Nitrogen Fertilizers

   Nitrogen Fertilizers The main condition for good plants living activity is nitrogen, which is needed for proteosynthesis. Though the quantity of nitrogen amounts to 4/5 in the atmosphere, plants, as well as animals, are unable to absorb nitrogen from air. It is next to impossible to reap good harvest without proper nitrogen fertilization. Nitrogen deficiency causes plants weak development, their foliage becomes light-green due to chlorophyll shortage, and fruits are late in ripening. However, wrong nitrogen fertilization can bring rather harm than benefit both to people and plants. In nature, plants get nitrogen from soil, but its content is rather low in it, amounting to 1…3% of nitrogen mineral formulations which are directly involved in plants nutrition. The rest of formulations are not consumed by plants. The first ideas for using nitrogen fertilizers date back to the 19th century, the time when, due to rapid population boost, issues on foodstuff production and agricultural output increase arose. Chilean saltpetre was widely used back then as nitrogen fertilizer; its natural resources were found in Chile, Atacama Desert. However, as natural saltpetre resources were rapidly running low, and transportation to Europe influenced the cost greatly, issues concerning considerable volumes of industrial production of nitrogen fertilizers had to be solved urgently. At the very beginning of the 20th century, cyanamide process for nitrogen fertilizers production was suggested: first, from a mixture of coal and lime calcium carbide was obtained by heating the components; at high temperature, calcium carbide would react with nitrogen in air forming calcium cyanimide. This one was used for obtaining ammonia with the help of overheated steam; after that, ammonium sulphate was obtained from ammonia and sulphuric acid. Chemists from Norway obtained nitrogen fertilizers in another way: they made pass wet air through an electric arc, so that nitric acid would be retrieved (about 1% of the air volume). Further, using lime, the acid would be turned into calcium nitrate (Norwegian saltpetre). Nitrogen fertilizers obtained in such ways were too expensive, that is why neither of them was widely used. Nowadays, nitric acid and ammonia which are the basic raw materials for nitrogen fertilizers, are synthesized from atmospheric nitrogen or by recovering off-gases from oil, gas, and coal processing. Nitrogen fertilizers are divided into four types: nitrate, amidic, ammonia, and ammonia-nitrate. Nitrate Fertilizers Contain nitrogen in form of nitric acid salts (HNO3). Nitrate fertilizers are divided into two types: • Sodium saltpetre (NaNO3) is a by-product formed while obtaining nitric acid from ammonia; • Calcium nitrate (Ca(NO3)2) is a by-product in complex fertilizers production using nitric-acid phosphates processing method. It can also be produced by neutralizing nitric acid with lime. At present, production output of sodium saltpetre and calcium nitrate in Russia total 1% of nitrogen fertilizers at most. Nitrates are well-soluble in water, however, not absorbed by soil, and easily washed out by ground waters from the plough horizon. It is better to introduce nitrate fertilizers shortly before plants are sowed, or for top-dressing during the period of their intensive growth, when they need intensive nitrogen feeding. Sodium saltpetre is especially efficient for root crops top-dressing: sodium helps carbohydrates migration from leaves to roots, thus increasing crop yield and the content of sugary elements in the root crops. Nitrate fertilizers are well taken up by plants, but as they take up mainly NO3- anions, Са2+ and Na+ cations are left in soil and alkalize it. Regular use of nitrate fertilizers (especially calcium nitrate) in sour soddy-podzolic soils can significantly decrease their acidity and increase physical characteristics. Amidic Nitrogen Fertilizers They contain nitrogen in amidic form. Amides turn into ammonia and nitrates in soil. Amidic nitrogen fertilizers are divided into three types: • Carbamide, or urea (CO(NH2)2), is obtained from carbon dioxide and ammonia at 200 atm pressure and 185 to 200 °С temperature. Carbamide contains 46% nitrogen at least, and is the most concentrated one among all nitrogen fertilizers; • Calcium cyanamide (Ca(HCN2)2) is obtained from calcium carbide and nitrogen at 1100°С. It is highly dusty powder; to decrease its dusting, approx. 3% of petroleum oils are added to it; • Urea-formaldehyde fertilizers: UFF, ureaform, and carbamiform are fertilizers with extended release of nitrogen. They are either slow-soluble or their pellets are coated with ordinary sulphur or synthetic substances. UFFs contain up to 42% of nitrogen, of which no more than 10% are water-soluble, and this type of fertilizers can be introduced into soil beforehand even in high humidity areas. Ammonia Nitrogen Fertilizers These fertilizers contain nitrogen in ammonium form, which is excellently taken up by all plant species. Ammonia nitrogen fertilizers are well absorbed by soil, and are not washed out by spring floods or abundant rainfalls. This group of fertilizers includes: • Ammonium sulphate ((NH4)2 SО4), obtained by recovering ammonia by sulphuric acid from gas, which, in its turn, is formed during coal coking; or by neutralizing waste sulphuric acid, which can be found in enormous quantities at any chemical production; • Ammonium-sodium sulphate (NaSO4), which contains 18% nitrogen and 7% sodium, being an especially valuable nitrogen fertilizer for root crops top-dressing; • Liquid ammonia (NH3), which contains 82,2% nitrogen, however, this type of fertilizers requires increased safety measures for its storage, transportation, and crops treatment; • Ammonia water (NH4OH), which is ammonia water solution of two types: with 20.5% or 18% nitrogen content. Its disadvantageous feature is nitrogen volatile form; therefore, losses while introducing this type of fertilizers into soil are inevitable. Ammonia-Nitrate Fertilizers This is the most multi-purpose type of nitrogen fertilizers, which are in high demand thanks to high nitrogen content and easy utilization. Produced in white pellets. This group of fertilizers includes: • Ammonium saltpetre (ammonium nitrate) (NH4NO3), 34% nitrogen content, 50% of which are fluent nitrate form, and 50% are slow ammonia form. Used for almost all croppers. • CAN (NH4NO3 + CaCO3), contains 18… 22% nitrogen. Lime contained in it fully neutralizes ammonium nitrate, thus rendering this type of fertilizers more efficient in sour soils than ammonium saltpetre. Nitrogen fertilizers should be introduced into soil in such a way that plants might take them up prior to intensive growth. That is why, it is advisable to introduce fertilizers to winter crops in spring; otherwise, during autumn top dressing with nitrogen fertilizers, plants will start growing quickly, and their winter resistance will decrease together with crop yield. Moreover, nitrogen unused by plants is generally washed out by melt water in spring. Introducing fertilizers in spring usually requires meeting strict terms. If their timely introduction is impossible, it is advisable to work on principle: better earlier than later.