Soil Health Indicators Used in Temperate Climates for Sustainable Soil Management

Sustainable management of soils is essential for food production and maintaining resilient agricultural systems. The concept of soil health promotes resilience by incorporating the three indicator categories of soil chemistry, biology and physics into decision making, especially in routine intervals for agricultural production. A great number of methodologies and indicators proposed for measuring soil quality exist but only a limited number can reasonably be employed due to constraints on sampling time, labour and costs of analysis. Analysis and testing of indicators can be performed in the field (e.g. soil structure), informally analytically (e.g. aggregate stability test), or formally analytically (e.g. macronutrients, pH). A structured literature review was undertaken to summarise indicators used for mainly agricultural system in a cool temperate climate, similar to that found in Scotland. These were ranked by occurrence: soil organic matter was the most cited indicator (63.3%) followed by soil pH (51.3%), nitrogen, available phosphorus and potassium (45.6, 44.3 and 44.3%, respectively). Though these were the most occurring indicators, they are classified as chemical due to their routine analysis for agriculture, exemplifying the lack of routine use of physical and biological indicators. Further investigation revealed that physical indicators (e.g. aggregate stability tests and penetration resistance) and biological indicators (e.g. earthworm counts, nematode abundance and diversity) have scope for application in routine lab-based analytical testing but also informal home-based testing, with some development required. Generally, biological indicators are currently the fewest and most expensive methods, and development of protocols for routine must be the focus of future research.