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

of inorganic fertilizer and the crops, the green manure
legumes appeared to respond better than
maize to the increasing rate of inorganic fertilizer
(Table 6). The differences in response to inorganic
fertilizer application among the crop species are
graphed in Figure 3.
Biomass production in the first year (199912000 season).
The four crops produced different amounts of
biomass across the twe sites (P= 0.001). Mucuna pruriens
had the highest biomass followed by Tephrosia
vogelii, Zea mays and Cajanus cajan (Table 7). In general,
all legumes except pigeonpea outperformed
maize. The difference in dry matter production between
maize, mucuna and tephrosia was not significant.
Pigeonpea had lowest dry matter, probably
due to poor crop establishment.
With nitrogen being a limiting plant nutrient in
most Malawian soils (Kumwenda and Gilbert,
1998), green manure legume crops are likely to outperform
cereals in their dry matter production. Ad-
Table 6. The effect of rate of inorganic fertilizer on N
accumulated (kg ha I dry matter) in different crop species at
harvest
Crop spedes
Rates of inorganic fertilizer (kg hal)
Nil S 20 kg P20S 40 kg
+ 4 S P20S + 8 S
Zeamays 40.8 53.4 54.3
Mucuna pruriens 124.8 162.0 169.9
Cajanus cajan 50.3 70.8 96.0
Tephrosia vogelii 105.2 172.9 190.2
~..
250 T---r=======c=~==============~~~
200
~ 150
~
c
~ 100
o
~
Z
50
o
maize mucuna pigeon pea tephrosia
Crops species
Figure 3. Nitrogen (k hat) accumulated by crop species as affected
by rate of inorganic fertilizer
Table 7. Dry matter production (kg hat) of crops at harvest in
the first growing Season (1999·2000)
Crop Species Champhira Nchenachena Mean
Maize 4204 ' 5741 b 4972 '
Mucuna pruriens 4352 ' 6407 b 5380 '
Pigeonpea 1906 b 3432 ' 2669 b
Tephrosia vogelii 3497 • 7020,b 5258. '
SED ± 576.6
CV % 20.0
Key: SED ±. Standard error of difference; CV. Coefficient of variation;
NB: Means followed by same letters are not statistically different
ditionally, some legumes explore a deeper volume
of soil owing to the~r tap root system and therefore
can extract nutrients that may have been leached to
lower soil depths. Mucuna pruriens produces a
dense vegetative cover, mainly leafy biomass, that
include a mass of creeping stems, during its vegetative
growth stages. Kumwenda and Gilbert, (1998)
found similar results.' Mucuna pruriens had the
greatest mean biomass and a greater response to the
added phosphorus than Cajanus cajan and Tephrosia
vogelii. The other green manure legumes crops, pigeonpea
and Tephrosia vogelii, have a slower early
growth rate and tend to lose much of their leafy biomass
by the time they attain physiological maturity
(Giller and Cadish, 1995; Sakala, 1994).
Application of inorganic fertilizer increased biomass
production. There were significant differences (P =
0.001) in ciomass production among the crops due
to inorganic fertilizer. The higher-rate of inorganic
fertilizer applied had the highest mean dry matter
produced followed by the second rate and the treatment
without any inorganic fertilizer gave the lowest
dry matter yield (Table 8). This positive response
to inorganic fertilizer application is indicative of the
need to supplement the green manure crops with.
external nutrients and that the soils need nutrients.
Maize had the best response to the inorganic fertilizer
applied, giving a difference of 2764 kg ha·J between
the treatment without inorganic fertilizer and
the treatment with 20 kg PzOs + 4 kg S of inorganic
fertilizer. This was followed by Tephrosia vogelii,
(2050 kg ha·1), Mucuna pruriens (1069 kg ha·1) and
pigeonpea (1005 kg ha·l ). The difference in biomass
produced between treatments that received 20 kg
PzOs + 4 kg S and those that received 40 kg PzOs + 8
kg S was generally lower. The apparently smaller
response to inorganic fertilizer application by green
manure legume crops compared with maize is because
legumes are relatively independent of external
nutrient supply, particularly nitrogen, and
hence require relatively smaller doses.
Second Season Results
The type of preceding crop significantly (P < 0.01)
influenced maize stover nitrogen content at harvest.
Maize grown after Mucuna pruriens had the highest
Table 8. The effect of rate of fertilizer on biomass production (kg
ha·t)
across the sites
Rate of fertilizer (kg hat) Champhira Nchenachena Mean (kg hal)
No fertilizer 2357 4133 3245'
20 kg pzDs + 4 kg S 3908 6013 4961 b
40 kg P20S + 8 kg S 4204 6803 5503 b
SED ± 306.2
CV % 21.2
Key: SEO:t. Standard error of difference; CV. Coefficient of variation; NB: Means
followed by same letters are not statistically different.
Grain legumes and Green Manures for Soil Fertility in Southern Africa
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