Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

fresh supply of seedlings or seed reserves to generate
their fallows. Trials at Msekera Research Station,
Zambia have shown that natural regeneration
of Sesbania fallows through seed reserves is possible,
but highly erratic. Farmers therefore prefer to reestablish
fallows from bare-rooted seedlings.
The residual effects of sesbania fallows on subsequent
maize yields have been shown to be high for
two or three seasons, but they will start to decline
rapidly in the third season (Table 1). This may be
related to depletion of soil nutrients and deterioration
in soil chemical and physical properties. It can
be hypothesized that fallows with coppicing species
will increase residual effects beyond 2 to 3 years,
because of the additional organic inputs derived
each year from coppice regrowth. Coppicing species
include Gliricidia sepium, Leucaena leucocephala,
Calliandra calothyrsus, Senna siamea and Flemingia
macrophylla. An experiment was established in the
early 1990's at Msekera Research Station to test this
hypothesis. The species tested were Senna siamea,
Gliricidia sepium, Leucaena leucocephla and Flemingia
macrophylla, which were compared with grass fallows,
and continuous maize with or without recommended
fertilizer as additional controls. The experiment
has been cropped for 8 seasons during
which maize and coppice growth were monitored
(Figure 1).
The species showed significant differences in coppicing
ability and biomass production (Table 2).
Leucaena, gliricidia and Senna siamea had the highest
coppicing ability and biomass production while calliandra
and flemingia performed less. Sesbania, as
expected, did not coppice. The trends in maize
yields over the 8 seasons are shown in Figure 1.
Maize yields were high for the first 3 seasons and
declined to the same level as control plots for sesbania.
Flemingia and calliandra showed low maize
8.0
7.0
~ 5.0
~ 4.0
.'"
.lij 3.0
i3
2.0
""""-Gliricidia ~L eucaena ~M+F
-+- M·F ....- Sesbania --lIE- Nalural fallow
6.0
I I I I I I I I
I = SED
1.0
0.0
1995 1996 1997 1998 1999 2000 2001 2002
Years/seasons
Figure 1. Grain yield (t ha l) of maize obtained from various
fallow species for eight seasons at Msekera, eastern Zambia
yields over years. There were no significant differences
in maize grain between gliricidia and leucaena
fallows over the seasons.
The effects of different fallow species on maize yield
can be explained partly by the different amounts of
biomass added and the quality of the biomass and
coppice regrowth during the dry season. Species
such as leucaena and gliricidia have good coppicing
ability and produce large amounts of high quality
biomass, with high nitrogen content and low contents
of lignin and polyphenols. Biomass with low
lignin and polyphenols and high N release N rapidly,
resulting in higher maize yields. Although sesbania
produces high quality biomass, it's inability to
coppice renders it unable to supply biomass during
the cropping period leading to less prolonged residual
effects. Species such as flemingia, calliandra and
Senna siamea produce low-quality biomass, which is
high in lignin, polyphenols and low in nitrogen.
This will lead to N immobilization and reduced
maize yields.
We hypothesized that the coppicing of gliricidia can
utilize the residual soil water after maize harvest
and recover soil nitrogen below the maize rooting
depth during the long dry season from April to October.
We monitored the soil water and nitrogen
dynamics in. all treatments for two seasons, 1997 to
1998, to test this hypothesis. This information will
be used to simulate the long-term trend of maize
yield, water and nitrogen dynamics using the
WaNuLCAS model. Theoretical simulations indicated
that gliricidia coppicing could utilize enough
residual soil water in an average rainfall year of 980
mm/year to produce 2-4 t/ha of tree biomass and
increased maize yield.
At the end of the dry season, soil moisture profiles
confirmed that the coppicing gliricidia treatment
utilized about 40 mm more water, primarily from
below 75 cm soil depth, than in either the sesbania or
continuous cropping treatments. This is probably
an under estimation of the total deep uptake of residual
water by the coppicing gliricidia since soil wa-
Table 2. Total seasonal coppice biomass (t ha I) recorded from
various fallow species at Msekera, eastern Zambia during 1995·
2002
1996 1997 1998 1999 2000" 2001 2002
C. calothyrsus 0.3 0.4 0.2 0.4 0.6 0.4 0.6
S.siamea 2.8 2.1 1.6 1.7 1.8 1.2 2.2
F. mycrophylla 0.6 0.6 0.3 0.6 0.7 0.4 0.5
G. sepium" 1.7 1.5 1.3 1.1 3.1 1.4 1.2
L. leucocephalla" 3.5 2.6 1.7 2.8 3.4 2.2 1.9
"Ieucaena has more twig biomass added to the system than Gliricidia which also
has low survival
"" Biomass cut in 2 months interval INov. Jan & Mar) normal- Nov. Dec & Jan)
Grain legumes and Green Manures for Soil Fertility in Southern Africa
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