· Plants need large amounts of , nitrogen with a dry matter content of 3 to 4% in nitrogen. Despite its abundance, atmospheric nitrogen is not available for plant growth. * Most plants source it exclusively from , soil and in addition take it in only two inorganic forms: ammoniacal and nitrate. Whilst experiments have shown that plants grow best under the influence of a mixture of ammonia and , nitrates in proportion dependent on the , plant species, most nitrogen is ingested in the form of nitrates.
* Due to the rapid microbial conversion of ammonia to nitrate in soil and the greater mobility of the latter , roots are more exposed to nitrates than to ammonia. In humid or acidic ecosystems this may vary. * For example , crops grown under , bedding conditions such as , rice take up the largest amount of nitrogen in the form of ammonia.
· Nitrogen ingested by the roots is metabolized and transported to the upper parts of the , plant usually in the form of the amino group (NH2). In the aboveground part of the plant the nitrogen of the amino group is converted into amino acids and then into proteins. Thus, the intensity of nitrogen metabolism and the rate of protein synthesis control the entry of nitrogen into the various parts of the plant. · Generally , nitrogen in plants is concentrated in the newer , segments with the highest growth rates. · When nitrogen uptake from the roots is insufficient , then nitrogen from the older leaves is moved in order to nourish the newer organs of the plant. The proteins in these leaves are hydrolyzed into their amino acids (proteolysis) which in turn are redistributed to the growing ends and younger leaves. Proteolysis in older leaves has the effect of reducing the chlorophyll content and the appearance of a yellow color which is often a symptom of nitrogen deficiency.
In green plant material protein nitrogen is by far the largest fraction of compounds with nitrogen content concentrating about 80-85% total nitrogen. * Many plants (e.g. , peas , beans ) soybeans are grown specifically for the production of plant proteins for human and animal food. The growth rate and protein content of plants is significantly influenced by available nitrogen from soil and fertilizers.
* Other parts of nitrogen in plants are the nucleic acids , RNA and DNA , which account for about 10% total nitrogen and free amino acids together with the other compounds with an amino group present representing 5%.
* In , plants nitrogen predominates in functional compounds such as enzymes and less in building blocks such as fibers. * Most plants store energy for seedlings in the form of hydrocarbons (starch and fat) , but legumes such as peas , lentils and beans accumulate extra protein reserves in their seeds. Wild leguminous plants have their own ecological significance in nitrogen-poor soils because they do not depend on available soil reserves. · To prevent nitrogen deficiency in the seedling before it has its own symbiotic system for fixing atmospheric nitrogen , the protein reserves of the seed act as a temporary source of nitrogen.
· Plants need large amounts of , nitrogen with a dry matter content of 3 to 4% in nitrogen. Despite its abundance, atmospheric nitrogen is not available for plant growth.
Source : Kummer Karl-Friedrich (BASF AG) and Chris Dawson and Associates , (2003). Understanding Nitrogen and its Use in Agriculture. Published by European Fertillizer Manufacturers Association (EFMA)
