Geology Reference
In-Depth Information
WEPP variation
(%)
(%)
400
200
0
L20S1
L20S7
L40S1
L40S7
-200
-400
Runoff (L)
Soil loss (kg)
-600
-800
-1000
-1200
Segments
Fig. 10.3
Percentage variation between the observed and predicted runoff and soil loss in different segments.
Estimate 2 used a value for
K
i
obtained according
to the methodology proposed by Kinnell (1993),
and the other parameter values were the same as
for Estimate 1. Estimate 3 used the parameter
values generated by WEPP.
The six plots used for this experiment had the
following characteristics: soybean grown along
the contour (SCL); soybean grown up-and-down
slope (SUD); maize along the contour (MCL);
maize up-and-down slope (MUD); bare soil along
the contour (BCL) and bare soil up-and-down
slope (BUD). The mean effect of vegetation cover
(SCL, SUD, MCL and MUD) compared with the
bare plots (BCL and BUD) resulted in a mean
reduction of soil loss by 84% and runoff by 52%.
Maize was more efficient in decreasing soil loss
and runoff than soybean.
The combined effect of soil management prac-
tices and vegetation cover increased the efficiency
of the mean reduction of soil loss by 92% (MCL)
and 88% (SCL), compared to the bare plots (BCL).
Runoff was less influenced by soil management
practices and vegetation type than soil loss. There
was a mean reduction of 73% on the maize on the
contour-line plot (MCL), compared with the bare
plot (BUD).
Runoff was obtained through simulated rain-
fall. Ultisol (Red Yellow Argisol) and Inceptisol
(Distrofic Haplic Cambisol) presented distinct
behaviours. Sediment concentration was higher
at the beginning of the simulated rainfall and
decreased during the experiment. The Argisol
(34% sand, 13% silt and 53% clay) presented
higher soil loss concentrations during the whole
experiment, whereas the Cambisol only had
higher soil loss concentrations at the beginning of
the experiment. This situation is associated with
the higher proportion of loose particles due to
recent soil ploughing.
Inter-rill erosion increased during the simu-
lated rainfall, although rates of inter-rill erosion
stabilized on the Cambisol before the Argisol.
