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Revision as of 06:23, 30 July 2003 by Marshman (talk | contribs) (Add links; edit some)(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. 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.
The Haber-Bosch process uses about one percent of the Earth's total energy supply in order to provide half of the nitrogen used in agriculture.
Excessive use of fertilizer can lead to algal blooms in lakes and streams that receive the run-off from the land being fertilized, and lead to long-term degradation of the soil. See also eutrophication and nutrients.