Estimating the very fine sand fraction for calculating the soil erodibility K‐factor

Abstract

The K‐factor of the universal soil loss equation is a core component in many erosion models, as a measure of soil erodibility. It can be estimated by a nomograph, where the summed fractions of silt and very fine sand (VFS) are basic inputs. Frequently, only the three broad particle‐size classes of sand, silt, and clay are measured in laboratories; thus, the VFS fraction must be estimated. Three models are currently available for this estimation, namely, (a) the Revised Universal Soil Loss Equation formula, (b) the European Soil Data Centre method, and (c) the Shirazi–Boersma theory, all three use just the sand fraction as explanatory variable. Nevertheless, their accuracy has never been assessed, and this is the main purpose of this study. The data used to test the VFS estimation methods were drawn from the National Cooperative Soil Survey Soil Characterization Database, incorporating data from more than 300,000 soil horizon samples. The test results show a poor performance of the models, all of which were found to be unsuitable for 31.1% of the textural triangle, accounting for 32.3% of the soil samples. Moreover, it is demonstrated that any conceivable model based solely on the broad particle‐size classes would suffer from a high degree of uncertainty. Consequently, the number of explanatory variables should be increased in order to improve the performance of models. An alternative prediction chart is provided for the first approximation of K‐factor, based on the textural triangle.

GUEST EDITORIAL—SPECIAL ISSUE: Mapping and modelling soil erosion to address societal challenges in a changing world

“…A third group of articles presents new methodologies for assessing the impacts of landuse on soil erosion. A statistical‐based method for calculating the soil erodibility factor (K) of RUSLE was developed by Corral‐Pazos‐de‐Provens, Domingo‐Santos, and Rapp‐Arrarás (2018), based on more than 300,000 horizon samples from the United States of America. Mapping and measuring techniques applied by Balaguer‐Puig, Marqués‐Mateu, Lerma, and Ibáñez‐Asensio (2018) and Gudino‐Elizondo et al (2018) present state‐of‐the‐art methods for event‐scale rill and gully erosion analysis, respectively.…”

Spatial Variation Characteristics of Soil Erodibility in the Yingwugou Watershed of the Middle Dan River, China

“…Standard deviation of k-values for the determination of changes in the basin was 0.006; the variation coefficient was 12.367. Many studies have demonstrated that soil erodibility varies with the location, properties of soil, human activities, vegetation types [34][35][36][37]. Therefore, the k-value in the study area was moderately variable because of the differences in soil texture, terrain, vegetation, farming systems, and other factors.…”