ABSTRACT
Soil health is a cornerstone of ecosystem resilience and sustainability, enabling soils to maintain or recover their capacity to support the increasing demands placed on ecosystems by human activities. This resilience is underpinned by critical soil functions which drive the delivery of vital soil-based ecosystem services. The soil functions commonly considered in soil health assessments are those supporting primary productivity and biomass production, carbon and climate regulation, water regulation and filtration, cycling of nutrients and habitat provision for biodiversity. Soil health indicator selection heretofore has been widely debated, with diverse approaches and viewpoints on how best to capture the health of a given soil. This frequently results in indicator selection that is based on resource constraints or legacy data and does not consider the purpose or scale of monitoring, nor what functions are being considered. This chapter focuses on four essential soil functions (nutrient cycling, water regulation and filtration, carbon and climate regulation, and habitat provision for biodiversity), each represented through comprehensive cognitive models that illustrate the key processes supporting these functions. While these processes can often be measured, this generally requires controlled laboratory conditions, limiting their applicability for monitoring. Therefore, where it is not feasible to measure the processes directly, indicator selection for soil health monitoring should be defined by the soil and landscape parameters that underpin or support the delivery of those processes.
A fundamental aspect of this discussion is the role of soil biodiversity in shaping and sustaining soil health. Soil biological actors do not merely respond to soil conditions but actively drive many of the key processes that define soil health. The interactions between soil biota and physicochemical parameters are a continuous cycle that underpin the many soil processes, thereby directly influencing the functionality of agricultural soils. While factors such as soil type, climate conditions and topography set constraints on soil properties, soil health itself is largely determined by dynamic properties that can be influenced by management decisions, particularly through practices that enhance soil biodiversity and biological activity. Given this perspective, soil biodiversity should be viewed as a foundational layer that supports and regulates soil functions, reinforcing that biological properties are not merely a consequence of soil health but one of its primary determinants and therefore a cornerstone of ecosystem resilience.
The cognitive models presented in this chapter offer a structured way to integrate biodiversity into soil health assessments, alongside chemical, physical and environmental parameters, ensuring that biological indicators are given appropriate weight in evaluation frameworks.
