Organic carbon ranges in arable soils of England and Wales

Knowledge of the stocks and the potential range of soil organic carbon (SOC) in various land-soil combinations is an important precursor to policies aimed at linking, for example, management of SOC to greenhouse gas emission controls. To investigate the factors controlling the percentage of SOC (%SOC) of soils in England and Wales, we made a multiple regression analysis of data for the 2448 arable and ley-arable sites in the 1980 England and Wales National Soil Inventory (NSI). Clay content, average annual precipitation and depth of topsoil explained 25.5% of the variation in %SOC, when calcareous and peaty soils and those susceptible to flooding were excluded. Using 'robust' statistics, 'indicative SOC management ranges' were estimated for different physiotopes, that is, landscape units for which the environmental factors governing %SOC are similar, namely soil clay content and precipitation. These ranges describe the expected %SOC range for an arable soil in a given physiotope. They have potential to support approximate targets for the %SOC of arable soils and for estimating upper and lower limits for sequestered soil carbon in arable systems.