Agriculture Reference
In-Depth Information
Ayuk and Mafongoya (2002) reported a successive decline in maize yields
with the number of cropping years after fallow termination. After fallowing with
Sesbania
, maize yields were 3.6, 2.0, and 1.6 Mg ha
−1
for the first, second, and third
year, respectively, after fallow termination, while after
Tephrosia
maize yields were
3.1, 2.4, and 1.3 Mg ha
−1
for the first, second, and third year, respectively, after fal-
low termination. Mafongoya et al. (2003) reported that fallow species had a positive
N balance in the first year of cropping after the fallow phase. In the second year of
cropping, the N balance in the fallow systems decreased, partly due to large offtake
in the large yields and partly due to leaching through the soils and other associated
losses of N due to immobilization, volatilization, and denitrification. These obser-
vations were supported by Mafongoya and Dzowela (1999), who suggested that the
postfallow cropping phase should be restricted to 2 years.
In Kenya, Niang et al. (2002) tested
Tithonia
(
Tithonia diversifolia
),
Tephrosia
,
and
Sesbania
in a single year of fallow, followed by two rainy season maize crops
in the following year. The fallow species produced 1.2, 1.4, and 1.6 times as much
maize as the sole maize control.
Tithonia
was propagated from cuttings,
Tephrosia
was direct-seeded in the maize, and
Sesbania
seedlings were transplanted into the
fields.
Improved fallows usually follow a 2-year fallow plus 2-year cropping pattern, so
that the yields in the cropping years must be more than double the yields under sole
maize for the fallow to be worthwhile for the smallholder. In Table 11.3, all of the
2-year yield increments save one in Zimbabwe are well above two, so that the prac-
tice produces worthwhile yield gains for the smallholders, while at the same time
improving soil and ecosystem health.
The addition of half the recommended fertilizer dose to tree fallow plots may
provide higher yields than fertilizer alone or tree fallows alone. In Zambia, cumula-
tive maize yields were 10.7 Mg in fallows with half of the recommended fertilizer
rate, compared with 10.4 Mg for sole fallow over a 3-year period (Ajayi et al. 2005).
Similar results were also reported by Chikowo (2004) and Makumba et al. (2006),
who reported better maize yields in plots where half the recommended fertilizer
rates were applied compared with sole fertilizers or unfertilized fallows. From these
observations, it was concluded that at certain levels of fertilizer use, there is some
synergy between mineral fertilizers and improved fallow species such as
Sesbania
and
Tephrosia
(Ajayi et al. 2005).
11.2.2.2 Intercrops
Harawa et al. (2006) found yields to be 1.6 times higher with
Gliricidia
intercrop,
compared with the sole maize control, across all slope positions. Maize yields were
1.4 and 1.8 times those in the sole maize control with
Sesbania
and
Tephrosia
relay
intercrops in the same study. In the relay intercrop, the fallow species are planted
annually directly following maize planting. Leaf biomass developed during the dry
season is incorporated annually during land preparation.
Each of the agroforestry species fits into specific agroecological niches in cereal-
based cropping systems. Harawa et al. (2006) tested
Sesbania
,
Tephrosia
, and
Gliricidia
on upper-slope, mid-slope, and bottom-slope positions near Zomba in
southern Malawi.
Sesbania
was found better adapted for the bottom-slope position,
