Agriculture Reference
In-Depth Information
2003; Fabrizzi et al. 2005). Studies conducted in the volcanic highlands of Central
Mexico demonstrated positive effects, including nutrient improvement and increased
crop yields during 12 years of zero tillage seeding systems when practiced with
proper crop rotation and crop residue management (Govaerts et al. 2006). Maize-
wheat rotation combined with full residue retention under zero tillage was observed
to increase crop yields significantly. High water infiltration rates and favorable mois-
ture dynamics were reported to explain the observed high crop yields in this area
(Govaerts et al. 2007).
In Ethiopia, two local tillage systems, terwah + and derdero +, using the traditional
mahresha ard plough on Vertisol under crop rotation (wheat, grass, pea, wheat) sig-
nificantly 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
the terwah + and derdero + tillage systems (Araya et al. 2012). The effect of contour
furrows at 60-70 cm interval without any soil movement in the bed (permanent
raised bed system), as well as contour furrows at 1.5-2 m spacing after ploughing
( terwah cultivation) on runoff and soil loss in comparison with the conventional
ploughing system, was evaluated in Tigray, northern Ethiopia (Gebregziabher et al.
2009). In this study, the total soil loss decreased from 19.5 Mg/ha for the conventional
ploughing system to 7.6 Mg/ha for terwah cultivation and to 4.7 Mg/ha for the perma-
nent raised bed system (Gebregziabher et al. 2009). The study concluded that contour
furrows and permanent raised beds can be part of an agricultural intensification pro-
cess that includes physical soil and water conservation, slope reforestation, irrigation
development, and agroforestry in croplands. In addition, the use of permanent raised
beds if combined with crop mulching and crop diversification is an important com-
ponent for the development of sustainable CA practices in the region.
Thus far, in sub-Saharan Africa, particularly in East Africa, CA has been
restricted to only large estate farming (IFAD/FAO 2004) and the practices remain
poorly implemented among smallholder farmers, particularly in the highland farm-
ing communities (Tittonell et al. 2008). CA that has been practiced in East Africa,
especially in Kenya and Tanzania, comprised three principles that have been applied
simultaneously: minimum soil disturbance, permanent soil cover, and complex rota-
tions/crop associations (Owenya et al. 2011). Recent studies have indicated a posi-
tive trend in practicing CA in many areas of East Africa owing to the integration of
both indigenous and scientific knowledge (Shetto and Owenya 2007). However, in
Tanzania, for example, knowledge on the application and implementation of CA prac-
tices toward improvement of soil qualities is still scanty (Tenge et al. 2003; Triomphe
et al. 2007), and limited research efforts have been put toward this direction.
Studies conducted on three sites in West Usambara Mountains, Tanzania, identi-
fied farmers' CA practices linked to different cropping and management patterns
(TableĀ 12.13). The identified CA practices include (i) terrace with animal manure,
inorganic fertilizers, crop residues, and crop rotation; (ii) miraba with animal
manure, crop residues, crop rotation, and agroforestry; and (iii) raised beds with
animal manure, inorganic fertilizers, crop residues, and crop rotation. Crop rotation
was the most common management practice identified in the studied sites. The most
common rotations were maize ( Z. mays ) mixed with beans ( Phaseolus vulgaris ) in
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