Maize (Zea mays)

Subordinate taxa:

Zea mays L. subsp. Mays

Family/tribe

Family: Poaceae (alt. Gramineae)

Sub-family: Panicoideae

Tribe: Andropogoneae

Common names

Corn, dent corn, field corn, flint corn, maize, pod corn, popcorn, sweet corn, mais (French)

,jagung (Malay, Indonesian), to-morokoshi (Japanese), milho (Potruguese), maiz (Spanish)

Morphological description

An erect fast growing short lived growing to 7 m, but more commonly to 2-3 m in height, usually with a single main culm and culm and one or occasionally 2 lateral branches in the leaf axils in the upper part of plant. Internodes cylindrical in the upper part, alternately grooved on the lower part with a bud in the groove. Leaves alternate with broad, sword-shaped leaf blades, parallel veins with a prominent mid-rib, and small ligules. Upper surface hairy, lower surface hairless. The main culm produces at least 8 leaves, with temperate hybrids producing an average of 15 leaves and tropical hybrids producing 48 leaves. Convectional roots are supplemented with aerial brace roots, which protect against lodging. Flowers monoecious, born in separate parts of plant. Female flowers (ears) arise axillary bud apices. Male flowers (tassels) arise from the apical stem. Ears consist of a robust rachis (cob), with 4-30 rows of almost sessile spikelet bearing the caryopses (kernels). Kernels are highly variable, producing a range of commercial types including dent, flint, flour, waxy, pop and sweet corn.

Distribution

Native to: The region of origin is presumed to be the western Sierra Madre in Mexico (Michoacán and Jalisco). Domestication is thought to have occurred 7000-12000 years ago. Early forms were very small, with very small kernels. It is possible that very early domestication facilitated the co-evolution of corn in Peru. Substantial genetic manipulation occurred in the 20^th century, predominantly through inbreeding lines for hybrid seed production.

Uses/applications

As forage, corn is normally or made into silage before being fed to animals, however it can also be directly gazed or conserved as hay. Makes excellent silage due to its high yield and no requirement for additives to assist the ensiling process. Stover from corn grown for grain (dry leaves and stems) is a major source of feed for ruminants. In regions of south-east Asia, older leaves are stripped from the plants while they grow and are fed to ruminants.

Pest and diseases

Susceptible to many diseases, including maize smut (Ustilago maydis), head smut (Sphacelotheca reiliana),  and various stalk and ear rots such as Gibblerella and Diplodia. Plant breeding programs have strongly focused on diseases resistance with considerable success.

Attacked by a wide variety of insect pests including chinch bug (Blissus leucopterus) in United States, and corn ear worm (Heliothis armigera) in Australia. Pesticides are commonly used to achieve control.

Nutritive value

Maize silage is high in metabolisable energy (9-12 MJ/Kg DM) but relatively low in crude protein(7-8%). Digestibility of silage can be increased by the addition of urea or molasses. Urea also increases the crude protein concentration as does intercropping with a compatible legume, whilst molasses improves the water-soluble carbohydrate concentration.

Stover contains 3.5-4% crude protein and requires an additional crude protein source to achieve moderate levels of animal production. Crude protein concentration can be increased to 8-10% through urea treatment or to 10-14% by addition of high quality legume forage, however low digestible energy concentration may also limit growth.

Palatability/acceptability

Highly palatable to ruminants as a green feed, silage or a hay. Silage is palatable without the use of additives.

Toxicity

Lactic acidosis can occur if moderate to large quantities of grain, such as corn, are fed to ruminants not yet adapted to grain diets. Acidosis results from the rapid fermentation of highly digestible carbohydrates, resulting in a dramatic increase in production of lactic acid and lowering of rumen pH. Mild cases cause dehydration and loss od appetite, whereas serious cases results in acidification of the blood causing heart failure, kidney failure and death. Livestock should be gradually introduced to high grain diets over a periods of 3 weeks to prevent risk of acidosis.

Dry matter

As forage, maize is capable of producing 15-25 tones of DM with 10-12MJ/Kg DM of metabolisable energy within a four to five month period if correctly managed. Yield is directly related to days to maturity, so that long duration cultivar (120 days) have a greats yield potential than short duration cultivars (80-90 days), assuming adequate soil moisture over the growing season. Maize grown in the tropics generally produces a larger number of leaves and is generally leafier then temperate grown maize.

Animal production

Animal production for maize silage depends on the quality and amount of the silage fed. At 50% of total DM intake, cattle growth rates of 0.6-1.0kg/head/day can be expected. Additional digestible protein will further increase live weight gains.

Genetics/breeding

Cultivated corns and the wild members of diploid and tetraploid Zea can be crossed to produce fertile F1 hybrids. In the wild, introgressive hybridization doesn?t occur because of difference in flowering time, geographical separation, block inheritance, developmental morphology and timing of the reproductive structures, dissemination, and democracy. Most of today?s high yielding fodder cultivars are hybrid or double-hybrid strains because maize shows especially high heterosis effects. Less than 5% of the genetic diversity within Zea is currently utilized in commercial cultivars. 2n= 20, 21, 22, 24. ?Leafy? and ?stay green? genes are useful for forage types.

Seed production

Primarily developed as a grain crop, grain yields of 8-10t/ha are commonly achieved from hybrids growing under ideal conditions, but yields of 1-5t/ha are more common under dry land conditions in the tropic and subtropic (world average 3.6t/ha). Hybrid cultivars are most commonly grown today and hybrid seed crops require significant isolation distance to avoid pollen contamination. For the reason hybrid seed crops are not normally produced on small holder farms, although cooperation among villagers has enabled hybrid seed to be produced in certain regions of China. Dry weather at teaseling can severely affect pollination and grain yields.

Herbicide effect

Arzaine or simazine at 1.5-2.5kg/ha can be used for pre-emergent weed control. 2.4D amine at 0.45-0.55kg/ha is used post-emergence on crops at least 25cm high for control of broad-leafed weeds.

Strengths

Produces high DM yields over short season; high metabolisable energy concentration; excellent for silage production.

Limitations

High soil moisture and fertility requirement; poor acid-soil tolerance; must be replanted annually.

Other comments

Crops are generally green chopped and fed to stock or the material is cut and ensiled. Maize silage is generally made from the entire plant, which comprises highly digestible components (kernels, pith) and less digestible components (rind, tassel, midrib, stem fiber). Breeders are aiming to increase the percentage of highly digestible components in forage maize.

Cultivars

A wide variety of cultivars are available around the world and local expertise should be sought to ascertain the appropriate cultivars for the specific location. Dent maize (Zea mays var. indentata) is the main variety grown commercially for grain and fodder. Commercial dent maize cultivars are single, or double cross hybrids bred for special areas, soils and climatic conditions. Modern forage cultivars cntain ?stay green? and ?leafy? genes which prolong the vegetative growth, delay tassel and ear initiation and increase leaf number. Short-season varieties have been developed to produce a crop with only 300 mm of rain.