compensating for different plant populations, which can vary from between about
15,000 and 90,000 plants per hectare. In general the plant population should be
higher in good growing conditions, but if there are too many plants they may lodge
(bend and fall over), leading to lower yields, more harvesting problems and damage
by termites, fungi, pests, etc. Plant Population is also discussed on page 4.
The seed company that supplies the seed should be able to advise on the
appropriate spacings for their varieties in different growing conditions.
Two or more seeds are often planted per hole, or station, but it is very important
that only the strongest plant is allowed to grow per hole. There are about 13–40,000
seeds per kg.
Depth: 3–5 cm in moist soil, 5–10 cm in drier soil. There are certain varieties that
have been bred especially for growing in dry, sandy soils and which are sown very
deep.
Intercropping: very common. Legumes are the obvious choice, and this was done
thousands of years ago, in South America for example where maize is still
traditionally grown with beans.
Rotation: maize is often cropped continuously, but this is only acceptable when
large amounts of fertiliser and high level management is practised. Nevertheless,
continuous cropping of maize has less negative effect on yield than continuous
cropping of many other crops.
GROWTH CONDITIONS
Day length: short-day. Long days increase the duration of the vegetative stage, the
plant size, and number of leaves.
Growth period: varies from about 50 to 365 and more ... Averages are 90–120
days at low altitudes, and 180–240 days at approximately 2500 m above sea level.
Temperature: even a light frost can kill maize plants, so it normally needs about
120 frost-free days. For germination, 18–21C is optimum—it is very slow below
13 C, and does not germinate below about 10 C. The ideal temperature at tasselling
is 21-30C.
Rainfall: in temperate or subtropical regions 450–600 mm during the growth period
is enough; in the tropics it needs 600–900 mm. A very dry spell just before or during
tasselling is bad news for the plant, reducing yields. Maize responds very well to
irrigation, if water is a limiting factor to plant growth. If only one irrigation is
possible it should be at silking or tasselling. In arid regions, fast growing varieties
such as Kalahari, Katumani or Kito can be grown.
Altitude: 0–3300 m (in Mexico and the Andes).
Pests: maize is attacked by more than 200 different insects, some of which are
described below. Plant breeders have recently made good progress in developing
varieties resistant to multiple species of insects.
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found mainly in higher altitudes. The adult moths lay eggs on leaves, between the
edges of the leaves and the stem; the larvae eat some of these leaves, leaving “shot-
holes or “windows” as the leaves open, then enter the stem and feed near the growing ”
Stem (Stalk) Borer— there are at least 4 spp.—Busseola fusca is an important one,