Soil Repellency Research Articles

Soil water repellency: its causes, characteristics and hydro-geomorphological significance

Water repellency (hydrophobicity) of soils is a property with major repercussions for plant growth, surface and subsurface hydrology, and for soil erosion. Important advances have been made since the late 1980s in identifying the range of environments affected by water repellency, its characteristics and its hydro-geomorphological impacts. This review summarises earlier work, but focusses particularly on these recent advances and identifies remaining research gaps. The associations of water repellency with (a) soils other than coarse-textured ones, (b) an expanding list of plant species, and (c) a widening range of climates other than seasonally dry types have been recurrent themes emphasised in recent literature. Nevertheless, knowledge about the extent of water repellency amongst world soils is still comparatively sparse. Its origin by the accumulation of long-chained organic compounds on or between soil particles is now widely accepted, but understanding of their exact chemical composition and means of attachment to particle surfaces remains incomplete. The transient nature of water repellency has been found to be mainly associated with fluctuations in soil moisture, but the precise processes and required conditions for the changes from hydrophobic to hydrophilic and vice versa are so far only poorly understood. Significant advances relating to the hydro-geomorphological impacts of hydrophobic layers have been made since the late 1980s in identifying and separating the various effects of such layers on surface and subsurface water flow. It has become evident that these effects in turn are influenced by variables such as the frequency and effectiveness of flow pathways through hydrophobic layers as well as their position and transitory behaviour. Recent literature has continued to highlight the role of water repellency in promoting soil erosion and it is now recognised that it can promote rainsplash detachment and soil loss not only by water, but also by wind. Major research gaps, however, remain in (a) isolating the erosional impact of water repellency from other factors, and (b) identifying the exact role of, and the interactions between the different variables controlling development and effectiveness of flow pathways through hydrophobic soil. Improved understanding of the effects of soil water repellency will enable its overall role in surface and subsurface hydrological and erosional processes to become more clearly defined.

Development and application of a new sessile drop contact angle method to assess soil water repellency

Existing methods for determining the contact angle as a measure of the water repellency of soils are either indirect, or cumbersome and time-consuming. Our objective was to develop a new method that is simpler than the existing procedures like the capillary rise method and that still yields accurate and reproducible results. To this end, we applied the so-called sessile drop method. To obtain the needed plane sample surface and to reduce geometrical effects, a single layer of air-dry soil particles is sprinkled on double-sided adhesive tape. Eight droplets of deionized water are placed carefully on this horizontal particle layer. Immediately after sample preparation, the contact angle at the three-phase boundary was measured with a goniometer-fitted microscope. In order to test the new method, contact angle measurements were carried out with wettable soil material that was hydrophobized, and with soils showing a wide range of natural water repellency. Both wettable silt and sand were made hydrophobic with Dimethyldichlorosilane and diluted with untreated soil to obtain a defined variation in the solid surface tension. Contact angle measurements showed a nonlinear decrease with increasing amounts of wettable particles in the 40–90° contact angle domain. Generally, the contact angle decrease was predictable and could be described with an empirical model. For volcanic ash soils showing a wide range of repellency, the contact angles of different, narrowly sieved soils fractions (<20μm, 20–38μm, 38–63μm, and 63–100μm) were within the range of 25–110°. The impact of the different sieved soil fractions on the contact angles was found to be small. Measurements performed with independent replicates showed good reproducibility across the whole range of contact angles.

Modification of polyester fabrics by in situ plasma or post‐plasma polymerisation of acrylic acid

In order to increase the hydrophilicities, thereby to impart soil resistance and to improve dyeability, poly(ethylene terephatalate) (polyester) fabrics were treated in low‐temperature plasmas. Two alternative modifications were applied. Fabrics were directly treated in acrylic acid plasma in one investigation, while in the other they were first treated in argon plasma and then immersed in an aqueous acrylic acid bath. The plasma conditions (i.e. exposure time and discharge power) were changed to control the extent of plasma surface modification in the first approach, while the acrylic acid content and the incubation time were changed in the second procedure. The wettability, and therefore the dyeability and soil repellency, of polyester fabrics was significantly improved by both methods. The second method resulted in better dyeability and soil repellency in contrast to lower surface wettability.

Soil Water Repellency: Effects of Water Content, Temperature, and Particle Size

Water repellency (WR) of soils is a common problem in many countries. It can cause a reduction in the rate of water infiltration into soils as well as an unstable water flow within the soil matrix. Water repellency has typically been related to dry soils. We investigated the effect of soil water content and soil pretreatment temperature on the degree of WR in soils and soil size fractions. Water repellency was measured with an ethanol test as the minimum liquid surface tension of an aqueous ethanol droplet that can stay on the soil surface for at least 5 sec. The WR varied greatly with water content. The lowest water contents were achieved by drying soil at different temperatures between 40 and 105°C. Hence, the apparent effect of water content on WR for low water contents may be a combination of a direct water content effect and the effect of pretreatment temperature. High WR was observed at soil water contents up to 0.08 g g-1. Out of 14 soil samples, three did not show WR regardless of temperature treatment or soil water content, four had single peaks in WR as a function of water content, and seven had double peaks in WR, one peak at very low and one peak at higher soil water content. Results from comparison experiments with freeze-dried soil samples implied that the WR peak at lower soil water contents was caused mainly by temperature effects, while the peak at higher soil water contents was related to water content only. In water repellent soil the smaller soil size fractions exhibited the highest degree of water repellency. This can partly be explained by higher organic matter content in the fractions with smaller particle size. As water repellency is dependent on soil water content, performing the WR test solely on dry soils can lead to the wrong classification regarding whether a soil is water repellent or not.

Measurement of Initial Soil-Water Contact Angle of Water Repellent Soils

Water repellent soils are common throughout the world. Water repellency significantly affects infiltration, evaporation, and other water-soil interactions. Various indices, such as the water-solid contact angle (θ), water drop penetration time (WDPT), and 90° surface tension (γND), have been proposed to characterize the degree of water repellency. The water repellency of many soils is not stable, but changes with time after contact with water. No method is available to measure the initial soil-water contact angle. The purpose of this study was to establish a technique to measure the initial soil-water contact angle. We combined previously published theoretical relationships to develop the equations cosθ = [(γND/γw)1/2 − 1] and hp = 2[(γwγND)1/2 − γw]/rρg, where γw is the water surface tension, hp is the breakthrough pressure head, r is the pore radius, ρ is the water density, and g is the gravitational constant. The validity of these relationships was established by treating two sand materials with octadecylamine or solvent extracts from peat moss to create various levels of water repellency. An instrument was developed to measure hp. A linear relationship was found between hp and γ1/2ND, as specified by the equation. The value of r was computed from the slope hp vs. γ1/2ND curve, and this r value was combined with hp in the capillary rise equation to compute cosθ. Good agreement was found between measured and predicted relationships between cosθ and γ1/2ND. The major conclusion is that the value of θ can be determined by measuring γND, which is easily done in the field or laboratory.

Synthesis of fluorine-containing dispersions and an environmental scanning electron microscope analysis of their morphology when applied to cotton fabrics

Environmental scanning electron microscopy (ESEM) was used to monitor surface wetting, adsorption and film formation of aqueous fluorine-containing polymer dispersions on cotton fabrics. Performance of such dispersions, useful as water, oil, and soil repellent finishes, was correlated with homopolymer and copolymer composition. In addition to the commercially available. fluorine-containing dispersions (Dipolir® 480) model dispersions of hydrophobic and amphiphilic fluorine-containing polymers were prepared. Amphiphilic copolymer dispersions were obtained by emulsion copolymerizations of perfluorooctylethylmethacrylate with hydrophobic trimethylsilylmethacrylate, which serves as a precursor of the hydrophilic methacrylic acid and permits random incorporation of methacrylic acid upon insitu hydrolysis of poly(perfluorooctylethylmethacrylate-co-trimethylsilylmethacrylate). While poly(perfluorooctylethylmethacrylate) failed to wet cotton surfaces, incorporation of methacrylic acid promoted both wetting and film formation, as evidenced by film bridges between single fibers.

Toxicity and Repellency of Potting Soil Treated with Bifenthrin and Tefluthrin to Red Imported Fire Ants (Hymenoptera: Formicidae)

The Lc 50 and LC 90 of bifenthrin in potting soil for female alates of the red imported fire ant, Solenopsis invicta Buren, were 1.1 and 5.2 ppm, respectively. For tefluthrin, the Lc 50 and LC 90 were 8.5 and 19.0 ppm, respectively. These results may provide a basis for setting minimum residue levels for the enforcement of quarantine regulations. Pots filled with soil treated with either bifenthrin or tefluthrin at the label rate of 25 ppm were exposed to small colonies of S. invicta without alternative nesting sites. After 48 h, 6% of the bifenthrin-treated pots and 24% of the tefluthrin-treated pots were considered infested under quarantine standards. When exposure was lengthened to 2 wk, all pots were uninfested. Implications for the imported fire ant quarantine program are discussed.

Toxicity of Ionic Thiocyanate-Amended Soil to the Wireworm Limonius californicus (Coleoptera: Elateridae)

Glucosinolates contained in cruciferous plant tissues are hydrolyzed to a variety of biologically active products that are potentially useful for control of soil-borne pests. Isothiocyanates have been shown to be toxic and repellent to wire worms, but little is known about the toxicity of another important glucosinolate degradation product, ionic thiocyanate (SCN). This study reports on bioassays assessing acute and sublethal toxicity and repellency of soil amended with SCN- (supplied as KSCN) to the sugar beet wire worm, Limonius californicus (Mannerheim). Wire worms exposed to 0, 150, and 300 nmol SCN-/g soil for 7 d showed little mortality and no significant differences in mortality among treatment levels. There were no significant differences in mortality among treatments for surviving wire worms maintained in untreated soil with germinating wheat seeds for an additional 35 d, suggesting no sublethal effects from the initial 7-d exposure. An LC50 of 12.36 × 104 nmol SCN-/g of soil, a concentration 600-fold greater than that generated from defatted Brassica napus L. (Brassicaceae) seed meal, was estimated for wire worms exposed to SCN- for 24 h. Laboratory bioassays also indicated that wire worms were not repelled by SCN -treated soil. Thus, at concentrations generated from Brassica tissues, SCN- does not appear to play a major role in reducing wire worm populations.

Toxicity and Repellency of Components in Formulated Termiticides Against Western Subterranean Termites (Isoptera: Rhinotermitidae)

Sands treated with solvent systems used to formulate commercially available termiticides, except for isofenphos, were toxic to western subterranean termites, Recticulitermes hesperus Banks, killing 24–86% after a 24-h exposure to sand air dried for 1 d. After air-drying deposits for 7 d, no solvent systems were still toxic. Irrigating solvent-treated sands with the equivalent of 1.27 cm of rainfall removed all toxicity, except for permethrin and cypermethrin solvent systems. After a second irrigation, all sands treated with the solvent systems were not toxic. Sands treated with solvent systems of all termiticides tested were repellent, except for that of isofenphos, and remained repellent after being air dried for 7 d. The loss of toxicity, but not repellency, after air drying suggests different chemical bases for the two effects or a concentration dependent effect. None of the termiticides tested were repellent after two rinses with water (equivalent of 2.54 cm rainfall). The effects of solvents must be considered when evaluating the repellency and toxicity of soils treated with commercially available termiticides.

Water repellency of sieve fractions from sandy soils and relationships with organic material and soil structure

In soil micromorphology most studies are done with light and electron microscopes on thin sections from selected samples. Information is obtained on nature, distribution, size, form, quantity, etc. of soil constituents and features. Significant data, not readily obtainable from thin sections, can be supplied by using sieve fractions. Amongst such data are specific soil structures (rounded macro-aggregates, micro-aggregates and coated plant fragments) which may, partly or wholly, have been made by soil biota. During the study of water repellency of agricultural and uncultivated sandy soils in the southwestern Netherlands, each sample was sieved, washed and treated with hydrogen peroxide. By measuring the water drop penetration time (WDPT) of a soil sample and of its sieve fractions, and by microscopic examination of soil components and features in each of these, one can indicate which soil constituents are important to the building up of water repellency. The appearance and degree of water repellency are closely related with organic matter (plant fragments, roots, etc.). This organic matter can form a part of soil structures (e.g. micro- and macro-aggregates) or be the principal component itself. Water repellency (WDPT > 5 s), caused by micro-aggregates, can already occur in wettable soils, in the finest (<53 μm) out of ten sieve fractions. Water repellency of the finest sieve fraction did not affect the wettability of the whole sample because the other nine sieve fractions (53 μm to > 2000 μm) were wettable. With increasing water repellency, from slightly to extremely water-repellent soils, more sieve fractions are occupied by soil structures and components that contain water-repellent organic remains, e.g. macro-aggregates, plant fragments and coatings on sand grains. Most of these structures and micro-aggregates have presumably, partly or wholly, been made by soil biota. Conversely, the degree of water repellency of soils can be reduced by decomposition of organic matter and by coating of plant fragments with fine non-water-repellent soil materials; processes in which soil biota are also active.

Modelling water erosion and the impact of water repellency

Three years of weekly measurements of surface runoff and sediment yield from two small plots in a dune terrain along the Dutch coast have been used to model water erosion. The measurements of the third year have been used to validate the regression model based on the first two years of measurements. A major effect on runoff and concomitant erosion is exerted by water repellency of soils, which results in impeded infiltration of dune soils when dry. In a spatial context, water repellency is associated with more runoff and less erosion (per unit area). For a given catchment, however, water repellent conditions generally lead to both more runoff and erosion. This temporal aspect is due to the fact that the degree of water repellency decreases with soil moisture content. Consequently, antecedent rainfall affects the degree of water repellency of dune sands, and taking this into account leads to profoundly distinct predictions of water erosion.

Evaluating UV Absorbers and Antioxidants for Topical Treatment of Upholstery Fabrics

UV absorbers and antioxidants topically applied to upholstery fabrics to reduce fading, separately and in conjunction with soil repellent finish formulations containing UV absorbers, were evaluated in this study. Over fifty upholstery fabrics were initially evaluated and fourteen were selected for further study. The fabrics were then topically treated with commercially available soil repellent finishes (a fluorocarbon and a silicone finish) containing UV absorbers or immersion-treated with one of thirteen UV ab sorbers or antioxidants. Following light exposure, color changes were evaluated visually and instrumentally. The results showed that neither the fluorocarbon nor silicone- based soil repellent finishes containing UV absorbers significantly reduced fading in the upholstery fabrics. Furthermore none of the UV absorbers and antioxidants applied to the upholstery fabrics improved lightfastness properties substantially, so they cannot be recommended as additives to soil repellent finish formulations.

Antisoiling of polyester (PET) by a novel method of plasma treatments and its evaluation by color measurement

AbstractDirect current and radiofrequency plasma treatment of different durations were given to polyester fabric to impart soil resistance. The soil repellency increased with increasing time of treatment. The possible mechanism of soil repellency is outlined. The evaluation of soiling has been made from CIE brightness variable Y with source D65 using Minolta Chromameter Reflectance II. This was well in agreement with the conventional reflectance measurement method using spectrophotometer. The plasma treatment system has the advantage of energy and floor space savings and pollution‐free atmosphere

Laundry parameters as factors in lowering methyl parathion residue in cotton/polyester fabrics.

Cotton/polyester fabrics were contaminated with a 1.25% solution of methyl parathion (MeP) emulsifiable concentrate formulation, then laboratory laundered. The laundering variables were detergent type, concentration, water volume, and mechanical agitation. Specimens were unfinished (UN) and soil repellent finished (SR) fabrics. Heavy duty liquid and phosphate-built powdered detergents were equally effective when used in combination with a prewash product. A negative linear relationship between detergent concentration and MeP residue remaining after laundering was established. An interaction between detergent concentration and fabric finish was observed. Soil repellent finished fabrics required detergent concentrations above the recommended amount for more efficient soil removal. A negative linear relationship between water volume and after-laundering residue was observed. Water volume played a more significant role in pesticide removal than agitation during laundering.

The use of dispersible clays to reduce water repellency of sandy soils

Water-repellency in sandy soils is determined by the amount of hydrophobic organic matter coating the sand particles and the specific surface area of the sands. The hydrophobic state can be simulated by coating hydrophilic sand with cetyl alcohol. Admixture of finely particulate materials with either naturally occurring water-repellent sands or the model cetyl alcohol-coated sand markedly reduced the water-repellency. Dispersible sodic clays were more effective than calcium saturated clays in reducing water-repellency, suggesting that the addition of dispersible, fine-grained illites and kaolinites couid play an important role in the rapid control of water-repellent soils in field situations.

Reaction of fatty acids with 3,3′‐iminobis‐propylamine to produce soil hydrophobic agents

AbstractThe reaction between two moles of fatty acid and one of 3,3′‐iminobis‐propylamine (DPTA) is somewhat analogous to the reaction between fatty acid and diethylenetriamine (DETA) that we had reported previously, but there are significant differences. Conversion to the diamide HN(CH2CH2CH2NHCOR)2 proceeds much more rapidly but less efficiently than does the reaction of fatty acid with DETA. The former diamide is obtained in only about a 70% yield and byproducts are obtained, whereas the reaction with DETA yields the diamide almost quantitatively. Cyclization to the pyrimidine urn:x-wiley:0003021X:media:aocs0744:equation:aocs0744-math-0001is extremely slow and incomplete. The analogous cyclization of α,ω‐diamides of DETA produces high yields of imidazolines. The AOCs wet method for amine titration gave erroneous structural information when the test was applied to the diamides of DPTA, as was the case for the DETA‐diamide. The water repellency of soils treated with a homologous series of fatty iminobis‐propylamine (DPTA)‐diamides was studied, and the following observations were made: 1) the fatty DPTA‐diamides were slightly more hydrophobic than the fatty DETA‐diamides, which we ascribe to the additional methylene groups of the former; 2) hydrophobicity intensified with increasing molecular weight of the saturated fatty acids; and 3) unsaturation, as in the oleic derivative, enhanced hydrophilicity.

Origin and assessment of water repellency of a sandy South Australian soil

The water repellency of a sandy lucerne pasture soil is critically dependent on aqueous extraction and subsequent drying procedures. Freeze-drying converts a very severely water-repellent soil into a readily wettable soil, but subsequent rewetting and oven-drying regenerates water repellency. These changes are ascribed to changes in the molecular conformation of the organic matter. Prolonged shaking detaches organic matter coatings from sand particles and so reduces repellency. Allowing for these effects, it is shown that a sequence of alcohol-benzene extraction, acid leaching, and NaOH extraction removes the major part of the water-repellent substances present.

Soil Repellent and Soil Release Fiber

Soil Repellent and Soil Release Fiber

The effect of slash burning on the water repellency of forest soils at Vancouver, British Columbia

Soil from 10 slash burned and 3 unburned clear-cuts was tested for water repellency by the water drop penetration method and compared with naturally occurring soil water repellency in uncut mature forest. There was no difference in soil water repellency between unburned clear-cuts and the uncut forest control. Soil was more frequently water repellent in slash burned sites (35% of samples) than in the control sites (21% of samples), but differences were significant only for the first 2 years after burning. All humus samples were severely water repellent. At the 0- to 4-cm depth below the humus, burned samples were more frequently repellent than control samples, but there was no difference at the 8- to 10-cm and 15+ cm depths. Water repellence decreased with depth in both burned and control sites.

Relationships between Stand Age and Water Repellency of Chaparral Soils

TERAMURA, ALAN H. (Biol. Dept., Calif. State Univ., Fullerton, CA 92634). Relationships between stand age and water repellency of chaparral soils. Bull. Torrey Bot. Club 107: 42-46. 1980.-Percent incorporated organic matter and Water Drop Penetration Time (WDPT) were determined for soils beneath four southern California chaparral shrub species. Soils beneath Adenostoma fasiculatum H. & A., Arctostaphylos glauca Lindl., Garrya flavescens Wats., and Quercus dumosa Nutt. were collected from 8, 48, and 62-year old stands. Percent incorporated organic matter did not substantially differ among species within a site; however, it differed with respect to stand age. WDPT increased with stand age in all but those soils collected beneath A. glauca. Significant differences in WDPT were found among species only in the oldest stand. The data presented in this paper indicate that the intensity of water repellency varies among species and stand age.