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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. In order to grow, the crops and livestock draw energy from the soil, air, water, and sunlight. As crops are harvested, the energy they used must be replaced in order to continue the production cycle. Some of that energy comes from the larger environment, from sun, air, and rain. Some can be recycled: crop residues and manure from livestock retain nutrients that can be returned to the soil. Using animals (including the farmers!) that are fed by the farm to perform farm labor is another form of energy recycling. Anything that has to be imported, like fertilizer for plants, or petroleum products to run machinery, reduces sustainability. 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 afford scarce resources, and cease to be viable. And agriculture that relies mainly on outside inputs contributes to the depletion and degradation of natural resources.

In an economic context, the farm must generate revenue in order 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 growing and harvest. Food that is packaged and sold at a remote location, like a farmers' market, incurs a greater energy cost, for materials, labor, transportation, and so forth. The more complex the food system in which the farm participates, the greater the farm's costs, including energy consumption, and the more it relies economically on externals, notably, the price of oil.

In a social context, the approaches required for higher sustainability profoundly affect business methods and our way of life. Current large-scale agricultural practices are not conducive to sustainability. In order to increase sustainability, significant changes in agribusiness would be required.

From a systems 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 without cost, as they are part of the larger planetary processes. Of the three, the soil quality and quantity are most amiable to human intervention, at the cost of time and labour. (the economic input depends solely on the price of labour, the time on the cost of machinery)

Natural growth occurs, and the outputs are also under control of human intervention. What grows, and where it is grown can be chosen by an individual. At this point, crop rotation and soil amendments may be required to insure the health of the crop. The natural outcome of monocultures is the potential for crop disease and the resultant crop failure leading to events like the irish potato famine.

The use of pesticides; though beneficial in the shorter term, has bad effects on the soil food web, that ecology of micro-organisms that sustain the plant from the roots down. Experiments have shown a 33% higher growth with beneficial soil microorganisms compared to not having them while growing by hydroponics.

Pesticides tend to be toxic to humans, livestock and insect pollenators, such as bees and butterflies, necessary for crop 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 effected by the use of rotation patterns.

Notice to this point, that the entire cycle does not incur extensive transportation costs, save for 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, changing the climate and influencing weather patterns.

The last part of the cycle, the human activity, favors social trends towards such practices as co-housing, co-operatives and other interdependent human relationships, with the limiting factor of full independence and solitude an achievable goal. Historical experience with the panopticon suggests that this might not be a viable and healthy option. Small villages may be a better social form.

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
• sustainable development
• List of sustainable agriculture topics

• Environment
• Sustainable agriculture