Organic carbon to clay ratios can help to optimize organic amendment use at the farm level

Realistic targets for soil organic carbon (SOC) concentrations are needed, accounting for differences between soils and land uses, to help farmers manage the SOC across their farms. We assess the use of SOC/clay ratio for this purpose using data from the the National Soil Inventory of England and Wales and (b) two long-term experiments under ley-arable rotations on contrasting soils in the East of England. The results showed that normalising for clay concentration provides a more meaningful separation between land uses than changes in SOC alone. The results suggest realistic long-term targets for SOC/clay in arable, ley grass, permanent grass and woodland soils. Given the wide range of soils and land uses across England and Wales in the datasets used to test these targets, they should apply across similar temperate regions globally, and at national to sub-regional scales. We use these results to outline a strategy for organic amendment management at the farm level, enabling optimal use of this scarce resource.