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.