The productivity of the mixtures:
Intercropping resulted in yield advantages in both
cropping seasons; the total land equivalent ratio
(LER) was between 1.76 and 2.17 (2004/2005) and
between 2.04 and 2.24 (2005/2006) thus showing
higher productivity of between 26% and 117%
(2004/2005) and 104% and 124% (2005/2006) due
to intercropping (Table 6). In 2004/2005 and
2005/2006 cropping seasons, these yield
advantages were highest with intercropping at
80,000 cowpea plants ha
-1
(117% and 224%,
respectively). The partial LER of the component
crops showed that cassava always contributed more
to the total yield than cowpea, except in 2004/2005
cropping season when intercropping with 40,000
cowpea plants ha
-1
had more partial LER ( 0.89)
than cassava (0.87). The higher partial LER of
cassava, at almost all cowpea densities indicated
that cassava was more competitive than cowpea
and that cassava utilized the N fixed by cowpea for
better growth and yield.
For each cowpea planting density in
2004/2005 and 2005/2006 cropping seasons, the
partial monetary returns were always higher in sole
than in intercropping (Table 7). In cassava,
monetary return was higher with sole crop in
2004/2005 whereas in 2005/2006, monetary returns
were higher in intercropped than in sole cassava.
Among the intercropped cassava, monetary return
was highest with cassava intercropped with the
highest cowpea planting density. The total
monetary return was highest when cassava was
intercropped with the highest cowpea density
(80,000 plants ha
-1
) in both seasons indicating
highest income to the farmer at that intercropping
system. The high total monetary return in
intercropping was contributed considerably by the
cassava component as depicted by its higher partial
monetary returns and land equivalent ratio due
mainly to its higher output than cowpea. Ogbuehi
and Orzolek (1987) had reported that intercropping
where land is scarce would always generate a
higher gross monetary return per unit area of land
compared to sole cropping but Ifenkwe and
Odurukwe (1990) and Kumar and Yusuf (1991)
observed that the highest LER would not always
reflect the highest monetary return to the farmer.
The work reported here did not take into
account additional yield of cowpea hay, an
important product in a ruminant livestock based
farming system where it is even as important as
grain yield. Inclusion of this might raise both LER
and gross return and thus further improve the
productivity of the cropping system. Based on both
the LER and gross monetary returns of the system,
cassava/cowpea intercropping, at 80,000 cowpea
plant ha
-1
seemed to be the most productive with
the highest income to the farmer, and is
recommended over sole cropping system. The
cassava crop benefits from the residual nitrogen
fixed by the cowpea. The two crops are compatible
as their growth stages for competition for growth
factors do not overlap.