Physical Crusts Research Articles

Litter cover breaks soil water repellency of biocrusts, enhancing initial soil water infiltration and content in a semi-arid sandy land

Soil biocrusts are an important type of surface cover in sandy ecosystems, covering about 12% of the terrestrial surface. The biocrusts affect the hydrological process of sandy land by means of inhibiting soil water initial infiltration and exchange in the topsoil, and thus hinder vegetation recovery of sandy land. This study was conducted to explore the response of the soil infiltration performance and soil water content underneath the biocrusts (dominated by lichen and moss) in litter cover. The differences in soil infiltration rate and soil water content among five treatments (bare sandy land, physical crusts, biocrusts, litter covered biocrusts, and litter crusts) in the Mu Us Desert were investigated by the single-rings infiltrometer and the oven-drying method. Results showed that the initial soil infiltration rate of litter covered biocrusts and litter crusts were 215% and 280% higher than that of biocrusts. The average soil water content in litter crusts (11.7%) and litter covered biocrusts (10.2%) were 3.3 and 2.9 times greater than that in biocrusts, respectively. Our results indicated that litter cover could break the water repellency of biocrusts, increase the initial soil infiltration rates, and increase the soil surface water content. This criterion will help promote ecological restoration in sandy ecosystems.

Influence of physical crust cover on the wind erodibility of soils in the inland Pacific Northwest, USA

AbstractSoil crusts are especially important for agricultural fields in the inland Pacific Northwest where there is a high wind erosion risk due to exposure of fine erodible soils in fallow croplands. The objective of this study was therefore to evaluate the effect of physical soil crust cover on wind erosion and identify critical soil crust cover amounts to control wind erosion. The effect of crust cover of five loessial soils on wind erosion was tested in a wind tunnel. The results indicated that crust cover appeared to have little influence on soil loss until crust cover was > 30%. Soil loss at this percentage of crust cover was 55.04% to 68.08% lower as compared with a soil surface devoid of crust cover for the five soil types. The relationship between soil loss and crust cover appeared to be nearly a linear function, although an exponential function also provided a good fit to the data. With progressive development of a crust cover, the rate of change in soil loss varied among soil types. From 0 to 100% crust cover, the rate of change in soil loss ranged from −312.8 g m−2 for Palouse silt loam to −1449.1 g m−2 for Warden sandy loam. The rate was not only associated with intrinsic soil erodibility, but also crust stability and abrasion flux. Due to the lower intrinsic soil erodibility and greater crust stability, Palouse silt loam crust was characterized by lower flaking potential and limited abrasion flux relative to the other tested soil types. The Single‐event Wind Erosion Evaluation Program (SWEEP) was used to simulate and identify the effect of crust cover on erosion processes. Differences between simulated and measured soil loss suggest that cracks in soil crusts may affect soil loss and should be incorporated into the SWEEP to expand the model capability for representing crusted soils.

Bacterial diversity patterns of desert dunes in the northeastern Qinghai-Tibet Plateau, China.

Limited knowledge about the variation patterns of bacterial community composition in the sand and vegetative ecosystems confines our understanding regarding the contribution of the sand dune to desert areas. In this study, 454 pyrosequencing platforms were adopted to determine the community structure of bacteria and diversity of sand dunes in northeastern Qinghai-Tibet Plateau, China: 50cm deep, rhizosphere, physical crusts, and biological crusts representing sand and vegetative ecosystems, respectively. The findings revealed significant variation in bacterial diversities and the structure of communities in the sand and vegetative ecosystems. The dominant bacterial phyla of sand and vegetative ecosystems were Firmicutes (47%), Actinobacteria (21%), Proteobacteria (16%), and Bacteroidetes (13%), while Lactococcus (50%) was found to be the dominant genus. Furthermore, samples with high alpha-diversity indices (Chao 1 and Shannon) for the vegetative ecosystem have the lowest modularity index and the largest number of biomarkers, with some exceptions. Redundancy analysis exhibited that environmental factors could explain 72% (phyla) and 67% (genera) of the bacterial communities, with EC, TC, and TOC being the major driving factors. This study expands our understanding of bacterial community composition in the desert ecosystem. The findings suggest that variations in the sand and vegetative ecosystems, such as those predicted by environmental factors, may reduce the abundance and diversity of bacteria, a response that likely affects the provision of key ecosystem processes by desert regions.

Gravel-Desert Surface Properties and Their Influences on the Wind-Erosion Threshold Friction Velocity in North-West China

In north-west China, extensive areas of gravel desert exist, whose surface properties have an important effect on the wind-erosion threshold friction velocity $$ u_{*t} $$ . In this study, we use four models and field observations of gravel mass fraction, soil physical crust, and soil clay content to assess the effect of gravel-surface properties on the value of $$ u_{*t} $$ . Results show that gravel coverage in north-west China ranges between 0.07 and 1.00 (with a mean of 0.67), and about 81% of the sites investigated are covered by soil physical crust. Clay content is 2.4% on average in the study region, less than 2% in 52.1% of that region, and between 2 and 4% in the remaining study regions. The four regions where clay content is greater than the mean include the western Alxa Plain, the alluvial fan of the western Alxa Plain, the northern Alxa Plain, and the Hexi Corridor. In the study region, the value of $$ u_{*t} $$ ranges between 0.12 and 0.78 m s−1 (with a mean of 0.45 m s−1). Soil moisture, gravel coverage, and soil physical crust all affect the magnitude of $$ u_{*t} $$ . A principal component analysis indicates that the soil crust contributes of about 62% of the $$ u_{{*{\text{t}}}} $$ variations, soil moisture 25%, and surface roughness 9%. A variance analysis shows clear spatial differences in the magnitude of $$ u_{*t} $$ in north-west China due to the spatial variations in gravel land-surface properties.

Physical Crust Formation on Sandy Soils and Their Potential to Reduce Dust Emissions from Croplands

The sandy croplands in the Free State have been identified as one of the main dust sources in South Africa. The aim of this study was to investigate the occurrence and strength of physical soil crusts on cropland soils in the Free State, to identify the rainfall required to form a stable crust, and to test their impact on dust emissions. Crust strength was measured using a fall cone penetrometer and a torvane, while laboratory rainfall simulations were used to form experimental crusts. Dust emissions were measured with a Portable In-Situ Wind Erosion Laboratory (PI-SWERL). The laboratory rainfall simulations showed that stable crusts could be formed by 15 mm of rainfall. The PI-SWERL experiments illustrated that the PM10 emission flux of such crusts is between 0.14% and 0.26% of that of a non-crusted Luvisol and Arenosol, respectively. The presence of abraders on the crust can increase the emissions up to 4% and 8% of the non-crusted dust flux. Overall, our study shows that crusts in the field are potentially strong enough to protect the soil surfaces against wind erosion during a phase of the cropping cycle when the soil surface is not protected by plants.

Litter cover promotes biocrust decomposition and surface soil functions in sandy ecosystem

Ecological restoration of sandy inland ecosystems is important for achieving global sustainability. In the world’s semi-arid regions, soil crusts play crucial roles in maintaining ecosystem functioning. However, the true extent of soil quality improvement during the development of crusts is an issue not solved. In this study, four development stages of natural soil crusts, i.e., physical crusts (PC), biocrusts (BC), litter covered biocrusts (LBC) and litter crusts (LC) were selected in a semi-arid sandy ecosystem, along with a bare sandy land (BSL) as control area, to evaluate soil physicochemical properties at different soil depths. The coverage of litter (mainly leaves of Populus simonii) increased soil moisture and reduced soil bulk density. Compared with BC, the content of total soil organic matter (SOM) decreased in LBC by 13.83% and increased in LC by 36.57%. In contrast with BC, LC promoted a significant increase in soil nutrients, such as total nitrogen (30.30%), total phosphorus (46.89%) and available potassium (34.40%) in the topsoil layer (0–2 cm). Besides, LC contained higher clay and silt contents (10.47% and 29.81%) and lower sand content (−1.02%) than BC. In the 0–10 cm soil layer, the D (fractal dimension of the soil particle size distribution) of LC was the largest, with a value 5.71%, 6.1%, 2.44% and 0.93% higher than D in BSL, PC, BC and LBC, respectively. These findings reveal that litter covering facilitate the disintegration of BC, which further forms LC, and these processes clearly promote the enhancement of soil quality under sandy semi-arid conditions. Our findings are particularly important for predicting the transformation processes of sandy soil crusts and are of interest in ecological restoration programs.

Network analysis reveals the strengthening of microbial interaction in biological soil crust development in the Mu Us Sandy Land, northwestern China

Although studies examining changes in the structure and diversity of microbial communities in biological soil crusts (BSCs) have increased, microbial interactions in BSCs are not currently fully understood. In this study, we applied a random matrix theory (RMT)-based network approach to construct bacterial, fungal and bacteria-fungal interaction networks for the four developmental stages of BSCs (bare sand, physical crusts, algae crusts and moss crusts) in the Mu Us Sandy Land, northwestern China. Our results showed that Firmicutes, Proteobacteria, Cyanobacteria and Actinobacteria were the keystone phylum in bacterial networks in the four developmental stages, respectively. Ascomycota was the keystone phylum in the fungal networks in all stages, and Basidiomycota was a further keystone phylum in the algae and moss crust networks. With the development of BSCs, complexity in bacterial and fungal networks increased, becoming more clustered and connected, indicating a strengthened pattern in microbial interactions with BSC development. Positive links dominated in all networks, showing that microbial synergism was important in the development of BSCs. Interestingly, with the development of BSCs, the proportion of negative links in bacterial networks increased and they decreased in fungal networks, suggesting more inter-community competition was present in the bacterial communities and less inter-community competition was present in the fungal communities. Environmental factors, especially total carbon and total organic carbon, constrained most bacterial and fungal communities, respectively. Our findings provided a new insight into understanding BSC developmental mechanisms and ecological functions in a desert ecosystem composed of a sandy land landscape in arid and semi-arid regions.

Spatial and Temporal Evolution of the Infiltration Characteristics of a Loess Landslide

Infiltration plays an important role in influencing slope stability. However, the influences of slope failure on infiltration and the evolution of infiltration over time and space remain unclear. We studied and compared the infiltration rates in undisturbed loess and disturbed loess in different years and at different sites on loess landslide bodies. The results showed that the average initial infiltration rate in a new landslide body (triggered on 11 October 2017) were dramatically higher than those in a previous landslide body (triggered on 17 September 2011) and that the infiltration rates of both landslide types were higher than the rate of undisturbed loess. The initial infiltration rate in the new landslide body sharply decreased over the 4–5 months following the landslide because of the appearance of physical crusts. Our observations indicated that the infiltration rate of the disturbed soil in a landslide evolved over time and that the infiltration rate gradually approached that of undisturbed loess. Furthermore, in the undisturbed loess, both the initial and quasi-steady infiltration rates were slightly higher in the loess than in the paleosol, and in the previous landslide body, the infiltration rate was highest in the upper part, intermediate in the middle part, and lowest in the lower part. This study can help us to better understand the evolution process of infiltration in undisturbed loess, previous landslides, and new landslides.

Measuring and estimating the hydrological properties of a soil crust

Formation of soil crusts results in reduced infiltration, increased runoff, and reduced rainfall and irrigation efficiency. Improved knowledge of the hydrological properties of soil crusts is required to improve simulation of infiltration and soil water movement in crop-soil-water models. Development of soil crust algorithms in soil water models is limited by a lack of in situ and laboratory approaches for measuring the physical properties of soil crusts. In this study we evaluate a number of novel and modified approaches for determining changes in the hydraulic properties of soil crusts formed in an intensively cropped sandy loam. Physical crust formation over a 71 day period resulted in an increase in surface soil density from 1.17 to 1.51 g cm−3, a reduction in infiltration from 474 to 33.2 mm h−1, and a decrease in unsaturated hydraulic conductivity at −0.05 kPa from 136.9 to 10.14 mm h−1. Whilst the ability to determine the van Genuchten properties of soil crusts was progressed, uncertainty with matching crust thickness to sampling depth, and difficulty measuring the total porosity of soil crusts resulted in error and uncertainty in the estimation of the θs parameter and to a lesser extent the α and ɳ parameters. Further work is required to improve the development of simple, in situ means of measuring or estimating the physical properties of soil crusts.

Biocrust research: A critical view on eight common hydrological‐related paradigms and dubious theses

AbstractAlthough being relatively young, research on biocrusts has already yielded numerous paradigms and/or dubious theses. The very existence of these “truths” may lead to erroneous conclusions and/or hinder research on these topics. In the current summary, eight paradigms and dubious theses are examined: (a) Biocrusts require physical crusts for establishment; (b) plant establishment is necessary for biocrust establishment on dunes; (c) developmental stages of biocrusts are often regarded as successional stages; (d) climate‐driven crust morphology determines crust hydrology; (e) infiltration (and subsequently run‐off) over biocrusts is determined by soil pores; (f) run‐off in dryland may stem from hydrophobicity; (g) exopolysaccharides trigger infiltration; and (h) mosses impede infiltration and subsequently the growth of perennial plants. During this summary, reasons that lie behind these paradigms and dubious theses are examined using data and/or rationale for a critical analysis. Experimental data, mostly gathered from the Nizzana research site of the Hallamish dune field (Negev Desert, Israel), and published material (mainly from the Tabernas and Tengger deserts) are used. It is argued that most of the paradigms were either based on improper techniques or never thoroughly investigated. The argument presented herein does not necessarily imply that none of the paradigms may take place under very specific conditions but that their acceptance as general “truth” is questionable.

Runoff and Soil Erosion on Slope Cropland: A Review

Soil erosion has become a serious environmental problem worldwide, and slope land is the main source of soil erosion. As a primary cover of slope land, crops have an important influence on the occurrence and development of runoff and soil erosion on slope land. This paper reviews the current understanding of runoff and soil erosion on slope cropland. Crops mainly impact splash detachment, slope runoff, and sediment yield. In this review paper, the effects of crop growth and rainfall on the splash detachment rate and the spatial distribution of splash detachment are summarized. Crop growth has a significant impact on runoff and sediment yield. Rainfall intensity and slope gradient can influence the level of erosive energy that causes soil erosion. Furthermore, other factors such as antecedent soil water content, soil properties, soil surface physical crust, and soil surface roughness can affect soil anti-erodibility. The varying effects of different crops and with different influence mechanisms on runoff and soil erosion, as well as changes in their ability to influence erosion under different external conditions should all remain focal points of future research. The effect of crop vegetation on runoff and soil erosion on slope land is a very important factor in understanding large-scale soil erosion systems, and in-depth study of this topic is highly significant for both theory and practice.

Development of bacterial communities in biological soil crusts along a revegetation chronosequence in the Tengger Desert, northwest China

Abstract. Knowledge of structure and function of microbial communities in different successional stages of biological soil crusts (BSCs) is still scarce for desert areas. In this study, Illumina MiSeq sequencing was used to assess the compositional changes of bacterial communities in different ages of BSCs in the revegetation of Shapotou in the Tengger Desert. The most dominant phyla of bacterial communities shifted with the changed types of BSCs in the successional stages, from Firmicutes in mobile sand and physical crusts to Actinobacteria and Proteobacteria in BSCs, and the most dominant genera shifted from Bacillus, Enterococcus and Lactococcus to RB41_norank and JG34-KF-361_norank. Alpha diversity and quantitative real-time polymerase chain reaction (PCR) analysis indicated that bacterial richness and abundance reached their highest levels after 15 years of BSC development. Redundancy analysis showed that silt + clay content and total K were the prime determinants of the bacterial communities of BSCs. The results suggested that bacterial communities of BSCs recovered quickly with the improved soil physicochemical properties in the early stages of BSC succession. Changes in the bacterial community structure may be an important indicator in the biogeochemical cycling and nutrient storage in early successional stages of BSCs in desert ecosystems.

Developing a predictive environment-based model for mapping biological soil crust patterns at the local scale in the Sahel

Several studies have demonstrated the great range of possibilities offered by remote sensing in identifying, estimating and mapping biological soil crust (BSC) patterns, i.e. a feature recognised to play major functions in drylands. However those techniques are suitable mainly where BSC patterns are abundant (>30%) and vegetation cover low (<10%), otherwise reflectance values matched different levels of BSCs mixed with vegetation and bare soil surfaces.This study developed an alternative methodology in mapping BSC presence in areas with a wide range of BSC cover associated with different mosaics encompassing vegetation and bare surfaces in the Sahel.Data were collected during intensive field surveys and remote sensing imagery of two typical Sahelian watersheds in western Niger (Banizoumbou and Tamou). Statistical methods were used to explore relationships between BSC occurrence and abundance and key environmental factors (rainfall, land use, land cover, vegetation, physical crusts).A predictive model of BSC spatial distribution was developed based on logistic regressions. This model allowed predicting and mapping BSC occurrence in areas where BSC cover ranged from 0 to 65% at Tamou (15% in average) and 1 to 48% at Banizoumbou (4% in average) and where vegetation cover ranged from <1% to >75%. Predicted values were obtained with an overall accuracy of 77.7% (kappa=0.54), classifying the model as good and discriminant.This work is the first step in assessing the local scale ecological functions of BSC. Further work is needed for extrapolation at the regional scale in order to provide a useful tool for ecological surveys and for predictions of soil surface dynamics related to global changes in dryland areas.

Soil nutrients losses by wind erosion in a citrus crop at southeast Spain

The purpose of this study was to analyze the influence of wind erosion on the productivity of citric crops over gypsiric Fluvisols in Gador area (Almeria, SE Spain) by blowing air through a wind tunnel. Wind erosion varies considerably depending on time since the last tillage. This is because a physical crust forms after tilling which protects the soil from wind. Crust formation in the study area is strongly favored by dew, which causes them to form in around a week. The repeated measurements ANOVA, as a nonparametric alternative to the ANOVA, using the Geiiser method and the Friedman test shows significant differences (P ≤ 0.05) in the fractions of very fine sand and coarse silt, which confirmed that very fine sand and coarse silt are the fractions most susceptible to loss from wind. The same statistical analysis for fertility showed smaller differences in organic carbon and K2O content, while N and P2O5 increased. Nutrients lost from wind imply an additional fertilization cost for a crop to be economically feasible. The cost of this restoration of nutrients lost from the soil because of wind erosion was based on experimental data taken in crusted soil and immediately after tilling. Losses in organic matter (O.M.), N, P2O5 and K2O were estimated based on the cost of fertilizers most commonly used in the area.

Relationships between Soil Crust Development and Soil Properties in the Desert Region of North China

This study investigated the effects of soil crust development on the underlying soil properties. The field sampling work was conducted in June 2016 in the Hobq Desert in Inner Mongolia, North China. Soil crust samples and 0–6, 6–12, 12–18, 18–24, and 24–30 cm deep underlying soil samples were taken from five representative areas of different soil crust development stages. All samples were analyzed for physicochemical properties, including water content, bulk density, aggregate content, organic matter content, enzyme activities, and microbial biomass carbon and nitrogen. The results showed that the thickness, water content, macro-aggregate (&gt;250 μm) content, organic matter content, microbial biomass, and enzyme activities of the soil crusts gradually increased along the soil crust development gradient, while the bulk density of the soil crusts decreased. Meanwhile, the physicochemical and biological properties of the soils below the algal and moss crusts were significantly ameliorated when compared with the physical crust. Moreover, the amelioration effects were significant in the upper horizons (approx. 0–12 cm deep) and diminished quickly in the deeper soil layers.

Recovery of microbial community structure of biological soil crusts in successional stages of Shapotou desert revegetation, northwest China

Microbial community structure of biological soil crusts (BSCs) in successional stages of Shapotou desert revegetation, northwest China, was assessed using Illumina MiSeq sequencing. Bacterial diversity and richness were highest after 15 years, while those of fungi increased along a chronosequence of stabilized dunes. Hierarchical clustering and principal coordinate analysis showed significant differences in bacterial communities between biocrusts and physical crusts, whereas fungal communities clustered into four groups. Each age of BSCs exhibited the same dominant phyla at different proportions. The recovery time for bacteria was more than 15 years, whereas that for fungi ranged from decades to centuries, indicating that fungal richness might be a potential indicator for predicting the degree of BSC recovery.

Economic Impact of Nutrient Losses From Wind Erosion of Cereal Soils in Southeast Spain

The influence of wind erosion on soil productivity was studied applying fan-forced wind in a wind tunnel located in the Campo de Nijar area in SE Spain where the main crops are cereals. Wind erosion is highly variable depending on the type of soil (aric-haplic Calcisols, aric-calcaric Cambisols or aric-calcic Luvisols, according to IUSS Working Group WRB, 2014) and the time elapsed since the last tillage. This is because of the formation of a physical crust after tillage, which protects the soil from wind. Crusting in our area is favored by the strong effect of dew, which makes crust form in from eight to ten days. Nutrient losses from wind involve an additional cost in fertilization for a crop to be economically viable. The repeated measures ANOVA shows that very fine sand and coarse silt are the fractions most susceptible to loss due to the effect of wind. The same statistical analysis shows that the smallest differences in fertility appear in OC and K2O, increasing in N and P2O5. Based on experimental data, we calculated the approximate cost of restoring organic matter, N, P2O5 and K2O losses to the soil proportional to wind erosion, on the base of mineral fertilizers usually employed and average prices. This does not include the contribution to maintaining short and long-term productivity and soil fertility required for growing, or natural contributions from wind deposits and runoff.

Physical crust formation and steady-state infiltration rate in soils dominated by primary minerals in some South African ecotopes

Physical crust formation is affected by the inherent soil properties such as texture and mineralogy. However, inconsistencies exist in soil mineralogy effects of soil crusting. In addition, investigations of soils dominated by primary minerals such as quartz, especially in South Africa, are scant despite the abundance of such soils. Effects of texture and aggregate size on crust formation and steady-state infiltration rate (SSIR) in soils dominated by primary minerals were investigated. Soil aggregate sizes of <2, 2–3 and 3–5 mm were exposed to ∼60 mm h−1 simulated rainfall. Aggregate size significantly affected crust strength (P < 0.05). Physical crusts ∼0.2 to ∼0.8 mm thick with a surface layer of loose grains formed over a thin plasmic layer. Crusts with strengths between 0.25 and 3.42 × 10−4 kg m−2 developed on the <2 mm aggregates compared with <2.23 × 10−4 kg m−2 in the >2 mm aggregates. The reverse occurred in the Alice Jozini ecotope, which had a relatively low clay content of 120 g kg−1. The SSIR was between 1.24 and 3.60 mm h−1 in ecotopes dominated by primary minerals and clay content between 12% and 26%. In the Amatola Jozini ecotope, which was dominated by kaolinite and higher clay content, SSIR was 15.23 mm h−1. Consequently, physical crust formation decreased but SSIR increased with increase in aggregate size if there was a concomitant increase in the clay fraction, decrease in primary minerals and presence of kaolinite.

The dual role of soil crusts in desertification

AbstractVegetation cover in dry regions is a key variable in determining desertification. Soils exposed to rainfall by desertification can form physical crusts that reduce infiltration, exacerbating water stress on the remaining vegetation. Paradoxically, field studies show that crust removal is associated with plant mortality in desert systems, while artificial biological crusts can improve plant regeneration. Here it is shown how physical crusts can act as either drivers of or buffers against desertification depending on their environmental context. The behavior of crusts is first explored using a simplified theory for water movement on a uniform, partly vegetated slope subject to stationary hydrologic conditions. Numerical model runs supplemented with field data from a semiarid Long‐Term Ecological Research site are then applied to represent more realistic environmental conditions. When vegetation cover is significant, crusts can drive desertification, but this process is potentially self‐limiting. For low vegetation cover, crusts mitigate against desertification by providing water subsidy to plant communities through a runoff‐runon mechanism.

Wind erosion potential of lacustrine and alluvial soils before and after disturbance in the eastern Great Basin, USA: Estimating threshold friction velocity using easier-to-measure soil properties

Abstract Disturbance of lacustrine and alluvial soils could increase aeolian dust emissions in the eastern Great Basin, but little is known about the susceptibility of these land surfaces to wind erosion. Threshold friction velocity (u∗t), a necessary parameter to estimate wind erosion potential, is difficult to accurately measure; methods to estimate u∗t from alternate measurements would be useful. We measured u∗t and sediment production rate with a portable wind tunnel, and quantified relationships between u∗t and eleven easier-to-measure soil surface properties for both undisturbed and disturbed lacustrine and alluvial soils in Snake Valley, Utah. Soil surface type and disturbance significantly influenced u∗t, sediment production rate, and the relationships between u∗t and easier-to-measure soil surface properties. Only soils with surficial rock fragments and weak physical crusts reached u∗t before disturbance, whereas all surface types reached u∗t following disturbance. Soils with weak physical crusts had the lowest average u∗t and highest average sediment production rate before and after disturbance. Surprisingly, however, disturbance reduced sediment production rate. Soils with weak physical crusts and surficial rock cover are likely the most susceptible to wind erosion and subsequent dust generation both before and after disturbance. Silt concentration and penetrometer resistance were significant predictors of u∗t in undisturbed soils with weak physical crusts and surficial rock cover. Following disturbance, clay concentration and aggregate stability were significant predictors for soils with hard salt crusts and surficial rock cover. Prediction of u∗t using alternate measurements is promising, but u∗t measurement uncertainty must be considered.