Agriculture

May 4, 2013, 2:03 pm
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A row crop agricultural field. Source: Oklahoma State University

Agriculture includes cultivation of crops as tending of livestock for the purpose of production of food and fiber for humans. Mankind began to cultivate food crops about 10,000 years ago. Prior to that time, hunter-gatherers secured their food as they traveled in the nearby environment. When they observed some of the grains left behind at their campsites sprouting and growing to harvest, they began to cultivate these grains. From these humble beginnings agriculture began. Slash and burn, an early type of crop culture, remains today a truly sustainable agriculture, one that is independent of fossil fuel energy. In such a system, about ten hectares of productive land is held in fallow for each planted hectare. With this rotation system, a hectare is planted once every 20 years, allowing the soil to reaccumulate vital plant nutrients. Although the practice requires large acreages and large labor inputs, the crop yields are adequate. For example, corn with ample rainfall can yield about 2000 kilograms per hectare (kg/ha).

Over time, human labor in agriculture has decreased, first because of the use of animals and finally with machinery powered by fossil fuels. Currently, plentiful and economical fossil energy supports an era of machinery and agricultural chemicals. About 1000 liters of oil equivalent are used to produce a hectare of corn with a yield of 9,000 kg/ha. One-third of this energy is used to replace labor, one-third for fertilizers, and one-third for others.

Worldwide, more than 99.7% of human food (calories) comes from the land. Serious environmental impacts, such as soil erosion, water pollution from surface runoff, and pesticide pollution, result from fossil fuel-intensive agriculture. A critical need exists to assess fossil energy limits, the sustainability of agriculture, and the food needs of a rapidly growing world population.

Humans began to cultivate food crops and domesticate livestock approximately 10,000 years ago. Prior to that time, hunter-gatherers secured their food as they traveled in the nearby environment. When they observed some of the grains left behind at their campsites sprouting and growing to harvest, they began to cultivate these grains. From these humble beginnings agriculture began.

Slash and burn, an early type of crop culture, remains today a widespread form of agriculture in developing countries, that is independent of fossil fuel energy. In such a system, about ten hectares of productive land is held in fallow for each planted hectare. With this rotation system, a hectare is planted once every 20 years, allowing the soil to reaccumulate vital plant nutrients. Although the practice requires large acreages and large labor inputs, the crop yields are adequate for a family unit. For example, corn with ample rainfall can yield about 2000 kilograms per hectare (kg/ha).

caption Camels pulling plough in western Morocco north of Essaouira. Source: Michael Hogan

 Prehistory

Pollen core analysis and other forms of scientific research have revealed details of early human agricultural enterprises.  Some of the world regions with clearly defined agriculture as early as the early to mid  Holocene are the Nile Delta, (Boahen and Josephy, 1971) Mesopotamia, Indus Valley, China, Scandinavia, Orkney Islands, southern Europe and ancient Mauritania. As hunter-gatherer patterns transitioned to seasonal or permanent agricultural settlements, the human energy savings afforded by agricultural practices became translated into the first major public works projects of building elaborate structures of stone and mud-dried brick. By the later mid-Holocene (e.g. 5000 to 3000 years before present) advances in agricultural techniques spread by diffusion and innovation to more remote parts of Asia, the Mediterranean islands, the Americas and throughout the British Isles.There is evidence in disparate world regions that agriculture was practiced in non-sustainable fashions in some areas as early as the period 1400 to 4000 years before present; for example architectural and pollen core records in such locations as Crete and in the Mayan culture of Central America that fiber and food harvesting exceeded the local environment's capablity for time continuity of production.

Over time, human labor in agriculture has decreased, both due to the use of animals and later with machinery powered by fossil fuels. Currently, plentiful and economical fossil energy supports an era of machinery and agricultural chemicals. About 1000 liters of petroleum equivalent are used to produce a hectare of corn with a yield of 9000 kg/ha. One-third of this energy is used to replace labor, one-third for fertilizers, and one-third for others

Production practices

caption Polyculture of rice paddy/fish farming valley and benched upland crops. eastern madagascar. Source: C Michael Hogan Agricultural practices for crops can be classified as to cropping patterns, water management, tillage methods, nutrient supply, pest control and harvesting techniques. Cropping patterns consider such variables as seasonal or annual rotation, fallow periods, geometry of planted area, and monoculture versus polyculture planting. Choice among these patterns will affect the ability of soils to regenerate, the ability to sustain water supplies over an indefinite period and the total demand on external  resources needed to sustain the activity.For example soil regeneration of one centimeter in depth requires approximately one millennium.

Water management choices may involve selection of groundwater, surface water or unirrigated  strategies. Groundwater use is a method that must be very carefully constructed, since it may subject the aquifer to  overdraft, potentially leading to catastrophic cessation of water yields; this phenomenon is currently observable in parts of the western plains in the USA (House. 2006) and on the North China Plain, as well as numerous other world regions. Furthermore, groundwater extraction generally requires a very high energy input in order to pump water to the root zone.

Major crops

Biomass derived from plants is by far the most energy efficient way of delivering food to humans (or any omnivorous species). The limiting factors of producing such vegetative biomass are the processes of carbon and nitrogen fixation. Carbon fixation is chiefly conducted through photosynthesis, whereas nitrogen fixation in the natural environment is mainly conducted through symbiosis of certain host root systems with soil bacteria. Nitrogen fixation in vegetation normally produces ammonia, which in turn is used by plants to produce amino acids and proteins. Nitrogen fixation can also be accelerated by the very energy intensive industrial process of ammonia manufacture.

Photosynthetic biomass production is important in a large variety of basic foods including leafy vegetables, tubers and pulses. Nitrogen fixation is key in growth of legumes such as soybeans, lima beans, peanuts and kidney beans. Indirectly it is important for many other plants by producing nitrogen in the fallow cycle for such crops as alfalfa.

About half of the caloric intake of the human population derives from cereals. While these crops are relatively energy efficient to produce, the expansion of rice cultivation is placing an increasing pressure on water resources, a scarce commodity in today's world.

Cereals

Cereal production is the mainstay of human foods with wheat, rice, maize (corn), barley, rye, sorghum and oats being the chief components. The worldwide 2007 production of cereals amounted to 2.3 billion metric tons, with notably high yields coming from Europe, North and Central America and notably low yield coming from Africa. This wide variations in yield per hectare arise due to the chemical intensive nature of famring in developed countries and also due to the low nutrient content of tropical soils. It is also worth noting that rice is essentially a wetland crop and efforts to expand rice production inevitably lead to very high water demands, exacerbating the world water crisis. It is surprising to observe that the world cereal production has only expanded about 27 percent in the last 23 years, notwithstanding the enormous increase in human population and the aggressive use of chemical fertilizers. This meager increase can best be explained in that the preponderance of productive agricultural lands have been placed into use decades ago, and that overdrafting of groundwater and steady decline in topsoil capability is working against increasing production. One should also note that the collective production of wheat, barley, rye and sorghum has been declining to level over recent years. It is also worth noting that a considerable portion of maize production goes to non-food uses such as ethanol fuel.

Environmental sustainability

See also: Overgrazing; Overfishing

The environmental sustainabiltiy of agriculture consists of three components: agricultural production, demand for agricultural products and food policy. (Pimentel et al., 2000) There are several gauges of environmental sustainability including the Input and Output Rules advanced by Daly, Cobb and Goodman (Daly and Cobb, 1994) and the Serafian Rule. (El Serafy, 1993) The Output Rule states that waste emissions of an action should be kept within the assimilative capacity of the local environment without unacceptable degradation of future waste absorptive capacity or othe ecosystem services. The Input Rule for renewables states that harvesting rates of renewables must be within regenerative capacity of the natural system. For non-renewables the Input Rule says that depletion rates should be under the historical rate at which renewable substitutes were developed according to the Serafian Quasi-sustainablity Rule.  The key parameters of agricultural production that impact sustainability are (a) intensiveness of fossil fuel use; (b) application of excessive chemicals to the soil; (c) overharvesting that leaves insufficient residual plant material; (d) intensive water use; and (e) excessive compaction or erosion of topsoils.

Specific sustainablity practices are found in the application of polycultural cultivation; steady state fishery production; use of grazing practices that minimize erosion and are compatible with native plant survival; rotational cropping and grazing practices that allow sustaining of carbon, nitrogen and other geochemical cycles

Environmental Impact

caption Vineyard on sonoma mountain, california. this is a relatively recent agricultural conversion of native oak woodland. source: C Michael Hogan Worldwide, more than 99.7% of human food (calories) comes from the land. Significant adverse environmental impacts, such as soil erosion, biodiversity loss, and surface water runoff carrying sediment pollution may result from all forms of terrestrial agriculture. In addition, fossil fuel-intensive agriculture causes accumulation of agricultural chemicals in soils and their discharge to surface waters.  The chief chemicals applied are nitrates and phosphates in fertilizers and a host of pesticides and herbicides, most of which have significant toxicity. When these chemicals enter the environment they alter biotic productivity cycles and can affect the metabolism of plants and animals. This metabolic change may induce stunted growth, impaired function and even mortality. As a consequence loading of extraneous chemicals into the environment is a threat to biodiversity and ecosystem function  There is a critical need to assess fossil energy limits, the sustainability of agriculture, biodiversity implications and the food needs of a rapidly growing world population.

References

  • A. Adu Boahen and Alvin M. Josephy. 1971. The Horizon history of Africa. vol. 2,  528 pages ASIN: B000H5EI4M
  • C. Michael Hogan. 2013. Grzimek's Animal Life Encyclopedia: Extinction. Ed. Norman MacLeod. Gale Publishing, Detroit. pp. 759-768.
  • David Pimentel, Laura Westra and Reed F Noss. 2000. Ecological integrity: integrating environment, conservation and health, page 121  ISBN: 1559638087
  • Frank J. House. 2006. Agricultural programs, terms and laws. 304 pages ISBN: 1594548927
  • H.E. Daly and J. Cobb. 1994. For the Common Good. (2nd ed.) Beacon Press, Boston, Mass.B    ISBN: 0807047058
  • S. El Serafy. 1993. Country macroeconomic work and natural resources. Environmental Working Paper 58. The World Bank, Washington D.C. ASIN: B0006PEGY0

 

Glossary

Citation

Pimentel, D., & Hogan, C. (2013). Agriculture. Retrieved from http://www.eoearth.org/view/article/149911

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