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Organic farming is a form of agriculture which avoids or largely excludes the use of synthetic fertilizers and pesticides, plant growth regulators, and livestock feed additives. As far as possible, organic farmers rely on crop rotation, crop residues, animal manures and mechanical cultivation to maintain soil productivity and tilth to supply plant nutrients, and to control weeds, insects and other pests.
According to the international organic farming organization IFOAM : "The role of organic agriculture, whether in farming, processing, distribution, or consumption, is to sustain and enhance the health of ecosystems and organisms from the smallest in the soil to human beings." 
Approximately 31 million hectares (75 million acres) worldwide are now grown organically.
"An organic farm, properly speaking, is not one that uses certain methods and substances and avoids others; it is a farm whose structure is formed in imitation of the structure of a natural system that has the integrity, the independence and the benign dependence of an organism"
Wendell Berry, "The Gift of Good Land"
Organic farming excludes the use of certain synthetic inputs, such as synthetic fertilizers, pesticides, herbicides and genetically modified organisms (GMOs). In a number of countries, including the US, China and most of Europe organic farming is also defined by law, so that the commercial use of the term organic to describe farming and food products is regulated by the government. Where laws exist, organic certification is available to farms for a fee, and it is usually illegal for a non-certified farm to call itself or its products organic. Elsewhere, for example, in Canada, voluntary certification is available, while legislation may be pending.
Methods of organic farming vary. However, organic approaches share common goals and practices. In addition to the exclusion of synthetic agrichemicals, these include protection of the soil (from erosion, nutrient depletion, structural breakdown), promotion of biodiversity (for example growing a variety of crops rather than a single crop or planting hedges around fields), and outdoor grazing for livestock and poultry, though none of these is required in the United States to earn the USDA organic seal . Within this framework, individual farmers develop their own organic production systems, determined by factors such as climate, market conditions, and local agricultural regulations.
Main article: Organic farming methods
The term holistic in often used to describe organic farming , . Anthony Trewavas, in a nature-published article  rejects the notion that a holist view is superior to reductionist 'chemical' agriculture.
Enhancing soil health is the cornerstone of organic farming . A variety of methods are employed, including crop rotation, green manure, cover cropping, application of compost, and mulching. Organic farmers also use certain processed fertilizers such as seed meal, and various mineral powders such as rock phosphate and greensand, a naturally occurring form of potash.
Pest control targets animal pests (including insects), weeds and disease. Organic pest control involves the cumulative effect of many techniques, including, allowing for an acceptable level of pest damage, encouraging or even introducing beneficial organisms, careful crop selection and crop rotation, and mechanical controls such as row covers and traps. These techniques generally provide benefits in addition to pest control—soil protection and improvement, fertilization, pollination, water conservation, season extension, etc.—and these benefits are both complementary and cumulative in overall effect on farm health. Effective organic pest control requires a thorough understanding of pest life cycles and interactions.
Weeds are controlled mechanically, thermically and through the use of mulches.資料來源： Wikipedia