The N-P-K elements: essential for crops, their absence does not allow plants to complete the vegetative and reproductive cycle.

Nitrogen (N) is the main constituent of many compounds such as chlorophyll as well as of hormones, vitamins and enzymes, useful for the crops life cycle. Plants are unable to absorb the atmospheric nitrogen, with the exception of legumes thanks to symbiosis with nitrogen-fixing bacteria. Most plants, however, absorb nitrogen through their roots, in nitrate (NO3-) or ammonia (NH4+) form. Nitrogen can also be supplied to plants in ureic form. In such case, absorption is ensured by the urease hydrolysis carried out by soil microorganisms able to turn urea into ammonia and, subsequently, nitric nitrogen. Fertilizers based on nitrate ions are readily assimilated though easily leached, so applications during absorption peaks (vegetative growth/vegetative regrowth) are recommended. Ammoniacal and ureic fertilizers, on the other hand, have a more slowly absorption, due to the oxidation processes.

Phosphorus (P) is present in many environments both in organic and inorganic forms and plays a fundamental role during multiplication, reproduction and formation of seeds and fruits. The absorption of phosphorus by plants and the soil fertility depend on its availability. This varies based on the constituent minerals, the presence of organic matter and the soil pH. Very often, such conditions make phosphorus insoluble and difficult to be absorbed, so it is necessary to provide it through fertilization, thus avoiding a potential deficiency that could lead to dwarf plants, abnormal leaf coloration and stunted growth.

Potassium (K), which is fundamental for all the major plants functions (photosynthesis, respiration and sugar translocation), plays a very important role in the regulation of osmotic pressure and, therefore, in the evapotranspiration processes of crops. It has been shown that potassium-deficient plants are more sensitive to light and may show symptoms of chlorosis and necrosis.