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Crops

Crops

Crops are plants or animals or their products cultivated (grown, tended, and harvested) by humans as a source of food, materials, or energy. Humans are rather particular in their choice of crops. Though they select a wide range of useful species of plants and animals to raise, there are vast diversities of species available in particular places or regions.

Farming can involve the cultivation of plants and livestock on farms, fish and other aquatic animals in aquaculture, and trees in agroforestry plantations.

Words to Know

Agroforestry: Cultivation of crops of trees under managed conditions, usually in single-species plantations.

Aquaculture: Managed breeding of aquatic animals and plants for use as food.

Fallow: Cultivated land that is allowed to lie idle during the growing season so that it can recover some of its nutrients and organic matter.

Organic matter: Remains, residues, or waste products of any living organism.

Plants

Hundreds of species of plants are cultivated by humans under managed conditions. However, a remarkably small number of species contribute greatly to the global harvest of plant crops. Ranked in order of their annual production, the world's 15 most important food crops are:

sugar cane, wheat, rice, corn (maize), white potatoes, sugar beets, barley, sweet potatoes, cassava, soybeans, wine grapes, tomatoes, bananas, legumes (beans and peas), and oranges.

Most farm crops are managed as annual plants, meaning they are cultivated in a cycle of one year or less. This is true of all of the grains and legumes and most vegetables. Other species, however, are managed as perennial plants, which once established are capable of yielding crops on a continued basis. This is typically the manner in which tree-fruit crops such as oranges are managed and harvested.

Foot-and-mouth disease

Diseases and severe weather can easily destroy the cropsanimals or plantscultivated on a farm. The effect can be economically devastating. One such agricultural blight occurred in England in early 2001. In February of that year, on a farm in Essex in eastern England, 27 pigs contracted foot-and-mouth disease (also called hoof- and-mouth disease).

This virus affects animals with hooves, such as cattle, pigs, sheep, goats, and deer. Elephants, rats, and hedgehogs are also susceptible. Animals afflicted with the disease suffer from fever, followed by the eruption of blisters in the mouth, on the hooves or feet, on tender skin areas such as the udder in females, and in the nostrils. The blisters grow large, then break, exposing raw surfaces. Eating becomes difficult and painful. Because the soft tissues under the afflicted animal's hooves are inflamed, the animal becomes lame and may even shed its hooves. Pregnant female animals often abort and dairy cattle may give less milk. The disease is rarely fatal, although it can cause death in very young animals. Only very rarely is the disease transmitted to humans. When it has been, only mild symptoms have appeared.

Foot-and-mouth disease is a highly contagious virus spread by direct or indirect contact. It can be carried by birds, on clothes, on the tires of vehicles, on dust, and in infected meat eaten by animals. It can travel many miles simply borne on the wind. Once an animal is infected, symptoms begin to show one to ten days later. Heat, sunlight, and disinfectants destroy the virus. Scientists have made progress in developing a vaccine against the disease, but the cost of vaccinating all susceptible animals (possibly up to $1 billion a year) is seen by some public officials as prohibitive. Consequently, to prevent a widespread outbreak that could cause massive production losses, infected animals must be destroyed by incineration and affected areas must be isolated.

The most serious outbreak in the United States occurred in 1914 when animals in 22 states and the District of Columbia were stricken. The last major incidence of foot-and-mouth disease in England occurred in 1967. Some 440,000 animals were slaughtered, costing the farming industry $200 million (equivalent to $2.3 billion today).

Within weeks of the 2001 outbreak in England, hundreds of thousands of animals were infected and had to be killed and incinerated. Many others who were not infected were killed as a precautionary measure to stop the spread. The virus soon showed up in other European countries: France, the Netherlands, and Ireland all reported confirmed cases. Farming was not the only industry hit hard by the outbreak. Tourism was also severely affected as footpaths and walking trails in the English countryside that meandered near farms were closed to the public in an effort to halt the spread of the virus. The tourism industry lost an estimated $150 million a week as a result. The total cost to all industries affected in England (farming, sports, tourism) was estimated to be over $13 billion.

Some crops are cultivated to produce important medicines. An example is rosy periwinkle, which produces several chemicals that are extremely useful in the treatment of certain types of cancers. Other crops are cultivated to produce extremely profitable but illegal drugs for unlawful markets. Examples of these sorts of crops include marijuana, coca, and opium poppy.

Animals

Enormous numbers of domesticated animals are raised by humans for use as food and materials. In many cases, the animals are used to produce some product that can be harvested without killing the animals. For example, milk can be continuously collected from various species of mammals, especially cows. Similarly, chickens can produce eggs regularly.

However, these plus many other domesticated animals are routinely slaughtered for their meat. The populations of some of these domesticated animals are enormously large. In addition to 6 billion people, the world today supports about 1.7 billion sheep and goats; 1.3 billion cows; 0.9 billion pigs; and 0.3 billion horses, camels, and water buffalo. In addition, there are about 10 to 11 billion domestic fowl, most of which are chickens.

Mad-cow disease

Mad-cow disease (known properly as bovine spongiform encephalopathy or BSE) is another disease that can destroy a population of farm animals. Unlike foot-and-mouth disease, mad-cow disease primarily attacks cattle, and it is fatal. Even more, mad-cow disease has spawned a human form of the disease called variant Creutzfeldt-Jacob disease (vCJD). At present, vCJD is incurable and fatal.

Scientists believe mad-cow disease is caused not by a bacterium or virus but by a self-replicating, abnormally folded protein called a prion. Scientists are still unsure of the complete nature of this agent. It resists freezing, drying, and heating at normal cooking temperatures, even those used for pasteurization and sterilization. Once inside an animal, it incubates for a period of four or five years. Once the disease appears, the animal is dead within weeks or months. The abnormal protein affects the brain and spinal cord of cattle, converting normal proteins into the abnormal form. The accumulation of abnormal proteins in the brain is marked by the formation of spongy holes. Cows afflicted with the disease grow ill-tempered and wobbly, lose weight, then suffer seizures, paralysis, blindness, and, finally, death.

In 1984, on a farm in South Downs, England, a number of cows died from a strange malady that veterinarians could not identify. Two years later, the scientific community specifically diagnosed the malady as mad-cow disease. In 1988, officials in England ordered the destruction of stricken cows and banned the use of cows, sheep, and other various hoofed animals in cattle feed. However, the banned cattle feed was exported to other countries for another eight years. Between 1988 and 1996, nations in Asia alone bought nearly 1 million tons (0.9 million metric tons).

Between November 1986 and December 2000, approximately 180,000 cases of mad-cow disease were confirmed in England. The epidemic peaked in the period 1992 to 1993 with almost 1,000 cases reported a week. Since that time, the disease has been reported in domestic cattle in Ireland, France, Portugal, and Switzerland, and in a number of countries that received cattle feed from England. No cases of mad-cow disease have been found in the United States. England has banned the recycling of farm animals and has stopped exporting meat-based cattle feed. It has also spent billions of dollars destroying and disposing of cows, both those that were infected and those that were merely old.

The first person to develop symptoms of what turned out to be vCJD became ill in January 1994. Scientists now believe this brain-wasting malady, with symptoms similar to mad-cow disease, is caused by eating the meat of animals who suffered from mad-cow disease. The incubation period for vCJD is thought to be between ten and sixteen years. From the time it was first identified until December 2000, 87 cases of vCJD were reported in England, 3 in France, and 1 in the Republic of Ireland. Because of its long incubation period, scientists are unsure how many more cases of vCJD will arise around the world in the future.

Aquaculture

Aquaculture refers to the managed breeding of aquatic animals and plants for use as food. Increasingly, aquaculture or fish farming is seen as an alternative to the exploitation of wild species of aquatic animals and plants.

Most freshwater aquaculture occurs in inland areas where there are many ponds and small lakes. Freshwater aquaculture is particularly important in Asia, where various species of fish, especially carp and tilapia, are raised in artificial ponds. In North America, the most common species of fish grown in small ponds are rainbow trout and catfish.

Aquaculture is also becoming increasingly important along sheltered ocean coastlines in many parts of the world. In the tropics, extensive areas of mangrove forest are being converted into shallow ponds for the cultivation of prawns. In North America and Western Europe, the cultivation of Atlantic salmon became an extensive industry in the late twentieth century, using pens floating in shallow, coastal bays and sometimes in the open ocean.

Agroforestry

In agroforestry, trees are raised as a source of lumber, pulpwood, or fuel. In many regions, this sort of intensive forestry is being developed as an alternative to the harvesting of natural forests.

In temperate zones, the most important trees grown are species of pine, spruce, larch, and poplar. Depending on the species and site conditions, these trees can be harvested after a growth period of only 10 to 60 years, compared with 60 to more than 100 years for natural, unmanaged forests in the same regions.

In the tropics, fast-growing, high-yield species of trees are grown for use locally as fuel, animal fodder, lumber, and pulpwood. Various tree species include pine, eucalyptus she-oak, and tree-legumes. Slowergrowing tropical hardwoods, such as mahogany and teak, are grown for their high-quality lumber.

Climate and crops

Climate dominates agriculture, second only to irrigation. Crops are especially vulnerable to weather variations, such as late or early frosts, heavy rains, or drought. Because of their ability to grow within a climate range, rice, wheat, and corn have become the dominant crops globally.

These crops all need a wet season for germination and growth, followed by a dry season to allow spoilage-free storage. Rice was domesticated in the monsoonal lands of Southeast Asia, while wheat originated in the Fertile Crescent of the Middle East. Historically, wheat was planted in the fall and harvested in late spring, coinciding with the cycle of wet and dry seasons in the Mediterranean region. Corn needs the heavy summer rains provided by the Mexican highland climate.

Other crops are prevalent in areas with less suitable climates. These include barley in semiarid lands (those with light rainfall); oats and potatoes in cool, moist lands; rye in colder climates with short growing seasons; and dry rice on hillsides and drier lands.

Although food production is the main emphasis in farming, more and more industrial applications have evolved. Cloth fibers, such as cotton, have been a mainstay, but paper products and many chemicals now come from cultivated plants.

Crop rotation

When farmers grow two or more crops alternately on the same land, they are rotating crops. Farmers rotate crops to control erosion; promote the fertility of the soil; and control weeds, insects, and plant diseases.

Farmers have been following the practice of crop rotation since the time of the ancient Romans. With the advent of chemical fertilizers following World War II (193945), crop rotation fell out of favor somewhat. Farmers could provide their crops with nutrients without leaving some of their lands fallow (plowed and tilled but unseeded) each year. But some farmers eventually returned to the practice of rotating crops as a way to improve the structure and health of their soils.

Farmers rotate crops to assure that the soil is covered for as much of the year as possible to protect it from exposure to water, wind, and other elements that cause erosion. On sloping lands, rotating crops increases the organic content (remains or residue of living organisms) and overall stability of the soil, further decreasing the chance for erosion. Another method farmers use to increase the organic matter of soil is to plant rotation crops that help build the structure of the soil, such as alfalfa, sweet clover, or red clover. When plowed under the soil, these crops decompose quickly, giving the soil a high level of nutrients.

To control insects and weeds, farmers can rotate crops that have different characteristics: rotate weed-suppressing crops with those that do not suppress weeds and rotate crops susceptible to specific insects with those that are not. If the same crop is not grown in the same field one year after another, the reproductive cycles of insects preying on a specific plant are interrupted. Farmers can also control insects by planting next to each other certain crops that do not attract the same insects.

[See also Agriculture; Agrochemicals; Aquaculture; Forestry; Organic farming ]

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Crops

CROPS

Commodities produced from the earth which are planted, raised, and gathered within the course of a single season.

Crops might be produced either naturally or under cultivation. This distinction becomes important when determining whether a crop is to be sold as personal property or as real estate, and also in terms of how crops are to be devised.

Fructus naturales are crops that are produced by the powers of nature alone, without any harvesting methods. They include fruit trees, berries growing on bushes, and hay growing spontaneously from perennial roots. They are considered real property when they are not severed from the land, but personal property when severed.

Fructus industriales, or emblements, are annual crops that are raised by yearly labor and owe their existence to human intervention and cultivation. Such crops include wheat, corn, and vegetables. Authorities differ as to whether they constitute real or personal property.

The ownership of crops is generally held to be in the owner of the land, whether the crops are natural or cultivated. The owner may voluntarily choose to sever and sell the crops, without being obligated to sell the land upon which they are grown. The situation often arises in which the land belongs to one person and the crops belong to another, such as in the case of one person leasing land from another person. In such a case, whoever is in possession of the land subject to the consent of the owner may take and carry away the products of land resulting from his or her own care and labor.

Ordinarily, crops that are attached to land at the time of a sale pass automatically to the buyer, except where the owner has provided to the contrary. Someone disposing of land may, therefore, stipulate the retention of the title to the crops.

It has been widely held that a trespasser who enters another person's land and cultivates crops does not acquire title to them, since the owner is lawfully entitled to full possession and enjoyment of his or her property. Some authorities have held that as long as crops planted by an intruder remain unsevered, they are the property of the owner of the land upon which they are planted, whereas severed crops belong to the trespasser if he or she possesses the land when the crops are ready to be harvested.

cross-references

Agricultural Law.

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crop

crop / kräp/ • n. 1. a cultivated plant that is grown as food, esp. a grain, fruit, or vegetable. ∎  an amount of such plants or their produce harvested at one time: a heavy crop of fruit. ∎  an abundance of something, esp. a person's hair: he had a thick crop of wiry hair. ∎  the total number of young farm animals born in a particular year on one farm. ∎  a group or amount of related people or things appearing or occurring at one time: the current crop of politicians. ∎  the entire tanned hide of an animal. 2. a hairstyle in which the hair is cut very short. 3. short for riding crop. 4. a pouch in a bird's gullet where food is stored or prepared for digestion. ∎  a similar organ in an insect or earthworm. • v. (cropped , crop·ping ) [tr.] 1. cut (something, esp. a person's hair) very short: [as adj.] (cropped) cropped blond hair. ∎  (of an animal) bite off and eat the tops of (plants). ∎  cut the edges of (a photograph) in order to produce a better picture or to fit a given space. 2. (often be cropped) harvest (plants or their produce) from a particular area. ∎  sow or plant (land) with plants that will produce food or fodder, esp. on a large commercial scale. PHRASAL VERBS: crop out (of rock) appear or be exposed at the surface of the earth. crop up appear, occur, or come to one's notice unexpectedly: some urgent business had cropped up.

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crop

crop
1. A plant that is cultivated for the purpose of harvesting its seeds, roots, leaves, or other parts that are useful to humans. See agriculture.

2. An enlarged portion of the anterior section of the alimentary canal in some animals, in which food may be stored and/or undergo preliminary digestion. The term is most commonly applied to the thin-walled sac in birds between the oesophagus and the proventriculus. In female pigeons the crop contains glands that secrete crop milk, used to feed nestlings.

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crop

crop
A. bird's craw OE.;

B. †head of a plant OE.; top of an object XV; upper part of a whip XVI (hence, whipstock with a handle and loop XIX);

C. produce of plants used for food XIII. OE. crop(p), corr. to MLG., MDu. kropp, (O)HG. kropf, ON. kroppr; further relations uncert.
Hence crop vb. lop. poll XIII; pluck, pull XIV; raise a crop on, bear a crop XVI; come up to the surface XVII; whence a new sb. crop cropping (in various uses) XVII.

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crop

crop1 crop circle an area of standing crops which has been flattened in the form of a circle or more complex form. No general cause of crop circles has been identified although various natural and unorthodox explanations have been put forward; many are known to have been hoaxes.
crop-over a West Indian celebration marking the end of the sugar-cane harvest.

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Crop

Crop

the product or yield of anything growing; something resembling a crop; the offspring of animals and birds.

Examples: crop of beardless youths, 1830; of corn, 1440; of crystals; of petty discussions, 1862; of geese, 1825; of goose pimples; of lambs, 1825; of lies; of logs, 1879; of turkeys, 1825; of ulcers; of wheat, 1530.

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crop

crop2 crop-eared of a Roundhead in the English Civil War, having the hair cut very short; the term was probably intended by their opponents to associate them with those whose ears had been cut off as a punishment.

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crop

crop, crope. Gothic knop of sculptured unfolding leaf-like forms surmounting a finial, gable, spire, etc. A more rounded, less leafy, ball-like finial is a pommel.

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crop

crop A thin-walled extension of the oesophagus of a bird or insect, used for food storage. It is particularly well developed in grain-eating birds.

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crop

cropatop, bop, chop, clop, cop, crop, dop, drop, Dunlop, estop, flop, fop, glop, hop, intercrop, knop, kop, lop, mop, op, plop, pop, prop, screw-top, shop, slop, sop, stop, strop, swap, tiptop, top, underprop, whop, wop •co-op • bebop • sweatshop • carhop •hedgehop • bellhop • hiphop • flipflop •clip-clop • bellyflop • megaflop •gigaflop • teraflop • rollmop • coin-op •lollipop • backdrop • airdrop •sharecrop • namedrop • raindrop •eavesdrop • Ribbentrop • Winthrop •agitprop • outcrop • snowdrop •stonecrop • turboprop • dewdrop •gumdrop • teardrop • malaprop •Aesop • sweetsop • milksop •pawnshop • window-shop • toyshop •bookshop, cookshop •barbershop • workshop • ragtop •blacktop • tanktop • laptop • backstop •flat-top • hardtop • palmtop • desktop •tabletop • maintop • treetop • hilltop •whistle-stop • ripstop • longstop •foretop • doorstop • shortstop •screwtop • rooftop • worktop

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Crops

Crops

Hunting and gathering; crops obtained from unmanaged ecosystems

Plants

Terrestrial animals

Aquatic animals

Agriculture; crops from managed ecosystems

Agricultural plants

Agricultural animals

Aquaculture

Agroforestry

Resources

Crops are any organisms that humans utilize as a source of food, materials, or energy. Crops may be utilized for subsistence purposes, to barter for other goods, or to sell for a cash profit. They may be harvested from wild ecosystems, or they may be husbanded and managed, as occurs with domesticated species in agriculture. As of the 2000s, farming of crops is performed by over 40% of the worlds people. However, less than 5% of the gross world product comes from the production of agricultural products. Due to advanced technology and scientific methods, one farmer in a developed country such as the United States, in the twenty-first century, produces enough food to feed over 130 people. One hundred years earlier, that same farmer produced only enough food to feed fewer than three people.

In general, the purpose of management is to increase the amount of crop productivity that is available for use by humans. There is, however, a continuum in the intensity of crop-management systems. Species cultivated in agriculture are subjected to relatively intensive management systems. However, essentially wild, free-ranging species may also be managed to some degree. This occurs, for example, in forestry and in the management of ocean fisheries and certain species of hunted animals. Most crops are plant species, but animals and microorganisms (e.g., yeast) can also be crops.

In general, unmanaged, free-ranging crops are little modified genetically or morphologically (in form) from their non-crop ancestors. However, modern, domesticated crops that are intensively managed are remarkably different from their wild ancestors. In some cases a non-domesticated variety of the species no longer exists.

Hunting and gathering; crops obtained from unmanaged ecosystems

Human beings can only be sustained by utilizing other species as sources of food, material, and energy. Humans have thus always had an absolute requirement for the goods and services provided by other species, and this will always be the case. Although direct genetic modification has in the last few years been added (controversially) to artificial selection as a technique for adjusting plant and animal species to human needs, there is no prospect of a time when technology will make it possible to meet human needs by applying energy directly to raw materials. Humans have always needed and always will need to harvest other living things.

Prior to the discovery of the first agricultural techniques about 9, 000 to 11, 000 years ago, almost all human societies were sustained by gathering edible or otherwise useful products of wild plants, and by hunting wild animals. The plant foods that were gathered as crops by these early peoples included starchy tubers, fruits, and seeds. Other plants were harvested as sources of fuel or to provide materials such as wood and bark for the construction of shelters, canoes, and other tools or weapons. Animals, meanwhile, were hunted for their meat, hide, and bones. Prior to the development of agriculturethe breeding and deliberate nurturing of useful plants and animalsthese activities were undertaken in essentially natural ecosystemsecosystems not intensively modified by the hunting and gathering activities of people.

Humans have been rather eclectic in their choice of crops, selecting a wide range of useful species of plants, animals, and microorganisms from among the vast diversity of species available in most places or regions. Humans are considered omnivorous, because they feed at all levels of ecological food webs: on plants, animals, and other types of organisms, both living and dead.

Human societies that subsist only by the hunting and gathering of wild crops are now virtually extinct. However, modern human societies continue to obtain important plant and animal crops from essentially unmanaged ecosystems.

Plants

Among plant crops that humans continue to obtain from natural ecosystems, trees are among the most notable. In the parlance of forestry, the terms virgin and primary are used to refer to older, natural forests from which wild, unmanaged trees have not yet been harvested by humans. Secondary forests have sustained at least one intensive harvest of their resource of trees in the past, and have since grown back. In general, the ecological characteristics of secondary forests are quite different from those of the more natural, primary forests that may have once occurred on the same site.

Trees have always been an important crop for humans, being useful as sources of fuel, food (edible fruits and nuts), and wood for tools, structures, furniture, paper, and vehicles (boats, wagons, etc.). Even today, trees harvested from natural forests are important crops in most countries. Tree biomass is an essential source of energy for cooking and space heating for more than one-half of the worlds people, almost all of whom live in relatively poor, tropical countries. Trees are also an important crop for people living in richer countries, mostly as a source of lumber for the construction of buildings and furniture and as a source of pulpwood for paper manufacture.

In many places, the primary natural forest has been depleted by the cutting of trees, which has often been followed by conversion of the land to agriculture and urban land-uses. This pattern of forest loss has been common in North America, Europe, and elsewhere. To compensate to some degree for the loss of natural forests in those regions, efforts have been made to establish managed forests, so that tree crops will continue to be available.

Trees are not the only plant crops gathered from wild, unmanaged ecosystems. In particular, people who live a subsistence lifestyle in tropical forests continue to obtain much of their food, medicine, and materials from wild plants, usually in combination with hunting and subsistence agriculture. Even in North America, small crops of a few wild food plants continue to be gathered. Some examples include harvests of wild rice (Zizania aquatica ), strawberry (Fragaria virginiana ), low-bush blueberry (Vaccinium angustifolium ), and fiddleheads (from the ostrich fern, Matteucia struthiopteris ). Other minor wild crops include various species of edible mushrooms and marine algae.

Terrestrial animals

Wild animals have always been an important source of food and useful materials for humans. Most people who live in rural areas in poorer countries supplement their diet with meat obtained by hunting wild animals. Hunting is also popular as a sport among many rural people in wealthier countries. For example, each year in North America millions of deer are killed by hunters as food and a source of hide, especially white-tailed deer (Odocoileus virginianus ), mule deer (O. hemionus ), and elk (Cervus canadensis ). There are also large hunts of upland game birds, such as ruffled grouse (Bonasa umbellus ) and of wild ducks and geese, especially the mallard (Anas platyrhynchos ), Canada goose or honker (Branta canadensis ), and snow goose (Chen hyperboreus ).

Aquatic animals

Aquatic animals have also provided important wild-meat crops for people living in places where there is access to the natural bounties of streams, rivers, lakes, and marine shores. Important food crops harvested from freshwater ecosystems of North America include species of salmon, trout, and other fish, as well as crayfish, freshwater mussels, and other invertebrates. Most of the modern marine fisheries also rely on harvesting the productivity of unmanaged populations of fish, invertebrates (e.g., shellfish), seals, and whales as wild crops.

Agriculture; crops from managed ecosystems

As considered here, agricultural crops are managed relatively intensively for the sustained productivity of food and materials useful to humans. In this sense, agricultural systems can involve the cultivation of plants and livestock on farms, as well as the cultivation of fish and invertebrates in aquaculture and the growing of trees in agroforestry plantations.

Agricultural systems can vary tremendously in the intensity of their management practices. For example, species of terrestrial crop plants may be grown in mixed populations, a system known as polyculture. These systems are often not weeded or fertilized intensively. Mixed-cropping systems are common in non-industrial agriculture, for example, in subsistence agriculture in many tropical countries.

In contrast, some monocultural systems in agriculture attempt to grow crops in single-species populations. Such intensively managed systems usually rely heavily on the use of fertilizers, irrigation, and pesticides such as insecticides, herbicides, and fungicides. Of course, heavy, sophisticated, energy-requiring machinery is also required in intensive agricultural systems to plow the land, apply agrochemicals, and harvest the crops. The intensive-management techniques are used in order to substantially increase the productivity of the species of crop plants. However, these gains are expensive in of both terms money and environmental damage. The U.S. Environmental Protection Agency (EPA) estimates that pollution from agricultural runoffsediment, animal wastes, pesticides, salts, and nutrientsaccount for (on average) 70% of the river miles in the United States that are impaired by pollution; 49% of the impaired freshwater lake acreage; and 27% of the impaired square miles of marine estuary (inlets where rivers mingle with the ocean). According to the U.S. Department of Agriculture, an average of 11, 600 lb (5, 270 kg) of soil is being eroded from every acre of cultivated U.S. cropland; even this is a notable improvement over soil-loss rates of 25 years ago. Soil-loss rates are even higher in poorer parts of the world.

Agricultural plants

Hundreds of species of plants are cultivated by humans under managed agricultural conditions. However, most of these species are tropical crops of relatively minor importanceminor in terms of their contribution to the global production of all agricultural plants. In fact, a small number of plant species contribute disproportionately to the global harvest of plant crops in agricultural systems. Ranked in order of their annual production, according to the United Nations Food and Agricultural Organization, the worlds ten most-produced food crops are: sugar cane, maize or corn, wheat, rice, potatoes, sugar beets, soybeans, palm fruit oil, barley, and tomatoes. Sugar cane leads all crops with about 1.459 billion short tons [where one short ton equals 2, 000 pounds] (1.324 billion metric tons) produced in 2004, and maize and corn coming in at second place with about 0.795 billion short tons (0.721 billion metric tons).

Some care should be taken in interpreting these data in terms of the yield of actual foodstuffs. The production data for sugar cane, for example, reflect the entire harvested plant, and not just the refined sugar that is the major economic product of this crop. In contrast, the data for wheat and other grain crops reflect the actual harvest of seeds, which are much more useful nutritionally, pound for pound, than whole sugar cane (or even refined sugar).

Most agricultural crops are managed as annual plants, meaning that they are cultivated over a cycle of one year or less, with a single rotation involving sowing, growth, and harvesting. This is true of all the grains and legumes and most vegetables. Other agricultural species are managed as perennial crops, which are capable of yielding crops on a sustained basis once established. This is typically the manner in which tree-fruit crops such as oranges are managed and harvested, as are certain tropical species such as oil-palm (Elaeis guineensis ) and para rubber (Hevea brasiliensis ).

Some extremely valuable crops are not utilized for food, raw material, or energy. Instead, these crops are used for the production of important medicines, as is the case of the rosy periwinkle (Catharantus roseus ), which produces several chemicals that are extremely useful in treatment of certain types of cancers. Other crops are used to produce very profitable but illegal drugs. Examples of these sorts of crops include marijuana (Cannabis sativa ), cocaine (from Erythroxylon coca ), and the opium poppy (Papaver somniferum ).

Agricultural animals

Enormous numbers of domesticated animals are cultivated by people as food crops. In many cases, the animals are used to continuously produce some edible product that can be harvested without killing them. For example, milk can be collected daily from various species of mammals, including cows, goats, sheep, horses, and camels. Similarly, chickens can produce eggs regularly. All of the above animals, plus many other domesticated species, are also routinely slaughtered for their meat.

The populations of some of these domesticated animals are very large. In addition to approximately 6.5 billion people (as of November 2006), the world today supports over 1.7 billion sheep and goats (Ovis aries and Capra hircus ), 1.3 billion cows (Bos taurus and B. indica ), 0.9 billion pigs (Sus scrofa ), and 0.3 billion horses, camels, and water buffalo (Equus caballus, Camelus dromedarius, and Bubalus bubalis ). In addition, there are about 10 to 11 billion domestic fowl, most of which are chickens (Gallus gallus ).

These populations of domesticated animals are much larger than those maintained by any wild large animals. For example, no wild mammals of a comparable size to those listed above have populations greater than about 50 million, which is equivalent to less than 1% of a typical domestic-livestock population.

Aquaculture

Aquaculture is an aquatic analogue of terrestrial agriculture. In aquaculture, animals or seaweeds are cultivated under controlled, sometimes intensively managed conditions, to be eventually harvested as food for humans. Increasingly, aquaculture is being viewed as an alternative to the exploitation of wild stocks of aquatic animals and seaweeds.

The best opportunities to develop aquaculture occur in inland regions where there are many ponds and small lakes, and in protected coastal locations on the oceans. Freshwater aquaculture is especially important in Asia, where various species of fish are cultivated in artificial ponds, especially carp (Cyprinus carpio ) and tilapia (Aureochromis niloticus ). In North America, various species of fish are grown in inland aquaculture in small ponds, most commonly rainbow trout (Salmo gairdneri ) and catfish (Ictalurus spp.).

Aquaculture is also becoming increasingly important along sheltered marine coastlines in many parts of the world. In the tropics, extensive areas of mangrove forest are being converted into shallow ponds for the cultivation of prawns (Penaeus monodon ) and giant prawns (Macrobrachium rosenbergii ). Negative impacts of this practice include the destruction of the mangrove forests themselves (and of other coastal environ-ments)already endangered by other types of coastal developmentand the nonselective mass harvesting of fish and other sea life supply feed for the shrimp. In North America and Western Europe, the cultivation of Atlantic salmon (Salmo salar ) has become an important industry in recent decades, using pens floating in shallow, coastal embayments, and sometimes in the open ocean. Research is being undertaken into the potential domestication of other marine crops, including species of fish and seaweeds that are now harvested from unmanaged ecosystems.

Agroforestry

Agroforestry is a forest-related analogue of agriculture. In agroforestry, trees are usually cultivated under intensively managed conditions, to eventually be harvested as a source of lumber, pulpwood, or fuel

KEY TERMS

Agroforestry The cultivation of crops of trees under intensively managed conditions, usually in single-species plantations.

Domestic This refers to crop species that live in an intimate association with humans, often with a significant co-dependence between the species.

Monoculture The cultivation of an exclusive population of a particular species of crop.

Polyculture The agricultural cultivation of mixed populations of different crop species.

wood. In many regions, this sort of intensive forestry is being developed as a high-yield alternative to the harvesting of natural forests.

The most important trees grown in plantations in the temperate zones as agroforestry crops are species of pines (Pinus spp.), spruces (Picea spp.), larch (Larix spp.), and poplar (Populus spp.). Depending on the species, site conditions, and economic product that is desired, intensively managed plantations of these trees can be harvested after a growth period of only 10 to 40 60 years, compared with 60 to more than 100 years for natural, unmanaged forest in the same regions. Increasingly, these temperate species of trees are being selectively bred and hybridized to develop high-yield varieties, in parallel with the ways in which food crops have been culturally selected from their wild progenitors during the process of domestication.

Unfortunately, there is a downside to such practices. Large monocultures of genetically uniform crops, whether of trees, corn, or any other plant, are by their very nature more vulnerable to climate variation, pests, and disease than are more diverse plant communities. The large-scale replacement of managed natural forests with uniform high-yield varieties has led to the appearance of pseudoforests in places such as Sweden and parts of the United States: large tracts of land covered by uniform specimens of one species of tree, supporting little wildlife. Habitat loss from monocultural tree cropping has placed over one thousand forest-dwelling species on the endangered list in Sweden alone.

Fast-growing, high-yield species of trees are also being grown under agroforestry systems in the tropics, for use locally as a source of fuel wood, and also for animal fodder, lumber, and pulpwood. Various tree species are being grown in this way, including species of pine, eucalyptus (Eucalyptus spp.), she-oak (Casuarina spp.), and tree-legumes (such as Albizia procera and Leucaena leucocephala ). Plantations of slower-growing tropical hardwoods are also being established for the production of high-value lumber, for example, of mahogany (Swietenia mahogani ) and teak (Tectona grandis ).

See also Livestock.

Resources

BOOKS

Clements, David, and Anil Shrestha, eds. New Dimensions in Agroecology. Binghamton, NY: Food Products Press, 2004.

Hatfield, Jerry L, ed. The Farmers Decision: Balancing Economic Agriculture Production with Environmental Quality. Ankeny, IA: Soil and Water Conservation Society, 2005.

Krishna, K.R., ed. Soil Fertility and Crop Production. Enfield, NH: Science Publishers, 2002.

Ondersteiin, Christien J.M., ed. Quantifying the Agri-food Supply Chain. Dordrecht, Germany: Springer, 2006.

Taji, Acram, and John Reganold, eds. Organic Agriculture: A Global Perspective. Collingwood, Canada: CSIRO Publishing, 2006.

OTHER

U.S. Department of Agriculture.National Resources Inventory.Natural Resources Conservation Service. August 24, 2006. <http://www.nrcs.usda.gov/technical/NRI/> (assessed November 12, 2006).

Bill Freedman

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Crops

Crops

Crops are any organisms that humans utilize as a source of food, materials, or energy . Crops may be utilized for subsistence purposes, to barter for other goods, or to sell for a cash profit. They may be harvested from wild ecosystems, or they may be husbanded and managed, as occurs with domesticated species in agriculture.

In general, the purpose of management is to increase the amount of crop productivity that is available for use by humans. There is, however, a continuum in the intensity of crop-management systems. Species cultivated in agriculture are subjected to relatively intensive management systems. However, essentially wild, free-ranging species may also be managed to some degree. This occurs, for example, in forestry and in the management of ocean fisheries and certain species of hunted animals. Most crops are plant species, but animals and microorganisms (e.g., yeast ) can also be crops.

In general, unmanaged, free-ranging crops are little modified genetically or morphologically (in form) from their non-crop ancestors. However, modern, domesticated crops that are intensively managed are remarkably different from their wild ancestors. In some cases a nondomesticated variety of the species no longer exists.


Hunting and gathering; crops obtained from unmanaged ecosystems

Human beings can only be sustained by utilizing other species as sources of food, material, and energy. Humans have thus always had an absolute requirement for the goods and services provided by other species, and this will always be the case. Although direct genetic modification has in the last few years been added (controversially) to artificial selection as a technique for adjusting plant and animal species to our needs, there is no prospect of a time when technology will make it possible to meet our needs by applying energy directly to raw materials. Humans have always needed and always will need to harvest other living things.

Prior to the discovery of the first agricultural techniques about 9,000–11,000 years ago, almost all human societies were sustained by gathering edible or otherwise useful products of wild plants, and by hunting wild animals. The plant foods that were gathered as crops by these early peoples included starchy tubers, fruits , and seeds . Other plants were harvested as sources of fuel or to provide materials such as wood and bark for the construction of shelters, canoes, and other tools or weapons. Animals, meanwhile, were hunted for their meat, hide, and bones. Prior to the development of agriculture—the breeding and deliberate nurturing of useful plants and animals—these activities were undertaken in essentially natural ecosystems—ecosystems not intensively modified by the hunting and gathering activities of people.

Humans have been rather eclectic in their choice of crops, selecting a wide range of useful species of plants, animals, and microorganisms from among the vast diversity of species available in most places or regions. Humans are considered omnivorous, because they feed at all levels of ecological food webs: on plants, animals, and other types of organisms, both living and dead.

Human societies that subsist only by the hunting and gathering of wild crops are now virtually extinct. However, modern human societies continue to obtain important plant and animal crops from essentially unmanaged ecosystems.


Plants

Among plant crops that humans continue to obtain from natural ecosystems, trees are among the most no-table. In the parlance of forestry, the terms "virgin" and "primary" are used to refer to older, natural forests from which wild, unmanaged trees have not yet been harvested by humans. "Secondary" forests have sustained at least one intensive harvest of their resource of trees in the past, and have since grown back. In general, the ecological characteristics of secondary forests are quite different from those of the more natural, primary forests that may have once occurred on the same site.

Trees have always been an important crop for humans, being useful as sources of fuel, food (edible fruits and nuts), and wood for tools, structures, furniture, paper , and vehicles (boats, wagons, etc.). Even today, trees harvested from natural forests are important crops in most countries. Tree biomass is an essential source of energy for cooking and space heating for more than one-half of the world's people, almost all of whom live in relatively poor, tropical countries. Trees are also an important crop for people living in richer countries, mostly as a source of lumber for the construction of buildings and furniture and as a source of pulpwood for paper manufacture.

In many places, the primary natural forest has been depleted by the cutting of trees, which has often been followed by conversion of the land to agriculture and urban land-uses. This pattern of forest loss has been common in North America , Europe , and elsewhere. To compensate to some degree for the loss of natural forests in those regions, efforts have been made to establish managed forests, so that tree crops will continue to be available.

Trees are not the only plant crops gathered from wild, unmanaged ecosystems. In particular, people who live a subsistence lifestyle in tropical forests continue to obtain much of their food, medicine, and materials from wild plants, usually in combination with hunting and subsistence agriculture. Even in North America, small crops of a few wild food plants continue to be gathered. Some examples include harvests of wild rice (Zizania aquatica), strawberry (Fragaria virginiana), low-bush blueberry (Vaccinium angustifolium), and fiddleheads (from the ostrich fern, Matteucia struthiopteris). Other minor wild crops include various species of edible mushrooms and marine algae .


Terrestrial animals

Wild animals have always been an important source of food and useful materials for humans. Most people who live in rural areas in poorer countries supplement their diet with meat obtained by hunting wild animals. Hunting is also popular as a sport among many rural people in wealthier countries. For example, each year in North America millions of deer are killed by hunters as food and a source of hide, especially white-tailed deer (Odocoileus virginianus), mule deer (O. hemionus), and elk (Cervus canadensis). There are also large hunts of upland game birds , such as ruffled grouse (Bonasa umbellus) and of wild ducks and geese , especially the mallard (Anas platyrhynchos), Canada goose or honker (Branta canadensis), and snow goose (Chen hyperboreus).


Aquatic animals

Aquatic animals have also provided important wild-meat crops for people living in places where there is access to the natural bounties of streams, rivers , lakes, and marine shores. Important food crops harvested from freshwater ecosystems of North America include species of salmon , trout, and other fish , as well as crayfish , freshwater mussels, and other invertebrates . Most of the modern marine fisheries also rely on harvesting the productivity of unmanaged populations of fish, invertebrates (e.g., shellfish), seals , and whales as wild crops.


Agriculture; crops from managed ecosystems

As considered here, agricultural crops are managed relatively intensively for the sustained productivity of food and materials useful to humans. In this sense, agricultural systems can involve the cultivation of plants and livestock on farms, as well as the cultivation of fish and invertebrates in aquaculture and the growing of trees in agroforestry plantations.

Agricultural systems can vary tremendously in the intensity of their management practices. For example, species of terrestrial crop plants may be grown in mixed populations, a system known as polyculture. These systems are often not weeded or fertilized very intensively. Mixed-cropping systems are common in nonindustrial agriculture, for example, in subsistence agriculture in many tropical countries.

In contrast, some monocultural systems in agriculture attempt to grow crops in single-species populations. Such intensively managed systems usually rely heavily on the use of fertilizers , irrigation , and pesticides such as insecticides , herbicides , and fungicides. Of course, heavy, sophisticated, energy-requiring machinery is also required in intensive agricultural systems to plow the land, apply agrochemicals , and harvest the crops. The intensive-management techniques are used in order to substantially increase the productivity of the species of crop plants. However, these gains are expensive in of both terms money and environmental damage. The U.S. Environmental Protection Agency estimates that pollution from agricultural runoff—sediment, animal wastes, pesticides, salts, and nutrients—account for 70% of the river miles in the United States that are impaired by pollution, 49% of the impaired fresh-water lake acreage, and 27% of the impaired square miles of marine estuary (inlets where rivers mingle with the ocean). According to the U.S. Department of Agriculture, an average of 11,600 lbs (5270 kg) of soil is being eroded from every acre of cultivated U.S. cropland; even this is a no-table improvement over soil-loss rates of 20 years ago. Soil-loss rates are even higher in poorer parts of the world.


Agricultural plants

Hundreds of species of plants are cultivated by humans under managed agricultural conditions. However, most of these species are tropical crops of relatively minor importance—minor in terms of their contribution to the global production of all agricultural plants. In fact, a small number of plant species contribute disproportionately to the global harvest of plant crops in agricultural systems. Ranked in order of their annual production (measured in millions of metric tons per year), the world's 15 most-important food crops are: 1) sugar cane (740 million tonnes per year); 2) wheat (390); 3) rice (370); 4) corn or maize (350); 5) white potato (300); 6) sugar beet (260); 7) barley (180); 8) sweet potato (150); 9) cassava (110); 10) soybean (80); 11) wine grapes (60); 12) tomato (45); 13) banana (40); 14) beans and peas (40); 15) orange (33).

Some care should be taken in interpreting these data in terms of the yield of actual foodstuffs. The production data for sugar cane, for example, reflect the entire harvested plant, and not just the refined sugar that is the major economic product of this crop. In contrast, the data for wheat and other grain crops reflect the actual harvest of seeds, which are much more useful nutritionally, pound for pound, than whole sugar cane (or even refined sugar).

Most agricultural crops are managed as annual plants, meaning that they are cultivated over a cycle of one year or less, with a single rotation involving sowing, growth, and harvesting. This is true of all the grains and legumes and most vegetables . Other agricultural species are managed as perennial crops, which are capable of yielding crops on a sustained basis once established. This is typically the manner in which tree-fruit crops such as oranges are managed and harvested, as are certain tropical species such as oil-palm (Elaeis guineensis) and para rubber (Hevea brasiliensis).

Some extremely valuable crops are not utilized for food, raw material, or energy. Instead, these crops are used for the production of important medicines, as is the case of the rosy periwinkle (Catharantus roseus), which produces several chemicals that are extremely useful in treatment of certain types of cancers. Other crops are used to produce very profitable but illegal drugs. Examples of these sorts of crops include marijuana (Cannabis sativa), cocaine (from Erythroxylon coca), and the opium poppy (Papaver somniferum).


Agricultural animals

Enormous numbers of domesticated animals are cultivated by people as food crops. In many cases the animals are used to continuously produce some edible product that can be harvested without killing them. For example, milk can be collected daily from various species of mammals , including cows, goats , sheep , horses , andcamels . Similarly, chickens can produce eggs regularly. All of the above animals, plus many other domesticated species, are also routinely slaughtered for their meat.

The populations of some of these domesticated animals are very large. In addition to approximately six billion people, the world today supports about 1.7 billion sheep and goats (Ovis aries and Capra hircus), 1.3 billion cows (Bos taurus and B. indica), 0.9 billion pigs (Sus scrofa), and 0.3 billion horses, camels, and water buffalo (Equus caballus, Camelus dromedarius, and Bubalus bubalis). In addition, there are about 10–11 billion domestic fowl, most of which are chickens (Gallus gallus).

These populations of domesticated animals are much larger than those maintained by any wild large animals. For example, no wild mammals of a comparable size to those listed above have populations greater than about 50 million, which is equivalent to less than 1% of a typical domestic-livestock population.


Aquaculture

Aquaculture is an aquatic analogue of terrestrial agriculture. In aquaculture, animals or seaweeds are cultivated under controlled, sometimes intensively managed conditions, to be eventually harvested as food for humans. Increasingly, aquaculture is being viewed as an alternative to the exploitation of wild stocks of aquatic animals and seaweeds.

The best opportunities to develop aquaculture occur in inland regions where there are many ponds and small lakes, and in protected coastal locations on the oceans. Fresh-water aquaculture is especially important in Asia , where various species of fish are cultivated in artificial ponds, especially carp (Cyprinus carpio) and tilapia (Aureochromis niloticus). In North America, various species of fish are grown in inland aquaculture in small ponds, most commonly rainbow trout (Salmo gairdneri) and catfish (Ictalurus spp.).

Aquaculture is also becoming increasingly important along sheltered marine coastlines in many parts of the world. In the tropics, extensive areas of mangrove forest are being converted into shallow ponds for the cultivation of prawns (Penaeus monodon) and giant prawns (Macrobrachium rosenbergii). Negative impacts of this practice include the destruction of the mangrove forests themselves (and of other coastal environments)—already endangered by other types of coastal development—and the nonselective mass harvesting of fish and other sea life supply feed for the shrimp . In North America and Western Europe, the cultivation of Atlantic salmon (Salmo salar) has become an important industry in recent decades, using pens floating in shallow, coastal embayments, and sometimes in the open ocean. Research is being undertaken into the potential domestication of other marine crops, including species of fish and seaweeds that are now harvested from unmanaged ecosystems.

Agroforestry

Agroforestry is a forest-related analogue of agriculture. In agroforestry, trees are usually cultivated under intensively managed conditions, to eventually be harvested as a source of lumber, pulpwood, or fuelwood. In many regions, this sort of intensive forestry is being developed as a high-yield alternative to the harvesting of natural forests.

The most important trees grown in plantations in the temperate zones as agroforestry crops are species of pines (Pinus spp.), spruces (Picea spp.), larch (Larix spp.), and poplar (Populus spp.). Depending on the species, site conditions, and economic product that is desired, intensively managed plantations of these trees can be harvested after a growth period of only 10 to 40–60 years, compared with 60 to more than 100 years for natural, unmanaged forest in the same regions. Increasingly, these temperate species of trees are being selectively bred and hybridized to develop high-yield varieties, in parallel with the ways in which food crops have been culturally selected from their wild progenitors during the process of domestication.

Unfortunately, there is a downside to such practices. Large monocultures of genetically uniform crops, whether of trees, corn, or any other plant, are by their very nature more vulnerable to climate variation, pests , and disease than are more diverse plant communities. The large-scale replacement of managed natural forests with uniform high-yield varieties has led to the appearance of pseudoforests in places such as Sweden and parts of the United States: large tracts of land covered by uniform specimens of one species of tree, supporting little wildlife . Habitat loss from monocultural tree cropping has placed over a thousand forest-dwelling species on the endangered list in Sweden alone.

Fast-growing, high-yield species of trees are also being grown under agroforestry systems in the tropics, for use locally as a source of fuelwood, and also for animal fodder, lumber, and pulpwood. Various tree species are being grown in this way, including species of pine, eucalyptus (Eucalyptus spp.), she-oak (Casuarina spp.), and tree-legumes (such as Albizia procera and Leucaena leucocephala). Plantations of slower-growing tropical hardwoods are also being established for the production of high-value lumber, for example, of mahogany (Swietenia mahogani) and teak (Tectona grandis).

See also Livestock.

Resources

books

Conger, R. H. M., and G. D. Hill. Agricultural Plants. 2nd ed. Cambridge, U.K.: Cambridge University Press, 1991.

Freedman, B. Environmental Ecology. 2nd ed. San Diego Academic Press, 1994.

Klein, R. M. The Green World. An Introduction to Plants andPeople. New York: Harper & Row, 1987.

other

U.S. Department of Agriculture. "1997 National Resources Inventory." Natural Resources Conservation Service. December 2000 [cited October 18, 2002]. <http://www.nrcs.usda.gov/technical/NRI/>.

U.S. Environmental Protection Agency. "National Management Measures to Control Nonpoint Source Pollution from Agriculture." 2000 [cited October 18, 2002]. <http://www.nrcs.usda.gov/technical/NRI/1997/summary_report/body.html#revised>.


Bill Freedman

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Agroforestry

—The cultivation of crops of trees under intensively managed conditions, usually in single-species plantations.

Domestic

—This refers to crop species that live in an intimate association with humans, often with a significant co-dependence between the species.

Monoculture

—The cultivation of an exclusive population of a particular species of crop.

Polyculture

—The agricultural cultivation of mixed populations of different crop species.

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