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

Results
Table 1. Adaptation of green manure and grain legume species to the moist and dry mid·altitude and tropical
lowland ecologies of Eastern Africa"
Legume adaptation in Legume species Establish· Nodula· Ground Diseases Seeding
ment
•
tion cov·er and pests capacity
.ECA ecologies
Table 1 summarizes re­ Calopogonium mucunoides 2 2 1
~
sults of regional legume Canavafia ensiformis 2
species evaluation trials Crotalaria ochroleuca 2
across five sites for 12 Dolichos lablab 7.6
species according to six Mucuna pruriens (black) 10.6
criteria using a 5-point Mucuna pruriens (white) 8.3
scale from very good Sesbania sesban
through fair to very Glycine max (Soybean-Nyala)
poor. Species consid- Glycine max (Soybean.SCs)
ered include green ma-
Vigna unguiculata (Cowpea)
nures and grain legumes.
Visually, the Vicia dyascarpa (=lana vetch)
most adapted green ma- Vicia vil/osa (=purple vetch)
nure species appeared to
be Mucuna pruriens, Ooli­
2
"Legend for evaluations
v.good ' good
••
does not include potential further biomass accumu­
cos lablab, Crotalaria
ochroleuca and Canavalia ensiformis although there
were regiona1 variations in adaptation. Grain legume
species tended to be less adapted than gre.en
manure species but this may be a reflection of the
evaluation criteria tha t favoured attribu tes for soil
fertility enhancement and sequenced maize production.
lation that may occur if they are allowed to continue
growing on residual moisture subsequent to the
maize harvest, the possibility of which depends on
the presence or absence of free-ranging cattle that
are often allowed to graze crop residues in these
systems.
­
The potential contribution of green manure and Effects of legumes in rotations on maize producgrain
legume species to soil N status is shown in tion
Table 2, based on the mean biomass production The effects of green manures grown in rotations
across one or more sites in the region and thei;
measured or estimated N contents.
Table 2. Biomass production and estimated nitrogen content of green manure and
Green manures were grown as sole
grain legume residues at ECAMAW regional screening sites (1998-99)
crops and sampled at the end of the sea­
No. of
Mean N
son at a· growth stage considered appro­ Legume species Common name Biomass yield
sites
content§
priate for incorporation into the soil. min max mean
With few exceptions, the mean levels of -- _.. (I-OM/ha) · -- - - (kg-N/ha)
N provided by green manures were well Calopogonium mucunoides Calopo 3 1.4 4.2 3.U 61
in excess of a maize crop's requirements. Canavalia ensiformis Jackbean 5 2_9 18.2 12.5 316
Grain legumes such as cowpea and Crotalaria brevidens Sunhemp 3.4 3.4 3.4 85"
groundnut left suboptimal amounts of Crotalaria ochroleuca 4 2.0 15.0 8.1 267
N for a subsequent maize crop.
lablab purpureus Oolicos lablab 5 2_1 16.6 7_6 131
Macroptylium atropurpureum Siratro 2.0 2.0 2.0 50"
Mucurla pruriens (black) Velvet bean 5 2.5 20.7 10.6 289
Shading and competition for water and
Mucuna pruriens (white) Velvet bean 2 4.5 12.0 8.3 208"
nutrients reduces the growth of green
Pueraria phaseoloides Tropical kudzu 2.1 2.1 2.1 33"
manures sown as intercrops with maize,
Sesbania sesban Sesban 12.3 12.3 12.3 308"
and hence reduces the amount of N Vicia dasycarpa Lana vetch 2 0.5 3.0 1.8 45"
available for subsequent maize crops. Vicia vil/osa Purple vetch 2 0.6 5.0 2.8 70"
Figure 1 compares biomass production Cajanus cajan Pigeon pea 1 17.1 17.1 17.1 428"
of mucuna, canavalia and crotalaria Glycine max (Nyala) Soybean 3 0.5 4.7 3_3 83"
grown as sole crops, or intercropped Glycine max (SCs-l) Soybean 3 0.3 3.7 1.5 117
with maize 2-3 weeks after maize emer­ Phaseolus vulgaris Field bean 0.1 0.1 0.1 3"
.gence, or relay planted into maize at 2 Vigna radiata Green gram 1 2.0 2.0 2.0 50"
weeks after tasseling at Jimma, Ethiopia, Vigna unguiculata Cowpea 2 1.2 4.5 2.9 70
and Namulonge, Uganda. Legume bio­
Bambara
Voandleia subterranea 1.1 1.1 1.1 28"
groundnut
mass was measured at the time of har­
§ mean Ncontents calculated from measured N concentrations of biomass except those marked with
vesting the maize and, consequently,
*
·which are estimated Ncontents based on an average concentration of 2.5% N in the biomass.
Grain Legumes and Green Manures for Soil Fertility in Southern Africa 1/5