Cowpea and sorghum grain crops, fertilized with 26 kg of phosphorus
(P) per ha from either a
P-soluble (SP) or a slightly P-soluble fertilizer (Kodjari, a natural rock
phosphate (RP) indigenous to
Burkina Faso), and cowpea and crotalaria (Crotalaria retusa) green
manure crops, either unfertilized
or fertilized with 26 kg P/ha from RP; were studied for their effects
as preceding crop treatments for
maize. The experiment was conducted in semi-arid West Africa (SAWA) at
Farako-Bâ in Burkina
Faso in 1983–86. Nitrogen (N) and soluble P fertilized and unfertilized
subtreatments, applied to
maize the following year, allowed the effects of the preceding crop treatments
in improving soil
fertility and the direct effects of P and N fertilizers applied to the
maize crop to be assessed. Maize
productivity was increased both by P fertilization and by soil improvements
following cowpea and
crotalaria; N fertilization in excess of 60 kg N/ha was not beneficial.
Cowpea grain crop treatments,
especially when fertilized with a P-soluble source, maximized maize yields,
whereas cowpea and
crotalaria green manure treatments were either similar to the cowpea grain
treatment fertilized with
RP or were intermediate between the latter and the sorghum treatment fertilized
with SP. Sorghum,
regardless of the source of P-fertilizer used, appeared not to be a suitable
preceding crop for maize
in SAWA.