Corn, also called maize, is a plant whose food value and wide variety of uses make it one of the world’s most important crops. Corn and two other grains, rice and wheat, provide the chief sources of energy in the human diet.
Corn has a remarkable number of uses. The kernels—that is, the corn grain, or seeds—can simply be cooked and eaten. The kernels can also be used in making breakfast cereals, baked goods, salad dressing, and many other foods. Farmers use large quantities of corn grain, as well as cornstalks and other parts of corn plants, to feed to livestock. People eat this corn indirectly in the form of meat, eggs, and dairy products. Corn is also used in making many kinds of nonfood products, including ceramics, drugs, paints, paper goods, and textiles.
Corn is a cereal grass distantly related to wheat, rice, oats, and barley. American Indians living in what is now Mexico learned how to grow corn thousands of years ago. Thus, corn came to be called Indian corn. But today the term generally refers only to varieties of corn that produce ears with multicolored kernels.
Depending on the variety, corn can be grown in most mild and tropical regions of the world. The United States ranks as one of the world’s leading producers and exporters of corn. It produces about 30 percent of the world’s supply, chiefly in a region of the Midwest called the Corn Belt. Other major corn producers include Argentina, Brazil, China, India, Indonesia, Mexico, and Ukraine.
Uses of corn
Food for people.
Corn grain provides an especially rich source of starch. Starch is a carbohydrate, a nourishing substance in food that gives the body energy. Corn also supplies fats and protein. But corn protein lacks some of the important chemical units called amino acids that the body needs. In many less developed countries in Latin America, Africa, and Asia, corn forms a major part of the human diet. Therefore, a large number of people in those countries can suffer from protein malnutrition if an alternative protein source is not available. Scientists working in Mexico have developed quality protein maize for these populations. This type of modified corn has higher levels of protein.
People can eat corn in several ways. Many enjoy eating sweet corn on the cob after the ears have been boiled or roasted. Sweet corn kernels that have been removed from the cob are sold canned or frozen for easy preparation. Popcorn ranks as a favorite snack food. People eat it plain or flavored with such foods and seasonings as salt, butter, caramel, or cheese.
Corn also serves as an important ingredient in many processed foods. A typical supermarket might carry hundreds of foods that contain corn or corn products. Such foods include breakfast cereals, salad dressing, margarine, syrup, cornstarch, and snack items. Corn meal, a flourlike substance made from ground corn grain, comes in such foods as corn bread, tamales, and tortillas. Corn is also an ingredient in beer and whiskey.
Livestock feed.
Corn provides a major livestock feed in many countries. In the United States, about a third of the corn grain harvested each year becomes feed for hogs, cattle, sheep, and poultry. Some of the U.S. corn crop is made into silage, or livestock feed. Farmers produce silage from entire corn plants, except for the roots, or from the parts that remain after the ears are removed. Livestock also eat feed made from ground ears, whole shelled corn, or ground shelled corn.
Industrial uses.
Manufacturers use corn to make many industrial products. Such products include ceramics, explosives, construction materials, metal molds, paints, paper goods, and textiles. Industrial alcohols, including ethanol and butyl alcohol, also contain corn. Alcohol made from corn and other plants is used in some gasolines to improve the fuel’s performance and to make the fuel safer for the environment. Corn also comes in penicillin and other antibiotics, vitamins, and industrial enzymes.
The corn plant
There are several thousand varieties of corn. Originally, varieties were developed by the farmers who grew them. Today, scientists develop nearly all corn varieties used on commercial farms. Varieties grown in the same region may have many characteristics in common but differ greatly from varieties in other regions. For example, most Corn Belt varieties grow about 8 feet (2.4 meters) tall. Varieties in other regions may range from as little as 3 feet (0.9 meter) to as much as 20 feet (6 meters) tall. If the similarities among varieties are great enough, the varieties are considered to belong to the same race. Scientists have identified about 250 corn races. However, all varieties develop in the same manner and can breed with one another.
Appearance.
A mature corn plant consists of the roots, stalk, leaves, and flowering parts. The typical Corn Belt plant has a single sturdy stalk supported by a root system with many branches. About 20 long, broad leaves grow along the stalk, and 15 of these survive to maturity. The flowering parts of a corn plant are the tassel, the male reproductive structure at the top of the stalk, and the ear, the female reproductive structure about in the middle of the stalk. An ear consists of a cob covered by rows of kernels. The ear is enclosed and protected by special leaves called husks. A plant may have one or several ears. Most Corn Belt varieties bear one ear about 9 inches (23 centimeters) long per plant. Each ear has about 18 rows of kernels.
How the plant develops.
A corn plant begins life as a seed. Mature corn seeds have three main parts: (1) the embryo, or germ; (2) the endosperm; and (3) the seed coat, or fruit case. The embryo is the part of the seed that develops into a new plant. The endosperm is a storehouse of food energy, mostly in the form of starch. The corn seedling uses that energy in its early development. The seed coat is a thin, tough outer covering around the endosperm and embryo that protects them from damage.
Physical development of the new corn plant begins two or three days after the seed is planted. Moisture absorbed by the seed causes it to swell. The lower part of the embryo, called the primary root, breaks through the seed coat and pushes down into the soil. One or two days later, several seminal roots start to form. Those roots are usually temporary. They anchor the seedling and absorb water and nourishment from the soil. About three to five days later, the upper part of the embryo breaks through, and the first leaves emerge.
Additional leaves appear during the next three or four weeks as the cornstalk grows taller. After four to six weeks, when all the leaves have started growing, the tassel, which is not yet visible, begins to form at the top of the plant. About the same time, buds start to form where the stalk and lower leaves meet. The lowest buds may form branches called tillers. Higher buds will develop into one or more ears. The plant then enters a period of rapid growth. During that time, which lasts about five or six weeks, a permanent root system develops and the leaves grow to their largest size. The flowering parts continue to develop. Prop roots, also called brace roots, extend into the ground from the lower part of the stalk and provide additional support to the plant. The plant reaches its full size about 9 to 11 weeks after sprouting.
How the plant reproduces.
A corn plant reproduces sexually. Sperm (male sex cells) from the pollen released by the tassel unite with eggs (female sex cells) in the ear in a process called fertilization. The fertilized eggs develop into kernels on the cob.
A tassel consists of small male flowers that grow in clusters. Each flower has three baglike structures called anthers, which produce pollen. An anther may contain as many as 2,500 pollen grains.
An unfertilized ear of corn consists of female flowers arranged in pairs on a cob. In most varieties, only one flower of each pair develops and is able to reproduce. Each developing flower sends out a long, threadlike silk from its ovary, an egg-bearing structure at the base of the flower. At blossoming time, a mass of silks extends beyond the tip of the husks.
When the corn plant has nearly reached its maximum height, its anthers split open and shed their pollen. The pollen shed usually lasts five to eight days. The wind blows the pollen about like dust. Most of the pollen falls on other corn plants, though some self-pollination will occur. When a pollen grain lands on a silk, it germinates and sends a pollen tube down through the silk. Two sperm nuclei, male structures that fertilize, travel down the tube. One nucleus fertilizes the egg inside the ovary, forming the embryo of the new seed. The other unites with two female structures called the polar nuclei, forming the endosperm. In a commercially grown plant, the kernels reach maturity about eight weeks after fertilization. The rest of the plant dies at that time or soon after.
Kinds of corn
Biologists classify corn in many ways. One useful classification system is based chiefly on the different characteristics of the kernels. According to this system, the six major kinds of corn are (1) dent corn, (2) flint corn, (3) flour corn, (4) sweet corn, (5) popcorn, and (6) waxy corn.
Dent corn
gets its name from the dent on the top of mature kernels. The dent forms when the soft, floury starch in the kernel dries and shrinks as the seed matures. Most kernels are yellow or white. Dent corn ranks as the most common corn in North America. It is used chiefly for livestock feed. It is also used in making many processed foods and industrial products.
Flint corn
has hard, round kernels with a smooth coat. The kernels range from white to deep red. Flint corn grows well in cool climates and reaches maturity early. It resists insect pests that attack kernels better than corn with softer kernels, such as dent corn. The American colonists found that breeding flint corn with dent corn produced a superior dent variety. Like dent corn, flint corn is used as food for people and livestock. In the fall, many people decorate their homes with ears of flint corn or other colorful corn. People often call such corn Indian corn. Flint corn is widely grown in Asia, Europe, and Central and South America.
Flour corn
is one of the oldest kinds of corn. The Indians of central Mexico and western South America have grown flour corn for thousands of years. The kernels on most ears are white, blue, or a variety of colors. The kernels contain mainly soft starch and can be easily crushed into a flour. Farmers cultivate most flour corn in the southwestern United States, western South America, and South Africa. This corn provides mainly food for the people who grow it.
Sweet corn
is the sweetest corn. People eat the cooked kernels directly from the cob or after they have been removed. Sweet corn is harvested before the kernels mature so it has the sweetest flavor. The kernels are soft and may be white or yellow. People grow sweet corn chiefly in the northern United States and the southern part of the Canadian province of Ontario.
Popcorn
is a highly popular snack food. Like flour corn, it is one of the oldest kinds of corn and was grown by American Indians thousands of years ago. There are two main types of popcorn—pearl popcorn and rice popcorn. Pearl popcorn has rounded kernels that are usually yellow or orange. Rice popcorn, also called hull-less popcorn, has pointed, white kernels. Popcorn kernels possess a hard endosperm with a small amount of soft, moist starch in the center. Steam created inside the kernels during heating causes them to explode, or pop. They turn inside out and produce a light, fluffy mass. The United States produces almost all the world’s popcorn. See Popcorn .
Waxy corn
gets its name from the waxlike appearance of its endosperm. The endosperm consists almost entirely of a starch called amylopectin. Such starch is especially useful as a thickener in manufacturing instant pudding mixes, gravies and sauces, and glues. Most waxy corn is grown in the United States and China.
Hybrid corn
Farmers in most developed countries grow hybrid corn almost exclusively. Plant breeders develop such corn to produce high yields.
Hybrid corn is developed through controlled crosses. In this process, breeders select varieties of corn with the characteristics they want future generations of corn to inherit. For example, one variety of dent corn may resist diseases better than another variety. However, the second variety may produce larger ears than the first variety. The plant breeders then cause plants of each selected variety to inbreed (self-pollinate) for several generations until plants with pure hereditary lines (ancestry) are established. They then cross the two inbred lines to obtain seed of a single-cross hybrid. Such seed, is properly developed, will produce uniform plants that combine the hereditary traits of the inbred parents and yield more than the parents. This increased yield capacity is known as hybrid vigor.
Farmers who grow hybrid corn do not save their own seed for planting the following year’s crop. This is because plants grown from such seed will be of varying quality and lower yield. As a result, corn farmers must purchase new single-cross hybrid seeds for planting the crop each year. Most breeders of hybrid corn use dent corn. See Hybrid .
Where corn is grown
There are so many varieties of corn with such different growing needs that one variety or another can be raised in most temperate (mild) and tropical areas of the world. Each year, about 1.3 billion tons (1.2 billion metric tons) of corn are produced worldwide on about 500 million acres (200 million hectares) of land. The annual harvest is approximately 50 billion bushels.
Corn production in the United States
accounts for about 30 percent of the world’s total grain corn supply. Most of the U.S. crop is grown in the Corn Belt, which covers parts of Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Nebraska, Ohio, South Dakota, and Wisconsin. The United States also ranks as the world’s top producer of corn for silage. About 15 percent of the yearly grain corn harvest in the United States is exported, accounting for about 30 percent of the world’s total corn exports.
Corn production in other countries.
China ranks as the second largest producer of corn in the world. It produces about a fourth of the world’s supply. Other leading producers of corn include Argentina, Brazil, France, India, Indonesia, Mexico, and Ukraine. Argentina, Brazil, Romania, and Ukraine are among the leading corn-exporting countries in the world. China, Japan, and Mexico rank as the world’s largest importers of corn. Ontario and Quebec produce the vast majority of corn grown in Canada.
How corn is grown
Most types of corn have a growing season of four to six months, usually beginning in April or early May. Much of the world’s high-yield corn is grown on large farms that use modern machinery to perform nearly all the operations involved in producing corn. However, more than half of the world’s corn-producing areas lie in developing countries, where people grow the grain to feed themselves. Such farming accounts for about one-fifth of the world’s corn production.
Growing conditions.
Most kinds of corn grow best in loamy, well-drained soils that range from slightly acid to neutral. Corn also needs such nutrients (nourishing substances) as nitrogen, phosphorus, and potassium. Those and other nutrients are generally added to the soil in the form of chemical fertilizers or manure. Many corn farmers also rotate their corn crop each year with such crops as alfalfa, clover, or soybeans. Crop rotation returns some nutrients to the soil and helps control soil erosion, weeds, insects, and diseases.
Most types of corn produce the highest yields at daytime temperatures of about 86 °F (30 °C) and average nighttime temperatures above 50 °F (10 °C) around flowering time. Ideal rainfall for growing is 18 to 25 inches (46 to 64 centimeters) in temperate regions and 25 to 36 inches (64 to 91 centimeters) in the tropics. 
Preparing the soil.
Most corn farmers use a chisel plow to prepare the soil for planting. This plow turns ruptures the soil to a depth of 6 to 10 inches (15 to 25 centimeters) in rows spaced 12 to 16 inches (30 to 41 centimeters) apart. Such soil preparation leaves the field surface rough and with a significant cover of crop residue (remains), giving the soil greater protection against erosion. Farmers may add chemical fertilizers or manure to the soil before plowing, at planting time, or as the plants grow. Immediately before planting, the ground may be tilled shallowly one or more times to break up clods of earth and produce an even, firm seedbed.
Planting
begins when the soil temperature reaches about 55 °F (13 °C). Farmers generally begin planting in early spring. Seeds are usually planted about 2 inches (5 centimeters) deep in rows from 15 to 30 inches (38 to 76 centimeters) apart. But they may be planted at shallower or deeper levels, depending on the type of soil and its temperature and moisture content. The most commonly used corn-planting machines are called row planters. They can plant from 2 to 31 rows of seeds at a time. In the Corn Belt, farmers usually plant 6 to 12 rows at a time. Farmers may grow 28,000 to 35,000 plants per acre (70,000 to 86,500 per hectare), depending on soil fertility, rainfall, and the availability of irrigation water.
Controlling pests and diseases.
The major threats to corn crops are weeds, insects, birds, and fungi that cause such diseases as ear rot, stalk rot, and root rot. Chemicals also help protect corn from pests. Farmers use herbicides to control weeds, insecticides to control certain seed- and root-eating insects, and fungicides to control fungi that rot seeds. However, such chemicals can cause pollution if they are released into the environment.
Since the early 1900’s, farmers have used hybrid corn that can resist insects and diseases. In the late 1960’s, scientists introduced new kinds of corns called GMO corns. GMO stands for genetically modified organism. Scientists developed GMO corns by modifying the genetic (hereditary) makeup of certain corn varieties. These genetic modifications made the corn resistant to pests and diseases that once could only be eradicated through chemical pesticides. Since farmers began using GMO corns, they have reduced their need for certain pesticides. However, GMO corns have not achieved widespread acceptance because many people oppose growing and consuming genetically modified foods. One concern raised by such opponents is that genetically modified crops may cause illness in people and livestock.
Harvesting.
The harvesting of corn for grain begins when the moisture content of the mature kernels has dropped to about 28 percent. However, many farmers will delay the harvest until the grain is drier to reduce artificial drying costs. Harvesting may take place as early as August or as late as October. Almost all harvesting is done with a corn combine, a machine that picks the ears from the stalks, removes the husks, shells the corn, and cleans it in one operation (see Combine ). The shelled grain is then dried with heated air and stored in bins for later sale or for use on the farm as livestock feed.
Harvesting corn for silage begins when the kernel moisture has dropped to about 50 percent and the overall moisture of the plant is about 65 percent. A machine called a forage harvester cuts up to eight rows of plants at a time near ground level. It then chops the plants into small pieces and blows the pieces into a wagon. The chopped corn is packed into a storage place, where chemical changes called fermentation occur in the silage. Fermentation preserves the silage until it can be used.
Corn in industry
Grain corn that is not used on producing farms to feed livestock is sold for export or to industry for processing. Four main industries process corn. They are, in order of the quantity of corn used: (1) the mixed-feed industry, (2) the wet-milling industry, (3) the dry-milling industry, and (4) the fermentation and distilling industry.
The mixed-feed industry
uses whole grain corn and by-products of the other industries to make livestock and pet feeds. Manufacturers usually grind or crack the whole grain and then add other ingredients to produce a tasty, nutritious feed. They often shape the feed into pellets, which keep the ingredients from separating.
The wet-milling industry
chiefly produces cornstarch. Manufacturers use cornstarch in making bakery items, corn syrup, drugs, laundry starch, paper goods, textiles, and many other products. By-products of wet milling include corn oil and animal feed, such as corn germ meal and corn gluten meal. Corn oil is used in such foods as salad dressing and margarine.
In the wet-milling process, cleaned and shelled corn is soaked in warm alkaline (acid-neutralizing) water for 24 to 48 hours to soften the kernels. The processors then coarsely grind the kernels, which frees the germ, or embryo, from each kernel. The germ is removed for use in corn oil and corn germ meal. The remaining material is finely ground and passed through screens to remove the seed coat and larger fragments. The material that passes through the screens consists of starch and a protein substance called gluten. The gluten is removed for use in corn gluten meal. The starch that remains is pure cornstarch.
The dry-milling industry
separates the kernel parts and processes them into corn meal, corn flour, grits, or corn oil. Manufacturers use those products to make such items as cornflakes, explosives, and snack foods. There are two systems of dry milling: (1) the new process system and (2) the old process system.
The new process system,
or degerming system, processes about 80 percent of the corn used by the dry-milling industry. In this system, processors first clean the kernels and then increase their moisture content by treating them with water or steam. The grain is then fed into a machine called a degermer. The degermer separates the germ and the seed coat from the endosperm by coarse grinding. It also breaks up the endosperm and passes the particles through screens that sift out the large pieces. Processors use the germ to make corn oil and corn germ meal. They use the seed coats and bits of the kernel stuck to them to make an animal feed known as hominy feed. The largest endosperm pieces are called flaking grits and are used to make cornflakes. The remaining endosperm pieces are ground to produce such products as brewers’ grits, corn meal, and corn flour.
The old process system,
or nondegerming system, involves grinding whole corn kernels into corn meal called old process meal or whole corn meal. The meal generally has all parts of the kernel, though some meal is made without the seed coat. Old process meal has a high oil content from the germ and cannot be stored long. It is used to make tortillas and snack foods.
The fermentation and distilling industry
uses corn grain to produce alcohol. To produce alcohol from corn, many processors first remove the germ through coarse grinding. They then grind the remaining material into a meal and cook it to produce a mash. Barley malt and water are also cooked into a mash. The two mashes are combined, and enzymes in the barley malt convert the starch in the combined mash to sugar. The processors next add yeast or bacteria to the mash, which cause the sugar to ferment, or convert to alcohol. Manufacturers can then remove and purify the alcohol from the fermented mash by distillation. Distillation involves turning the alcohol into vapor by heating the mash and then cooling the vapor back into a liquid. Products and by-products of the fermentation and distilling industry include beer and whiskey, antibiotics, industrial enzymes, vitamins, and distillers’ feeds.
History
Scientists have determined that a strain of the grass teosinte, is the direct ancestor of modern corn. Teosinte still grows wild in parts of Mexico’s western Sierra Madre. The ear of this plant in very unlike that of cultivated corn, and scientists do not know exactly how Native American farmers transformed the teosinte ear into the corn ear. This transformation probably took farming cultures many centuries to achieve.
The oldest known fossil corncobs date from more than 6,000 years ago. They measure about 1 inch (2.5 centimeters) long and often bore fewer than 10 kernels.
Expansion of corn production.
The cultivation of corn gradually spread to much of the Americas. Corn was most widely cultivated by the large urbanized civilizations, such as the Aztec of central Mexico, the Maya of southern Mexico and northern Central America, and the Inca of western South America. By the late 1400’s, Indians grew corn as far south as Argentina and Chile and as far north as Canada.
Europeans knew nothing of corn until Christopher Columbus landed in Cuba in 1492. Columbus brought some corn seeds from the island back to Spain. Later explorers introduced corn from other parts of the Americas into many areas of the world. By the late 1500’s, corn had become a well-established crop in Africa, Asia, southern Europe, and the Middle East.
Corn was a basic food in the American Colonies during the 1600’s and 1700’s. The colonists learned how to grow corn from Native Americans. During the 1800’s, the demand for corn increased rapidly in the United States, and corn became a major commercial crop. Production soared as farmers competed for the growing livestock feed market.
Mechanization of corn farming.
Before the 1800’s, farmers used wooden or cast-iron plows. The heavy, gummy soil of the Midwestern prairies stuck to the surface of such plows, making it difficult to turn the soil. The problem was solved in 1837, when an American inventor named John Deere introduced the steel plow (see Deere, John ). The sticky soil slid off Deere’s smooth steel plow, enabling farmers to work the rich land of the Corn Belt far more easily.
Mechanical corn planters were developed in the early 1800’s. Mechanical corn pickers came into common use during the 1930’s and 1940’s. Today, almost all grain corn is harvested by combines that pick, husk, shell, and clean the corn in one operation.
Development of hybrids.
During the early 1900’s, an American geneticist named George H. Shull began experiments to produce vigorous, high-yielding hybrid corn. Shull established pure hereditary lines by inbreeding plants of the same variety. He then crossed two inbred lines to develop the first single-cross hybrids, which displayed vigor. But because the inbred parents produced very low hybrid seed yields, seed production was costly. About 1918, another American geneticist, Donald F. Jones, bred two single-cross hybrids and developed the first double-cross hybrids. The single-cross female parent produced enough double-cross hybrid seeds to lower production costs and so make hybrids commercially important. Producers began selling double-cross hybrid corn seed in the 1920’s.
By the 1960’s, producers had begun marketing single-cross hybrids that produced more uniform, vigorous plants with higher grain yields than double-cross hybrids. Today, most corn seed comes from single-cross hybrids.
Beginning in the late 1900’s, scientists developed a number of genetically modified corns, or GMO corns. Many GMO corns resist difficult diseases and pests. At the same time, other scientists used more traditional breeding techniques to produce corn with greater nutritional value. One type, the Mexican-produced quality protein maize, may provide a source of protein to people in developing countries.
