Chemical fertility of forest soils: basic concepts

Fertility is a very old concept and many definitions are available in literature. The first edition of the Dictionnaire de l’Academie Francaise in 1694 defines fertility as: “quality of that which is fertile; good farming is that which contributes most to the fertility of the soil” (the capacity of a soil to produce a large harvest). A more accurate definition appeared in the 18th century in the Dictionnaire Critique de la Langue Francaise (1787): “Fertility refers exclusively to soil and plants: Fecundity refers to animals”. At the beginning of the 19th century, the first scientific studies on fertility enabled to characterize soil properties and measure water and mineral uptake in the perspective of increasing crop yields. In this context, fertility referred to the “chemical richness” of a soil in terms of the presence of mineral elements essential to plant growth: both macronutrients (N, P, K, Ca, Mg, S) and micronutrients (Cu, Zn, Fe). The “natural” fertility of the soil is, in this case, defined as the potential of a soil to provide these mineral elements and may be supplemented with an “artificial” fertility related to added fertilizers. Barbier (1955) proposes two visions of fertility; that which can be characterized by i) a production (fertility levels thus depend on the soil properties as well the cultivation techniques), or ii) the capacity to produce (the fertility of a soil determines a potential production capacity without taking into account cultivation techniques). All of these studies in the field of agronomy perfectly illustrate the complexity of the concept of soil fertility.