RA 00048.pdf - OAR@ICRISAT

systems observable may seem confusing; the
variety, however, represents a logical response to
environmental diversity. It is within this framework
that one should examine the merits and
weaknesses of local sorghums, and into which
new varieties and technologies need to be fitted.
Given the uncertain rainfall, and low soil waterholding
capacity, one can seriously question
whether crop improvement programs based primarily
on the same high-yielding variety (HYV) and
input package strategies as used in the Indian
environment can be equally effective in West
Africa. Most HYVs require a high plant density in a
pure stand to realize yield potential. This in turn
requires a rather dependable soil moisture supply
and high soil fertility.
Jha (1980) in a study of fertilizer use patterns in
India arrived at conclusions on the use of improved
varieties that have direct relevance to the
West African situation. Fertilizer use was found to
be largely explained by the size and certainty of
returns that in turn were closely correlated with
rainfall and irrigation density. This fertilizer use
was greater in the irrigated and high rainfall
districts and HYVs were also most common in
these same areas. He concluded that, in SAT
areas with high and more dependable rainfall or on
soil with good moisture holding capacity, farmers
will more readily adopt fertilizers and HWs than in
areas with poor soils. Unfortunately poor soils and
Table 3.
Available water-holding capacity in toils dominated by low (kaolinitic) and high (montmorillionitic)
activity clays (after Moormann and van Wambeke 1978.)
Low-activity clays
(CEC < 2 4 meq/100 g clay)
Av. CEC
Av. AWC a
(meq/100 g)
14.6 ± 3.6 16.5 ± 6
High-activity clays
(CEC > 2 4 meq/100 g clay)
Av. CEC
Av. AWC a
(meq/100 g)
62.8 ± 13.5 38.7 ± 19.4
a. Available waterholding capacity (0.3 minus 15 bar water) expressed in percent per 100 g clay.
Table 4.
Relationships between rainfall zone, soil types, and prevailing cereal cropping systems in use in
various areas of West Africa.
Rainfall zone
(mm/year)
Area
Start of
rains
End of
rains
Soil type
Cropping
system
Harvest
period
900-1000 North Ghana Apr/May Oct/Nov Coarse
(upland)
Coarse
(low land)
Early millet
+ late millet
Early millet
+ late sorghum
July
Nov
July
Nov
900-1000 South Upper Volta Apr/May Oct/Nov Sandy loam Red sorghum
+ late millet
900-1000 South Mali Apr/May Oct/Nov Sandy loam Maize
+ late sorghum
Maize
+ late sorghum
Aug/Sept
Nov/Dec
Aug/Sept
Dec
Aug/Sept
Nov
6 0 0 - 7 0 0 Central Upper
Volta and
Mali
June
-
Sept
-
Loamy sand
(upland)
Sandy loam
(lowland)
Late millet
+ cowpea
Late sorghum
+ cowpea
Oct
Oct
Oct
Oct
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