Migration

Part 2 - Agriculture

Agriculture may have begun more than 50 000 years ago as hunter gatherers slowly learned that desirable wild food plants grew better when supplied with water and sunlight.  To provide more sunlight in forested areas they cleared away undesirable plants (weeds) by setting fires, which also killed insects, micro-organisms and small animals while provided plant nutrients from the burned plants. They killed shade trees by cutting or burning away the cambium layer around the trunks. When soil nutrients were exhausted they simply moved to another area and repeated this 'slash and burn' technique.

There were some areas, such as the river Nile in Egypt, the Yellow river in China and the Euphrates and Tigris rivers of Iraq where an annual flooding deposited a layer of silt containing plant nutrients to replace those exhausted by intensive agriculture. 

The transition from hunter-gatherer to agricultural societies began when people began planting seeds and protecting plants until they provided fruit, nuts or edible shoots, leaves or roots. About 8000 years ago European farmers noticed that plants grew better where animal had dropped excrement and urine and began fertilizing crops with manure. This provided plants with the nutrients (later known as nitrogen, phosphorus, potassium and small amounts of other elements) they needed for healthy growth. Animals such as horses, cattle, pigs, goats, sheep, ducks, geese and chicken, caught alive and kept for later consumption developed into livestock farming, supplying milk, eggs, meat and labour while also providing manure to fertilize plants. As populations grew bigger, wild food plants and animals were less readily available, forcing people to grow more and, as they became farmers living in permanent settlements, they quickly discovered these had to be fortified because they now had something worth stealing . . . livestock and stored food.

Early farmers discovered that preparing the soil by digging or plowing produced more food and began using animals to pull simple scratch plows. The loosened earth not only reduced the presence of weeds but also retained more water and allowed plant roots to grow more easily. Then they discovered selective breeding by planting the seeds of the best yielding plants.

In Mesoamerica, wild teosinte was transformed into maize (corn), more than 6000 years ago, by human selection, an early example of a genetically improved (modified) food crop. Mesoamericans also grew squash, beans and cocoa, and domesticated wild turkeys.

The Aztecs fertilized soil and built irrigation systems, chinampas or artificial islands and terraced hillsides. The Mayas from 400 BCE, built extensive canals and raised-field systems to farm swampland.

The Incas grew potatoes more than 7,000 years ago. Coca, peanuts, tomatoes, tobacco, pineapples and cotton were also domesticated in the Andes, as were llamas, alpacas, and guinea pigs.

They planted winter squash, maize (corn) and climbing beans together. The beans climbing on the maize stems (avoiding the need for poles) while also provide the nitrogen to the soil for the other plants. The squash leaves blocked sunlight to stop weeds from growing and also served as mulch to prevent water from evaporating.

The cacao tree, native to the Amazon Basin, was domesticated, by the Olmecs more than 4,000 years ago, and consumed by pre-Columbian cultures along the Yucatán.

Indigenous Australians used controlled burning (to limit catastrophic wild fires) and 'fire-stick' farming; burning off mature grass to promote new growth of fresh grass for the wild kangaroos. (Modern Canada geese congregate in suburban parks where the grass is continually mowed short and the new grass is fresh).Remains of domesticated millet have been found in northern China dating from 7000 BCE and settled rice agriculture dates from 4500 BCE. While soybeans were domesticated by Chinese farmers around 1100 BCE and by the first century CE, soybeans were grown in Japan and many other countries.

Between 722 and 481 BCE, Chinese farmers began using seed drills, cast iron tools and oxen to pull plows. They also began large-scale irrigation and water conservation systems. By the 1st century BCE the Chinese were using water powered trip hammers for agriculture. In the 1st century CE the square-pallet chain pump was invented to lift water from a lower to higher level filling irrigation channels. By the Tang dynasty (618–907), the mouldboard plow and watermill were developed and 1271 and 1368 CE the farmers were growing cotton.

Around 1250 CE, 75% of the Chinese population lived south of the river Yangste because of the introduction of strains of rice from Vietnam that permitted multiple crops in a season.

The depletion of soil nutrients, especially nitrogen, was a problem for sustained agriculture. Productive land was often left fallow and in some places crop were rotated so that the soil could recover. Clover and other legumes were often grown as these plants rejuvenated old farm fields by extracting nitrogen from the air and replenished soil nitrates through their roots.

Roman agriculture used a two-field system with a crop grown in one field while the other was left fallow (unplowed and often planted with grass to feed grazing animals) or plowed to reduce weeds, insects, small animals and disease organisms that would not survive in a fallow field.By 900 CE, improved iron smelting and metal working techniques provided better plows, hand tools and horse shoes. Better horse collars and harnesses and the whippletree linkage permitted use of horse drawn plows. The carruca heavy plow and the Chinese mouldboard plough were more effective than the scratch plow at turning over the heavy, wet soils of northern Europe. The northern European forests were rapidly cleared for farming and farmers began using a three field crop rotation system, one field of three was left fallow every year and another was used to grow nitrogen-fixing legumes such as peas, lentils and beans. This also improved productivity and nutrition which allowed population growth. Crops included wheat, rye, barley, oats, peas, beans and vetches.

Watermills and windmills, used to grind grains into flour, to cut wood and to process flax and wool, were improved throughout the Middle Ages.