Revolution

In the Middle Ages, both in the Islamic world and in Europe, agriculture transformed with improved techniques and the diffusion of crop plants, including the introduction of sugar, rice, cotton and fruit trees (such as the orange) to Europe by way of Al-Andalus. After 1492 the Columbian exchange brought New World crops such as maize, potatoes, tomatoes, sweet potatoes and manioc to Europe, and Old World crops such as wheat, barley, rice and turnips, and livestock (including horses, cattle, sheep and goats) to the Americas. Irrigation, crop rotation, and fertilizers advanced from the 17th century with the British Agricultural Revolution, allowing global population to rise significantly. Since 1900 agriculture in developed nations, and to a lesser extent in the developing world, has seen large rises in productivity as mechanization replaces human labor, and assisted by synthetic fertilizers, pesticides, and selective breeding. The Haber-Bosch method allowed the synthesis of ammonium nitrate fertilizer on an industrial scale, greatly increasing crop yields and sustaining a further increase in global population.Modern agriculture has raised or encountered ecological, political, and economic issues including water pollution, biofuels, genetically modified organisms, tariffs and farm subsidies, leading to alternative approaches such as the organic movement.

Types

Pastoralism involves managing domesticated animals. In nomadic pastoralism, herds of livestock are moved from place to place in search of pasture, fodder, and water. This type of farming is practised in arid and semi-arid regions of Sahara, Central Asia and some parts of India.

In shifting cultivation, a small area of forest is cleared by cutting and burning the trees. The cleared land is used for growing crops for a few years until the soil becomes too infertile, and the area is abandoned. Another patch of land is selected and the process is repeated. This type of farming is practiced mainly in areas with abundant rainfall where the forest regenerates quickly. This practice is used in Northeast India, Southeast Asia, and the Amazon Basin.

Spreading manure by hand in Zambia Subsistence farming is practiced to satisfy family or local needs alone, with little left over for transport elsewhere. It is intensively practiced in Monsoon Asia and South-East Asia. An estimated 2.5 billion subsistence farmers worked in 2018, cultivating about 60% of the earth's arable land.

Intensive farming is cultivation to maximise productivity, with a low fallow ratio and a high use of inputs (water, fertilizer, pesticide and automation). It is practiced mainly in developed countries.

Plant breeding

Crop alteration has been practiced by humankind for thousands of years, since the beginning of civilization. Altering crops through breeding practices changes the genetic make-up of a plant to develop crops with more beneficial characteristics for humans, for example, larger fruits or seeds, drought-tolerance, or resistance to pests. Significant advances in plant breeding ensued after the work of geneticist Gregor Mendel. His work on dominant and recessive alleles, although initially largely ignored for almost 50 years, gave plant breeders a better understanding of genetics and breeding techniques. Crop breeding includes techniques such as plant selection with desirable traits, self-pollination and cross-pollination, and molecular techniques that genetically modify the organism.

Domestication of plants has, over the centuries increased yield, improved disease resistance and drought tolerance, eased harvest and improved the taste and nutritional value of crop plants. Careful selection and breeding have had enormous effects on the characteristics of crop plants. Plant selection and breeding in the 1920s and 1930s improved pasture (grasses and clover) in New Zealand. Extensive X-ray and ultraviolet induced mutagenesis efforts (i.e. primitive genetic engineering) during the 1950s produced the modern commercial varieties of grains such as wheat, corn (maize) and barley.

Genetic engineering

Genetically modified organisms (GMO) are organisms whose genetic material has been altered by genetic engineering techniques generally known as recombinant DNA technology. Genetic engineering has expanded the genes available to breeders to utilize in creating desired germlines for new crops. Increased durability, nutritional content, insect and virus resistance and herbicide tolerance are a few of the attributes bred into crops through genetic engineering. For some, GMO crops cause food safety and food labeling concerns. Numerous countries have placed restrictions on the production, import or use of GMO foods and crops. Currently a global treaty, the Biosafety Protocol, regulates the trade of GMOs. There is ongoing discussion regarding the labeling of foods made from GMOs, and while the EU currently requires all GMO foods to be labeled, the US does not.

Herbicide-resistant seed has a gene implanted into its genome that allows the plants to tolerate exposure to herbicides, including glyphosate. These seeds allow the farmer to grow a crop that can be sprayed with herbicides to control weeds without harming the resistant crop. Herbicide-tolerant crops are used by farmers worldwide. With the increasing use of herbicide-tolerant crops, comes an increase in the use of glyphosate-based herbicide sprays. In some areas glyphosate resistant weeds have developed, causing farmers to switch to other herbicides. Some studies also link widespread glyphosate usage to iron deficiencies in some crops, which is both a crop production and a nutritional quality concern, with potential economic and health implications.

Effects and costs

Agriculture imposes multiple external costs upon society through effects such as pesticide damage to nature (especially herbicides and insecticides), nutrient runoff, excessive water usage, and loss of natural environment. A 2000 assessment of agriculture in the UK determined total external costs for 1996 of £2,343 million, or £208 per hectare. A 2005 analysis of these costs in the US concluded that cropland imposes approximately $5 to $16 billion ($30 to $96 per hectare), while livestock production imposes $714 million. Both studies, which focused solely on the fiscal impacts, concluded that more should be done to internalize external costs. Neither included subsidies in their analysis, but they noted that subsidies also influence the cost of agriculture to society.

Agriculture seeks to increase yield and to reduce costs. Yield increases with inputs such as fertilisers and removal of pathogens, predators, and competitors (such as weeds). Costs decrease with increasing scale of farm units, such as making fields larger; this means removing hedges, ditches and other areas of habitat. Pesticides kill insects, plants and fungi. These and other measures have cut biodiversity to very low levels on intensively farmed land.

Livestock issues

A senior UN official, Henning Steinfeld, said that "Livestock are one of the most significant contributors to today's most serious environmental problems". Livestock production occupies 70% of all land used for agriculture, or 30% of the land surface of the planet. It is one of the largest sources of greenhouse gases, responsible for 18% of the world's greenhouse gas emissions as measured in CO2 equivalents. By comparison, all transportation emits 13.5% of the CO2. It produces 65% of human-related nitrous oxide (which has 296 times the global warming potential of CO2,) and 37% of all human-induced methane (which is 23 times as warming as CO2.) It also generates 64% of the ammonia emission. Livestock expansion is cited as a key factor driving deforestation; in the Amazon basin 70% of previously forested area is now occupied by pastures and the remainder used for feedcrops. Through deforestation and land degradation, livestock is also driving reductions in biodiversity. Furthermore, the UNEP states that "methane emissions from global livestock are projected to increase by 60 per cent by 2030 under current practices and consumption patterns."

Land and water issues

Land transformation, the use of land to yield goods and services, is the most substantial way humans alter the Earth's ecosystems, and is considered the driving force in the loss of biodiversity. Estimates of the amount of land transformed by humans vary from 39 to 50%. Land degradation, the long-term decline in ecosystem function and productivity, is estimated to be occurring on 24% of land worldwide, with cropland overrepresented. The UN-FAO report cites land management as the driving factor behind degradation and reports that 1.5 billion people rely upon the degrading land. Degradation can be deforestation, desertification, soil erosion, mineral depletion, or chemical degradation (acidification and salinization).

Eutrophication, excessive nutrients in aquatic ecosystems resulting in algal bloom and anoxia, leads to fish kills, loss of biodiversity, and renders water unfit for drinking and other industrial uses. Excessive fertilization and manure application to cropland, as well as high livestock stocking densities cause nutrient (mainly nitrogen and phosphorus) runoff and leaching from agricultural land. These nutrients are major nonpoint pollutants contributing to eutrophication of aquatic ecosystems and pollution of groundwater, with harmful effects on human populations. Fertilisers also reduce terrestrial biodiversity by increasing competition for light, favouring those species that are able to benefit from the added nutrients. Agriculture accounts for 70 percent of withdrawals of freshwater resources. Agriculture is a major draw on water from aquifers, and currently draws from those underground water sources at an unsustainable rate.

Pesticides

Pesticide use has increased since 1950 to 2.5 million short tons annually worldwide, yet crop loss from pests has remained relatively constant. The World Health Organization estimated in 1992 that three million pesticide poisonings occur annually, causing 220,000 deaths. Pesticides select for pesticide resistance in the pest population, leading to a condition termed the "pesticide treadmill" in which pest resistance warrants the development of a new pesticide.

An alternative argument is that the way to "save the environment" and prevent famine is by using pesticides and intensive high yield farming, a view exemplified by a quote heading the Center for Global Food Issues website: 'Growing more per acre leaves more land for nature'. However, critics argue that a trade-off between the environment and a need for food is not inevitable, and that pesticides simply replace good agronomic practices such as crop rotation. The Push–pull agricultural pest management technique involves intercropping, using plant aromas to repel pests from crops (push) and to lure them to a place from which they can then be removed (pull).

Climate change

Climate change and agriculture are interrelated on a global scale. Global warming affects agriculture through changes in average temperatures, rainfall, and weather extremes (like storms and heat waves); changes in pests and diseases; changes in atmospheric carbon dioxide and ground-level ozone concentrations; changes in the nutritional quality of some foods; and changes in sea level. Global warming is already affecting agriculture, with effects unevenly distributed across the world. Future climate change will probably negatively affect crop production in low latitude countries, while effects in northern latitudes may be positive or negative. Global warming will probably increase the risk of food insecurity for some vulnerable groups, such as the poor.

Animal husbandry is also responsible for greenhouse gas production of CO 2 and a percentage of the world's methane, and future land infertility, and the displacement of wildlife. Agriculture contributes to climate change by anthropogenic emissions of greenhouse gases, and by the conversion of non-agricultural land such as forest for agricultural use. Agriculture, forestry and land-use change contributed around 20 to 25% to global annual emissions in 2010. A range of policies can reduce the risk of negative climate change impacts on agriculture, and greenhouse gas emissions from the agriculture sector.

Sustainability

Current farming methods have resulted in over-stretched water resources, high levels of erosion and reduced soil fertility. There is not enough water to continue farming using current practices; therefore how critical water, land, and ecosystem resources are used to boost crop yields must be reconsidered. A solution would be to give value to ecosystems, recognizing environmental and livelihood tradeoffs, and balancing the rights of a variety of users and interests. Inequities that result when such measures are adopted would need to be addressed, such as the reallocation of water from poor to rich, the clearing of land to make way for more productive farmland, or the preservation of a wetland system that limits fishing rights.

Technological advancements help provide farmers with tools and resources to make farming more sustainable. Technology permits innovations like conservation tillage, a farming process which helps prevent land loss to erosion, reduces water pollution, and enhances carbon sequestration. Other potential practices include conservation agriculture, agroforestry, improved grazing, avoided grassland conversion, and biochar. Current mono-crop farming practices in the United States preclude widespread adoption of sustainable practices, such as 2-3 crop rotations that incorporate grass or hay with annual crops, unless negative emission goals such as soil carbon sequestration become policy.

Energy dependence

Since the 1940s, agricultural productivity has increased dramatically, due largely to the increased use of energy-intensive mechanization, fertilizers and pesticides. The vast majority of this energy input comes from fossil fuel sources. Between the 1960s and the 1980s, the Green Revolution transformed agriculture around the globe, with world grain production increasing significantly (between 70% and 390% for wheat and 60% to 150% for rice, depending on geographic area) as world population doubled. Heavy reliance on petrochemicals has raised concerns that oil shortages could increase costs and reduce agricultural output.

Industrialized agriculture depends on fossil fuels in two fundamental ways: direct consumption on the farm and manufacture of inputs used on the farm. Direct consumption includes the use of lubricants and fuels to operate farm vehicles and machinery.

Systems

Traditionally, animal husbandry was part of the subsistence farmer's way of life, producing not only the food needed by the family but also the fuel, fertiliser, clothing, transport and draught power. Killing the animal for food was a secondary consideration, and wherever possible its products, such as wool, eggs, milk and blood (by the Maasai) were harvested while the animal was still alive.In the traditional system of transhumance, people and livestock moved seasonally between fixed summer and winter pastures; in montane regions the summer pasture was up in the mountains, the winter pasture in the valleys.

Animals can be kept extensively or intensively. Extensive systems involve animals roaming at will, or under the supervision of a herdsman, often for their protection from predators. Ranching in the Western United States involves large herds of cattle grazing widely over public and private lands.Similar cattle stations are found in South America, Australia and other places with large areas of land and low rainfall. Ranching systems have been used for sheep, deer, ostrich, emu, llama and alpaca.

At the other extreme, in the more developed parts of the world, animals are often intensively managed; dairy cows may be kept in zero-grazing conditions with all their forage brought to them; beef cattle may be kept in high density feedlots; pigs may be housed in climate-controlled buildings and never go outdoors; poultry may be reared in barns and kept in cages as laying birds under lighting-controlled conditions. In between these two extremes are semi-intensive, often family-run farms where livestock graze outside for much of the year, silage or hay is made to cover the times of year when the grass stops growing, and fertiliser, feed, and other inputs are brought onto the farm from outside.

Feeding

Animals used as livestock are predominantly herbivorous, the main exceptions being the pig and the chicken which are omnivorous. The herbivores can be divided into "concentrate selectors" which selectively feed on seeds, fruits and highly nutritious young foliage, "grazers" which mainly feed on grass, and "intermediate feeders" which choose their diet from the whole range of available plant material. Cattle, sheep, goats, deer and antelopes are ruminants; they digest food in two steps, chewing and swallowing in the normal way, and then regurgitating the semidigested cud to chew it again and thus extract the maximum possible food value. The dietary needs of these animals is mostly met by eating grass. Grasses grow from the base of the leaf-blade, enabling it to thrive even when heavily grazed or cut.

Extensively reared animals may subsist entirely on forage, but more intensively kept livestock will require energy and protein-rich foods in addition. Energy is mainly derived from cereals and cereal by-products, fats and oils and sugar-rich foods, while protein may come from fish or meat meal, milk products, legumes and other plant foods, often the by-products of vegetable oil extraction.[34] Pigs and poultry are non-ruminants and unable to digest the cellulose in grass and other forages, so they are fed entirely on cereals and other high-energy foodstuffs. The ingredients for the animals' rations can be grown on the farm or can be bought, in the form of pelleted or cubed, compound foodstuffs specially formulated for the different classes of livestock, their growth stages and their specific nutritional requirements. Vitamins and minerals are added to balance the diet.[35] Farmed fish are usually fed pelleted food.[35]

Breeding

The breeding of farm animals seldom occurs spontaneously but is managed by farmers with a view to encouraging traits seen as desirable. These include hardiness, fertility, docility, mothering abilities, fast growth rates, low feed consumption per unit of growth, better body proportions, higher yields, and better fibre qualities. Undesirable traits such as health defects and aggressiveness are selected against.[36][37]

Selective breeding has been responsible for large increases in productivity. For example, in 2007, a typical broiler chicken at eight weeks old was 4.8 times as heavy as a bird of similar age in 1957,[36] while in the thirty years to 2007, the average milk yield of a dairy cow in the United States nearly doubled.[36]

Animal health

Good husbandry, proper feeding, and hygiene are the main contributors to animal health on the farm, bringing economic benefits through maximised production. When, despite these precautions, animals still become sick, they are treated with veterinary medicines, by the farmer and the veterinarian. In the European Union, when farmers treat their own animals, they are required to follow the guidelines for treatment and to record the treatments given.[38] Animals are susceptible to a number of diseases and conditions that may affect their health. Some, like classical swine fever[39] and scrapie[40] are specific to one type of stock, while others, like foot-and-mouth disease affect all cloven-hoofed animals.[41] Animals living under intensive conditions are prone to internal and external parasites; increasing numbers of sea lice are affecting farmed salmon in Scotland.[42] Reducing the parasite burdens of livestock results in increased productivity and profitability.[43]

overnments are concerned with zoonoses, diseases that humans may acquire from animals. Wild animal populations may harbour diseases that can affect domestic animals which may acquire them as a result of insufficient biosecurity. An outbreak of Nipah virus in Malaysia in 1999 was traced back to pigs becoming ill after contact with fruit-eating flying foxes, their faeces and urine. The pigs in turn passed the infection to humans.[45] Avian flu H5N1 is present in wild bird populations and can be carried large distances by migrating birds. This virus is easily transmissible to domestic poultry, and to humans living in close proximity with them. Other infectious diseases affecting wild animals, farm animals and humans include rabies, leptospirosis, brucellosis, tuberculosis and trichinosis.[46]

Range of species

There is no single universally agreed definition of which species are livestock. Widely agreed types of livestock include cattle for beef and dairy, sheep, goats, pigs, and poultry. Various other species are sometimes considered livestock, such as horses,[47] while poultry birds are sometimes excluded. In some parts of the world, livestock includes species such as buffalo, and the South American camelids, the alpaca and llama.[48][49][50] Some authorities use much broader definitions to include fish in aquaculture, micro-livestock such as rabbits and rodents like guinea pigs, as well as insects from honey bees to crickets raised for human consumption.[51]

Products

Animals are raised for a wide variety of products, principally meat, wool, milk, and eggs, but also including tallow, isinglass and rennet.[52][53] Animals are also kept for more specialised purposes, such as to produce vaccines[54] and antiserum (containing antibodies) for medical use.[55] Where fodder or other crops are grown alongside animals, manure can serve as a fertiliser, returning minerals and organic matter to the soil in a semi-closed organic system.[56]

Dairy

Although all mammals produce milk to nourish their young, the cow is predominantly used throughout the world to produce milk and milk products for human consumption. Other animals used to a lesser extent for this purpose include sheep, goats, camels, buffaloes, yaks, reindeer, horses and donkeys.[57]

All these animals have been domesticated over the centuries, being bred for such desirable characteristics as fecundity, productivity, docility and the ability to thrive under the prevailing conditions. Whereas in the past, cattle had multiple functions, modern dairy cow breeding has resulted in specialised Holstein Friesian-type animals that produce large quantities of milk economically. Artificial insemination is widely available to allow farmers to select for the particular traits that suit their circumstances.[58]

Whereas in the past, cows were kept in small herds on family farms, grazing pastures and being fed hay in winter, nowadays there is a trend towards larger herds, more intensive systems, the feeding of silage and "zero grazing", a system where grass is cut and brought to the cow, which is housed year-round.[59] In many communities, milk production is only part of the purpose of keeping an animal which may also be used as a beast of burden or to draw a plough, or for the production of fibre, meat and leather, with the dung being used for fuel or for the improvement of soil fertility. Sheep and goats may be favoured for dairy production in climates and conditions that do not suit dairy cows.[57]

Meat

Meat, mainly from farmed animals, is a major source of dietary protein around the world, averaging about 8% of man's energy intake. The actual types eaten depend on local preferences, availability, cost and other factors, with cattle, sheep, pigs and goats being the main species involved. Cattle generally produce a single offspring annually which takes more than a year to mature; sheep and goats often have twins and these are ready for slaughter in less than a year; pigs are more prolific, producing more than one litter of up to about 11[60] piglets each year.[61] Horses, donkeys, deer, buffalo, llamas, alpacas, guanacos and vicunas are farmed for meat in various regions. Some desirable traits of animals raised for meat include fecundity, hardiness, fast growth rate, ease of management and high food conversion efficiency. About half of the world's meat is produced from animals grazing on open ranges or on enclosed pastures, the other half being produced intensively in various factory-farming systems; these are mostly cows, pigs or poultry, and often reared indoors, typically at high densities.[62]

Poultry

Poultry, kept for their eggs and for their meat, include chickens, turkeys, geese and ducks. The great majority of laying birds used for egg production are chickens. Methods for keeping layers range from free-range systems, where the birds can roam as they will but are housed at night for their own protection, through semi-intensive systems where they are housed in barns and have perches, litter and some freedom of movement, to intensive systems where they are kept in cages. The battery cages are arranged in long rows in multiple tiers, with external feeders, drinkers, and egg collection facilities. This is the most labour saving and economical method of egg production but has been criticised on animal welfare grounds as the birds are unable to exhibit their normal behaviours.[63]

In the developed world, the majority of the poultry reared for meat is raised indoors in big sheds, with automated equipment under environmentally controlled conditions. Chickens raised in this way are known as broilers, and genetic improvements have meant that they can be grown to slaughter weight within six or seven weeks of hatching. Newly hatched chicks are restricted to a small area and given supplementary heating. Litter on the floor absorbs the droppings and the area occupied is expanded as they grow. Feed and water is supplied automatically and the lighting is controlled. The birds may be harvested on several occasions or the whole shed may be cleared at one time.[64]

Aquaculture

Aquaculture has been defined as "the farming of aquatic organisms including fish, molluscs, crustaceans and aquatic plants and implies some form of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators, etc. Farming also implies individual or corporate ownership of the stock being cultivated."[67] In practice it can take place in the sea or in freshwater, and be extensive or intensive. Whole bays, lakes or ponds may be devoted to aquaculture, or the farmed animal may be retained in cages (fish), artificial reefs, racks or strings (shellfish). Fish and prawns can be cultivated in rice paddies, either arriving naturally or being introduced, and both crops can be harvested together.[68]

Fish hatcheries provide larval and juvenile fish, crustaceans and shellfish, for use in aquaculture systems. When large enough these are transferred to growing-on tanks and sold to fish farms to reach harvest size. Some species that are commonly raised in hatcheries include shrimps, prawns, salmon, tilapia, oysters and scallops. Similar facilities can be used to raise species with conservation needs to be released into the wild, or game fish for restocking waterways. Important aspects of husbandry at these early stages include selection of breeding stock, control of water quality and nutrition. In the wild, there is a massive amount of mortality at the nursery stage; farmers seek to minimise this while at the same time maximising growth rates.[69]

Insects

Bees have been kept in hives since at least the First Dynasty of Egypt, five thousand years ago,[70] and man had been harvesting honey from the wild long before that. Fixed comb hives are used in many parts of the world and are made from any locally available material.[71] In more advanced economies, where modern strains of domestic bee have been selected for docility and productiveness, various designs of hive are used which enable the combs to be removed for processing and extraction of honey. Quite apart from the honey and wax they produce, honey bees are important pollinators of crops and wild plants, and in many places hives are transported around the countryside to assist in pollination.[72]

Sericulture, the rearing of silkworms, was first adopted by the Chinese during the Shang dynasty.[73] The only species farmed commercially is the domesticated silkmoth. When it spins its cocoon, each larva produces an exceedingly long, slender thread of silk. The larvae feed on mulberry leaves and in Europe, only one generation is normally raised each year as this is a deciduous tree. In China, Korea and Japan however, two generations are normal, and in the tropics, multiple generations are expected. Most production of silk occurs in the Far East, with a synthetic diet being used to rear the silkworms in Japan.[74]

Insects form part of the human diet in many cultures.[75] In Thailand, crickets are farmed for this purpose in the north of the country, and palm weevil larvae in the south. The crickets are kept in pens, boxes or drawers and fed on commercial pelleted poultry food, while the palm weevil larvae live on cabbage palm and sago palm trees, which limits their production to areas where these trees grow.[76] Another delicacy of this region is the bamboo caterpillar, and the best rearing and harvesting techniques in semi-natural habitats are being studied.[76]