What are fertilizers?
Fertilizers are any solid, liquid or gaseous substances containing one or more plant nutrients.
They are either applied to the soil, directly on the plant (foliage) or added to aqueous solutions, in order to maintain soil fertility, improve crop development, yield and/or crop quality.
The purpose of fertilizers are to supplement the natural supply of soil nutrients, build up soil fertility in order to satisfy the demand of crops, and to compensate for the nutrients taken by harvested products or lost by unavoidable leakages to the environment, in order to maintain good soil conditions for cropping.
What are plant nutrients?
As a precondition for growth, health and the production of nutritious food, plants require essential nutrients (macro and micronutrients) in sufficient quantities.
Seventeen elements have been shown to be essential for plants: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulphur (S), magnesium (Mg), calcium (Ca), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl), nickel (Ni).
Furthermore, additional elements may be essential to a few plant species, e.g. sodium (Na) and cobalt (Co).
Carbon, H and O are obtained from the atmosphere and water, and are not considered mineral elements.
The remaining essential elements can be divided into three groups: primary macronutrients (N, P and K), secondary macronutrients (S, Mg and Ca) and micronutrients (Fe, Mn, Zn, Cu, B, Mo, Cl and Ni) based on average concentrations in plants. If a single essential plant nutrient is available in insufficient quantity, it affects plant growth and thus the yield.