Agriculture Reference
In-Depth Information
TABLE 12.3
Effect of Tillage Depth and Soil Surface Condition on Soil Flux Due to
Manual Tillage Cultivation in Uluguru Mountains, Tanzania
Mean
Soil Flux
Standard
Deviation
Minimum
Maximum
Parameter
(kg/m/tillage pass)
N
Shallow tillage with residues
31
a
3
7
47
24
Shallow tillage with bare soil surface
44
b
4
12
79
24
Deep tillage with residues
62
c
6
17
89
24
Deep tillage with bare soil surface
78
d
7
22
111
24
Source:
Kimaro, D.N., J. Poesen, J.A. Deckers, and H.B. Msita. 2010. Effects of agroecological condi-
tions and slope gradient on tillage erosion in the northern slopes of the Uluguru Mountains,
Tanzania. Chapter 9 in Earl T. Nardali (Ed.).
No-Till Farming: Effects on Soil, Pros and Cons
and Potential
. Agriculture Issues and Policies Series. ISBN: 978-1-60741-402-5. Nova Science
Publishers Inc., New York. pp. 159-172. With permission.
Note:
Means with the same superscript letters are not significantly different (
P
< .05).
N,
number of
observations.
et al. 2010). Mean soil flux increased significantly (
P
< .05) from 16 kg/m/tillage
pass at a slope gradient of 31% to >60 kg/m/tillage pass at a slope gradient >60%.
The rates of soil flux from bare soil surfaces for both shallow and deep tillage were
significantly higher by 20% and 30% (
P
< .05), respectively, than soil flux from soil
surface with residues. Bare soil surface promoted tillage erosion in contrast to soil
surface with residues. Further analysis showed that a combination of shallow tillage
and the presence of residues on the soil surface can cut down the rates of soil flux by
60% compared with deep tillage on a bare soil surface. The study concluded, there-
fore, that farmers should be discouraged from clearing their fields by removing all
the residues before cultivation.
12.2.1.2 Landslides
Landslides are a result of gravity affecting the stability and evolution of ridge slopes
in the major areas of East Africa, particularly the mountainous areas (Westerberg
1999; Kimaro 2003). The triggering of landslides depends on several complex
but interrelated factors, such as prolonged heavy rainfall (Temple and Rapp 1972;
Larsson 1989), soil characteristics (Westerberg 1999; Mburu 2001), slope char-
acteristics (Lopez and Zinck 1991) and geomorphology (Ahmad and McCalpin
1999; Westerberg and Christiansson 1999), vegetation, land use, and infrastructure
(Larsen and Torres-Sanches 1998). In the Uluguru Mountains, Tanzania, a study
was conducted to investigate the extent of cropland damage due to the El Niño rains
that occurred in 1997-1998 (Kimaro 2003). The rain-induced landslides domi-
nated on the mountain ridges with a slope gradient of >47% (Table 12.4), where
they have affected >20% of the land. Their distribution follows the following trend:
