The relationships between amounts of soil eroded and both runoff and EI15 were
non-linear and showed a high degree of scatter on all the terraces. The variance in
soil loss explained by runoff varies tremendously (Table 5). For most terraces, the
EI15 index explained slightly more of the variance in erosion losses than total runoff.
Coefficients of determination for some terraces were poor. This is not unusual in
erosion research. It may suggest that soil particles are being detached and transported
in several stages and in different ways. Thus, their final removal from the terrace may
occur in events of lesser magnitude than those that effected the initial detachment of
the particles. Moreover, small rills develop across the terraces during the rainy-season
crop cycles and episodic erosion into the banks of these may supply eroded material
in bursts. Moreover, the storms are very complex in their magnitude and intensity
profiles, and both the total runoff and EI15 parameters are crude approaches to summarizing
the storm profile. Other soil and vegetation parameters will also affect
erosion losses. If vegetation cover is added to the analysis, coefficients of determination
are generally increased for both soil loss and runoff and soil loss and EI15.
It must also be remembered that considerable soil loss can occur during a single
rainfall event. Thus, maximum erosion losses recorded in a single event varied from
39.4 g m–2 on Bari 10, to 316.0 g m–2 (equivalent to 3.16 t ha–1
) on Bari 2.
As with variations in runoff, some of the variations in soil loss between the terraces
may be due to variation in soil properties. A number of methods are available for
estimating soil erodibility. Some of the simpler approaches using soil physical and
chemical properties have been used here. Erodibility is often highly correlated with
the silt and fine sand fractions (positively), the organic contents (negatively) and
water-stable aggregate contents (negatively). These values for the terrace soils have
been listed in Table 6. The combination of moderately high silt and fine sand fractions,
low to moderate clay-size fractions, low organic carbon contents and, for most
terraces, low soil aggregate stabilities, rendered the surface soils moderately to highly
erodible. The high potential erodibility was readily seen in the field by the frequent
The relationships between amounts of soil eroded and both runoff and EI15 werenon-linear and showed a high degree of scatter on all the terraces. The variance insoil loss explained by runoff varies tremendously (Table 5). For most terraces, theEI15 index explained slightly more of the variance in erosion losses than total runoff.Coefficients of determination for some terraces were poor. This is not unusual inerosion research. It may suggest that soil particles are being detached and transportedin several stages and in different ways. Thus, their final removal from the terrace mayoccur in events of lesser magnitude than those that effected the initial detachment ofthe particles. Moreover, small rills develop across the terraces during the rainy-seasoncrop cycles and episodic erosion into the banks of these may supply eroded materialin bursts. Moreover, the storms are very complex in their magnitude and intensityprofiles, and both the total runoff and EI15 parameters are crude approaches to summarizingthe storm profile. Other soil and vegetation parameters will also affecterosion losses. If vegetation cover is added to the analysis, coefficients of determinationare generally increased for both soil loss and runoff and soil loss and EI15.It must also be remembered that considerable soil loss can occur during a singlerainfall event. Thus, maximum erosion losses recorded in a single event varied from39.4 g m–2 on Bari 10, to 316.0 g m–2 (equivalent to 3.16 t ha–1) on Bari 2.As with variations in runoff, some of the variations in soil loss between the terracesmay be due to variation in soil properties. A number of methods are available forestimating soil erodibility. Some of the simpler approaches using soil physical andchemical properties have been used here. Erodibility is often highly correlated withthe silt and fine sand fractions (positively), the organic contents (negatively) andwater-stable aggregate contents (negatively). These values for the terrace soils havebeen listed in Table 6. The combination of moderately high silt and fine sand fractions,low to moderate clay-size fractions, low organic carbon contents and, for mostterraces, low soil aggregate stabilities, rendered the surface soils moderately to highlyerodible. The high potential erodibility was readily seen in the field by the frequent
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