The effectiveness of commercially available wetting agents for combating on-site soil water repellency in sandy soil (original) (raw)
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Do surface active substances from water repellent soils aid wetting?
European Journal of Soil Science, 2007
Soil water repellency is usually unstable, as exemplified by the common method of quantifying repellency degree-the water drop penetration time (WDPT) test. Dynamic penetration and infiltration of water into repellent soils is generally attributed to either reduction of the solid-liquid interfacial energy (g SL) or reduction of the liquid-vapour interfacial energy (g LV), or both. The reduction of g SL can result from conformation changes, hydration, or rearrangement of organic molecules coating soil particle surfaces as a result of contact with water, while the reduction of g LV can result from dissolution of soil-borne surface active organic compounds into the water drop. The purpose of this study was to explicitly test the role of the second mechanism in dynamic wetting processes in unstably repellent soils, by examining the drop penetration time (DPT) of water extracts from repellent soils obtained after varying extraction times and at different soil : water ratios. It was indeed found that soil extracts had lower surface tensions (g LV approx. 51-54 mN m À1) than distilled water. However, DPT of the soil extracts in water repellent soils was generally the same or greater than that of water. Salt solutions with the same electrical conductivity and monovalent/divalent cation ratio as the soil extracts, but lacking surface active organic substances, had the same DPT as did the extracts. In contrast, DPT of ethanol solutions prepared with the same g LV , electrical conductivity, and monovalent/divalent cation ratio as the soil extracts, was much faster. Ethanol solutions are usually used as an agent to reduce g LV and as such, to reduce DPT. It is concluded that the surface-active, soil-derived organic substances in aqueous soil extracts do not contribute to wetting dynamics, and as such, this mechanism for explaining kinetics of water penetration into water repellent soils is rejected. It is also concluded that the rapid penetration of ethanol solutions must be due not only to changes in g LV , but to also to changes in either or both g SL and the solid-vapour interfacial energy (g SV). These results stand in sharp contrast to well-accepted logical paradigms. where g is the interfacial energy. According to the classic Young equation, at y > 90°, the water drop will remain on the surface and the soil will be classified as repellent. In natural
Soil wetting agents influences on soil hydrophobicity : the effects and mechanisms
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Soil water repellency causes non-uniform water infiltration at slow flow rates, which leads to localized dry spot (LDS) on golf course putting greens. Wetting agents are the primary tool used to reduce soil water repellency on golf courses. Field experiments evaluating the efficacy of wetting agents often result in inconsistent conclusions due to variable environmental conditions, management intensity, and level of hydrophobicity. This study used octadecylamine treated sand, which exhibits stable and consistent water repellency, to test the influence of six commercially available wetting agents on water infiltration and sand rewettability. Replicated and repeated experiments were conducted using an infiltration tube system with a 4.4-cm ponding depth (ho). Results showed that Cascade Plus, Tournament-Ready, and Hydro-Wet solutions exhibited significantly faster infiltration with steady flow rates at 35 mm min or more, followed by Revolution and LescoFlo Ultra with a 25 mm min steady...
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In this work, we modelled the response of soil water repellency (SWR) persistence to the decrease in moisture in drying soils, and we explored the implication of soil particle size distribution and specific surface area on the SWR severity and persistence. A new equation for the relationship between SWR persistence and soil moisture (θ) is described in this paper. The persistence of SWR was measured on ten different hydrophobic soils using water drop penetration time (WDPT) at decreasing levels of gravimetric water content. The actual repellency persistence showed a sigmoidal response to soil moisture decrease, where Ra(θ)=Rp/1+eδ(θ−θc). The suggested equation enables one to model the actual SWR persistence (Ra) using θ, the potential repellency (Rp) and two characteristic parameters related to the shape of the response curve. The two parameters are the critical soil moisture θc, where the Ra increase rate reaches its maximum, and the parameter δ affecting the steepness of the curve...
Soil surfactant stops water repellency and preferential flow paths
Soil Use and Management, 2008
This study reports the effects of a soil surfactant on reduction and prevention of water repellency and preferential flow paths in a sandy soil of a golf course fairway, located at Bosch en Duin near Utrecht, the Netherlands. The golf course is constructed on inland dunes composed of fine sand with low organic matter content. The topsoil (0-25 cm) of the fairways exhibits an extremely water repellent behaviour resulting in the development of numerous localized dry spots during dry periods in spring and summer. The influence of surfactant treatments on the wetting of the soil was studied by measuring the volumetric water content with a hand-held Time Domain Reflectometry (TDR) device. Actual water repellency was assessed by placing water drops at regular distances on soil cores taken to a depth of 25 cm with a small (1.5 cm diameter) auger at intervals of 25 cm over a distance of 25 m across the untreated and treated parts of the fairway. Surfactant applications resulted in more homogeneous wetting of the soil profile and elimination of actual water repellency in the fairway soil. Treatments significantly increased water uptake and moisture levels of the soil and prevented the development of preferential flow paths. A visible improvement in turf quality and density was evident on the treated part of the fairway.
Soil Science Society of America Journal, 2012
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Moisture-Dependent Wettability of Artifi cial Hydrophobic Soils and Its Relevance for Soil Water Desorption Curves Soil Physics S oil wettability strongly depends on soil water content. King (1981) indicated that soil hydrophobicity was stable between oven-dry and air-dry water contents, was either unchanged or increased between air-dry water content and wilting point, and fi nally decreased rapidly and became wettable near fi eld capacity. Th is is so-called single peak wettability (de Jonge et al., 1999). de Jonge et al. (1999) and Regalado et al. (2008) reported double peak wettability in the soil water repellency-water content curve, that is, there were two strong water repellent points from saturation to oven-dry state, one in the dry region and the other one at higher water contents. Poulenard et al. (2004) and Lichner et al. (2006) showed that soil hydrophobicity increased with decreasing water content. Experimental data from a natural water repellent soil showed that water repellency decreased with increasing soil water content on heterogeneous soil-water interfaces (Täumer et al., 2005). de Jonge et al. (2007) proposed that water repellency was markedly increased between pF (= log 10 (h), where h is the pressure head expressed in cm) 2.5 and 3 for natural hydrophobic coarse sandy soils. Karunarathna et al. (2010)
Effects of hydrophobic and hydrophilic organic matter on the water repellency of model sandy soils
Soil Science and Plant Nutrition, 2009
Soil water repellency affects the hydrological functions of soil systems. Water repellency is associated with the content and the composition of soil organic matter. In the present study, we examined the effects of hydrophobic and hydrophilic organic matter contents, the hydrophobic ⁄ hydrophilic organic matter ratio and the total organic matter content on water repellency using model sandy soils. Stearic acid and guar gum were used as the hydrophobic and hydrophilic organic compounds, respectively. Water repellency was estimated using the sessile drop method. Hydrophobic organic matter content was found to be the dominant factor affecting soil water repellency. Hydrophilic organic matter was found to increase the contact angle to some extent without the presence of hydrophobic organic matter. With the presence of both hydrophobic and hydrophilic organic matter, the effects of the hydrophilic organic matter content on contact angle were found to be dependent on the hydrophobic organic matter content of the soil. This relationship was explained by the differences in the surface free energies of different organic matter and mineral surfaces. The contact angle increased with increasing hydrophobic ⁄ hydrophilic organic matter ratio when the hydrophilic organic matter content was constant. When the hydrophobic organic matter content was constant, contact angles were roughly comparable, irrespective of the hydrophobic ⁄ hydrophilic organic matter ratio. The contact angles were not comparable at each total organic matter content. Accordingly, the hydrophobic ⁄ hydrophilic organic matter ratio and the total organic matter content in soil may not provide satisfactory information about soil water repellency.
Extent and persistence of water repellency in two Iranian soils
Soil water repellency (SWR) can affect the hydrophysical properties of soils. The objective of this study was to evaluate a new approach, which allows estimating both the extent (the modified soil water repellency index, RIm) and persistence (the water repellency cessation time, WRCT) of water repellency from a single measurement of the combined infiltration of water against time. The measurements were carried out on wettable and water repellent soil samples from 0-60 cm depth. Combined soil water repellency index, RIc, was estimated from all the water and ethanol sorptivity values. The persistence of water repellency in soil aggregates (about 20 mm × 20 mm × 20 mm in size) was measured with the water drop penetration time (WDPT) test on both the field-moist aggregates (actual WDPT, A-WDPT) and aggregates dried at 65-70 • C for 24 hours (potential WDPT, P-WDPT). In comparison with the wettable soil, hydrophysical parameters of the repellent soil were significantly different at the upper part of the profile (0-40 cm, P < 0.01), what can be attributed to the differences in organic matter content in both soils. Maximum organic matter (OM) content of the repellent soil was observed at the depth of 30-40 cm. Curiously, an insignificant difference between the studied soils was found in the saturated hydraulic conductivity, Ks. The mean values of A-WDPT and P-WDPT for water repellent soil were 438-and 106-times greater than those for wettable soil, respectively. All the water and ethanol sorptivities (Sw, Se, Sww, and S wh ) were significantly (P < 0.01) greater in the wettable soil than those in the water repellent soil. The repellency indices RIc and RIm in water repellent soil were about seven-and two-times higher than those in the wettable soil, respectively. Our findings pointed out the proposed method to estimate SWR can be used as a new approach. Considering that the contact angle (CA) of soil and water intrinsically depends on sorptivity state, it is suggested that the relation of CA and RIm is investigated to find reference classes for WRCT and RIm (i.e. WDPT > 5 s) and to classify water repellency states of soils.
Effects of organic compounds, water content and clay on the water repellency of a model sandy soil
Soil water repellency is related to organic matter and clay, and varies non-linearly with soil water content. The purpose of this study is to assess the combined effects of organic compounds, water content and clays on water repellency of a model sandy soil under wetting and drying processes. Hydrophobic stearic acid and hydrophilic glucomannan were used as the organic compounds, and kaolinite or montmorillonite was used as the clay conditioner. Water repellency was estimated using the water drop penetration time test. Repellency did not appear in samples free of stearic acid. Samples containing both stearic acid and glucomannan showed higher repellency compared with samples containing stearic acid alone during the wetting process. Glucomannan with stearic acid increased the critical water content and widened the range of water content at which soils showed slight repellency. During the wetting process, the repellency of most samples increased with increasing water content under relative humidity conditions ranging from 33 to 94%. During the drying process, repellency appeared, reached a maximum and then decreased in samples containing stearic acid. Maximum repellency was observed not at oven-dried but at air-dried water content. Repellency was highly sensitive to water content at around air-dried condition. The effects of organic compounds and clay on the water repellency of sandy soils were negligible in oven-dried condition. Repellency tended to increase with the addition of a small amount of clay (1–2%) as a dry mix during the wetting process. Once wetted, repellency disappeared with the addition of montmorillonite, but not with kaolinite. The higher the kaolinite content, the higher the critical water content.