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A generalized modular framework for partitioning soil hydraulic property (SHP) functions into a capillary and a noncapillary part is developed. The full water retention curve (WRC) is modeled as a weighted sum of a parametric capillary saturation function and a new general model for the noncapillary saturation function. This model is directly computed from any selected capillary saturation function. With it, a physically complete, continuous, and flexible representation of the WRC is achieved, ensuring zero water content at oven dryness. In a modular and hierarchical framework, the expressions for the capillary and noncapillary saturation function are used to calculate the respective hydraulic conductivity curves (HCC). This is achieved by adopting Mualem's integral for the capillary part of the HCC only and calculating the noncapillary HCC directly from the new noncapillary saturation function. This leads to consistent descriptions of measured HCC data, including the often observed change in slope beyond −100 cm pressure head. Compared to the classical van Genuchten‐Mualem approach, it requires only one additional model parameter. The SHP framework model describes both WRC and HCC adequately and coherently. We demonstrate the suitability of the SHP framework and versatility by describing measured WRC and HCC data across the full moisture range using soil samples from a wide range of textures and origins. The modular framework was implemented in the soil physics and soil hydrology (spsh) R‐package, available from the Comprehensive R Archive Network. It contains several SHP models, model parameter estimation, and features options for goodness of fit statistics, and model selection.

ABSTRACTSoil‐specific properties like water retention and hydraulic conductivity are largely used in soil and environmental modelling and are typically obtained after laboratory analyses. So far, no single method is available to measure the entire suction range for water retention or hydraulic conductivity. Common methods for describing the soil water retention curve (SWRC) include simplified evaporation, pressure plates, neutron spectroscopy, and dewpoint. Regarding hydraulic conductivity, the techniques vary for the saturated or unsaturated condition, using tension disks and transient evaporation methods. In the search for a procedure to describe the entire water retention and hydraulic conductivity curves, the objective of this study was to illustrate the combination and use of a series of laboratory methods in eight different semi‐hierarchical combinations to cover the whole suction range (0 pF 7). The data obtained from each combination was used to fit the van Genuchten‐Mualem equation and compared using the RMSE and Akaike statistics. The main results show that using a combination of many methods for the water retention and hydraulic conductivity curves did not necessarily improve the curve fitting. However, adding data points at near saturation (pF close to 0) or from the driest part of the curve (pF 4) improved the estimates on both curves. Specifically, for the clay soil, the RMSE for the hydraulic conductivity curve decreased from 0.0372 to 0.0369 cm/d when measurements from near saturation were added. For the sandy loam 2 soil, the RMSE for the water retention curve decreased from 0.039 to 0038 when including data from the driest part of the curve. Among all the soil‐water‐related parameters tested in this study, the estimates for the water retention content at the permanent wilting point (θ1500 kPa) showed the largest difference among all the combinations of methods, up to 52%. In contrast, the difference in the water content at field capacity (θ33 kPa) estimates was only 3%. This study provides an evaluation and insights to identify the best combination of methods when measuring or parametrizing the soil water retention and hydraulic conductivity curves.

The role of rock fragments in evaporation from cultivated soils under mediterranean climatic conditions

Windthrows are the most important type of disturbance occurring in the forests of Central Europe. On 19 November 2004, the strong northeastern katabatic winds caused significant damage and land cover change to more than 126 km2 of spruce forests in the Tatra National Park. The risk of subsequent soil erosion and accelerated runoff has increased in the affected habitats. Similar situations may reoccur this century as a consequence of climate change. A geographical approach and detailed research of the damaged area with more comprehensive statistical analyses of 47 independent variables will help us to obtain a deeper insight into the problem of windthrow disturbances. The results are based on a detailed investigation of the damaged stands, soil, and topography. A comprehensive input dataset enabled the evaluation of abiotic controls on windthrow disturbance through the use of a generalized additive model (GAM). The GAM revealed causal linear and nonlinear relationships between the local dependent quantitative variables (the damage index and the uprooting index) and independent variables (various soil and topography properties). Our model explains 69% of the deviance of the total damage. The distribution of the wind force depended upon the topographical position—mainly on the distance from the slope’s foot lines. The soil properties (mainly the soil skeleton, i.e., rock fragments in stony soils) affect the rate and manner of damage (uprooting), especially on sites with less wind force. Stem breakage with no relation to the soil prevailed in places with high force winds. The largest number of uprooted trees was recorded in localities without a soil skeleton. The spruce’s waterlogged shallow root system is significantly prone to uprooting. The comprehensive research found a significant relationship between the abiotic variables and two different measures of forest damage, and can expand the knowledge on wind impact in Central European forests.

ABSTRACTField and laboratory studies have indicated that rock fragments in the topsoil may have a large impact on soil properties, soil quality, hydraulic, hydrological and erosion processes. In most studies, the rock fragments investigated still remain visible at the soil surface and only properties of these visible rock fragments are used for predicting runoff and soil loss. However, there are indications that rock fragments completely incorporated in the topsoil could also significantly influence the percolation and water distribution in stony soils and therefore, also infiltration, runoff and soil loss rates. Therefore, in this study interrill laboratory experiments with simulated rainfall for 60 min were conducted to assess the influence of subsurface rock fragments incorporated in a disturbed silt loam soil at different depths below the soil surface (i.e. 0.001, 0.01, 0.05 and 0.10 m), on infiltration, surface runoff and interrill erosion processes for small and large rock fragment sizes (i.e. mean diameter 0.04 and 0.20 m, respectively). Although only small differences in infiltration rate and runoff volume are observed between the soil without rock fragments (control) and the one with subsurface rock fragments, considerable differences in total interrill soil loss are observed between the control treatment and both contrasting rock fragments sizes. This is explained by a rapid increase in soil moisture in the areas above the rock fragments and therefore a decrease in topsoil cohesion compared with the control soil profile. The observed differences in runoff volume and interrill soil loss between the control plots and those with subsurface rock fragments is largest after a cumulative rainfall (Pcum) of 11 mm and progressively decreases with increasing Pcum. The results highlight the impacts and complexity of subsurface rock fragments on the production of runoff volume and soil loss and requires their inclusion in process‐based runoff and erosion models. Copyright © 2011 John Wiley & Sons, Ltd.

Estimating soil hydraulic properties from oven-dry to full saturation using shortwave infrared imaging and inverse modeling

The classical determination of the soil water retention curve (SWRC) by measuring soil water content θ at different matric potentials ψ using undisturbed soil samples is time consuming and expensive. Furthermore, undisturbed soil sampling can be an intricate task when coarse soil fragments (>2 mm) are present. The objective of this study was to test whether tension infiltrometry could be used to estimate the SWRC of stony soils and to investigate to what extent the coarse fragments affected the SWRC. Tension infiltrometer measurements were conducted at 44 sites with stony soils in arid Chile. Soil water retention curves obtained through inverse modeling were compared with laboratory‐determined water retention (θ, ψ) data pairs. Differences were found to be small, confirming the applicability of the inverse modeling method. Rock fragments had a significant indirect influence on water retention for matric potentials higher than −0.30 kPa, which could be attributed to their direct influence on pore size distribution.

Soil pore size distribution and pore functional characteristics are the most important for soil physical properties, water retention, and transmission. Furthermore, considerable amounts of rock fragments are present in hilly region soils. In this study, we discuss the pore size distribution and pore functional characteristics of soils as affected by rock fragments in the hilly regions of Sichuan Basin, China. The soil water characteristic curve was measured to calculate the soil total porosity and the ratio of equivalent pores in each diameter class. The results suggest that the soil total porosity decreases with increasing rock fragments size. The proportion of transmission pores increased gradually with increasing rock fragment content, whereas the fractions of storage pores and residual-bonding pores decrease gradually. Furthermore, the ratio of effective soil porosity to total porosity is higher than that of ineffective porosity to total porosity with increasing rock fragment content. In summary, increasing the rock fragment content can notably increase the proportion of soil transmission pores, thereby increasing soil aeration and water permeability. However, a high rock fragment content is not conducive to maintaining the water needed for normal plant growth.

A scaling-based model to describe temporal variability in soil hydraulic properties

Mine tailings storage poses significant environmental risks such as the formation of acid mine drainage. Engineered covers offer a solution by controlling water ingress. Their performance is based on specific soil hydrogeological properties (SHPs). They must support vegetation which can impact saturated hydraulic conductivity ( ksat) and water retention curve (WRC). This study assesses the impact of 4-year-old willow root colonization on silty soil covers using flexible wall parameters and water retention tests. The obtained SHPs were compared with root traits. The results suggested that the hydrogeological properties of the studied in situ samples were not significantly affected by roots. The variation of measured and predicted ksat values spanned an order of magnitude, regardless of the root colonization intensity, up to a root length density (RLD) of 2.98 cm/cm3. RLD showed a significant and positive linear relationship with measured ksat values ( R2 = 0.54). However, when root colonization was low (RLD < 1 cm/cm3), RLD was negatively correlated with the nvG ( R2 = 0.44) parameter of the van Genuchten WRC model, while the opposite relationship was observed for samples with RLD > 1 cm/cm3 ( R2 = 0.61). Additionally, RLD and the coarse root (diameter > 1 mm) volume to fine root volume (C/F ratio) influenced WRCs. Over time, coarser roots may have a more pronounced impact on SHPs; further research is needed.

Rock fragments within topsoil have important effects on soil properties and plant growth. This study mainly aimed to investigate the relationships between rock fragments, soil carbon (C) and nitrogen (N) densities and vegetation biomass in an alpine steppe. Rock fragments, plant and soil samples were collected from four topographic positions (top, upper, lower, and bottom) on a hillslope. Volumetric rock fragment content within the 0–30 cm soil profile varied from 17.8 to 30.5%, the upper position value was significantly greater (P < 0.05) than those at other positions. The highest aboveground biomass was observed at the lower position (921 kg ha−1), while the highest belowground biomass within the 0–30 cm profile was found at the upper position (4460 kg ha−1). More fine earth and plant litter input accompanied by lower C and N losses induced by rainfall erosion resulted in higher soil organic C and total N densities (28.6 Mg C ha−1 and 2.87 Mg N ha−1) at the lower position. Rock fragments may promote root growth but limit aboveground biomass production, and can therefore change the biomass distribution pattern. Our findings provide more evidence for scientifically assessing alpine steppe productivity.

Effective cleanup of contaminated sites requires characterization of the hydraulic properties of impacted soils. To this end, we present a new method for estimating soil-water characteristic and hydraulic conductivity curves with a modified cone penetrometer. A prototype has been designed and fabricated with a screen close to the penetrometer tip and two tensiometer rings 5 and 9 cm above the screen. Water is injected into the soil under constant pressure. The volume of water imbibed into the soil is monitored, as are the tensiometer ring readings registering the advancement of the wetting front. These transient flow data are used to estimate soil hydraulic properties via numerical inversion of Richards' equation. We present the results of cone tests performed under variably saturated conditions in a laboratory aquifer system. Results are compared with independent measurements of the soil hydraulic properties to benchmark the performance of the instrument and method of analysis. The saturated hydraulic co...

Divergent effects of food waste derived hydrochar on hydraulic properties and infiltration in a sandy soil

Numerical assessment of effective evapotranspiration from maize plots to estimate groundwater recharge in lowlands

Effect of rock fragments content on water consumption, biomass and water-use efficiency of plants under different water conditions