Maize is also known as ‘Indian corn’ or simply ‘corn’. It is perhaps the most completely domesticated of all arable crops. It is widely grown because it is able to adapt to different ecological conditions.
In some parts of Africa, especially, Nigeria, it constitutes the basic food of most states where sorghum and millet have hitherto formed the main cereal crops.
Maize originated in the new world, around Mexico or central America. There is no reliable evidence that it reached the old world prior to 1492. At the time of the discovery of the New World in 1492, maize had spread widely throughout the Americas, except in areas which were too cold for it.
Maize played an important role in the conquest of the Americas and became one of the main stepping stones to abundant evidence that the Portuguese introduced maize into West Africa.
Maize is adapted to a very wide range of environments and it is more extensively distributed over the earth than any other cereal crop. It is essentially a crop of warm countries with adequate moisture.
The bulk of the crop is grown in the warmer parts of the temperate regions and in the humid subtropics and tropics. It is not suited to semi-arid climates, nor to the ever wet tropical evergreen rain forests.
It is grown across a wide range of latitudes and from sea level to over 3000m in the Andes and Mexico. It is mostly grown in regions with a temperature range of 21-30°C. It does well in sandy loam soils, rich in nutrients, especially nitrogen.
The time of flowering is influenced by photoperiod and temperature. It is considered a short-day plant , that is, flowering is hastened and vegetative growth retarded by long nights.
Long days increase the leaf number, plant size and length of the growing period. The varieties that succeed best in any region are those fitted to the particular length of day.
Maize is a stout annual grass and like most plants in the grass family, the roots are adventitious and arise from the lowest nodes of the stem below ground level.
Prop, brace, buttress or aerial roots arise from nodes above the ground and help to support the plant. They are thick, partially photosynthetic and often deeply pigmented. On entering the soil, they branch and behave like ordinary roots.
Maize usually has a single stem and unlike most grasses, the stalk (culm) is solid. The height varies from about 1/5m in short varieties to over 3m in all varieties.
The leaves are sessile and are made up of a leaf blade, sheath and collar-like ligule. The number of leaves varies from 10 to 18 depending in varieties.
The maize plant is monoecious with male and female inflorescences borne in separate positions on the same plant. The male or staminate inflorescence is a panicle called ‘tassel’ which terminates the main axis.
Main axis carries the paired spikelets in several rows while the lateral branches carry two rows of paired spikelets. The pair of spikelets consists of one sessile and one pedicelled, but the structure of both is the same, viz. they both contain two main flowers enclosed by two similar glumes, longer than the spikelets and affording almost complete protection for it.
Each flower is composed of oval, concave lemma enclosing a membranous palea with the three stamens and two lodicules between them.
The filament of the stamens elongate rapidly at maturity, exposing the colored anthers, often purple, pink, yellow or green.
The female inflorescence is known as the ‘ear’ and is carried in the axil of the maize leaf just below the middle part of the plant. It consists of a modified lateral branch deriving from an axillary bud of the main stem.
The internodes of the lateral branch are compressed and the leaves are reduced or modified to structures, which overlap each other closely, forming the husk.
The husk gives complete protection to the flowers and developing seeds. The ear is subtended by the ear leaf which is the most physiologically reliable leaf for growth measurements, e.g. nutrient composition, area of leaf, etc (Rem,1997)
The female inflorescence itself is made up of pairs of spikelets, but both members of a pair are sessile on the thickened axis. Each spikelet is made up to flowers, the lower of which is reduced to a lemma and palea and is not functional, while the upper flower contains the knob-shaped ovary surrounded by the short, broad, membranous lemma and palea.
The ovary itself is surmounted by a long style, the silk, which grows rapidly and emerges from the top of the husk.
Maize is normally cross-pollinated; it is protandrous with pollen being shed before the silks are receptive but there is some overlap and up to 5% self pollination can occur.
The fertilized ovary develops into a caryopsis called ‘kernel’ or ‘grain’. The so called maize seed is really a fruit as the pericarp and testa, which are both thin are fused together to form a single membrane.
On one side of the grain, there is an oblong area of a lighter color. This is the embryo; the rest is the endosperm.
On the same side of the grain as the embryo, in the middle, near the broad end, is a projecting point, the remains of the stigma. This shows that the outer covering is the pericarp and that we are dealing with a fruit.
A normal maize ear contains 8 to 28 rows of grains and a row bears 20 to 70 grains. The color of the grains varies from white, yellow, red, purple to almost black.
There are seven types of maize- pod, flint, dent, flour, sweet and waxy. Most maize cultivars belong to the dent and flint groups; the dent cultivars are those with the greatest yield potential.
Some of the well known improved varieties in Nigeria are ‘TZ series’ developed at the International Institute for Tropical Agriculture (IITA) and the ‘FARZ series’ developed at the former Federal Department of Agricultural Research (FDAR) now National Cereals Research Institute. Examples are TZSR-W, TZSR-Y, TZESR-Y, TZESR-W, FARZ 27, FARZ 34 and several hybrids.
The seed rate is 25-35 kg/ha and the recommended spacing is 75x25cm, which will give a plant population of 53000 plants/ha . Cultivars, with upright leaf orientation can however be planted at higher plant populations.
In the south and forest areas of Nigeria, where the rainy season is long enough for two crops, planting is done in March/April for the first (early) crop and in August for the second (late) crop.
In the Northern Guinea, Sudan and Sahel Zones where only one crop is possible, planting is done as soon as the rains are established in June. Planting can be done on the flat with two seeds per stand which may be thinned to one seedling per stand after 2-3 weeks.
With regard to weed control, atrazine or atrazine based herbicides are recommended at the rate of 3kg a.I/ha. This should be applied pre-emergency, at planting or 1 or 2 days before or after planting.
In the absence of herbicide, two weeding at 3 and 7 weeks after planting should suffice.
Maize responds to fertilizer application, especially nitrogen. The recommended fertilizer is NPK (15-15-15) at the rate of 300kg/ha, preferably applied at 2-3 weeks after planting.
Nitrogen can also be applied as ammonium nitrate at the rate of 100kg N/ha. Phosphorus can be applied as single or triple super phosphate at the rate of 50kg P2O5/ha and potassium as potassium chloride or sulphate at the rate of 50kg K2O/ha.
The period from planting to harvesting varies considerably; it may as short as 90 days in very early varieties and as long as 120 or more days in late maturing varieties.
Maturity can be recognized by yellowing of the leaves, yellow dry husks and hard grain with a glossy surface.
Maize is usually physiologically mature about 6-8 weeks after flowering, when the grain contains 35-40% moisture and has a maximum dry weight.
A green harvest can be done when the crop is physiologically mature. The ears can be left on the stalk to dry to a moisture content if 15-25%. A dry harvest can then be taken by dehusking or with the husks still attached.
Maize can also be harvested for silage when the grains have hardened and the lower leaves at this stage. Harvesting can be done mechanically or by hand.
The yields from farmers’ plots are low, about 200-2000kg/ha of dry grains. Yields of up to 5000kg (5ft)/ha or more of grain are possible using improved practices.
To reduce or prevent insect damage and disease infection during storage, the grains should be properly dried to a moisture content of 12-15% by sun drying or artificially.
Drying in the sun is the cheapest and commonest method in most developing countries. This can be done both before and after harvest.
Storage of ears with the husks still attached can be done by typing part of the husks together and hanging them on poles outdoors. Local farmers also hang ears under the edges of house roofs preferably near a fire place.
Storage of maize is also done in cribs, which can be made from wooden slats, or wire mesh, which permit free access and circulation of air. Simple granaries can also be used. These are usually circular and raised off the ground; they may be made of basket work or a frame work plastered with mud.
Bulk storage is done in silos which are often made of bricks, concrete blocks or aluminium. Grains in storage may be dusted or fumigated with chemicals against insect attack. Gamma- BHC, malathion and phostoxin are used for this purpose.
Maize grain contains 76-88% carbohydrate, 6-15% protein, 4-5.7 fat and 1.3% minerals.
Uses of maize can be grouped into three- staple human food, feed for livestock and industrial raw materials.
I. As a staple human food
Maize is a stable food particularly in the tropics. It is eaten as boiled or roasted maize( maize on the cob). C
Corn meal, grits and cornflakes are examples of food products made for human consumption. Maize is however unsuitable for bread making as it is deficient in Gluten.
2. As feed for livestock.
It is used for livestock feed especially in temperate and developed countries. It is the cheapest and most palatable carbonaceous feed for animals such as pigs, cattle, sheep and poultry.
Most of the maize crop is fed to livestock as grain, silage or fodder on the farms where it is produced. The grain is relatively high in fat and starch but is low in proteins. It is therefore essential to feed it together with protein feeds to provide a balanced diet.
3. As industrial raw material
Corn starch, corn oil, corn syrup and corn sugar are the chief industrial products obtained from maize.
- Corn starch, is a universal food stuff. It is used for starching clothes, in the manufacture of asbestos, ceramics, dyes, plastics, oil cloths and linoleum.
- Corn oil us used in the manufacture of soaps, vanishes, paints and other similar products.
- Corn syrup is used in shoe Polish and in the tobacco industry. Corn sugar is also used in the manufacture of jams and jellies, chemicals, dyes and explosives.
- Other minor uses include the use of stalks and leaves for making paper, paper board and wall-board.