Fertilizers are an indispensable agri-input and are added to aid and increase the supply of essential nutrients required for growth and development of plants. There are 16 nutrient elements required to grow crops. Three essential nutrients – carbon (C), hydrogen (H), and oxygen (O2) – are taken up from atmospheric carbon dioxide and water. The other 13 nutrients are taken up from the soil and are usually grouped as primary nutrients, secondary nutrients, and micronutrients.
The primary nutrients are nitrogen (N), phosphorus (P), and potassium (K). Primary nutrients are utilized in the largest amounts by crops, and therefore, are applied at higher rates than secondary nutrients and micronutrients. The secondary nutrients – calcium (Ca), magnesium (Mg), and sulphur (S) – are required in smaller amounts than the primary nutrients, although there are opinions that S may be a major nutrient in some cases. Micronutrients – iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), and molybdenum (Mo), selenium (Se) – are required in even smaller amounts than secondary nutrients. They are available as manganese, zinc and copper sulphates, oxides, oxy-sulphates and chelates, as well as in boric acid and ammonium molybdate.
Entire focus on use of fertilizers have been almost exclusively on NPK since their “discovery” in the mid-1800s. Owing to the role of these primary nutrients in the crop cycle, they have been overused to increase the production without realizing the long-term effects on the soil and environment. Thus, the negative impact of fertilizers has often been highlighted. But as the fertilizers are required for proper growth of plants, and plants are the primary source of food for human and animal consumption, the former does have an impact on human and animal health as well.