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From Citizendium, the Citizens' Compendium
Agriculture has provided food for mankind since the time people moved from hunting and gathering to systematically growing crops some 10,000 years ago.
See Agriculture for current practice.
Origins of agriculture
Pinpointing the absolute beginnings of agriculture is problematic, because the transition from purely hunter-gatherer societies, in some areas, began many thousands of years before the invention of writing. Nonetheless, Archaeobotanists/Paleoethnobotanists have traced the selection and cultivation of specific food plant characteristics, such as a semi-tough rachis and larger seeds, to just after the Younger Dryas (about 9,500 BCE) in the early Holocene in the Levant region of the Fertile Crescent. Limited anthropological and archaeological evidence both indicate a grain-grinding culture farming along the Nile in the 10th millennium BCE using the world's earliest known type of sickle blades. There is even earlier evidence for conscious cultivation and seasonal harvest: grains of rye with domestic traits have been recovered from Epi-Palaeolithic (10,000+ BCE) contexts at Abu Hureyra in Syria, but this appears to be a localised phenomenon resulting from cultivation of stands of wild rye, rather than a definitive step towards domestication. In these contexts lie the origins of the eight so-called founder crops of agriculture: first emmer and einkorn wheat, then hulled barley, peas, lentils, bitter vetch, chick peas ,and flax. These eight crops occur more or less simultaneously on PPNB sites in this region, although the consensus is that wheat was the first to be sown and harvested on a significant scale.
By 7000 BCE sowing and harvesting reached Mesopotamia and there, in the super fertile soil just north of the Persian Gulf, Sumerian ingenuity systematized it and scaled it up. By 6000 BCE farming was entrenched on the banks of the Nile River, and by 5000 BCE it spread to Greece on one side and to India on the other. About this time, agriculture was developed independently in China, with rice rather than wheat as the primary crop. Maize was first domesticated from teosinte in the Americas around 3000-2700 BC. Somewhat surprisingly, systematic farming, principally of emmer and einkorn, reached northwestern Europe not via the Levant-to-Southern Europe but from central Asia by ca. 4,500 BCE. 
The reasons for the earliest introduction of farming may have included climate change, but possibly there were also social reasons (e.g. accumulation of food surplus for competitive gift-giving). Most certainly there was a gradual transition from hunter-gatherer to agricultural economies after a lengthy period when some crops were deliberately planted and other foods were gathered from the wild. Although localised climate change is the favoured explanation for the origins of agriculture in the Levant, the fact that farming was "invented" at least three times, possibly more, suggests that social reasons may have been instrumental.
Full dependency on domestic crops and animals did not occur until the Bronze Age, by which time wild resources contributed a nutritionally insignificant component to the diet. If the operative definition of agriculture includes large scale intensive cultivation of land, mono-cropping, organized irrigation, and use of a specialized labour force, the title "inventors of agriculture" would fall to the Sumerians, starting c. 5500 BCE. Intensive farming allows a much greater density of population than can be supported by hunting and gathering and allows for the accumulation of excess product to keep for winter use or to sell for profit. The ability of farmers to feed large numbers of people whose activities have nothing to do with material production was the crucial factor in the rise of standing armies. The agriculturalism of the Sumerians allowed them to embark on an unprecedented territorial expansion, making them the first empire builders. Not long after, the Egyptians, powered by effective farming of the Nile valley, achieved a population density from which enough warriors could be drawn for a territorial expansion more than tripling the Sumerian empire in area .
Early developments in Mesoamerica
Farmers of several South and Central American societies practiced "raised-field" agriculture up to 4,000 years ago. Raised fields are what their name implies: cropland built up with soil and vegetative material to mitigate the negative effects of high water tables and periodic flooding.
Scholars of raised-field agriculture generally concur that the Mayan people of the lowlands of southern Yucatan in Mexico, parts of Belize and Guatemela, developed the system, whose adoption by other agriculture-based societies then proceeded northward. By the first century, raised-field agriculture was the modus operandi of food production in Teotihuacan, near present-day Mexico City. By the sixteenthth century, the elevated rectangular fields, called chinampas, supplied grains, vegetables, and fruits to a quarter million Aztecs in Teotihuacan.
The chinampas system was still used in Teotihuacan in the late nineteenthth century. Functional examples of the system persist today in Xochimilco in Mexico City and southwest Tlaxcala State, Mexico. Similar systems flourished in present-day Peru, Bolivia, and Ecuador well before Columbus' arrival in the New World. Popular use of the system began to decline at the time of the Spanish Conquest, and rapidly disintegrated over the next twenty years. Factors that influenced the decline include salinization, population pressures, inequitable access to technologies which affect labor use, such as plows. In some areas the Spanish completely destroyed the systems, breaking up the waterways and plowing into the chinampas. Recent studies are reviving interest in the chinampas system as a way to sustain food production in specific ecological conditions with minimal imported inputs.
To construct the chinampas system, the Aztecs removed and piled up aquatic vegetation and muck to create horticultural platforms flanked by waterways and drainage canals (zanjas). By dredging one vertical meter of canal debris every one to four years, farmers in Tlaxcala who employ the system today can add an estimated 1,000 kilogramme total N, 10 kilogramme P, and 120 kg K per hectare to their cropland. Trees such as willow and alder, which often grows in symbiosis with a nitrogen-fixing actinomycete (Frankia sp.), are planted around the islands' perimeters. The trees provide shade, increase diversity and anchor the soil in the wet environment reducing erosion.
A typical field measures 150 by 20 meters. The system's environment also provides habitat for fish and waterfowl. Today, alfalfa (originally brought over by the Spanish) is often grown for two to five years in a three-meter strip that runs lengthwise in a raised field. The alfalfa is usually followed by corn in rotation. Thus, every fifteen to twenty years, an entire raised field benefits from the nitrogen fixed by an alfalfa stand (from 30 to 300 kilogrammes N per hectare per year).
Some 200 kilometers east of Mexico City, another innovative agricultural system developed among the Aztecs as early as 1000 BCE. Operating at 2,200 meters above sea level, this system featured canals, terraces, and earthen water storage tanks. Certain aspects of the system remain functional today, more so than the chinampas which were constructed on what is today an urban area, while the cajetes were originally built in what remains a rural area. These include the funneling of rain runoff to a network of relatively small water tanks (cajetes) situated at the base of hillside terraces on cropland. The cajetes serve as catchments and compost pits for soil and organic debris carried by runoff water. The runoff is directed from cropland via the tank network. Nutrient-laden soil and decomposed debris is returned to the fields while trapped water percolates to recharge the water table. In the meantime, the tanks protect the terraces from structural damage due to runoff. The system's design reflects the concerns of its architects about intense rainfall events, a scenario that harbors the most potential damage to the tank network. Yet the most vital facet of the tank system is neither engineering nor agronomic, but social. All farmers who manage land within a given catchment area must agree to participate as needed to clean out the cajetes and replace the soil on the terraces, and to ensure that runoff from large storms is channelled from the crop area.
Another characteristic of the cajete system is its accent on plant diversity through intercropping, crop rotation, fallowing, and the maintenance of border areas. Fallowing is a means to restore soil fertility and suppress weed species. The border areas provide space for high- value plants such as fruit, fuel, and fodder trees, and medicinal species.
The trees that grow along field borders stabilize terraces, recycle soil nutrients, and serve as windbreaks, but more research is needed on the effects of many other border species on crops.
The Middle Ages owe much of its development to the advances made by the Muslims, as Islamic culture flowered while Europe and other Roman and Byzantine administered lands entered an extended period of societal stagnation. As early as the ninth century, a modern agricultural system became central to economic life and organization in the Arab caliphates. The great cities of the Near East, North Africa and Moorish Spain were supported by elaborate agricultural systems that included extensive irrigation based on expert knowledge of hydraulic principles. In later centuries, Persian Muslims became a radically active force, transmitting cultural elements including advanced agriculture into Turkic lands and western India. The Muslims introduced what was to become an agricultural revolution based on four key areas:
- Development of a sophisticated system of irrigation using machines such as norias (newly invented water raising machines), dams and reservoirs. With such technology they managed to greatly expand the exploitable land area.
- The adoption of a scientific approach to farming enabled them to improve farming techniques derived from the collection and collation of relevant information throughout the whole of the known world. Farming manuals were produced in every corner of the Muslim world detailing where, when and how to plant and grow various crops. Advanced scientific techniques allowed leaders like Ibn al-Baytar to introduce new crops and breeds and strains of livestock into areas where they were previously unknown.
- Incentives based on a new approach to land ownership and labourers' rights, combining the recognition of private ownership and the rewarding of cultivators with a harvest share commensurate with their efforts. Their counterparts in Europe struggled under a feudal system in which they were almost slaves (serfs) with little hope of improving their lot by hard work.
- The introduction of new and a variety of crops transforming private farming into a new global industry exported everywhere including Europe, where farming was mostly restricted to wheat strains obtained much earlier via central Asia. Spain received what she in turn transmitted to most Europe; all manner of agricultural and fruit-growing processes, together with a vast number of new plants, fruit and vegetables. These new crops included sugar cane, rice, citrus fruit, apricots, cotton, artichokes, aubergines, and saffron. Others, previously known, were developed further. Muslims also brought to that country lemons, oranges, cotton, almonds, figs and sub-tropical crops such as bananas and sugar cane were grown on the coastal parts of the country, many to be taken later to the Spanish colonies in the Americas. Also owing to the Muslim influence, a silk industry flourished, flax was cultivated and linen exported, and esparto grass, which grew wild in the more arid parts, was collected and turned into various articles.
Rennaisance to 1800
After 1492 the world's agricultural patterns were shuffled in the widespread exchange of plants and animals known as the Columbian Exchange. Crops and animals that were previously only known in the Old World were now transplanted to the New and vice versa. Perhaps most notably, the tomato became a favorite in European cuisine, with maize also widely grown, while certain wheat strains quickly took to western hemisphere soils and became a dietary staple even for native North, Central and South Americans. The potato became one of the major food crops of Europe.
see also Agriculture, history, U.S.
By the early 1800s agricultural practices, particularly careful selection of hardy strains and cultivars, had so improved that yield per land unit was many times that seen in the Middle Ages and before, especially in the largely virgin lands of North and South America.
20th century: Mechanization
With the rapid rise of mechanization in the twentieth century, with equipment pulled by gasoline-powered tractors, the demanding tasks of sowing, harvesting, and threshing could be performed with a speed and on a scale barely imaginable before. Breeding techniques such as artificial hybridization have yielded better yielding and more stress tolerant crops, and many new options for weed and pest management. These advances have led to efficiencies enabling certain modern farms in the United States, Argentina, Israel, Germany and a few other nations to output volumes of high quality produce per land unit at what may be the practical limit.
This high productivity per unit area has important positive ecological consequences as agricultural output has expanded to meet the needs of a growing world population. Since around 1960 there has been relatively little expansion of global arable land area, and farming output has largely kept pace with substantial inceased demand for food and feed because of introduction of better crop varieties and larger use of irrigation and fertilizer. This productivity boost has spared millions of hectares of forest and wilderness from conversion to agriculture, and is highly relevant to addressing the extra challeges of global agriculture posed by twenty-first century demands such as the biofuels ethanol and biodiesel, and manufacturing of polymers from renewable resources..
Main food crops
Corn (maize), wheat, rice, potatoes and soybeans are the main food crops, and each has undergone major advances in productivity. The potato provides more calories and more nutrients, more quickly, using less land and in a wider range of climates than any other plant.
In the 20th century, global wheat output expanded by about 5-fold, but until about 1955 most of this reflected increases in wheat crop area, with lesser (about 20%) increases in crop yields per unit area. After 1955 however, there was a dramatic ten-fold increase in the rate of wheat yield improvement per year, and this became the major factor allowing global wheat production to increase. Thus technological innovation and scientific crop management with synthetic nitrogen fertilizer, irrigation and wheat breeding were the main drivers of wheat output growth in the second half of the century. There were some significant decreases in wheat crop area, for instance in North America.
Soaring food prices
The long-term tendency toward lower food prices was reversed in 2006, as prices rose 50% to 200% across the world. Rice — the staple for billions of Asians — tripled in price in early 2008, reaching its highest price in 20 years, while supplies fell to their lowest level since the early 1980s; the global supply of wheat dipped to the lowest point in 50 years. Analysts point to short term factors such as the weather and the spike in oil prices, along with long-term factors such as price support programs in the European Union and U.S., diversion of corn into ethanol, and steadily growing demand in China and India for upscale foods. The U.N.'s World Food Program (WFP) calls this emergency a "silent tsunami" that could have dire consequences for more than 100 million of the world's poor in countries as varied as Somalia and North Korea. 
- ↑ See "A conversation with Christopher Ehret"
- ↑ See D. Price, ed. Europe's First Farmers (2000); D. Harris, ed. The Origins and Spread of Agriculture in Eurasia (1996).
- ↑ Robert C. Allen, "Agriculture and the Origins of the State in Ancient Egypt," Explorations in Economic History (1997) v34, 135–154, provides citations and discussion of the pre-history of the agriculture in Egypt]
- ↑ John Reader, Propitious Esculent: The Potato in World History (2008),
- ↑ Lloyd T. Evans, Feeding the Ten Billion: Plants and Population Growth. (1998); Anthony J. Trewavas, The Population/Biodiversity Paradox. Agricultural Efficiency to Save Wilderness, Plant Physiol, January 2001, Vol. 125, pp. 174-179
- ↑ See GA Slafer, and EH Satorre, Wheat: Ecology and Physiology of Yield Determination (1999)
- ↑ Vivienne Walt, "The World's Growing Food-Price Crisis," Time Feb. 27, 2008; Walt, "Food Prices: Hunger Strikes" Time, June 5, 2008