Consequences of chemical pretreatments in particle size analysis for modelling wind erosion

Abstract

The particle size distribution (PSD) of soil plays a vital role in wind erosion prediction. However, the impact of different pretreatments to remove binding agents for PSD and consequences for wind erosion modelling have not been tested. We collected 90 topsoil samples of Chernozems and Kastanozems from different test sites in Kazakhstan. Soil samples covered typical land-use types and farming methods with calcium carbonate contents reaching from 2.2 to 117.3 g kg−1 and soil organic carbon content from 11.2 to 48.7 g kg−1. Prior to particle size analysis by laser diffraction, samples were chemically pretreated separately and successively with 10% hydrochloric acid (HCl), to dissolve carbonates and 30% hydrogen peroxide (H2O2), to oxidise organic binding material. The HCl pretreatment resulted in incomplete dispersion or even aggregation due to calcium ions released by the dissolution of carbonates, while removing organic matter with H2O2 caused complete sample dispersion. The associated changes in PSD were overall minor, and only a few of our samples were assigned to a different texture class. Obtained PSD data was used to calculate texture-based properties, such as the geometric mean diameter (GMD), with a pedotransfer function. Calculated and measured input data were applied to the Single–event Wind Erosion Evaluation Program (SWEEP) to estimate potential soil losses. As a result, SWEEP's simulations showed substantial variations if the GMD is calculated based on PSD under the influence of different pretreatments. At the same time, there was no variation if the GMD was independently measured. We suggest that for standard particle size analysis of calcareous soils, pretreatment with HCl should be avoided because it might cause misleading results. Considering the variation induced by PSD analysis and resulting potential soil losses, pretreatments for laser diffraction analysis can be omitted for the investigated, silt-dominated Chernozems and Kastanozems if additional texture-based parameters are measured.