbean (8.9 MtCO 2 -eq yr –1 ) using the IPCC AR4 GWP100 value for CH 4 ( [[#Roe--2021|Roe et al. 2021]] ).

'''Critical assessment and conclusion.''' There is ''medium confidence'' that improved rice management has a technical potential of 0.3 (0.1–0.8) GtCO 2 -eq yr –1 between 2020 and 2050, of which 0.2 (0.05–0.3) GtCO 2 -eq yr –1 is available up to USD100 tCO 2 -eq –1 (Figure 7.11). Improving rice cultivation practices will not only reduce GHG emissions, but also improve production sustainability in terms of resource utilisation including water consumption and fertiliser application. However, emission reductions show high variability and are dependent on site specific conditions and cultivation practices.

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