Agriculture, also called farming or husbandry, is the cultivation of animals, plants, fungi, and other life forms for food, fiber, biofuel, drugs and other products used to sustain and enhance human life. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the development of civilization. The study of agriculture is known as agricultural science. The history of agriculture dates back thousands of years, and its development has been driven and defined by greatly different climates, cultures, and technologies. However, all farming generally relies on techniques to expand and maintain the lands that are suitable for raising domesticated species. For plants, this usually requires some form of irrigation, although there are methods of dryland farming; pastoral herding on rangeland is still the most common means of raising livestock. In the developed world, industrial agriculture based on large-scale monoculture has become the dominant system of modern farming, although there is growing support for sustainable agriculture (e.g. permaculture or organic agriculture).
Until the Industrial Revolution, the vast majority of the human population labored in agriculture. Pre-industrial agriculture was typically subsistence agriculture in which farmers raised most of their crops for their own consumption instead of for trade. A remarkable shift in agricultural practices has occurred over the past century in response to new technologies, and the development of world markets. This also led to technological improvements in agricultural techniques, such as the Haber-Bosch method for synthesizing ammonium nitrate which made the traditional practice of recycling nutrients with crop rotation and animal manure less necessary.
Modern agronomy, plant breeding, agrochemicals such as pesticides and fertilizers, and technological improvements have sharply increased yields from cultivation, but at the same time have caused widespread ecological damage and negative human health effects. Selective breeding and modern practices in animal husbandry have similarly increased the output of meat, but have raised concerns about animal welfare and the health effects of the antibiotics, growth hormones, and other chemicals commonly used in industrial meat production. Genetically Modified Organisms are an increasing component of agriculture today, although they are banned in several countries. Agricultural food production and water management is targeted as an increasingly global issue that is fostering debate on a number of issues. Significant degradation of land and water resources, including the depletion of aquifers, has been seen in recent decades, and the effects of global warming on agriculture and of agriculture on global warming are still not fully known.
The major agricultural products can be broadly grouped into foods, fibers, fuels, and raw materials. Specific foods include cereals (grains), vegetables, fruits, oils, meat and spices. Fibers include cotton, wool, hemp, silk and flax. Raw materials include lumber and bamboo. Other useful materials are produced by plants, such as resins, dyes, drugs, perfume, biofuels and ornamental products such as cut flowers and nursery plants. Over one third of the world's workers are employed in agriculture, second only to the services sector, although the percentages of agricultural workers in developed countries has decreased significantly over the past several centuries.
Etymology and terminology
The word agriculture is a late Middle English adaptation of Latin agricultūra, from ager, "field", and cultūra, "cultivation" or "growing". Agriculture usually refers to human activities, although it is also observed in certain species of ant, termite and ambrosia beetle. To practice agriculture means to use natural resources to "produce commodities which maintain life, including food, fiber, forest products, horticultural crops, and their related services." This definition includes arable farming or agronomy, and horticulture, all terms for the growing of plants, animal husbandry and forestry. A distinction is sometimes made between forestry and agriculture, based on the former's longer management rotations, extensive versus intensive management practices and development mainly by nature, rather than by man. Even then, it is acknowledged that there is a large amount of knowledge transfer and overlap between silviculture (the management of forests) and agriculture. In traditional farming, the two are often combined even on small landholdings, leading to the term agroforestry.
Agricultural practices such as irrigation, crop rotation, fertilizers, pesticides and the domestication of livestock were developed a long time ago, but have made great progress in the past century. The history of agriculture has played a major role in human history, as agricultural progress has been a crucial factor in worldwide socio-economic change. Division of labor in agricultural societies made commonplace specializations rarely seen in hunter-gatherer cultures, which allowed the growth of towns and cities, and the complex societies we call civilizations. When farmers became capable of producing food beyond the needs of their own families, others in their society were freed to devote themselves to projects other than food acquisition. Historians and anthropologists have long argued that the development of agriculture made civilization possible. The total world population probably never exceeded 15 million inhabitants before the development of agriculture.
Forest gardening, a plant-based food production system, is thought to be the world's oldest agroecosystem. Forest gardens originated in prehistoric times along jungle-clad river banks and in the wet foothills of monsoon regions. In the gradual process of a family improving their immediate environment, useful tree and vine species were identified, protected and improved whilst undesirable species were eliminated. Eventually superior foreign species were selected and incorporated into the family's garden.
The Fertile Crescent of the Near East first saw the domestication of animals, starting the Neolithic Revolution. Between 10,000 and 13,000 years ago, the ancestors of modern cattle, sheep, goats and pigs were domesticated in this area. The gradual transition from wild harvesting to deliberate cultivation happened independently in several areas around the globe. Agriculture allowed for the support of an increased population, leading to larger societies and eventually the development of cities. It also created the need for greater organization of political power (and the creation of social stratification), as decisions had to be made regarding labor and harvest allocation and access rights to water and land. Agriculture bred immobility, as populations settled down for long periods of time, which led to the accumulation of material goods.
Early Neolithic villages show evidence of the ability to process grain, and the Near East is the ancient home of the ancestors of wheat, barley and peas. There is evidence of the cultivation of figs in the Jordan Valley as long as 11,300 years ago, and cereal (grain) production in Syria approximately 9,000 years ago. During the same period, farmers in China began to farm rice and millet, using man-made floods and fires as part of their cultivation regimen. Fiber crops were domesticated as early as food crops, with China domesticating hemp, cotton being developed independently in Africa and South America and the Near East domesticating flax. The use of soil amendments, including manure, fish, compost and ashes, appears to have begun early, and developed independently in several areas of the world, including Mesopotamia, the Nile Valley and eastern Asia.
Squash was grown in Mexico nearly 10,000 years ago, while maize-like plants, derived from the wild teosinte, began to be seen at around 9,000 years ago. The derivation of teosinte into modern corn was slow, however, and it took until 5,500 to 6,000 years ago to turn into what we know today as maize. It then gradually spread across North America and was the major crop of Native Americans at the time of European exploration. Beans were domesticated around the same time, and together these three plants formed the Three Sisters nutritional foundation of many native populations in North and Central America. Combined with peppers, these crops provided a balanced diet for much of the continent. Grapes were first grown for wine approximately 8,000 years ago, in the Southern Caucasus, and by 3000 BC had spread to the Fertile Crescent, the Jordan Valley and Egypt.
Agriculture advanced to Europe slightly later, reaching the northeast of the continent from the east around 4000 BC. The idea that agriculture spread to Europe, rather than independently developing there, has led to two main hypotheses. The first is a "wave of advance", which holds that agriculture traveled slowly and steadily across the continent, while the second, "population pulse" theory, holds that it moved in jumps. Also around 6000 years ago, horses first began to be domesticated in the Eurasian steppes. Initially used for food, it was quickly discovered that they were useful for field work and carrying goods and people. Around 5,000 years ago, sunflowers were first cultivated in North America, while South America's Andes region was developing the potato. A minor center of domestication, the indigenous people of the eastern US appear to have domesticated numerous crops, including tobacco.
Bronze and Iron Ages
Between 2500 and 2000 BC, the simplest form of the plough, called the ard, spread throughout Europe, replacing the hoe. This change in equipment significantly increased cultivation ability, and affected the demand for land, as well as ideas about property, inheritance and family rights. Before this period, simple digging sticks or hoes were used. These tools would have also been easier to transport, which was a benefit as people only stayed until the soil's nutrients were depleted. However, as the continuous cultivating of smaller pieces of land became a sustaining practice throughout the world, ards were much more efficient than digging sticks. As humanity became more stationary, empires, such as the New Kingdom of Egypt and the Ancient Romans, arose, dependent upon agriculture to feed their growing populations, and slavery, which was used to provide the labor needed for continually intensifying agricultural processes. Agricultural technology continued to improve, allowing the expansion of available crop varieties, including a wide range of fruits, vegetables, oil crops, spices and other products. China was also an important center for agricultural technology development during this period. During the Zhou dynasty (1666-221 BC), the first canals were built, and irrigation was used extensively. The later Three Kingdoms and Northern and Southern dynasties (221-581 AD) brought the first biological pest control, extensive writings on agricultural topics and technological innovations such as steel and the wheelbarrow.
In the ancient world, fresh products, such as meats, dairy products and fresh fruits and vegetables, were likely consumed relatively close to where they were produced. Less perishable products, such as grains, preserved foods, olive oil and wine, were often traded over an extensive network of land and sea routes. The ancient trade in agricultural goods was well established, with wine traded in the Mediterranean region in the 6th century BC and Rome receiving extensive shipments of grain as tax payments by the 2nd century BC. Huge amounts of grain were transported, mainly by sea, and it was during this period that the subsidization of grain farming began, for the prevention of famine. Ancient Rome was a major center for agricultural trade. Trade routes stretched from Britain and Scandinavia in the west to India and China in the east, and included major crops, such as grain, wine and olive oil, as well as additional products, including spices, fabrics and drugs.
During the time of the Greco-Romans, scholars, including Plato (428-348 BC) and Aristotle (384-322 BC), documented farming techniques, including the use of fertilizers. Much of what scholars believed about farming and plant nutrition at this time was later found to be incorrect, but their theories provided the scientific foundation for the development of agricultural theories through the Middle Ages. Ideas about soil fertility and fertilization remained much the same from the time of Greco-Roman scholars until the 19th century, with correspondingly low crop yields. By the time of Alexander the Great's conquests (330-323 BC), the role of horses had developed, and they played a huge role in warfare and agriculture. Innovations continued to be developed which allowed them to work longer, harder and more efficiently. By medieval times they became the primary source of power for agriculture, transport and warfare, a position they held until the development of the steam and internal combustion engines. The Mayan culture developed several innovations in agriculture during its peak, which ranged from 400 BC to 900 AD and was heavily dependent upon agriculture to support its population. The Mayans used extensive canal and raised field systems to farm the large portions of swampland on the Yucatán Peninsula.
The Middle Ages saw significant improvements in the agricultural techniques and technology. During this time period, monasteries spread throughout Europe and became important centers for the collection of knowledge related to agriculture and forestry. The manorial system, which existed under different names throughout Europe and Asia, allowed large landowners significant control over both their land and its laborers, in the form of peasants or serfs. During the medieval period, the Arab world was critical in the exchange of crops and technology between the European, Asia and African continents. Besides transporting numerous crops, they introduced the concept of summer irrigation to Europe and developed the beginnings of the plantation system through the use of slaves for intensive cultivation.
By 900 AD in Europe, developments in iron smelting allowed for increased production, leading to developments in the production of agricultural implements such as ploughs, hand tools and horse shoes. The plough was significantly improved, developing into the mouldboard plough, capable of turning over the heavy, wet soils of northern Europe. This led to the clearing of forests in that area and a significant increase in agricultural production, which in turn led to an increase in population. A similar plough, which may have developed independently, was also found in China as early as the 9th century. At the same time, farmers in Europe moved from a two field crop rotation to a three field crop rotation in which one field of three was left fallow every year. This resulted in increased productivity and nutrition, as the change in rotations led to different crops being planted, including legumes such as peas, lentils and beans. Inventions such as improved horse harnesses and the whippletree also changed methods of cultivation. Watermills were initially developed by the Romans, but were improved throughout the Middle Ages, along with windmills, and used to grind grains into flour, cut wood and process flax and wool, among other uses.
Crops included wheat, rye, barley and oats. Peas, beans, and vetches became common from the 13th century onward as a fodder crop for animals and also for their nitrogen-fixation fertilizing properties. Crop yields peaked in the 13th century, and stayed more or less steady until the 18th century. Though the limitations of medieval farming were once thought to have provided a ceiling for the population growth in the Middle Ages, recent studies have shown that the technology of medieval agriculture was always sufficient for the needs of the people under normal circumstances, and that it was only during exceptionally harsh times, such as the terrible weather of 1315–17, that the needs of the population could not be met. The Medieval Warm Period, between 900-1300 AD, brought generally warmer global temperatures, leading to increased harvests throughout Europe and a greater northern range for subtropical crops such as figs and olives. Greenland and Iceland were settled by Europeans during this period, and supported agricultural activities. The long-term warming period is generally thought to have occurred mainly in Europe, but other areas of the world experienced shorter warming periods at different times during this period, including China in the 11th and 12th centuries, with similar effects on agriculture. The climate variations found in Europe during the Medieval Warm Period returned to more moderate levels in the 15th century, and terminated in the Little Ice Age of the 16th-mid 19th centuries.
After 1492, a global exchange of previously local crops and livestock breeds occurred. Key crops involved in this exchange included maize, potatoes, sweet potatoes and manioc traveling from the New World to the Old, and several varieties of wheat, barley, rice and turnips going from the Old World to the New. There were very few livestock species in the New World, with horses, cattle, sheep and goats being completely unknown before their arrival with Old World settlers. Crops moving in both directions across the Atlantic Ocean caused population growth around the world, and had a lasting effect on many cultures. Since being introduced by Portuguese in the 16th century, maize and manioc have replaced traditional African crops as the continent's most important staple food crops.
After its introduction from South America to Spain in the late 1500s, the potato became an important staple crop throughout Europe by the late 1700s. The potato allowed farmers to produce more food, and initially added variety to the European diet. The nutrition boost caused by increased potato consumption resulted in lower disease rates, higher birth rates and lower mortality rates, causing a population boom throughout the British Empire, the US and Europe. The introduction of the potato also brought about the first intensive use of fertilizer, in the form of guano imported to Europe from Peru, and the first artificial pesticide, in the form of an arsenic compound used to fight Colorado potato beetles. Before the adoption of the potato as a major crop, the dependence on grain caused repetitive regional and national famines when the crops failed: 17 major famines in England alone between 1523 and 1623. Although initially almost eliminating the danger of famine, the resulting dependence on the potato eventually caused the European Potato Failure, a disastrous crop failure from disease resulting in widespread famine, and the death of over one million people in Ireland alone.
By the early 19th century, agricultural techniques, implements, seed stocks and cultivars had so improved that yield per land unit was many times that seen in the Middle Ages. The work of Charles Darwin and Gregor Mendel created the scientific foundation for plant breeding that led to its explosive impact over the past 150 years. The development of agriculture into its modern form has been possible through a continuing process of mechanization, with huge advances made starting in the early 19th century. Horse drawn machinery, such as the McCormick reaper, revolutionized harvesting, while inventions such as the cotton gin made possible the processing of large amounts of crops. During this same period, farmers experimented with steam-powered machinery, which was found to be expensive, dangerous and a fire hazard. In 1892, the first gasoline-powered tractor was successfully developed, and in 1923, the International Harvester Farmall tractor became the first all-purpose tractor, and marked a major point in the replacement of draft animals (particularly horses) with machines. Since that time, self-propelled mechanical harvesters (combines), planters, transplanters and other equipment have been developed, further revolutionizing agriculture. These inventions allowed farming tasks to be done with a speed and on a scale previously impossible, leading modern farms to output much greater volumes of high-quality produce per land unit.
In 1909 the Haber-Bosch method to synthesize ammonium nitrate was first demonstrated; it represented a major breakthrough and allowed crop yields to overcome previous constraints. In the years after World War II, the use of synthetic fertilizer increased rapidly, in sync with the increasing world population. In the past century agriculture has been characterized by increased productivity, the substitution of synthetic fertilizers and pesticides for labor, water pollution, and farm subsidies. In recent years there has been a backlash against the external environmental effects of conventional agriculture, resulting in the organic movement. Famines continued to sweep the globe through the 20th century. Through the effects of climactic events, government policy, war and crop failure, millions of people died in each of at least ten famines between the 1920s and the 1990s.
The cereals rice, corn, and wheat provide 60% of human food supply. Between 1700 and 1980, "the total area of cultivated land worldwide increased 466%" and yields increased dramatically, particularly because of selectively bred high-yielding varieties, fertilizers, pesticides, irrigation, and machinery. However, concerns have been raised over the sustainability of intensive agriculture. Intensive agriculture has become associated with decreased soil quality in India and Asia, and there has been increased concern over the effects of fertilizers and pesticides on the environment, particularly as population increases and food demand expands. The monocultures typically used in intensive agriculture increase the number of pests, which are controlled through pesticides. Integrated pest management (IPM), which "has been promoted for decades and has had some notable successes" has not significantly affected the use of pesticides because policies encourage the use of pesticides and IPM is knowledge-intensive.
Since the late 19th century, agricultural exploration expeditions have been mounted to find new species and new agricultural practices in different areas of the world. Two early American examples of expeditions include Frank N. Meyer's fruit- and nut-collecting trip to China and Japan from 1916 to 1918 and the Dorsett-Morse Oriental Agricultural Exploration Expedition to China, Japan, and Korea from 1929 to 1931 to collect soybean germplasm to support the rise in soybean agriculture in the United States. In the 21st century, plants have been used to grow biofuels, pharmaceuticals (including biopharmaceuticals), and bioplastics.
The Green Revolution refers to a series of research, development, and technology transfer initiatives, occurring between the 1940s and the late 1970s, that increased agriculture production around the world, beginning most markedly in the late 1960s. The initiatives, led by Norman Borlaug, the "Father of the Green Revolution" credited with saving over a billion people from starvation, involved the development of high-yielding varieties of cereal grains, expansion of irrigation infrastructure, modernization of management techniques, distribution of hybridized seeds, synthetic fertilizers, and pesticides to farmers.
Synthetic nitrogen, along with mined rock phosphate, pesticides and mechanization, have greatly increased crop yields in the early 20th century. Increased supply of grains has led to cheaper livestock as well. Further, global yield increases were experienced later in the 20th century when high-yield varieties of common staple grains such as rice, wheat, and corn were introduced as a part of the Green Revolution. The Green Revolution exported the technologies (including pesticides and synthetic nitrogen) of the developed world to the developing world. Thomas Malthus famously predicted that the Earth would not be able to support its growing population, but technologies such as the Green Revolution have allowed the world to produce a surplus of food.
Although the Green Revolution significantly increased rice yields in Asia, yield increases have not occurred in the past 15–20 years. The genetic "yield potential" has increased for wheat, but the yield potential for rice has not increased since 1966, and the yield potential for maize has "barely increased in 35 years". It takes a decade or two for herbicide-resistant weeds to emerge, and insects become resistant to insecticides within about a decade. Crop rotation helps to prevent resistances.
In the past century agriculture has been characterized by enhanced productivity, the use of synthetic fertilizers and pesticides, selective breeding, mechanization, water contamination, and farm subsidies. Proponents of organic farming such as Sir Albert Howard argued in the early 20th century that the overuse of pesticides and synthetic fertilizers damages the long-term fertility of the soil. While this feeling lay dormant for decades, as environmental awareness has increased in the 21st century there has been a movement towards sustainable agriculture by some farmers, consumers, and policymakers.
Since the 1990s, there has been a backlash against perceived external environmental effects of mainstream agriculture, particularly regarding water pollution, resulting in the organic movement. One of the major forces behind this movement has been the European Union, which first certified organic food in 1991 and began reform of its Common Agricultural Policy (CAP) in 2005 to phase out commodity-linked farm subsidies, also known as decoupling. The growth of organic farming has renewed research in alternative technologies such as integrated pest management and selective breeding. Recent mainstream technological developments include genetically modified food.
In late 2007, several factors pushed up the price of grains consumed by humans as well as used to feed poultry and dairy cows and other cattle, causing higher prices of wheat (up 58%), soybean (up 32%), and maize (up 11%) over the year. Contributing factors included increased demand for grain-fed animal products from the growing middle classes of countries such as China and India and the diversion of food grain to biofuel production. Food riots took place in several countries across the world. The International Fund for Agricultural Development posits that an increase in smallholder agriculture may be part of the solution to concerns about food prices and overall food security. They in part base this on the experience of Vietnam, which went from a food importer to large food exporter and saw a significant drop in poverty, due mainly to the development of smallholder agriculture in the country.
An epidemic of stem rust on wheat caused by race Ug99 is currently spreading across Africa and into Asia and is causing major concern. Approximately 40% of the world's agricultural land is seriously degraded. In Africa, if current trends of soil degradation continue, the continent might be able to feed just 25% of its population by 2025, according to UNU's Ghana-based Institute for Natural Resources in Africa.
In 2009, the agricultural output of China was the largest in the world, followed by the European Union, India and the United States, according to the International Monetary Fund (see below). Economists measure the total factor productivity of agriculture and by this measure agriculture in the United States is roughly 1.7 times more productive than it was in 1948. Six countries – the US, Canada, France, Australia, Argentina and Thailand – supply 90% of grain exports. Water deficits, which are already spurring heavy grain imports in numerous middle-sized countries, including Algeria, Iran, Egypt, and Mexico, may soon do the same in larger countries, such as China or India.
The Food and Agriculture Organization of the United Nations (FAO) leads international efforts to defeat hunger and provides forum for the negotiation of global agricultural regulations and agreements. Dr. Samuel Jutzi, director of FAO's animal production and health division, states that lobbying by large corporations has stopped reforms that would improve human health and the environment. For example, proposals in 2010 for a voluntary code of conduct for the livestock industry that would have provided incentives for improving standards for health, and environmental regulations, such as the number of animals an area of land can support without long-term damage, were successfully defeated due to large food company pressure.
As of 2011, the International Labour Organization states that approximately one billion people, or over 1/3 of the available work force, are employed in the global agricultural sector. Agriculture constitutes approximately 70 percent of the global employment of children, and in many countries employs the largest percentage of women of any industry. In 2007, the services sector overtook the agricultural sector as the largest employer. Between 1997 and 2007, the percentage of people employed in agriculture fell by over four percentage points, a trend that is expected to continue. The number of people employed in agriculture varies widely on a per-country basis, ranging from less than 2 percent in countries like the US and Canada to over 80 percent in many African nations. In developed countries, these figures are significantly lower than in previous centuries. During the 16th century in Europe, for example, between 55 and 75 percent of the population was engaged in agriculture, depending on the country. By the 19th century in Europe, this had dropped to between 35 and 65 percent. In the same countries today, the figure is less than 10 percent.
Agriculture remains a hazardous industry, and farmers worldwide remain at high risk of work-related injuries, lung disease, noise-induced hearing loss, skin diseases, as well as certain cancers related to chemical use and prolonged sun exposure. On industrialized farms, injuries frequently involve the use of agricultural machinery, and a common cause of fatal agricultural injuries in developed countries is tractor rollovers. Pesticides and other chemicals used in farming can also be hazardous to worker health, and workers exposed to pesticides may experience illnesses or birth defects. As an industry in which families commonly share in work and live on the farm itself, entire families can be at risk for injuries, illness, and death. Common causes of fatal injuries among young farm workers include drowning, machinery and motor vehicle-related accidents.
The International Labour Organization considers agriculture "one of the most hazardous of all economic sectors." It estimates that the annual work-related death toll among agricultural employees is at least 170,000, twice the average rate of other jobs. In addition, incidences of death, injury and illness related to agricultural activities often go unreported. The organization has developed the Safety and Health in Agriculture Convention, 2001, which covers the range of risks in the agriculture occupation, the prevention of these risks and the role that individuals and organizations engaged in agriculture should play.
Agricultural production systems
Crop cultivation systems
Cropping systems vary among farms depending on the available resources and constraints; geography and climate of the farm; government policy; economic, social and political pressures; and the philosophy and culture of the farmer.
Shifting cultivation (or slash and burn) is a system in which forests are burnt, releasing nutrients to support cultivation of annual and then perennial crops for a period of several years. Then the plot is left fallow to regrow forest, and the farmer moves to a new plot, returning after many more years (10–20). This fallow period is shortened if population density grows, requiring the input of nutrients (fertilizer or manure) and some manual pest control. Annual cultivation is the next phase of intensity in which there is no fallow period. This requires even greater nutrient and pest control inputs.
Further industrialization lead to the use of monocultures, when one cultivar is planted on a large acreage. Because of the low biodiversity, nutrient use is uniform and pests tend to build up, necessitating the greater use of pesticides and fertilizers. Multiple cropping, in which several crops are grown sequentially in one year, and intercropping, when several crops are grown at the same time are other kinds of annual cropping systems known as polycultures.
In subtropical and arid environments, the timing and extent of agriculture may be limited by rainfall, either not allowing multiple annual crops in a year, or requiring irrigation. In all of these environments perennial crops are grown (coffee, chocolate) and systems are practiced such as agroforestry. In temperate environments, where ecosystems were predominantly grassland or prairie, highly productive annual cropping is the dominant farming system.
The last century has seen the intensification, concentration and specialization of agriculture, relying upon new technologies of agricultural chemicals (fertilizers and pesticides), mechanization, and plant breeding (hybrids and GMO's). In the past few decades, a move towards sustainability in agriculture has also developed, integrating ideas of socio-economic justice and conservation of resources and the environment within a farming system. This has led to the development of many responses to the conventional agriculture approach, including organic agriculture, urban agriculture, community supported agriculture, ecological or biological agriculture, integrated farming and holistic management, as well as an increased trend towards agricultural diversification.
Important categories of crops include cereals and pseudocereals, pulses (legumes), forage, and fruits and vegetables. Specific crops are cultivated in distinct growing regions throughout the world. In millions of metric tons, based on FAO estimate.
|Top agricultural products, by crop types
(million tonnes) 2004 data
|Vegetables and melons||866|
|Roots and Tubers||715|
|Fish (2001 estimate)||130|
Food and Agriculture Organization (FAO)
|Top agricultural products, by individual crops
(million tonnes) 2011 data
Food and Agriculture Organization (FAO)
Livestock production systems
Animals, including horses, mules, oxen, water buffalo, camels, llamas, alpacas, donkeys, and dogs, are often used to help cultivate fields, harvest crops, wrangle other animals, and transport farm products to buyers. Animal husbandry not only refers to the breeding and raising of animals for meat or to harvest animal products (like milk, eggs, or wool) on a continual basis, but also to the breeding and care of species for work and companionship. Livestock production systems can be defined based on feed source, as grassland – based, mixed, and landless.
Grassland based livestock production relies upon plant material such as shrubland, rangeland, and pastures for feeding ruminant animals. Outside nutrient inputs may be used, however manure is returned directly to the grassland as a major nutrient source. This system is particularly important in areas where crop production is not feasible because of climate or soil, representing 30–40 million pastoralists. Mixed production systems use grassland, fodder crops and grain feed crops as feed for ruminant and monogastic (one stomach; mainly chickens and pigs) livestock. Manure is typically recycled in mixed systems as a fertilizer for crops. Approximately 68% of all agricultural land is permanent pastures used in the production of livestock.
Landless systems rely upon feed from outside the farm, representing the de-linking of crop and livestock production found more prevalently in OECD member countries. In the U.S., 70% of the grain grown is fed to animals on feedlots. Some of the practices used in commercial livestock production, including the usage of growth hormones, are controversial. Synthetic fertilizers are more heavily relied upon for crop production and manure utilization becomes a challenge as well as a source for pollution.
Tillage is the practice of plowing soil to prepare for planting or for nutrient incorporation or for pest control. Tillage varies in intensity from conventional to no-till. It may improve productivity by warming the soil, incorporating fertilizer and controlling weeds, but also renders soil more prone to erosion, triggers the decomposition of organic matter releasing CO2, and reduces the abundance and diversity of soil organisms.
Pest control includes the management of weeds, insects/mites, and diseases. Chemical (pesticides), biological (biocontrol), mechanical (tillage), and cultural practices are used. Cultural practices include crop rotation, culling, cover crops, intercropping, composting, avoidance, and resistance. Integrated pest management attempts to use all of these methods to keep pest populations below the number which would cause economic loss, and recommends pesticides as a last resort.
Nutrient management includes both the source of nutrient inputs for crop and livestock production, and the method of utilization of manure produced by livestock. Nutrient inputs can be chemical inorganic fertilizers, manure, green manure, compost and mined minerals. Crop nutrient use may also be managed using cultural techniques such as crop rotation or a fallow period. Manure is used either by holding livestock where the feed crop is growing, such as in managed intensive rotational grazing, or by spreading either dry or liquid formulations of manure on cropland or pastures.
Water management is where rainfall is insufficient or variable, which occurs to some degree in most regions of the world. Some farmers use irrigation to supplement rainfall. In other areas such as the Great Plains in the U.S. and Canada, farmers use a fallow year to conserve soil moisture to use for growing a crop in the following year. Agriculture represents 70% of freshwater use worldwide.
Crop alteration and biotechnology
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.
The Green Revolution popularized the use of conventional hybridization to increase yield many folds by creating "high-yielding varieties". For example, average yields of corn (maize) in the USA have increased from around 2.5 tons per hectare (t/ha) (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001. 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. Variations in yields are due mainly to variation in climate, genetics, and the level of intensive farming techniques (use of fertilizers, chemical pest control, growth control to avoid lodging).
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 and/or use of GMO foods and crops, which have been put in place due to concerns over potential health issues, declining agricultural diversity and contamination of non-GMO 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 glyphosates. 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.
Other GMO crops used by growers include insect-resistant crops, which have a gene from the soil bacterium Bacillus thuringiensis (Bt), which produces a toxin specific to insects. These crops protect plants from damage by insects. Some believe that similar or better pest-resistance traits can be acquired through traditional breeding practices, and resistance to various pests can be gained through hybridization or cross-pollination with wild species. In some cases, wild species are the primary source of resistance traits; some tomato cultivars that have gained resistance to at least 19 diseases did so through crossing with wild populations of tomatoes.
Agriculture imposes external costs upon society through pesticides, nutrient runoff, excessive water usage, and assorted other problems. 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 USA 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. In 2010, the International Resource Panel of the United Nations Environment Programme published a report assessing the environmental impacts of consumption and production. The study found that agriculture and food consumption are two of the most important drivers of environmental pressures, particularly habitat change, climate change, water use and toxic emissions.
A senior UN official and co-author of a UN report detailing this problem, Henning Steinfeld, said "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.
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 39–50%. 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 blooms 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.
Agriculture accounts for 70 per cent of withdrawals of freshwater resources. Agriculture is a major draw on water from aquifers, and currently draws from these underground water sources at an unsustainable rate. It is long known that aquifers in areas as diverse as northern China, the Upper Ganges and the western US are being depleted, and new research extends these problems to aquifers in Iran, Mexico and Saudi Arabian. Increasing pressure is being placed on water resources by industry and urban areas, meaning that water scarcity is increasing and agriculture is facing the challenge of producing more food for the world's growing population with fewer water resources. Agricultural water usage can also cause major environmental problems, including the destruction of natural wetlands, the spread of water-borne diseases, and land degradation through salinization and waterlogging, when irrigation is performed incorrectly.
Pesticide use has increased since 1950 to 2.5 million tons annually worldwide, yet crop loss from pests has remained relatively constant. The World Health Organization estimated in 1992 that 3 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.
Climate change has the potential to affect agriculture through changes in temperature, rainfall (timing and quantity), CO2, solar radiation and the interaction of these elements. Extreme events, such as droughts and floods, are forecast to increase as climate change takes hold. Agriculture is among sectors most vulnerable to the impacts of climate change; water supply for example, will be critical to sustain agricultural production and provide the increase in food output required to sustain the world's growing population. Transformational approaches will be needed to manage natural resources in future. For example, policies, practices and tools promoting climate-smart agriculture will be important, as will better use of scientific information on climate for assessing risks and vulnerability. Planners and policy-makers will need to help create suitable policies that encourage funding for such agricultural transformation.
Agriculture can both mitigate or worsen global warming. Some of the increase in CO2 in the atmosphere comes from the decomposition of organic matter in the soil, and much of the methane emitted into the atmosphere is caused by the decomposition of organic matter in wet soils such as rice paddies, as well as the normal digestive activities of farm animals. Further, wet or anaerobic soils also lose nitrogen through denitrification, releasing the greenhouse gases nitric oxide and nitrous oxide. Changes in management can reduce the release of these greenhouse gases, and soil can further be used to sequester some of the CO2 in the atmosphere.
Some major organisations are hailing farming within agroecosystems as the way forward for mainstream agriculture. Current farming methods have resulted in over-stretched water resources, high levels of erosion and reduced soil fertility. According to a report by the International Water Management Institute and UNEP, 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. The report suggested assigning 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. New technologies have given rise to innovations like conservation tillage, a farming process which helps prevent land loss to erosion, water pollution and enhances carbon sequestration.
Agricultural economics relates to the "production, distribution and consumption of [agricultural] goods and services". National government policies can significantly change the economic marketplace for agricultural products, in the form of taxation, subsidies, tariffs and other measures. Since at least the 1960s, a combination of import/export restrictions, exchange rate policies and subsidies have affected farmers in both the developing and developed world. In the 1980s, it was clear that non-subsidized farmers in developing countries were experiencing adverse affects from national policies that created artificially low global prices for farm products. Between the mid-1980s and the early 2000s, several international agreements were put into place that limited agricultural tariffs, subsidies and other trade restrictions.
However, as of 2009, there was still a significant amount of policy-driven distortion in global agricultural product prices. The three agricultural products with the greatest amount of trade distortion were sugar, milk and rice, mainly due to taxation. Among the oilseeds, sesame had the greatest amount of taxation, but overall, feed grains and oilseeds had much lower levels of taxation than livestock products. Since the 1980s, policy-driven distortions have seen a greater decrease among livestock products than crops during the worldwide reforms in agricultural policy. Despite this progress, certain crops, such as cotton, still see subsidies in developed countries artificially deflating global prices, causing hardship in developing countries with non-subsidized farmers.
In the United States, food costs attributed to food processing, distribution, and agricultural marketing have risen while the costs attributed to farming have declined. This is related to the greater efficiency of farming, combined with the increased level of value addition (e.g. more highly processed products) provided by the supply chain. From 1960 to 1980 the farm share was around 40%, but by 1990 it had declined to 30% and by 1998, 22.2%. Market concentration has increased in the sector as well, with the top 20 food manufacturers accounting for half the food-processing value in 1995, over double that produced in 1954. As of 2000 the top six US supermarket groups had 50% of sales compared to 32% in 1992. Although the total effect of the increased market concentration is likely increased efficiency, the changes redistribute economic surplus from producers (farmers) and consumers, and may have negative implications for rural communities.
List of countries by agricultural output
Below is a list of countries by agricultural output in 2011.
billions of US$
of GDP (%)
|% of Global
Energy and agriculture
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 1960–65 measuring cycle and the cycle from 1986 to 1990, 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. Modern agriculture's heavy reliance on petrochemicals and mechanization has raised concerns that oil shortages could increase costs and reduce agricultural output, causing food shortages.
|Agriculture and food system share (%) of total energy
consumption by three industrialized nations
(direct & indirect)
Modern or industrialized agriculture is dependent on fossil fuels in two fundamental ways: 1) direct consumption on the farm and 2) indirect consumption to manufacture inputs used on the farm. Direct consumption includes the use of lubricants and fuels to operate farm vehicles and machinery; and use of gas, liquid propane, and electricity to power dryers, pumps, lights, heaters, and coolers. American farms directly consumed about 1.2 exajoules (1.1 quadrillion BTU) in 2002, or just over 1 percent of the nation's total energy.
Indirect consumption is mainly oil and natural gas used to manufacture fertilizers and pesticides, which accounted for 0.6 exajoules (0.6 quadrillion BTU) in 2002. The natural gas and coal consumed by the production of nitrogen fertilizer can account for over half of the agricultural energy usage. China utilizes mostly coal in the production of nitrogen fertilizer, while most of Europe uses large amounts of natural gas and small amounts of coal. According to a 2010 report published by The Royal Society, agriculture is increasingly dependent on the direct and indirect input of fossil fuels. Overall, the fuels used in agriculture vary based on several factors, including crop, production system and location. The energy used to manufacture farm machinery is also a form of indirect agricultural energy consumption. Together, direct and indirect consumption by US farms accounts for about 2 percent of the nation's energy use. Direct and indirect energy consumption by U.S. farms peaked in 1979, and has gradually declined over the past 30 years. Food systems encompass not just agricultural production, but also off-farm processing, packaging, transporting, marketing, consumption, and disposal of food and food-related items. Agriculture accounts for less than one-fifth of food system energy use in the US.
In 2007, higher incentives for farmers to grow non-food biofuel crops combined with other factors, such as overdevelopment of former farm lands, rising transportation costs, climate change, growing consumer demand in China and India, and population growth, caused food shortages in Asia, the Middle East, Africa, and Mexico, as well as rising food prices around the globe. As of December 2007, 37 countries faced food crises, and 20 had imposed some sort of food-price controls. Some of these shortages resulted in food riots and even deadly stampedes.
Mitigation of effects of petroleum shortages
In the event of a petroleum shortage (see peak oil for global concerns), organic agriculture can be more attractive than conventional practices that use petroleum-based pesticides, herbicides, or fertilizers. Some studies using modern organic-farming methods have reported yields as high as those available from conventional farming. In the aftermath of the fall of the Soviet Union, with shortages of conventional petroleum-based inputs, Cuba made use of mostly organic practices, including biopesticides, plant-based pesticides and sustainable cropping practices, to feed its populace. However, organic farming may be more labor-intensive and would require a shift of the workforce from urban to rural areas. The reconditioning of soil to restore nutrients lost during the use of monoculture agriculture techniques also takes time.
It has been suggested that rural communities might obtain fuel from the biochar and synfuel process, which uses agricultural waste to provide charcoal fertilizer, some fuel and food, instead of the normal food vs fuel debate. As the synfuel would be used on-site, the process would be more efficient and might just provide enough fuel for a new organic-agriculture fusion.
It has been suggested that some transgenic plants may some day be developed which would allow for maintaining or increasing yields while requiring fewer fossil-fuel-derived inputs than conventional crops. The possibility of success of these programs is questioned by ecologists and economists concerned with unsustainable GMO practices such as terminator seeds.
While there has been some research on sustainability using GMO crops, at least one prominent multi-year attempt by Monsanto Company has been unsuccessful, though during the same period traditional breeding techniques yielded a more sustainable variety of the same crop.
Agricultural policy is the set of government decisions and actions relating to domestic agriculture and imports of foreign agricultural products. Governments usually implement agricultural policies with the goal of achieving a specific outcome in the domestic agricultural product markets. Some overarching themes include risk management and adjustment (including policies related to climate change, food safety and natural disasters), economic stability (including policies related to taxes), natural resources and environmental sustainability (especially water policy), research and development, and market access for domestic commodities (including relations with global organizations and agreements with other countries). Agricultural policy can also touch on food quality, ensuring that the food supply is of a consistent and known quality, food security, ensuring that the food supply meets the population's needs, and conservation. Policy programs can range from financial programs, such as subsidies, to encouraging producers to enroll in voluntary quality assurance programs.
- Agricultural engineering
- Building-integrated agriculture
- Contract farming
- Factory farming
- Feed additive
- Hill farming
- List of basic agriculture topics
- List of subsistence techniques
- Pharming (genetics)
- Remote sensing
- Vertical farming
- Safety and health in agriculture. International Labour Organization. 1999. pp. 77–. ISBN 978-92-2-111517-5. Retrieved 13 September 2010.
- Chantrell, Glynnis, ed. (2002). The Oxford Dictionary of Word Histories. Oxford University Press. p. 14. ISBN 0-19-863121-9.
- Ulrich G. Mueller, Nicole M. Gerardo, Duur K. Aanen, Diana L. Six, and Ted R. Schultz (December 2005). "The Evolution of Agriculture in Insects". Annual Review of Ecology, Evolution, and Systematics 36: 563–595. doi:10.1146/annurev.ecolsys.36.102003.152626.
- "Definition of Agriculture". State of Maine. Retrieved 2013-05-06.
- Committee on Forestry Research, National Research Council (1990). Forestry Research: A Mandate for Change. National Academies Press. pp. 15–16. ISBN 0309042488.
- Budowski, Gerardo (1982). "Applicability of agro-forestry systems". In MacDonald, L.H. Agro-forestry in the African Humid Tropics. United Nations University. ISBN 92-808-0364-6.
- Tellier, Luc-Normand (2009). Urban world history: an economic and geographical perspective. PUQ. p. 26. ISBN 2-7605-1588-5.
- Douglas John McConnell (2003). The Forest Farms of Kandy: And Other Gardens of Complete Design. p. 1. ISBN 978-0-7546-0958-2.
- Douglas John McConnell (1992). The forest-garden farms of Kandy, Sri Lanka. p. 1. ISBN 978-92-5-102898-8.
- "The Development of Agriculture". National Geographic. Retrieved 2013-04-22.
- DK Jordan (November 24, 2012). "Living the Revolution". The Neolithic. University of California – San Diego. Retrieved 2013-04-22.
- Hancock, James F. (2012). Plant evolution and the origin of crop species (3rd ed.). CABI. p. 119. ISBN 1845938011.
- UN Industrial Development Organization, International Fertilizer Development Center (1998). The Fertilizer Manual (3rd ed.). Springer. p. 46. ISBN 0792350324.
- S. Johannessen and C. A. Hastorf (eds.), ed. (1994). Corn and Culture in the Prehistoric New World. Boulder, Colorado: Westview Press. ISBN 0813383757.
- DK Jordan (November 24, 2012). "Beyond Wheat". The Neolithic. University of California – San Diego. Retrieved 2013-04-22.
- Vergano, Dan (January 19, 2011). "Grapes domesticated 8,000 years ago". USA Today. Retrieved 2013-05-04.
- DK Jordan (November 24, 2012). "The "Agricultural Revolution"". The Neolithic. University of California – San Diego. Retrieved 2013-04-22.
- Adams, Kristina. "Horses in History: A Bibliography". USDA National Agricultural Library. Retrieved 2013-05-24.
- Heiser, Carl B., Jr. (1992). "On Possible Sources of the Tobacco of Prehistoric Eastern North America". Current Anthropology 33: 54–56.
- Michael Moïssey Postan, H. J. Habakkuk, Miller, Edward, ed. (1987). Cambridge Economic History of Europe: Vol. 2: Trade and Industry in the Middle Ages. Cambridge University Press. p. 28. ISBN 0521087090.
- Brian M. Fagan (2004). The Seventy Great Inventions of the Ancient World. Thames & Hudson. ISBN 0500051305.
- "Farming". Egypt's Golden Empire. PBS. Retrieved 2013-05-22.
- Janick, Jules (2008). "Roman Agricultural History". Purdue University. Retrieved 2013-05-22.
- Janick, Jules. "History of Agricultural and Horticultural Technology in Asia" (PDF). Purdue University. pp. 3–4. Retrieved 2013-05-23.
- Lesley Adkins, Roy A. Adkins (1998). Handbook to Life in Ancient Rome. Oxford University Press. pp. 194–196. ISBN 0195123328.
- Mascarelli, Amanda (November 5, 2010). "Mayans converted wetlands to farmland". Nature. doi:10.1038/news.2010.587.
- Morgan, John (November 6, 2013). "Invisible Artifacts: Uncovering Secrets of Ancient Maya Agriculture with Modern Soil Science". Soil Horizons 53 (6). doi:10.2136/sh2012-53-6-lf.
- Jourdan, Pablo. "Medieval Horticulture/Agriculture". Ohio State University. Retrieved 2013-04-24.
- Janick, Jules (2008). "Islamic Influences on Western Agriculture". Purdue University. Retrieved 2013-05-23.
- Backer, Patricia. "Part 1 – Medieval European history". History of Technology. San Jose State University. Retrieved 2013-04-24.
- Glick, Thomas F. (2005). Medieval Science, Technology And Medicine: An Encyclopedia. Volume 11 of The Routledge Encyclopedias of the Middle Ages Series. Psychology Press. p. 270. ISBN 0415969301.
- Newman, Paul B. (2001). Daily Life in the Middle Ages. McFarland. pp. 88–89. ISBN 0786450525.
- Campbell, Bruce M. S.; M. Overton (1993). "A New Perspective on Medieval and Early Modern Agriculture: Six Centuries of Norfolk Farming, c.1250-c.1850". Past and Present 141: 38–105. doi:10.1093/past/141.1.38.
- Campbell, Bruce M.S. (2000). English Seigniorial Agriculture, 1250–1450. Cambridge: Cambridge University Press. ISBN 0-521-30412-1.
- Stone, David (2005). Decision-Making in Medieval Agriculture. Oxford: Oxford University Press. ISBN 0-19-924776-5.
- John Langdon (2010). Robert E. Bjork, ed. The Oxford Dictionary of the Middle Ages. Oxford, England: Oxford University Press. pp. 20–23. ISBN 978-0-19-866262-4.
- Mann, Michael E. (2002). "Medieval Climactic Optimum". In Munn, Ted. Encyclopedia of Global Environmental Change 1. John Wiley & Sons. pp. 514–516.
- Crosby, Alfred. "The Columbian Exchange". The Gilder Lehrman Institute of American History. Retrieved 2013-05-11.
- Wagner, Holly. "Super-Sized Cassava Plants May Help Fight Hunger In Africa". The Ohio State University. Retrieved 2013-05-11.
- Florence Wambugu and John Wafula, ed. (2000). "Advances in Maize Streak Virus Disease Research in Eastern and Southern Africa". International Service for the Acquisition of of Agri-Biotech Applications. Retrieved 2013-04-16.
- Chapman, Jeff. "The Impact of the Potato". History Magazine (2).
- Mann, Charles C. (November 2011). "How the Potato Changed History". Smithsonian.
- Noel Kingsbury (2009). Hybrid: The History and Science of Plant Breeding. Chicago: University of Chicago Press.
- Janick, Jules. "Agricultural Scientific Revolution: Mechanical". Purdue University. Retrieved 2013-05-24.
- Reid, John F. (Fall 2011). "The Impact of Mechanization on Agriculture". The Bridge on Agriculture and Information Technology 41 (3).
- "A Historical Perspective". International Fertilizer Industry Association. Retrieved 2013-05-07.
- Philpott, Tom (April 19, 2013). "A Brief History of Our Deadly Addiction to Nitrogen Fertilizer". Mother Jones. Retrieved 2013-05-07.
- "Ten worst famines of the 20th century". Sydney Morning Herald. August 15, 2011.
- Matson et al. (1997). "Agricultural Intensification and Ecosystem Properties". Science.
- "South China explorations: typescript, 25 July 1916 – 21 September 1918". USDA National Agricultural Library. Retrieved 2013-05-24.
- "Dorsett-Morse Oriental Agricultural Exploration Expedition Collection". USDA National Agricultural Library. Retrieved 2013-05-24.
- P. Byrne (April 2008). "Bio-pharming". Colorado State University. Retrieved 2013-04-16.
- Brickates Kennedy, Val (16 October 2007). "Plastics that are green in more ways than one". The Wall Street Journal (New York).
- Hazell, Peter B.R. (2009). "The Asian Green Revolution". IFPRI Discussion Paper (Intl Food Policy Res Inst). GGKEY:HS2UT4LADZD.
- Barrionuevo, Alexei; Bradsher, Keith (8 December 2005). "Sometimes a Bumper Crop Is Too Much of a Good Thing". The New York Times.
- Tilman D, Cassman KG, Matson PA, Naylor R, Polasky S (August 2002). "Agricultural sustainability and intensive production practices". Nature 418 (6898): 671–7. doi:10.1038/nature01014. PMID 12167873.
- Scheierling, Susanne M. (1995). "Overcoming agricultural pollution of water : the challenge of integrating agricultural and environmental policies in the European Union, Volume 1". The World Bank. Retrieved 2013-04-15.
- "CAP Reform". European Commission. 2003. Retrieved 2013-04-15.
- "At Tyson and Kraft, Grain Costs Limit Profit". The New York Times. Bloomberg. 6 September 2007.
- McMullen, Alia (7 January 2008). "Forget oil, the new global crisis is food". Financial Post (Toronto).
- Watts, Jonathan (4 December 2007). "Riots and hunger feared as demand for grain sends food costs soaring", The Guardian (London).
- Mortished, Carl (7 March 2008)."Already we have riots, hoarding, panic: the sign of things to come?", The Times (London).
- Borger, Julian (26 February 2008). "Feed the world? We are fighting a losing battle, UN admits", The Guardian (London).
- "Food prices: smallholder farmers can be part of the solution". International Fund for Agricultural Development. Retrieved 2013-04-24.
- McKie, Robin; Rice, Xan (22 April 2007). "Millions face famine as crop disease rages", The Observer' (London).
- Mackenzie, Debora (3 April 2007). "Billions at risk from wheat super-blight". New Scientist (London) (2598): 6–7. Retrieved 19 April 2007.
- Leonard, K.J. (February 2001). "Black stem rust biology and threat to wheat growers". USDA Agricultural Research Service. Retrieved 2013-04-22.
- Sample, Ian (31 August 2007). "Global food crisis looms as climate change and population growth strip fertile land", The Guardian (London).
- "Africa may be able to feed only 25% of its population by 2025", mongabay.com, 14 December 2006.
- "Agricultural Productivity in the United States". USDA Economic Research Service. July 5, 2012. Retrieved 2013-04-22.
- "The Food Bubble Economy". The Institute of Science in Society.
- Brown, Lester R. "Global Water Shortages May Lead to Food Shortages-Aquifer Depletion". Archived from the original on 24 July 2010.
- "India grows a grain crisis", Asia Times (Hong Kong). 21 July 2006.
- Jowit, Juliette (Sept. 22 2010). "Corporate Lobbying Is Blocking Food Reforms, Senior UN Official Warns: Farming Summit Told of Delaying Tactics by Large Agribusiness and Food Producers on Decisions that Would Improve Human Health and the Environment". The Guardian (London).
- "Safety and health in agriculture". International Labour Organization. March 21, 2011. Retrieved 2013-04-24.
- AP (January 26, 2007). "Services sector overtakes farming as world's biggest employer: ILO". The Financial Express. Retrieved 2013-04-24.
- "Labor Force – By Occupation". The World Factbook. Central Intelligence Agency. Retrieved 2013-05-04.
- Allen, Robert C. "Economic structure and agricultural productivity in Europe, 1300–1800" (PDF). European Review of Economic History 3: 1–25.
- "NIOSH Workplace Safety & Health Topic: Agricultural Injuries". Centers for Disease Control and Prevention. Retrieved 2013-04-16.
- "NIOSH Pesticide Poisoning Monitoring Program Protects Farmworkers". Centers for Disease Control and Prevention. Retrieved 2013-04-15.
- "NIOSH Workplace Safety & Health Topic: Agriculture". Centers for Disease Control and Prevention. Retrieved 2013-04-16.
- "Agriculture: A hazardous work". International Labour Organization. June 15, 2009. Retrieved 2013-04-24.
- "Analysis of farming systems". Food and Agriculture Organization. Retrieved 2013-05-22.
- Acquaah, G. 2002. Agricultural Production Systems. pp. 283–317 in "Principles of Crop Production, Theories, Techniques and Technology". Prentice Hall, Upper Saddle River, NJ.
- Chrispeels, M.J.; Sadava, D.E. 1994. "Farming Systems: Development, Productivity, and Sustainability". pp. 25–57 in Plants, Genes, and Agriculture. Jones and Bartlett, Boston, MA.
- Gold, M.V. 1999. USDA National Agriculture Library. Beltsville, MD. "Sustainable Agriculture: Definitions and Terms". Retrieved 7 December 2008.
- Earles, R.; Williams, P. 2005. ATTRA National Sustainable Agriculture Information Service. Fayetville, AR. "Sustainable Agriculture:An Introduction". Retrieved 7 December 2008.
- "Food and Agriculture Organization of the United Nations (FAOSTAT)". Archived from the original on 18 January 2013. Retrieved 2 February 2013.
- Sere, C.; Steinfeld, H.; Groeneweld, J. 1995. "Description of Systems in World Livestock Systems – Current status issues and trends". U.N. Food and Agriculture Organization. Rome. Retrieved 7 December 2008.
- FAO Database, 2003
- "Growth Promoting Hormones Pose Health Risk to Consumers, Confirms EU Scientific Committee". European Union. April 23, 2002. Retrieved 2013-04-06.
- Brady, N.C. and R.R. Weil. 2002. Elements of the Nature and Properties of Soils. Pearson Prentice Hall, Upper Saddle River, NJ.
- Acquaah, G. 2002. "Land Preparation and Farm Energy" pp.318–338 in Principles of Crop Production, Theories, Techniques and Technology. Prentice Hall, Upper Saddle River, NJ.
- Acquaah, G. 2002. "Pesticide Use in U.S. Crop Production" pp.240–282 in Principles of Crop Production, Theories, Techniques and Technology. Prentice Hall, Upper Saddle River, NJ.
- Acquaah, G. 2002. "Soil and Land" pp.165–210 in Principles of Crop Production, Theories, Techniques and Technology. Prentice Hall, Upper Saddle River, NJ.
- Chrispeels, M.J.; Sadava, D.E. 1994. "Nutrition from the Soil" pp.187–218 in Plants, Genes, and Agriculture. Jones and Bartlett, Boston, MA.
- Brady, N.C.; Weil, R.R. 2002. "Practical Nutrient Management" pp.472–515 in Elements of the Nature and Properties of Soils. Pearson Prentice Hall, Upper Saddle River, NJ.
- Acquaah, G. 2002. "Plants and Soil Water" pp.211–239 in Principles of Crop Production, Theories, Techniques and Technology. Prentice Hall, Upper Saddle River, NJ.
- Pimentel, D.; Berger, D.; Filberto, D.; Newton, M.; et al. (2004). "Water Resources: Agricultural and Environmental Issues". Bioscience 54: 909–918.
- "History of Plant Breeding". Colorado State University. January 29, 2004. Retrieved 2013-05-11.
- Stadler, L. J.; Sprague, G.F. (15 October 1936). "Genetic Effects of Ultra-Violet Radiation in Maize: I. Unfiltered Radiation" (PDF). Proceedings of the National Academy of Sciences of the United States of America (US Department of Agriculture and Missouri Agricultural Experiment Station) 22 (10): 572–578. doi:10.1073/pnas.22.10.572. PMC 1076819. PMID 16588111. Archived from the original on 24 October 2007. Retrieved 11 October 2007.
- Berg, Paul; Singer, Maxine (15 August 2003). George Beadle: An Uncommon Farmer. The Emergence of Genetics in the 20th century. Cold Springs Harbor Laboratory Press. ISBN 978-0-87969-688-7.
- Ruttan, Vernon W. (December 1999). "Biotechnology and Agriculture: A Skeptical Perspective" (PDF). AgBioForum 2 (1): 54–60.
- Cassman, K. (5 December 1998). "Ecological intensification of cereal production systems: The Challenge of increasing crop yield potential and precision agriculture". Proceedings of a National Academy of Sciences Colloquium, Irvine, California (University of Nebraska). Archived from the original on 24 October 2007. Retrieved 11 October 2007.
- Conversion note: 1 bushel of wheat = 60 pounds (lb) ≈ 27.215 kg. 1 bushel of maize = 56 pounds ≈ 25.401 kg
- "20 Questions on Genetically Modified Foods". World Health Organization. Retrieved 2013-04-16.
- Whiteside, Stephanie (November 28, 2012). "Peru bans genetically modified foods as US lags". Current TV. Retrieved 2013-05-07.
- Shiva, Vandana (2005). Earth Democracy: Justice, Sustainability, and Peace. Cambridge, MA: South End Press.
- Kathrine Hauge Madsen and Jens Carl Streibig. "Benefits and risks of the use of herbicide-resistant crops". Weed Management for Developing Countries. FAO. Retrieved 2013-05-04.
- "Farmers Guide to GMOs". Rural Advancement Foundation International. Retrieved 2013-04-16.
- Brian Hindo (February 13, 2008). "Report Raises Alarm over 'Super-weeds'". Bloomberg BusinessWeek.
- Ozturk, et al., "Glyphosate inhibition of ferric reductase activity in iron deficient sunflower roots", New Phtologist, 177:899–906, 2008.
- "Insect-resistant Crops Through Genetic Engineering". University of Illinois. Retrieved 2013-05-04.
- Kimbrell, A. (2002). Fatal Harvest: The Tragedy of Industrial Agriculture. Washington: Island Press.
- Pretty, J et al. (2000). "An assessment of the total external costs of UK agriculture". Agricultural Systems 65 (2): 113–136. doi:10.1016/S0308-521X(00)00031-7.
- Tegtmeier, E.M.; Duffy, M. (2005). "External Costs of Agricultural Production in the United States". The Earthscan Reader in Sustainable Agriculture.
- International Resource Panel (2010). "Priority products and materials: assessing the environmental impacts of consumption and production". United Nations Environment Programme. Retrieved 2013-05-07.
- "Livestock a major threat to environment". UN Food and Agriculture Organization. 29 November 2006. Archived from the original on 28 March 2008. Retrieved 2013-04-24.
- Steinfeld, H.; Gerber, P.; Wassenaar, T.; Castel, V.; Rosales, M.; de Haan, C. (2006). "Livestock's Long Shadow – Environmental issues and options". Rome: U.N. Food and Agriculture Organization. Archived from the original on 25 June 2008. Retrieved 5 December 2008.
- Vitousek, P.M.; Mooney, H.A.; Lubchenco, J.; Melillo, J.M. 1997. "Human Domination of Earth's Ecosystems". Science 277:494–499.
- Bai, Z.G., D.L. Dent, L. Olsson, and M.E. Schaepman (November 2008). "Global assessment of land degradation and improvement 1:identification by remote sensing" (PDF). FAO/ISRIC. Retrieved 2013-05-24.
- Carpenter, S.R., N.F. Caraco, D.L. Correll, R.W. Howarth, A.N. Sharpley, and V.H. Smith (1998). "Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen". Ecological Applications 8: 559–568.
- Molden, D. (ed.). "Findings of the Comprehensive Assessment of Water Management in Agriculture". Annual Report 2006/2007. International Water Management Institute. Retrieved 2013-05-07.
- Li, Sophia (August 13, 2012). "Stressed Aquifers Around the Globe". New York Times. Retrieved 2013-05-07.
- "Water Use in Agriculture". FAO. November 2005. Retrieved 2013-05-07.
- "Water Management: Towards 2030". FAO. March 2003. Retrieved 2013-05-07.
- Pimentel, D. T.W. Culliney, and T. Bashore (1996.). "Public health risks associated with pesticides and natural toxins in foods". Radcliffe's IPM World Textbook. Retrieved 2013-05-07.
- WHO. 1992. Our planet, our health: Report of the WHU commission on health and environment. Geneva: World Health Organization.
- Chrispeels, M.J. and D.E. Sadava. 1994. "Strategies for Pest Control" pp.355–383 in Plants, Genes, and Agriculture. Jones and Bartlett, Boston, MA.
- Avery, D.T. (2000). Saving the Planet with Pesticides and Plastic: The Environmental Triumph of High-Yield Farming. Indianapolis, IN: Hudson Institute.
- "Home". Center for Global Food Issues. Retrieved 2013-05-24.
- Lappe, F.M., J. Collins, and P. Rosset. 1998. "Myth 4: Food vs. Our Environment" pp. 42–57 in World Hunger, Twelve Myths, Grove Press, New York.
- Harvey, Fiona (November 18, 2011). "Extreme weather will strike as climate change takes hold, IPCC warns". The Guardian.
- "SREX: Lessons for the agricultural sector". Climate & Development Knowledge Network. Retrieved 2013-05-24.
- Brady, N.C. and R.R. Weil. 2002. "Soil Organic Matter" pp. 353–385 in Elements of the Nature and Properties of Soils. Pearson Prentice Hall, Upper Saddle River, NJ.
- Brady, N.C. and R.R. Weil. 2002. "Nitrogen and Sulfur Economy of Soils" pp. 386–421 in Elements of the Nature and Properties of Soils. Pearson Prentice Hall, Upper Saddle River, NJ.
- Boelee, E. (Ed) (2011). "Ecosystems for water and food security". IWMI/UNEP. Retrieved 2013-05-24.
- Molden, D. "Opinion: The Water Deficit" (PDF). The Scientist. Retrieved 2011-08-23.
- Safefood Consulting, Inc. (2005). "Benefits of Crop Protection Technologies on Canadian Food Production, Nutrition, Economy and the Environment". CropLife International. Retrieved 2013-05-24.
- Trewavas, Anthony (2004). "A critical assessment of organic farming-and-food assertions with particular respect to the UK and the potential environmental benefits of no-till agriculture". Crop Protection: 757–781.
- "Agricultural Economics". University of Idaho. Retrieved 2013-04-16.
- Peter J. Lloyd, Johanna L. Croser, Kym Anderson (March 2009). "How Do Agricultural Policy Restrictions to Global Trade and Welfare Differ Across Commodities". Policy Research Working Paper #4864. The World Bank. pp. 2–3. Retrieved 2013-04-16.
- Kym Anderson and Ernesto Valenzuela (April 2006). "Do Global Trade Distortions Still Harm Developing Country Farmers?". World Bank Policy Research Working Paper 3901. World Bank. pp. 1–2. Retrieved 2013-04-16.
- Peter J. Lloyd, Johanna L. Croser, Kym Anderson (March 2009). "How Do Agricultural Policy Restrictions to Global Trade and Welfare Differ Across Commodities". Policy Research Working Paper #4864. The World Bank. p. 21. Retrieved 2013-04-16.
- Glenys Kinnock (May 24, 2011). "America's $24bn subsidy damages developing world cotton farmers". The Guardian. Retrieved 2013-04-16.
- Sexton, R.J. (2000). "Industrialization and Consolidation in the US Food Sector: Implications for Competition and Welfare". American Journal of Agricultural Economics 82 (5): 1087–1104. doi:10.1111/0002-9092.00106.
- "World oil supplies are set to run out faster than expected, warn scientists". The Independent. 14 June 2007.
- Robert W. Herdt (May 30, 1997). "The Future of the Green Revolution: Implications for International Grain Markets" (PDF). The Rockefeller Foundation. p. 2. Retrieved 2013-04-16.
- Randy Schnepf (November 19, 2004). "Energy use in Agriculture: Background and Issues" (PDF). CRS Report for Congress. Congressional Research Service.
- Rebecca White (2007). "Carbon governance from a systems perspective: an investigation of food production and consumption in the UK" (PDF). Oxford University Center for the Environment.
- Martin Heller and Gregory Keoleian (2000). "Life Cycle-Based Sustainability Indicators for Assessment of the U.S. Food System" (PDF). University of Michigan Center for Sustainable Food Systems.
- Patrick Canning, Ainsley Charles, Sonya Huang, Karen R. Polenske, and Arnold Waters (2010). "Energy Use in the U.S. Food System". USDA Economic Research Service Report No. ERR-94. United States Department of Agriculture.
- Wallgren, Christine; Höjer, Mattias (2009). "Eating energy—Identifying possibilities for reduced energy use in the future food supply system". Energy Policy 37 (12): 5803–5813. doi:10.1016/j.enpol.2009.08.046. ISSN 03014215.
- Jeremy Woods, Adrian Williams, John K. Hughes, Mairi Black and Richard Murphy (August 2010). "Energy and the food system". Philosophical Transactions of the Royal Society 365 (1554): 2991–3006. doi:10.1098/rstb.2010.0172.
- Smith, Kate; Edwards, Rob (8 March 2008). "2008: The year of global food crisis". The Herald (Glasgow).
- "The global grain bubble", The Christian Science Monitor (Boston), 18 January 2008.
- "The cost of food: Facts and figures", BBC News Online (London), 16 October 2008.
- Walt, Vivienne (27 February 2008)."The World's Growing Food-Price Crisis", Time (New York).
- "World oil supplies are set to run out faster than expected, warn scientists". The Independent. 14 June 2007.
- "Can Sustainable Agriculture Really Feed the World?". University of Minnesota. August 2010. Retrieved 2013-04-15.
- "Cuban Organic Farming Experiment". Harvard School of Public Health. Retrieved 2013-04-15.
- Strochlic, R.; Sierra, L. (2007). "Conventional, Mixed, and "Deregistered" Organic Farmers: Entry Barriers and Reasons for Exiting Organic Production in California". California Institute for Rural Studies. Retrieved 2013-04-15.
- P. Read (2005). "Carbon cycle management with increased photo-synthesis and long-term sinks". Geophysical Research Abstracts 7: 11082.
- Greene, Nathanael (December 2004). "How biofuels can help end America's energy dependence". Biotechnology Industry Organization.
- Srinivas (June 2008). Reviewing The Methodologies For Sustainable Living 7. The Electronic Journal of Environmental, Agricultural and Food Chemistry.
- R. Pillarisetti and Kylie Radel (June 2004). Economic and Environmental Issues in International Trade and Production of Genetically Modified Foods and Crops and the WTO 19 (2). Journal of Economic Integration. pp. 332–352.
- Conway, G. (2000). Genetically modified crops: risks and promise. 4(1): 2. Conservation Ecology.
- "Monsanto failure". New Scientist 181 (2433) (London). 7 February 2004. Retrieved 18 April 2008.
- Lindsay Hogan and Paul Morris (October 2010). "Agricultural and food policy choices in Australia" (PDF). Sustainable agriculture and food policy in the 21st century: challenges and solutions (Australian Bureau of Agricultural and Resource Economics – Bureau of Rural Sciences): 13. Retrieved 2013-04-22.
- "Agriculture: Not Just Farming...". European Union. Retrieved 2013-04-22.
- Alvarez, Robert A. (2007). "The March of Empire: Mangos, Avocados, and the Politics of Transfer". Gastronomica, Vol. 7, No. 3, 28–33. Retrieved on 12 November 2008.
- Bolens, L. (1997). "Agriculture" in Selin, Helaine (ed.), Encyclopedia of the history of Science, technology, and Medicine in Non Western Cultures. Kluwer Academic Publishers, Dordrecht/Boston/London, pp. 20–22.
- Collinson, M. (ed.) A History of Farming Systems Research. CABI Publishing, 2000. ISBN 978-0-85199-405-5
- Mazoyer, Marcel; Roudart, Laurence (2006). A history of world agriculture : from the Neolithic Age to the current crisis. Monthly Review Press, New York. ISBN 978-1-58367-121-4
- Watson, A.M. (1983). Agricultural Innovation in the Early Islamic World, Cambridge University Press.
|Wikimedia Commons has media related to: Agriculture|
|Wikiquote has a collection of quotations related to: Agriculture|
|Look up agriculture in Wiktionary, the free dictionary.|
|Wikiversity has learning materials about Agriculture at|
- Agriculture from UCB Libraries GovPubs
- Agriculture and Rural development from the World Bank
- The World Bank on Agricultural water management
- Gender in agriculture and rural development (FAO)
- Index to the Manuscript Collections Special Collections, National Agricultural Library
- The American Society of Agronomy (ASA)
- International Federation of Agricultural Producers (IFAP)
- NIOSH Agriculture Page – safety laws, tips, and guidelines
- National Ag Safety Database
- North American Guidelines for Children's Agricultural Tasks
- UKAgriculture.com – Advance the education of the public in all aspects of agriculture, the countryside and the rural economy
- Collection of Agriculture Dictionaries
- Peace Palace Library – Research Guide
- Farmer Power: The Continuing Confrontation between Subsistence Farmers and Development Bureaucrats by Tony Waters at Ethnography.com