mineral soil surface crusts and wind and water erosion

MINERAL SOIL SURFACE CRUSTS 1065

Copyright © 2004 John Wiley & Sons, Ltd. Earth Surf. Process. Landforms 29, 1065–1075 (2004)

Earth Surface Processes and Landforms

Earth Surf. Process. Landforms 29, 1065–1075 (2004)Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/esp.1102

MINERAL SOIL SURFACE CRUSTS AND WIND AND

WATER EROSION

MICHAEL J. SINGER1* AND ISAAC SHAINBERG2

1 Department of Land, Air and Water Resources, One Shields Avenue, University of California, Davis, CA 95616, USA2 Institute of Soil, Water and Environmental Sciences Volcani Center, PO Box 6, Bet Dagan, Israel

Received 6 November 2001; Revised 27 November 2002; Accepted 4 March 2004

ABSTRACT

The first few millimetres of soil largely control the soil’s response to the eroding forces of wind and water. The tendencyof soils to form surface seals and crusts influences the processes of wind and water erosion differently. For wind, dry particlesize distribution and particle organization determine the shear strength and threshold wind velocity necessary to initiateparticle movement. In loams and clay loams, seals and crusts decrease roughness but increase surface soil strength, generallydecreasing wind erosion. Conversely, in sand and sandy loams, loose erodible sandy material may either deposit on the crustand is subject to erosion or it may disrupt the crust, accelerating the erosion process. For water erosion, particle sizedistribution and structure determine infiltration rate, time to ponding, and energy required for soil particle detachment. Sealsand crusts tend to decrease infiltration rate and time to ponding thus increasing overland flow and soil erosion. This paperbriefly reviews how permanent and time-dependent soil properties influence surface seals and crusts and how these affectsoil erosion by wind and water. The tendency of a soil to form a seal and crust depends to some degree on the time-dependentproperty of soil structural stability, which tends to increase with increasing clay content and smectitic mineralogy which arepermanent properties. These permanent properties and their effect on structure are variable depending on dynamic propertiesof exchangeable sodium percentage and soil solution electrical conductivity. Antecedent water content prior to irrigation orrainfall, rate of wetting before an erosive event and aging, the time between wetting and an erosive event, greatly influencethe response of soil structure to raindrop impact. The effect of these dynamic processes is further influenced by the staticand dynamic properties of the soil. Weak structure will be less influenced by wetting rate than will a soil with strong structure.Process-based models of wind and water erosion need to consider the details of the interactions between soil static anddynamic properties and the dynamic processes that occur prior to erosive events. Copyright © 2004 John Wiley & Sons, Ltd.

KEY WORDS: texture; mineralogy; exchangeable sodium percentage; organic matter; wetting rate; aging; antecedent moisture content;

amendments

INTRODUCTION

The first few millimetres of soil largely control the soil’s response to the eroding forces of wind and water. For

wind, it is the dry particle size distribution and organization of the dry particles that determine the shear strength

and threshold wind velocity necessary to initiate particle movement. For water, particle size distribution and

structure (or lack of structure) determine infiltration rate, time to ponding, and energy required for soil particle

detachment. Soil surface seals and crusts are thin ephemeral layers on the soil surface that restrict the entrance

of water into the soil and change soil strength. Seals and crusts are differentiated by their moisture contents.

Seals are wet and crusts are dry. Microbiotic, depositional and structural crusts are recognized as distinct types.

Crusts and seals are known to be important in affecting wind and water erosion of soil (Chepil, 1951; Bajracharya

and Lal, 1999; Graef and Stahr, 2000; Rice and McEwan, 2001). Although microbiotic crusts have been shown

to reduce wind erosion in sandy soils (Leys and Eldridge, 1998) and increase the threshold wind velocity

(Belnap and Gillette, 1998) they are not considered in this paper.

Here, we briefly review how permanent and time-dependent soil properties influence surface seals and crusts

and how these affect soil erosion by wind and water. We conclude with some comments on strategies for

management of soil surface conditions.

* Correspondence to: M. J. Singer, Department of Land, Air and Water Resources, One Shields Avenue, University of California, Davis,CA 95616, USA. E-mail: [email protected]

1066 M. J. SINGER AND I. SHAINBERG


PERMANENT SOIL PROPERTIES AND SURFACE CHARACTERISTICS

Soil seals have been characterized by measurements such as the flow properties through a seal (McIntyre, 1958),

raindrop splash detachment (Bradford et al., 1986), and surface strength (Bradford et al., 1986). Morphology of

seals and crusts has also been studied directly (Gal et al., 1984; Onofiok and Singer, 1984; West et al., 1992).

None of the methods provides a completely satisfactory description of the seal. In this review, infiltration rate

is used most often to describe seal formation.

Effect of soil texture on seal formation

The tendency of a soil to form a seal and crust depends to some degree on soil structural stability, which tends

to increase with increasing clay content (Kemper and Koch, 1966; Kay and Angers, 1999). Clay particles bind

particles together in aggregates (Kemper and Koch, 1966). Thus, stability of aggregates against the wetting

effect and the impact action of the rain also increases with an increase in clay content. Clay content also played

an important role in sealing of sandy soils in the Sahel where it was found that soils with less than 5 per cent

clay did not seal and those with more than 5 per cent formed seals (Heil et al., 1997). Low organic matter also

contributed to the tendency to form seals.

Ben Hur et al. (1985) found that soils with 20–30 per cent clay were the most susceptible to seal formation

and had the lowest infiltration rate (IR). With increasing clay content above 40 per cent, soil structure became

more stable, seal formation was diminished and IR increased. In soils with clay contents <10 per cent, the

amount of clay was too low for clogging the interparticle pores and seal development. Fox and Le Bissonnais

(1998) also demonstrated that in the two soils they tested, the soil with the higher clay content had a lower

erosion rate and less sealing.

Effect of clay mineralogy

Smectitic soils are known to be very susceptible to seal formation (Shainberg and Letey, 1984; Stern et al.,

1991). Kaolinitic soils are much less susceptible to seal formation (Stern et al., 1991; Wakindiki and Ben Hur,

2002). The effect of mixed clay mineralogy on seal formation was also studied by Stern et al. (1991) using 19

loamy soils from South Africa. Kaolinitic soils in which smectites were not detected were not susceptible to seal

formation. Conversely, kaolinitic soils with a small amount of smectite were dispersive and susceptible to seal

formation. A similar observation was made by Frenkel et al. (1978) who found that the hydraulic conductivity

of pure kaolinitic soils was not affected by different exchangeable sodium contents. However, mixing 2 per cent

smectite with the kaolinitic soils made them very susceptible to increasing sodicity.

Effect of soil sodicity and electrolyte concentration

Kazman et al. (1983) studied the sensitivity of seal formation to low levels of exchangeable sodium percent-

age (ESP) when exposed to deionized water. They found that even at the lowest sodicity (ESP = 1), a seal was

formed on a sandy loam, and the initial IR dropped from >100 mm h−1 to a final value of 7 mm h−1. An ESP

of 2·2 was sufficient to cause a further drop in final IR to 2·4 mm h−1. The high sensitivity of the soil surface

to low ESP was explained by three factors: (1) the mechanical impact of the raindrops which enhances clay

dispersion; (2) the absence of a surrounding soil matrix, which when present slows clay dispersion and move-

ment; and (3) the almost total absence of electrolytes in the applied deionized water (Oster and Schroer, 1979;

Kazman et al., 1983). Bouza et al. (1993) working in Argentina also found that ESP was a major cause of crust

formation.

Agassi et al. (1981) found that the IR of their experimental soils increased markedly as the EC of the applied

water increased in the range between distilled water and 5·6 dS m−1. When electrolyte solutions are applied, clay

dispersion and aggregate disintegration are diminished and seals of high infiltration rate are formed (Agassi

et al., 1981).

Soil ESP and electrolyte concentration affect crust micromorphology. Gal et al. (1984) studied scanning

electron micrographs (SEM) of a sandy loam with ESP values of 1·0 and 11·6 exposed to distilled water rain.

At ESP = 1·0, sand grains covered with a skin of clay were observed in the upper 2 mm layer. Conversely, in

the ESP = 11·6 sample, naked sand grains stripped of the clay skin were observed. Following clay dispersion,



some downward movement of clay particles occurred and clay accumulation in the ‘washed-in’ layer was

observed. The washed-in layer was formed only in soils and under conditions where the clays were easily

dispersed. When the ESP of the soil is below 1·0 and electrolyte concentration in the rain exceeds 2 meq l−1, the

accumulation of fine particles in the washed-in layer is absent (Gal et al., 1984).

Effect of organic and inorganic polymers

Seal formation diminishes as soil structure and aggregate stability increase (Bradford and Huang, 1992;

Le Bissonnais and Singer, 1993). Even though the importance of aggregation to soil erosion and seal formation

has been recognized, researchers have been unable to quantify a relationship between erosion or sealing and

aggregate stability (Bradford and Huang, 1992). Aggregate stability increases with increasing organic matter and

sesquioxide content (Kay and Angers, 1999). Studying seal formation, runoff and interrill erosion from

17 California soils, Le Bissonnais and Singer (1993) concluded that soils that had 31 to 70 g kg−1 organic C and

2·4 to 10·7 per cent citrate-bicarbonate-dithionate (CBD) extractable Fe plus Al did not form a seal, infiltration

rate remained high and neither runoff nor erosion occurred. Soils with low organic C and low CBD extractable

Fe plus Al readily formed seals, produced runoff and soil erosion (Le Bissonnais and Singer, 1993).

TIME-DEPENDENT PROPERTIES AND SURFACE CHARACTERISTICS

Much effort has been devoted to studying the relation between the permanent properties of soils and soil surface

characteristics. However, the success of these efforts in predicting the susceptibility of soils to sealing, runoff

and erosion has been inadequate (e.g. Elliot et al., 1989). Most studies on the effects of soil properties on seal

formation were done on dry soils that were subjected to simulated high intensity rain (e.g. Elliot et al., 1989).

In other studies, the soil samples were fast wetted, from below or from above, prior to their exposure to the

simulated rain (e.g. Agassi et al., 1981; Kazman et al., 1983). These conditions lead to intensive aggregate

disintegration and do not occur in the field where soils with different antecedent moisture contents are exposed

to low intensity rain before eroding rain occurs. Although it is known that erosion is a time-dependent process,

little effort has been made to understand the time dependence (e.g. De Ploey, 1981; Roth and Helming, 1992).

In this section, the effect of antecedent moisture content, the length of time the soil was aged at this moisture

content (= aging time) and the effect of wetting rate on soil surface characteristics and soil sealing are discussed.

The effect of wetting rate on soil sealing

Seal formation is the result of two complementary mechanisms (Agassi et al., 1981): (i) physical disintegra-

tion of surface aggregates caused by wetting of the dry aggregates (Loch, 1994) and/or the beating action of the

rain drops, and subsequent compaction of the disintegrated aggregates by raindrop impact; and (ii) the

physicochemical dispersion of soil clays which migrate downward with the infiltrating water clogging pores

immediately beneath the surface (McIntyre, 1958; Gal et al., 1984). The mechanical process that breaks soil

aggregates upon wetting is affected by the wetting rate (WR) of the surface aggregates (Loch, 1994; Levy

et al., 1997). Rapid wetting of aggregates leads to their slaking because of stresses produced by differential

swelling, and entrapped air explosion (Quirk and Panabokke, 1962; Loch, 1994; Kay and Angers, 1999). Levy

et al. (1997) showed that slow wetting of the aggregates reduced the susceptibility of the soils to seal formation.

Mamedov et al. (2001) studied the effect of three wetting rates (2, 8, and 64 mm h−1) on infiltration rate and

runoff from six soils exposed to 60 mm of simulated deionized water rain of moderate to high kinetic energy

(15·9 kJ m−3). Clay content in the soils ranged from 8·8 to 68·3 per cent and ESP levels from 0·9 to 20·4. Effects

of WR on soil infiltration rate and runoff depended on soil texture and ESP. The effect of WR on soil sealing in

the soils with ESP values of 2 and 5 was less pronounced as the clay content decreased (Figure 1). In soils with

high clay content and stable aggregates, WR was the predominant factor determining the susceptibility to seal

formation (Figure 1). Loch (1994) also found that seal formation in clay soils with stable aggregates occurred only

when the WR exceeded 100 mm h−1. In soils with unstable structure (sandy loams to silt loams), slow WR and

raindrop impact is enough to disintegrate the aggregates and to form a seal (Mamedov et al., 2001). The effect

of WR was most pronounced in the soils with low ESP. In the very high ESP treatment (ESP 20), the aggregates

were so weak that slow WR was sufficient to disintegrate the aggregates (Mamedov et al., 2001).



Figure 1. The effect of wetting rate on runoff from six soils varying in their clay content and ESP (reproduced by permission of CSIROPublishing, Melbourne, Australia, from the Australian Journal of Soil Research 39: 1293–1305 (Mamedov AI, Levy GJ, Shainberg I and

Letey J, 2001))

The effect of wetting rate and rain energy on seal formation and erosion

The relative importance of WR and rain kinetic energy (KE) in seal formation, runoff production and erosion

in soils varying in their clay and silt content was studied by Shainberg et al. (2003). Four soils, ranging in clay

content from 22·5 to 61·2 per cent were prewetted at WR values of 2, 8 or 64 mm h−1 and were exposed to

60 mm simulated distilled water rainfall with two kinetic energies (KE of 8 and 15·9 kJ m−3). Runoff and ero-

sion increased as rain KE and WR increased; however, the magnitude of change depended on clay content.

In the loam, the effect of rain KE on seal formation and runoff was significant and the effect of WR was small.

Conversely, in the clay soils (51·3 and 61·2 per cent clay), the effect of WR on seal formation was significant

and the effect of rain KE was negligible (Mamedov et al., 2001; Shainberg et al., 2003). The effect of rain

energy on soil erosion was significant in all soils. Since water erosion is the product of sediment detachment

and transport of the particles by overland flow, increase in the impact of rain drops increases both soil detach-

ment and transport capacity and increases soil erosion in all soils. In clay soils erosion also increased with

increase in WR. Disintegration of the aggregates by fast WR combined with detachment by rain impact increased

erosion from clay soils. It is concluded that for seal formation and runoff production, rain KE predominates

in medium- and light-textured soils and WR predominates in heavy-textured soils. Conversely, for soil erosion

from laboratory trays, detachment by rain KE is essential in all soils.

The effect of antecedent moisture content

The moisture condition of soil surface aggregates at the beginning of a rainstorm greatly affects the resistance

of aggregates to breakdown or dispersion. Antecedent water content determines the aggregate breakdown



Figure 2. Effect of antecedent moisture content on infiltration rate and soil splash (adapted from Le Bissonnais and Singer, 1992, by permissionof the Soil Science Society of America)

mechanism, the resulting particle size distribution, and seal formation (Le Bissonnais, 1990). Le Bissonnais et al.

(1989) and Le Bissonnais (1990) presented a conceptual model of the role of water status of aggregates on

aggregate breakdown and seal formation. For initially dry aggregates, aggregate breakdown under rainfall is

mainly due to slaking. If the soil surface has high water content before rainfall, intensity of aggregate breakdown

and surface sealing is low and results primarily from the mechanical impact of raindrops.

Bradford and Huang (1992) measured the effect of antecedent moisture content on seal formation of six soils.

Three soils had low clay contents and low aggregate stability and three soils had high clay contents and were

strongly aggregated. In the unstable soils, more sealing took place in the wet treatment compared with the dry

treatment. Conversely, in the more stable clay soils, more sealing occurred in the dry treatment. Le Bissonnais

and Singer (1992), studying the effect of initial moisture content on sealing, runoff and erosion from two

California soils with clay content above 30 per cent found that slow prewetting reduced seal formation, runoff

and erosion (Figure 2). In low clay and high silt soils with low aggregate stability, neither antecedent moisture

content nor WR play an important role (Bradford and Huang, 1992; Mamedov et al., 2001). In these soils,

aggregate stability is low in both wet and dry aggregates and raindrop impact energy determines seal formation.

Conversely, in clay soils with stable aggregates, disintegration of the aggregate by fast wetting of the dry

aggregates is essential for seal formation. When the antecedent moisture content of the stable aggregates is high,

fast wetting does not disintegrate the aggregates and a seal is not formed.

In many of the rain simulation studies, not explicitly designed to study the effect of antecedent moisture

content, the soils were prewetted before exposure to rain and were found to be susceptible to seal formation,

runoff and soil erosion (e.g. Agassi et al., 1981; Kazman et al., 1983; Ben Hur et al., 1985). In these experiments

the soils were prewetted at a fast rate and aggregate disintegration occurred even in soils with stable aggregates.

Thus these soils were susceptible to seal formation.



The effect of aging and moisture content on sealing

The effects of aging duration, water content, and temperature during aging on aggregate stability, infiltration

rate, and erosion have been discussed by Blake and Gilman (1970), Kemper and Rosenau, (1984), Le Bissonnais

and Singer (1992), Shainberg et al. (1996), and Levy et al. (1997). It has been suggested that: (i) some binding

of soil particles is independent of organic matter content and of the activities of a viable microbial population

(Blake and Gilman, 1970; Kemper et al., 1987); (ii) the chemical processes involving precipitation of CaCO3

and silica might be responsible for particle binding (Kemper et al., 1987); (iii) face-to-face and edge-to-face

forces might be responsible for the development of cohesion forces (Shainberg et al., 1996); (iv) clay movement

and reorientation, which increases with an increase in water content, Brownian motion (aging temperature), and

clay content, might control the rate of development of cohesive forces (Shainberg et al., 1996). Significant

changes in aggregate stability were observed within 20 to 24 hours (Blake and Gilman, 1970; Shainberg et al.,

1996; Singer et al., 1992).

An increase in aggregate stability decreases the formation of seals. Thus soils that are aged between wetting

and exposure to rain are less susceptible to seal formation. Levy et al. (1997) found that aging a grumusol and

loess for 18 h reduced soil erosion to 40 and 25 per cent of the values in soils that were not exposed to aging.

SOIL SURFACE PROPERTIES AND EROSION

Wind erosion

Wind erosion occurs when the threshold wind velocity at the soil surface is exceeded and individual grains

are detached and transported by creep, saltation or suspension. Creep rolls particles, 100–2000 µm in diameter,

along the surface. Saltation moves particles 100–1000 µm in diameter in a series of short hops depending on

surface roughness, particle size and wind speed. They are largely responsible for abrasion of soil aggregates and

plant seedlings. Suspended particles are less than about 100 µm in diameter, and move into the upper atmosphere

(Fryrear, 1999). Threshold velocities decrease for individual grains as grain size decreases to about 80 µm and

then increases because of cohesion among the finer particles (Bagnold, 1941). Chepil (1953) showed that

increasing clay content from <15 to 27 per cent decreased the susceptibility of soil to wind erosion because of

the formation of big and stable soil aggregates. Higher clay contents were not helpful in reducing susceptibility

to wind erosion because the shrinking and swelling tendency of the clay broke clods into easily eroded sizes

(Chepil, 1953). When the soil surface is exposed to rain, breakdown of the non-erodible aggregates facilitates

wind erosion. However, upon drying and crust formation, the crust with high cohesion forces between particles

may protect the soil surface from wind erosion (Chepil, 1951).

In the case of wind erosion that is produced by saltating grains, Rice et al. (1999) have reasoned that the

process can best be modelled as probability distributions of surface strength and energy of saltating grains. The

critical concept for this review is that the surface strength increases when crusting occurs. Rice and McEwan

(2001) directly examined the role of crust strength in wind erosion by saltating particles. They found that as the

proportion of fine materials and hence crust strength increased, the amount of abrasion from saltating grains

decreased. Zobeck (1991) created an abrasion coefficient (AC) as a measure of crust effect on wind erosion. He

found that AC was five to 5000 times greater for unconsolidated soils than for crusted soils.

Wind erosion models have recognized the importance of surface roughness and crust strength but often do

not include crusting as an explicit variable in the model (e.g. Lyons et al., 1998). Generally, random roughness

and oriented roughness are recognized but are not always included in wind erosion equations (Saleh and Fryrear,

1999). Random roughness accounts for soil surface conditions such as presence of soil surface aggregates and

oriented roughness accounts for ridges. Oriented roughness that is perpendicular to the wind can be effective

in reducing soil loss by wind, but the ridges are susceptible to degradation by rain and irrigation and thus may

lose their effectiveness. For example, Bielders et al. (2000) found that after 100 mm of rain, ridges lost effec-

tiveness in reducing wind erosion in Niger. In the West African Sahel, wind erosion was significantly reduced

and crop yield increased by surface mulching which decreased detachment and increased deposition of eroding

sand (Buerkert and Lamers, 1999).



The revised wind erosion equation includes a soil crust factor that reflects crust development and impact on

wind erosion (Fryrear et al., 2000). It does not describe crust strength directly. Clay and organic matter content

are used to compute the soil crust factor as well as the degradation of soil roughness.

Water erosion

Water erosion occurs when the kinetic energy of impacting raindrops and the shearing force of overland flow

exceed the shear strength of the soil surface, producing detachment and transport of soil particles. Raindrop

detachment is much greater than flow shear detachment because the kinetic energy of raindrops is much higher

than that of surface flow (Hudson, 1971). However, movement of detached soil downslope by rain splash is

minimal, and most of the sediment is removed from the interrill area by runoff flow (Young and Wiersma, 1972).

A surface seal or crust affects the process by changing the infiltration characteristics of the soil surface, the time

to ponding, surface roughness, and soil strength that affects the ease (or difficulty) of detaching soil particles

(e.g. Al-Qinna and Abu-Awwad, 1998). The net effect of sealing on erosion depends on the balance between

detachment and transport. If erosion is transport limited, insufficient overland flow occurs to transport all the

detached sediment, and sealing will increase erosion. If detachment is limited, sealing will reduce erosion. Under

dispersive conditions (e.g. sodic soils and distilled water rain), runoff flow may be sufficient to initiate rilling

and soil erosion may increase sharply with slope (Warrington et al., 1989; Shainberg et al., 1992).

Soil erodibility has been defined as the inherent tendency of soils to erode at different rates due solely to

differences in soil properties. It is commonly quantified as the K-factor in the Universal Soil Loss Equation

(USLE) (Wischmeier and Smith, 1978). Numerous studies have been undertaken to establish statistical relations

between soil chemical and physical properties and erodibility (e.g. Wischmeier and Mannering, 1969; Meyer and

Harmon, 1984; Elliot et al., 1989; Le Bissonnais and Singer, 1993). One of the most important results was the

erodibility nomograph (Wischmeier et al., 1971), which related erodibility to particle size distribution, organic

matter content, soil structure and permeability. The USLE does not include, explicitly, surface sealing and

crusting in the soil erodibility factor ‘K’. Surface properties are implicitly included because the K-factor rep-

resents long-term average annual erodibilities.

The Water Erosion Prediction Project (WEPP) (Nearing et al., 1990) includes sealing and crusting both

implicitly and explicitly in its equations. The rill erodibility equation includes a rill erodibility term Kr and a

critical soil shear stress term τc, both of which are soil dependent and sensitive to sealing and crusting. The

interrill erosion portion of the model also has an interrill erodibility term Ki that incorporates the effect of soil

properties on infiltration and soil resistance to detachment. Although WEPP considers surface sealing and

crusting, it does not adjust the interrill erosion rate for effects of surface sealing (Nearing et al., 1990). In fact,

the effect is considered the same for all soils.

MANAGEMENT OF SURFACE CHARACTERISTICS

The various management options can be classified as those requiring physical soil and water manipulation and

those requiring chemical amendments. A critical consideration in choosing a management option is its economic

viability.

Physical soil management

Mulching. As the breakdown of aggregates and clay dispersion are catalysed by raindrop impact, any man-

agement practice that protects the soil surface from raindrop impact maintains infiltration and reduces soil losses.

An obvious way to protect the soil surface is by mulching. Wherever feasible and where undesirable side effects

(plant diseases) are absent, some type of minimum tillage practice is best suited to reduce crusting. Numerous

studies have demonstrated the beneficial effect of plant residue mulches on reducing surface crusting (e.g.

Scholte, 1989; Kooistra et al., 1990; West et al., 1991).

Tillage. Tillage often results in improvements in soil physical and hydraulic properties, reduces their bulk

densities and increases total porosity (Blackwell et al., 1991). However, the beneficial effects of tillage on soils

are often not long-lasting (Mead and Chan, 1988) because soils tend to reconsolidate under their own weight



when wetted. Tillage may increase infiltration when it loosens surface crusts, or decrease infiltration when it

smoothes the surface, disrupts aggregates, eliminates surface residues or causes compaction. Generally, culti-

vated soils are susceptible to sealing whereas soils under no till have more stable structure and are less suscep-

tible to sealing. The effect of aging cultivated soils, in the appropriate moisture content, on their aggregate

stability was discussed above (Kemper and Rosenau, 1984; Kemper et al., 1987). Deep ploughing the soil to

increase the clay content of the surface soil and to bring up non-erodible clods is still used to control wind

erosion on sandy soils (Fryrear, 1999).

Use of amendments

Gypsum. Chemical dispersion at the soil surface exposed to rain may be prevented by spreading gypsum at

the soil surface. Upon dissolution, the gypsum supplies electrolytes to the rainwater and chemical dispersion of

the clay at the soil surface is prevented. The beneficial effect of gypsum on decreasing sealing, runoff and

erosion was demonstrated on many soils in both laboratory and field experiments (Agassi et al., 1985; Miller,

1987; Stern et al., 1991). The amount of gypsum required to prevent sealing depends on rain depth (Agassi et

al., 1985; Keren et al., 1983). Assuming that gypsum dissolves in rainwater to 50 per cent of saturation it is

recommended that gypsum be applied at the rate of 1 Mg per ha per 100 mm of rain.

Organic polymers. Soil structure may be improved by mixing the soil with organic polymers (Shainberg and

Levy, 1994). The use of organic polymers, mainly polyacrylamide (PAM), for stabilizing the soil surface and

decreasing runoff and erosion has been studied in laboratory (e.g. Ben Hur and Letey, 1989; Shainberg et al.,

1990) and field studies (Flanagan et al., 1997a,b). Treatment of the soil surface with 5–20 kg ha−1 of anionic

PAM increased the final IR of the soils by an order of magnitude and reduced runoff and erosion several fold.

The current understanding of the role of soil seals in determining rain infiltration, runoff and erosion has led to

the concept of treating only the soil surface rather than mixing the polymer with the cultivated layer. This

reduces the amounts of polymer required, thus making its use more cost effective.

In most of the polymer studies, the polymer was dissolved with irrigation water prior to its application. This

makes it impractical under rain-fed conditions where irrigation water is not applied. Also, dissolving the polymer

is difficult and costly. Thus, spreading PAM in solution to prevent sealing, runoff and erosion under rain has

not been commercialized. If spreading of dry PAM at the soil surface becomes effective in preventing seal

formation, this may become a great step forward in controlling water erosion.

The characteristics of the soil surface and their effect on wind erosion can also be modified by the use of

synthetic polymers which increases substantially the proportion of water-stable aggregates (Chepil, 1954). The

Monsanto Chemical company produced polymers of vinyl acetate maleic acid (VAMA) with a trade name of

Krilium. The soils treated with VAMA were loose and friable and had a granular surface (Chepil, 1954). The

untreated soils had a developed surface crust that was resistant to wind erosion. The soils treated with VAMA

were more susceptible to wind erosion. Chepil (1954) observed that the great majority of the water-stable

aggregates formed by VAMA were small and of the size erodible by wind. It is likely that the new polymers

available today such as PAM with high molecular weight may be more effective in stabilizing bigger aggregates

at the soil surface and preventing wind erosion. In a preliminary study, PAM solutions (7·5 kg ha−1) were

sprayed on the surface of a sandy soil (5 per cent clay and 10 per cent silt) in a commercial carrot field in the

western Negev in Israel. The PAM treatment was very effective in preventing wind erosion damage to the carrot

seedlings.

CONCLUSIONS

Soil surface conditions and erosion depend on soil permanent properties (such as soil texture, mineralogy,

organic matter and lime content, composition of exchangeable cations, and pH). In this review we demonstrated

that temporary conditions prevailing in the soil, such as wetting rate, antecedent moisture content and aging, also

significantly affect soil susceptibility to crusting and erosion. Fast wetting of dry soil caused aggregate slaking

and crusting whereas high antecedent moisture content and long aging decreased aggregate disintegration and

erosion. Crusting and erosion may also be prevented by mechanical management (mulching and tillage) and by



the use of amendments. The use of polyacrylamide (PAM) of high molecular weight (10–15 × 106 g mol−1) and

moderate negative charge (15–20 per cent hydrolysis) for stabilizing the soil surface structure and decreasing

erosion have been demonstrated in laboratory and field studies. The current understanding of the role of the soil

surface in determining erosion has led to the concept of treating only the soil surface with the polymers, rather

than the cultivated layer, thus making their use cost effective.

REFERENCES

Agassi M, Shainberg I, Morin J. 1981. Effect of electrolyte concentration and soil sodicity on the infiltration rate and crust formation. Soil

Science Society of America Journal 45: 848–851.Agassi M, Shainberg I, Morin J. 1985. Infiltration and runoff in wheat fields in the semiarid regions of Israel. Geoderma 36: 263–

276.Al-Qinna MI, Abu-Awwad AM. 1998. Soil water storage and surface runoff as influenced by irrigation method in arid soils with surface

crust. Agricultural Water Management 37: 189–203.Bagnold RA. 1941. The Physics of Blown Sand and Desert Dunes. Methuen: London.Bajracharya RM, Lal R. 1999. Land use effects on soil crusting and hydraulic response of surface crusts on a tropical Alfisol. Hydrological

Processes 13: 59–72.Belnap J, Gillette DA. 1998. Vulnerability of desert biological soil crusts to wind erosion: the influences of crust development, soil texture,

and disturbance. Journal of Arid Environments 39: 133–142.Ben-Hur M, Letey J. 1989. Effect of polysaccharides, clay dispersion, and impact energy on water infiltration. Soil Science Society of

America Journal 53: 233–238.Ben-Hur M, Shainberg I, Bakker D, Keren R. 1985. Effect of soil texture and CaCO3 content on water infiltration in crusted soil. Irrigation

Science 6: 281–294.Bielders CL, Michels K, Rajot, JL. 2000. On-farm evaluation of ridging and residue management practices to reduce wind erosion in Niger.

Soil Science Society of America Journal 64: 1776–1785.Blackwell PS, Jayawardane NS, Greene TW, Wood JT, Blackwell J, Beatty HJ. 1991. Subsoil macropores space of a transitional Red-Brown

earth after either deep tillage, gypsum or both. I. Physical effects and short term changes. Australian Journal of Soil Research 29: 123–140.

Blake GR, Gilman RD. 1970. Thixotropic changes with aging of synthetic soil aggregates. Soil Science Society of America Proceedings 34:561–564.

Bouza P, Delvalle HF, Imbellone PA. 1993. Micromorphological, physical and chemical characteristics of soil crust types of the centralPatagonia region, Argentina. Arid Soil Research & Rehabilitation 7: 355–368.

Bradford JM, Huang CH. 1992. Mechanisms of seal formation: Physical components. In Soil Sealing: Physical and Chemical Processes,Sumner ME, Stewart BA (eds). Lewis: Boca Raton, FL; 55–72.

Bradford JM, Remly PA, Ferris JE, Santini JB. 1986. Effect of soil surface sealing on splash from a single water drop. Soil Science Society

of America Journal 50: 1547–1552.Buerkert A, Lamers JPA. 1999. Soil erosion and deposition effects on surface characteristics and pearl millet growth in the West African

Sahel. Plant & Soil 215: 239–253.Chepil WS. 1951. Properties of soil which influence wind erosion: V Mechanical stability of structure. Soil Science 72: 465–478.Chepil WS. 1953. Factors that influence clod structure and erodibility of soil by wind I. Soil texture. Soil Science 75: 473–483.Chepil WS. 1954. The effect of synthetic conditioners on some phases of soil structure and erodibility by wind. Soil Science Society of

America Proceedings 18: 386–391.De Ploey J. 1981. Crusting and time-dependent rainwash mechanisms on loamy soil. In Soil Conservation Problems and Perspectives,

Morgan RPC (ed.). J. Wiley and Sons: New York; 139–152.Elliot WJ, Laflen JM, Kohl KD. 1989. Effect of soil properties on soil erodibility. ASAE/CSAE Meeting, Paper No. 89a2150. ASAE: St

Joseph MI.Flanagan DC, Norton LD, Shainberg I. 1997a. Effect of water chemistry and soil amendments on a silt loam. Part I: Infiltration and runoff.

Transactions American Society of Agricultural Engineers 40: 1549–1554.Flanagan DC, Norton LD, Shainberg I 1997b. Effect of water chemistry and soil amendments on a silt loam. Part II: Soil erosion.

Transactions American Society of Agricultural Engineers 40: 1555–1561.Fox, DM, Le Bissonnais Y. 1998. Process-based analysis of aggregate stability effects on sealing, infiltration, and interrill erosion. Soil

Science Society of America Journal 62: 717–724.Frenkel H, Goertzen JO, Rhoades JD. 1978. Effects of clay type and content, exchangeable sodium percentage, and electrolyte concentration

on clay dispersion and soil hydraulic conductivity. Soil Science Society of America Journal 42: 32–39.Fryrear DW. 1999. Wind erosion. In Handbook of Soil Science, Sumner ME (ed.). CRC Press: Boca Raton, FL; G195–G216.Fryrear DW, Bilbro JD, Saleh A, Schomberg H, Stout JE, Zobeck TM. 2000. RWEQ: Improved wind erosion technology. Journal of Soil

and Water Conservation 55(2): 183–189.Gal M, Arkan L, Shainberg I, Keren R. 1984. The effect of exchangeable Na and phosphogypsum on the structure of soil crust-SEM

observation. Soil Science Society of America Journal 48: 872–878.Graef F, Stahr K. 2000. Incidence of soil surface crust types in semi-arid Niger. Soil & Tillage Research 55: 213–218.Heil JW, Juo ASR, Mcinnes KJ. 1997. Soil properties influencing surface sealing of some sandy soils in the Sahel. Soil Science 162: 459–

469.Hudson N. 1971. Soil Conservation. Cornell University Press: Ithaca, NY.Kay BD, Angers DA. 1999. Soil structure. In Handbook of Soil Science, Sumner ME (ed.). CRC Press: Boca Raton, FL; A229–

A276.



Kazman Z, Shainberg I, Gal M. 1983. Effect of low levels of exchangeable Na and applied phosphogypsum on the infiltration rates ofvarious soils. Soil Science 135: 184–192.

Kemper WD, Koch EJ. 1966. Aggregate stability of soils from western US and Canada. Technical Bulletin 1355. USDA-ARS, USGovernment Printing Office: Washington, DC.

Kemper WD, Rosenau RC. 1984. Soil cohesion as affected by time and water content. Soil Science Society of America Journal 48: 1001–1006.

Kemper WD, Rosenau RC, Dexter AR. 1987. Cohesion development in disrupted soils as affected by clay and organic matter content andtemperature. Soil Science Society of America Journal 51: 860–867.

Keren R, Shainberg I, Frenkel H, Kalo Y. 1983. The effect of exchangeable sodium and gypsum on surface runoff from loess soil. Soil

Science Society of America Journal 47: 1001–1004.Kooistra MJ, Juo ASR, Schoonderbeek D. 1990. Soil degradation in cultivated alfisols under different management systems in southwestern

Nigeria. In Soil Micromorphology, Douglas LA (ed.). Elsevier: Amsterdam; 61–69.Le Bissonnais Y. 1990. Experimental study and modeling of soil surface crusting processes In Soil Erosion – Experiments and Models,

Bryan RB (ed.). Catena Supplement 17. Catena Verlag: Cremlingen-Destedt, W. Germany; 13–28.Le Bissonnais Y, Singer MJ. 1992. Crusting, runoff, and erosion response to soil water content and successive rainfalls. Soil Science Society

of America Journal 56: 1898–1903.Le Bissonnais Y, Singer MJ. 1993. Seal formation, runoff, and interrill erosion from seventeen California soils. Soil Science Society of

America Journal 57: 224–229.Le Bissonnais Y. Bruand A. Jamagne M. 1989. Laboratory Experimental study of soil crusting: relation between aggregate breakdown

mechanisms and crust structure. Catena 16: 377–392.Levy GJ, Levin J, Shainberg I. 1997. Prewetting rate and aging effects on seal formation and interrill soil erosion. Soil Science 162: 131–

139.Leys JF, Eldridge DJ. 1998. Influence of cryptogramic crust disturbance to wind erosion on sand and loam rangeland soils. Earth Surface

Processes and Landforms 23: 963–974.Loch RJ. 1994. Structure breakdown on wetting. In: Sealing, Crusting and Hardsetting Soils, Productivity and Conservation, So HB, Smith

GD, Raine SR, Schafer BM, Loch RJ (eds). Australian Society of Soil Science: Brisbane; 113–132.Lyons WF, Munro RK, Wood MS, Shao Y, Leslie LM. 1998. Broadscale wind erosion model for environmental assessment and manage-

ment. Advances in Ecological Sciences 1: 275–294.Mamedov AI, Levy GJ, Shainberg I, Letey J. 2001. Wetting rate, sodicity and soil texture effects on infiltration rate and runoff. Australian

Journal of Soil Research 39: 1293–1305. http://www.publish.csiro.au/journals/ajsrMcIntyre DS. 1958. Permeability measurements of soil crusts formed by raindrop impact. Soil Science 85: 185–189.Mead JA, Chan KY. 1988. Effect of deep tillage and seedbed preparation on the growth and yield of wheat on a hard setting soil. Australian

Journal of Soil Experimental Biology 28: 491–498.Meyer LD, Harmon WC. 1984. Susceptibility of agricultural soils to interrill erosion. Soil Science Society of America Journal 48: 1152–

1157.Miller WP. 1987. Infiltration and soil loss of three gypsum amended Ultisols under simulated rainfall. Soil Science Society of America

Journal 51: 1314–1320.Nearing MA, Lane LJ, Alberts EE, Laflen JM. 1990. Prediction technology for soil erosion by water: Status and research needs. Soil Science

Society of America Journal 54: 1702–1711.Onofiok O, Singer MJ. 1984. Scanning electron microscopy studies of surface crust formed by simulated rainfall. Soil Science Society of

America Journal 48: 1137–1143.Oster JD, Schroer FW. 1979. Infiltration as influenced by irrigation water quality. Soil Science Society of America Journal 43: 444–447.Quirk JP, Panabokke CR. 1962. Incipient failure of soil aggregates. Journal of Soil Science 13: 60–69.Rice MA, McEwan IK. 2001. Crust strength: A wind tunnel study of the effect of impact by saltating particles on cohesive soil surfaces.

Earth Surface Processes and Landforms 26: 721–733.Rice MA, Mcewan IK, Mullins CE. 1999. A conceptual model of wind erosion of soil surfaces by saltating particles. Earth Surface

Processes and Landforms 24: 383–392.Roth CH, Helming K. 1992. Dynamics of surface sealing, runoff formation and interrill soil loss as related to rainfall intensity, microrelief

and slope. Zeitschrift fur Pflanzenernahrung und Bodenkunde 155(3): 209–216.Saleh A, Fryrear DW. 1999. Soil roughness for the revised wind erosion equation. Journal of Soil and Water Conservation 54(2): 473–

476.Scholte PT. 1989. Vegetation soil relations in an area with sealed Chromic Luvisols, Kenya. Arid Soil Research Rehabilitation. 3: 337–348.Shainberg I, Letey J. 1984. Response of soils to sodic and saline conditions. Hilgardia 52: 1–57.Shainberg I, Levy GJ. 1994. Organic polymers and soil sealing in cultivated soils. Soil Science 158: 267–273.Shainberg I, Warrington D, Rengasamy P. 1990. Water quality and PAM interactions in reducing surface sealing. Soil Science 149: 301–

307.Shainberg I, Warrington D, Laflen JM. 1992. Soil Dispersibility, rain properties and slope interaction in rill formation and erosion. Soil

Science Society of America Journal 56: 278–283.Shainberg I, Goldstein D, Levy GJ. 1996. Rill erosion dependence on soil moisture content, aging duration and temperature. Soil Science

Society of America Journal 59: 916–922.Shainberg I, Mamedov AI, Levy GJ. 2003. Role of wetting rate and rain energy in seal formation and erosion. Soil Science 168(1): 54–

62.Singer MJ, Southard RJ, Warrington DN, Janitzky P. 1992. Stability of synthetic sand-clay aggregates after wetting and drying cycles. Soil

Science Society of America Journal 56: 1843–1848.Stern R, Ben Hur M, Shainberg I. 1991. Clay mineralogy effect on rain infiltration, seal formation and soil losses. Soil Science 152: 455–

462.Wakindiki IIC, Ben-Hur M. 2002. Soil mineralogy and texture effects on crust micromorphology, infiltration, and erosion. Soil Science

Society of America Journal 66: 897–905.



Warrington D, Shainberg I, Agassi M, Morin J. 1989. Slope and phosphogypsum effects on runoff and erosion. Soil Science Society of

America Journal 53: 1201–1205.West LT, Miller WP, Langdale GW, Bruce RR, Laflen JM, Thomas AW. 1991. Cropping system and prior erosion effects on interrill soil

loss in the southern Piedmoint of Georgia. Soil Science Society of America Journal 55: 460–466.West LT, Chiang SC, Norton LD. 1992. The morphology of surface crusts. In Soil Crusting, Sumner ME, Stewart BA (eds). Lewis

Publishers: Boca Raton FL; 73–92.Wischmeier WH, Mannering J. 1969. Relation of soil properties to its erodibility. Soil Science Society of America Proceedings 33(1): 131–

137.Wischmeier WH, Smith DD. 1978. Predicting Rainfall Erosion Losses – a Guide to Conservation Planning. Agricultural Handbook 537.

USDA: Washington.Wischmeier WH, Johnson CB, Cross BV. 1971. A soil erodibility monograph for farmland and construction sites. Journal of Soil and Water

Conservation 20: 150–152.Young RA, Wiersma JL. 1972. The role of rainfall impact in soil detachment and transport. Water Resources Research 9: 1629–1636.Zobeck TM. 1991. Abrasion of crusted soils: Influence of abrader flux and soil properties. Soil Science Society of America Journal 55(4):

1091–1097.

mineral soil surface crusts and wind and water erosion

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