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Soil water repellency (SWR) has been reported under different soils, land uses and regions of the world, particularly in forest land and after wildfires, yet the understanding of this variable in agricultural lands is still rather limited. This study presents the characterization from field-based measurements of SWR in four contrasted olive groves ( Olea europaea L.) in Spain in terms of different environmental conditions and management: abandoned and commercial farms under permanent cover crop, conventional tillage and herbicide use. The main objectives were [1] to evaluate the potential occurrence, intensity and persistence of soil water repellency in different types of olive groves and [2] to explore its spatio-temporal features as well as the influence of soil properties such as organic matter (OM) and soil moisture. The Water Drop Penetration Time test (WDPT) was used in situ to assess SWR values. Measurements were carried out in two areas for each of the four groves: below and between the tree canopies. A high spatial and seasonal variability was observed. SWR was absent (WDPT = 0 s) for the olive groves under conventional tillage and with the lowest values of OM (OM-mean = 2.04%). The maximum WDPT values were found for cover crop under canopy in summer (WDPT-max = 610 s) and on the lanes in autumn (WDPT-max = 468 s). SWR was developed during the dry season, and to be reduced during the rainfall season as the organic compounds might be reoriented and turned amphiphilic. Strong water repellent values (> 60 s) were related with extremely high OM values (> 12%) for the cover crop orchard. [ABSTRACT FROM AUTHOR]

Abstract: This study reports the soil–plant relationships within a protected landscape in semiarid SE Spain that includes salt marshes and temporary streams and that is affected by agricultural water leaching. The main objective was to establish a conceptual model in order to use vegetation as bioindicator of soil conditions. With this model, environmental changes – based on the observation of vegetation – could be detectable, allowing the prevention of environmental impacts and the improvement of the environmental management of the studied area. Eight sampling stations with a total of 39 plots were established for the sampling of vegetation (floristic composition and species abundance) and soil (moisture, pH, redox potential, electrical conductivity and soluble ions). Multivariate analysis showed that vegetation was closely related to soil moisture and salinity. The soils colonised by steppe grasses (dominated by Lygeum spartum) and halophilus and halonitrophilus shrubs (dominated by Suaeda vera and Limonium spp.) were the driest (moisture <~20%) and least saline (EC <~30dSm−1). Phragmites australis, Sarcocornia fruticosa and Arthrocnemum macrostachyum dominated in the most saline and wettest soils. P. australis reached maximum cover at EC values ~40dS m−1 and soil moisture ~30% and consistently appeared on those soils with lower seasonal contrasts of moisture and salinity. Between 30 and 80dSm−1 of soil salinity, S. fruticosa reached maximum cover (~100%) while A. macrostachyum did not exceed ~80%. Outside this range of salinity S. fruticosa declined (cover <10%), while the other species maintained cover >~40%. In addition, A. macrostachyum grew in soils with stronger seasonal changes of moisture and salinity. Based on the model established, if an expansion of P. australis is detected, an increase in soil moisture and a decrease in soil salinity during the year could be inferred. These changes could be due to an increased entry of effluents of fresh and/or brackish water from agricultural areas. In turn, an increase in the cover of A. macrostachyum would indicate higher soil salinity, which could be a consequence of an increase in the evaporation rates (due to rising temperatures) and a decrease in rainfall (predicted consequences of global warming). The expansion of S. fruticosa would be favoured under relatively high soil salinity conditions (which limit P. australis expansion) jointly with high soil moisture, without strong seasonal changes (which limit A. macrostachyum expansion). Our results support the role of vegetation as bioindicator of disturbances and the use of soil–plant relationships models to improve the environmental management of saline ecosystems. [Copyright &y& Elsevier]

Abstract: This study evaluates the spatial and temporal variability in soil water repellency (SWR) in two Mediterranean rangelands (with similar tree and shrub species) and its relationships to different eco-geomorphologic variables (climate, aspect, soil cover and some soil properties). Every month from October 2008 to May 2009 (rainy season), soil moisture and SWR was measured in field conditions by means of gravimetric method and Water Drop Penetration Test, respectively. Also, disturbed and undisturbed soil samples were taken to analyze some soil properties: bulk density, texture, organic matter, pH and electrical conductivity. The entire tests were performed in north and south aspect hillslopes and beneath shrub and bare soil in every of them. The results indicated that: i) climatic conditions seem to be more transcendent than the vegetal species for explaining the variability in SWR; ii) thus, SWR appears to be controlled by the antecedent rainfall and soil moisture; iii) more severe SWR were observed in patches characterized by sandier soils and/or higher organic matter contents; and iv) the factor ‘hillslope aspect’ was not found so crucial as it was expected. [Copyright &y& Elsevier]

Abstract: Soil water repellency has been studied for different soil types and plant covers, but uncertainty exists regarding the representativeness of water repellency measured on unaltered soil surfaces compared to sieved samples. Two different methods are used to characterize water repellency, which provide a certain degree of different information: the persistence of soil water repellency, measured by the water drop penetration time (WDPT) test; and the intensity of soil water repellency, measured by the ethanol percentage (EP) test. The main objectives of this research were to analyze the relationships between soil water repellency measured on undisturbed soil blocks and 2-mm hand sieved samples, and to compare the results between both methods (WDPT and EP tests). Water repellency was measured on the surface and at soil depths of 2cm and 5cm for three fine textured soil types (Rendzic Phaeozem, Hypercalcic Calcisol, and Eutric Cambisol) developed below different plant covers (mossy pine forest, evergreen oak forest, and meadow, respectively). At the class level, WDPT and EP tests offered similar results for unaltered and sieved samples. The EP test tends to slightly overestimate values on sieved samples, whereas the WDPT test tends to slightly underestimate measurements on sieved samples. Based on the good relationship between the two types of soil samples used (unaltered and sieved), conversion formulas for both tests have been obtained: a linear regression for EP test (R2 =0.862; p <0.001) and a logarithmic model for WDPT test (R2 =0.913; p <0.001). Differences in the wettability has been observed between soil depths and soil types: Rendzic Phaeozem under pinewood is very strongly hydrophobic and consistently severely water repellent at any soil depth; Hypercalcic Calcisol under oakwood has the same behavior on the surface, but water repellency decreases progressively with depth; finally, Eutric Cambisol under meadows is hydrophilic and mainly wettable for all depths. [Copyright &y& Elsevier]

Abstract: Soil water repellency (WR) is one of the properties most affected by combustion during a forest fire. Different factors such as temperatures reached, type and amount of fuel, affect the changes observed in this property. Measurements of water repellency can be made directly in the field or in soil samples under laboratory conditions. On the other hand, previous laboratory findings have demonstrated that some soil properties can be key factors controlling the development of WR by burning. One of the objectives of this research was to confirm findings from laboratory-burning under wildfire field conditions. In summer 2008 WR was assessed in five areas recently affected by fires in Mt. Carmel (NW Israel) and Alicante (SE Spain). Study sites are quite similar with regard to vegetation and climate, the main difference between sites being the type of soil and therefore soil characteristics. In each one of the study areas WR was tested beneath Pinus halepensis in both burned and unburned (control) adjacent sites. WR test were conducted under field conditions in triplicate using the water drop penetration time (WDPT) test in the top of the A horizon. A total of 300 field measurements were done. Soil samples from the first 0–2.5cm depth were also taken from the same microsites where WR was assessed for laboratory measurements. Estimations of temperatures reached in burned samples were also made using NIR models developed under laboratory conditions. In general terms, without distinguishing between areas, fire increased the frequency of occurrence of WR in affected soils. However, the magnitude of this effect was quite different depending on the studied area. Three of the study sites, showed very low WR values both in burned and unburned areas. The results are in agreement with those from our previous laboratory experiments (Arcenegui et al., 2007; Mataix-Solera et al., 2008), and are not explained as a consequence of different temperatures reached in the soils. Organic matter and clay content together with the mineralogy of the clay fraction seem to be responsible for the different soil behaviour. Although there is a correlation between field and laboratory WR data (R2 =0.549; P<0.01), the comparison between field and laboratory measurements of WR showed differences, with higher values for the field data. Since the soil water content was very low when field measurements of WR were made – similar to air-dried samples in laboratory – this factor is not suspected to be the responsible. The observed differences could be explained however because the measurements in field were made on the soil surface, while in laboratory the measurements are made in disturbed samples taken from the top to some depth (in our case from 0 to 2.5cm). Taking into account that soil WR is a property that can vary with depth probably diminishing in parallel with soil organic matter content, the results seem to be logical. Moreover, the disturbance of samples and the sieving could also be partly responsible for the observed differences. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: Due to particular soil and climate conditions and inappropriate agricultural practices, Aragon (NE Spain) is a region prone to land degradation by water erosion. For this reason, the adoption of conservation tillage systems has been encouraged as an alternative to preserve soil and water in this region. However, little information concerning soils on which these techniques are applied is available. The main objectives of this study were to assess the effect of long-term no tillage (NT) on water aggregate stability in five different cereal production areas of Aragon and identify the main mechanisms involved on aggregate breakdown. The study was conducted under on-farm conditions where pairs of adjacent fields under NT and conventional tillage (CT) were compared. In all cases, a nearby undisturbed soil under native vegetation was included. Soils were slightly to highly calcareous with medium textures ranging from sandy loam to silty clay loam. Results indicate that NT increased surface aggregate stability with respect to CT systems through lower soil disturbance and higher organic carbon (OC) content at the soil surface (0–5cm depth). Slaking was the dominant disaggregation process of the cultivated soils, representing 40–80% of total soil disruption, and was strongly and negatively affected by aggregate-associated OC. This soil property together with the silt content (weak and positive effect) explained more than 80% of the slaking variation. Swelling and clay dispersion were less frequent processes and their occurrence seemed to be associated with high silt and CaCO3 contents. This study shows that, under the rainfed conditions of semiarid Aragon, NT reduces the susceptibility of soil surface to crusting and water erosion as compared to CT systems. [Copyright &y& Elsevier]

Abstract: The purpose of this paper is to outline a procedure for soil block extraction, which is highly appropriate for clay soils. The method described here is rapid and cheap and has been used successfully by us in clay soils in southern Spain for the last six years. A wooden box is used to shape the soil block in situ and protect it during its transport from the field to the laboratory. Polyurethane foam was selected as the bonding agent, between the wooden framework and the soil block in order to avoid any possible alterations of the soil. This type of foam is used because it is strong, durable and non-toxic. The polyurethane foam is applied to the soil block as a permanent coating. This technique allows us to extract the clay soil solution in the laboratory. [Copyright &y& Elsevier]

Abstract: Semiarid karst landscapes represent an important ecosystem surrounding the Mediterranean Basin for which little is known on runoff generation. Knowledge of the sources and patterns of variation in infiltration–runoff processes and their controls is important for understanding and modelling the hydrological functions of such ecosystems. The objectives of this paper are to determine the infiltration rates and their controls in a representative mountain karst area (Sierra de Gádor, SE Spain) at micro-plots and to investigate the integrated response of rainfall on a typical hillslope. Rainfall simulations in micro-plots and natural rainfall-runoff monitoring on a hillslope were carried out complementarily. We investigated the role of soil surface components (vegetation, rock outcrop, fracture, and soil crust), topographic position, antecedent soil moisture, and rainfall characteristics in regulating infiltration–runoff processes. Results of rainfall simulation revealed the importance of vegetation cover and the presence of rock fractures in promoting the infiltration in the limestone karst landscape, while bare patches and rock outcrops acted as sources for runoff. All plots with >50% vegetation cover had no runoff with up to 55mmh−1 of simulated rain. In contrast, nearly all bare plots had runoff under the same simulated rain, with runoff coefficients ranging from 3.1 to 20.6% on dry soil surface conditions, and from 2.0 to 65.4% on wet soil surfaces. Runoff coefficients amounted to 59.0–79.5% for rock outcrops without cracks, but were drastically reduced by the presence of cracks. The surfaces with rock fragments resting on the soil (generally located in the middle of the slopes) prevented more effectively the runoff generation than those surfaces where rock fragments were embedded in the top soil. Antecedent soil moisture had significant impact on runoff generation, with wet soil having doubled runoff coefficient, shortened time to runoff, and increased runoff rate compared to the same but dry soil. Linear regressions indicated that the main controls for constant infiltration rate were the cover percentages of vegetation and litter, plus rainfall intensity; while the major controls for runoff coefficient were the bare soil and vegetation coverage, plus rainfall intensity. High infiltration rates measured at the micro-plots agreed with low intra-event runoff coefficients (mostly below 1%) observed under natural rainfalls at the hillslope. Runoff depth and coefficient at the hillslope was significantly correlated with rainfall depth, maximum hourly rainfall intensity and antecedent precipitation over 20days (AP20). During the 1.5-year monitoring period from Sep-2003 to Mar-2005, the overall infiltration was 41% of the total rainfall amount and the maximum infiltration rate was almost 94% of the largest single rainfall event. The results from this study contribute to improved understanding of the magnitude and controls of the surface runoff in semiarid karst mountain areas. [Copyright &y& Elsevier]

Abstract: The present work aims to assess the effects of wildfires on soil aggregate stability and the role therein of contrasting lithologies as well as of fire-induced changes in organic matter content and soil water repellency. To this end, a pair-wise comparison of neighbouring burned and unburned soils was carried out and complemented by laboratory heating experiments to clarify the role of fire intensity. In total, 18 pairs of adjacent burned and unburned pine forest soils were sampled within one month after wildfire. At each site, five samples were collected of the top 5cm of the A horizon at randomly selected sample points and were mixed in the field to obtain one composite sample per site. Three additional samples were collected at each site but stored separately, and those of three sites were selected for the laboratory heating experiments. Laboratory heating involved five different temperatures ranging from 25 to 460°C. Aggregate stability of the field and laboratory samples was determined using the water drop impact test, organic carbon content using a modified Sauerlandt method and soil water repellency using the ‘Molarity of an Ethanol Droplet’ test. The wildfire effects on field aggregate stability were highly variable and results indicated that these changes depend primarily on organic matter combustion and, thus, fire intensity. Controlled heating up to 220°C either did not alter aggregate stability or increased it with increasing temperature, possibly due to the development of a protective coating of organic compounds inducing water repellency. Heating at 380 and 460°C, by contrast, produced considerable to massive combustion of organic matter and, thereby, very pronounced reduction of aggregate stability as well as water repellency. [Copyright &y& Elsevier]

Abstract: The distribution and variation with soil depth of water repellency has been studied in fire-affected sand dunes under three different vegetation types (pine forest, shrubland and sparse herbaceous vegetation) in SW Spain. The persistence and intensity of water repellency at the exposed surface of soil was measured using the water drop penetration time test and the contact angle method, respectively, in surface samples (0–3 cm) collected at burned and unburned areas. The variation of water repellency with depth in burned areas was studied in soil profiles every 5 cm between 0 and 40 cm depth. None or slight soil water repellency was observed at unburned soil sites, whereas burned soil sites showed a high degree of repellency, especially under pines and shrubland. The spatial pattern of fire-induced soil water repellency was found to be associated to vegetation types, although it was modulated by soil acidity and the soil organic carbon content. Soil water repellency was generally higher at the soil surface, and decreased with depth. Dense pine forests and shrublands showed strong and/or severe water repellency in depth, but it was rare and limited to the first five centimeters under sparse herbaceous vegetation. The heterogeneity of moisture patterns under dense pine forests or shrublands showed the existence of wetting and water repellent three-dimensional soil patches. [Copyright &y& Elsevier]

Abstract: The effectiveness of water harvesting systems collecting surface runoff form rangeland hillslopes in semi-arid regions is difficult to predict, since the hydrological response at the outlet depends on the heterogeneity of hydrological processes. The lack of continuous runoff pathways, due to the irregular spatial patterns of soil properties and the variety of antecedent soil moisture conditions directly influence runoff generation and control discharge into the water harvesting cisterns. The aim of this paper is to evaluate the effectiveness of semi-arid hillslopes in generating runoff for water harvesting systems. Runoff was estimated by the STREAM expert-based model which was applied to three semi-arid hillslopes (0.4 to 6 ha). On the one hand the STREAM model rules were adapted to the regional conditions i.e. an antecedent precipitation index was adjusted to local soil moisture conditions and the rainfall duration was defined as the total rainfall event quantity and the effective rainfall duration (P tot/t eff). On the other hand, the distribution of rock outcrop and vegetation cover along the slopes was used to define homogeneous hydrological units. Final infiltration capacities were attributed to these hydrological units based on values found in the literature. The prediction performances are acceptable for the three water harvesting systems with an RMSE of 13.9 m3. It was shown that the rainfall/runoff model was more sensitive to the duration of the storm than to the antecedent soil moisture conditions. The use of a unique set of hydrological parameters for the three water harvesting systems on representative hillslopes allows the runoff prediction from any rangeland hillslope within the same region. Furthermore, the spatial patterns of soil surface characteristics are crucial for collecting runoff at the outlet of the system. Model runs demonstrated that degradation of vegetation and sealing of very small areas within flow paths can lead to an increase of annual runoff by as much as a factor two. [Copyright &y& Elsevier]

Abstract: Preferential flow may strongly affect hydrology at different scales. Measurement of preferential flow however remains very difficult. Tracer-infiltration profiles are often used to measure the degree of preferential flow at plot scale. These experiments are time-consuming, costly and destructive. As a result existing dye-tracer studies are often based on a limited number of profiles. The aim of this study is therefore to select a limited number of soil and landscape characteristics with high predictive value for the degree of preferential flow. 18 rainfall simulations with a dye-tracer and additional site measurements such as soil type, vegetation type and soil physical parameters were performed in a 1 km2 catchment in the Dehesa (Extremadura, Spain). A stepwise multiple regression procedure was used to select variables with a high predictive value for the degree of preferential flow. The infiltration patterns show that preferential flow is potentially present throughout the area and is spatially variable. At first inspection the spatial variability seems to relate to the site specific variables. This is corroborated by the stepwise multiple regression results, with R 2 values of 56% to 67% for the different preferential flow parameters (uniform infiltration front, maximum infiltration depth, total stained area and preferential flow fraction of stained area). A bootstrapping procedure however indicated that the bias due to stepwise variable selection with a large number of independent input variables and a low number of cases was high. Pre-selection of a limited set of variables (vegetation, texture, slope and location) based on expert knowledge gives lower but more powerful R 2 values (50% to 66%), without the bias due to stepwise variable selection. As a large part of the spatial variability of infiltration patterns can be explained with the selected site characteristics, the regression equations were used in combination with detailed maps of the four selected input variables to calculate maps of catchment scale spatial variability in infiltration patterns, thereby delineating sub-areas within the catchment with different infiltration patterns. [Copyright &y& Elsevier]

• Effect of grazing on soil hydraulic properties of gypseous soils were studied. • Three grazing intensities, High, Medium and Low, were compared. • Soil surface S and K c and subsurface ρ b , K s , θ s , α and n were measured. • H presented the highest ρ b and the lowest K c values. • In semiarid gypseous soils M did not have a negative effect of soil properties. Although is well known that grazing has a significant effect on the soil hydraulic properties and through them on the pasture productivity in semi-arid regions, there is still little data about the effect of this management on soils with high gypsum content. This work compares the effect of three increasing grazing intensities (low, medium, and high) on the hydraulic properties of the upper soil layers, measured on two areas with increasing gypsum content (56 and 73%, respectively) located in a semi-arid region of the Middle Ebro Valley (NE, Spain). 90 soil samplings were taken on bare soil surface areas. The measured soil parameters included the saturated sorptivity (S c) and hydraulic conductivity (K c) of the soil surface layer and the soil bulk density (ρ b), saturated hydraulic conductivity (K s), saturated volumetric water content, θ s , and α and n parameters of the water retention curve of the 1–8 cm depth soil layer. Increasing gypsum content increased the soil water infiltration but did not affect the water retention capacity and total porosity. All studied gypseous soils presented low water retention. High grazing intensities decreased the soil water infiltration. While soils with high gypsum content tended to attenuate the effect of the livestock trampling on ρ b , a significant influence of grazing on ρ b was observed in the fields with moderate soil gypsum content. No effect of livestock trampling on the soil water retention characteristics was observed. Moderate grazing, which did not show negative effects on the soil hydro-physical properties, could be an acceptable management for soil conservation in these semiarid regions of soils with high gypsum content. [ABSTRACT FROM AUTHOR]

Abstract: Dehesa ecosystems are open woodlands with scattered oak trees as their main component. As a result of differing land-uses, the structure of vegetation found within dehesas varies between: (i) oak trees and intercropped cereals (cropped), (ii) oak trees and native grass vegetation (grazed), and (iii) oak trees with abundant understorey shrubs (encroached). The aim of this study is to investigate whether land-use influences the water dynamics of dehesas by measuring available soil water content (AWC) in the upper 250 cm of the soil at different distances from tree trunks (maximum 30 m) at four Quercus ilex dehesas in Central–Western Spain. The technique used was Time Domain Reflectometry and the study was undertaken between May of 2002 and December of 2005. Leaf water potential (Ψ) was also measured on trees at one site by mean of a pressure chamber. Within the upper meter of the soil, it appears that trees, grasses and shrubs extracted soil water resources in a similar way from both beneath and beyond the tree canopy. However, encroached plots in general showed lower average AWC values than cropped or grazed plots (3.7, 5.6, and 6.2% in encroached, cropped and grazed, respectively). Cereal crops do not compete more strongly than grasses with trees for available soil water resources. The similar Ψ values found at cropped and grazed plots supported these results. From our results, it could be hypothesized that ploughed dehesas could facilitate soil re-watering in the plots with pronounced slopes. The decrease of AWC values at encroached plots with respect to the cropped and grazed plots was found mostly beyond the tree trunk at deeper soil layers, indicating that shrubs use water partly not accessible to trees. The presence of an understory of shrubs seems to have slightly increased the water constraints on trees during the summer period (Ψ d values of −0.5, −0.5, and −0.8 MPa in cropped, grazed, and encroached plots, respectively). In cropped and grazed plots, an important amount of water seems to have remained unused for trees and grasses. [Copyright &y& Elsevier]

Abstract: This paper analyses the differences in soil moisture, runoff and sediment concentration resulting from land levelling works carried out before new vineyard establishment in a reference wine region of NE Spain. In low disturbed soils, low differences in soil moisture were observed, while in high disturbed soils, soil moisture and water infiltration of the surface were always lower than in the low disturbed ones, while soil sealing was higher in high disturbed than in the low disturbed soils. Differences in runoff and sediment concentrations were also observed. The most disturbed plot showed a higher sediment concentration in runoff, which together with higher runoff volumes gave higher erosion rates and soil losses than the low disturbed one. The differences within the most disturbed soils were high after high intensity rainfall events, while no significant variations were observed in the least disturbed ones. [Copyright &y& Elsevier]