Agriculture Reference
In-Depth Information
TABLE 12.9
Mean Annual Soil Loss (Mg/ha) Measured on Runoff
Plots within Various Land Use Types in Tanzanian
Shoreline of Magu District
Land Use
(2004-2005)
Mean
Median
SD
Min
Max
N
Rice
3
1.2
1.0
0.4
0.6
2.2
Cassava
3
7.9
6.3
4.8
1.3
19.5
Maize
3
15.6
13.8
5.8
6.7
29.1
Cotton
3
22.7
20.3
9.6
10.5
50.9
Source:
Adapted from Isabirye, M., D. Kimaro, and O. Semalulu,
Tropicultura
, 28, 89, 2010. With permission.
Note:
N
, number of sediment plots where soil loss was measured during
the years 2004-2005.
year) of sediment (Table 12.9). The size and cropping pattern of the field parcels,
and the overall farming techniques in the riparian zone of Lake Victoria have an
overall effect of protecting soil structure against raindrop impact, encouraging
water infiltration, obstructing runoff, and therefore minimizing sediment yield.
The high rates of sediment yield observed under cassava and the settlements in
Uganda and cotton in Tanzania call for soil conservation practices, including tar-
geting settlements as well that ensure complete surface cover and encourage good
soil structure that enhance infiltration.
Other studies conducted in Bududa District, Uganda (Semalulu et al. 2012), to
investigate the effect of different farmer cropping and soil conservation practices
on runoff, soil loss, and nutrient loss demonstrated that soil loss was significantly
(
P
< .05) higher on annuals than on banana or banana-coffee farming systems in
the order of 38.5 > 6.6 > 0.87 Mg/ha/year (Table 12.10). Soil loss values for fields
without conservation structures were much higher than those where there were struc-
tures. Soil loss values were much higher than the tolerable limit for Uganda, which is
5 t/ha/year, and calls for immediate action to scale up sustainable land management
practices.
In West Usambara Mountains, the effectiveness of the
miraba
land utilization
type in reducing runoff, soil loss, and nutrient loss was determined for the pur-
pose of establishing insights to support soil and water conservation planning in the
area.
Miraba
represents a generic word for an indigenous technology and a specific
agricultural landscape type (Figure 12.3).
Miraba
is also referred to as a manage-
ment unit: one field can be subdivided in different numbers of
Miraba
, each being a
square or a rectangular plot fully surrounded by a strip of tall grass of napier grass
(
Pennisetum purpureum
), Guatemala grass (
Tripsacum laxum
), or
Hyparrhenia
grass (
Hyparrhenia
spp.) (Msita et al. 2010a). Results from this study have demon-
strated that the annual soil loss is different (
P
< .05) among the bare plot, cropped
