Organic fertilizers are naturally occurring fertilizers (e.g. compost, manure).

Naturally occurring organic fertilizers include manure, slurry, worm castings, peat, seaweed, humic acid, and guano. Sewage sludge use in organic agricultural operations in the U.S. has been extremely limited and rare due to USDA prohibition of the practice (due to toxic metal accumulation, among other factors).^{[1 ][2 ][3 ]}

Processed organic fertilizers include compost, bloodmeal, bone meal, humic acid, amino acids, and seaweed extracts. Other examples are natural enzyme-digested proteins, fish meal, and feather meal. Decomposing crop residue (green manure) from prior years is another source of fertility.

Discussion of the term 'organic'

There used to be a distinction between the term "organic" and the term "pesticide-free"^{[citation needed]}. Organic simply dealt with the use of fertilizer types. Once the term "organic" became regulated, many other factors^{[ which?]} were added. "Pesticide-free" is not at all related to fertilization^{[citation needed]} (plant nutrition), but has become a legal inclusion. In scientific terms, organic compounds must include Carbon.

Likewise, in scientific terms, a fish emulsion can be a good organic fertilizer, but in some jurisdictions{{like Oregon|date=November 2010}} fish emulsion must be certified "dolphin-safe" to be considered "organic"^{[citation needed]}.

Natural sourcing

Animal-sourced Urea and Urea-Formaldehyde (from urine) are suitable for application organic agriculture; however, pure (synthetically produced) urea is not.^{[4 ][5 ]} The common thread that can be seen through these examples is that organic agriculture attempts to define itself through minimal processing (e.g., via chemical energy such as petroleum — see Haber process), as well as being naturally occurring or via natural biological processes such as composting.

Cover crops are also grown to enrich soil as a green manure through nitrogen fixation from the atmosphere;^{[6 ]} as well as phosphorus (through nutrient mobilization)^{[7 ]} content of soils.

Powdered limestone, mined rock phosphate, and Chilean saltpeter are inorganic chemicals in the technical (organic chemistry) sense of the word but are considered suitable for organic agriculture in limited amounts ^{[8][9 ][10 ]}..

Advantages

Although the density of nutrients in organic material is comparatively modest, they have many advantages. The majority of nitrogen-supplying organic fertilizers contain insoluble nitrogen and act as a slow-release fertilizer. By their nature, organic fertilizers increase physical and biological nutrient storage mechanisms in soils, mitigating risks of over-fertilization. Organic fertilizer nutrient content, solubility, and nutrient release rates are typically much lower than mineral (inorganic) fertilizers.^{[11 ][12 ]} A University of North Carolina study found that potential mineralizable nitrogen (PMN) in the soil was 182–285% higher in organic mulched systems than in the synthetics control.^{[13 ]}

Organic fertilizers also re-emphasize the role of humus and other organic components of soil,^{[14 ]} which are believed to play several important roles:

• Mobilizing existing soil nutrients, so that good growth is achieved with lower nutrient densities while wasting less ^[15] 
• Releasing nutrients at a slower, more consistent rate, helping to avoid a boom-and-bust pattern ^[15] 
• Helping to retain soil moisture, reducing the stress due to temporary moisture stress^{[citation needed]} 
• Improving the soil structure^{[citation needed]} 
• Helping to prevent topsoil erosion (responsible for desertfication and the Dust bowl^{[citation needed]} 

Organic fertilizers also have the advantage of avoiding certain problems associated with the regular heavy use of artificial fertilizers:

• The necessity of reapplying artificial fertilizers regularly (and perhaps in increasing quantities) to maintain fertility^{[citation needed]} 
• Extensive runoff of soluble nitrogen and phosphorus,^{[citation needed]} leading to eutrophication of bodies of water (which causes fish kills^{[16 ]})
• Costs are lower for if fertilizer is locally available^{[citation needed]} 

Disadvantages

Organic fertilizers have the following disadvantages:

• As a dilute source of nutrients when compared to inorganic fertilizers, transporting large amount of fertilizer incurs higher costs, especially with slurry and manure.^{[17 ]} 
• The composition of organic fertilizers tends to be more complex and variable than a standardized inorganic product.^{[citation needed]} 
• Improperly-processed organic fertilizers may contain pathogens from plant or animal matter that are harmful to humans or plants. However, proper composting should remove them. ^[18] 
• More labor is needed to compost organic fertilizer, increasing labor costs. Some of this cost is offset by reduced cash purchase.

Conventional farming application

In non-organic farming, a compromise between the use of artificial and organic fertilizers is common^{[citation needed]}, often using inorganic fertilizers supplemented with the application of organics that are readily available such as the return of crop residues or the application of manure.

See also

• Biosecurity 
• Compost 
• Composting 
• Compost bin 
• Controlled release fertiliser 
• Cover crop 
• Fertilizer 
• Food additive 
• Manure 
• Vermicompost 

References

External links