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Description
A coarse annual, culms 60-80 cm high, straight, internodes
cylindrical in the upper part, alternately grooved on the lower part with
a bud in the groove. The stem is filled with pith. Leaf-blades broad. Has
separate staminate (male) and pistillate (female) inflorescences. The staminate
inflorescence is a tassel borne at the apex, the pistillate flowers occur
as spikes (cobs) rising from axils of the lower leaves. The ovary develops
a long style or silk which extends from the cob and receives the pollen
from the tassel.
Distribution
Originated in Mexico or Central America, now pan- tropical;
also grown as a summer crop in temperate Europe.
Season of growth
Summer.
Altitude range
The period of flowering and to maturity varies greatly in East
Africa. Allan (1973) divides Kenya into four zones:
below 200 m. Lowland tropics with high maximum and minimum
temperatures. Quick-maturing varieties flower in two months and mature
in four.
200-1 200 m. Most of these areas have low rainfalls and
little maize is grown. In Australia most of the maize is grown from sea-level
to 500 m.
1 200-2 100 m. Contains over 90 percent of the maize grown
in Kenya. The highest yields are regularly obtained in this area. The Kitale
hybrids (prefixed by the number 6) flower in about three months and mature
in six at 1 500 m. At 1 800 m, flowering is at 3.5 months and maturity
at 7, while at 2 100 m, the figures are 4 and 8, respectively.
2 100-3 200 m. Little maize is grown above 2 000 m, as only
long-term varieties can survive in such high altitudes. At Ol Joro Orok
(2 400 m) the maize takes 6.5 months to flower and more than a year to
mature.
Rainfall requirements
An annual rainfall of more than 500 mm is needed, with best
yields usually in the 1 200-1 500 mm area; it is often an irrigated crop.
Kitale experiments show that the more rainfall after five weeks' growth,
the higher the yield.
Drought tolerance
It is fairly drought tolerant up to five weeks, but thereafter
is very susceptible. Dry weather at pollination time seriously affects
pollination and hence yields.
Soil requirements
It requires a well-drained, fertile soil. Alluvial loams, deep
latosols and clay loams are preferred.
Land preparation for establishment
A deep (20 cm) friable seed-bed should be prepared, as maize
is comparatively shallow rooted and needs loose soil in which the roots
can forage.
Sowing methods
It is usually drilled in rows for grain and fodder, though
it can be broadcast thickly for turning in as a green manure.
Sowing depth and cover
Sow at 7.5-10 cm depth and cover using a fined instrument,
then compact with a following press wheel.
Sowing time and rate
Late spring to midsummer, at row spacings of 105135 cm, using
9-11 kg seed per hectare with populations from 25 000 to 70 000 plants
per hectare.
Tolerance to herbicides
Pre-emergence treatment with atrazine or simazine at 1.5-2.5
kg/ha controls most weeds, while 2,4-D amine at 0.45-0.55 kg/ha used on
crops 25 cm high is a useful post-emergence weed-killer.
Dry-matter and green-matter
yields
Yields of 10-50 tonnes of green matter per hectare are obtained
for silage.
Suitability for hay and
silage
Maize is conserved as stover in the United States and southern
Africa, but the main use of the whole plant is as silage. It makes probably
the best silage of the grass family, with heavy yields and high acceptability
and without the need for additives. It is cut when the grain is full and
glazed, in the medium dough stage.
Value as a standover or
deferred feed
After the grain is harvested the residue usually contains 3.5-4.0
percent crude protein; in a drought year it can be as high as 9 percent.
The protein level usually does not decline as it stands in the field. Moisture
content at harvest is 40-50 percent in the United States, too low to make
silage. The digestibility is 40-50 percent at harvest, but falls to 3638
percent after 40-60 days in the field. In the United States, good practice
is to graze 25-35 percent immediately after harvest with one beast to 0.8-0.9
ha, and then harvest the rest for winter storage (Corah, 1979). In Kenya,
it is usually dried in the field for several weeks after maturity (Acland,
1971).
Seed yield
1-4 tonnes of grain per hectare, which should be stored at
14 percent moisture or less. Minimum germination and quality required for
commercial sale. 80 percent germinable seed and 98.6 percent purity in
Queensland.
Cultivars
Numerous cultivars are available throughout the world and contact
should be made with local extension officers to ascertain what is the current
preference to specific conditions. Most countries have bred their own cultivars
to suit their varying conditions.
Dent maize (Zea mays indentata) is the main variety grown commercially
for grain and fodder, but there are other types such as pod corn (Zea mays
tunicata), a curiosity; flour corn (Zea mays amylacea) for human consumption;
flint corn (Zea mays indurata), preferred for the European market, with
horny endosperm; sweet corn (Zea mays saccharata), used as a vegetable;
pop corn (Zea mays everta), used as a snack food. High-lysine corn has
been improved for human nutrition. Open pollinated varieties have been
used for a long time but now most of the commercial dent maize is either
a single cross or a double cross hybrid bred for special areas, soils and
climatic conditions.
Diseases
Maize is subject to many diseases, chief of which are maize
smut ( Ustilago maydis), head smut (Sphacelotheca reiliana), and various
stalk and ear rots such as Gibberella and Diplodia. They have been overcome
by chemical seed treatment or by breeding resistant varieties.
Optimum temperature for
growth
Peak germination was at 20-30°C and growth at 18-21°C
(Hughes, 1979).p
Minimum temperature for
growth
8.7°C for Kitale hybrids in Kenya.
Frost tolerance
It is very susceptible to frosts.
Latitudinal limits
It has a wide range, from 58°N in Canada to 40°S.i
Ability to compete with
weeds
It has poor competitive ability until the crop canopy has closed.
Pests
A variety of pests are encountered. Chinch bug (Blissus leucopterus)
is a major pest in the United States. The corn ear worm (Heliothis armigera)
is a problem in Australia.
Palatability
Excellent for all green matter.
Response to photoperiod
Some varieties are indifferent to day length, others require
short days for flowering (Evans, Wardlaw & Williams, 1964).
Tolerance to flooding
Maize has no tolerance to flooding.
Fertilizer requirements
The needs for maize are best determined by soil tests. It generally
requires a complete fertilizer, with heavy demands from about 40 days until
maturity. Zinc deficiency causes leaf chlorosis and can easily be overcome
by the use of zinc sulphate.
Compatibility with other
grasses and legumes
To improve the nutritive value of forage, legumes such as cowpea
can be planted between rows of maize. Lablab purpureus is used in Brazil.
Grass seed can be undersown in maize as a means of establishment.
Genetics and reproduction
2n=20, 21, 22, 24 (Fedorov, 1974).
Seed production and harvesting
Maize matures in 80-120 days according to variety, and is either
hand-picked and later threshed or is harvested with a combine.
Economics
Maize is a major human food grain in Africa and in eastern
Indonesia. Some 85 percent of the maize crop in the United States is fed
to livestock as grain and silage.
Further reading
Martin & Leonard, 1959.
Dormancy
There is little dormancy in maize seed.
Value for erosion control
As maize is usually a row crop and has a poorly developed root
system, crops are very susceptible to erosion.
Tolerance to salinity
Maize gave maximum yields at ECe of 2 mmhos/cm, 50 percent
at ECe 9 mmhos/cm and nil at 15.3 mmhos/cm (Maas & Hoffman, 1977).
Further studies showed that in water cultures, or on mineral soils with
surface irrigation and continuous leaching, the maximum salt concentration
in the soil saturation extract that does not reduce maize yields is about
1 100 mg/l total dissolved salts (ECe - 1.7 dS/m). The maximum permissible
salt concentration of irrigation water to sustain maize production is about
300 mg/l, an ECW of 0.45 dS/m (Hoffman et al., 1979).
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