Introduction
Wind erosion is a serious problem in arid and semiarid regions where
soil is loose and dry and not well protected by vegetation cover. Wind
erosion is a process involving the detachment, transport, and deposition
of soil particles by wind. Wind erosion not only causes soil loss from
the soil surface, but also land degeneration or desertification. Land
degradation may result from removing fertile top soil, namely, the clays
and organic matter, and leaving the infertile and coarse soil. In
addition, fine suspended particulates due to wind erosion is always a
concern for air quality for cities located in or around arid and
semiarid regions (Sharratt and Lauer, 2006; Chen et al., 2017).
Moreover, severe and sustained wind erosion events have resulted in
regional dust storms, which threatened aircraft, road transportation,
and health of humans and animals (Hudson and Cary, 1999; Nel, 2005).
The inland Pacific Northwest region (iPNW) of the Unites States is
surrounded by a series of tall Mountains, which intercept the flow of
moist and relatively mild air from the Pacific Ocean, thus resulting in
a semi-arid environment. The PM10 concentration caused by wind erosion
events has exceeded National Ambient Air Quality Standard (NAAQS)
several times per year at Kennewick, WA (Sharratt and Lauer, 2006). An
estimated 98 Mg ha-1 soil and 2.7 Mg
ha-1 PM10 are eroded each year from the
agro-ecological classes of the iPNW (Pi et al., 2019a).
Wind erosion is influenced by a series of plant, soil and wind
parameters. For example, plants reduce wind erosion as a result of
directly intercepting saltating particle. Soil crusts also reduce wind
erosion by binding soil particles together into a cohesive structure,
thereby minimizing the availability of loose particles susceptible to
transport by wind. Wind speed determines the energy imparted to soil
particles and thus the transport capacity of wind erosion. Some wind
erosion parameters are nearly static and change very slowly through
time. For example, intrinsic soil properties such as clay and organic
matter content change slowly with time. In contrast, some wind erosion
parameters change very rapidly in response to management or weather.
Aggregate and crust properties can be altered by tillage or rainfall
events thus are called temporal or external soil properties (Zobeck,
1991a). Temporal soil properties appear to be relevant in controlling
daily soil wind erosion whereas intrinsic soil properties largely
control long-term soil wind erosion, the latter of which is called soil
wind erosion potential (Zobeck, 1991a). Intrinsic or temporal soil
properties do not simultaneously influence wind erosion because
intrinsic soil properties more or less influence the temporal soil
properties. For instance, soil clay content is one of the primary
intrinsic soil properties affecting wind erodibility, but it rarely
influences wind erosion other than through its impact on crust or
aggregate crushing energy (Zobeck, 1991a). Temporal soil properties
influencing wind erosion include random roughness, soil water content,
as well as aggregate and crust properties (USDA, 2016).
Soil crusting is one of the most important factors influencing wind
erosion. Crust crushing energy is highly dependent on clay and organic
matter content which are the cohesive forces acting on particles. Crust
crushing energy influences wind erosion in terms of its impact on
controlling the amount of flaking (Gillette et al., 1982) and abrading
(Hagen et al., 1992), Flaking and abrading contribute to the particle
load which can be transported by wind, especially for weak crusts with
lower crust crushing energy. In addition, crust crushing energy
influence wind erosion through its impact on controlling threshold
friction velocity (u*t) . Gillette et al. (2001)
indicated that hard crusts with greater crust crushing energy
tended
to show almost no change in u*t with time whereas
weak crusts with lower crust crushing energy resulted in a rapid
decrease in u*t with time.
Tillage is the primary factor influencing crust degradation on
agricultural lands. Other crust properties influencing wind erosion
include crust type (Belnap, 2003), crust hardness (Gillette et al.,
2001), crust micro-topography (Gillette et al., 2001), crust thickness
(Sharratt and Vaddella., 2014), progressive development of a crust cover
(Pi and Sharratt, 2019), and loose material on the crust surface.
Aggregation is another essential factor influencing soil wind erosion.
The Agricultural Policy /Environmental eXtender (APEX) model considers
the aggregate size distribution (ASD) as the sole factor determining
soil erodibility (Williams et al., 2015). Aggregate size distribution
can influence soil wind erosion because ASD influences (1) the amount of
available creep (0.84 to 2.0 mm), saltation (0.10 to 0.84 mm),
suspension (<0.1 mm), and PM10 (<0.01 mm) components
(USDA, 2016); (2) aggregate stability (Hevia et al., 2007); (3)
threshold friction velocity (Gillette et al., 1980); (4) source of
abrasion (Mirzamostafa et al., 1998); (5) random roughness (USDA, 2016);
(6) the amount of nonerodible components transported by wind
(> 2 mm) (Zobeck, 1991b). Kheirabadi et al. (2018) examined
the effect of soil bed length, wind velocity and ASD on sediment flux.
They found finer aggregates (D2mm) at the surface are
more susceptible to transport by wind while soil containing coarser
aggregates exhibited less sediment flux. Mirzamostafa et al. (1998)
examined the effect of soil aggregate and texture on suspension
emission. They found suspension emission was directly related to soil
texture (r2= 0.87), whereas abraded emission was
directly related to clay content (r2= 0.69). Other
aggregate properties influencing wind erosion include aggregate density
and stability and minimum and maximum aggregate sizes (USDA, 2016).
The impact of random roughness in controlling wind erosion has been
studied by Zobeck and Onstad (1987), Hagen and Armbrust (1992), and
Gillette et al. (2001). They found wind erosion increased
logarithmically with random roughness. Random roughness is associate
with soil surface microrelief which can impact surface aerodynamic
roughness and shear stress (Shao, 2008; Okin, 2008). Surface microrelief
is greatly influenced by maximum aggregate size and crust rough (Zobeck,
1991a).
Soil clay content is a primary soil component due to its various
influences for soil ecological processes. Soil clay amendment can impact
soil ecosystems as a result of modifying enzyme activity (Abd-elgwad,
2019), hydraulic conductivity (Frenkel et al., 1978), soil-water
retention curves (Gupta and Larson, 1979), soil moisture distribution
and water use efficiency (Ismail and Ozawa, 2007; Mi et al., 2017),
evaporation (Zayani et al., 1996), soil fertility (Mi et al., 2017), and
crop yield (Mojid et al., 2012). Although Diouf et al. (1990) reported
soil clay amendment impacted wind erosion as a result of influencing
aggregate stability, little information is available that documents the
effect of clay amendment on other soil properties such soil wind
erosion.
We are not aware of any studies that have measured the change in wind
erosion of clay-amended soils, which is a primary soil component that
binds individual particles together resulting in changes to aggregate
and crust properties. Therefore, the objective of this study was to: (1)
identify the impact of clay amendment (Wyoming bentonite) on wind
erosion from disturbed crusts of four major loessial soils in the inland
Pacific Northwest, USA; (2) test the effect of clay amendment on crust
crushing energy; and (3) evaluate the effect of clay amendment on
surface characteristics affecting wind erosion such as random roughness,
aggregate crushing energy, and ASD.