Shear strength of compacted soil: effects on splash erosion by single water drops

The persistence of soil compaction, caused by farmers' vehicles (tractors wheelings) during the dry season, can affect splash distribution and soil erosion so that surface flow starts at an earlier stage than between the wheelings. To investigate the effects of soil compaction on splash distribution, a dry clayey agricultural soil was compacted in steel cups with a hydraulic piston, and the shear strength was measured with a fall‐cone penetrometer. Two cups were compacted in the same manner, using one to measure the shear strength and the second for splash erosion measurements. A laboratory splash board of 1 m radius, divided into 13 concentric compartments, was used to collect the splashed particles. The water drop diameter used was 4·9 mm falling onto a soil splash cup of 50·2 cm² area from 8 m height with a terminal velocity of 8·8 m s^?1. The spatial distribution of the splashed particles, for different soil compactions, fitted the fundamental splash distribution function (FSDF) model better than the exponential function. The shapes of the curves of this function demonstrated the importance of the source area size; the smaller the cup diameter the better the spatial distribution is expressed by an exponential function. In addition, variability in soil surface conditions contributes to variation in splash characteristics. Detachment rates and average radial distance followed second degree relationships in terms of shear strength. Copyright © 2010 John Wiley & Sons, Ltd.     

Response of soil aggregate disintegration to the different content of organic carbon and its fractions during splash erosion

Aggregate disintegration is a critical process in soil splash erosion. However, the effect of soil organic carbon (SOC) and its fractions on soil aggregates disintegration is still not clear. In this study, five soils with similar clay contents and different contents of SOC have been used. The effects of slaking and mechanical striking on splash erosion were distinguished by using deionized water and 95% ethanol as raindrops. The simulated rainfall experiments were carried out in four heights (0.5, 1.0, 1.5 and 2.0 m). The result indicated that the soil aggregate stability increased with the increases of SOC and light fraction organic carbon (LFOC). The relative slaking and the mechanical striking index increased with the decreases of SOC and LFOC. The reduction of macroaggregates in eroded soil gradually decreased with the increase of SOC and LFOC, especially in alcohol test. The amount of macroaggregates (>0.25 mm) in deionized water tests were significantly less than that in alcohol tests under the same rainfall heights. The contribution of slaking to splash erosion increased with the decrease of heavy fractions organic carbon. The contribution of mechanical striking was dominant when the rainfall kinetic energy increased to a range of threshold between 9 J m⁻² mm⁻¹ and 12 m⁻² mm⁻¹. This study could provide the scientific basis for deeply understanding the mechanism of soil aggregates disintegration and splash erosion.     

A conceptual model for determining soil erosion by water

Current estimates of rates of soil erosion by water derived from plots are incompatible with estimates of long‐term lowering of large drainage basins. Traditional arguments to reconcile these two disparate rates are ?awed. The ?ux of sediment leaving a speci?ed area cannot be converted to a yield simply by dividing by the area, because there is no simple relationship between ?ux and area. Here, we develop an approach to the determination of erosion rates that is based upon the entrainment rates and travel distances of individual particles. The limited available empirical data is consistent with the predictions of this approach. Parameterization of the equations to take account of such factors as gradient and sediment supply is required to proceed from the conceptual framework to quantitative measurements of erosion. However, our conceptual model solves the apparent paradox of the sediment delivery ratio, resolves recent discussion about the validity of erosion rates made using USLE erosion plots, and potentially can reconcile erosion rates with known lifespans of continents. Our results imply that previous estimates of soil erosion are fallacious. Copyright © 2004 John Wiley & Sons, Ltd.     

Changes of soil surface roughness under water erosion process

The objective of this study was to determine the changing characteristics of soil surface roughness under different rainfall intensities and examine the interaction between soil surface roughness and different water erosion processes. Four artificial management practices (raking cropland, artificial hoeing, artificial digging, and contour tillage) were used according to the local agriculture customs of the Loess Plateau of China to simulate different types of soil surface roughness, using an additional smooth slope for comparison purposes. A total of 20 rainfall simulation experiments were conducted in five 1 m by 2 m boxes under two rainfall intensities (0.68 and 1.50 mm min^?1) on a 15° slope. During splash erosion, soil surface roughness decreased in all treatments except raking cropland and smooth baseline under rainfall intensity of 0.68 mm min^?1, while increasing for all treatments except smooth baseline under rainfall intensity of 1.50 mm min^?1. During sheet erosion, soil surface roughness decreased for all treatments except hoeing cropland under rainfall intensity of 0.68 mm min^?1. However, soil surface roughness increased for the artificial hoeing and raking cropland under rainfall intensity of 1.50 mm min^?1. Soil surface roughness has a control effect on sheet erosion for different treatments under two rainfall intensities. For rill erosion, soil surface roughness increased for raking cropland and artificial hoeing treatments, and soil surface roughness decreased for artificial digging and the contour tillage treatments under two rainfall intensities. Under rainfall intensity of 0.68 mm min^?1, the critical soil surface roughness was 0.706 cm for the resistance control of runoff and sediment yield. Under rainfall intensity of 1.50 mm min^?1, the critical soil surface roughness was 1.633 cm for the resistance control of runoff, while the critical soil surface roughness was 0.706 cm for the resistance control of sediment yield. These findings have important implications for clarifying the erosive nature of soil surface roughness and harnessing sloped farmland. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of a water infiltration model for simulating water repellency of humus soil

One-dimensional infiltration experiments were conducted using hydrophilic and water-repellent soils from the Guishui River Basin to study the effects of soil water repellency on cumulative infiltration (CI) and the infiltration rate (IR). The test results show that, for the hydrophilic soil (HS) sample, CI increases monotonously with time and IR decreases monotonously. For the water-repellent soil (W-RS), however, the following characteristics were observed: (a) There is an inflection point in CI and a sudden increase in IR. Larger values of the initial soil water content produce an earlier and more significant inflection point in CI, and a larger peak value of IR. (b) The post-peak stable IR is greater than the pre-peak value, ignoring the beginning of rapid infiltration, and the overall IR presents a single peak. The applicability of various water infiltration models was analysed for the two soil types. Numerical analysis suggests the following conclusions: (a) For both HS and W-RS, the Kostiakov function, Gamma function, and Beta function (BF) models exhibit good applicability. (b) For W-RS, the Gauss function model not only reflects the monotonous decrease in IR, but also produces a steady IR in the initial stage, a gradual increase before the peak value, and a gradual decrease after the peak value. Similarly, the BF model reflects the monotonous decrease in IR. A piecewise BF reproduces the U-shaped change in rapid infiltration before the inflection point, as well as the gradual increase and right-skewed distribution curve of W-RS infiltration before and after the inflection point. The BF model achieves the best simulation accuracy and has the widest applicability.     

On standardizing the ‘Water Drop Penetration Time’ and the ‘Molarity of an Ethanol Droplet’ techniques to classify soil hydrophobicity: A case study using medium textured soils

Two common methods to assess soil hydrophobicity are the ‘Water Drop Penetration Time’ and ‘Molarity of an Ethanol Droplet’ techniques. For these, uncertainty exists regarding the representativeness of laboratory tests reflecting field conditions, their replicability, and the comparability of results between the two techniques. Using air-dried soils with a broad particle size and hydrophobicity range, this study shows that a high representativeness and replicability of results can be achieved. A close relationship between the two tests was found for highly, but not for moderately hydrophobic soils. Guidelines are suggested to increase representativeness, replicability and comparability of results in future studies. © 1998 John Wiley & Sons, Ltd.     

A physically-based model of the dispersion of splash droplets ejected from a water drop impact

A model has been developed which predicts the dispersion of splash droplets produced by the impact of a water drop on a sloping soil surface. Experimental results of the ejection velocities and ejection angles of the splash droplets are generalized to a planar slope and the resulting splash distances are calculated taking into account the effects of air resistance. The predictions are presented in terms of the numbers of splash droplets from the impact point to surrounding squares arranged in a grid on the slope. The model explains many experimentally observed features of raindrop splash in terms of the mechanics of the processes involved and can make predictions of the effects of slope, wind, raindrop size, and soil properties on droplet dispersion. The component of the raindrop velocity parallel to the surface of the slope is identified as the main factor determining the degree and the direction of the asymmetry in the splash droplet dispersion. By combining the model with a theory of the entrapment of soil in the splash droplets it is possible to extend it to predict the dispersion of soil particles by raindrop impact, which is the basis of a model of soil erosion by rainsplash.     

A conceptual model of wind erosion of soil surfaces by saltating particles

A conceptual model is described for the prediction of wind erosion rates dependent on the distribution of impact energy delivered to the surface by saltating grains, P[Ei], and the distribution of local surface strength, P[Es]. Methods are presented for the measurement of both distributions and consequent loss of material from the bed. It is concluded that saltating sand grains can rupture weak crusts under even moderate wind conditions, and that the rate of erosion will depend on the shape of the distribution tails. Copyright © 1999 John Wiley & Sons, Ltd.     

Spatial and temporal variations of actual soil water repellency and their influence on surface runoff

The increase of surface runoff at the plot scale caused by soil water repellency is a generally accepted phenomenon. However, to improve the understanding of the effect of water repellency on runoff at the catchment scale, spatio‐temporal dynamics of water repellency have to be analysed in more detail. The experimental setup of this study allowed the investigation of the relationship between water repellency and runoff generation on Quaternary and Tertiary sandy substrates while ensuring similar conditions in terms of terrain characteristics, meteorological and vegetation‐free conditions on both areas. Measurements of water drop penetration time and contact angle were carried out over a period from September 2003 to December 2005. Spatial variability of actual soil water repellency was related to heterogeneity of substrate and geomorphologic units, variations in time were related with the seasons and their meteorological conditions. To relate variable degrees of actual water repellency to surface runoff generation, both variables were measured in parallel at the plot scale (1 m × 1 m) and at the hillslope scale from September 2004 to December 2005. Soil water repellency of the Tertiary sands showed a temporal variability depending on the season, with the highest degree during summer and autumn. Variation of hydrophobicity between the seasons caused higher runoff coefficients in summer and autumn. Spatial heterogeneity of the soil water repellency revealed lower values in fine‐textured erosion rills and higher values for interrills and top areas. The measured runoff coefficients decreased from the scale of microplots to the hillslope scale due to infiltration in hydrophilic rills on the hillslope. The results suggest that improved hydrological modelling approaches on water‐repellent soils can be based on a geomorphological subdivision of the catchment area and seasonally varying infiltration parameters. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of soil properties on erosion by wash and splash

This paper describes laboratory testing of 148 samples collected from Southern Alberta for erosion by wash and splash. Rainfall intensity was held constant during these tests. Soil aggregation was the most significant variable explaining soil loss. The significance of other soil properties, such as organic carbon and clay content is variable, depending on the interrelationships among aggregate stability, organic content, and clay content of particular soils. Variations in erodibility of the major soils examined are explained by the resistance of aggregates to compaction and dispersion. Splash detachment and wash transport are the dominant erosion mechanisms in inter-rill areas.     

Modelling water erosion in the Sahel: application of a physically based soil erosion model in a gentle sloping environment

Water is a major limiting factor in arid and semi‐arid agriculture. In the Sahelian zone of Africa, it is not always the limited amount of annual rainfall that constrains crop production, but rather the proportion of rainfall that enters the root zone and becomes plant‐available soil moisture. Maximizing the rain‐use efficiency and therefore limiting overland flow is an important issue for farmers. The objectives of this research were to model the processes of infiltration, runoff and subsequent erosion in a Sahelian environment and to study the spatial distribution of overland flow and soil erosion. The wide variety of existing water erosion models are not developed for the Sahel and so do not include the unique Sahelian processes. The topography of the Sahelian agricultural lands in northern Burkina Faso is such that field slopes are generally low (0–5°) and overland flow mostly occurs in the form of sheet flow, which may transport large amounts of fine, nutrient‐rich particles despite its low sediment transport capacity. Furthermore, pool formation in a field limits overland flow and causes resettlement of sediment resulting in the development of a surface crust. The EUROSEM model was rewritten in the dynamic modelling code of PCRaster and extended to account for the pool formation and crust development. The modelling results were calibrated with field data from the 2001 rainy season in the Katacheri catchment in northern Burkina Faso. It is concluded that the modified version of EUROSEM for the Sahel is a fully dynamic erosion model, able to simulate infiltration, runoff routing, pool formation, sediment transport, and erosion and deposition by inter‐rill processes over the land surface in individual storms at the scale of both runoff plots and fields. A good agreement is obtained between simulated and measured amounts of runoff and sediment discharge. Incorporating crust development during the event may enhance model performance, since the process has a large influence on infiltration capacity and sediment detachment in the Sahel. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparison of the effects of litter covering and incorporation on infiltration and soil erosion under simulated rainfall

Plant litter can either cover on soil surface or be incorporated into top-soil layer in natural ecosystems. Their effects on infiltration and soil erosion are likely quite different. This study was performed to compare the effects of litter covering on soil surface and being incorporated into top-soil layer on infiltration and soil erosion under simulated rainfall. Four litter types (needle-leaf, broad-leaf, brush, and herb) were collected from fields and applied to cover on soil surface or to be incorporated into top-soil layer (5 cm) at the same rate (0.2 kg/m²). The simulated rainfalls (40 and 80 mm/hr) were run at two slope angles (10° and 20°). The results showed that the mean infiltration rate of litter covering treatment was 1.4 times as great as that of litter incorporated. Litter covering enhanced infiltration via protecting surface from soil sealing. Whereas, litter incorporation affected infiltration by its water repellency. Soil erosion of litter incorporated treatment was 5.4 times as large as that of litter covered treatment, which was attributed to the changes in surface litter coverage and soil erosion resistance. Litter type affected soil erosion through the variations in litter coverage and litter morphology. For litter covering treatment, litter coverage can explain the major variance of soil loss on the slopes. Whereas, for litter incorporated treatment, both the influences of litter coverage and litter length on soil erosion resistance were considered necessary to well explain the variance of soil loss. The results also showed that the benefits of litter to control soil erosion declined with rainfall intensity and slope gradient for both covering and incorporated treatments. The results of this study are helpful to understand the mechanisms of litter influencing hydrological and erosion processes on hillslopes.     

Alternative analysis of transient infiltration experiment to estimate soil water repellency

The repellency index (RI) defined as the adjusted ratio between soil‐ethanol, S_e, and soil‐water, S_w, sorptivities estimated from minidisk infiltrometer experiments has been used instead of the widely used water drop penetration time and molarity of ethanol drop tests to assess soil water repellency. However, sorptivity calculated by the usual early‐time infiltration equation may be overestimated as the effects of gravity and lateral capillary are neglected. With the aim to establish the best applicative procedure to assess RI, different approaches to estimate S_e and S_w were compared that make use of both the early‐time infiltration equation (namely, the 1 min, S1, and the short‐time linearization approaches), and the two‐term axisymmetric infiltration equation, valid for early to intermediate times (namely, the cumulative linearization and differentiated linearization approaches). The dataset included 85 minidisk infiltrometer tests conducted in three sites in Italy and Spain under different vegetation habitats (forest of Pinus pinaster and Pinus halepensis, burned pine forest, and annual grasses), soil horizons (organic and mineral), postfire treatments, and initial soil water contents. The S1 approach was inapplicable in 42% of experiments as water infiltration did not start in the first minute. The short‐time linearization approach yielded a systematic overestimation of S_e and S_w that resulted in an overestimation of RI by a factor of 1.57 and 1.23 as compared with the cumulative linearization and differentiated linearization approaches. A new repellency index, RI_s, was proposed as the ratio between the slopes of the linearized data for the wettable and hydrophobic stages obtained by a single water infiltration test. For the experimental conditions considered, RI_s was significantly correlated with RI and WDPT. Compared with RI, RI_s includes information on both soil sorptivity and hydraulic conductivity and, therefore, it can be considered more physically linked to the hydrological processes affected by soil water repellency.     

Effects of physical soil crusts on infiltration and splash erosion in three typical Chinese soils

Physical soil crusts likely have significant effects on infiltration and soil erosion, however, little is known on whether the effects of the crusts change during a rainfall event. Further, there is a lack of discussions on the differences among the crusting effects of different soil types. The objectives of this study are as follows： （i） to study the effects of soil crusts on infiltration, runoff, and splash erosion using three typical soils in China, （ii） to distinguish the different effects on hydrology and erosion of the three soils and discuss the primary reasons for these differences, and （iii） to understand the variations in real soil shear strength of the three soils during rainfall events and mathematically model the effects of the crusts on soil erosion. This study showed that the soil crusts delayed the onset of infiltration by 5 to 15 min and reduced the total amount of infiltration by 42.9 to 53.4% during rainfall events. For a purple soil and a loess soil, the initial crust increased the runoff by 2.8% and 3.4%, respectively, and reduced the splash erosion by 3.1% and 8.9%, respectively. For a black soil, the soil crust increased the runoff by 42.9% and unexpectedly increased the splash erosion by 95.2%. In general, the effects of crusts on the purple and loess soils were similar and negligible, but the effects were significant for the black soil. The soil shear strength decreased dynamically and gradually during the rainfall events, and the values of crusted soils were higher than those of incrusted soils, especially during the early stage of the rainfall. Mathematical models were developed to describe the effects of soil crusts on the splash erosion for the three soils as follows： purple soil, Fc= 0.002t- 0.384 ; black soil, Fc. =-0.022t ＋ 3.060 ; and loess soil, Fc = 0.233 In t- 1.239 . Combined with the equation Rc= Fc （Ruc - 1）, the splash erosion of the crusted soil can be predicted over time.     

Effect of soil water-repellent layer depth on post-wildfire hydrological processes

Soil water repellency induced by wildfires can alter hydraulic properties and hydrologic processes; however, the persistence and vertical position (i.e., depth) of water-repellent layers can vary between systems and fires, with limited understanding of how those variations affect infiltration processes. This study occurred in two forested locations in the south-central Appalachian Mountains that experienced wildfires in late 2016: Mount Pleasant Wildfire Refuge, Virginia, and Chimney Rock State Park, North Carolina. In each location, sites were selected to represent unburned conditions and low to moderate burn intensities. At each site, we measured the soil water repellency at the surface (ash layer or O horizon) and ~2 cm below the surface (A horizon) using the water drop penetration time method (n = 10–14). Soil water content was also measured over the upper 10 cm of the soil (n = 10), and infiltration tests were conducted using a tension infiltrometer (n = 6–8). The results showed that soil repellency was highest in the surface layer at the Mount Pleasant location and was highest in the subsurface layer at the Chimney Rock location. Soil water content was lower in unburned soil than in burned soil, especially for measurements taken immediately postfire, with soil water content negatively correlated with water repellency. Water repellency in the surface layer significantly reduced relative infiltration rates (estimated as differences between initial and steady-state rates), whereas subsurface water repellency did not affect relative infiltration. As a result, water repellency persisted longer in sites with surface as opposed to subsurface water repellency. Finally, differences between burned and unburned sites showed that although the wildfires increased the occurrence of water repellency, they did not alter the underlying relationship between relative infiltration and water repellency of the surface soil.     

A bimodal four‐parameter lognormal linear model of soil water repellency persistence

Soil water repellency may be characterized in terms of the delayed infiltration time of a water droplet resting on the soil surface, which is, water drop penetration time (WDPT), or repellency persistence. Such repellency persistence varies nonlinearly with soil water content (θ_g), although no models have been proposed to reproduce the variation of WDPT with θ_g in soils. Dynamic factor analysis (DFA) is used to identify two common patterns of unexplained variability in a scattered dataset of WDPT versus θ_g measurements. A four‐parameter lognormal distribution was fitted to both common patterns obtained by DFA, and these were combined additively in a weighted multiple linear bimodal model. We show how such an empirical model is capable of reproducing a large variety of WDPT versus θ_g curve shapes (N = 80) both within a wide range of measured WDPTs (0–17 000 s) and for samples with organic matter content ranging from 21·7 to 80·6 g (100 g)^?1. Copyright © 2009 John Wiley & Sons, Ltd.     

A simple water balance model adapted for soil water repellency: application on Portuguese burned and unburned eucalypt stands

Soil water repellency can impact soil hydrology, overland flow generation and associated soil losses. However, current hydrological models do not take it into account, which creates a challenge in repellency‐prone regions. This work focused on the adaptation for soil water repellency of a daily water balance model. Repellency is estimated from soil moisture content using site‐specific empirical relations and used to limit maximum soil moisture. This model was developed and tested using approximately 2 years of data from one long‐unburned and two recently burned eucalypt plantations in northern Portugal, all of which showed strong seasonal soil water repellency cycles. Results indicated important improvements for the burned plantations, with the Nash–Sutcliffe efficiency increasing from ?0.55 and ?0.49 to 0.55 and 0.65. For the unburned site, model performance was already good without the modification and efficiency only improved slightly from 0.71 to 0.74, mostly due to the better simulation of delayed soil wetting after dry periods. Results suggested that even a simple approach to simulate soil water repellency can markedly improve the performance of hydrological models in eucalypt forests, especially after fire. Copyright © 2015 John Wiley & Sons, Ltd.     

Unsteady soil erosion due to rainfall impact: a model of sediment sorting on the hillslope

A new method is presented for predicting sediment sorting associated with soil erosion by raindrop impact for non-equilibrium conditions. The form of soil erosion considered is that which results from raindrop impact in the presence of shallow overland flow itself where the flow is not capable of eroding sediment. The method specifically considers early time runoff and erosion when sediment leaving an eroding area is generally finer and thus may have a higher potential for transport of sorbed pollutants. The new mechanism described is the formation of a deposited layer on the soil surface, which is shown to lead to sediment sorting during an erosion event. The deposited layer is taken to have two roles in this process: to temporarily store sediment on the surface between successive trajectories, and to shield the underlying soil from erosive stresses. Equations describing the dynamics of the suspended sediment mixture and the deposited layer are developed. By integrating these equations over the length of eroding land element and over the duration of the erosion event, an event-based solution is proposed which predicts total sediment sorting over the event. This solution is shown to be consistent with experimentally observed trends in enrichment of fine sediment. Predictions using this approach are found to only partly explain measured enrichment for sets of experimental data for two quite different soils, but to be in poor agreement for an aridsol of dispersive character. It is concluded that the formation of the deposited layer is a significant mechanism in the enrichment of fine sediment and associated sorbed pollutants, but that processes in the dispersive soil are not as well described by the theory presented.     

Impact of wildfires on surface water repellency in soils of northwest Spain

Soil water repellency (hydrophobicity) is a naturally occurring phenomenon that can be intensified by soil heating during fires. Fire‐induced water repellency, together with the loss of plant cover, is reportedly the principal source of increased surface runoff and accelerated erosion in burned soils. In this study, the surface water repellency of several soils affected by summer forest fires in northwest Spain was studied and compared with that of adjacent unburned soils. Soil water repellency was determined using the ethanol percentage test (MED). Most of the unburned soil samples exhibited water repellency that ranged from strong to very strong; only four of the unburned soil samples were non‐repellent. Water repellency in the unburned soils was significantly correlated with the organic carbon content (r = 0·64, p < 0·05). Overall, fires increased the surface water repellency in soils with previously low degrees of water repellency and caused little change in that of originally strongly hydrophobic soils. In order to examine in detail the changes in water repellency with temperature, three unburned soil samples were subjected to a controlled heating program. Water repellency increased between 25 and 220 °C, water repellency peaked between 220 and 240 °C and disappeared above 260–280 °C. Extrapolation of the results of the heating tests to field conditions suggested that the intensity of fire (temperature and time of residence) reached by most soils during fires is not too high. Based on the results, the determination of water repellency could be used as a simple test for the indirect estimation of the intensity levels reached on the soil surface during a fire. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of eastern redcedar encroachment on soil hydraulic properties along Oklahoma's grassland‐forest ecotone

In north‐central Oklahoma eastern redcedar (Juniperus virginiana), encroachment into grassland is widespread and is suspected of reducing streamflow, but the effects of this encroachment on soil hydraulic properties are unknown. This knowledge gap creates uncertainty in understanding the hydrologic effects of eastern redcedar encroachment and obstructs fact‐based management of encroached systems. The objective of this study was to quantify the effects of eastern redcedar encroachment into tallgrass prairie on soil hydraulic properties. Leaf litter depth, soil organic matter, soil water repellency, soil water content, sorptivity, and unsaturated hydraulic conductivity were measured near Stillwater, OK, along 12 radial transects from eastern redcedar trunks to the center of the grassy intercanopy space. Eastern redcedar encroachment in the second half of the 20th century caused the accumulation of 3 cm of hydrophobic leaf litter near the trunks of eastern redcedar trees. This leaf litter was associated with increased soil organic matter in the upper 6 cm of soil under eastern redcedar trees (5.96% by mass) relative to the grass‐dominated intercanopy area (3.99% by mass). Water repellency was more prevalent under eastern redcedar than under grass, and sorptivity under eastern redcedar was 0.10 mm s^?1/2, one seventh the sorptivity under adjacent prairie grasses (0.68 mm s^?1/2). Median unsaturated hydraulic conductivity under grass was 2.52 cm h^?1, four times greater than under eastern redcedar canopies (0.57 cm h^?1). Lower sorptivity and unsaturated hydraulic conductivity would tend to decrease infiltration and increase runoff, but other factors such as rainfall interception by the eastern redcedar canopy and litter layer, and preferential flow induced by hydrophobicity must be examined before the effects of encroachment on streamflow can be predicted. Copyright © 2011 John Wiley & Sons, Ltd.