Impact of clay on crust crushing energy
Significant differences in crust crushing energy were found between 0
and 2% clay amendment treatments for the four soil series according to
ANOVA (Table 2). However, no statistical significant differences in
crust crushing energy were found between 2 and 4% clay amendment
treatments for two silt loams and between 4 and 8% and 8 and 16% clay
amendment treatments for the four soil series except Athena silt loam.
This suggests that the effectiveness in increasing crust crushing energy
diminished with progressive increase in clay amendment.
The relationship between clay amendment and crust crushing energy for
the four soil types examined in this study is illustrated in Figure 5a.
The relationship between clay amendment and crust crushing energy
appeared to be nearly a binomial function for all soil types. This
binomial trend was consistent with previous studies for a variety of
soil types (e.g., Diouf et al., 1990; Hagen, 1995; Pi et al., 2019b).
Clay particles play an important function in cementing sand grains
together which then can cause considerable change in crust strength.
Crust crushing energy increased with increasing clay content. However,
Skidmore and Layton (1992) reported crust crushing energy steadily
increased with the increasing clay content until clay content reached
33%. In this study, the clay content for all the soil types was much
less than 33%, thus we did not find a decrease in crust crushing energy
with increasing clay amendment.
Regression analysis revealed similar trends with ANOVA in that the rate
of change in crust crushing energy diminished with progressive increase
in clay amendment. Crust crushing energy increased by 226, 357, 306 and
7473% for Athena, Walla Walla, Warden and Farrell when clay amendment
increased from 0 to 2%. Nonetheless, crust crushing energy increased by
only 69, 41, 218 and 144 % for the four soil types when clay amendment
increased from 2 to 4%.
The rate of change in crust crushing energy with progressive increase in
clay amendment varied among soil types based on regression coefficients.
The relationships between clay amendment and rate of change in crust
crushing energy for the four soil types examined in this study is
illustrated in Figure 5b. The relationship appeared to be nearly a
linear function for all soil types. The higher regression coefficients
suggest the rate of change in crust crushing energy 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.
Clay amendment was more effective in increasing crust crushing energy
for Farrell sandy loam than other soil types. Actually, clay amendment
was more effective in increasing crust crushing energy for two sandy
loams than two silt loams.
For example, crust crushing
energy increased by 30 and 17 fold for Athena silt loam and Walla Walla
silt loam and by 32 and 229 fold for Warden sandy loam and Farrell sandy
loam in the presence of 16% clay amendment. This was expected because
of lower clay content for sandy loam than silt loam.