Impact of clay on wind erosion for an erodible soil crust
surface
In this study, we found the crust crushing energy increased binomially
with increasing clay amendment (Figure 5a). These results are consistent
with previous studies (e.g., Diouf et al., 1990; Hagen, 1995; Pi et al.,
2019b). However, the rate of change in crust crushing energy decreased
linearly with increasing clay amendment (Figure 5b). The rate of change
in crust crushing energy was higher for the two sandy loams than two
silt loams. In addition, soil loss significantly decreased with the
increasing aggregate GMD. Soil loss was higher for the two sandy loams
than two silt loams. Both trends appeared consistent and indicated that
decreased soil loss was directly associated with increasing clay
amendment, crust crushing energy and aggregate GMD.
Significant differences in soil loss were found between 0 and 2% clay
amendment treatments for Warden sandy loam and Farrell sandy loam
according to ANOVA (Table 3). The relationship between clay amendment
and soil loss is illustrated in Figure 8. Regression analysis revealed
similar trends with ANOVA. The relationship between clay amendment and
soil loss appeared to be nearly an exponential function for all soil
types. Clay particles are important in cementing sand grains together
and thereby changing crust strength and soil loss. In fact, we found
soil loss decreased with the increasing clay content for the erodible
soil crust surface. This trend was consistent with previous studies for
a variety of soil types where soil loss was inversely related to clay
content (e.g., Zobeck, 1991b; Hagen et al., 1992; Pi et al., 2020b). No
statistical differences in soil loss were found with increasing clay
amendment for Athena silt loam and Walla Walla silt loam until clay
amendment reached 16 and 8% respectively. No significant differences in
soil loss were found between 8% and 16% clay amendment for all the
soil types except for the Athena silt loam. Regression analysis also
suggested that the rate of change in erosion decreased with increasing
amounts of clay amendment.
For example, soil loss
decreased by 3.33, 4.31, 6.32, and 94.1 g m-2 for
Athena silt loam, Walla Walla silt loam, Warden sandy loam and Farrell
sandy loam when amended clay content increased from 0 to 2%.
Nonetheless, soil loss decreased by only 1.66, 1.75, 2.86 and 3.17 g
m-2 for the four respective soil types when amended
clay content increased from 14 to 16%. Soil loss was thus sensitive to
the low clay amendment treatment; this trend was consistent with the
effect of clay amendment on crust crushing energy.
Our results indicate that clay amendment protects the soil surface from
erosion for the soil types used in this study, at least until the clay
amendment exceeded a certain value in which case the protective effect
of clay amendment may have reached a peak. For example, strong crust due
to greater clay amendment may be more prone to break down into greater
aggregate or cloud when undergoing a disruptive tillage, the former of
which may be very hard to be eroded. However, we assume soil loss will
not decrease to zero because loose and small soil particles are present
along the vertical cracks caused by tillage.
Based on the coefficients of linear regression (Figure 8), the
effectiveness of clay amendments in decreasing soil loss varied among
soil types. The higher regression coefficients suggest the rate of
change in soil loss with progressive increase in clay amendment was
higher for Farrell sandy loam than Warden sandy loam, followed by Athena
silt loam, and Walla Walla silt loam.
For example, soil loss
decreased by 56 and 66% for Athena silt loam and Walla Walla silt loam
and by 82 and 99% for Warden sandy loam and Warden sandy loam in the
presence of 16% clay amendment. This was expected because of greater
wind soil erodibility and lower clay content for two sandy loams than
two silt loams. Clay therefore appeared to influence soil wind erosion
with greater sand content in this study. In fact, amending sandy soil
using clay has been considered a sustainable and economical reclamation
strategy for enhancing plant productivity and soil water retention in
previous studies (Zayani et al., 2006; Ismail and Ozawa, 2006).
The impact of clay amendment on soil loss may be primarily due to the
changes in aggregate GMD. Aggregates influence soil loss primarily
through the amount of available saltation and suspension components
which directly causes variations in soil loss. Nonetheless, the flux of
abrading particles from aggregates is an additional available source of
saltation and suspension. Aggregates with lower crushing energy can
result in considerable flux of abrading particles (Hagen, 1991).
Mirzamostafa et al. (1998) investigated fraction of the flux of abrading
particles in suspension as influenced by
clay
content for four Kansas soils. They found abrasion flux decreased with
clay content ranging from 0 to 17%. In this study, we assumed that
aggregate crushing energy and aggregate GMD similarly impacted soil
loss. Crust crushing energy has been considered to equal aggregate
crushing energy according to the Single-event Wind Erosion Evaluation
Program (SWEEP) user guide (USDA, 2016).
Impact of aggregate
crushing energy on soil loss through abrasion flux
Soil wind erosion degrades aggregates as a result of abrading (Hagen et
al., 1991). Abrasion influences particles potentially available for
emissions and aides in the initiation of erosion. In the Jornada Desert
of New Mexico, Webb et al. (2016) found that horizontal mass flux was
controlled by the supply and abrasion efficiency of saltators.
The abrasion of aggregates is determined by aggregate crushing energy
(Hagen et al., 1993). Weak aggregates can be eroded rapidly, especially
by wind which carries suspended or blowing soil particles (Zobeck,
1991a), whereas strong aggregates are more resistant to erosion. We
found soil loss was sensitive to clay amendment when aggregate crushing
energy was low. Indeed, weak aggregates with low aggregate crushing
energy may have greater abrading potential. With an increase in clay
amendment, the abrading potential decreased until sufficient aggregate
strength was achieved to resist an further abrasion. Hagen et al. (1993)
found aggregate crushing energy determined aggregate abrasion
coefficients and thus abrasion flux. In this study, we used the SWEEP to
simulate abrasion flux in order to interpret the effect of clay
amendment on aggregate crushing energy. The SWEEP wind erosion submodel
was described in detail by USDA (2016) and simulates abrasion flux
following:
Qabrasion=\(\sum_{i=1}^{m}Q\)*Fani*Cani(4)
where Qabrasion is simulated vertical abrasion
flux (g m-2); Q is saltation discharge (g
m-2), which was caused by wind speed at 12 m
s-1 for 180 s within abrader environment (Table 3).Fani, Cani are respectively the
fraction of saltation abrading surface with ith abrasion coefficient,
and abrasion coefficient of ith surface (1/m). Hagen et al. (1993)
recommended using a single target surface in wind tunnel tests. TheFani was calculated as:
Fani=[1-4Bf-2SVroc(1-
Bf)]*[1-(1- \((\frac{\text{SF}_{84}-\text{SF}_{10}}{\text{SF}_{200}-\text{SF}_{10}})\)) \(e^{(\frac{{-SFA}_{12}}{20})}\)]
(5)
where Bf is biomass fraction of flat cover,SVroc is soil volume with rock
(m-3 m-3),SF10,SF84,SF200are the aggregate fraction less than 0.1, 0.84, and 2 mm,SFA12 is soil surface fraction with shelter
angles greater than 12 degrees. Bf ,
SVroc, and SFA12 are consistent
zero for all the treatments. The Cani was
calculated as:
Cani= \(e^{(-2.07-0.077X^{2.5}+Ln(x))}\)