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The founder of the Soviet agrochemical school-Academician Dmitry Pryanishnikov, on the basis of the analysis of the history of agriculture in Western Europe, convincingly showed that the main condition determining the average value in different eras was the degree of supply of agricultural plants with nitrogen
The enormous importance of nitrogen fertilizers in increasing yields, due to the exceptional role of nitrogen in plant life.
Nitrogen is part of:
- Proteins-the basis of life;
- Nucleic acids-providing the transfer of hereditary properties of organisms;
- Chlorophyll-accumulating solar energy in the process of photosynthesis;
- Enzymes-biological catalysts of all biochemical processes;
- Phosphatides, vitamins, alkaloids and other organic compounds-playing an important role in metabolism.
The normal level of nitrogen nutrition stimulates protein synthesis of other organic compounds and ensures the intensity of growth processes. With a lack of nitrogen, there is a weak development of vegetative organs, which limits fruiting, leads to a decrease in yield and protein content in products.
The production of nitrogen fertilizers is based on the synthesis of ammonia. The source of nitrogen is the atmosphere, and hydrogen is natural gas or associated petroleum gases. Liquid ammonia, solid ammonium fertilizers and urea are produced from ammonia.
When ammonia is oxidized, nitric acid is obtained. It is used to produce saltpeter, as well as complex fertilizers in the nitric-acid processing of phosphates
The main forms of nitrogen fertilizers in our country are ammonium nitrate and urea. They account for almost two-thirds of gross production.
Ammonium nitrate or ammonium nitrate
Contains 34% nitrogen. It is obtained by neutralization of nitric acid with ammonia gas followed by evaporation and crystallization.
Crystalline ammonium nitrate is very hygroscopic when moistened, it spreads, and when dried, it compacts and solidifies, so ammonium nitrate is granulated with the addition of conditioning agents. The finished product is Packed in bitumen or polyethylene bags.
Ammonium nitrate is flammable and explosive. During its storage and transportation it is necessary to observe the rules of fire safety.
In ammonium nitrate, all nitrogen is water-soluble and well accessible to plants, with half being in nitrate and the other in ammonium form.
Nitrates have high mobility in soil solution, and ammonium nitrogen is metabolically absorbed by soil colloids.
With heavy rainfall and irrigation especially on light soils, nitrate nitrogen can be lost due to leaching.
The risk of ammonium nitrogen leaching is less and increases as it nitrifies through nitrites to nitrates.
Ammonium nitrate has an acidifying effect on the soil this is due to the weak physiological acidity of the fertilizer and the nitrification of its ammonium nitrogen.
The combination of fast-acting easily mobile nitrate and less mobile ammonium nitrogen determines the versatility of this fertilizer.
Ammonium nitrate is suitable for application under all crops and in all ways in the main fertilizer.
With a large amount of precipitation in the autumn-winter period, ammonium nitrate is better to make not in the autumn, but in the spring for pre-sowing treatment.
Ammonium nitrate when sowing or planting is used in small doses in combination with superphosphate, using combined seeders. It is successfully used for surface application when fertilizing winter crops, grasses, as well as in the quality of root fertilization of row crops.
On soils saturated with bases, the acidifying effect of ammonium nitrate is weakly expressed. On these soils, ammonium nitrate is one of the best forms of nitrogen fertilizers.
The most concentrated solid nitrogen fertilizer. It contains 46% nitrogen.
Urea is produced from ammonia and carbon dioxide at high pressure and temperature.
For agriculture, urea is produced in the form of granules coated with oily substances.
Granular urea is not caked during storage and is well dispersed.
Urea is well soluble in water, it is less hygroscopic than ammonium nitrate.
Under the influence of the enzyme urease, secreted by soil microorganisms, urea quickly within a few days turns into ammonium carbonate.
Ammonium carbonate compound is very fragile in the air quickly decomposes to form ammonium bicarbonate and ammonia gas. In order to prevent the loss of nitrogen during the surface application of urea, it should be immediately embedded in the soil.
At the stage of hydrolysis of ammonium carbonate, local alkalinization of the soil occurs, and the formed ammonium ions are metabolically absorbed.
With their subsequent nitrification, a shift of the reaction to the acid side is observed. According to the ability of soil acidification and agronomic efficiency, urea is equivalent to ammonium nitrate.
Urea is the best form of nitrogen fertilizers for foliar fertilizing of fruit and vegetable crops. It is also used for late feedings of wheat, in order to increase the protein content of the grain.
Another form of nitrogen fertilizer is ammonium sulfate
It is produced by trapping ammonia sulfuric acid from coke oven gases.
Ammonium sulfate has a weak hygroscopicity, does not freeze during storage and can be transported without packaging.
The disadvantage of this fertilizer is a low nitrogen content-21% and high physiological acidity.
It is related to the fact that from ammonium sulfate plants consume nitrogen in the form of ammonium faster and in larger quantities than sulfur in the form of sulfuric acid anion.
The greatest shift of the reaction occurs in low buffer soils not saturated with bases. On these soils, ammonium sulfate is inferior to other nitrogen fertilizers in efficiency, especially when cultivating crops sensitive to acidity.
Ammonium nitrogen fertilizer metabolically absorbed by soil colloids, slowly nitrified and not washed away, so ammonium sulfate is advisable to use in irrigated agriculture for rice and cotton, as well as in the subtropical zone for fertilizing tea and other crops
Pure nitrate forms of nitrogen fertilizers are used in limited quantities, they have a low nitrogen content, and calcium nitrate due to high hygroscopicity has poor physical and mechanical properties it complicates and storage, transportation and application.
From sodium and calcium nitrate, NO3-anions are absorbed by plants more intensively than sodium or calcium cations.
These fertilizers are physiologically alkaline, especially effective on acidic soils.
Nitrate fertilizers are easy-moving and fast-acting sources of nitrogen, it is advisable to use them for application in rows and for fertilizing.
In the main fertilizer nitrate should be made under pre-sowing treatment because of the danger of leaching nitrates.
Especially sodium nitrate has a positive effect on sugar beet and other root crops, responsive to the introduction of sodium.
Along with solid nitrogen fertilizers in agriculture, liquid - Anhydrous ammonia and aqueous ammonia are used
Anhydrous ammonia is the most concentrated ballast-free fertilizer.
It is produced by liquefying ammonia gas under pressure.
At all stages of storage, transportation and application anhydrous ammonia is contained in containers designed for high pressure.
Anhydrous ammonia colorless liquid, it is one and seven tenths of a time lighter than air, boiling point plus 34 degrees Celsius. In the air, anhydrous ammonia evaporates quickly. The transition to the gaseous state is accompanied by cooling.
In high concentrations, ammonia has a strong toxic effect on the human body. Only specially trained personnel are allowed to work with anhydrous ammonia and it is necessary to strictly observe the rules of safety and labor protection.
Transportation of anhydrous ammonia from the manufacturer to the rail warehouses is carried out in special railway tanks. At the warehouses located in the depths of the served area, fertilizer is transported in tanker trucks.
The introduction of anhydrous ammonia is produced with the help of a special unit that allows to evenly distribute fertilizers in the soil with simultaneous sealing to the desired depth.
On heavy soils, anhydrous ammonia is sealed to a depth of 12 -14 cm, on light slightly deeper. This avoids losses due to volatilization of ammonia in the soil.
Anhydrous ammonia is converted from liquid to gas, which is absorbed by colloids and absorbed by moisture to form ammonium hydroxide. This causes a temporary local alkalinization of the soil, which then changes to weak acidification as ammonium nitrifies.
Ammonium nitrogen is metabolically absorbed and chemically bound by organic and humic acids.
With a high concentration of ammonia in the application zone, the vital activity of the soil microflora, including nitrifying bacteria, is temporarily suppressed, so at first the nitrogen of the fertilizer is localized near the application site, mainly in the ammonium form.
Anhydrous ammonia can be introduced in autumn under the main soil treatment without fear of nitrogen losses due to leaching and denitrification. When fertilizing row crops, anhydrous ammonia is introduced into the middle of the row spacing to avoid oppression of plants at high concentrations of ammonia.
Unlike anhydrous ammonia, the use of ammonia water is easier and safer.
It can be stored and transported in conventional pressurized tanks designed for low pressure.
Aqueous ammonia is produced in two varieties.
Like anhydrous ammonia, ammonia water is introduced into the soil with simultaneous sealing to the required depth. Experiments with different crops show that anhydrous ammonia and ammonia water are not inferior in efficiency to solid forms of nitrogen fertilizers, and on light soils under irrigation conditions and in humid areas they are superior.
It should also be noted that the cost per unit of nitrogen in the production of liquid fertilizers is much lower than solid.
Application of liquid fertilizers allows to carry out full mechanization of all processes connected with transportation, filling and introduction. This is one of the main advantages of liquid fertilizers.
Plants use only 50-60 % of the nitrogen introduced into the soil, and 20-30% is lost mainly in the form of molecular nitrogen and its gaseous oxides on light soils, in regions with a large amount of precipitation.
In irrigated agriculture, there are also significant nitrogen losses due to nitrate leaching.
Can these losses be reduced?
Currently, experimental batches of slow-acting nitrogen fertilizers based on slightly soluble compounds, primarily urea condensation products with aliphatic aldehydes, are already being produced and tested.
Granular nitrogen fertilizer coated with polymer films is also being studied.
Nitrification inhibitors, chemical compounds that are able to selectively suppress nitrification until intensive nitrogen consumption by plants, are introduced into the urea composition of solid and liquid ammonium fertilizers.
Ending the story about nitrogen, it is appropriate to cite the wonderful words from the book of Dmitry Pryanishnikov:
"Not counting water, nitrogen is the most powerful engine in the processes of development and creativity of nature. To catch it, to master it, that is the task, to preserve it, that is the key to the economy, to subdue its source, that is the secret of welfare"