Raindrop energy and distribution above/below the canopy of
seedling corn
As shown in Tables 1 and 2, the energy and size distribution of
raindrops were significantly different between above and below the
canopy of seedling corn. For the two rainfall intensities, the canopy
mitigation of raindrop energy was observed more in conservation than
conventional tillage measures. The percentage of raindrops with less
than 2.5 mm diameter decreased when the raindrops larger than 2.5 mm
diameter decreased at the rainfall intensity of 50 mm
h-1, whereas the percentage of raindrops with less
than 2.0 mm diameter decreased when that of raindrops larger than 2.0 mm
diameter increased at the rainfall intensity of 100 mm/h.
Runoff-yielding time and runoffvelocity
Table 3 shows that conservation tillage measures could significantly
delay the runoff-yielding time and decrease surface flow velocity,
compared to CK and Vr, at the maize seedling stage. Compared with CK and
Vr, the runoff-yielding times of the Cm, Hr, Hr+Cm, and Vr+Cm treatments
were significantly postponed; the runoff-yielding time advanced at 100
mm h-1 than at 50-mm h-1. The Hr+Cm
treatment successfully prevented runoff yielding throughout the rainfall
event under 50 mm h-1, and the averagely prolonged
runoff-yielding time was approximately 26.1 min,
which was 23.8 times longer than
that of the CK treatment under 100 mm h-1. The average
delay time durations for other treatments from long to short were 23.6
min for Hr, 5.6 min for Cm, and 2.8 min for Vr+Cm.
Table 3 also shows that the declining effects on surface flow velocity
were more obvious under light than under heavy rainfall intensity
conditions. Compared to CK, the Hr+Cm, Cm, Vr+Cm, and Hr treatments
significantly reduced the surface flow velocity, with a decline of 100%
(no runoff generation), 75.8%, 71.9%, and 83.5%, respectively, at the
rainfall intensity of 50 mm h-1 and 96.4%, 82.9%,
77.7%, and 71.5%, respectively, at the rainfall intensity of 100 mm
h-1. However, Vr significantly increased the runoff
velocity by 50.3% and 10.1% at the rainfall intensities of 50 and 100
mm h-1, respectively.
Total runoff and soil loss