Any natural or manufactured material that contains at least 5% of one or more of the three primary nutrients - nitrogen (N), phosphorous (P), or potassium (K) - can be considered a fertilizer. Industrially manufactured fertilizers are sometimes referred to as "mineral" fertilizers.
There are several sources of plant nutrients. The two most important are organic manure and mineral fertilizers. When manure and crop residues are used, mineral fertilizers supply the outstanding nutrient balance needed for good crop yields. In most parts of the world, the balance to be supplied by mineral fertilizers is substantial.
Fertilizer production entails gathering raw materials from nature; treating them in order to purify them or increase their concentration; converting them into plant-available forms; and often combining them into products that contain more than one nutrient.