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Sustainable agriculture integrates three main goals: environmental stewardship, farm profitability, and prosperous farming communities. These goals have been defined by a variety of philosophies, policies and practices, from the vision of farmers and consumers.

In production terms, sustainable agriculture refers to the ability of a farm to continue producing indefinitely, with a minimum of outside inputs. Crops depend on nutrients from soil, air, water, and sunlight to produce the foodstuff that human beings need to grow. When farmers harvest crops, they take what crops have produced from the resources available to them. These resources must be replenished to allow the production cycle to continue. Otherwise, they would be exhausted and the land would be unusable for further farming. Although resources like the sun, air, and rain are generally available in geographic locations, nutrients in soil are easily exhausted. Crop residues and manure from livestock retain nutrients and can be recycled to the soil. Farm labor, by animals or farmers themselves, is another form of energy recycling if they were fed by the food that they have grown and harvested. Anything that has to be imported, like fertilizer for plants, or petroleum products to run machinery, reduces sustainability because it depends on non-renewable resources and incurs negative externality. The less the farm needs outside inputs to maintain production levels, the greater its level of sustainability.

In environmental terms, given the finite supply of natural resources, agriculture that is very inefficient - low on the sustainability scale - will eventually run out of resources, or the ability to afford them, and cease to be viable as a farming method. Agriculture that relies mainly on outside inputs contributes to the depletion and degradation of environment.

In an economic context, the farm must generate revenue to acquire things that cannot be produced directly. The way that crops are sold then becomes part of the sustainability equation. Fresh food sold from a farm stand requires little additional energy, beyond cultivation and harvest. Food that is packaged and sold at a remote location, like a farmers' market, incurs a greater energy cost for materials, labour, transport, and so forth. A more complex the economic system in which the farm producer participates leads to greater costs and greater reliance on importations of externals to fund the resulting increase in energy consumption. Such as system may be more vulnerable to fluctuation in prices of external material it must import, such as the price of oil.

In a social context, the approaches required for higher sustainability profoundly affect business methods and our way of life. It is believed that current large-scale agricultural practices are not conducive to the goals of sustainable agriculture. Progressing toward sustainability would require significant changes in agriculture practices by such corporations engaged in agribusiness.

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

Natural growth and outputs are also under control of human intervention. What grows, how and where it is grown can be chosen by an individual. Two of the many possible practices of sustainable agriculture are crop rotation and soil amendments, both designed to ensure that crops being cultivated will obtain all the necessary nutrients for healthy growth.

One of the hope of sustainable agriculture is to have a diverse number of crops grown in a single field, separated by season, rather than one type of crop grown annually. This system would replicate the biodiversity already offered by nature in rainforests, resulting in increased resistance to diseases and decrease in effects of erosion and loss of nutrients in soil.

Current unsustainable practice of growing one crop annually is known as monocultures. Growing crops without genetic diversity tends to make the plants more susceptible to crop diseases and crop failure. The Irish potato famine illustrates a well-known example of the dangers of monocultural crop cultivation.

The use of pesticides, though beneficial in the shorter term, has bad effects on the soil food web, a complex ecology of micro-organisms that help sustain the plant from the roots down. Experiments have shown a 33% higher growth on soil with beneficial soil microorganisms compared to growth by hydroponics.

Certain pesticides also impart a sometimes fatal toxicity to humans, livestock and insect pollinators, such as bees and butterflies, which may be necessary for plant success.

The byproducts from the crops are either fed to the livestock, used as bedding or composted with the excreta of livestock and humans, and are tended for two or more years to allow the destruction of soil born disease causing pathogens. They then become a soil amendment available to add biomass to marginal soils, making them more fertile.

Consider a single crop such as Canola, an oilseed bred for human consumption. The oilseed is mechanically expressed and can be used, with simple processing, as a biodiesel to power the processing plant. The byproducts of combustion: heat, motive power and nitrogen oxides can be used for process heat to express the oil, mechanical energy to process the seed, and as a compost amendment as part of the nitrogen cycle (this is an area for further research).

The meal can be used as a high protein source for animal feed. Suggested uses are for high conversion rate meat livestock such as chicken and rabbit.

The canola crop requires a crop rotation cycle of at least four years, with more being considered better. A grain crop is suggested by agonomists as the next crop to be grown in that field.

Disease control is affected by the use of rotation patterns.

Notice to this point, that the entire cycle does not incur extensive transport costs, save that of soil amendments and initial startup capital costs.

The current trend to separate the rural and urban activities is based on cheap oil. Use of petrochemicals as a fuel source, however, adds to the emission of greenhouse gases, which has been determined as causing climate change and influencing weather patterns negatively.

Relationship between the City and Agricultural Land

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 sustainablity in that such communites tend to provide a cooperative environment that supports farming.

Many environmentalists pushing for population density to preserve agricultural land point out that urban sprawl is more damaging to the overall environment and unsustainable than living in the cities where cars are generally not needed because food and other purchases can be reached by walking. However, other environmentalists have proposed that a sustainable ecocities, a combination of cities and farming side by side, to maintain close proximity between the producers and the consumers may be a better practice.

In practice, there is no single approach to sustainable agriculture, as the precise goals and methods must be adapted to each individual case.

See Also

• agriculture
• agroecology
• organic farming
• organic movement
• permaculture
• sustainable development
• List of sustainable agriculture topics

• Environment
• Sustainable agriculture