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Zea mays L.

Poaceae
Corn, Maize, Mealie, Indian corn

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.


  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Description
  5. Germplasm
  6. Distribution
  7. Ecology
  8. Cultivation
  9. Harvesting
  10. Yields and Economics
  11. Energy
  12. Biotic Factors
  13. Chemical Analysis of Biomass Fuels
  14. References

Uses

Few plants are grown more extensively or put to more diversified use than corn. It is becoming increasingly important as fodder, extending into cool temperate regions where summers are not normally sufficiently warm to mature the grain crop. Corn is a staple cereal for human food in Central and South America, and many parts of Africa. In the US and Europe it is used almost entirely for animal feeding, as grain or fodder. Corn is used as vegetable, as corn-on-the-cob, fresh, canned or frozen. Kernels may be cut from the cob and used in many ways, in succotash, custards, fritters, soups and chowders. They are also used in mixed pickles and vegetable relishes. Corn meal, grits, and hominy are prepared forms of corn kernels. Corn is also converted into various substances which have a wide range Of usage, as starch, syrup, cornstarch, dextrin, corn oil, zein, and in the making of whiskey and other alcoholic products. These substances are used in the printing, confectionery, condensced milk, tanning leather, plastics, food, brewing, soap, paint, and textile industries. Corn has been used as currency (in Peru).

Folk Medicine

Decoctions, poultices, cataplasms and the flour of the seed are said to be folk remedies for tumors, warts, and corns. The tea made from the seed is said to be a cure for breast cancer. The silks are still sold, even in the US, as a diuretic. Considered alexeritic, alterative, analgesic, anodyne, antiseptic, astringent, cardiac, choleretic, cyanogenetic, demulcent, diuretic, litholytic, Stimulant, and stomachic, corn is a reputed folk remedy for such diverse ailments as amenorrhea, Bright's disease, corns, cystitis, diabetes, dropsy, dysentery, dysmenorrhea, gingivitis, gout, gravel, hepatitis, hypertension, inflammation, influenza, menorrhagia, metritis, nephritis, oliguria, pneumonia, prostatitis, renitis, rheumatism, stones, strangury, tumors, urogenital ailments, and warts (Duke and Wain, 1981).

Chemistry

Per 100 g, the green fruit is reported to contain 134 calories, 62.5 g H2O, 4.2 g protein, 1.7 g fat, 30.7 g total carbohydrate, 1.1 g fiber, 0.9 g ash, 5.0 mg Ca, 126.0 mg P, 0.9 mg Fe, 3.0 mg Na, 259 mg K, 160 mg b-carotene equivalent, 0.20 mg thiamine, 0.11 mg riboflavin, 1.5 mg niacin, and 8 mg ascorbic acid. The seedling, per 100 g, is reported to contain 319 calories, 20.6 g H2O, 7.4 g protein, 2.8 g fat, 68.3 g total carbohydrate, 2.9 g fiber, 0.9 g ash, 210 mg P, 2.9 mg Fe, 0.16 mg riboflavin, and 3.0 mg niacin. Per 100 g, the seed is reported to contain 96 calories, 72.7 g H2O, 3.5 g protein, 1.0 g fat, 22.1 g total carbohydrate, 0.7 g fiber, 0.7 g ash, 3.0 mg Ca, 111 mg P, 0.7 mg Fe, trace mg Na, 280 mg K, 240 mg b-carotene equivalent, 0.15 mg thiamine, 0.12 mg riboflavin, 1.70 mg niacin, and 12.0 mg ascorbic acid.

Description

Vigorous annual grass, varying greatly in size according to race and growth conditions; culms stout, often with prop roots from the lower nodes, many-noded, terminated by inflorescences of male spikelets (tassel), and with one or more female spikelets (ears) in the axils of leaves below the tassel; leafblades expanded, usually drooping, usually green, but may be variegated white, yellow or purple-red; tassel erect or spreading racemes forming a panicle 30 cm or more long, the spikelets in pairs, one sessile, the other pedicelled, those of each pair alike, 8–12 mm long, awnless, 2-flowered, florets both male; glumes papery, equal, enclosing florets; female inflorescence variable in size and shape, borne on short branch with several short internodes with a papery sheath at each node, these forming the husk and enclosing the thick central axis (cob) on which the spikelets are arranged in more or less longitudinal rows; spikelets in pairs, both sessile, awnless, 2-flowered, the lower floret small, rarely female, the upper one female; glumes broad, rounded or notched at apex, fleshy towards base; styles projecting from apex of ear as long silky tassels; grains (caryopsis) variable as to size, shape, color and sugar-starch content. Fl. mid-summer; fr. late summer–early fall.

Germplasm

Cultivars may be divided into six or more general types: popcorn (everta), flint corn (indurata), dent corn (indents), flour corn (amylacea), and sometimes called soft corn, sweet corn (saccharata) and pod corn (tunicata). Popcorn is characterized by its ability to pop when subjected to high temperatures. Two types of kernels are known, one is rice-shaped with a pointed end and the other flat with rounded end; both are small and hard. Flint corn is characterized by its hardness of kernel with a rounded top and a small area of soft endosperm around the embryo completely surrounded by corneous endosperm. Dent corn is characterized by wedge-shaped kernels with an indented top and with the soft or floury endosperm extending to the top, while the corneous is confined mainly to the sides of the kernel. Flour or soft corn has the endosperm entirely soft and floury in character, with the shape and outward appearance similar to flint corn but varying in size from kernels not much larger than those in popcorn to kernels nearly 2.5 cm long. Sweet corn has the endosperm translucent and horny in appearance and the starch partially replaced by sugar. Pod corn has each kernel as well as the ear itself, covered with a husk, the kernels varying greatly in size and shape, a type of corn rarely grown. Most of the corn grown today for human consumption is sugar corn, about 200 cvs of which are grown in the US. Also most of the corn grown is of hybrid origin, where two or more genetic different strains are used to produce the hybrid corn, some are named, others orily bear numbers. Each state and country has its named cvs which grow best under its particular climatic and agronomic conditions. Reported from the Middle America to South America and China-Japan Centers of Diversity, corn or cvs thereof is reported to tolerate aluminum, bacteria, disease, drought, fungus, herbicide, hydrogen fluoride, high pH, heat, insects, laterite, low pH, mildew, photoperiod, poor soil, slope, smog, SO2 ultra-violet, and virus. (2n = 20) (Duke, 1978).

Distribution

Corn is only known in the cultivated state, and is believed to have originated in Mexico in prehistoric times. It is now distributed over the world and grown wherever summers are reasonably warm.

Ecology

Corn is essentially a subtropical plant, but will grow now with its cultivars far into the temperate climate, as far north as Canada and Russia, where summers are long enough to produce good vegetative growth but rarely long enough to produce grain. It is known to grow from 58°N to 40°S latitude, and from altitudes below sea level to 4,000 m in the Andes. It is easily killed by frost. Most sweet corn is grown in areas with a mean temperature of 19–21°C during the summer months. Annual rainfall of 750 mm or more is required for adequate moisture. Deep, naturally rich, easily tilled soil is preferred. Corn grows on great variety of soil types. Ranging from Boreal Moist to Rain through Tropical Desert to Wet Forest Life Zones, corn is reported to tolerate annual precipitation of 2.3 to 41.0 dm (mean of 12.2 cases = 259), annual temperature of 4.9 to 28.5°C (mean of 19.2 cases = 258), and pH of 4.3 to 8.7 (mean of 6.4 cases = 175).

Cultivation

Propagated only from seed. A deep, firm seedbed, free of clods, trash and surface irregularities should be prepared, either in the spring, or preferably on moderately heavy to heavy soil, in the fall and left rough over winter, thus allowing them to be worked and planted earlier in the spring. Light soil should be kept covered during the winter to prevent erosion and worked in the early spring. Soil should be worked and disked about 3–4 weeks before planting, thus allowing for partial decomposition or organic material. Corn is usually planted about 2 weeks after the average date for the last killing frost. The harvest period may be lengthened by planting successive crops, or by planting early, medium and late varieties at one time. In Florida sweet corn production is arranged for continuous harvest, with plantings from August to April. Several methods for planting the seeds are used. Planting seed singly in drills is preferred to the check-row system of planting 3–4 seeds in hills. Recommended planting rates vary from 40,000 plants per ha for medium-sized cvs to 50,000 plants per ha for small, early cvs. These rates require 11.5 to 16 kg/ha. For hills in checkrows, 3–4 plants per hill are best with hills spaced about 0.8 m x 0.8 m for small cvs and 0.9 m x 0.9 m for medium types, and 1 m x 1 m for large cvs. Seed should be planted only deep enough to place it in moist soil below the dry surface layer, this being about 2.5 cm; in sandy loams, this might be 5 cm deep. Soils should be irrigated if necessary to provide an equivalent of about an acre-inch of water every week. Yield increases in irrigated corn are greater on soils well supplied with organic matter. Green manures increase productivity of most soils. In the North, an increase in the percentage of legumes for hay or pasture and a better conservation of crop by-products and manure is frequently sufficient to maintain organic matter in moderately productive soils. A second crop of clover or a last crop of alfalfa may be turned under profitably. Sweetclover, grown with the small-grain crop and turned under the following spring is probably the most important green-manure crop in the North and is particularly useful on heavier soils. In the South where the decay and consequent loss of organic matter is more rapid than in the North, continuous during winter and summer, a larger replacement is necessary and the winter-grown green-manuring crop serves as a cover crop and checks winter erosion and loss of plant food. Also, in the South, more different crops can be grown successfully during the winter, making possible selections to fit different cropping systems. Well rotted manure may be applied to land for corn about equally well in the fall or spring unless the soil is sandy, and then it is applied in spring to prevent excessive leaching. There is little difference in the effect of well-rotted manure whether plowed under or applied as a top dressing after plowing. Commercial fertilizers are used to supply one or more of the most frequently deficient nutrients, nitrogen, phosphorous or potash. Nitrogen fertilizers promote quick and vigorous growth of stalks and leaves. Nitrogen supply of soil generally maintained more economically by turning under legumes such as cowpeas, clover, alfalfa and the like. Phosphorous fertilizers tend particularly to increase the yield of grain. Bone meal is an excellent fertilizer of this type, but it is costly. Superphosphate is the most practical form in which to supply phosphorus for immediate utilization. It may be applied after the ground is plowed and ready for planting, and can be broadcast, or applied in the row or in the hill, or both. Potash fertilizers contribute generally to the health of the plants and quality of grain. Both muriate and sulfate of potash, containing about 50% of potash, are good sources. Mixed fertilizer may also be used to advantage, but it is important to know that the fertilizer selected provides the elements needed for a particular soil. Application of commercial fertilizers in the row or hill is generally more efficient than broadcast applications. Cultivation accomplishes several purposes: controls weeds, increases absorption of water by reducing run-off, checks evaporation by maintaining a mulch and increases aeration of the soil. Weeds can be killed most easily and cheaply when the field is being prepared for planting and before the corn is up or while it is small enough to stand harrowing without injury. At such times the land can be gone over quickly with the harrow, weeder or rotary hoe. These implements are highly efficient in controlling weeds if used before the corn becomes established, and they hold down the cost of cultivation. Harrowing from just before to just after the seedlings emerge should be avoided. After corn plants are well up they may be harrowed with little danger until they are about 10 cm tall. Later cultivations can be made satisfactorily with any of the usual cultivators. Corn should be cultivated often enough to control the weeds. Cultivation should be no deeper than needed to control weeds. Shallow cultivation is less likely to injure the corn roots and does not bring many weed seeds to the surface.

Harvesting

Sweet corn is harvested for eating from the cob when 50–75 days old depending on the cv, or when the kernels are fully developed but still juicy, producing a milky liquid when punctured, husk should be tight and the silks somewhat dried. When harvested by hand, sweet corn is picked with a downward twist, put into picking sacks or on trailers and rushed to sorting sheds. Sweet corn loses about 50% of its sugar in the first 24 hours after picking, getting it to market as soon as possible is very important. Mechanical harvesters are also used for sweet corn for the fresh market. When corn is harvested for grain, several methods may be used: ears may be snapped or husked by hand from the standing stalks, mature stalks may be cut by hand or machine and shucked and the ears husked later, grain may be gathered from the standing stalks by mechanical pickers, or machines may be used which will pick and husk the ear corn, or pick the ears and shell the corn simultaneously. Corn harvested for silage may be cut by hand, sled, mower or corn binder, and later chopped by a stationary cutter just before it is put into the silo; or it may be cut and chopped in the field in one operation by the ensilage harvester. Harvesting corn for forage applies only to that portion of the crop which is harvested for feeding, the whole plant being used either as silage or dry forage (Reed, 1976).

Yields and Economics

Average yields of sweet corn for the fresh market is about 8.75 MT/ha, ranging from 3.6 MT/ha to 10.75 MT/ha, depending on cv and area. Most sweet corns used for human consumption are yellow, high in vitamin A. Grain corn used for animal feed is more often white and sometimes called horse-corn. Average yields are slightly higher for field corn due to the larger ears and heavier kernels. Average yields for silage corn is about 32.5 MT/ha in the US. In 1969 over 1.25 million ha of silage corn harvested, or 42% of all corn grown in the US that year. Corn is the leading crop in the US, grown in every state on more than 40 million hectares, with a total production of ca 1.3 billion pounds of fresh sweet corn, and billions of tons of grain corn and silage corn. Dibb (1983) compares US yields of 5,400 kg/ha with 1,300 kg/ha in the developing countries and a world record of 21,200 kg/ha.

Energy

It is usually considered possible to reach an ethanol yield of 90–95% of theoretical. A ton of dried corn would yield about 370 kg ethanol. With an energy content of 28 Mj/kg and an energy density of 28,000 MJ/m3 ethanol is one of the most attractive synthetic fuels (petrol is 44 MJ/kg, 32,000 MJ/m3) (Palz and Chartier, 1980). The residue coefficient tells us there should be at least 1,300 kg/ha stover left, after the ton of corn is harvested. Where the whole plant could be harvested after 88 days, 4 crops are theoretically possible in the tropics, with biomass yields of more than 60 MT/ha. Noting that US 1982 record 114.8 bushels per acre, Dibb adds that is less than 1/4 the estimated potential. "Geneticists and plant physiologists have estimated that the theoretical genetic potential of the best corn hybrids with all inputs optimum would be in the 500 to 600 bushel per acre range." Thus in tropical sections, we might assume 1 MT stover per ha minimum, 60 MT as a remote maximum, with 10 as a comfortable target. Husks and cobs amount to more than 60% of the harvested ear. Over 117 days, however, the growth rate averaged less than half this, 23 g/m2/day as compared with 52 g/m2/day. Corn biomass in the US is only 10.8 MT/ha, representing an efficiency of solar energy conversion of 0.2% (Boardman, 1980). Westlake (1963) speculates that digging and weighing underestimate while core samples overestimate, the first method giving 7.3% of corn biomass as root, the latter giving 29–49%. Further, Westlake reports a growing season productivity of 18 g/m2/day for a maximum seasonal biomass of 25 MT/ha, annual productivity of 26 MT/ha in Minnesota, seasonal productivity of 42 g/m2/day, for an annual productivity of 36 MT/ha in Israel (based on annual crops of hybrid corn reaching 112 MT green forage/ha grown in 80–90 days; dry weight was 23–25% of fresh weight. High organic productivity of 66 MT/ha is explained by Westlake as including the whole plant, harvested ca 88 days after planting, and assuming continuous cultivation giving 4.1 harvests/year. The corn residue coefficient, defined as the ratio of the weight of dry matter of residue to recorded harvested weight, ranges from 0.55 to 1.20 (NAS, 1977a). One of the largest producers of alcohol from corn for gasahol is moving into hydroponics to see if the two main byproducts of the alcohol production process—hot water and carbon dioxide—can be used more efficiently, according to an article in the April issue of Food Processing (p. 38). Archer Daniels Midland Company of Decatur, Illinois, will attempt to grow a wide variety of vegetables, ornamental plants, and cut flowers in hydroponic greenhouses. The hot water comes from water being used for cooling in certain segments of the alcohol production process. Currently, this heat is dispensed into the air via a cooling tower. Plans are to use the heat from this water to heat the greenhouses. Carbon dioxide—used by plants for growth—is given off during fermentation in the making of alcohol. The company wants to use that element to increase the carbon dioxide content of the air surrounding the plants. They already are using the extra carbon dioxide for carbonating beverages, and see it as useful as refrigerant and as a fire smothering agent in coal mines. But apparently the alcohol making process produces more of the carbon dioxide than can be used in these other ways. As of June 15, 1981, corn oil was $0.232/lb., compared to $0.38 for peanut oil, $1.39 for poppyseed oil, $0.65 for tung oil, $0.33 for linseed oil, $0.275 for coconut oil, $0.265 for cottonseed oil, $0.21 for soybean oil (Chemical Marketing Reporter, June 15, 1981). At $2.00 per gallon, gasoline is roughly $0.25/lb. According to Swift (1983), methanol was already $0.41 a gallon "directly competitive with gasoline." According to Hitzhusen and Abdallah (1980), the economic feasibility of utilizing maize stover as coal supplement in small to medium-sized, coal-burning steam-electric plants appears promising, particularly when the low sulphur emission value of maize stover is considered.

Biotic Factors

A great number of diseases and pests attack corn in its various stages. Wherever fungal, bacterial or virus disease are prevailent, or pests, as insects or nematodes, are serious problems, local agriculture agents should be consulted to determine the best mehtods for controlling them. Corn smut probably is the most common disease of corn in the US. Galls incident to this disease develop on any of the aboveground parts of the plant and may become several cm in diameter. In the earlier stages they are white or gray, later becoming black. When mature, they rupture, releasing the dense powdery mass of black spores inside. No highly resistant cvs so far are available. Rot diseases of roots, stalks and ears of corn are caused by a number of different fungi and are widely distributed. More than 300 different insect pests are known to attack corn, of which over 160 are particularly injurious. Most destructive are corn ear worm, European corn borer, grasshoppers, cutworms, rootworms, armyworms, sugarcane borer, grain weevils, various kinds of aphids, white grubs and several kinds of beetles, bugs and borers.

Chemical Analysis of Biomass Fuels

Analysing 62 kinds of biomass for heating value, Jenkins and Ebeling (1985) reported a spread of 18.77 to 17.58 Mj/kg, compared to 13.76 for weathered rice straw to 23.28 MJ/kg for prune pits. On a % DM basis, the cobs contained 80.10% volatiles, 1.36% ash, 18.54% fixed carbon, 46.58% C, 5.87% % H, 45.46% O, 0.47% N, 0.01% S, 0.21% Cl, and undetermined residue.

References

Complete list of references for Duke, Handbook of Energy Crops
Last update Friday, January 9, 1998 by aw