Ecological quality of soils

For a long time, and until recently, soil has been the domain of pedologists and geologists, and has been defined by these scientific fields. For geologists, soil is an almost insignificant layer on the surface of the earth's crust, ranging from a few centimetres to several metres in thickness. For soil scientists, soil is a three-dimensional matrix (horizontal, vertical and temporal), formed by the assembly of mineral particles (sands, silts, clays) into aggregates of different sizes, shapes and stability. This physical structure makes it highly complex. As such, soil represents the most heterogeneous and structured environmental matrix on our planet.

While ecology is a scientific field that emerged in the 18th century, ecologists began to take a serious interest in soil some sixty years ago. The reasons for this lack of interest lie in the complexity of this matrix and its inaccessibility, but also in the "ordinary" nature of the biodiversity it harbors, which is far less media-friendly than the diversity of emblematic species known to the general public. To all this, we must add that the soil suffers from a somewhat negative cultural image that equates it with a burial ground or waste burial site. However, this renewed interest on the part of ecologists, coupled with major technological and methodological advances in our ability to characterize living organisms, has led to an almost exponential increase in knowledge of soil biology and ecology in recent years. Over the last five years, more than 5,000 articles on soil ecology have been published out of the 15,000 referenced since 1950 (source Web of science, 2019). ).

This accumulation of new knowledge has enabled us to look at soil differently, no longer as a simple inert support for food production or construction, but as an ecosystem that contains almost 1/3 of our planet's biological diversity. What's more, this biodiversity has now been shown to be fundamental to the production of ecosystem services necessary to the development and sustainability of our society. Its importance was reaffirmed in the recent IPBES (Intergovernmental Platform on Biodiversity and Ecosystem Services) report, which highlighted the accelerating rate of species extinction and the urgent need to take action to restore and protect environments, including soil, for the benefit of all (for more information, see https://www.ipbes.net/news/Media-Release-Global-Assessment-Fr ).

In this article, we present a review of current knowledge...