Relationships between physico-chemical, biological and functional approaches for soil quality assessment. A case study along a gradient of disturbance

The assessment of the impacts of land management on soil quality is crucial in the current environmental context. Among the many approaches available to assess soil quality, most of studies or monitoring programs consist in the measurement of stock measurements using an additive approach of physical, chemical and biological, parameters. More recently, functional methods have been developed to provide tools which better account the abiotic-biotic interactions. The objective of our study was to evaluate and compare the capacity of physico-chemical, biological and functional parameters to assess the effect of land management on soil quality over a gradient of disturbance based on rubber tree plantations in Chachoengsao province, Thailand. Three sets of indicators were applied based on i. soil physico-chemical analyses, ii. biological analyses, based on soil free-living nematode indices iii. functional analyses, with Biofunctool® indicators linked to three main soil functions (carbon transformation, nutrient cycling, soil structure maintenance). A soil quality index resulting from the aggregation of each set of indicators into a single score showed that functional assessment was the most sensitive to the gradient of disturbance. Co-inertia analysis between sets revealed a significant relationship between functional analysis and both physico-chemical and biological sets of indicators, whereas the two latter were not related. Our results validated the ability of the functional method to better reflect the complexity of the abiotic-biotic interactions of the soil system.