Impact of clay on soil erodibility through crust crushing
energy
Clay was used to amend the original four soils in terms of increasing
crust crushing energy. After an erodible soil surface is created by
tilling a crusted surface, soil loss can influence temporal wind erosion
factors such as random roughness, aggregate GMD as well as aggregate
crushing energy and density within the erodible soil surface
environment.
No statistical relationships were found between crust crushing energy
and soil water content, random roughness, and aggregate density for the
four soil types according to the p-value (>0.1) (Figure 6)
except the aggregate geometric mean diameter (GMD) and crushing energy.
Crust crushing energy appeared to increase logarithmically with GMD for
all soil types (Figure
7a).
As the disruptive force is imparted to a crust surface by tillage, the
crust fractures into aggregates. Crusts with low stability may fracture
into smaller sizes due to their limited cohesive forces. Aggregate size
distributions are highly correlated with aggregate stability, which is
also called aggregate crushing energy (Kemper and Rosenau, 1986). Colazo
and Buschiazzo (2010) and Hevia et al. (2007) used aggregate size
distributions to determine aggregate stability. Aggregate stability
increased with aggregate size for aggregates > 0.84 mm. In
this study, we assumed that crust crushing energy was equal to aggregate
crushing energy because both are controlled by the magnitude of cohesive
forces between soil particles (Amézketa,1999, Saleh, 1993; USDA, 2016).
This therefore is not surprising that aggregate GMD increased with
increasing crust crushing energy as well as aggregate crushing energy.
These results indicated that crust crushing energy also was an important
factor affecting ASD for a disturbed crust surface. As clay amendment
increased, the crust surface was more difficult to disturb even though
the crust could be broken into greater aggregate sizes. However, as the
crust crushing energy exceeds a certain value, the crust will not break
down into aggregate but rather into clods (often called secondary
aggregates, Zobeck, 1991a) due to their considerable cohesive forces.
Not only does tillage practices affect dry ASD (Hevia et al., 2007), but
aggregate crushing energy also appears to impact ASD.
Gillette et al. (2001) found crust hardness correlated with rough
crusts, the latter of which may influence microrelief. Large aggregates
associated with high crushing energy may be more prone to result in high
random roughness. However, we found no statistical relationships between
crust crushing energy and random roughness in this study (Table 2). This
was not surprising because random roughness usually associates with
tillage intensity (Hagen, 1991), rainfall amount and kinetic energy, and
runoff (Zobeck and Onstad, 1987). These parameters was assumed not to
change due to the application of standard tillage and rainfall
simulator. Similarly, no consistent increase or decrease in soil water
content was found with increasing crust crushing energy. In addition,
soil water content varied little and was much less than the wilting
point water content, thus water content and random roughness were
expected to have little effect on soil loss in this study.