Along with ceramics production, sedentism, and herding, agriculture is a major component of the Neolithic as it is defined in Europe. Therefore, the agricultural system of the first Neolithic societies and the dispersal of exogenous cultivated plants to Europe are the subject of many scientific studies. To work on these issues, archaeobotanists rely on residual plant remains—crop seeds, weeds, and wild plants—from archaeological structures like detritic pits, and, less often, storage contexts. To date, no plant with an economic value has been identified as domesticated in Western Europe except possibly opium poppy. The earliest seeds identified at archaeological sites dated to about 5500–5200
The Neolithic pioneers settled in an area that had experienced a long tradition of hunting and gathering. The Neolithization of Europe followed a colonization model. The Mesolithic groups, although exploiting plant resources such as hazelnut more or less intensively, did not significantly change the landscape. The impact of their settlements and their activities are hardly noticeable through palynology, for example. The control of the mode of reproduction of plants has certainly increased the prevalence of Homo sapiens, involving, among others, a demographic increase and the ability to settle down in areas that were not well adapted to year-round occupation up to that point. The characterization of past agricultural systems, such as crop plants, technical processes, and the impact of anthropogenic activities on the landscape, is essential for understanding the interrelation of human societies and the plant environment. This interrelation has undoubtedly changed deeply with the Neolithic Revolution.
Kandace D. Hollenbach and Stephen B. Carmody
The possibility that native peoples in eastern North America had cultivated plants prior to the introduction of maize was first raised in 1924. Scant evidence was available to support this speculation, however, until the “flotation revolution” of the 1960s and 1970s. As archaeologists involved in large-scale projects began implementing flotation, paleoethnobotanists soon had hundreds of samples and thousands of seeds that demonstrated that indigenous peoples grew a suite of crops, including cucurbit squashes and gourds, sunflower, sumpweed, and chenopod, which displayed signs of domestication. The application of accelerator mass spectrometry (AMS) dating to cucurbit rinds and seeds in the 1980s placed the domestication of these four crops in the Late Archaic period 5000–3800
With evidence in hand that refuted notions of the diffusion of plant domestication from Mesoamerica, models developed in the 1980s for the transition from foraging to farming in the Eastern Woodlands emphasized the coevolutionary relationship between people and these crop plants. As Archaic-period groups began to occupy river valleys more intensively, in part due to changing climatic patterns during the mid-Holocene that created more stable river systems, their activities created disturbed areas in which these weedy plants thrive. With these useful plants available as more productive stands in closer proximity to base camps, people increasingly used the plants, which in turn responded to people’s selection. Critics noted that these models left little room for intentionality or innovation on the part of early farmers.
Models derived from human behavioral ecology explore the circumstances in which foragers choose to start using these small-seeded plants in greater quantities. In contrast to the resource-rich valley settings of the coevolutionary models, human behavioral ecology models posit that foragers would only use these plants, which provide relatively few calories per time spent obtaining them, when existing resources could no longer support growing populations. In these scenarios, Late Archaic peoples cultivated these crops as insurance against shortages in nut supplies.
Despite their apparent differences, current iterations of both models recognize humans as agents who actively change their environments, with intentional and unintentional results. Both also are concerned with understanding the social and ecological contexts within which people began cultivating and eventually domesticating plants.
The “when” and “where” questions of domestication in eastern North America are relatively well established, although researchers continue to fill significant gaps in geographic data. These primarily include regions where large-scale contract archaeology projects have not been conducted. Researchers are also actively debating the “how” and “why” of domestication, but the cultural ramifications of the transition from foraging to farming have yet to be meaningfully incorporated into the archaeological understanding of the region. The significance of these native crops to the economies of Late Archaic and subsequent Early and Middle Woodland peoples is poorly understood and often woefully underestimated by researchers. The socioeconomic roles of these native crops to past peoples, as well as the possibilities for farmers and cooks to incorporate them into their practices in the early 21st century, are exciting areas for new research.
Alexander N. Hristov
Agriculture is a significant source of methane, contributing about 12% of the global anthropogenic methane emissions. Major sources of methane from agricultural activities are fermentation in the reticulo-rumen of ruminant animals (i.e., enteric methane), fermentation in animal manure, and rice cultivation. Enteric methane is the largest agricultural source of methane and is mainly controlled by feed dry matter intake and composition of the animal diet (i.e., fiber, starch, lipids). Processes that lead to generation of methane from animal manure are similar to those taking place in the reticulo-rumen. Methane emissions from manure, however, are greatly influenced by factors such as manure management system and ambient temperature. Systems that handle manure as a liquid generate much more methane than systems in which manure is handled as a solid. Low ambient temperatures drastically decrease methane emissions from manure. Once applied to soil, animal manure does not generate significant amounts of methane. Globally, methane emissions from rice cultivation represent about 10% of the total agricultural greenhouse gas emissions. In the rice plant, methane dissolves in the soil water surrounding the roots, diffuses into the cell-wall water of the root cells, and is eventually released through the micropores in the leaves. Various strategies have been explored to mitigate agricultural methane emissions. Animal nutrition, including balancing dietary nutrients and replacement of fiber with starch or lipids; alternative sinks for hydrogen; manipulation of ruminal fermentation; and direct inhibition of methanogenesis have been shown to effectively decrease enteric methane emissions. Manure management solutions include solid-liquid separation, manure covers, flaring of generated methane, acidification and cooling of manure, and decreasing manure storage time before soil application. There are also effective mitigation strategies for rice that can be categorized broadly into selection of rice cultivars, water regime, and fertilization. Alternate wetting and drying and mid-season drainage of rice paddies have been shown to be very effective practices for mitigating methane emissions from rice production.
Marianne Bechmann and Per Stålnacke
Nutrient pollution can have a negative impact on the aquatic environment, with loss of biodiversity, toxic algal blooms, and a deficiency in dissolved oxygen in surface waters. Agricultural production is one of the main contributors to these problems; this article provides an overview of and background for the main biogeochemical processes causing agricultural nutrient pollution of surface waters. It discusses the main features of the agricultural impact on nutrient loads to surface waters, focusing on nitrogen and phosphorus, and describes some of the main characteristics of agricultural management, including processes and pathways from soil to surface waters. An overview of mitigation measures to reduce pollution, retention in the landscape, and challenges regarding quantification of nutrient losses are also dealt with. Examples are presented from different spatial scales, from field and catchment to river basin scale.
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
Despite millennia of success as hunters and gatherers, some human groups made a monumental transition to agricultural economies and more sedentary lifeways, a period broadly referred to as the Neolithic. This major tipping point in human history is best documented in the Near East, Anatolia, and the eastern Mediterranean around 12,000 years ago. Much research has focused on the origins of agriculture, asking questions about why this event occurred after so much success at hunting and gathering. While early investigations concentrated on the economic significance of the Neolithic, recent studies are now also addressing what are perhaps more significant issues related to social, ritual, political, and ecological aspects of the Neolithic. Equally important is a focus on not only why the Neolithic first occurred, but also the consequences that it had on human society. These often are addressed in relation to the subsequent development of so-called civilizations and the environmental impacts that these had, but increasingly there are investigations on consequences within the Neolithic itself.
The development of agriculture brought positive and negative consequences within Neolithic societies on both the Near Eastern mainlands and adjacent Mediterranean islands. These include not only economic consequences, but also ones related to social organization and complexity, trade, and health and disease. What is apparent is that consequential events during the Neolithic were not linear—they did not follow a predictable path. For example, there is strong evidence for substantial environmental deterioration during the Neolithic at sites such as Ain Ghazal in Jordan, where adaptive responses may have included divisions of domestic animal and plant resources. This may represent the beginning of the classic Near Eastern economic and social dichotomy between the “desert and the sown.” However, in Cyprus, where the Neolithic appeared as early as it did on the mainlands, there is only limited evidence for severe ecological degradation throughout the period. There, the impacts of human activity associated with the Neolithic appeared much later. Consequences within the Neolithic can be examined from a broad perspective, considering both successes and failures.
Deborah L. Nichols
The Basin of Mexico is a key world region for understanding agricultural intensification and the development of ancient and historic cities and states. Archaeologists working in the region have had a long-standing interest in understanding the dynamics of interactions between society and environment and their research has been at the forefront of advances in both method and theory. The Basin of Mexico was the geopolitical core of the Aztec empire, the largest state in the history of Mesoamerica. Its growth was sustained by a complex economy that has been the subject of much research.
Two themes underlie a broad interest in the pre-Hispanic agriculture of the Basin of Mexico. First, how with a Neolithic technology did the Aztecs and their predecessors sustain the growth of large cites, dense rural populations, and the largest state system in the history of pre-Hispanic Mesoamerica? Second, what is the relationship of agricultural intensification and urbanization and state formation? Mesoamerica is the only world region where primary civilizations developed that lacked domestic herbivores for either food or transportation. Their farming depended entirely on human labor and hand tools but sustained large cities, dense populations, and complex social institutions. Intensive agriculture began early and was promoted by risk, ecological diversity, and social differentiation, and included irrigation, terracing, and drained fields (chinampas). Most farming was managed by smallholder households and local communities, which encouraged corporate forms of governance and collective action. Environmental impacts included erosion and deposition, but were limited compared with the degradation that took place in the colonial period.
Worldwide, governments subsidize agriculture at the rate of approximately 1 billion dollars per day. This figure rises to about twice that when export and biofuels production subsidies and state financing for dams and river basin engineering are included. These policies guide land use in numerous ways, including growers’ choices of crop and buyers’ demand for commodities. The three types of state subsidies that shape land use and the environment are land settlement programs, price and income supports, and energy and emissions initiatives. Together these subsidies have created perennial surpluses in global stores of cereal grains, cotton, and dairy, with production increases outstripping population growth. Subsidies to land settlement, to crop prices, and to processing and refining of cereals and fiber, therefore, can be shown to have independent and largely deleterious effect on soil fertility, fresh water supplies, biodiversity, and atmospheric carbon.
John M. Marston
The ancient Near East was one of the earliest centers of agriculture in the world, giving rise to domesticated herd animals, cereals, and legumes that today have become primary agricultural staples worldwide. Although much attention has been paid to the origins of agriculture, identifying when, where, and how plants and animals were domesticated, equally important are the social and environmental consequences of agriculture. Shortly after the advent of domestication, agricultural economies quickly replaced hunting and gathering across Mesopotamia, the Levant, and Anatolia. The social and environmental context of this transition has profound implications for understanding the rise of social complexity and incipient urbanism in the Near East.
Economic transformation accompanied the expansion of agriculture throughout small-scale societies of the Near East. These farmsteads and villages, as well as mobile pastoral groups, formed the backbone of agricultural production, which enabled tradable surpluses necessary for more expansive, community-scale economic networks. The role of such economies in the development of social complexity remains debated, but they did play an essential role in the rise of urbanism. Cities depended on agricultural specialists, including farmers and herders, to feed urban populations and to enable craft and ritual specializations that became manifest in the first cities of southern Mesopotamia. The environmental implications of these agricultural systems in the Mesopotamian lowlands, especially soil salinization, were equally substantial. The environmental implications of Mesopotamian agriculture are distinct from those accompanying the spread of agriculture to the Levant and Anatolia, where deforestation, erosion, and loss of biodiversity can be identified as the hallmarks of agricultural expansion.
Agriculture is intimately connected with the rise of territorial empires across the Near East. Such empires often controlled agricultural production closely, for both economic and strategic ends, but the methods by which they encouraged the production of specific agricultural products and the adoption of particular agricultural strategies, especially irrigation, varied considerably between empires. By combining written records, archaeological data from surveys and excavation, and paleoenvironmental reconstruction, together with the study of plant and animal remains from archaeological sites occupied during multiple imperial periods, it is possible to reconstruct the environmental consequences of imperial agricultural systems across the Near East. Divergent environmental histories across space and time allow us to assess the sustainability of the agricultural policies of each empire and to consider how resulting environmental change contributed to the success or failure of those polities.
Charlene Murphy and Dorian Q. Fuller
South Asia possesses a unique Neolithic transition to agricultural domestication. India has received far less attention in the quest for evidence of early agriculture than other regions of the world traditionally recognized as “centers of domestication” such as southwest Asia, western Asia, China, Mesoamerica, South America, New Guinea, and Africa. Hunter-gatherers with agricultural production appeared around the middle of the Holocene, 4000 to 1500
As a case study for the origins of agriculture, South Asia has much to offer archaeologists and environmental scientists alike for understanding domestication processes and local transitions from foraging to farming as well as the ways in which early farmers adapted to and transformed the environment and regional vegetation. Information exchange from distant farmers from other agricultural centers into the subcontinent cannot be ruled out. However, it is clear that local agricultural origins occurred via a series of processes, including the dispersal of pastoral and agro-pastoral peoples across regions, the local domestication of animals and plants and the adoption by indigenous hunter-gatherers of food production techniques from neighboring cultures. Indeed, it is posited that local domestication events in India were occurring alongside agricultural dispersals from other parts of the world in an interconnected mosaic of cultivation, pastoralism, and sedentism. As humans in South Asia increasingly relied on a more restricted range of plant species, they became entangled in an increasingly fixed trajectory that allowed greater food production levels to sustain larger populations and support their developing social, cultural and food traditions.
Juha Helenius, Alexander Wezel, and Charles A. Francis
Agroecology can be defined as scientific research on ecological sustainability of food systems.
In addressing food production and consumption systems in their entirety, the focus of agroecology is on interactions and processes that are relevant for transitioning and maintaining ecological, economic, political, and social-cultural sustainability.
As a field of sustainability science, agroecology explores agriculture and food with explicit linkages to two other widespread interpretations of the concept of agroecology: environmentally sound farming practices and social movements for food security and food sovereignty. In the study of agroecology as science, both farming practices and social movements emerge as integrated components of agroecological research and development.
In the context of agroecology, the concept of ecology refers not only to the science of ecology as biological research but also to environmental and social sciences with research on social systems as integrated social and ecological systems. In agroecological theory, all these three are merged so that agroecology can broadly be defined as “human food ecology” or “the ecology of food systems.”
Since the last decades of the 20th century many developments have led to an increased emphasis on agroecology in universities, nonprofit organizations, movements, government programs, and the United Nations. All of these have raised a growing attention to ecological, environmental, and social dimensions of farming and food, and to the question of how to make the transition to sustainable farming and food systems.
One part of the foundation of agroecology was built during the 1960s when ecologically oriented environmental research on agriculture emerged as the era of optimism about component research began to erode. Largely, this took place as a reaction to unexpected and unwanted ecological and social consequences of the Green Revolution, a post–World War II scaling-up, chemicalization, and mechanization of agriculture. Another part of the foundation was a nongovernmental movement among thoughtful farmers wanting to develop sustainable and more ecological/organic ways of production and the demand by consumers for such food products. Finally, a greater societal acceptance, demand for research and education, and public funding for not only environmental ecology but also for wider sustainability in food and agriculture was ignited by an almost sudden high-level political awakening to the need for sustainable development by the end of 1980s.
Agroecology as science evolved from early studies on agricultural ecosystems, from research agendas for environmentally sound farming practices, and from concerns about addressing wider sustainability; all these shared several forms of systems thinking. In universities and research institutions, agroecologists most often work in faculties of food and agriculture. They share resources and projects among scientists having disciplinary backgrounds in genetics (breeding of plants and animals), physiology (crop science, animal husbandry, human nutrition), microbiology or entomology (crop protection), chemistry and physics (soil science, agricultural and food chemistry, agricultural and food technology), economics (of agriculture and food systems), marketing, behavioral sciences (consumer studies), and policy research (agricultural and food policy).
While agroecologists clearly have a mandate to address ecology of farmland, its biodiversity, and ecosystem services, one of the greatest added values from agroecology in research communities comes from its wider systems approach. Agroecologists complement reductionist research programs where scientists seek more detailed understanding of detail and mechanisms and put these into context by developing a broader appreciation of the whole. Those in agroecology integrate results from disciplinary research and increase relevance and adoption by introducing transdisciplinarity, co-creation of information and practices, together with other actors in the system. Agroecology is the field in sustainability science that is devoted to food system transformation and resilience.
Agroecology uses the concept of “agroecosystem” in broad ecological and social terms and uses these at multiple scales, from fields to farms to farming landscapes and regions. Food systems depend on functioning agroecosystems as one of their subsystems, and all the subsystems of a food system interact through positive and negative feedbacks, in their complex biophysical, sociocultural, and economic dimensions. In embracing wholeness and connectivity, proponents of agroecology focus on the uniqueness of each place and food system, as well as solutions appropriate to their resources and constraints.
Geoffrey L. Taylor and Katherine L. Chiou
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
The Andean highland region of South America was a center for the domestication of crops and the development of novel agricultural intensification strategies. These advances provided the social and economic foundations for one of the largest pre-Hispanic states in the Americas—the Inca—as well as numerous preceding and contemporaneous cultures. The legacy created by Andean agriculturalists includes terraced and raised fields that remain in use today as well as globally consumed foods including chili pepper (Capsicum spp.), potato (Solanum tuberosum), and quinoa (Chenopodium quinoa).
Research on modern forms of traditional agriculture in South America by ethnographers, geographers, and agronomists can be grouped into three general themes: (1) the physical, social, and ritual practices of farming; (2) the environmental impacts of farming; and (3) agrobiodiversity and genetic conservation of crop varieties. Due to conquest by European invaders in the 16th century and the resulting demographic collapse, aspects of native knowledge and traditions were lost. Consequently, much of what is known about pre-Hispanic traditional agricultural practices is derived from archaeological research.
To farm the steep mountainous slopes in the quechua and suni zones, native Andean peoples developed a suite of field types ranging from rainfed sloping fields to irrigated bench terracing that flattened the ground to increase surface area, raised soil temperatures, and reduced soil erosion. In the high plains or puna zone, flat wetlands were transformed into a patchwork of alternating raised fields and irrigation canals. By employing this strategy, Andean peoples created microclimates that resisted frost, managed moisture availability, and improved soil nutrient quality.
These agricultural approaches cannot be divorced from enduring Andean cosmological and social concepts such as the ayni and minka exchange-labor systems based on reciprocity and the ayllu, a lineage and community group that also integrates the land itself and the wakas (nonhuman agentive beings) that reside there with the people. To understand traditional agriculture in the highland Andes and how it supported large populations in antiquity, facilitated the rapid expansion of the Inca Empire, and created field systems that are still farmed sustainably by populations today, it is essential to examine not only the physical practices themselves, but also the social context surrounding their development and use in ancient and modern times.
Richard W. Hazlett and Joshua Peck
Satellite reconnaissance of the Earth’s surface provides critical information about the state of human interaction with the natural environment. The strongest impact is agricultural, reflecting land-use approaches to food production extending back to the dawn of civilization. To variable degrees, depending upon location, regional field patterns result from traditional farming practices, surveying methods, regional histories, policies, political agendas, environmental circumstances, and economic welfare. Satellite imaging in photographic true or false color is an important means of evaluating the nature and implications of agricultural practices and their impacts on the surrounding world. Important platforms with publicly accessible links to satellite image sets include those of the European Space Agency, U.S. National Aeronautics and Space Administration, the Centre D’etudes Spatiales, Airbus, and various other governmental programs. Reprocessing of data worldwide in scope by commercial concerns including Digital Globe, Terrametrics, and GoogleEarth in the 21st century enable ready examination of most of the Earth’s surface in great detail and natural colors. The potential for monitoring and improving understanding of agriculture and its role in the Earth system is considerable thanks to these new ways of viewing the planet.
Space reconnaissance starkly reveals the consequences of unique land surveys for the rapid development of agriculture and political control in wilderness areas, including the U.S. Public Land Survey and Tierras Bajas systems. Traditional approaches toward agriculture are clearly shown in ribbon farms, English enclosures and medieval field systems, and terracing in many parts of the world. Irrigation works, some thousands of years old, may be seen in floodplains and dryland areas, notably the Maghreb and the deep Sahara, where center-pivot fields have recently appeared in areas once considered too dry to cultivate. Approaches for controlling erosion, including buffer zones, shelter belts, strip and contour farming, can be easily identified. Also evident are features related to field erosion and soil alteration that have advanced to crisis stage, such as badland development and widespread salinization. Pollution related to farm runoff, and the piecemeal (if not rapid) loss of farmlands due to urbanization can be examined in ways favoring more comprehensive evaluation of human impacts on the planetary surface. Developments in space technologies and observational platforms will continue indefinitely, promising ever-increasing capacity to understand how humans relate to the environment.
In 2018 barley accounts for only 5% of the cereal production worldwide, and regionally for up to 40% of cereal production. The cereal represents the oldest crop species and is one of the best adapted crop plants to a broad diversity of climates and environments.
Originating from the wild progenitor species Hordeum vulgare ssp. spontaneum, biogeographically located in the Fertile Crescent of the Near East, the domesticated form developed as a founder crop in aceramic Neolithic societies 11,000 years ago, was cultivated in monocultures in Bronze Age Mesopotamia, entered the New World after 1492
Its stress tolerance in response to increased aridity and salinity on one hand and adaptability to cool climates on the other, partially explains its broad range of applications for subsistence and economy across different cultures, such as for baking, cooking, beer brewing and as an animal feed.
Although the use of fermented starch for producing alcoholic beverages and foods is globally documented in archaeological contexts dating from at least the beginning of the Holocene era, it becomes concrete only in societies with a written culture, such as Bronze Age Mesopotamia and Egypt, where beer played a considerable role in everyday diet and its production represented an important sector of productivity.
In 2004 approximately 85% of barley production was destined for feeding animals. However, as a component of the human diet, studies on the health benefits of the micronutrients in barley have found that it has a positive effect on blood cholesterol and glucose levels, and in turn impacts cardiovascular health and diabetes control. The increasing number of barley-breeding programs worldwide focus on improving the processing characteristics, nutritional value, and stress tolerance of barley within the context of global climate change.
James M. MacDonald
Industrialized livestock production can be characterized by five key attributes: confinement feeding of animals, separation of feed and livestock production, specialization, large size, and close vertical linkages with buyers. Industrialized livestock operations—popularly known as CAFOs, for Concentrated Animal Feeding Operations—have spread rapidly in developed and developing countries; by the early 21st century, they accounted for three quarters of poultry production and over half of global pork production, and held a growing foothold in dairy production.
Industrialized systems have created significant improvements in agricultural productivity, leading to greater output of meat and dairy products for given commitments of land, feed, labor, housing, and equipment. They have also been effective at developing, applying, and disseminating research leading to persistent improvements in animal genetics, breeding, feed formulations, and biosecurity. The reduced prices associated with productivity improvements support increased meat and dairy product consumption in low and middle income countries, while reducing the resources used for such consumption in higher income countries.
The high-stocking densities associated with confined feeding also exacerbate several social costs associated with livestock production. Animals in high-density environments may be exposed to diseases, subject to attacks from other animals, and unable to engage in natural behaviors, raising concerns about higher levels of fear, pain, stress, and boredom. Such animal welfare concerns have realized greater salience in recent years.
By consolidating large numbers of animals in a location, industrial systems also concentrate animal wastes, often in levels that exceed the capacity of local cropland to absorb the nutrients in manure. While the productivity improvements associated with industrial systems reduce the resource demands of agriculture, excessive localized concentrations of manure can lean to environmental damage through contamination of ground and surface water and through volatilization of nitrogen nutrients into airborne pollutants.
Finally, animals in industrialized systems are often provided with antibiotics in their feed or water, in order to treat and prevent disease, but also to realize improved feed absorption (“a production purpose”). Bacteria are developing resistance to many important antibiotic drugs; the extensive use of such drugs in human and animal medicine has contributed to the spread of antibiotic resistance, with consequent health risks to humans.
The social costs associated with industrialized production have led to a range of regulatory interventions, primarily in North America and Europe, as well as private sector attempts to alter the incentives that producers face through the development of labels and through associated adjustments within supply chains.
Elisabeth N. Bui
Driving forces for natural soil salinity and alkalinity are climate, rock weathering, ion exchange, and mineral equilibria reactions that ultimately control the chemical composition of soil and water. The major weathering reactions that produce soluble ions are tabled. Where evapotranspiration is greater than precipitation, downward water movement is insufficient to leach solutes out of the soil profile and salts can precipitate. Microbes involved in organic matter mineralization and thus the carbon, nitrogen, and sulfur biogeochemical cycles are also implicated. Seasonal contrast and evaporative concentration during dry periods accelerate short-term oxidation-reduction reactions and local and regional accumulation of carbonate and sulfur minerals. The presence of salts and alkaline conditions, together with the occurrence of drought and seasonal waterlogging, creates some of the most extreme soil environments where only specially adapted organisms are able to survive. Sodic soils are alkaline, rich in sodium carbonates, with an exchange complex dominated by sodium ions. Such sodic soils, when low in other salts, exhibit dispersive behavior, and they are difficult to manage for cropping. Maintaining the productivity of sodic soils requires control of the flocculation-dispersion behavior of the soil. Poor land management can also lead to anthropogenically induced secondary salinity. New developments in physical chemistry are providing insights into ion exchange and how it controls flocculation-dispersion in soil. New water and solute transport models are enabling better options of remediation of saline and/or sodic soils.
Paolo Inglese and Giuseppe Sortino
In May, every year since 1857, in the great park of Sans-Souci in Potsdam just outside Berlin—a park begun in 1745 by Emperor Frederick II of Hohenzollern and expanded a century later by Frederick William IV—the doors of the great Orangerie open in and a Renaissance-style garden called Sizilianischer Garten is set up. On horse-drawn carriages, large olive and citrus trees are brought outdoors, and are then raised in masters.
For the young European who, in the second half of the 18th century and in the first decades of the following, traveled to Italy to see and study Renaissance culture and the remains of Greek civilization, the citrus species and fruits and groves of southern Italy became the ultimate symbol of beauty and a sort of status symbol of wealth, particularly that of landowners. Nothing is more expressive of the fascination of their fruit than Abu-l-Hasan Ali’s 12th-century writings: “Come on, enjoy your harvested orange: happiness is present when it is present. / Welcome the cheeks of the branches, and welcome the stars of the trees! / It seems that the sky has lavished gold and that the earth has formed some shiny spheres.”
Indeed, Citrus spp. are among the most important crops and consumed fruit worldwide. Their co-evolution due to a millennial agricultural utilization resulted in a complexity of species and cultivated varieties derived by natural or induced mutations, crossing and breeding the “original” species (Citrus medica, Citrus maxima, Citrus reticulate, Fortunella japonica) and their main progenies (C. aurantium, C. sinensis, Citrus limon, Citrus paradisi, Citrus clementina, etc.). Citrus spread from the original tropical and subtropical regions of southeast Asia toward the Mediterranean countries of Europe and North Africa and, after 1492, in the Americas, not to mention South Africa and Australia, where they still have a very important role. Citrus species, wherever they have been cultivated, quickly became the protagonists of the letters and the arts, as well as the markets and gastronomy, and can even be found in religious ceremonies, such as for Feast of Tabernacles (Sukkot). Studies on Citrus botany, cultivation, and utilization have been pursued since the early stages of the fruit’s domestication and grew following their introduction in Europe, the Americas, Africa, and Australia. Citrus research involves many different aspects: such as the study of citrus origin and botanical classification; citrus growing, propagation, and orchard management; citrus fruit quality, utilization and industry; citrus gardening and ornamentals; citrus in arts and manufacturing.
Soil salinity has been causing problems for agriculturists for millennia, primarily in irrigated lands. The importance of salinity issues is increasing, since large areas are affected by irrigation-induced salt accumulation. A wide knowledge base has been collected to better understand the major processes of salt accumulation and choose the right method of mitigation. There are two major types of soil salinity that are distinguished because of different properties and mitigation requirements. The first is caused mostly by the large salt concentration and is called saline soil, typically corresponding to Solonchak soils. The second is caused mainly by the dominance of sodium in the soil solution or on the soil exchange complex. This latter type is called “sodic” soil, corresponding to Solonetz soils. Saline soils have homogeneous soil profiles with relatively good soil structure, and their appropriate mitigation measure is leaching. Naturally sodic soils have markedly different horizons and unfavorable physical properties, such as low permeability, swelling, plasticity when wet, and hardness when dry, and their limitation for agriculture is mitigated typically by applying gypsum. Salinity and sodicity need to be chemically quantified before deciding on the proper management strategy. The most complex management and mitigation of salinized irrigated lands involves modern engineering including calculations of irrigation water rates and reclamation materials, provisions for drainage, and drainage disposal. Mapping-oriented soil classification was developed for naturally saline and sodic soils and inherited the first soil categories introduced more than a century ago, such as Solonchak and Solonetz in most of the total of 24 soil classification systems used currently. USDA Soil Taxonomy is one exception, which uses names composed of formative elements.
Confidence in the projected impacts of climate change on agricultural systems has increased substantially since the first Intergovernmental Panel on Climate Change (IPCC) reports. In Africa, much work has gone into downscaling global climate models to understand regional impacts, but there remains a dearth of local level understanding of impacts and communities’ capacity to adapt. It is well understood that Africa is vulnerable to climate change, not only because of its high exposure to climate change, but also because many African communities lack the capacity to respond or adapt to the impacts of climate change. Warming trends have already become evident across the continent, and it is likely that the continent’s 2000 mean annual temperature change will exceed +2°C by 2100. Added to this warming trend, changes in precipitation patterns are also of concern: Even if rainfall remains constant, due to increasing temperatures, existing water stress will be amplified, putting even more pressure on agricultural systems, especially in semiarid areas. In general, high temperatures and changes in rainfall patterns are likely to reduce cereal crop productivity, and new evidence is emerging that high-value perennial crops will also be negatively impacted by rising temperatures. Pressures from pests, weeds, and diseases are also expected to increase, with detrimental effects on crops and livestock.
Much of African agriculture’s vulnerability to climate change lies in the fact that its agricultural systems remain largely rain-fed and underdeveloped, as the majority of Africa’s farmers are small-scale farmers with few financial resources, limited access to infrastructure, and disparate access to information. At the same time, as these systems are highly reliant on their environment, and farmers are dependent on farming for their livelihoods, their diversity, context specificity, and the existence of generations of traditional knowledge offer elements of resilience in the face of climate change. Overall, however, the combination of climatic and nonclimatic drivers and stressors will exacerbate the vulnerability of Africa’s agricultural systems to climate change, but the impacts will not be universally felt. Climate change will impact farmers and their agricultural systems in different ways, and adapting to these impacts will need to be context-specific.
Current adaptation efforts on the continent are increasing across the continent, but it is expected that in the long term these will be insufficient in enabling communities to cope with the changes due to longer-term climate change. African famers are increasingly adopting a variety of conservation and agroecological practices such as agroforestry, contouring, terracing, mulching, and no-till. These practices have the twin benefits of lowering carbon emissions while adapting to climate change as well as broadening the sources of livelihoods for poor farmers, but there are constraints to their widespread adoption. These challenges vary from insecure land tenure to difficulties with knowledge-sharing.
While African agriculture faces exposure to climate change as well as broader socioeconomic and political challenges, many of its diverse agricultural systems remain resilient. As the continent with the highest population growth rate, rapid urbanization trends, and rising GDP in many countries, Africa’s agricultural systems will need to become adaptive to more than just climate change as the uncertainties of the 21st century unfold.
Charles A. Francis
Adaptation of cropping systems to weather uncertainty and climate change is essential for resilient food production and long-term food security. Changes in climate result in substantial temporal modifications of cropping conditions, and rainfall and temperature patterns vary greatly with location. These challenges come at a time when global human population and demand for food are both increasing, and it appears to be difficult to find ways to satisfy growing needs with conventional systems of production. Agriculture in the future will need to feature greater biodiversity of crop species and appropriate design and management of cropping and integrated crop/animal systems. More diverse and longer-cycle crop rotations will need to combine sequences of annual row crops such as maize and soybean with close-drilled cereals, shallow-rooted with deep-rooted crops, summer crops with winter crops, and annuals with perennials in the same fields. Resilience to unpredictable weather will also depend on intercropping, with the creative arrangement of multiple interacting crop species to diversify the field and the landscape. Other multiple-cropping systems and strategies to integrate animals and crops will make more efficient use of natural resources and applied inputs; these include systems such as permaculture, agroforestry, and alley cropping. Future systems will be spatially diverse and adapted to specific fields, soil conditions, and unique agroecozones. Production resilience will be achieved by planting diverse combinations of species together in the same field, and economic resilience through producing a range of products that can be marketed through different channels. The creation of local food webs will be more appropriate in the future, as contrasted with the dominance of global food chains today. Materials considered “waste” from the food system, including human urine and feces, will become valuable resources to be cycled back into the natural environment and into food production. Due to the increasing scarcity of fertile land, the negative contributions of chemicals to environmental pollution, the costs of fossil fuels, and the potential for the economic and political disruption of supply chains, future systems will increasingly need to be local in character while still achieving adaptation to the most favorable conditions for each system and location. It is essential that biologically and economically resilient systems become productive and profitable, as well as environmentally sound and socially equitable, in order to contribute to stability of food production, security of the food supply, and food sovereignty, to the extent that this is possible. The food system cannot continue along the lines of “business as usual,” and its path will need to radically diverge from the recognized trends toward specialization and globalization of the early 21st century. The goal needs to shift from exploitation and short-term profits to conservation of resources, greater equity in distribution of benefits, and resilience in food supply, even with global climate change.
Muhammad Farooq, Ahmad Nawaz, and Faisal Nadeem
Planned crop rotation offers a pragmatic option to improve soil fertility, manage insect pests and diseases, and offset the emission of greenhouse gases. The inclusion of legume crops in crop rotations helps to reduce the use of external nitrogen inputs for legumes and other crops because legumes may fix the atmospheric nitrogen. This also helps to reduce the environmental pollution caused by volatilization and leaching of applied nitrogen. The inclusion of allelopathic crops in rotation may be useful to suppress noxious weeds due to release of the allelochemicals in the rhizosphere. The rotation of tap-rooted crops with shallow rooted crops may result in efficient and productive use of nutrient resources and conservation of soil moisture. Continuous monoculture systems may cause the loss of biodiversity. Land fallowing is an efficient agricultural management technique mostly practiced in arid regions to capture rainwater and store it in the soil profile for later use in crop production. During fallowing, tillage operations are practiced to enhance moisture conservation in the soil. Keeping soil fallow for a season or more restores soil fertility through nutrient deposits; increases organic matter, microbial carbon, and soil microbial diversity; and improves the soil’s physical properties, including aggregation stability and reduced soil compaction due to decreased traffic. In addition, fallowing of land provides biological means of pest (weeds and insects) control by disrupting the life cycle of pests and decreasing reliance on pesticides. Land fallowing can help offset the emission of greenhouse gases from agricultural fields by reducing traffic and increasing carbon sequestration within the soil. Summer fallowing may help to preserve moisture in diverse soil types in the rainfed regions of the world, although it may reduce the carbon sequestration potential of soils over the long term. Energy resources are decreasing, and the inclusion of energy crops in crop rotation may be highly beneficial. Many of the processes, factors, and mechanisms involved in crop rotation and land fallowing are poorly understood and require further investigation.