Soil structural vulnerability: Critical review and conceptual development

Soil structure affects a range of soil functions (e.g., water, air, heat, and nutrient transport) and ecosystem services (e.g., production, climate regulation). Agricultural intensification is a dominant factor in global soil structural degradation. Understanding the vulnerability of soils to structural degradation may be important to land use planning and identifying management practices that mitigate the risk of degradation. We review the current methods for assessing soil structural vulnerability and the influencing factors, focussing on soil compaction and aggregate breakdown as two key measures of structural degradation. Methods for assessing risk of soil structural degradation and management practices affecting the risk are also discussed. Critical research gaps are identified, including the lack of studies that demonstrate the link between soil structural vulnerability and loss of soil functions or ecosystem services. Our review of the literature identified that the terms susceptibility, vulnerability, and risk are often used interchangeably. We propose definitions that can be used to distinguish these terms. Soil properties (relatively static), soil wetness, and land use stress (e.g., climate and management practices) are progressively included in the assessments of soil structural susceptibility, vulnerability, and risk. Existing indicators for assessing soil structural vulnerability may not be suitable to predict potential effects on ecosystem services. We highlight that soil structural vulnerability assessments should focus on key soil structural indicators (e.g., pore network-based hydraulic properties) affecting soil functions and ecosystem services. Both the state (i.e., condition) of soil structure and its vulnerability should be included for assessing soil structural degradation. To overcome the limitations of previous assessments, we developed a conceptual model linking soil structural vulnerability assessment to loss of soil functions and ecosystem services. Our review provides insights on assessment metrics and frameworks to develop management practices that improve soil structure and delivery of ecosystem services.