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United States Department of Agriculture

Agricultural Research Service

Title: Estimating Soil Water Retention in Aggregated Soils Using the 'additivity' Model

Authors
item Rawls, Walter
item Zeiliguer, Anatole - MOSCOW STATE UNIVERSITY
item Feddes, Reinder - WAGENINGEN UNIVERSITY

Submitted to: International Soil Science Society Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 2, 2001
Publication Date: N/A

Technical Abstract: Soil structure has a major effect on soil's ability to retain and to transport water. This is especially true for aggregated soils in which pore space consists of interconnected intra- and inter-aggregate pores with different hydraulic properties. We developed a model to estimate the aggregated soil water retention based on the following assumptions: (a) pore space of an aggregated porous medium can be subdivided into textural and structural quasi-homogeneous pore regions using the values of bulk density and aggregate density;(b) water retention of both regions in the range of soil potentials between-1500 and 0 kPa can be estimated separately using the 'additivity' model;(c) water retention associated with soil textural fractions is measured on samples consisting exclusively of those textural fractions;(d) water retention of aggregate and textural fractions of the same size are assumed to have the same parameters; (e) contributions of textural and structural fractions into the total wate retention are proportional to the volumes of pore subspaces associated with the corresponding fractions. This model was tested with data on water retention of soil cores consisting of aggregates with sizes within narrow ranges of 10.0-7.0 mm, 7.0-5.0 mm, 5.0-3.0 mm, 3.0-2.0 mm, 2.0-1.0 mm, 1.0- 0.5 mm, 0.5-0.25 mm, and <0.25mm. The fractions were obtained for Haplic Chernozem, Podzoluvisol, and Halpic Kastanozem, soils. Results demonstrate the sensitivity of the model aggregates sizes, textural component distribution and aggregate density. Sources of errors are discussed. The extension of 'additivity' model to describe the water retention of aggregated soils by inclusion data of soil aggregate composition is proposed.

Last Modified: 4/16/2014
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