The essential elements can be divided into two groups: macronutrients and micronutrients. Nutrients that plants require in larger amounts are called macronutrients. About half of the essential elements are considered macronutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulfur (S). Instead, micronutrients, or trace elements, are present in very small quantities. They include boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo) and nickel (Ni). Additional elements may be essential to a few plant species, like sodium (Na) and cobalt (Co).
Deficiencies in any of these nutrients can adversely affect plant growth and development. Depending on the specific nutrient, a lack can cause stunted growth, slow growth, or chlorosis (yellowing of the leaves).
Plants take up most nutrients as ions from the soil solution. As nutrients are taken up, the soil solution is replenished from soil reserves. The rate of replenishment of nutrients to the soil solution is critical to the maintenance of the growth of a crop. If the amount of a nutrient in the soil solution is not maintained from soil reserves, then additions of that nutrient in the form of a fertilizer may be required to maintain plant growth and yield.
In addition to the mere nutrients, plants also need a supporting soil structure for their roots to grow in. A high organic matter content in the soil improves the soil structure and supports microorganisms in the soil. It also improves the water and nutrient retention capacity and the capacity to buffer pH and pollutants like heavy metals by holding them in the soil. Besides, the soil organic matter contains significant reserves of macro and micronutrients within its structure that become available for plants after the mineralization process carried out by soil microorganisms.
Yield and the quality of products from crops are strongly linked to the supply of nutrients through fertilizers product. However, nowadays sustainable fertilization management is essential to increase the overall performance of cropping systems by providing economically optimum nourishment to the crop while minimizing nutrient losses and supporting agricultural system sustainability by increasing Nutrient Use Efficiency (NUE). Plant biostimulants represent a promising strategy to boost sustainable agricultural production thanks to their capacity of improving directly or indirectly nutrient use efficiency of crops especially under low nutrient availability.
