A fertilizer is any material of natural or synthetic origin (other than liming materials) that is applied to soils or to plant tissues to supply one or more plant nutrients essential to the growth of plants.
Fertilizers enhance the growth of plants. This goal is met in two ways, the traditional one being additives that provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration. Fertilizers typically provide, in varying proportions:
Three main macronutrients:
Nitrogen (N): leaf growth
Phosphorus (P): Development of roots, flowers, seeds, fruit
Potassium (K): Strong stem growth, movement of water in plants, promotion of flowering and fruiting
Three secondary macronutrients:
Calcium (Ca), magnesium (Mg), and sulfur (S)
Copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B), and of occasional significance there are silicon (Si), cobalt (Co) plus rare mineral catalysts.
Fertilizers are commonly used for growing all crops, with application rates depending on the soil fertility, usually as measured by a soil test and according to the particular crop.
Fertilizers are applied to crops both as solids and as liquid. About 90% of fertilizers are applied as solids. Foliar fertilizers (Liquid Fertilizers) are applied directly to leaves. The method is almost invariably used to apply water-soluble straight nitrogen fertilizers and used especially for high value crops such as fruits. Advantages of liquid fertilizer are its more rapid effect and easier coverage.