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Title: Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal development

Author
item WARRINGTON, D - ARO, ISRAEL
item Iliasson, Amrax
item BHARDWAJ, A - ARO, ISRAEL
item LEVY, G - ARO, ISRAEL

Submitted to: European Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2008
Publication Date: 1/16/2009
Citation: Warrington, D.N., Mamedov, A.I., Bhardwaj, A.K., Levy, G.L. 2009. Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal development. European Journal of Soil Science. 60:84-93. Online doi:10.1111/j.1365-2389.2008.01090.x.

Interpretive Summary: Soil erosion is an undesirable phenomenon from both agricultural and environmental points of view. The smaller soil particles in the eroded material are the major contributor to off-site contamination. These small soil particles contain pesticides, nutrients, etc. Many of the processes which contribute to soil eroding from a site are dependent not only upon the physical soil properties (texture) but also time dependent conditions such as the rate of wetting by rainfall events. The objective of this study was to determine whether the particle size distribution (PSD) of an eroding soil changes with rainfall amount and intensity and whether the changes in the PSD are affected by soil texture and the rate of wetting. The tests were conducted under various simulated rainfall amounts and intensities on two types of soils and the resulting PSD's of the eroding soil were accurately measured with a laser particle analyzer. It was found that generally soil loss resulting from fast wetted soils were greater than from slow wetted samples. The smallest soil particles (clay) usually were higher in concentration relative to the original soil's clay concentration early in the erosion experiments. With increasing rainfall duration, the concentration of clay enrichment decreased. The magnitude of this decrease in concentration and the final clay enrichment depended on both the wetting rate and the soil texture. The information obtained from this study should assist in improving water erosion models by better understanding these physical effects on eroding soil surfaces.

Technical Abstract: Primary particle size distribution (PSD) of eroded sediments can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 x 40 x 4 cm), that had undergone either minimal aggregate slaking (MAS) or severe aggregate slaking (SAS) prior to a 60 mm simulated rainstorm (kinetic energy, 15.9 kilojouls per cubic meter; droplet diameter, 2.97 mm)and collected runoff at regular intervals. The degree of aggregate slaking was controlled by the rate at which soils were wetted to saturation. The PSDs of eroded materials and of parent soils were determined using a laser particle size analyzer. For each soil, PSD frequency curves of eroded sediments and parent soils were generally of a similar shape but most eroded sediments had larger clay contents than their parent soils. In the SAS treatment, cumulative clay enrichment in the eroded materials was inversely related to the parent soil clay content, these being 28.5, 26.6, and 22.8% richer in clay than in their parent soils for the loam, sandy clay and clay, respectively. Generally, total clay loss was greater from soils with SAS than from those with MAS because of erosion rates; however, clay enrichment of sediments, compared with parent soil clay contents, was mostly greater in samples with MAS. Greater clay enrichment took place during the early seal development stage in the loam, but could not readily be associated with specific stages of seal development for the clay. In the sandy clay, the relation between seal development and clay enrichment in the eroded material depended on the initial degree of aggregate slaking. The observed large preferential loss of clay by erosion in cultivated soils re-emphasizes the need to employ erosion control measures.