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Title: HYDROPEDOLOGY AND PEDOTRANSFER FUNCTIONS

Author
item Pachepsky, Yakov
item RAWLS, WALTER
item LIN, HENRY - PENN STATE UNIVERSITY

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2004
Publication Date: 3/10/2005
Citation: Pachepsky, Y.A., Rawls, W.J., Lin, H. 2005. Hydropedology and pedotransfer functions. Geoderma. Vol. 131:308-316.

Interpretive Summary: The emerging transdisciplinary research field of hydropedology attracts a substantial attention because of its promise to bridging pedology and hydrology. Pedotransfer functions (PTFs) emerged as relationships between soil hydraulic parameters and the easier measurable properties usually available from soil survey. One hypothetical explanation of current PTF shortcomings is that PTF inputs, such as soil texture and bulk density, do not describe the structure of pore space per se and, therefore, do not represent relationships between structure and hydrologic function of soil pore space. The objective of this work was to research the applicability of the field pedological soil structure description for revealing relationships between the structure and hydrologic function of soil pore space. We used the data subset on 2200 samples from the US National Soil Characterization database. Classification and regression trees were used to group soil samples according to their water contents at -33 kPa. The structural parameters served as important grouping variables to define groups of soil samples with distinctly different average water retention for the groups. Currently PTFs are developed at the soil core scale and yet they are meant to be used at coarser scales of pedon, hillslope, or watershed. As the PTFs will be developed for soil hydraulic parameters coarser scale, the pedological information may become more valuable because it is collected at those scales.

Technical Abstract: The emerging transdisciplinary research field of hydropedology attracts a substantial attention because of its promise to bridging pedology and hydrology. Pedotransfer functions (PTFs) emerged as relationships between soil hydraulic parameters and the easier measurable properties usually available from soil survey. One hypothetical explanation of current PTF shortcomings is that PTF inputs do not describe the structure of pore space per se and, therefore, do not represent relationships between structure and function of soil pore space. A possible direction for improvement is to look for PTF predictors that are better related to the structure of water-bearing pathways, in particular using the pedological soil structure description. The objective of this work is to present an example of such relationship. We used the subset of 2149 samples from the US National Soil Characterization database that had values of water contents at -33 kPa and bulk densities on clods, structure characterized with grade, size and shape, textural class determined in the field and from lab textural analysis. Classification and regression trees were used to group soil samples according to their water contents at -33 kPa. The clay class was the best grouping parameter in all but loamy sand textural classes. The structural parameters served as important grouping variables to define groups of soil samples with distinctly different average water retention for the groups. As the PTFs will be developed for the coarser scale, the pedological information may become more valuable because it is collected at those scales.