Agriculture Reference
In-Depth Information
synchronization of nutrient release and crop demand, leading to increased fertilizer
and nutrient use efficiency and higher yields (Vanlauwe et al. 2002). For example,
CA technologies conducted in Kenya (DAP, FYM, and soil and water conservation)
demonstrated higher (>10 times) marginal returns from grain amaranth (
Amaranthus
hypochondriacus
) compared with maize, with the former being a better climate
change/variability adaptation strategy compared with the latter, and in Uganda
resulting in >30% increase in groundnut yield with 50-150 kg single superphosphate
per hectare (Semalulu et al. 2011a). Furthermore, CA (application of organic and
inorganic fertilizers, maize stover combined with inorganic fertilizers, and inter-
cropping maize with
Dolichos lablab
) resulted in yield gains of 55%, 130-270%,
and 160%, respectively, over the farmers' practice in the cereal-legume-livestock
systems (Matowo et al. 2011). In addition, yield increases of 80%, 130%, and 200%
above the farmers' practice were obtained using CA technologies under soybean
(
Glycine max
(L.) Merr. and groundnut (
Arachis hypogaea
L.), sorghum (
Sorghum
bicolor
(L.) Moench), and for both maize (
Zea mays
L.) and rice (
Oryza sativa
L.),
respectively (Mugwe et al. 2011). Other trials in Kenya showed that maize grain yield
increased from 1247 to 2678 kg/ha with the addition of 25 kg DAP/ha and 2 Mg of
stover (Semalulu et al. 2011b). Related CA work in Siaya county, Kenya, by KEFRI/
ICRAF/KARI based on fertilizer tree technology utilizing calliandra (
Calliandra
calothyrsus
Meissn) showed that short-duration improved fallows (fertilizer trees)
of 6-12 months increased the yield of subsequent maize crops by 1-3 Mg/ha in the
first season and had high economic benefits compared with continuous maize crop-
ping or natural weed fallows (Semalulu et al. 2011b). Although these technologies
have shown promising results, most of them were limited to participating farmers
within the project sites. The main goal of this chapter was to provide further insights
into the potential contribution of CA practices to sustainable smallholder agriculture
in East Africa in the context of climate change, soil restoration, and agricultural
productivity.
12.2
LAND DEGRADATION PROCESSES IN EAST AFRICA
12.2.1 i
interrill
and
r
ill
e
rosion
Soil erosion is a major environmental problem and is widespread worldwide (Xiao et
al. 2011). Soil erosion by water is rampant in both semiarid and mountainous areas,
leading to low productivity and increased poverty (Kimaro 2003; Liu et al. 2012). The
Highlands of East Africa suffer severely from soil erosion since the deforestation of the
natural mountain forests and the cultivation of large areas (Kimaro et al. 2008). High
rates of soil losses due to severe soil erosion by water are reported from arable lands
in the mountainous areas of East Africa (Oldeman et al. 1990). In these areas, past
studies show that rates of soil loss by combined processes of interrill and rill erosion
are very high, i.e., in excess of 50 Mg/ha/year, which exceeds the tolerable values
generally recommended to be 10-12 Mg/ha/year (Milliman and Meade 1983). Soil
erosion is a serious problem in mountainous areas of Tanzania (Kimaro 2003; Msita
2013). In the Usambara Mountains, soil erosion by water is estimated to vary from
72 to 120 Mg/ha/year (Lundgren 1980; Pfeiffer 1990), while a soil loss of 28-72
