Maize

Maize
Illustration depicting both male and female flowers of maize
Scientific classification
Clade:	Angiosperms
Clade:	Monocots
Clade:	Commelinids
Genus:	Zea
Species:
Binomial name
mays Carl Linnaeus

Maize (/meɪz/ MAYZ; Zea mays subsp. mays, from Spanish: maíz after Taíno mahiz), also known as corn. Maize has become a staple food in many parts of the world, with total production surpassing that of wheat or rice. However, not all of this maize is consumed directly by humans. Some of the maize production is used for corn ethanol, animal feed and other maize products, such as corn starch and corn syrup. The six major types of corn are dent corn, flint corn, pod corn, popcorn, flour corn, and sweet corn.

History

Guilá Naquitz Cave in Oaxaca, Mexico is the site of early domestication of several food crops, including teosinte (an ancestor of maize).

Cultivation of maize in an illustration from the 16th c. Florentine Codex

Most historians believe maize was domesticated in the Tehuacan Valley of Mexico. Recent research in the early 21st century has modified this view somewhat; scholars now indicate the adjacent Balsas River Valley of south-central Mexico as the center of domestication.

An influential 2002 study by Matsuoka et al. has demonstrated that, rather than the multiple independent domestications model, all maize arose from a single domestication in southern Mexico about 9,000 years ago. The study also demonstrated that the oldest surviving maize types are those of the Mexican highlands. Later, maize spread from this region over the Americas along two major paths. This is consistent with a model based on the archaeological record suggesting that maize diversified in the highlands of Mexico before spreading to the lowlands.

Archaeologist Dolores Piperno has said:

A large corpus of data indicates that it [maize] was dispersed into lower Central America by 7600 BP [5600 BC] and had moved into the inter-Andean valleys of Colombia between 7000 and 6000 BP [5000-4000 BC].

— Dolores Piperno, The Origins of Plant Cultivation and Domestication in the New World Tropics: Patterns, Process, and New Developments

Since then, even earlier dates have been published.

According to a genetic study by Embrapa, corn cultivation was introduced in South America from Mexico, in two great waves: the first, more than 6000 years ago, spread through the Andes. Evidence of cultivation in Peru has been found dating to about 6700 years ago. The second wave, about 2000 years ago, through the lowlands of South America.

Before domestication, maize plants grew only small, 25 millimetres (1 in) long corn cobs, and only one per plant. In Spielvogel's view, many centuries of artificial selection (rather than the current view that maize was exploited by interplanting with teosinte) by the indigenous people of the Americas resulted in the development of maize plants capable of growing several cobs per plant, which were usually several centimetres/inches long each. The Olmec and Maya cultivated maize in numerous varieties throughout Mesoamerica; they cooked, ground and processed it through nixtamalization. It was believed that beginning about 2500 BC, the crop spread through much of the Americas. Research of the 21st century has established even earlier dates. The region developed a trade network based on surplus and varieties of maize crops.

Maize is the most widely grown grain crop throughout the Americas, with 361 million metric tons grown in the United States in 2014 (Production table). Approximately 40% of the crop—130 million tons—is used for corn ethanol. Genetically modified maize made up 85% of the maize planted in the United States in 2009.

Sugar-rich varieties called sweet corn are usually grown for human consumption as kernels, while field corn varieties are used for animal feed, various corn-based human food uses (including grinding into cornmeal or masa, pressing into corn oil, and fermentation and distillation into alcoholic beverages like bourbon whiskey), and as chemical feedstocks.

Names

Many small male flowers make up the male inflorescence, called the tassel.

The word maize derives from the Spanish form of the indigenous Taíno word for the plant, mahiz. It is known by other names around the world.

The word "corn" outside North America, Australia, and New Zealand refers to any cereal crop, its meaning understood to vary geographically to refer to the local staple. In the United States, Canada, Australia, and New Zealand, corn primarily means maize; this usage started as a shortening of "Indian corn". "Indian corn" primarily means maize (the staple grain of indigenous Americans), but can refer more specifically to multicolored "flint corn" used for decoration.

In places outside North America, Australia, and New Zealand, corn often refers to maize in culinary contexts. The narrower meaning is usually indicated by some additional word, as in sweet corn, sweetcorn, corn on the cob, baby corn, the puffed confection known as popcorn and the breakfast cereal known as corn flakes.

In Southern Africa, maize is commonly called mielie (Afrikaans) or mealie (English), words derived from the Portuguese word for maize, milho.

Maize is preferred in formal, scientific, and international usage because it refers specifically to this one grain, unlike corn, which has a complex variety of meanings that vary by context and geographic region. Maize is used by agricultural bodies and research institutes such as the FAO and CSIRO. National agricultural and industry associations often include the word maize in their name even in English-speaking countries where the local, informal word is something other than maize; for example, the Maize Association of Australia, the Indian Maize Development Association, the Kenya Maize Consortium and Maize Breeders Network, the National Maize Association of Nigeria, the Zimbabwe Seed Maize Association. However, in commodities trading, corn consistently refers to maize and not other grains.

Breeding

Field of maize in Liechtenstein

Maize reproduces sexually each year. This randomly selects half the genes from a given plant to propagate to the next generation, meaning that desirable traits found in the crop (like high yield or good nutrition) can be lost in subsequent generations unless certain techniques are used.

Maize breeding in prehistory resulted in large plants producing large ears. Modern breeding began with individuals who selected highly productive varieties in their fields and then sold seed to other farmers. James L. Reid was one of the earliest and most successful developing Reid's Yellow Dent in the 1860s. These early efforts were based on mass selection. Later breeding efforts included ear to row selection, (C. G. Hopkins ca. 1896), hybrids made from selected inbred lines (G. H. Shull, 1909), and the highly successful double cross hybrids using 4 inbred lines (D. F. Jones ca. 1918, 1922). University supported breeding programs were especially important in developing and introducing modern hybrids. (Ref Jugenheimer Hybrid Maize Breeding and Seed Production pub. 1958) by the 1930s, companies such as Pioneer devoted to production of hybrid maize had begun to influence long term development. Internationally important seed banks such as International Maize and Wheat Improvement Center (CIMMYT) and the US bank at Maize Genetics Cooperation Stock Center University of Illinois at Urbana-Champaign maintain germplasm important for future crop development.

Since the 1940s the best strains of maize have been first-generation hybrids made from inbred strains that have been optimized for specific traits, such as yield, nutrition, drought, pest and disease tolerance. Both conventional cross-breeding and genetic modification have succeeded in increasing output and reducing the need for cropland, pesticides, water and fertilizer. There is conflicting evidence to support the hypothesis that maize yield potential has increased over the past few decades. This suggests that changes in yield potential are associated with leaf angle, lodging resistance, tolerance of high plant density, disease/pest tolerance, and other agronomic traits rather than increase of yield potential per individual plant.

Cultivation

Planting

Seedlings three weeks after sowing

Young stalks

Because it is cold-intolerant, in the temperate zones maize must be planted in the spring. Its root system is generally shallow, so the plant is dependent on soil moisture. As a C4 plant (a plant that uses C4 carbon fixation), maize is a considerably more water-efficient crop than C3 plants (plants that use C3 carbon fixation) like the small grains, alfalfa and soybeans. Maize is most sensitive to drought at the time of silk emergence, when the flowers are ready for pollination. In the United States, a good harvest was traditionally predicted if the maize were "knee-high by the Fourth of July", although modern hybrids generally exceed this growth rate. Maize used for silage is harvested while the plant is green and the fruit immature. Sweet corn is harvested in the "milk stage", after pollination but before starch has formed, between late summer and early to mid-autumn. Field maize is left in the field very late in the autumn to thoroughly dry the grain, and may, in fact, sometimes not be harvested until winter or even early spring. The importance of sufficient soil moisture is shown in many parts of Africa, where periodic drought regularly causes maize crop failure and consequent famine. Although it is grown mainly in wet, hot climates, it has been said to thrive in cold, hot, dry or wet conditions, meaning that it is an extremely versatile crop.

Mature plants showing ears

Maize was planted by the Native Americans in hills, in a complex system known to some as the Three Sisters. Maize provided support for beans, and the beans provided nitrogen derived from nitrogen-fixing rhizobia bacteria which live on the roots of beans and other legumes; and squashes provided ground cover to stop weeds and inhibit evaporation by providing shade over the soil. This method was replaced by single species hill planting where each hill 60–120 cm (2.0–3.9 ft) apart was planted with three or four seeds, a method still used by home gardeners. A later technique was "checked maize", where hills were placed 40 in (1.0 m) apart in each direction, allowing cultivators to run through the field in two directions. In more arid lands, this was altered and seeds were planted in the bottom of 10–12 cm (3.9–4.7 in) deep furrows to collect water. Modern technique plants maize in rows which allows for cultivation while the plant is young, although the hill technique is still used in the maize fields of some Native American reservations. When maize is planted in rows, it also allows for planting of other crops between these rows to make more efficient use of land space.

In most regions today, maize grown in residential gardens is still often planted manually with a hoe, whereas maize grown commercially is no longer planted manually but rather is planted with a planter. In North America, fields are often planted in a two-crop rotation with a nitrogen-fixing crop, often alfalfa in cooler climates and soybeans in regions with longer summers. Sometimes a third crop, winter wheat, is added to the rotation.

Many of the maize varieties grown in the United States and Canada are hybrids. Often the varieties have been genetically modified to tolerate glyphosate or to provide protection against natural pests. Glyphosate is an herbicide which kills all plants except those with genetic tolerance. This genetic tolerance is very rarely found in nature.

In the midwestern United States, low-till or no-till farming techniques are usually used. In low-till, fields are covered once, maybe twice, with a tillage implement either ahead of crop planting or after the previous harvest. The fields are planted and fertilized. Weeds are controlled through the use of herbicides, and no cultivation tillage is done during the growing season. This technique reduces moisture evaporation from the soil, and thus provides more moisture for the crop. The technologies mentioned in the previous paragraph enable low-till and no-till farming. Weeds compete with the crop for moisture and nutrients, making them undesirable.

Harvesting

Mature maize ears

Harvesting maize, Jones County, Iowa

Before the 20th century, all maize harvesting was by manual labour, by grazing, or by some combination of those. Whether the ears were hand-picked and the stover was grazed, or the whole plant was cut, gathered, and shocked, people and livestock did all the work. Between the 1890s and the 1970s, the technology of maize harvesting expanded greatly. Today, all such technologies, from entirely manual harvesting to entirely mechanized, are still in use to some degree, as appropriate to each farm's needs, although the thoroughly mechanized versions predominate, as they offer the lowest unit costs when scaled to large farm operations. For small farms, their unit cost can be too high, as their higher fixed cost cannot be amortized over as many units.

Before World War II, most maize in North America was harvested by hand. This involved a large numbers of workers and associated social events (husking or shucking bees). From the 1890s onward, some machinery became available to partially mechanize the processes, such as one- and two-row mechanical pickers (picking the ear, leaving the stover) and corn binders, which are reaper-binders designed specifically for maize (for example, Video on YouTube). The latter produce sheaves that can be shocked. By hand or mechanical picker, the entire ear is harvested, which then requires a separate operation of a maize sheller to remove the kernels from the ear. Whole ears of maize were often stored in corn cribs, and these whole ears are a sufficient form for some livestock feeding use. Today corn cribs with whole ears, and corn binders, are less common because most modern farms harvest the grain from the field with a combine and store it in bins. The combine with a corn head (with points and snap rolls instead of a reel) does not cut the stalk; it simply pulls the stalk down. The stalk continues downward and is crumpled into a mangled pile on the ground, where it usually is left to become organic matter for the soil. The ear of maize is too large to pass between slots in a plate as the snap rolls pull the stalk away, leaving only the ear and husk to enter the machinery. The combine separates out the husk and the cob, keeping only the kernels.

When maize is a silage crop, the entire plant is usually chopped at once with a forage harvester (chopper) and ensiled in silos or polymer wrappers. Ensiling of sheaves cut by a corn binder was formerly common in some regions but has become uncommon.

File:MaizeYield.png

Worldwide maize production

For storing grain in bins, the moisture of the grain must be sufficiently low to avoid spoiling. If the moisture content of the harvested grain is too high, grain dryers are used to reduce the moisture content by blowing heated air through the grain. This can require large amounts of energy in the form of combustible gases (propane or natural gas) and electricity to power the blowers.

Further reading

• Clampitt, Cynthia. Maize: How Corn Shaped the U.S. Heartland (2015)

External links

• Maize Genetics and Genomics Database
• Maize Genetics Cooperation Stock Center