Editing IPCC:AR6/SRCCL/Chapter-5 (section)

==== 5.5.1.1 Greenhouse gas mitigation in croplands and soils ====

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The mitigation potential of agricultural soils, cropland and grazing land management has been the subject of much research and was thoroughly summarised in the AR5 (Smith et al. 2014 <sup>[[#fn:r779|779]]</sup> ) (see also Chapter 2, Section 2.5.1 and Chapter 6, Section 6.3.1). Key mitigation pathways are related to practices reducing nitrous oxide emissions from fertiliser applications, reducing methane emissions from paddy rice, reducing both gases through livestock manure management and applications, and sequestering carbon or reducing its losses, with practices for improving grassland and cropland management identified as the largest mitigation opportunities. Better monitoring reporting and verification (MRV) systems are currently needed for reducing uncertainties and better quantifying the actual mitigation outcomes of these activities.

New work since AR5 has focused on identifying pathways for the reductions of GHG emissions from agriculture to help meet Paris Agreement goals (Paustian et al. 2016 <sup>[[#fn:r800|800]]</sup> and Wollenberg et al. 2016 <sup>[[#fn:r801|801]]</sup> ). Altieri and Nicholls (2017) <sup>[[#fn:r802|802]]</sup> have characterised mitigation potentials from traditional agriculture. Zomer et al. (2017) <sup>[[#fn:r803|803]]</sup> have updated previous estimates of global carbon sequestration potential in cropland soils. Mayer et al. (2018) <sup>[[#fn:r804|804]]</sup> converted soil carbon sequestration potential through agricultural land management into avoided temperature reductions. Fujisaki et al. (2018) identify drivers to increase soil organic carbon in tropical soils. For discussion of integrated practices such as sustainable intensification, conservation agriculture and agroecology, see Section 5.6.4.

Paustian et al. (2016) <sup>[[#fn:r805|805]]</sup> developed a decision-tree for facilitating implementation of mitigation practices on cropland and described the features of key practices. They observed that most individual mitigation practices will have a small effect per unit of land, and hence they need to be combined and applied at large scales for their impact to be significant. Examples included aggregation of cropland practices(for example, organic amendments, improved crop rotations and nutrient management and reduced tillage) and grazing land practices (e.g., grazing management, nutrient and fire management and species introduction) that could increase net soil carbon stocks while reducing emissions of N <sub>2</sub> O and CH <sub>4</sub> .

However, it is well-known that the portion of projected mitigation from soil carbon stock increase (about 90% of the total technical potential) is impermanent. It would be effective for only 20–30 years due to saturation of the soil capacity to sequester carbon, whereas non-CO <sub>2</sub> emission reductions could continue indefinitely. ‘Technical potential’ is the maximum amount of GHG mitigation achievable through technology diffusion.

Biochar application and management towards enhanced root systems are mitigation options that have been highlighted in recent literature (Dooley and Stabinsky 2018 <sup>[[#fn:r806|806]]</sup> ; Hawken 2017 <sup>[[#fn:r807|807]]</sup> ; Paustian et al. 2016 <sup>[[#fn:r808|808]]</sup> ; Woolf et al. 2010 <sup>[[#fn:r809|809]]</sup> and Lenton 2010 <sup>[[#fn:r810|810]]</sup> ).

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