GrassCARB: a tool to identify grassland sites for enhanced soil organic carbon sequestration

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Farmers and their advisers collect and send soil samples for analysis to determine their soil organic matter (SOM) concentration when grassland sites across England are considered for Agri-Environment schemes. To date Natural England have a database of 10 000 soil analyses. The question they often ask is: how much soil organic matter should we expect to find in the soil in a particular field? Currently there is no effective way to answer this question. The aim of this project is to provide advisers from Natural England with a simple tool (GrassCARB) that will provide an estimate of the likely concentration of organic matter in the soil, and an estimate of the associated uncertainty. The GrassCARB model will be developed using a combination of factors which, based on published studies, are known to influence SOM concentrations in grasslands. For example, fields in low-lying, wetter areas typically have more soil organic matter than those in dry parts of the landscape. Also, soils with a larger proportion of clay-sized material tend to have larger concentrations than soils dominated by sandy (sand-sized) material. We can use this and other information from national scale datasets, and that provided with each soil analysis, to improve the predictions of SOM concentration. It is also the case that fields close together typically have more similar properties than those further apart, and so we will use the locations of measurements in the soil database in GrassCARB to improve our local predictions of SOM concentrations.Once the model has been built I will make it accessible to all the farm advisers from Natural England through a simple web-interface which they can access. Each time the model is used, SOM data from new sites can be added to it. I will test the model with a set of farm advisers and provide a set of instructions on its use. GrassCARB could then be used to identify those sites with lower than expected SOM concentrations - these are places where changes in land management could lead to storage of SOM over a few years and therefore contribute to soil carbon sequestration. This is the main objective of the 4 per mille initiative which was supported as part of the Paris climate agreement. I will investigate how GrassCARB relates to other soil initiatives in the UK and internationally.