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Title: EVALUATION OF DIFFERENT REPRESENTATIONS OF THE PARTICLE SIZE DISTRIBUTION TO PREDICT WATER RETENTION

Author
item NEMES, ATTILA - VISITING SCIENTIST
item Rawls, Walter

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2005
Publication Date: 6/9/2006
Citation: Nemes, A., Rawls, W.J. 2006. Evaluation of different representations of the particle size distribution to predict water rentention. Geoderma. 132:47-58.

Interpretive Summary: Detailed particle-size distribution data or parameters derived from it are used in almost all methods to estimate soil hydraulic properties. Most commonly, the particle-size distribution is represented by the sand, silt and clay content of a soil. However, a number of standards exist and are in use internationally to describe particle-size distribution and particle-size classes. Overall, this study could not point out one particular representation of the particle-size distribution that would clearly provide better results in estimating soil hydraulic properties. The results suggest that using interpolated data poses fewer risks than using measured data with the wrong silt/sand boundary.

Technical Abstract: Detailed particle-size distribution data or parameters derived from it are used in almost all pedotransfer functions to estimate soil hydraulic properties. Most commonly, the particle-size distribution is represented by the sand, silt and clay content of a soil. However, a number of standards exist and are in use internationally to describe particle-size distribution and particle-size classes. Additionally, some authors use derived particle-size information, such as the geometric mean diameter and its standard deviation as input to their predictive equations. We compared the usefulness of some of the most common representations of the particle-size distribution in estimating water retention at '10 kPa, '33 kPa and '1500 kPa and the available water content of the soil, using Group Method of Data Handling and data of three databases. We simulated the cutoff limit between silt and sand content being at 20 m, 50 m and at 63 m ' as used in various countries and also used the geometric mean diameter and its standard deviation as predictors. We also examined the effect of using the wrong cutoff limit in the particle-size distribution curve while applying a pedotransfer function. Overall, we could not point out one particular representation of the particle-size distribution that would clearly provide better results in estimating the selected soil hydraulic properties. Results are heterogeneous. Using geometric mean diameter and its standard deviation to represent the entire particle-size distribution curve with two parameters did not result in significantly different estimates of the examined soil hydraulic properties, than models that use distinct particle-size classes as input. We found no evidence suggesting that using interpolated data would reduce the accuracy of the estimation of these soil hydraulic properties. It is not straightforward to pre-determine if using the wrong definition of the silt/sand boundary in the particle-size distribution data will result in significant loss of estimation accuracy or not; therefore, using such data should be avoided. Our study suggests that using interpolated data ' which of course carries a certain magnitude of interpolation error - poses fewer risks while using a pedotransfer function than using measured data with the wrong silt/sand boundary.