Pedotransfer Functions in Earth System Science: Challenges and Perspectives

Abstract

Soil, through its various functions, plays a vital role in the Earth's ecosystems and provides multiple ecosystem services to humanity. Pedotransfer functions (PTFs) are simple to complex knowledge rules that relate available soil information to soil properties and variables that are needed to parameterize soil processes. In this paper, we review the existing PTFs and document the new generation of PTFs developed in the different disciplines of Earth system science. To meet the methodological challenges for a successful application in Earth system modeling, we emphasize that PTF development has to go hand in hand with suitable extrapolation and upscaling techniques such that the PTFs correctly represent the spatial heterogeneity of soils. PTFs should encompass the variability of the estimated soil property or process, in such a way that the estimation of parameters allows for validation and can also confidently provide for extrapolation and upscaling purposes capturing the spatial variation in soils. Most actively pursued recent developments are related to parameterizations of solute transport, heat exchange, soil respiration, and organic carbon content, root density, and vegetation water uptake. Further challenges are to be addressed in parameterization of soil erosivity and land use change impacts at multiple scales. We argue that a comprehensive set of PTFs can be applied throughout a wide range of disciplines of Earth system science, with emphasis on land surface models. Novel sensing techniques provide a true breakthrough for this, yet further improvements are necessary for methods to deal with uncertainty and to validate applications at global scale.

Using Machine Learning for Prediction of Saturated Hydraulic Conductivity and Its Sensitivity to Soil Structural Perturbations

“…Lack of adequate information that captures the spatial heterogeneity and temporal dynamics of soil hydraulic conductivity and related processes are often identified as critical shortcomings in land surface models that simulate processes across large regions and long periods. In this regard, pedotransfer functions (PTFs)—models that predict soil hydraulic properties from other more easily obtained soil and land characteristics—are valuable tools (Padarian et al, ; Van Looy et al, ). PTFs that consider some soil structural variable can be particularly useful in modeling changes to soil hydraulic properties arising from alterations in soil structure (e.g., soil bulk density).…”

Infiltration from the Pedon to Global Grid Scales: An Overview and Outlook for Land Surface Modeling

“…Currently, PTFs for point‐scale K s are based on relatively small sample volumes. In addition, point‐scale K s shows a high spatial variability as it is not only controlled by textural properties but also by soil structural properties and by the management of soils (Strudley et al, 2008; Van Looy et al, 2017). Some of these aspects are elaborated in more detail below.…”

“…Some of these compacted or extremely dense soil layers are relatively thin and are therefore often neglected in soil maps at coarser scales. Additionally, changes in the saturated hydraulic conductivity due to soil compaction is often not accounted for in PTFs if bulk density is not used for the prediction of the hydraulic parameters (Van Looy et al, 2017). Nevertheless, these layers are of utmost importance because they control the infiltration of water into the soil and its redistribution to greater depth.…”

Leveraging Environmental Research and Observation Networks to Advance Soil Carbon Science

“…NEON will enable robust detection of ecosystem change across edaphic and climatic gradients using standardized observations, sensor measurements, and remote sensing. NEON sites monitor SOM along with continuous soil moisture, temperature, and CO 2 fluxes, offering the ability to link soil physical conditions with C dynamics and test assumed linkages applied in many soil modeling approaches (e.g., pedotransfer functions; Van Looy et al, ). NEON offers a unique airborne platform that will facilitate scaling of ecological and critical zone processes from the pedon to the landscape scale across different eco‐climatic domains.…”