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Nitrogen is the most critical element obtained by plants from the soil, to the exception of moist tropical forests where phosphorus is the limiting soil nutrient, [36] and nitrogen deficiency often limits plant growth. [37] Plants can use nitrogen as either the ammonium cation (NH 4 +) or the anion nitrate (NO 3 −).
Plants called legumes, including the agricultural crops alfalfa and soybeans, widely grown by farmers, harbour nitrogen-fixing bacteria that can convert atmospheric nitrogen into nitrogen the plant can use. Plants not classified as legumes such as wheat, corn and rice rely on nitrogen compounds present in the soil to support their growth.
Nitrogen assimilation is the formation of organic nitrogen compounds like amino acids from inorganic nitrogen compounds present in the environment. Organisms like plants , fungi and certain bacteria that can fix nitrogen gas (N 2 ) depend on the ability to assimilate nitrate or ammonia for their needs.
The Leaf Color Chart (LCC) is a diagnostic tool used to determine the nitrogen level in rice plants relative to the shade of green of the plant's leaves. It is a ruler-shaped strip containing at least four panels of color, ranging from yellowish green to dark green.
Urea (CO(NH 2) 2), with 45-46% nitrogen, another popular source of nitrogen, having the advantage that it is solid and non-explosive, unlike ammonia and ammonium nitrate. Calcium ammonium nitrate Is a blend of 20-30% limestone CaCO 3 or dolomite (Ca,Mg)CO 3 and 70-80% ammonium nitrate with 24-28 % nitrogen.
Nitrogen is the most commonly limiting nutrient in plants. Legumes use nitrogen fixing bacteria, specifically symbiotic rhizobia bacteria, within their root nodules to counter the limitation. Rhizobia bacteria convert nitrogen gas (N 2) to ammonia (NH 3) in a process called nitrogen fixation.
In the NO − 3 anion, the oxidation state of the central nitrogen atom is V (+5). This corresponds to the highest possible oxidation number of nitrogen. Nitrate is a potentially powerful oxidizer as evidenced by its explosive behaviour at high temperature when it is detonated in ammonium nitrate (NH 4 NO 3), or black powder, ignited by the shock wave of a primary explosive.
The nitrogen-fixing clade consists of four orders of flowering plants: Cucurbitales, Fabales, Fagales and Rosales. [a] This subgroup of the rosids encompasses 28 families of trees, shrubs, vines and herbaceous perennials and annuals. The roots of many of the species host bacteria that fix nitrogen into compounds the plants can use. [4] [5]