Agriculture Reference
In-Depth Information
resources, which has led to the development of various forms of land degradation.
Several studies have been initiated in the region aimed at sustainable land husbandry
and appropriate management of agricultural lands. This chapter focuses on land deg-
radation processes, plant nutrient depletion, and adaptation measures based on the
principles of conservation agriculture (CA) in the context of climate change. It pro-
vides broad experiences and an in-depth knowledge of smallholder farming adap-
tation to climate change using the principles of CA in East Africa. The highlights
from this chapter show that interrill and rill erosion, tillage erosion, and landslides
are dominant land degradation processes in the region of East Africa. Very high soil
losses are reported particularly from interrill and rill erosion ranging from 91 to 258
Mg/ha/year in mountainous areas. Studies have also demonstrated significant rates
of soil flux due to tillage erosion increasing with slope gradient, from 16 kg/m/tillage
pass at a slope gradient of 31% to 60 kg/m/tillage pass at a slope gradient of >60%.
Landslides dominate on the mountain ridges with slopes >45%, where they have
affected >20% of the land with significant crop damage, reducing crop yields by 50%.
Low soil fertility is also a form of land degradation contributing to low crop yields.
Most of the studied soils have very low organic matter content with organic carbon
<1.2%, nitrogen <0.1%, and available phosphorus <5 mg/kg. Inappropriate land uses
also have contributed significantly to soil and nutrient losses. In the Lake Victoria
Basin settlements, compounds and footpaths produced soil losses of up to 199 Mg/
ha/year, while agricultural lands cropped with cotton and cassava produced soil loss
of up to 27 Mg/ha/year. CA is among the adaptation strategies that have been prac-
ticed in East Africa by the smallholder farming community to reduce land degrada-
tion. It comprises three principles that have been applied simultaneously: minimum
soil disturbance, permanent soil cover, and complex rotations/crop associations with
some land management options, including application of farm yard manure, green
manure, composting, mineral fertilizer, weed control, and
in situ
rainwater harvest-
ing. Recent studies have indicated a positive trend in practicing CA in many areas
of East Africa owing to the integration of both indigenous and scientific knowledge.
In Ethiopia, for example, two local tillage systems,
terwah
+ and
derdero
+, using
the traditional
mahresha ard
plough on Vertisol under crop rotation (wheat, grass,
pea, wheat) significantly increased soil organic matter to 2.0% when compared with
conventional tillage (1.4%) for 0-15 and 15-30 cm soil depths. In this study, the
mean yield of wheat for 3 years increased from 2.8 Mg/ha for conventional tillage
to 3.7 Mg/ha for
terwah
+ and
derdero
+ tillage systems. CA has been also demon-
strated to increase the yield of vegetables in the Uluguru Mountains, Tanzania, from
0.88 to 44.68 Mg/ha. The combination of
miraba
(an indigenous soil erosion control
practice), farmyard manure (FYM), and mulching reduced annual soil and nutrient
loss from 132 to 0.5 Mg/ha/year, total nitrogen from 342 to 9 kg/ha/year, and avail-
able phosphorus from 0.4 to <0.1 kg/ha year, respectively, in the West Usambara
Mountains, Tanzania. In this study, grain maize and bean yield increased from 0.7
to 2.6 Mg/ha and 0.2 to 1.3 Mg/ha, respectively. It is obvious from these studies that
CA is a promising strategy that can address the complexities and peculiarities of soil
quality on smallholder farms. It has proven to help low resource endowed farmers
to mitigate problems of poverty, food insecurity, and low income. It enhances the
resilience of soil productive capacity in the context of climate change (Bationo et
