A fertilizer may be an organic or inorganic material
added to the soil to replace or increase plant nutrients.
Organic fertilizers – including animal and green
manure, fish and bone meal, guano (seabird excrement),
and compost – are decomposed by soil microorganisms,
and their elements are freed for plant use.
or chemical fertilizers contain the major nutrients
(nitrogen, phosphorus and potassium) in proportions
required by the crop.
Properly used, fertilizers increase
crop yields; they do not affect a crop's nutritive
properties unless specifically intended to do so.