Physical soil structure evaluation based on hydraulic energy functions

Qualitative analyses of physical, chemical, or biological variables are difficult and often ambiguous. Soil physical quality (SPQ) indices are not an exception to this rule. There is no unique revealing parameter or index that enables evaluating soil structure. In high-intensity biomass production systems, SPQ indices are useful tools for management decisions because they indicate the sustainability of soil organic matter dynamics, drainage, infiltration, heat transfer, and storage processes. This work examines five energy parameters and two hydraulic energy functions for evaluating physical quality in terrestrial vegetative ecosystems. These indices are based on numerical integration of the soil water retention curve (SWRC) and on soil water content at field capacity, and they manifest the absolute aeration energy, the absolute water retention energy, the relative aeration energy, the relative water retention energy, and the relative air-water energy. This integration technique includes the use of all points of the SWRC. A script for fitting the parameters of the van Genuchten equation and for solving all the presented indices in this work was developed and made available. The energy indices and hydraulic functions were derived and validated for SWRCs, from several German, US, and Brazilian soils under different management, comparing them with other previously published SPQ indices. Our findings reveal that the energy indices and functions can be applied to assess the energy associated with the soil physical structure.