Soil fauna to assess soil health and agricultural practices impacts

Soils are changing, whether as a result of natural factors or human activities. Scientists, soil users (farmers, green space managers, foresters, amateur gardeners, etc.) and stakeholders (decentralized government departments, local authorities, chambers of agriculture, farming unions, etc.) need indicators to assess the changes undergone by soils and their effects on their condition and functioning. Parameters such as color, texture, stoniness and depth have enabled farmers to judge the condition of their soils for themselves. Over the last few decades, indicators based on physico-chemical properties have become more widespread. However, these indicators, such as cation exchange capacity, carbon, phosphorus or nitrogen content, etc., provide only indirect information on the biological functioning of soils. Yet the soil is home to an extraordinary diversity of organisms that play a vital role in soil physical organization, plant nutrition and health, and ecosystem functioning in general. Soil fauna, from microscopic protozoa to earthworms and a multitude of insects and invertebrates, represents a very significant part of this biodiversity. It has a strong influence on soil evolution, particularly in terms of its physical and chemical properties, and therefore its fertility and production capacity, acting at very different scales of spatial and temporal organization and functioning. This soil fauna can then also be used as a bioindicator, particularly in an agricultural context. A bioindicator can be defined as a state of biological organization (a part of an organism, an organism or a community of organisms) that provides information on the state and functioning of an ecosystem. Although bioindicators using soil fauna can reflect responses at different scales (molecular, cellular, individual, behavioral, population and community), this article focuses on the community scale.