Four approaches to setting soil health targets and thresholds in agricultural soils

Soil health is a key concept in worldwide efforts to reverse soil degradation, but to be used as a tool to improve soils, it must be definable at a policy level and quantifiable in some way. Soil indicators can be used to define soil health and quantify the degree to which soils fulfil expected functions. Indicators are assessed using target and/or threshold values, which define achievable levels of the indicators or functions. However, defining robust targets and thresholds is not a trivial task, as they should account for soil, climate, land-use, management, and history, among others. This paper introduces and discusses (through theory and stakeholder feedback) four approaches to setting targets and thresholds: fixed, reference, distribution and relative change. Three approaches (not including relative change) are then illustrated using a case study, located in Denmark, Italy, and France, which highlights key strengths and weaknesses of each approach. Finally, a framework is presented that facilitates both choosing the most appropriate target/threshold method for a given context, and using targets/thresholds to trigger follow-up actions to promote soil health.