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Determining the origin of agriculture is problematic since it pre-dates writing. Some authorities insist localized farming took place more than 10,000 years ago, while others believe the earliest systematic plantings/harvestings took place no more than 7,000 years ago. The practice of agriculture is often used to distinguish the neolithic period from earlier parts of the stone age.
The first crops that humans domesticated included wheat, ( einkorn and emmer), and barley. It is clear that farming was invented at least twice, probably more often. Once in the Fertile Crescent, (some say by the Natufian culture others say by the Sumerians), once in East Asia (rice) and once in Central America (maize, squash). Most certainly there was a gradual transition from a hunter-gatherer economy to an agricultural one via a lengthy period when some crops were deliberately planted and other foods were gathered from the wild. The reasons for the earliest introduction of farming may have included climate change.
Farming allows a much greater density of population than can be supported by hunting and gathering. It also allows 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 food production was the crucial factor in the rise of standing armies.
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 in the New and vice versa.
In millions of metric tons, based on USDA estimates:
However, grazing grass and animal feed-crop production must exceed the total of those four crops.
Paddy rice is rice in its as-harvested state. Milled rice is rice after it is processed to remove the husk and to, sometimes, polish the kernel. California is the major US producer of rice but Thailand and Indonesia are the major producers in the world.
Domestication of plants is done in order to increase yield, improve disease resistance and drought tolerance, ease harvest and to improve the taste and nutritional value and many other characteristics. Centuries of careful selection and breeding have had enormous effects on the characteristics of crop plants. Plant breeders use greenhouses and other techniques to get as many as three generations of plants per year so that they can make improvements all the more quickly.
Plant selection and breeding in the 1920s and '30s improved pasture (grasses and clover) in New Zealand. Extensive radiation mutagenesis efforts (i.e. primitive genetic engineering) during the 1950s produced the modern commercial varieties of grains such as wheat, corn and barley.
For example, average yields of corn ( maize) in the USA have increased from around 2.5 tons per hectare (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001, primarily due to improvements in genetics. Similarly, worldwide average wheat yields have increased from less than 1 t/ha in 1900 to more than 2.5 t/ha in 1990. South American average wheat yields are around 2 t/ha, African under 1 t/ha, Egypt and Arabia up to 3.5 to 4 t/ha with irrigation. In contrast, the average wheat yield in countries such as France is over 8 t/ha. Higher yields are due to improvements in genetics, as well as use of intensive farming techniques (use of fertilizers, chemical pest control, growth control to avoid lodging).
[Conversion note: 1 bushel (q) of wheat = 60 pounds (lb) ≈ 27.215 kg. 1 bushel of corn = 56 pounds ≈ 25.401 kg]
Very recently, genetic engineering has begun to be employed in some parts of the world to speed up the selection and breeding process. The most widely used modification is a herbicide resistance gene that allows plants to tolerate exposure to glyphosate, which is used to control weeds in the crop. A less frequently used but more controversial modification causes the plant to produce a toxin to reduce damage from insects (c.f. Starlink).
There are specialty producers who raise less common types of livestock or plants.
Aquaculture, the farming of fish, shrimp, and algae, is closely associated with agriculture. Apiculture, the culture of bees, traditionally for honey—increasingly for crop pollination.See also : botany, List of domesticated plants, List of vegetables, List of herbs, List of fruit
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