Kimberly M. Carlson and Rachael D. Garrett
Oil crops play a critical role in global food and energy systems. Since these crops have high oil content, they provide cooking oils for human consumption, biofuels for energy, feed for animals, and ingredients in beauty products and industrial processes. In 2014, oil crops occupied about 20% of crop harvested area worldwide. While small-scale oil crop production for subsistence or local consumption continues in certain regions, global demand for these versatile crops has led to substantial expansion of oil crop agriculture destined for export or urban markets. This expansion and subsequent cultivation has diverse effects on the environment, including loss of forests, savannas, and grasslands, greenhouse gas emissions, regional climate change, biodiversity decline, fire, and altered water quality and hydrology. Oil palm in Southeast Asia and soybean in South America have been identified as major proximate causes of tropical deforestation and environmental degradation. Stringent conservation policies and yield increases are thought to be critical to reducing rates of soybean and oil palm expansion into natural ecosystems. However, the higher profits that often accompany greater yields may encourage further expansion, while policies that restrict oil crop expansion in one region may generate secondary “spillover” effects on other crops and regions. Due to these complex feedbacks, ensuring a sustainable supply of oil crop products to meet global demand remains a major challenge for agricultural companies, farmers, governments, and civil society.
Agriculture has been the principal influence on the physical structure of the English landscape for many thousands of years. Driven by a wider raft of demographic, social, and economic developments, farming has changed in complex ways over this lengthy period, with differing responses to the productive potential and problems of local environments leading to the emergence of distinct regional landscapes. The character and configuration of these, as much as any contemporary influences, have in turn structured the practice of agriculture at particular points in time. The increasing complexity of the wider economy has also been a key influence on the development of the farmed landscape, especially large-scale industrialization in the late 18th and 19th centuries; and, from the late 19th century, globalization and increasing levels of state intervention. Change in agricultural systems has not continued at a constant rate but has displayed periods of more and less innovation.
David E. Clay, Sharon A. Clay, Thomas DeSutter, and Cheryl Reese
Since the discovery that food security could be improved by pushing seeds into the soil and later harvesting a desirable crop, agriculture and agronomy have gone through cycles of discovery, implementation, and innovation. Discoveries have produced predicted and unpredicted impacts on the production and consumption of locally produced foods. Changes in technology, such as the development of the self-cleaning steel plow in the 18th century, provided a critical tool needed to cultivate and seed annual crops in the Great Plains of North America. However, plowing the Great Plains would not have been possible without the domestication of plants and animals and the discovery of the yoke and harness. Associated with plowing the prairies were extensive soil nutrient mining, a rapid loss of soil carbon, and increased wind and water erosion. More recently, the development of genetically modified organisms (GMOs) and no-tillage planters has contributed to increased adoption of conservation tillage, which is less damaging to the soil. In the future, the ultimate impact of climate change on agronomic practices in the North American Great Plains is unknown. However, projected increasing temperatures and decreased rainfall in the southern Great Plains (SGP) will likely reduce agricultural productivity. Different results are likely in the northern Great Plains (NGP) where higher temperatures can lead to increased agricultural intensification, the conversion of grassland to cropland, increased wildlife fragmentation, and increased soil erosion. Precision farming, conservation, cover crops, and the creation of plants better designed to their local environment can help mitigate these effects. However, changing practices require that farmers and their advisers understand the limitations of the soils, plants, and environment, and their production systems. Failure to implement appropriate management practices can result in a rapid decline in soil productivity, diminished water quality, and reduced wildlife habitat.
Agriculture is at the very center of the human enterprise; its trappings are in evidence all around, yet the agricultural past is an exceptionally distant place from modern America. While the majority of Americans once raised a significant portion of their own food, that ceased to be the case at the beginning of the 20th century. Only a very small portion of the American population today has a personal connection to agriculture. People still must eat, but the process by which food arrives on their plates is less evident than ever. The evolution of that process, with all of its many participants, is the stuff of agricultural history. The task of the agricultural historian is to make that past evident, and usable, for an audience that is divorced from the production of food. People need to know where their food comes from, past and present, and what has gone into the creation of the modern food system.
Edward B. Barbier
Globally, around 1.5 billion people in developing countries, or approximately 35% of the rural population, can be found on less-favored agricultural land (LFAL), which is susceptible to low productivity and degradation because the agricultural potential is constrained biophysically by terrain, poor soil quality, or limited rainfall. Around 323 million people in such areas also live in locations that are highly remote, and thus have limited access to infrastructure and markets. The households in such locations often face a vicious cycle of declining livelihoods, increased ecological degradation and loss of resource commons, and declining ecosystem services on which they depend. In short, these poor households are prone to a poverty-environment trap. Policies to eradicate poverty, therefore, need to be targeted to improve the economic livelihood, productivity, and income of the households located on remote LFAL. The specific elements of such a strategy include involving the poor in paying for ecosystem service schemes and other measures that enhance the environments on which the poor depend; targeting investments directly to improving the livelihoods of the rural poor, thus reducing their dependence on exploiting environmental resources; and tackling the lack of access by the rural poor in less-favored areas to well-functioning and affordable markets for credit, insurance, and land, as well as the high transportation and transaction costs that prohibit the poorest households in remote areas to engage in off-farm employment and limit smallholder participation in national and global markets.
Simon Holdaway and Rebecca Phillipps
Northeast Africa forms an interesting case study for investigating the relationship between changes in environment and agriculture. Major climatic changes in the early Holocene led to dramatic changes in the environment of the eastern Sahara and to the habitation of previously uninhabitable regions. Research programs in the eastern Sahara have uncovered a wealth of archaeological evidence for sustained occupation during the African Humid Period, from about 11,000 years ago. Initial studies of faunal remains seemed to indicate early shifts in economic practice toward cattle pastoralism. Although this interpretation was much debated when it was first proposed, the possibility of early pastoralism stimulated discussion concerning the relationships between people and animals in particular environmental contexts, and ultimately led to questions concerning the role of agriculture imported from elsewhere in contrast to local developments. Did agriculture, or indeed cultivation and domestication more generally (sensu Fuller & Hildebrand, 2013), develop in North Africa, or were the concepts and species imported from Southwest Asia? And if agriculture did spread from elsewhere, were just the plants and animals involved, or was the shift part of a full socioeconomic suite that included new subsistence strategies, settlement patterns, technologies, and an agricultural “culture”? And finally, was this shift, wherever and however it originated, related to changes in the environment during the early to mid-Holocene?
These questions refer to the “big ideas” that archaeologists explore, but before answers can be formed it is important to consider the nature of the material evidence on which they are based. Archaeologists must consider not only what they discover but also what might be missing. Materials from the past are preserved only in certain places, and of course some materials can be preserved better than others. In addition, people left behind the material remains of their activities, but in doing so they did not intend these remains to be an accurate historical record of their actions. Archaeologists need to consider how the remains found in one place may inform us about a range of activities that occurred elsewhere for which the evidence may be less abundant or missing. This is particularly true for Northeast Africa where environmental shifts and consequent changes in resource abundance often resulted in considerable mobility. This article considers the origins of agriculture in the region covering modern-day Egypt and Sudan, paying particular attention to the nature of the evidence from which inferences about past socioeconomies may be drawn.
Christopher Morgan, Shannon Tushingham, Raven Garvey, Loukas Barton, and Robert Bettinger
At the global scale, conceptions of hunter-gatherer economies have changed considerably over time and these changes were strongly affected by larger trends in Western history, philosophy, science, and culture. Seen as either “savage” or “noble” at the dawn of the Enlightenment, hunter-gatherers have been regarded as everything from holdovers from a basal level of human development, to affluent, ecologically-informed foragers, and ultimately to this: an extremely diverse economic orientation entailing the fullest scope of human behavioral diversity. The only thing linking studies of hunter-gatherers over time is consequently simply the definition of the term: people whose economic mode of production centers on wild resources. When hunter-gatherers are considered outside the general realm of their shared subsistence economies, it is clear that their behavioral diversity rivals or exceeds that of other economic orientations. Hunter-gatherer behaviors range in a multivariate continuum from: a focus on mainly large fauna to broad, wild plant-based diets similar to those of agriculturalists; from extremely mobile to sedentary; from relying on simple, generalized technologies to very specialized ones; from egalitarian sharing economies to privatized competitive ones; and from nuclear family or band-level to centralized and hierarchical decision-making. It is clear, however, that hunting and gathering modes of production had to have preceded and thus given rise to agricultural ones. What research into the development of human economies shows is that transitions from one type of hunting and gathering to another, or alternatively to agricultural modes of production, can take many different evolutionary pathways. The important thing to recognize is that behaviors which were essential to the development of agriculture—landscape modification, intensive labor practices, the division of labor and the production, storage, and redistribution of surplus—were present in a range of hunter-gatherer societies beginning at least as early as the Late Pleistocene in Africa, Europe, Asia, and the Americas. Whether these behaviors eventually led to the development of agriculture depended in part on the development of a less variable and CO2-rich climatic regime and atmosphere during the Holocene, but also a change in the social relations of production to allow for hoarding privatized resources. In the 20th and 21st centuries, ethnographic and archaeological research shows that modern and ancient peoples adopt or even revert to hunting and gathering after having engaged in agricultural or industrial pursuits when conditions allow and that macroeconomic perspectives often mask considerable intragroup diversity in economic decision making: the pursuits and goals of women versus men and young versus old within groups are often quite different or even at odds with one another, but often articulate to form cohesive and adaptive economic wholes. The future of hunter-gatherer research will be tested by the continued decline in traditional hunting and gathering but will also benefit from observation of people who revert to or supplement their income with wild resources. It will also draw heavily from archaeology, which holds considerable potential to document and explain the full range of human behavioral diversity, hunter-gatherer or otherwise, over the longest of timeframes and the broadest geographic scope.
Noa Kekuewa Lincoln and Peter Vitousek
Agriculture in Hawaiʻi was developed in response to the high spatial heterogeneity of climate and landscape of the archipelago, resulting in a broad range of agricultural strategies. Over time, highly intensive irrigated and rainfed systems emerged, supplemented by extensive use of more marginal lands that supported considerable populations. Due to the late colonization of the islands, the pathways of development are fairly well reconstructed in Hawaiʻi. The earliest agricultural developments took advantage of highly fertile areas with abundant freshwater, utilizing relatively simple techniques such as gardening and shifting cultivation. Over time, investments into land-based infrastructure led to the emergence of irrigated pondfield agriculture found elsewhere in Polynesia. This agricultural form was confined by climatic and geomorphological parameters, and typically occurred in wetter, older landscapes that had developed deep river valleys and alluvial plains. Once initiated, these wetland systems saw regular, continuous development and redevelopment. As populations expanded into areas unable to support irrigated agriculture, highly diverse rainfed agricultural systems emerged that were adapted to local environmental and climatic variables. Development of simple infrastructure over vast areas created intensive rainfed agricultural systems that were unique in Polynesia. Intensification of rainfed agriculture was confined to areas of naturally occurring soil fertility that typically occurred in drier and younger landscapes in the southern end of the archipelago. Both irrigated and rainfed agricultural areas applied supplementary agricultural strategies in surrounding areas such as agroforestry, home gardens, and built soils. Differences in yield, labor, surplus, and resilience of agricultural forms helped shape differentiated political economies, hierarchies, and motivations that played a key role in the development of sociopolitical complexity in the islands.
Vito Ferro and Vincenzo Bagarello
Field plots are often used to obtain experimental data (soil loss values corresponding to different climate, soil, topographic, crop, and management conditions) for predicting and evaluating soil erosion and sediment yield. Plots are used to study physical phenomena affecting soil detachment and transport, and their sizes are determined according to the experimental objectives and the type of data to be obtained. Studies on interrill erosion due to rainfall impact and overland flow need small plot width (2–3 m) and length (< 10 m), while studies on rill erosion require plot lengths greater than 6–13 m. Sites must be selected to represent the range of uniform slopes prevailing in the farming area under consideration. Plots equipped to study interrill and rill erosion, like those used for developing the Universal Soil Loss Equation (USLE), measure erosion from the top of a slope where runoff begins; they must be wide enough to minimize the edge or border effects and long enough to develop downslope rills. Experimental stations generally include bounded runoff plots of known rea, slope steepness, slope length, and soil type, from which both runoff and soil loss can be monitored. Once the boundaries defining the plot area are fixed, a collecting equipment must be used to catch the plot runoff. A conveyance system (H-flume or pipe) carries total runoff to a unit sampling the sediment and a storage system, such as a sequence of tanks, in which sediments are accumulated. Simple methods have been developed for estimating the mean sediment concentration of all runoff stored in a tank by using the vertical concentration profile measured on a side of the tank. When a large number of plots are equipped, the sampling of suspension and consequent oven-drying in the laboratory are highly time-consuming. For this purpose, a sampler that can extract a column of suspension, extending from the free surface to the bottom of the tank, can be used. For large plots, or where runoff volumes are high, a divisor that splits the flow into equal parts and passes one part in a storage tank as a sample can be used. Examples of these devices include the Geib multislot divisor and the Coshocton wheel. Specific equipment and procedures must be employed to detect the soil removed by rill and gully erosion. Because most of the soil organic matter is found close to the soil surface, erosion significantly decreases soil organic matter content. Several studies have demonstrated that the soil removed by erosion is 1.3–5 times richer in organic matter than the remaining soil. Soil organic matter facilitates the formation of soil aggregates, increases soil porosity, and improves soil structure, facilitating water infiltration. The removal of organic matter content can influence soil infiltration, soil structure, and soil erodibility.
Philip Carl Salzman
Nomadism is a technique of population movement used to accomplish a variety of goals. It is used for primary production when the resources to be tapped are distributed thinly over a wide space, or are located in different places in a large region. Commonly nomadism is a technique used in a spatially extensive adaptation. Pastoralists raising domestic animals on natural pasture move from grazed areas to areas with fresh pasture, and from dry areas to those with water.
Nomadism follows regular patterns where the resources tapped are reliable and thus predictable. This is common in macro-environmental adaptations to factors such as seasons and altitude. Some pastoralists have mountain adaptations, migrating to high altitudes in summer and low altitudes in winter, an adaptation called transhumance in Europe. Nomadic patterns are more irregular when rainfall patterns, and thus pasturage, are erratic and unpredictable, as is common in desert areas with low rainfall.
Among some pastoral peoples, all of the households in the community move together. Among other pastoral peoples, a sector of the populations is nomadic; young and/or mature men migrate with the livestock, while women, children, and elders remain in a stationary home settlement. This is also the pattern in European transhumance.
Many pastoral peoples produce primarily for their own subsistence; it is common that they have multi-resource or mixed economies, engaging also in hunting and gathering, horticulture, agriculture, and arboriculture. Economic activities are not limited to primary production; patterns of predation, including raiding and extortion, against other pastoralists, farmers, and traders are widespread. Other pastoral peoples are heavily market-oriented, producing for sale, or have symbiotic relations with hunters or cultivators; it is normal that they are more specialized in their production. But pastoralists can be found at all points on a continuum between subsistence- and market-oriented.
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.
Oats and the other small grains have been “rediscovered” with the drive towards intensifying agricultural production, integrating crops and livestock into diversified systems, and increasing environmental stewardship. Globally, oats and other winter annual small grains such as wheat, cereal rye, triticale, and barley, have been used primarily for grain production. The secondary market following grain production has been restricted to straw, used mainly as livestock bedding. In regions where livestock are economically important, oats and the other annual small grain crops can be used as a grazed forage or fodder crop, hay, or silage. There are several characteristics that make oats and other small grains suitable for multiple agricultural uses. All the small grains are fairly easy to establish, have rapid growth, can be productive, and have a high nutritional value for livestock. Recent improvements in cultivar development have allowed oats and wheat to be grown across a broader range of stressful environmental conditions. Similarly, cultivar development in oats and wheat has improved grazing tolerance, which is important in dual-purpose systems that emphasize both grazing and grain production. On a worldwide scale, oats and other annual small grains are economically and environmentally important forage crops, especially when used as focused components within intensified agricultural systems. Challenges include development of improved cultivars of oats and other small grains for use in intensified agricultural systems, including both grazing and no grazing, that serve as short rotation crops, dual-purpose crops, or are designed to mitigate a specific environmental issue.
Theodore J. K. Radovich
Organic farming occupies a unique position among the world’s agricultural systems. While not the only available model for sustainable food production, organic farmers and their supporters have been the most vocal advocates for a fully integrated agriculture that recognizes a link between the health of the land, the food it produces, and those that consume it. Advocacy for the biological basis of agriculture and the deliberate restriction or prohibition of many agricultural inputs arose in response to potential and observed negative environmental impacts of new agricultural technologies introduced in the 20th century. A primary focus of organic farming is to enhance soil ecological function by building soil organic matter that in turn enhances the biota that soil health and the health of the agroecosystem depends on.
The rapid growth in demand for organic products in the late 20th and early 21st centuries is based on consumer perception that organically grown food is better for the environment and human health. Although there have been some documented trends in chemical quality differences between organic and non-organic products, the meaningful impact of the magnitude of these differences is unclear. There is stronger evidence to suggest that organic systems pose less risk to the environment, particularly with regard to water quality; however, as intensity of management in organic farming increases, the potential risk to the environment is expected to also increase. In the early 21st century there has been much discussion centered on the apparent bifurcation of organic farming into two approaches: “input substitution” and “system redesign.” The former approach is a more recent phenomenon associated with pragmatic considerations of scaling up the size of operations and long distance shipping to take advantage of distant markets. Critics argue that this approach represents a “conventionalization” of organic agriculture that will erode potential benefits of organic farming to the environment, human health, and social welfare. A current challenge of organic farming systems is to reconcile the different views among organic producers regarding issues arising from the rapid growth of organic farming.
Early agricultural and arboricultural practices in the Pacific are based on vegetative principles, namely, the asexual propagation and transplantation of plants. A vegetative orientation is reflected in the exploitation of underground storage organs (USOs) within Near Oceania, as well as Island Southeast Asia, during the Pleistocene. During the early Holocene, people in the New Guinea region (including Near Oceania) began to intensify the management of plant resources in different landscapes. The increased degree of plant management, as well as associated environmental transformation, is most clearly manifest in the agricultural chronology at Kuk Swamp in the highlands of Papua New Guinea. At Kuk, shifting cultivation was potentially practiced during the early Holocene, with mounded cultivation by c. 7000–6400 cal BP and ditched drainage of wetlands for cultivation by c. 4400–4000 cal BP. Comparable agricultural records are lacking for other regions of Near Oceania; lowland sites indicate a range of arboricultural practices focused on fruit- and nut-bearing trees during the Terminal Pleistocene and throughout the Holocene, as well as potentially sago during the late Holocene. By c. 4000–3000 cal BP, indigenous agricultural and arboricultural elements were integrated with new cultural traits from Southeast Asia, including domestic animals, pottery and potentially new varieties of traditional crops. From c. 3250 to 2800 cal BP, different elements of agricultural and arboricultural practices from lowland New Guinea and Island Melanesia were taken by Lapita pottery–bearing colonists into the western Pacific. A later period of agricultural expansion occurred around c. 1000–750 cal BP with the colonization of eastern Polynesia. Agricultural practices and crops were variably taken and adapted to different islands and island groups across the Pacific. Additional transformations to agriculture occurred with the Polynesian adoption of the sweet potato (Ipomoea batatas), a South American domesticate, as well as following protohistoric and historic encounters.
Rene Van Acker, Motior Rahman, and S. Zahra H. Cici
The global area sown to genetically modified (GM) varieties of leading commercial crops (soybean, maize, canola, and cotton) has expanded over 100-fold over two decades. Thirty countries are producing GM crops and just five countries (United States, Brazil, Argentina, Canada, and India) account for almost 90% of the GM production. Only four crops account for 99% of worldwide GM crop area. Almost 100% of GM crops on the market are genetically engineered with herbicide tolerance (HT), and insect resistance (IR) traits. Approximately 70% of cultivated GM crops are HT, and GM HT crops have been credited with facilitating no-tillage and conservation tillage practices that conserve soil moisture and control soil erosion, and that also support carbon sequestration and reduced greenhouse gas emissions. Crop production and productivity increased significantly during the era of the adoption of GM crops; some of this increase can be attributed to GM technology and the yield protection traits that it has made possible even if the GM traits implemented to-date are not yield traits per se. GM crops have also been credited with helping to improve farm incomes and reduce pesticide use. Practical concerns around GM crops include the rise of insect pests and weeds that are resistant to pesticides. Other concerns around GM crops include broad seed variety access for farmers and rising seed costs as well as increased dependency on multinational seed companies. Citizens in many countries and especially in European countries are opposed to GM crops and have voiced concerns about possible impacts on human and environmental health. Nonetheless, proponents of GM crops argue that they are needed to enhance worldwide food production. The novelty of the technology and its potential to bring almost any trait into crops mean that there needs to remain dedicated diligence on the part of regulators to ensure that no GM crops are deregulated that may in fact pose risks to human health or the environment. The same will be true for the next wave of new breeding technologies, which include gene editing technologies.
Growing a cover crop between main crops imitates natural ecosystems where the soil is continuously covered with vegetation. This is an important management practice in preserving soil nutrient resources and reducing nitrogen (N) losses to waters. Cover crops also provide other functions that are important for the resilience and long-term stability of cropping systems, such as reduced erosion, increased soil fertility, carbon sequestration, increased soil phosphorus (P) availability, and suppression of weeds and pathogens.
Much is known about how to use cover crops to reduce N leaching, for climates where there is a water surplus outside the growing season. Non-legume cover crops reduce N leaching by 20%–80% and legumes reduce it by, on average, 23%. There are both synergies and possible conflicts between different environmental and production aspects that should be considered when developing efficient and multifunctional cover crop systems, but contradictions about different functions provided by cover crops can sometimes be overcome with site-specific adaptation of measures. One example is cover crop effects on P losses. Cover crops reduce losses of total P, but extract soil P to available forms and may increase losses of dissolved P. How to use this effect to increase soil P availability on subtropical soils needs further studies. Knowledge and examples of how to maximize the positive effects of cover crops on cropping systems are improving, thereby increasing the sustainability of agriculture. One example is combined weed suppression in order to reduce dependence on herbicides or intensive mechanical treatment.
Jean-François Bissonnette and Rodolphe De Koninck
Plantation farming emerged as a large-scale system of specialized agriculture in the tropics under European colonialism, in opposition to smallholding subsistence agriculture. Despite large-scale plantations in the tropics, smallholdings have consistently formed the backbone of rural economies, to the extent that they have become the main producers of some of the former plantation crops. In the early 21st century, oil palm has become the third most important cash crop in the world in terms of area cultivated, largely due to the expansion of this crop in Malaysia and Indonesia. Although in these countries, oil palm is primarily cultivated in large plantations, smallholders cultivate a large share of the territory devoted to this crop. This is related to the programs set up by governments of Malaysia and Indonesia during the second half of the 20th century, to provide smallholders with land plots in capital intensive large-scale oil palm schemes. Despite the relative success encountered by these programs in both countries, policymakers have continued to insist on the development of private centrally managed large-scale plantations. Yet, smallholding family farming has remained the most resilient economic activity in rural areas of the tropics. This system has proven adaptive to environmental change and, given proper access to markets and capital, particularly responsive to market signals. Today, many small-holdings are still characterized by the diversity of crops cultivated, low use of chemical inputs, reliance on family labor, and high levels of ecological knowledge. These are some of the main factors explaining why small family farms have proven more efficient than large plantations and, in the long term, more economically and ecologically resilient. Yet, large-scale land acquisitions for monocrop production remain a current issue, highlighting the paradox of the latest stage of agrarian capitalism and of its persistent built-in disregard for environmental deterioration.
Soils, the earth’s skin, are at the intersection of the lithosphere, hydrosphere, atmosphere, and biosphere. The persistence of life on our planet depends on the maintenance of soils as they constitute the biological engines of earth. Human population has increased exponentially in recent decades, along with the demand for food, materials, and energy, which have caused a shift from low-yield and subsistence agriculture to a more productive, high-cost, and intensive agriculture. However, soils are very fragile ecosystems and require centuries for their development, thus within the human timescale they are not renewable resources. Modern and intensive agriculture implies serious concern about the conservation of soil as living organism, i.e., of its capacity to perform the vast number of biochemical processes needed to complete the biogeochemical cycles of plant nutrients, such as nitrogen and phosphorus, crucial for crop primary production. Most practices related to intensive agriculture determine a deterioration even in the short-middle term of their physical, chemical, and biological properties, which all together contribute to soil quality, along with an overexploitation of soils as living organisms. Recent trends are turning toward styles of agriculture management that are more sustainable or conservative for soil quality.
Usually, use of soils for agricultural purposes deflect them at various degrees from the “natural” soil development processes (pedogenesis), and this shift may be assumed as a divergence from soil sustainability principles. For decades, the misuse of land due to intensive crop management has deteriorated soil health and quality. A huge plethora of microorganisms inhabits soils, thus acting as “the biological engine of the earth”; indeed, this microbiota serves the soil ecosystem, performing several fundamental functions. Therefore, management practices might be planned looking at the safeguard of soil microbial diversity and resilience. In addition, each unexpected alteration in numberless soil biochemical processes, being regulated by microbial communities, may represent an early and sensible signal of soil homeostasis weakening and, consequently, warn about soil conservation. Within the vast number of soil biochemical processes and connected features (bioindicators) virtually effective to measure the sustainable soil exploitation, those related to the mineralization or immobilization of the main nutrients (C and N), including enzyme activity (functioning) and composition (diversity) of microbial communities, exert a fundamental role because of their involvement in soil metabolism. Comparing the influence of many cropping factors (tillage, mulching and cover crops, rotations, mineral and organic fertilization) under both intensive and sustainable managements on soil microbial diversity and functioning, through both chemical and biological soil quality indicators, makes it possible to identify the most hazardous diversions from soil sustainability principles.
David A. Robinson, Fiona Seaton, Katrina Sharps, Amy Thomas, Francis Parry Roberts, Martine van der Ploeg, Laurence Jones, Jannes Stolte, Maria Puig de la Bellacasa, Paula Harrison, and Bridget Emmett
Soils provide important functions, which according to the European Commission include: biomass production (e.g., agriculture and forestry); storing, filtering, and transforming nutrients, substances, and water; harboring biodiversity (habitats, species, and genes); forming the physical and cultural environment for humans and their activities; providing raw materials; acting as a carbon pool; and forming an archive of geological and archaeological heritage, all of which support human society and planetary life. The basis of these functions is the soil natural capital, the stocks of soil material. Soil functions feed into a range of ecosystem services which in turn contribute to the United Nations sustainable development goals (SDGs). This overarching framework hides a range of complex, often nonlinear, biophysical interactions with feedbacks and perhaps yet to be discovered tipping points. Moreover, interwoven with this biophysical complexity are the interactions with human society and the socioeconomic system which often drives our attitudes toward, and the management and exploitation of, our environment.
Challenges abound, both social and environmental, in terms of how to feed an increasingly populous and material world, while maintaining some semblance of thriving ecosystems to pass on to future generations. How do we best steward the resources we have, keep them from degradation, and restore them where necessary as soils underpin life? How do we measure and quantify the soil resources we have, how are they changing in time and space, what can we predict about their future use and function? What is the value of soil resources, and how should we express it? This article explores how soil properties and processes underpin ecosystem services, how to measure and model them, and how to identify the wider benefits they provide to society. Furthermore, it considers value frameworks, including caring for our resources.
Salt accumulation in soils, affecting agricultural productivity, environmental health, and the economy of the community, is a global phenomenon since the decline of ancient Mesopotamian civilization by salinity. The global distribution of salt-affected soils is estimated to be around 830 million hectares extending over all the continents, including Africa, Asia, Australasia, and the Americas. The concentration and composition of salts depend on several resources and processes of salt accumulation in soil layers. Major types of soil salinization include groundwater associated salinity, non–groundwater-associated salinity, and irrigation-induced salinity. There are several soil processes which lead to salt build-up in the root zone interfering with the growth and physiological functions of plants.
Salts, depending on the ionic composition and concentration, can also affect many soil processes, such as soil water dynamics, soil structural stability, solubility of essential nutrients, and pH and pE of soil water—all indirectly hindering plant growth. The direct effect of salinity includes the osmotic effect affecting water and nutrient uptake and the toxicity or deficiency due to high concentration of certain ions. The plan of action to resolve the problems associated with soil salinization should focus on prevention of salt accumulation, removal of accumulated salts, and adaptation to a saline environment. Successful utilization of salinized soils needs appropriate soil and irrigation management and improvement of plants by breeding and genetic engineering techniques to tolerate different levels of salinity and associated abiotic stress.
Beyond damage to rainfed agricultural and forestry ecosystems, soil erosion due to water affects surrounding environments. Large amounts of eroded soil are deposited in streams, lakes, and other ecosystems. The most costly off-site damages occur when eroded particles, transported along the hillslopes of a basin, arrive at the river network or are deposited in lakes. The negative effects of soil erosion include water pollution and siltation, organic matter loss, nutrient loss, and reduction in water storage capacity. Sediment deposition raises the bottom of waterways, making them more prone to overflowing and flooding. Sediments contaminate water ecosystems with soil particles and the fertilizer and pesticide chemicals they contain. Siltation of reservoirs and dams reduces water storage, increases the maintenance cost of dams, and shortens the lifetime of reservoirs. Sediment yield is the quantity of transported sediments, in a given time interval, from eroding sources through the hillslopes and river network to a basin outlet. Chemicals can also be transported together with the eroded sediments. Sediment deposition inside a reservoir reduces the water storage of a dam.
The prediction of sediment yield can be carried out by coupling an erosion model with a mathematical operator which expresses the sediment transport efficiency of the hillslopes and the channel network. The sediment lag between sediment yield and erosion can be simply represented by the sediment delivery ratio, which can be calculated at the outlet of the considered basin, or by using a distributed approach. The former procedure couples the evaluation of basin soil loss with an estimate of the sediment delivery ratio SDRW for the whole watershed. The latter procedure requires that the watershed be discretized into morphological units, areas having a constant steepness and a clearly defined length, for which the corresponding sediment delivery ratio is calculated. When rainfall reaches the surface horizon of the soil, some pollutants are desorbed and go into solution while others remain adsorbed and move with soil particles. The spatial distribution of the loading of nitrogen, phosphorous, and total organic carbon can be deduced using the spatial distribution of sediment yield and the pollutant content measured on soil samples. The enrichment concept is applied to clay, organic matter, and all pollutants adsorbed by soil particles, such as nitrogen and phosphorous. Knowledge of both the rate and pattern of sediment deposition in a reservoir is required to establish the remedial strategies which may be practicable. Repeated reservoir capacity surveys are used to determine the total volume occupied by sediment, the sedimentation pattern, and the shift in the stage-area and stage-storage curves. By converting the sedimentation volume to sediment mass, on the basis of estimated or measured bulk density, and correcting for trap efficiency, the sediment yield from the basin can be computed.