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Revision as of 06:34, 30 July 2003 by Marshman (talk | contribs) (Rearrange material)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Fertilizers are substances added to soil with the intention of promoting plant growth. Fertilizers typically provide, in varying proportions, the three major plant nutrients (nitrogen, potassium and phosphorus), the secondary plant nutrients (calcium, sulfur, magnesium), and sometimes trace elements (or micronutrients) with a role in plant nutrition: boron, manganese, iron, zinc, copper and molybdenum.
Manure was the original fertilizer, and is still used. Fertilizer can be created either from natural organic material such as manure or compost (see also organic gardening), or artificially as through the Haber-Bosch process which produces ammonia. The Haber -Bosch process uses about one percent of the Earth's total energy supply in order to provide half of the nitrogen needed in agriculture. Organic material has the advantage of adding carbon compounds to the soil. A major source of soil fertility is the decomposing crop residue from prior years, though this is not considered "fertilizer."
Excessive use of fertilizer can lead to algal blooms in lakes and streams that receive run-off from crop lands, and lead to long-term degradation of the soil. See also eutrophication and nutrients.