Influence of climate, water content and leaching on seasonal variations in potential water repellence (original) (raw)
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Certain Soil Surfactants Could Become a Source of Soil Water Repellency after Repeated Application
Nanomaterials
Repeated application of soil surfactants, or wetting agents, is a common practice for alleviating soil water repellency associated with soil organic coatings. However, wetting agents are organic compounds that may also coat soil particle surfaces and reduce wettability. For this experiment, hydrophobic sands from the field and fresh, wettable sands were collected and treated with either a polyoxyalkylene polymer (PoAP) or alkyl block polymer (ABP) wetting agent, or water only treatments served as a control. Following repeated treatment application and sequential washings, dissolved and particulate organic carbon (OC) were detected in the leachates of both sand systems. The total amount of OC recovered in leachates was 88% or less than the OC introduced by the wetting agents, indicating sorption of wetting agent monomers to soil particle surfaces regardless of soil hydrophobicity status. While ABP treatment did not alter solid phase organic carbon (SOC) in the sands studied, PoAP app...
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.
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
Methods for determining soil water repellency on field-moist samples
Water Resources Research, 2009
1] In this paper we describe a simple and quick method for determining the presence of water repellency in a soil by using a small core sampler (1.5 cm in diameter, 25 cm long) and applying the water drop penetration time (WDPT) test at different depths on the sandy soil cores. Obtained results provide spatial distribution patterns of water repellency in a soil profile, demonstrating seasonal changes in repellency. An advantage of the method is that the soil is not disturbed by the sampling. For assessment of the persistence of water repellency in strongly to extremely water repellent soils, and for determination of the critical soil water contents, the WDPT test and volumetric water content determinations should preferably be performed in the laboratory.
Studies of the molecular basis of soil water repellency
2005
To identify the causes of water repellency in soils, a range of water repellent soils and wettable control soils, sampled from five countries (Australia, Greece, Portugal, The Netherlands, U.K.), were studied. Water repellency was assessed using the water drop penetration time (WDPT) test whilst total organic carbon (TOC) analysis and diffuse reflectance infrared spectroscopy (DRIFT) were used to measure the TOC and aliphatic content respectively in the soils. Water repellency correlated slightly better with aliphatic content than TOC content, although neither correlated well with water repellency. The efficiency of Soxhlet extractions with isopropanol: aqueous ammonia (7:3, v:v) in extracting compounds associated with water repellency was examined. Extraction efficiency was examined by determining: extract mass; severity of water repellency post-extraction; amounts of organic carbon and aliphatic C-H removed; and by assessing the ability of extracts to cause repellency in acid washed sand. Extraction removed repellency completely from 12 of 14 repellent samples and extracts from all soils (including the wettable control samples) were capable of inducing repellency. Samples were rendered wettable regardless of the mass extracted or the quantity of organic carbon removed, suggesting that provided there is some aliphatic material present, the amount is less important than its constitution and/or molecular arrangement. Low polarity solvents caused sample repellency to increase despite the removal of non-polar hydrocarbons, suggesting that compounds such as alkanes are not, in themselves, the main cause of repellency. Kinetics and selectivity of the extraction procedure (using isopropanol: aqueous ammonia) was also examined. Increasing extraction time caused an increase in extract mass and a decrease in soil water repellency. The same compound types were detected by GC-MS in all extracts, but their proportions varied with extraction time. In particular, the removal of alkanes from the soil sample was less rapid than that of more polar compounds.
Surfactant and irrigation effects on wettable soils: runoff, erosion, and water retention responses
Hydrological Processes, 2011
Surfactants are chemical compounds that can change the contact angle of a water drop on solid surfaces and are commonly used to increase infiltration into water repellent soil. Since production fields with water repellent soil often contain areas of wettable soil, surfactants applied to such fields worldwide will likely be applied to wettable soil, with unknown consequences for irrigation-induced erosion, runoff, or soil water relations. We evaluated surfactant and simulated sprinkler irrigation effects on these responses for three wettable, Pacific Northwest soils, Latahco and Rad silt loams, and Quincy sand. Along with an untreated control, we studied three surfactants: an alkyl polyglycoside (APG) in solution at a concentration of 18 g active ingredient (AI) kg 1 , a block copolymer at 26 g kg 1 , and a blend of the two at 43 g kg 1 . From 2005 to 2009 in the laboratory, each surfactant was sprayed at a rate of 46Ð8 l ha 1 onto each soil packed by tamping into 1Ð2-by 1Ð5-m steel boxes. Thereafter, each treated soil was irrigated twice at 88 mm h 1 with surfactant-free well water. After each irrigation, runoff and sediment loss were measured and soil samples were collected. While measured properties differed among soils and irrigations, surfactants had no effect on runoff, sediment loss, splash loss, or tension infiltration, compared to the control. Across all soils, however, the APG increased volumetric water contents by about 3% (significant at p Ä 0Ð08) at matric potentials from 0 to 20 kPa compared to the control. With a decrease in the liquid-solid contact angle on treated soil surfaces, surfactant-free water appeared able to enter, and be retained in pores with diameters ½15 µm. All told, surfactants applied at economic rates to these wettable Pacific Northwest soils posed little risk of increasing either runoff or erosion or harming soil water relations. Moreover, by increasing water retention at high potentials, surfactants applied to wettable soils may allow water containing pesticides or other agricultural chemicals to better penetrate soil pores, thereby increasing the efficacy of the co-applied materials.
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.
European Journal of Soil Science, 2006
Knowledge of soil water repellency distribution, of factors affecting its occurrence and of its hydrological effects stems primarily from regions with a distinct dry season, whereas comparatively little is known about its occurrence in humid temperate regions such as typified by the UK. To address this research gap, we have examined: (i) water repellency persistence (determined by the water drop penetration time method, WDPT) and degree (determined by the critical surface tension method, CST) for soil samples (0-5, 10-15 and 20-25 cm depth) taken from 41 common soil and land-use types in the humid temperate climate of the UK; (ii) the supposed relationship of soil moisture, textural composition and organic matter content with sample repellency; and (iii) the bulk wetting behaviour of undisturbed surface core samples (0-5 cm depth) over a period of up to 1 week. Repellency was found in surface samples of all major soil textural types amongst most permanently vegetated sites, whereas tilled sites were virtually unaffected. Repellency levels reached those of the most severely affected areas elsewhere in the world, decreased in persistence and degree with depth and showed no consistent relationship with soil textural characteristics, organic matter or soil moisture contents, except that above a water content of c. 28% by volume, repellency was absent. Wetting rate assessments of 100 cm 3 intact soil cores using continuous water contact (-20 mm pressure head) over a period of up to 7 days showed that across the whole sample range and irrespective of texture, severe to extreme repellency persistence consistently reduced the maximum water content at any given time to well below that of wettable soils. For slightly to moderately repellent soils the results were more variable and thus hydrological effects of such repellency levels are more difficult to predict. The results imply that: (i) repellency is common for many land-use types with permanent vegetation cover in humid temperate climates irrespective of soil texture; (ii) supposedly influential parameters (texture, organic matter, specific water content) are poor general predictors of water repellency, whereas land use and the moisture content below which repellency can occur seem more reliable; and (iii) infiltration and water storage capacity of very repellent soils are considerably less than for comparable wettable soils.
Geoderma, 2006
The occurrence of water repellent spots can inhibit a homogeneous wetting progress in soil. Although the wettability is an important factor for sorption and transport processes, the knowledge about the reasons for water repellent behavior and its effects on other soil properties is still insufficient. In this study, water repellent and wettable soil samples from two urban locations were compared. It was examined, to which extent differences in the actual water repellency of closely neighboring spots are associated to variable factors like the water content or to stable properties of soil organic matter (SOM). In order to analyze the interrelations between the moisture status and the wettability behavior, soil samples were either subjected to drying-remoistening cycles or preconditioned under various conditions. For the characterization of stable SOM properties, the soil samples were investigated by ESEM (Environmental Scanning Electron Microscope) and FT-IR spectroscopy. Beside the investigation of solid soil samples, selected properties of aqueous soil extracts were measured. The results of this study indicate that the water content is not the only factor responsible for the differences in actual water repellency. For different locations, the wettability behavior probably is based on different mechanisms. For one of the examined sites, differences in actual repellency of closely neighboring samples were interrelated with differences in pH and the ionic strength of the soil solutions. For both locations, amphiphilic substances probably are an important factor of influence for the wettability behavior. Additionally, the results suggest that the time which proceeds after a change of the moisture status in soil is an important factor for water repellency.