Sustainable agriculture is farming in sustainable ways based on an understanding of ecosystem services, the study of relationships between organisms and their environment.
Video Sustainable agriculture
History of the term
The phrase 'sustainable agriculture' was reportedly coined by the Australian agricultural scientist Gordon McClymont. Wes Jackson is credited with the first publication of the expression in his 1980 book New Roots for Agriculture. The term became popular in the late 1980s.
It has been defined as "an integrated system of plant and animal production practices having a site-specific application that will last over the long term", for example to satisfy human food and fiber needs, to enhance environmental quality and the natural resource base upon which the agricultural economy depends, to make the most efficient use of non-renewable and on-farm resources and integrate natural biological cycles and controls, to sustain the economic viability of farm operations, and to enhance the quality of life for farmers and society as a whole.
Maps Sustainable agriculture
Key principles
There are several key principles associated with sustainability in agriculture:
- The incorporation of biological and ecological processes into agricultural and food production practices. For example, these processes could include nutrient cycling, soil regeneration, and nitrogen fixation.
- Using decreased amounts of non-renewable and unsustainable inputs, particularly the ones that are environmentally harmful.
- Using the expertise of farmers to both productively work the land as well as to promote the self-reliance and self-sufficiency of farmers.
- Solving agricultural and natural resource problems through the cooperation and collaboration of people with different skills. The problems tackled include pest management and irrigation.
Farming and natural resources
Sustainable agriculture can be understood as an ecosystem approach to agriculture. Practices that can cause long-term damage to soil include excessive tilling of the soil (leading to erosion) and irrigation without adequate drainage (leading to salinization). Long-term experiments have provided some of the best data on how various practices affect soil properties essential to sustainability. In the United States a federal agency, USDA-Natural Resources Conservation Service, specializes in providing technical and financial assistance for those interested in pursuing natural resource conservation and production agriculture as compatible goals.
The most important factors for an individual site are sun, air, soil, nutrients, and water. Of the five, water and soil quality and quantity are most amenable to human intervention through time and labor.
Although air and sunlight are available everywhere on Earth, crops also depend on soil nutrients and the availability of water. When farmers grow and harvest crops, they remove some of these nutrients from the soil. Without replenishment, land suffers from nutrient depletion and becomes either unusable or suffers from reduced yields. Sustainable agriculture depends on replenishing the soil while minimizing the use or need of non-renewable resources, such as natural gas (used in converting atmospheric nitrogen into synthetic fertilizer), or mineral ores (e.g., phosphate). Possible sources of nitrogen that would, in principle, be available indefinitely, include:
- recycling crop waste and livestock or treated human manure
- growing legume crops and forages such as peanuts or alfalfa that form symbioses with nitrogen-fixing bacteria called rhizobia
- industrial production of nitrogen by the Haber process uses hydrogen, which is currently derived from natural gas (but this hydrogen could instead be made by electrolysis of water using electricity (perhaps from solar cells or windmills)) or
- genetically engineering (non-legume) crops to form nitrogen-fixing symbioses or fix nitrogen without microbial symbionts.
The last option was proposed in the 1970s, but is only gradually becoming feasible. Sustainable options for replacing other nutrient inputs such as phosphorus and potassium are more limited.
More realistic, and often overlooked, options include long-term crop rotations, returning to natural cycles that annually flood cultivated lands (returning lost nutrients indefinitely) such as the flooding of the Nile, the long-term use of biochar, and use of crop and livestock landraces that are adapted to less than ideal conditions such as pests, drought, or lack of nutrients. Crops that require high levels of soil nutrients can be cultivated in a more sustainable manner with appropriate fertilizer management practices.
Water
In some areas sufficient rainfall is available for crop growth, but many other areas require irrigation. For irrigation systems to be sustainable, they require proper management (to avoid salinization) and must not use more water from their source than is naturally replenishable. Otherwise, the water source effectively becomes a non-renewable resource. Improvements in water well drilling technology and submersible pumps, combined with the development of drip irrigation and low-pressure pivots, have made it possible to regularly achieve high crop yields in areas where reliance on rainfall alone had previously made successful agriculture unpredictable. However, this progress has come at a price. In many areas, such as the Ogallala Aquifer, the water is being used faster than it can be replenished.
Several steps must be taken to develop drought-resistant farming systems even in "normal" years with average rainfall. These measures include both policy and management actions:
- improving water conservation and storage measures,
- providing incentives for selection of drought-tolerant crop species,
- using reduced-volume irrigation systems,
- managing crops to reduce water loss, and
- not planting crops at all.
Indicators for sustainable water resource development are:
- Internal renewable water resources. This is the average annual flow of rivers and groundwater generated from endogenous precipitation, after ensuring that there is no double counting. It represents the maximum amount of water resource produced within the boundaries of a country. This value, which is expressed as an average on a yearly basis, is invariant in time (except in the case of proved climate change). The indicator can be expressed in three different units: in absolute terms (km³/yr), in mm/yr (it is a measure of the humidity of the country), and as a function of population (m³/person per year).
- Global renewable water resources. This is the sum of internal renewable water resources and incoming flow originating outside the country. Unlike internal resources, this value can vary with time if upstream development reduces water availability at the border. Treaties ensuring a specific flow to be reserved from upstream to downstream countries may be taken into account in the computation of global water resources in both countries.
- Dependency ratio. This is the proportion of the global renewable water resources originating outside the country, expressed in percentage. It is an expression of the level to which the water resources of a country depend on neighbouring countries.
- Water withdrawal. In view of the limitations described above, only gross water withdrawal can be computed systematically on a country basis as a measure of water use. Absolute or per-person value of yearly water withdrawal gives a measure of the importance of water in the country's economy. When expressed in percentage of water resources, it shows the degree of pressure on water resources. A rough estimate shows that if water withdrawal exceeds a quarter of global renewable water resources of a country, water can be considered a limiting factor to development and, reciprocally, the pressure on water resources can affect all sectors, from agriculture to environment and fisheries.
Soil
Soil erosion is fast becoming one of the world's severe problems. It is estimated that "more than a thousand million tonnes of southern Africa's soil are eroded every year. Experts predict that crop yields will be halved within thirty to fifty years if erosion continues at present rates." Soil erosion is occurring worldwide. The phenomenon is being called peak soil as present large-scale factory farming techniques are jeopardizing humanity's ability to grow food in the present and in the future. Without efforts to improve soil management practices, the availability of arable soil will become increasingly problematic. Intensive agriculture reduces the carbon level in soil, impairing soil structure, crop growth and ecosystem functioning, and accelerating climate change. Soil management techniques include no-till farming, keyline design, windbreaks to reduce wind erosion, incorporating carbon-containing organic matter back into fields, reducing chemical fertilizers, and protecting soil from water run-off.
Phosphate
Phosphate is a primary component in chemical fertilizer. It is the second most important nutrient for plant after nitrogen, and is often a limiting factor. It is important for sustainable agriculture as it can improve soil fertility and crop yields. Phosphorus is involved in all major metabolic processes including photosynthesis, energy transfer, signal transduction, macromolecular biosynthesis, and respiration. It is needed for root ramification and strength and seed formation, and can increase disease resistance.
Phosphorus is found in the soil in both inorganic and organic forms and makes up approximately 0.05% of soil biomass. However, only 0.1% of that phosphorus present can be absorbed by plants. This is due to poor solubility and phosphorus' high reactivity with elements in the soil such as aluminum, calcium, and iron, causing the phosphorus to be fixed. Long-term use of phosphate-containing chemical fertilizers cause eutrophication and deplete soil fertility, so people have looked to other sources.
An alternative is rock phosphate, a natural source already in some soils. In India, there are almost 260 million tons of rock phosphate. However, rock phosphate is a non-renewable resource and it is being depleted by mining for agricultural use: reserves are expected to be exhausted in 50-100 years; peak phosphorus will occur in about 2030. This is expected to increase food prices as phosphate fertilizer costs increase.
A way to make rock phosphate more effective and last longer is to implement microbial inoculants such as phosphate-solubilizing microorganisms, known as PSMs. A source of these PSMs is compost or the recycling of human and animal waste. Specific PSMs can be added to soil. These solubilize phosphorus already in the soil and use processes like organic acid production and ion exchange reactions to make that phosphorus available for plants. When these PSMs are present, there has been an increase in crop growth, particularly in terms of shoot height, dry biomass, and grain yield.
Phosphorus uptake is even more efficient with the presence of mycorrhizae in the soil. Mycorrhiza is a type of mutualistic symbiotic association between plants and fungi, which are well-equipped to absorb nutrients, including phosphorus, in soil. These fungi can increase nutrient uptake in soil where phosphorus has been fixed by aluminum, calcium, and iron. Mycorrhizae can also release organic acids that solubilize otherwise unavailable phosphorus.
Land
As the global population increases and demand for food increases, there is pressure on land resources. In land use planning and management, considering the impacts of land use changes on factors such as soil erosion can support long-term agricultural sustainability, as shown by a study of Wadi Ziqlab, a dry area in the Middle East where farmers graze livestock and grow olives, vegetables, and grains.
Looking back over the 20th century shows that for people in poverty, following environmentally sound land practices has not always been a viable option due to many complex and challenging life circumstances. Currently, increased land degradation in developing countries may be connected with rural poverty among smallholder farmers when forced into unsustainable agricultural practices out of necessity.
Land is a finite resource on Earth. And although expansion of agricultural land can decrease biodiversity and contribute to deforestation, the picture is complex; for instance, a study examining the introduction of sheep by Norse settlers (Vikings) to the Faroe Islands of the North Atlantic concluded that, over time, the fine partitioning of land plots contributed more to soil erosion and degradation than grazing itself.
The Food and Agriculture Organisation of the United Nations estimates that in coming decades, cropland will continue to be lost to industrial and urban development, along with reclamation of wetlands, and conversion of forest to cultivation, resulting in the loss of biodiversity and increased soil erosion. Many tools will be called upon to offset these projections. In Europe, one such tool is a geo-spatial data system called SoilConsWeb which is being developed to inform soil conservation minded decision making within agricultural sectors and other areas of land management.
Energy
Energy is used all the way down the food chain from farm to fork. In industrial agriculture, energy is used in on-farm mechanisation, food processing, storage, and transportation processes. It has therefore been found that energy prices are closely linked to food prices. Oil is also used as an input in agricultural chemicals. the International Energy Agency projects higher prices of non-renewable energy resources as a result of fossil fuel resources being depleted. It may therefore decrease global food security unless action is taken to 'decouple' fossil fuel energy from food production, with a move towards 'energy-smart' agricultural systems including renewable energy. The use of solar powered irrigation in Pakistan has come to be recognized as a leading example of energy use in creating a closed system for water irrigation in agricultural activity.
Economics
Socioeconomic aspects of sustainability are also partly understood. Regarding less concentrated farming, the best known analysis is Netting's study on smallholder systems through history.
Given the finite supply of natural resources at any specific cost and location, agriculture that is inefficient or damaging to needed resources may eventually exhaust the available resources or the ability to afford and acquire them. It may also generate negative externality, such as pollution as well as financial and production costs. There are several studies incorporating these negative externalities in an economic analysis concerning ecosystem services, biodiversity, land degradation and sustainable land management. These include The Economics of Ecosystems and Biodiversity study led by Pavan Sukhdev and the Economics of Land Degradation Initiative which seeks to establish an economic cost benefit analysis on the practice of sustainable land management and sustainable agriculture.
The way that crops are sold must be accounted for in the sustainability equation. Food sold locally does not require additional energy for transportation (including consumers). Food sold at a remote location, whether at a farmers' market or the supermarket, incurs a different set of energy cost for materials, labour, and transport.
Pursuing sustainable agriculture results in many localized benefits. Having the opportunities to sell products directly to consumers, rather than at wholesale or commodity prices, allows farmers to bring in optimal profit.
Triple bottom line frameworks (including social and environmental aspects alongside the financial) show that a sustainable company can be technologically and economically feasible. For this to happen, growth in material consumption and population need to be slowed down and there has to be a drastic increase in the efficiency of material and energy use. To make that transition, long- and short-term goals will need to be balanced enhancing equity and quality of life.
Methods
What grows where and how it is grown are a matter of choice. Two of the many possible practices of sustainable agriculture are crop rotation and soil amendment, both designed to ensure that crops being cultivated can obtain the necessary nutrients for healthy growth. Soil amendments would include using locally available compost from community recycling centers. These community recycling centers help produce the compost needed by the local organic farms.
Using community recycling from yard and kitchen waste utilizes a local area's commonly available resources. These resources in the past were thrown away into large waste disposal sites, are now used to produce low cost organic compost for organic farming. Other practices includes growing a diverse number of perennial crops in a single field, each of which would grow in separate season so as not to compete with each other for natural resources. This system would result in increased resistance to diseases and decreased effects of erosion and loss of nutrients in soil. Nitrogen fixation from legumes, for example, used in conjunction with plants that rely on nitrate from soil for growth, helps to allow the land to be reused annually. Legumes will grow for a season and replenish the soil with ammonium and nitrate, and the next season other plants can be seeded and grown in the field in preparation for harvest.
Monoculture, a method of growing only one crop at a time in a given field, is a very widespread practice, but there are questions about its sustainability, especially if the same crop is grown every year. Today it is realized to get around this problem local cities and farms can work together to produce the needed compost for the farmers around them. This combined with growing a mixture of crops (polyculture) sometimes reduces disease or pest problems but polyculture has rarely, if ever, been compared to the more widespread practice of growing different crops in successive years (crop rotation) with the same overall crop diversity. Such methods may also support sustainable weed management in that the development of herbicide-resistant weeds is reduced. Cropping systems that include a variety of crops (polyculture and/or rotation) may also replenish nitrogen (if legumes are included) and may also use resources such as sunlight, water, or nutrients more efficiently (Field Crops Res. 34:239).
Replacing a natural ecosystem with a few specifically chosen plant varieties reduces the genetic diversity found in wildlife and makes the organisms susceptible to widespread disease. The Great Irish Famine (1845-1849) is a well-known example of the dangers of monoculture. In practice, there is no single approach to sustainable agriculture, as the precise goals and methods must be adapted to each individual case. There may be some techniques of farming that are inherently in conflict with the concept of sustainability, but there is widespread misunderstanding on effects of some practices. Today the growth of local farmers' markets offer small farms the ability to sell the products that they have grown back to the cities that they got the recycled compost from. This will help move people away from the slash-and-burn or slash-and-char techniques that are the characteristic feature of shifting cultivation. These are often cited as inherently destructive, yet slash-and-burn cultivation has been practiced in the Amazon for at least 6000 years. Serious deforestation did not begin until the 1970s, largely as the result of Brazilian government programs and policies.
There are also many ways to practice sustainable animal husbandry. Some of the key tools to grazing management include fencing off the grazing area into smaller areas called paddocks, lowering stock density, and moving the stock between paddocks frequently.
Sustainable intensification
In light of concerns about food security, human population growth and dwindling land suitable for agriculture, sustainable intensive farming practises are needed to maintain high crop yields, while maintaining soil health and ecosystem services. The capacity for ecosystem services to be strong enough to allow a reduction in use of synthetic, non renewable inputs whilst maintaining or even boosting yields has been the subject of much debate. Recent work in the globally important irrigated rice production system of east Asia has suggested that - in relation to pest management at least - promoting the ecosystem service of biological control using nectar plants can reduce the need for insecticides by 70% whilst delivering a 5% yield advantage compared with standard practice.
Soil treatment
Soil steaming can be used as an ecological alternative to chemicals for soil sterilization. Different methods are available to induce steam into the soil in order to kill pests and increase soil health.
Solarizing is based on the same principle, used to increase the temperature of the soil to kill pathogens and pests.
Certain crops act as natural biofumigants, releasing pest suppressing compounds. Mustard, radishes, and other plants in the brassica family are best known for this effect. There exist varieties of mustard shown to be almost as effective as synthetic fumigants at a similar or lesser cost.
Off-farm impacts
A farm that is able to "produce perpetually", yet has negative effects on environmental quality elsewhere is not sustainable agriculture. An example of a case in which a global view may be warranted is over-application of synthetic fertilizer or animal manures, which can improve productivity of a farm but can pollute nearby rivers and coastal waters (eutrophication). The other extreme can also be undesirable, as the problem of low crop yields due to exhaustion of nutrients in the soil has been related to rainforest destruction, as in the case of slash and burn farming for livestock feed.In Asia, specific land for sustainable farming is about 12.5 acres which includes land for animal fodder, cereals productions lands for some cash crops and even recycling of related food crops.In some cases even a small unit of aquaculture is also included in this number (AARI-1996)
Sustainability affects overall production, which must increase to meet the increasing food and fiber requirements as the world's human population expands to a projected 9.3 billion people by 2050. Increased production may come from creating new farmland, which may ameliorate carbon dioxide emissions if done through reclamation of desert as in Israel and Palestine, or may worsen emissions if done through slash and burn farming, as in Brazil.
Anthropogenic changes
As the Earth is entering the Anthropocene, an epoch characterized by human impacts such as climate change, agriculture and agricultural development are at risk. Agriculture has an enormous environmental footprint, and is simultaneously leading to huge amounts of environmental changes globally and being hugely impacted by these global changes. Additionally, the human population is continuing to grow rapidly at a rate which will require an increase in food production globally. This is complicated by the fact that the Earth is undergoing rising amounts of environmental risks. Sustainable agriculture provides a potential solution to enable agricultural systems to feed a growing population while successfully operating within the changing environmental conditions.
Social
Development
In 2007, the United Nations reported on "Organic Agriculture and Food Security", stating that using organic and sustainable agriculture could be used as a tool to reach global food security without expanding land usage and reducing environmental impacts. Another way to define sustainable agriculture is to give attention to the "human and environmental aspects," because of the turn to a more unsustainable way of farming in U.S. agriculture. During the Great Depression in the United States many farming families were living in subhuman and hungry conditions and treated "sustainability as a resource-input and food-output equation." Though conditions have improved, the farming has not as much done so. There has been evidence provided by developing nations from the early 2000s stating that when people in their communities are not factored into the agricultural process that serious harm is done. Although global food security would most likely not drastically fall, these practices would impact, first hand, local, rural farming communities, making them unable to feed themselves and their families. The social scientist Charles Kellogg has stated that, "In a final effort, exploited people pass their suffering to the land." This turn to more unsustainable farming has seen suffering for many people. For if something is sustainable, it should be that way in all aspects of it, not just the crop yield or soil health. It has been seen in the developing country of Bangladesh, the starving of rural farming communities due to their unsustainable farming methods. Sustainable agriculture mean the ability to permanently and continuously "feed its constituent populations."
There are a lot of opportunities that can increase farmers' profits, better communities, and continue sustainable practices. For example, in Uganda Genetically Modified Organisms (GMOs) were originally illegal, however, under stressful circumstances where Banana Bacterial Wilt (BBW) has the potential to wipe out 90% of yield they decided to explore GMOs as a possible solution . Therefore, as a result of the banana crisis in Uganda caused by the BBW, the government issued the National Biotechnology and Biosafety bill which will allow scientists that are part of the National Banana Research Program to start experimenting with genetically modified organisms. This effort has the potential to help local communities because a significant portion live off the food they grow themselves and it will keep their economy in check because their main sources of produce will remain stable.
Women
In the past 30 years (1978-2007) in the United States the number of women farm operators has tripled. Today, women operate 14 percent of farms, compared to five percent in 1978. Much of the growth is due to women farming outside the "male dominated field of conventional agriculture". In community supported agriculture women represent 40 percent of farm operators, and 21 percent of organic farmers. With the change of laws in land ownership over the past century, women are now allowed all the same freedom of land ownership that men have.
International policy
Sustainable agriculture has become a topic of interest in the international policy arena, especially with regards to its potential to reduce the risks associated with a changing climate and growing human population.
The Commission on Sustainable Agriculture and Climate Change, as part of its recommendations for policy makers on achieving food security in the face of climate change, urged that sustainable agriculture must be integrated into national and international policy. The Commission stressed that increasing weather variability and climate shocks will negatively affect agricultural yields, necessitating early action to drive change in agricultural production systems towards increasing resilience. It also called for dramatically increased investments in sustainable agriculture in the next decade, including in national research and development budgets, land rehabilitation, economic incentives, and infrastructure improvement.
Policy ethics
Most agricultural professionals agree that there is a "moral obligation to pursue [the] goal [of] sustainability." The major debate comes from what system will provide a path to that goal. Because if an unsustainable method is used on a large scale it will have a massive negative effect on the environment and human population. The best way to create policy for agriculture is to be free of any bias. A good review would be done with "practical wisdom," a virtue identified by Aristotle, distinguishing practical wisdom from scientific knowledge, this coming from Nichomachean Ethics. The science of agriculture is called "agronomy", the root of this word relating to scientific law. Although agriculture may not fit well under scientific law, and may not be designed to be treated as an Aristotelian scientific knowledge, but more practical wisdom. Practical wisdom requires recognition of past failures in agriculture to better attain a more sustainable agricultural system.
Urban planning
The use of available city space (e.g., rooftop gardens, community gardens, garden sharing, and other forms of urban agriculture) for cooperative food production may be able to contribute to sustainability. A recent idea (2014) is to create large, urban, technical facilities for Vertical farming. Potential advantages include year-round production, isolation from pests and diseases, controllable resource recycling, and reduced transportation costs.
Increasing threats of climate change have influenced cities and public offiials are thinking more proactively about the ways they can deliver services and food more efficiently.The environmental cost of transportation could be avoided if people take back their connection to fresh food. This raises questions; however, about the excess environmental costs associated with local farming vs more large scale operations which offer food security around the world.
Key debates
There are several key debates involving sustainable agriculture:
Ecocentric vs technocentric
The main debate on how sustainable agriculture might be achieved centers around two different approaches: an ecocentric approach and a technocentric approach. The ecocentric approach emphasizes no- or low-growth levels of human development, and focuses on organic and biodynamic farming techniques with the goal of changing consumption patterns, and resource allocation and usage. The technocentric approach argues that sustainability can be attained through a variety of strategies, from the view that state-led modification of the industrial system like conservation-oriented farming systems should be implemented, to the argument that biotechnology is the best way to meet the increasing demand for food.
Multifunctional agriculture vs ecosystem services
There are different scientific communities that are looking at the topic of sustainable agriculture through two separate lenses: multifunctional agriculture (MFA) and ecosystem services (ES). While both of these frameworks are similar, they look at the function of agriculture in different lights. Those that employ the multifunctional agriculture philosophy focus on farm-centered approaches, and define function as being the outputs of agricultural activity. The central argument of MFA is that agriculture has other functions aside from the production of food and fiber, and therefore agriculture is a multifunctional enterprise. These additional functions include renewable natural resource management and conservation of landscape and biodiversity. On the other hand, ES focuses on service-centered approaches, and defines function as the provision of services to human beings. Specifically, ES posits that individuals and society as a whole receive benefits from ecosystems, which are called ecosystem services. Within the field of sustainable agriculture, the services that ecosystems provide include pollination, soil formation, and nutrient cycling, all of which are necessary functions for the production of food.
Barriers
Since World War II, dominant models of agriculture in the United States and the entire national food system have been characterized by a focus on monetary profitability at the expense of social and environmental integrity.
In sustainable agriculture, changes in lower rates of soil and nutrient loss, improved soil structure, and higher levels of beneficial microorganisms are not quick. The changes are not immediately evident to the operate when using sustainable agriculture. In conventional agriculture the benefits are easily visible with no weeds, pests, etc. and the "process of externalization" hides the costs to soil and ecosystems around it. A major barrier to sustainable agriculture is the lack of knowledge of its benefits. Many benefits are not visible, so they are often unknown.
Criticism
Efforts toward more sustainable agriculture are supported in the sustainability community, however, these are often viewed only as incremental steps and not as an end. Some foresee a true sustainable steady state economy that may be very different from today's: greatly reduced energy usage, minimal ecological footprint, fewer consumer packaged goods, local purchasing with short food supply chains, little processed foods, more home and community gardens, etc.
See also
- Alternatives to pesticides
- Declaration for Healthy Food and Agriculture
- Hydrozoning
- Local food
- Renewable Agriculture and Food Systems (journal)
- Sustainable Agriculture Innovation Network (between the UK and China)
- Sustainable Commodity Initiative
- Sustainable development
- Sustainable food system
- Sustainable landscaping
References
Further reading
- Dore, J. (1997) Sustainability Indicators for Agriculture: Introductory Guide to Regional/National and On-farm Indicators, Rural Industries Research and Development Corporation, Australia.
- Falvey, Lindsay (2004) Sustainability - Elusive or Illusion: Wise Environmental Management. Institute for International Development, Adelaide.
- Gold, Mary (1999) Sustainable Agriculture: Definitions and Terms. Special Reference Briefs Series no. SRB 99-02 Updates SRB 94-5 September 1999. National Agricultural Library, Agricultural Research Service, U.S. Department of Agriculture.
- Hayes, B. (2008) Trial Proposal: Soil Amelioration in the South Australian Riverland.
- Paull, J. (2014) Lord Northbourne, the man who invented organic farming, a biography. Journal of Organic Systems, 9(1), 31-53.
- Pender J., Place F., Ehui S. (2006) Strategies for Sustainable Land Management in the East African Highlands
- Pollan M. (2007) The Omnivore's Dilemma: A Natural History of Four Meals
- Roberts W. (2008) The No-Nonsense Guide to World Food
- Royal Society (February 2008) permanent dead link] Dedicated double issue of Philosophical Transactions B on Sustainable Agriculture. Some articles are freely available.
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