Sustainable agriculture

From Wikipedia, the free encyclopedia

Sustainable agriculture integrates three main goals: environmental stewardship, farm profitability, and prosperous farming communities. These goals have been defined by a variety of disciplines and may be looked at from the vantage point of the farmer or the consumer.

1 Description
2 Economics
3 Methods
4 Off-farm impacts
5 Urban planning
6 See also
7 External links
8 References

[edit] Description

Sustainable agriculture refers to the ability of a farm to produce perpetually. Two key issues are 1) long-term effects of various practices on soil properties and processes essential for crop productivity, and 2) the long-term availability of inputs. Practices that can cause long-term damage to soil include excessive tillage (leading to erosion) and irrigation without adequate drainage (leading to accumulation of salt in the soil). Long-term experiments provide some of the best data on how various practices affect soil properties essential to sustainability.

While air and sunlight are generally available in most geographic locations, 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, the land would suffer from nutrient depletion and be unusable for further farming. Sustainable agriculture depends on replenishing the soil while minimizing the use 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: 1) recycling crop waste and livestock or human manure, 2) growing legume crops and forages such as, peanuts, or alfalfa that form symbioses with nitrogen-fixing bacteria called rhizobia, 3) adapting the current industrial nitrogen fixation process to use hydrogen made by electrolysis (perhaps using electricity from solar cells or windmills) instead of natural gas^{[citation needed]}, or 4) genetically engineering (non-legume) crops to form nitrogen-fixing symbioses or fix nitrogen without microbial symbionts. The last option was proposed in the 1970's, but would be well beyond the capability of current (2006) technology, even if various concerns about biotechnology were addressed. Sustainable options for replacing other nutrient inputs (phosphorus, potassium, etc.) are more limited.

In some areas, sufficient rainfall is available for crop growth, but many other areas require irrigation. For irrigation systems to be sustainable they must be managed properly (to avoid salt accumulation) and not use more water from their source than is naturally replenished, otherwise the water source becomes, in effect, a non-renewable resource. Improvements in water well drilling technology and the development of submersible pumps have made it possible for large crops to be regularly grown where reliance on rainfall alone previously made this level of success unpredictable. However, this progress has come at a price, in that in many areas where this has occurred, such as the Ogallala Aquifer, the water is being used at a greater rate than its rate of recharge.

[edit] Economics

Given the finite supply of natural resources, agriculture that is inefficient will eventually exhaust the available resources or the ability to afford and acquire them. It will also generate negative externality, such as pollution as well as financial and production costs. Agriculture that relies mainly on inputs that are extracted from the earth's crust or produced by society, contributes to the depletion and degradation of the environment. Despite this continuing practice, unsustainable agriculture continues because it is financially more cost-effective than sustainable agriculture in the short term.

In an economic context, the farm must generate revenue. The way that crops are sold must be accounted for in the sustainability equation. Fresh food sold from a farm stand requires little additional energy, aside from that necessary for cultivation, harvest, and 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.

To be sold at a remote location requires a complex economic system in which the farm producers form the first link in a chain of processors and handlers to the consumers. This practice allows greater revenue because of efficient transport of a large number of items, but because it produces externalities and relies on the use of non-renewable resources, shipping, processing, and handling, it is not considered sustainable^{[citation needed]}. Moreover, such a system is considered vulnerable to fluctuations, such as strikes, oil prices, and global economic conditions including labour, interest rates, futures markets, and farm product prices^{[citation needed]}.

In a social context, the actions required for greater sustainability profoundly affect business methods and lifestyle^{[citation needed]}. Current large-scale agricultural practices do not meet the above sustainability criteria, but shifting toward practices that do meet them would require significant changes by corporations and individuals engaged in agribusiness^{[citation needed]}.

From a system's view, the gain and loss factors for sustainability can be listed. The most important factors for an individual site are sun, air, soil and water as rainfall. These are naturally present in the system as part of the larger planetary processes and incur no costs. Of the four, soil quality and quantity are most amenable to human intervention through time and labour. (The economic input depends solely on the price of labour and cost of machinery used).

Natural growth and outputs are also subject to human intervention. What grows and how and where 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.

[edit] Methods

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^{[citation needed]}. Growing a mixture of crops (polyculture) sometimes reduces disease or pest problems (Nature 406:718, Environ. Entomol. 12:625) 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^{[citation needed]}. For example, how does growing a corn-bean mixture every year compare with growing corn and bean in alternate years? Cropping systems that include a variety of crops (polyculture and/or rotation) may also use replenish nitrogen (if legumes are included) and may also use resources such as sunlight, water, or nutrients more efficiently (Field Crops Res. 34:239)^{[citation needed]}.

Pesticides, though sometimes useful in the short term, can harm the soil food web, a complex ecology of micro-organisms in soil that helps sustain the plant from the roots down^{[citation needed]}. Experiments comparing plants grown in soil compared to plants grown through hydroponics have shown a thirty-three percent higher growth rate when there are beneficial soil microorganisms available^{[citation needed]}.

Certain pesticides synthesized by chemical companies can impart a sometimes fatal toxicity to humans^{[citation needed]}, livestock and insect pollinators, such as bees and butterflies, which may be necessary for plant success^{[citation needed]}. Without insect pollinators, farm labor must be expended to manually pollinate each plant. Crops such as cacao beans and vanilla are examples of crops requiring highly labor-intensive practices in the absence of natural pollinators.

Throughout history, farmers seeking to grow crops usually confine themselves to growing only the fastest and most productive plants. Such practices can result in growing crops without the genetic diversity found in wildlife^{[citation needed]}. Without such diversity in the genes, crops may become more susceptible to disease and crop failure^{[citation needed]}. The Irish potato famine is a well-known example of the dangers of monocultural and mono-varietal crop cultivation^{[citation needed]}.

Many scientists, farmers, and businesses have debated how to make agriculture farming sustainable^{[citation needed]}. One of the many 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^{[citation needed]}. This system would replicate the biodiversity already found in a natural environment, resulting in increased resistance to diseases and decreased effects of erosion and loss of nutrients in soil^{[citation needed]}. Nitrogen fixation from legumes, for example, used in conjunction with plants that rely on nitrate from soil for growth, will allow the land to be reused annually^{[citation needed]}. 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^{[citation needed]}. This method is considered to require a minimal amount of outside resources^{[citation needed]}.

In practice, there is no single approach to sustainable agriculture, as the precise goals and methods must be adapted to each individual case. There are some techniques of farming which are inherently in conflict with the concept of sustainability. For example, the slash-and-burn technique, sometimes used by shifting cultivators, endangers the nutrient content of tropical soils by resultant erosion as well as stripping the land of biomass.

[edit] Off-farm impacts

What if a farm is able to "produce perpetually", yet has negative effects on environmental quality elsewhere? Most people concerned with sustainability take a global view, so they try to avoid negative off-farm impacts. For example, over-application of synthetic fertilizer or animal manures can pollute nearby rivers and coastal waters. On the other hand, if crop yields are too low, because of soil exhaustion of nutrients or reduced ability to retain water, farmers would need to access new lands for agriculture, leading to the decimation of the rainforest, draining wetlands, etc.

[edit] Urban planning

There has been considerable debate about which form of human residential habitat may be a better social form for sustainable agriculture. Generally, it is thought that village communities can improve sustainability in that such communities tend to provide a cooperative environment that supports farming^{[citation needed]}.

Many environmentalists pushing for increased population density to preserve agricultural land point out that urban sprawl is less sustainable and more damaging to the environment than living in the cities where cars are not needed because food and other necessities are within walking distance^{[citation needed]}. However, others have theorized that sustainable ecocities, or ecovillages which combine habitation and farming with close proximity between producers and consumers, may provide greater sustainability^{[citation needed]}.

The use of available city space (e.g., rooftop and community gardens) for cooperative food production is another way to achieve greater sustainability^{[citation needed]}.

One of the latest ideas in achieving sustainable agricultural involves shifting the production of food plants from major factory farming operations to large, urban, technical facilities called vertical farms. The advantages of vertical farming include year-round production, isolation from pests and diseases, controllable resource recycling, and on-site production that eliminates the need for transportation costs^{[citation needed]}. While a vertical farm has yet to become a reality, the idea is gaining momentum among those who believe that current sustainable farming methods will be insufficient to provide for a growing global population^{[citation needed]}.

[edit] See also

[edit] External links

Biodynamic Agriculture Australia Promoting the practice and understanding of the Biodynamic system of sustainable agriculture.
Sustainable Agriculture Research and Education
National Sustainable Agriculture Information Service
Rainforest Alliance's Sustainable Agriculture program
The Vertical Farm Project Envisioning the future of human food production as a mechanism for environmental restoration, protection from infectious disease, and a source of sustainable energy
SANREM CRSP Sustainable Agriculture and Natural Resource Management Collaborative Research Support Program at Virginia Tech
The Land Institute Research on sustainable perennial crop systems
Self Help Development InternationalSHDI is an Irish agency engaged in promoting long term sustainable development projects in Africa.