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The current state of our soils, as well as the opportunities and vulnerabilities that result from different land management practices, are of particular importance. Quantifying the optimal SOC storage capacity of soils would provide a benchmark to assess human impact on soils and help quantify potential benefits of altered soil management practices. In order to quantify potential SOC losses or sequestration at field, regional, and global scales, measurements for detecting changes in SOC are needed. Such measurements and soil-management best practices should be based on well established and emerging scientific understanding of processes of C stabilization and destabilization over various timescales, soil types, and spatial scales.

In order to understand soil’s contribution to ecosystem services, large-scale modelling and mapping soil properties and processes are needed. This increased global understanding will show how to tackle multiple land-based challenges through agricultural SOC sequestration. This report is detailing the harmonized spatial data sets and their use to create knowledge synthesis on the potential for SOC sequestration in agriculture and on the role of SOC for agricultural productivity, climate change mitigation and adaptation.
The combination of these data will establish the foundation for the knowledge information system (KIS) on SOC in agriculture and will support the development of meta-analyses showing the role of soil carbon for food supply, climate change mitigation and adaptation in different agricultural systems, soil and climate conditions. Moreover, those data sets can further contribute to proposing and designing management practices to improve the status of agricultural soils, stop land degradation, and better target policy interventions.

This work focuses on the following data:

Global maps at 250 m spatial resolution of SOC concentrations and SOC stocks

ISRIC SoilsGrids' SOC stock map, together with SOC concentration map, can be used as inputs for CIRCASA’s knowledge information system to support assessment of SOC sequestration potential with the RothC model. This work describes the tasks and (initial) results undertaken for this activity.

• Investigate if the bulk density dataset could be enlarged through the use of pedotransfer functions (PTF) that model
  and predict bulk density at sampling sites
• Modelling and mapping of global SOC stocks with the SoilGrids framework
• Modelling and mapping of prediction uncertainty at global level

Organic carbon inputs to soils and SOC balance in world arable systems

With the RothC model (used in an inverse mode) the amount of additional C that is necessary for increasing the SOC stock by 4‰ per year during 30 years and assessed the feasibility of the 4‰ target (increase the SOC stocks by 0.4% per year) in terms of available organic carbon flux going back to soils as litter in current cropping systems worldwide. This work has shown important methodological problems when using the RothC model n specific conditions (used on non-mineral-soils, simulating seasonal waterlogging...).

Costing strategies for crop and soil management in world arable systems

Estimated spatially explicit impacts from changing agricultural management practices on soil organic carbon, yields, and production costs. The different data are combined to generate global marginal abatement cost curves (MACCs) for different practices of conservation agriculture. The analysis is done for two crops (corn and wheat) and two management systems (reduced tillage and no-tillage) in comparison to conventional tillage, under rainfed and irrigated conditions.

Relating soil carbon sequestration with land-based challenges

Land use and land cover change has resulted in substantial losses of carbon from soils globally, but credible estimates of how much soil carbon has been lost have been difficult to generate. Using a data-driven statistical model and the History Database of the Global Environment v3.2 historic land-use dataset (Sanderman et al., 2017) estimated that agricultural land uses have resulted in the loss of 133 Pg C from the soil.results emphasize that large co-benefits for multiple land-based challenges can be expected from a strategy of SOC stock restoration focusing on soils that evidence a large historical soil C debt.

SOC Monitoring, Reporting and Verification

Since soil organic carbon content of soils cannot be easily measured, a key barrier to implementing programmes to increase soil organic carbon at large scale, is the need for credible and reliable measurement/monitoring, reporting and verification (MRV) platforms, both for national reporting and for emissions trading. Without such platforms, investments could be considered risky.

We propose a vision for a global framework to assess soil carbon change, based on a combination of mathematical models, spatial data to drive the models, short- and long-term data to evaluate the models, and a network of benchmarking sites to verify estimated changes in the light of the need to provide credible and robust MRV capabilities to support the growing International and National initiatives to increase SOC, such as the International “4p1000” initiative (Chabbi et al., 2017; Rumpel et al., 2019, 2018).

Read the full Deliverable with results: