Degree Of Soil Water Repellency Research Articles

Moisture-dependent Water Repellency of Greenlandic Cultivated Soils

The rapid warming of the Arctic is changing the conditions for agricultural activity in southwest Greenland markedly, which necessitates studies of the physical properties of the soil resource. Soil water repellency (SWR) is a soil property that changes soil functional behaviour across a soil-specific range in water-content (W). Although SWR occurs worldwide, it has not been studied in sub-arctic pasture and grass fields. Thus, the aim was to examine the prevalence of SWR in South Greenland and to establish pedotransfer functions for SWR on soil properties that are faster to measure than SWR, i.e. soil organic fractions, texture and soil water retention. This study included 145 soil samples from 22 sub-arctic agricultural fields distributed across three areas of South Greenland, with broad distributions in texture (clay: 0.017–0.194 kg kg−1) and organic carbon (OC) (0.009–0.241 kg kg−1) contents. The degree of soil water repellency (SWR) as a function of water content (SWR-W curve) was measured from oven-dry conditions to the water-content at which the soil became hydrophilic (WNON), and total SWR (SWRAREA) was calculated as the integrated trapezoidal area (SWRAREA) of the SWR-W curve. A total of 99% and 98% of the soil samples were water-repellent and extremely water repellent at their maximum SWR, respectively. Among the three soil organic fractions (OC, Loss-on-ignition at 550 °C, and 225 °C (LOI550 and LOI225)), LOI550 was the best predictor of SWRAREA and WNON (both with r2 = 0.93). Multiple linear regressions including clay content increased r2adj to 0.92 and 0.95 with OC and LOI550, respectively. The Campbell-Shiozawa (CS) model was fitted to the soil–water retention curves (pF 3.0–6.9), and the inverse slope (−α−1) of the CS model exhibited a high correlation to both SWRAREA (r2adj of 0.87) and WNON (r2adj of 0.93), thus suggesting that soil water retention governs SWR. Lastly, it was shown that the coefficient of proportionality between OC and both SWRAREA and WNON for these sub-arctic soils coincided with pasture soils from New Zealand.

The Relation between Soil Water Repellency and Water Content Can Be Predicted by Vis‐NIR Spectroscopy

The severity of soil water repellency (SWR) varies nonlinearly with water content (w), and it is extremely laborious to obtain complete SWR‐w curves, which are needed to predict the occurrence of SWR. In this study, we combined a three‐parameter moisture‐dependent SWR (MD‐SWR) model with visible near‐infrared spectroscopy (vis‐NIRS) as a fast and novel method to estimate the SWR‐w curve. The method was applied to a data set of SWR‐w curves determined for 71 soil samples (organic carbon [OC] content: 0.021–0.147 kg kg‐1, clay: 0.000–0.520 kg kg‐1). The degree of SWR was measured on air‐dried soil samples (SWRAD) and on soil samples with increasing water contents until the water content at which the soils became wettable (wNON) was reached. The three‐parameter MD‐SWR model was fitted to the measured SWR‐w curves between the water content at air‐dry conditions (wAD) and wNON. The total SWR was then calculated as the trapezoidal integrated area underneath the SWR‐w curves (SWRAREA). Air‐dried soil samples were scanned with a vis‐NIR spectrometer. Each of the three MD‐SWR model parameters was correlated to vis‐NIRS spectra using partial least squares regression. The SWRAREA was predicted using two approaches. For Approach I, the SWRAREA calculated from the MD‐SWR model was predicted with a single vis‐NIRS model. Approach II utilized predicted MD‐SWR model parameter values to obtain vis‐NIRS‐predicted SWR‐w curves between wAD and wNON, and the SWRAREA was calculated from these curves. Results show that vis‐NIRS can predict the shape of the SWR‐w curves as well as the SWRAREA (R2 = 0.58 and 0.56 for Approach I and II, respectively) across a highly variable dataset from a single vis‐NIRS scanning and one SWR measurement at air‐dried conditions.

Relationship between soil properties and enzyme activities with soil water repellency

Soil water repellency (SWR) is a common phenomenon observed throughout the world. It has a significant impact on water infiltration, altering soil hydrology and consequently the soil microbial community and nutrient cycling. Despite the importance of this phenomenon, the processes involved in the development and breakdown of SWR are poorly understood. The importance of the microbial community for SWR is becoming increasingly apparent. In this study, relationships between microbial activities and SWR were investigated by utilising the patchy occurrence of SWR to select both repellent and wettable soils in six locations of the east coast of the North Island of New Zealand. Samples were from directly adjacent locations in mid spring and late summer, and a range of soil physico-chemical properties and enzyme activities were measured. The degree and potential persistence of SWR did not change between the two sampling times, whereas actual persistence of SWR increased. Soil moisture decreased between the two times, and although there was an inverse relationship between moisture and actual persistence of SWR in late summer, unexpectedly, it was a positive relationship in spring. Phosphatase, arylsulfatase and polysaccharide degrading enzyme activities increased with increasing SWR, whereas peroxidase activity decreased. The possible effects of increasing temperature and decreasing water content were modelled, and the observed relationships were strengthened. Arylsulfatase activity was strongly correlated with the degree of SWR, as was extractable organic sulfate, suggesting that the breakdown of sulfate-esters within humic material in soil may be involved in the release and accumulation of SWR-inducing hydrophobic compounds.

Organic carbon content controls the severity of water repellency and the critical moisture level across New Zealand pasture soils

Organic matter can render soil hydrophobic and cause soil water repellency (SWR) which has large implications for agriculture. Consequences such as fingered flow, uneven wetting patterns, and increased overland flow reduce irrigation efficiency and plant nutrient availability. The phenomenon of SWR is a transient soil property depending, inter alia, on soil water content (w). Soil can exhibit SWR from oven-dry w until the critical w where it again becomes fully wettable (wNON). The total SWR can be obtained from the nonlinear SWR-w relationship as the integrated trapezoidal area under the SWR-w curve (SWRAREA). We analyzed 78 soil samples, representing five dominant soil orders in the South Island of New Zealand. The soils had a large range in clay (0.000–0.520 kg kg−1) and organic carbon (OC) content (0.021–0.217 kg kg−1). The degree of SWR was measured on soils at air-dry conditions (SWRAD) and after heat-pretreatment at 60 (SWR60) and 105°C (SWR105). Further, SWR was measured in small w increments above air-dry w until wNON was reached. The SWR-w curves were either unimodal or bimodal, or no SWR occurred. SWRAREA ranged from 0.16 to 26.82 mN m−1 kg kg−1. Among the five soil orders tested, the Podzols exhibited the highest severity in SWR, whereas the Semiarid soils were the least hydrophobic soils. In conclusion, OC was the main factor for controlling the severity of SWR. Though, pH also had minor effects on SWR. Further, an upper limit critical water content was derived from the simple relationship between the wNON and OC, which could be applied to improve irrigation practices of pastoral soils. However, there is a need for further testing on different soils and land uses.

Spatial variation of soil water repellency in a commercial orchard irrigated with treated wastewater

The recognition of treated wastewater (TWW) as an alternative water resource is expanding in areas with a shortage of freshwater (FW). While many studies have been devoted to the effects of long-term irrigation with TWW on soil wettability and spatial flow variations in the soil profile, much less attention has been given to the spatial distribution of soil water repellency in the soil surface layer. This is the objective of the current study. Undisturbed soil samples (5 cm thick) were taken at 15-cm intervals parallel to a drip lateral in two adjacent plots of a commercial citrus orchard in central Israel. Each soil sample was sectioned into five consecutive 1-cm layers for which soil water repellency was determined by water drop penetration time method, and soil organic matter by loss-on-ignition method. Geostatistics and multivariate empirical mode decomposition were used to investigate the overall and scale-specific spatial variation of soil water repellency and its dependence on dripper intervals along the lateral. A high degree of soil water repellency with strong spatial variation was found in the surface soil after 4–6 years of TWW irrigation. Weak to moderate spatial dependence of soil water repellency with maximum autocorrelation distance of around 30 cm was discovered by geostatistical analysis. The spatial distribution of soil water repellency was considered to be greatly affected by the location of the drippers, being higher between adjacent drippers and lower underneath them. This soil water repellency distribution is presumed to result from ongoing lateral displacement of the amphiphilic substances in the TWW toward the outer edge of the wetted plume periphery. Multivariate empirical mode decomposition of the overall spatial variation of soil water repellency yielded three scale-specific variations with corresponding characteristic scales of 30 cm, 110 cm and 200 cm. Most of the soil water repellency variation was separated into the 30 cm and 110 cm spatial scales, which were correlated to processes related to the drippers and trees. Replacing TWW with FW for the reclamation of water-repellent soils partially alleviated the intensity of TWW irrigation-induced soil water repellency. Moreover, an inconsistency between the hot spots of water-repellency development between adjacent drippers and the areas that are effectively ameliorated by FW irrigation below the drippers could be developed and affect the spatial distribution of flow pattern in an a priori unpredictable way.

The effect of pH modification on wetting kinetics of a naturally water‐repellent coniferous forest soil

The interfacial dynamics of soil–water interactions are greatly affected by the hydrophobic properties of organic matter. The causes and underlying mechanisms responsible for the development of soil water repellency (SWR) are still under discussion. Various environmental factors control the appearance and degree of SWR. In addition to water content and temperature, the wetting of soil depends greatly on the physicochemical characteristics of soil surfaces, which in turn depend on pH. In this contribution, we propose a reaction mechanism for the change in SWR that is observed when soil pH is changed. Wetting kinetics were studied by time‐dependent sessile drop measurements (TISED) of the contact angle, the work of spreading and the diameter of the base of the drop as time elapsed under controlled relative humidity. Modification of pH strongly affected the wetting kinetics, suggesting maximum resistance to wetting at the control pH (3.6), with decreased resistance to wetting as pH was changed in either direction. The enhancement in wetting kinetics by the modification of soil pH can be attributed to the chemical modification in organic materials that coat the soil particles. This conclusion is based on the magnitude of activation energy associated with the spreading process. The combined effect of pH and temperature on the wetting kinetics, together with the compensation effect seen between the logarithmic pre‐exponential factor and activation energy, suggests acid–base catalysed hydrolysis–condensation reactions are the dominant processes responsible for the chemical nature of SWR.HighlightsHow does the modification of pH affect soil wetting mechanisms? The dynamic sessile drop method was used to measure the wetting activation energy. Modification of soil pH decreases resistance to wetting and increases activation energy of wetting. Acid or base catalysed hydrolysis reactions increase chemical sorption sites for water molecules in soil.

Effect of Soil Water Repellency on Energy Partitioning Between Soil and Atmosphere: A Conceptual Approach

Water repellency (WR) is a phenomenon known from many soils around the world and can occur in arid as well as in humid climates; few studies, however, have examined the effect of soil WR on the soil-plant-atmosphere energy balance. The aim of our study was to estimate the effects of soil WR on the calculated soil-atmosphere energy balance, using a solely model-based approach. We made out evapotranspiration to have the largest influence on the energy balance; therefore the effect of WR on actual evapotranspiration was assessed. To achieve this we used climate data and measured soil hydraulic properties of a potentially water-repellent sandy soil from a site near Berlin, Germany. A numerical 1D soil water balance model in which WR was incorporated in a straightforward way was applied, using the effective cross section concept. Simulations were carried out with vegetated soil and bare soil. The simulation results showed a reduction in evapotranspiration of 30–300 mm year−1 (9%–76%) at different degrees of WR compared to completely wettable soil, depending on the severity degree of soil WR. The energy that is not being transported away by water vapor (i.e., due to reduced evapotranspiration) had to be transformed into other parts of the energy balance and thus would influence the local climate.

INFLUENCE OF A SINGLE SOIL SURFACTANT APPLICATION ON POTATO RIDGE MOISTURE DYNAMICS AND CROP YIELD IN A WATER REPELLENT SANDY SOIL

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Environmental, Edaphic, and Genetic Factors Affecting Plants, Seeds and Turfgrass INFLUENCE OF A SINGLE SOIL SURFACTANT APPLICATION ON POTATO RIDGE MOISTURE DYNAMICS AND CROP YIELD IN A WATER REPELLENT SANDY SOIL

Soil water repellency in rangelands of Extremadura (Spain) and its relationship with land management

Abstract Soil water repellency reduces infiltration capacity, enhancing overland flow and even runoff production, and may produce patchiness in water infiltration at the hillslope scale. Knowledge about hydrophobicity in rangelands of Mediterranean type climate and its relation with vegetation cover and land management is sparse. The objectives of the present work are to determine the degree and spatial occurrence of soil water repellency and to define its relationship with site characteristics, such as soil, vegetation and land management in rangelands of SW Spain. Field work was conducted in September 2009 in 22 environmental units belonging to 10 farms, distributed throughout the region of Extremadura. The Molarity of an Ethanol Droplet (MED) method was used for measuring water repellency of the soil surface. A total of 725 points were sampled and the study was combined with a detailed vegetation survey, the determination of soil properties and of land use and management characteristics. More than 70% of the measurement points were hydrophilic, however differences between farm units were found. The highest values of hydrophobicity were observed on soil surfaces below the canopy of holm oaks, as compared to the low values found below shrub canopies ( Retama sphaerocarpa ) and in open areas. With respect to ground cover, water repellency was highest at sites covered by holm oak litter. At soil surfaces covered by cork oak litter, dry grass and mosses the degree of repellency was lower. Almost all sites with a bare soil surface were hydrophilic, independent of whether these were located below a tree canopy or in open areas. A significant positive relationship between livestock density and the degree of bare soil existed, and consequently, areas with high animal numbers were dominantly hydrophilic. No significant relationships were encountered between the degree of soil water repellency and soil properties.

Is soil water repellency a function of soil order and proneness to drought? A survey of soils under pasture in the North Island of New Zealand

We conducted a survey of the occurrence of soil water repellency (SWR) in the top 40 mm of soils across 50 sites under pastoral land use in the North Island of New Zealand. The sites represented ten soil orders and covered five classes of proneness to drought. We found at least a moderate persistence of SWR in 35 out of 50 sites (70%) in summer 2009/2010 and a moderate potential persistence of SWR in 49 out of 50 sites (98%) after drying the soils. The soil orders had an influence on the degree and persistence of SWR. Both the degree and persistence of SWR were greatest for the soil orders Podzol, Organic and Recent, and least for the soil order Allophanic. On average, all soil orders had contact angles larger than 94°, with the exception of the soil order Allophanic. We found no relationship between SWR and drought-proneness. The degree of SWR and its persistence for air-dried samples were positively correlated with soil carbon and nitrogen contents and negatively with soil bulk density. The persistence of SWR for field-fresh samples was additionally negatively correlated with the soil water content. We identified a close relationship (R2 = 0.84) between the degree and persistence of SWR. The survey results indicate that SWR is at least moderately persistent in a soil with a contact angle larger than 93.8°. Using a water-drop penetration time of 60 s as the threshold for SWR being moderately persistent, we found that moderately persistent SWR occurred only for volumetric water contents below 45% or a relative saturation of 60%. The latter can be considered to be a generic value of the critical water content for the onset of SWR at the scale of the North Island of New Zealand.

Combined effect of fire and water scarcity on vegetation patterns in arid lands

In many arid zones around the word, the vegetation spontaneously forms regular patterns to optimize the use of the scarce water resources. The patterns act as early warning signal that fragile ecosystems may suddenly undergo irreversible shifts, thus, interpreting the structural shape of vegetation patterns is crucial to deciphering the ecosystem history and its expected further development. The sudden and irreversible shift of delicate ecosystems as a consequence of minor variation of the climatic forcing has been studied extensively in the past. The attitude of the ecosystem to recover after a catastrophic event, such as fire, did not receive as much attention so far. Here we modelled fire, as a sudden shift of the ecosystem state variables and functionality and evaluated post-fire scenarios under the hypothesis that two major feedbacks shaped the vegetation patterns: a positive feedback between preferential infiltration and plant growth, and a second feedback between infiltration and vegetation burning. A simple model solving a set of partial differential equations for soil moisture, plant biomass, surface water and dead biomass balance predicted significantly diverse post-fire vegetation patterns depending on the fire severity and on the degree of soil water repellency induced by the vegetation burning.

Are preferential flow paths perpetuated by microbial activity in the soil matrix? A review

Recently, the interactions between soil structure and microbes have been associated with water transport, retention and preferential or column flow development. Of particular significance is the potential impact of microbial extracellular polymeric substances (EPS) on soil porosity (i.e., hydraulic conductivity reduction or bioclogging) and of exudates from biota, including bacteria, fungi, roots and earthworms on the degree of soil water repellency. These structural and surface property changes create points of wetting instability, which under certain infiltrating conditions can often result in the formation of persistent preferential flow paths. Moreover, distinct differences in physical and chemical properties between regions of water flow (preferential flow paths) and no-flow (soil matrix) provide a unique set of environmental living conditions for adaptable microorganisms to exist. In this review, special consideration is given to: (1) the functional significance of microbial activity in the host porous medium in terms of feedback mechanisms instigated by irregular water availability and (2) the related physical and chemical conditions that force the organization and formation of unique microbial habitats in unsaturated soils that prompt and potentially perpetuate the formation of preferential flow paths in the vadose zone.

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Water repellency under natural conditions in sandy soils of southern Spain

The occurrence and consequences of fire-induced water repellency have been studied in several regions of Spain since 1989. The occurrence of water repellency formed under natural conditions, however, has only been described for a few areas in Spain since 1998. The purpose of the present study was to investigate the severity of naturally occurring water repellency in the sandy soils of the Natural Park of Doñana in southern Spain. The persistence and degree of soil water repellency were measured on field-moist and dried sandy soil samples taken beneath Pinus pinea trees. Around 50% of the field-moist soil samples taken at 0–0.10 m depths exhibited (actual) water repellency. Potential water repellency, measured after drying the samples at 60°C, showed for 68% of the samples slight to extreme water repellency. The organic matter content was found to be positively correlated with persistence and with degree of potential water repellency.

Approaches to characterize the degree of water repellency

Measurement techniques that quantify the degree of soil water repellency are important for research and for the communication of research findings. The water drop penetration time (WDPT) is a commonly used measurement. If a water drop does not enter the soil spontaneously, the soil–water contact angle is greater than 90° and the soil is considered to be water repellent. The time for the drop to enter the soil (WDPT) provides an indication of the stability of the repellency. The liquid–air surface tension of an aqueous ethanol concentration series that enters the soil in approximately 5s is identified as the ninety degree (ND) surface tension, γND, of the soil. The γND number can be used to calculate the solid–air surface tension, γs, by γs=γND/4. The water–soil contact angle can also be calculated from the γs value by the relationship cosθ=[(γND/γw)1/2−1], where θ is the contact angle and γw the water–air surface tension. The water entry pressure, hp, which is a function of both the soil water repellency and pore size, is an important parameter for predicting infiltration and the stability of water flow in the field. Measurements of WDPT, γND, and hp provide a complete characterization of the degree of water repellency.