Fertilizer

Fertilizers are substances added to soil with the intention of promoting plant growth.

Manure was the original fertilizer, and is still used.

Fertilizers typically provide, in varying proportions[?], the 3 major plant nutrients[?] (nitrogen, potassium and phosphorus), the secondary plant nutrients[?] (calcium, sulfur, magnesium) and sometimes trace elements with a role in plant nutrition: boron, manganese, iron, zinc, copper and molybdenum.

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 creates 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 leads to long-term degradation of the soil.