Exergy assessment of topsoil fertility

Abstract

Soil degradation, affecting around 38% of the world's cropland, threatens the global food supply. Due to the soil's complexity, the measure of soil degradation that involves the loss of soil fertility due to crop system management processes represents an unsolved problem. Exergy is a property with the potential to be used in soil fertility and/or degradation analysis. A methodology to determine the exergy value fenced in a fertile soil due to its inorganic and organic components is established in this study and will be applied to evaluate soil fertility, degradation, and quality. As a first step, the exergy of perfect topsoil with optimum characteristics called "OptSOIL" is determined. The "OptSOIL" is established by agronomic expertise and will allow establishing a general theoretical reference suitable to execute exergy assessments of soils and compare the degradation grade of any soil concerning the best possible. Consequently, we introduce a perfect fertile planetary crust made of “OptNUT” and “OptSOM” invariant and independent of the different local textures, but not independent of their water content and aeration. We call this imaginary crust -copiously fertile- Pristinia as opposed to Thanatia, a dead state referring to abiotic resources. Thus, any real agricultural soil will be an intermediate soil between Pristinia and Thanatia. This idea might serve to quantitatively diagnose an assessment of all the concepts by which soil is degraded. The methodology has been validated through laboratory agronomic tests for different soils, concluding that exergy is a rigorous indicator to measure topsoil fertility.