Applying a quantitative pedogenic energy model across a range of environmental gradients

Conceptual energy-based pedogenic models present a framework for quantitatively linking pedon energy throughflow to soil development. In this study, we utilized a quantitative pedogenic energy model (QPEM) based on rates of effective energy and mass transfer (EEMT, kJ m ² yr^-1) to the soil system to predict pedogenesis across a wide range of pedogenic environments. Our objectives were to: (i) derive a global equation for estimating EEMT; (ii) test the QPEM framework at the pedon scale across a series of environmental gradients on igneous rock residuum; and (iii) develop quantitative transfer functions between pedogenic indices and EEMT. We derived a simplified two-dimensional Gaussian expression for estimating EEMT from mean annual temperature (MAT) and mean annual precipitation (MAP) (R² = 0.96, significant at P ≤ 0.001) using a global climate data set. Environmental gradient data indicated significant differences in EEMT between soil orders (i.e., Entisol = 14,586 vs. Ultisol = 36,521 kJ m^-2 yr ¹), whereas neither MAT nor MAP demonstrated significant differences among soil orders. Pedon data from the gradients were used to derive quantitative transfer functions between EEMT and pedogenic indices, including pedon depth, clay content, subsurface chemical index of alteration minus potassium (CIA-K), and the ratio of free Fe oxides to total Fe (Fe _d/Fe_T). Significant linear and nonlinear functions were derived between EEMT and all of the pedogenic indices, whereas no significant functions could be fit between pedogenic indices, MAT, or MAP. The favorable results from this study suggest that the QPEM framework and EEMT may provide a basis for quantitative pedogenic modeling and prediction of soil properties.