Occurrence Of Soil Water Repellency Research Articles

Winter cover crop performance in the Southern Piedmont region of South Carolina

AbstractCover crops (CCs) offer in‐field and environmental benefits when integrated into cropping systems. Low CC adoption in the Southern Piedmont region of South Carolina is partially due to the lack of information on CC performance and benefits within the region. To address this, eight winter CCs and a fallow/pigweed (Amaranthus spp.) treatment were investigated for their influence on soil temperature, volumetric water content (VWC), percent cover, biomass, and the occurrence of soil water repellency (SWR). A randomized complete block design experiment was conducted in the fall and winter of 2021–2022 (EXP A) and repeated in 2022–2023 (EXP B). Experiments were treated separately as methods were revised for EXP B. CCs minimally influenced soil VWC over both experiments with no consistent trend. CC did not influence soil temperatures during EXP A. In EXP B, the fallow/pigweed had the highest soil temperatures on two (out of 10) measuring events (p < 0.05). No SWR was found in either experiment. Establishment and fresh and dry CC biomass were most likely influenced by air temperatures and daylight hours driving germination during days with minimal rainfall. In both experiments, annual rye (Lolium multiflorum) produced cover quickly and yielded high biomass. Crimson clover (Trifolium incarnatum) took longer to establish but also yielded one of the highest biomasses. This study demonstrated that winter CCs had little influence on soil physical properties and that while cereal rye (Secale cereale) is a common CC utilized for erosion control, the greater biomass and surface roots of annual rye make it a superior CC for use in Southern Piedmont agroecosystems.

Vertical distribution of soil water repellency in ortsteinic soils in relation to land use

Land use, soil organic carbon content and bulk density are important factors influencing the occurrence of soil water repellency (SWR) and water flow through the soil profile. This study elucidated the relations between the repellency index (RI) and contents of soil organic carbon (SOC), organic-complexed aluminium (Alp) and iron (Fep), pH, specific surface area (SSA) and bulk density in the ortstein horizon and the overlying and underlying horizons in two podzolic soils under grassland and forest. The soil under grassland was originally used as a cropland. The RI was quantified from the ethanol/water sorptivity ratio. The results showed that the RI in the ortstein horizon (20.6–27.3) in the air-dried state in both soils was many times greater than in the overlying (7.2–19.0) and underlying (6.1–11.5) horizons, whereas in moist conditions (from soil water content at sampling and air-dried state), all horizons were not repellent. The RI in the air-dried soil in the overlying horizon was higher under grassland than forest, whereas the inverse was true in both the ortstein and underlying horizons. SOC, organic-complexed Alp and Fep contents, and SSA were the highest in the ortstein horizons. The pH value increased from 5.3 in the overlying horizon to 6.0 in the underlying horizon in the grassland soil. The corresponding values in the forest soil were 4.2 and 5.0. The RI values in the dry condition were significantly correlated with Alp (R2 = 0.976), Fep (R2 = 0.798), SSA (R2 = 0.724), and SOC (R2 = 0.638). The study provides new information about the vertical distribution of soil water repellency in ortsteinic soils depending on the soil water status and the type of land use. The potential mechanisms of the distribution of SWR are discussed.

Soil water repellency in sandy soil depends on the soil drying method, incubation temperature and specific surface area

Soil water repellency (SWR) is problematic in rainfed cropping soils as it decreases plant water use efficiency. The occurrence of SWR is often dependent on the prevailing soil water content, but the response of SWR to soil water content varies among studies. We undertook three experiments to investigate how the (i) drying method prior to experimentation (oven-dried at 105 °C or vacuum-dried at 20 °C), (ii) incubation temperature (4 °C, 20 °C and 40 °C), and (iii) specific surface area (SSA) of four sieved soil fractions (0.49 m2 g−1, 0.59 m2 g−1, 0.65 m2 g−1 and 1.61 m2 g−1) influenced the response of SWR to soil water content. In all experiments, SWR (measured by molarity of ethanol droplet) remained constant up to a ‘threshold soil water content’, and then responded linearly with increasing soil water content. However, oven-dried soil at 105 °C had lower SWR than soil dried anoxically at 20 °C, which remained constant up to a threshold soil water content. The SWR response rate to soil water content above the threshold was also lower in the 105 °C oven-dried soil than the 20 °C anoxically vacuum-dried soil. Whereas, increasing the incubation temperature increased the SWR response rate to soil water content above the threshold. The four sieved soil fractions had increasing threshold soil water contents with increasing SSA, which could be related to the total carbon content of the soil. In conclusion, the same drying method and incubation temperature should be used throughout an experiment and between studies when investigating the response of SWR to soil water content to avoid methodological errors.

Time series of remote sensing and water deficit to predict the occurrence of soil water repellency in New Zealand pastures

Soil water repellency (SWR) is a natural phenomenon occurring in soils throughout the world, which impacts upon ecosystem services at multiple temporal and spatial scales (nano to ecosystem scale). In pastures, the development of SWR is primarily determined by the cycling of hydrophobic materials at the soil surface, and is controlled by climate, soil and water management, and soil properties. The complex interactions between these factors make it an intricate system to understand and model. Detailed spatiotemporal characterization of the surface moisture and biomass in pastoral ecosystems would allow for a better understanding of this phenomenon. Normalized Difference Vegetation Index (NDVI) and Synthetic Aperture Radar (SAR) backscatter are good predictors for surface biomass and soil moisture, respectively. Machine learning on remote sensing time series (TS) data shows promise to predict the occurrence of SWR in pastures. This study evaluates the ability of remote sensing TS data to predict the occurrence of SWR in New Zealand pastures, using three machine learning algorithms. Soil water repellency data were collected from 58 pastoral sites. Machine learning models were trained and cross-validated on a monthly aggregated remote sensing and water deficit TS data to predict SWR level. Prediction output from artificial neural networks (ANN), random forest (RF), and support vector machine (SVM) were compared using root mean squared error (RMSE). When using NDVI TS data from 58 site as predictors of SWR, SVM and RF (RMSE = 0.82 and 0.87, respectively) outperformed ANN (RMSE = 1.23). Random forest was used to map SWR magnitude over Hawke’s Bay region in the North Island of New Zealand, and the overall accuracy was equal to 86%. This study is the first investigation implicating remote sensing TS data to predict the occurrence of SWR at the regional scale. Mapping the potential SWR will aid in identifying critical zones of SWR, to attenuate its effect on pastures through adapted management.

An open-source instrumentation package for intensive soil hydraulic characterization

We present a new open-source and modular instrumentation package composed of up to ten automatic infiltrometers connected to data acquisition systems for automatic recording of multiple infiltration experiments. The infiltrometers are equipped with differential transducers to monitor water level changes in a Mariotte reservoir, and, in turn, to quantify water infiltration rates. The data acquisition systems consist of low-cost components and operate on the open-source microcontroller platform Arduino. The devices were tested both in the laboratory and on different urban and agricultural soils in France and India. More specifically, we tested three procedures to treat the transducers readings, including a filtering algorithm that substantially improved the ability to determine cumulative infiltration from raw data. We combined these three procedures with four methods for estimating the soil parameters from infiltrometer data, showing pros and cons of each scenario. We also demonstrated advantages in using the automatic infiltrometers when infiltration measurements were hindered by: i) linearity in cumulative infiltration curves owing to gravity-driven flow, ii) an imprecise description of the transient state of infiltration, and iii) the occurrence of soil water repellency. The use of the automatic infiltrometers allows the user to obtain more accurate estimates of soil hydraulic parameters, while also reducing the amount of effort needed to run multiple experiments.

Effects of Throughfall Exclusion, Soil Texture and Spatial Continuity on Soil Water Repellency in Fichtel Mountains, Germany

Core Ideas Drought reduces soil wettability even after eliminating the effect of soil moisture Sand and clay content significantly decreased, while silt content increased WDPT WDPT shows low spatial dependence on mesoscale at lags from 0.6 m to 5.2 m The occurrence of soil water repellency (SWR) in soil is controlled by soil organic matter (SOM) composition and is strongly soil‐moisture dependent. During drying the reduction of water content in soil has been shown to induce the outward orientation of nonpolar ends of organic compounds and hence the increase in SWR. A prolonged drought can however also induce changes in SOM composition which in turn can affect SWR. In this study, we eliminate differences in water content after prolonged throughfall exclusion and a control treatment by oven‐drying of the soil samples, to test if a prolonged drought affects SWR even after excluding the direct effect of soil moisture. In addition, the relevance of soil texture variability and spatial dependence of SWR for prediction of soil wettability distribution over the study area was explored. The samples of the upper mineral soil horizon were taken from six plots in Fichtel Mountains, subjected to a throughfall exclusion or control treatments, oven‐dried and analyzed for soil texture and water drop penetration time (WDPT). A linear model with spatially correlated random effects was used to quantify the effects of soil texture and treatment on the persistence of the SWR and to simultaneously evaluate the spatial structure of the SWR. Based on estimated parameters the persistence of SWR was calculated on unsampled locations by robust kriging with external drift. The throughfall exclusion treatment significantly increased the log(WDPT) (p < 0.01) of the oven‐dried soil by 0.46. The clay content and the sand content had highly significant (p < 0.001) negative effects, while silt content had positive effects on the log(WDPT). The variogram parameter with a range of 5.2 m, a nugget of 0.25, and a sill of 0.45 indicated a rather low degree of spatial dependence of log(WDPT). The main outcome of this study is that the positive effect of throughfall exclusion on SWR cannot be fully attributed to water content reduction. Most probably the drought‐induced changes in SOM composition and microbial community were responsible for the observed increase in SWR.

Water repellency under coniferous and deciduous forest — Experimental assessment and impact on overland flow

Current climate change makes it necessary to gain a deeper understanding of the runoff generation processes in Central European forests. A changing climate might affect soil water repellency (SWR) which can be seen as an import trigger for overland flow generation in forested areas. In this study the differences between coniferous and deciduous forest concerning SWR and overland flow generation were investigated in a small catchment in the Hunsrück low mountain range, Rhineland-Palatinate, Germany.To investigate the occurrence and persistence of SWR and its influence on overland flow generation, a combination of two experimental methods was applied: water drop penetration time (WDPT) test, and rainfall experiments. The field WDPT test results ranged from wettable (WDPT<5s) up to more than 900second persistence of water repellency in both forest types. The median WDPT was 30s for the coniferous forest and 1s for the deciduous forest sites. On the deciduous forest soils, only the Of-horizon showed considerable water repellency. Rainfall experiments with 40mmh−1 rainfall intensity yielded runoff coefficients between 0% and 63%. The lowest measured infiltration rate of the rainfall experiments was 11.6mmh−1. The highest runoff coefficients were measured on water repellent (WDPT>300s) coniferous forest sites. The overland flow starts significantly earlier with water repellent soil conditions. The median runoff rate for the wettable forest soils is 2.7%, whereas the water repellent sites show a median runoff coefficient of 11.4%.The results suggest that the occurrence of SWR can lead to considerable overland flow generation under forest.

Soil water repellency in riparian systems invaded by Eucalyptus camaldulensis: A restoration perspective from the Western Cape Province, South Africa

South African riparian systems are threatened by major alien plant invasions through the widespread replacement of native plant species by fast-growing alien species, including several Eucalyptus species. Since Eucalyptus species are known to cause soil water repellency, this study examined the occurrence of soil water repellency coupled with soil moisture and infiltration under laboratory conditions from soils collected along the Berg River which is heavily invaded by alien tree species, especially E. camaldulensis. The connection between alien clearing for restoration purposes and soil water repellency is important as it has the potential to affect the success of native vegetation recovery. The topsoil was sampled at 12 sites, under different restoration treatments, namely invaded by Eucalyptus, completely cleared, thinned and native (control) sites. The water drop penetration time (WDPT) and the critical surface tension (CST) methods were performed. Soil moisture was found to be higher in invaded and natural sites compared to completely cleared and thinned sites. Soil water repellency, measured with the WDPT test on dried samples taken at 5–10cm depth, differed with invasion status and/or restoration condition. In invaded sites water repellency varied from wettable to severely water repellent: in thinned sites from non-repellent to strongly water repellent; in natural sites from wettable to slightly water repellent; all samples from completely cleared sites were wettable. Soil water repellency had no impact on soil infiltration rates. We conclude that the removal of invasive Eucalyptus species has the potential to restore soils to a non-repellent state, thus improving soil related ecosystem functions, which will facilitate the restoration of indigenous species, vegetation composition and structure.

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.

Is there a link between elevated atmospheric carbon dioxide concentration, soil water repellency and soil carbon mineralization?

We hypothesized that elevated atmospheric carbon dioxide concentration [CO 2] as a feature of climate change promotes the occurrence of soil water repellency (SWR) which reduces soil carbon mineralization and thus increases carbon sequestration. Soil surface transects under elevated (475 μL L −1) and ambient atmospheric [CO 2] in a long-term Free Air Carbon Dioxide Enrichment experiment were sampled at a high spatial resolution. All samples were hydrophobic at the time of the sampling. At the micro-scale, the differences in degree and persistence of SWR, soil organic matter (SOM) content, microbial respiration rates (MRR) and water content between the treatments were not significant. SWR was not correlated with SOM or MRR. A strong correlation between water contents and SWR parameters demonstrated the importance of SWR for water redistribution. At the meso-scale of disc infiltrometry, infiltration rates were reduced by SWR, and were higher under ambient than under elevated [CO 2]. This corroborates the tendency of reduced SWR under elevated [CO 2] observed at the micro-scale. SWR showed a spatial structure, exhibiting short ranges. SOM and MRR showed no spatial pattern at the scale analyzed, emphasizing that SWR did not contribute to an increase of the long-term terrestrial C sink in response to increased atmospheric [CO 2].

The Occurrence of Soil Water Repellency Under Different Vegetation and Land Uses in Central Iran

The Occurrence of Soil Water Repellency Under Different Vegetation and Land Uses in Central Iran

Sieving crusts and macrofaunal activity control soil water repellency in semiarid environments: Evidences from SE Spain

Quick overland flow peaks observed in runoff hydrographs from rainfall experiments carried out on mica schist soils in Rambla Honda (SE Spain) suggest development of soil water repellency (SWR). In order to spatially characterize its occurrence and severity and the factors controlling it, potential water repellency was measured in 120 soil samples using the WDPT test at laboratory conditions. Actual water repellency measurements were additionally performed at field conditions in order to increase our knowledge about the occurrence of this phenomenon. Samples were taken in bare soils ( n = 23), beneath plant clumps of Retama sphaerocarpa ( n = 23) and Anthyllis cytisoides ( n = 10) and from soils affected by rabbit latrines ( n = 9). Soil organic matter was also determined in 47 selected samples with a broad range of potential water repellency values. Results indicate that occurrence of SWR in Rambla Honda (potential water repellency values) varies in the three soil dimensions, areal and depth. The areal variation is due to the patchy pattern of organic matter and the variation with depth of the washed-in layer of sieving crusts developed in colluvial and alluvial soils after abandonment by agriculture. These layers act as physical barriers that restrict or impede the translocation of hydrophobic compounds to deeper layers. Such three-dimensional heterogeneity stresses the importance of the sampling scheme used for adequate SWR assessment. The severity of water repellency is generally reduced in this area because of the relatively scarce organic matter content and its spatial variability. A weak exponential relationship was found between the severity of potential water repellency and total organic carbon ( r 2 = 0.38; p-value < 0.01). Extreme values of actual and potential water repellency were found in rabbit latrines, stressing the importance of macrofauna in its development. Water repellency has an important impact on the local hydrology controlling runoff–runon between vegetated and bare patches, and possibly flash flooding during heavy rains in early autumn or after long dry periods. Review of a series of runoff hydrographs from previous rainfall simulations has distinguished four types of runoff patterns based on the occurrence of SWR.

Behaviour and management of water repellent soils—Preface

Recently, it has become clear that soil water repellency is much more widespread than formerly thought. Water repellency has been reported in most continents of the world for varying land uses and climatic conditions. Soil water repellency often leads to severe runoff and erosion, rapid leaching of surface-applied agrichemicals, and losses of water and nutrient availability for crops. At present, no optimum management strategies exist for water repellent soils, focussing on minimising environmental risks while maintaining crop production. One of the reasons is that knowledge on water repellent soils is scattered among researchers of different disciplinesworking at different places throughout the world. In order to obtain a more integral view on many aspects related to soil water repellency, a joint trans-national research project had been funded by several donor organisations, and executed by research institutes and universities in Europe, the USA, and Australia. The present issue contains a selection of papers prepared after conclusion of the project, including an extensive soil water repellency bibliography. The soil water repellency project, entitled ‘Development of amelioration strategies to reduce environmental deterioration and agricultural production losses in water repellent regions’, is the first executed to include and address these issues. The project has been jointly prepared and executed by a research consortium of 8 European, American andAustralian research institutes and universities, i.e. Alterra (Wageningen, The Netherlands, project coordinator), University of Wales (Swansea, United Kingdom), University of Aveiro (Aveiro, Portugal), Democritus University of Thrace (Xanthi, Greece), University of Minnesota (Minneapolis, USA), Cornell University (Ithaca, USA), Agriculture Western Australia (Geraldton, Australia), and Deakin University (Warrnambool, Australia). The project was funded by the European Commission (FAIR Program, contract CT98-4027), and the DutchMinistry of Agriculture, Nature Management and Fisheries, and took place between 1998 and 2002. In the first section dealing with the assessment and characterisation of water repellent substances, 4 papers are presented, the first by Doerr et al. dealing with extracting soil compounds associated with water repellency in sandy soils of different origin. Morley et al. focus on various organic compounds and their role in generating water repellency. The role of tree stem proximity in the spatial variability of soil water repellency in a eucalypt plantation in coastal Portugal is presented by Keizer et al. A second paper of Doerr et al. highlights the effects of heating and postheating equilibration times on assessing the degree of water repellency. The second section of the special issue focusses on the occurrence of soil water repellency. The first paper in this section by Leighton-Boyce et al. deals with the temporal dynamics of water repellency and soil moisture in eucalypt plantations. The paper by Ziogas et al. focusses on the occurrence of soil water repellency in the north-eastern part of Greece, and the effects of drying on the degree of water repellency. A study on soil water repellency under natural conditions in sandy soils of southern Spain is presented by Moral Garcia et al. A second paper of Keizer et al. deals with the occurrence of soil water repellency under dry and wet antecedent weather conditions for selected land-cover types in the coastal region of central Portugal. Coelho et al. discusses the impact of soil water repellency on hydrological and erosional processes under forest land use in the Mediterranean. A study on the spatial and temporal variability of soil water repellency of Amazonian pastures is presented by Johnson et al. The third section of the special issue is devoted to hydrology and modelling aspects. Ferreira et al. present a detailed paper on the influence of burning intensity on water repellence and hydrological processes at forest and shrub sites. The effect of soil water repellency on overland flow generation in forest stands is presented in a third paper by Keizer et al. Xiong et al. discuss the implications of using recycled water in relation to competitive sorption of metals in water repellent soils. Steenhuis et al. apply percolation theory to describe water flow in hydrophobic soils. Furthermore, Ritsema et al. present a new modelling approach to simulate preferential flow and transport in water repellent porous

Occurrence of soil water repellency in arid and humid climates

Soil water repellency generally tends to increase during dry weather while it decreases or completely vanishes after heavy precipitation or during extended periods with high soil water contents. These observations lead to the hypothesis that soil water repellency is common in dry climates and rare in humid climates. The study objective is to test this hypothesis by examining the occurrence of soil water repellency in an arid and humid climate. The main conclusion of this study is that the effect of climate on soil water repellency is very limited. Field observations in the arid Middle Rio Grande Basin in New Mexico (USA) and the humid Piedras Blancas Watershed in Colombia show that the main impact of climate seems to be in which manner it affects the production of organic matter. An extremely dry climate will result in low organic matter production rates and, therefore, less potential for the development of soil water repellency. On the other hand, a very humid climate is favorable for organic matter production and, therefore, for the development of water repellency.