storing, transporting, and distribut-
ing a bulky input whose chemical
composition can be affected by ex-
posure to the elements. Conse-
quently, even when fertilizer is
available to farmers on time, its
potency often has been lowered by
improper handling.

Of course, applying chemical
fertilizer is only one strategy for
maintaining soil fertility. Other
technologies being investigated
include crop rotation, crop residue
management, use of live mulches,
planting of cover crops, and agro-
forestry techniques such as alley
cropping, in which woody legumi-
nous species are grown in hedge-
rows with food crops in between.
Research on experiment stations
has demonstrated the effectiveness
of these technologies in maintain-
ing soil fertility, but further on-
farm testing is required to deter-
mine whether or not they are
economically viable from the
farmer's point of view.

In some areas, large-scale commer-
cial farmers have begun to experi-
ment with zero-tillage techniques
(which use herbicides to replace
cultivation) to manage soil fertility.
Although early results are promis-
ing, it is important to keep in mind
that herbicides are complex to
manage; thus, zero-tillage can
succeed only where the supply of
inputs is dependable, site-specific
adaptive research is possible, and
support from extension is available
(Carr 1989).

Generally speaking, the adoption of
improved soil management tech-
nologies has been limited in Africa.
The abundance of arable land has
meant that pressure to adopt inten-
sifying technologies-including soil
management practices and chemi-
cal fertilizers-has not been as
great in Africa as in other parts of
the world. However, the situation is


changing rapidly. As population
has grown and land use has inten-
sified, soil fertility levels have
declined drastically in many maize-
growing areas, to the point where
inadequate soil fertility now poses
the single most important con-
straint to maize production.

The importance of pressing ahead
with research on soil management
technologies that offer an alterna-
tive to continuous use of chemical
fertilizer is highlighted by recent
evidence showing that fertilizer
alone may be insufficient in the
long run. Results of long-term IITA
fertilizer trials in alfisols (a major
soil type for maize production)
indicate that continuous application
of nitrogenous fertilizer can lead to
declines in soil pH, organic matter,
and nutrient status. Adding large
quantities of organic material can
alleviate some of these problems
(Kang and Balasubramanian 1990).
Clearly, an integrated approach to
soil fertility management that
combines biological nutrient
sources with inorganic fertilizer
will be needed to maintain sustain-
able production.

Limited Use of
Improved Germplasm
Improved maize germplasm has not
yet been developed for all African
agroecologies, but improved materi-
als are available for most of the
major lowland and subtropical pro-
duction environments. The superi-
ority of these materials has been
confirmed under a variety of
production conditions. In experi-
ment station trials involving high
levels of management, improved
materials yield substantially better
than local checks (CIMMYT 1989).
Under farmers' conditions, im-
proved materials usually retain
some yield advantage, even in
marginal zones. For example,
Rohrbach (1988) reports that in
Zimbabwe the hybrid R200 yields


30% more than local varieties
without fertilizer, and that the
yield advantage is even greater
under drought stress. Similarly, a
decade of on-farm experimentation
by the Ghana Grains Development
Project affirms that certain im-
proved maize varieties regularly
yield better under varied agrocli-
matic conditions and management
levels.

Given the superior performance of
many improved materials, it is
reasonable to assume that African
farmers would grow them if they
could. As noted earlier, seed of
improved varieties simply may not
be available to farmers. Most maize
seed in Africa is produced and
distributed by the public sector;
private sector involvement is rare,
because private seed companies
make most of their money on
hybrids, and use of hybrids is still
minimal in most areas. A high
degree of specialization and
considerable expertise are required
to produce maize seed (CIMMYT
1987). Constrained by insufficient
resources and inadequately trained
personnel, public sector seed com-
panies in Africa have not always
demonstrated the ability to produce
and distribute adequate supplies of
high quality maize seed.

This idea-that low use of im-
proved germplasm often can be
attributed to poor availability of
seed-is reinforced by the experi-
ences of Kenya and Zimbabwe. In
each of these countries, strong
demand from the commercial
farming sector for improved maize
materials led to the emergence of
an efficient private seed industry.
After building a solid base of sales
among commercial farmers, this in-
dustry extended its distribution
network into rural areas, making
improved materials readily avail-
able to smallholders lacking the
means to travel long distances to