Nitrogen is one of the most important mineral nutrients required by plants and is considered a primary macronutrient. Plants require it in relatively large quantities because it performs essential structural, physiological, biochemical and metabolic functions. Although the atmosphere contains nearly 78% nitrogen in the form of nitrogen gas (N₂), most plants cannot directly use atmospheric nitrogen. Plants mainly absorb nitrogen from the soil in inorganic forms such as ammonium (NH₄⁺) and nitrate (NO₃⁻). Therefore, the availability, transformation and cycling of nitrogen in the environment are extremely important for plant growth and agricultural productivity. Nitrogen is a major constituent of amino acids, which are the basic building blocks of proteins. Proteins are essential components of plant cells and participate in almost every biological process. Enzymes that regulate metabolic reactions are largely proteins, and therefore adequate nitrogen is necessary for enzyme formation and activity. Nitrogen is also present in nucleic acids such as DNA and RNA. DNA contains the genetic information of plants, while RNA is involved in the expression of this genetic information and in protein synthesis. Thus, nitrogen is directly associated with cell division, growth and reproduction. Another important role of nitrogen is its presence in chlorophyll. Chlorophyll is the green pigment responsible for photosynthesis, through which plants convert light energy into chemical energy. Nitrogen deficiency reduces chlorophyll formation and results in pale green or yellow leaves, a condition known as chlorosis. Since photosynthesis is the fundamental process by which plants manufacture carbohydrates, insufficient nitrogen can reduce photosynthetic activity and consequently decrease plant growth and productivity. Nitrogen is also involved in the formation of several important plant compounds, including certain vitamins, hormones, coenzymes and other nitrogen-containing metabolites. It contributes to the development of leaves, stems and roots and promotes vigorous vegetative growth. Adequate nitrogen generally results in healthy, dark-green foliage and greater leaf area. Nitrogen is particularly important during the early stages of plant development because rapid cell division and tissue formation require substantial amounts of proteins and nucleic acids. Nitrogen also influences crop yield and the quality of agricultural products. Adequate nitrogen availability promotes the formation of branches, leaves, flowers, fruits and seeds. In cereals such as wheat, rice and maize, nitrogen is especially important for the development