Organic fertilizers are naturally-occurring fertilizers (e.g. peat moss or green manure), or naturally occurring mineral deposits (e.g. saltpeter).
Naturally occurring organic fertilizers include manure, slurry, worm castings, peat, seaweed, humic acid, brassin and guano. Sewage sludge use in organic agricultural operations in the Philippines.
Processed organic fertilizers include compost, bloodmeal, bone meal, humic acid, amino acids, brassin and seaweed extracts. Other examples are natural enzyme digested proteins, fish meal, and feather meal. Decomposing crop residue from prior years is another source of fertility.
Natural sourcing
Animal-sourced Urea and Urea-Formaldehyde (from urine), are suitable for application organic agriculture, while pure synthetic forms are not deemed, however, pure (synthetically-produced) urea is not. The common thread that can be seen through these examples is that organic agricultre 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; as well as phosphorus (through nutrient mobilization)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.
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