Nitrogen – as an essential element for plant nutrition
Nitrogen is an integral part of vegetable proteins, chlorophyll, DNA (genetic code), enzymes, and many other components necessary for plant growth. Plants consume nitrogen in the form of nitrates (NO3-) and ammonium (NH4+) ions. The dominant form is nitrate. Ammonia is better at the stage of early plant growth, however, throughout the vegetative period, the need for nitrogen increases; plants absorb most of nitrogen in the form of nitrate.
The amount of nitrogen fertilizers required for a plant depends on the ability of the soil. The dynamic region of available sources of nitrogen includes:
1) organic nitrogen sources, such as manure, sewage and compost,
2) nitrogen, which is fixed by Rizobium bacteria from plant residues,
3) nitrogen fixed by the microbes
4) nitrogen fertilizers,
5) nitrogen is bound by the soil.
All these sources of nitrogen over time mineralize into nitrate.
Since nitrate is the predominant form of nitrogen used by plants, the method for determining the residual nitrate in the root zone before planting the intended culture (in addition to legumes) is the necessary method for evaluating the required amount of nitrogen fertilizer. The residual nitrate test is the main method for determining the available nitrate in the soils, especially where there is minimal leaching of nitrate. The exception is the soil where leaching and denitrification are taking place. Nitrate dissolves in water, thus becoming mobile. Where rainfall is high enough, nitrogen is washed away deeper than the root zone, becoming inaccessible to the plant. Consequently, the test for residual nitrogen is not reliable in poorly drained soils that retain moisture over a long period of time and which can be lost due to denitrification (see below).
The amount of applied nitrogen fertilizers depends on many factors. To begin with, you need to know the characteristics of the planned harvest, such as: how much nitrogen is produced by the culture, as well as its potential yield. Mineralization of soil organic nitrogen is an important factor. The high level of mineralization will reduce the rate of introduction of nitrogen fertilizers. Harvest legumes increase the degree of mineralization. When calculating the doses of nitrogen fertilizer, the residual nitrate of the soil is available, which is available for any given product, which reduces the amount of nitrogen fertilizer.
Sources of Nitrogen Fertilizer
Farmers are very interested in a stable source of nitrogen fertilizers that will be used for their crop. The biggest concern is evaporation, immobilization and availability of nitrogen fertilizers. All sources of nitrogen work efficiently when properly applied.
There are many sources of nitrogen fertilizers that have been used for many years. Nitrogen in most cases is used as a mixture of ammonium nitrate and urea (28-0-0 and 32-0-0), urea (46-0-0), ammonium nitrate (34-0-0), anhydrous ammonia (82- 0-0) and ammonium sulfate (21-0-0-24).
The choice of a source of nitrogen fertilizers – this is the main solution for the land user. There are advantages and disadvantages in each of them. Possible situations where one source is better than the other.
The main source of nitrogen fertilizers is anhydrous ammonia (NH3). Ammonia is obtained by the interaction of air nitrogen (78% of the atmosphere is nitrogen, N2) with natural gas at high temperature and pressure. With the increase in energy prices, the price of nitrogen fertilizers increases accordingly. Ammonia is converted to a liquid state at temperatures below -330C. Thus, ammonia is stored under pressure to be in liquid form. Ammonia, missed over platinum catalyst, passes into nitric acid (HNO3). Nitric acid, in admixture with ammonia, gives ammonium nitrate NH4NO3 (34-0-0). Urea (NH2) 2CO (46-0-0) is obtained by the interaction of an excess of ammonia with carbon dioxide (CO2). The interaction of ammonia with sulfuric acid gives ammonium sulfate. Interaction of ammonia with phosphoric acid gives ammonium phosphate.
For many years, anhydrous ammonia (NH3) was the main source of nitrogen fertilizers in the classical soil treatment. Anhydrous ammonia should be introduced into the ground deep enough to avoid the loss of gaseous ammonia. The entry can be done during sowing or at any other time. This method of introduction is quite rigid in relation to the microflora and microfauna of the soil. Today, No-Till farmers use other sources of nitrogen fertilizers, a milder effect. Such an NH3 is aggressive enough for the soil, which in turn bother farmers.
Evaporation of nitrogen from urea
Urea (NH2) 2CO (46-0-0) – dry nitrogen fertilizer, which is commonly used by farmers. Urea, introduced into the soil or on plant residues, reacts with water, and with the enzyme urease quickly turns into ammonium. This is the so-called hydrolysis of urea. Ammonium cation (NH4 +) is converted into ammonia (NH3). Since ammonia is a gas, it evaporates into the atmosphere. If ammonia admires particles of the soil, then it is contained in it and does not evaporate. The amount of precipitation or irrigation in the amount of 850 mm is sufficient to move urea into the soil. Since the reaction of the conversion of urea into ammonium is an enzyme reaction, the conversion rate increases with increasing temperature. It is best to use urea during cold periods, with high rainfall. Excess urea remains on the surface of the earth, allowing the evaporation of ammonia, especially under wet, warm conditions. It is better to use urea on dry residues than on wet ones, as the activity of urease is less, in the absence of water.
Dry urea can be added in a tape-like way. The tape should be 38 cm wide for small grains, or the width of the line. Urea can also be used as a starting fertilizer 5-8 cm from the side of the seed. The nitrogen rate could amount to 70-100 kg / ha.
Farmers use one of many ways to make nitrogen. For example, mixing solutions of urea and ammonium nitrate together produces liquid fertilizers containing about half the urea and half the ammonium nitrate. Such solutions are good sources of nitrogen for crops. In vsebezhanieuletuchivaniya NH3, such fertilizers can be injected into the ground. The depth of the introduction is not critical, however, it should be deep enough; With such a task a well-trained rotary cultivator.
The solution should be administered to reduce the activity of the urease. Strength should pass on 30-38 cm. Repeated introduction of this mixture, also works effectively. However, it is necessary to adhere to the rules of administration, in order to avoid loss of nitrogen by evaporation.
Other nitrogen fertilizers do not have NH3 loss problems. Evaporation of NH3 occurs because urease decomposes urea to NH3 and CO2. NH3 is dissolved in water to form ammonium (NH4 +). CO2 reduces the pH of the solution. Ammonium, which is part of nitrate, sulfate and ammonium phosphate, does not evaporate. The pH of these ammonium salts solutions is low, since nitric acid, sulfuric acid and phosphoric acid are strong acids, and NH4OH is a weak base. Strong acidity of salts prevents loss of NH3. CO2 is a weaker acid than NH3 is a weak base; Thus, acidity increases with increasing CO2.
Estimated usage time
The optimum time for applying nitrogen fertilizers depends on:
1) cultivated culture,
2) characteristics of nitrogen consumption,
3) the texture of the soil,
4) root zone,
6) the amount of nitrogen required.
Nitrogen management is most important for crops with a shallow root system grown on sandy soils than crops with a deep root system on loamy soils. Maximum nitrogen consumption occurs during a period of rapid growth. Wheat, for example, has the most rapid growth and, accordingly, the maximum nitrogen intake in the phase of the output of the tube. Most of all or all of the nitrogen fertilizer needs to be introduced early enough so that microorganisms have time to mineralize nitrogen fertilizers in nitrate, so that nitrogen becomes available to the plant. Reduced soil temperatures slow down the mineralization processes, so nitrogen fertilizers need to be introduced at least 3 weeks before sowing.
Fastest intake of nitrogen in corn occurs in the phase from 8-sheet to discharge vole. Most of the nitrogen should be introduced 2 weeks before the maximum consumption phase, provided that this nitrogen is available in the form of a plant – in the form of nitrate, or 2 weeks before the nitrogen itself is caught. In the case of irrigation, where practicing the introduction of nitrogen through water, it is necessary to make an introduction in 2 weeks before the period of active nitrogen consumption.
Nitrogen losses in washing and denitrification
Loss of nitrogen from the soil can take place at:
1) washing (leaching),
3) Evaporation of NH3.
The NH3 loss issue is discussed above. Leaching is the process of washing the soluble nitrate with water. Soils with a high water holding ability can accumulate a significant amount of water along with nitrate.
For soils with a light texture that have a high water holding capacity, nitric fertilizer can be introduced directly before sowing or as a fertilizer during the most active growth. The introduction of nitrogen should be carried out in time to avoid the washout in more than the root zone depth. In areas where the number of rains is small during the vegetation period, the above problem is not relevant. But in areas with high rainfall, the time of feeding is critical.
For soils with a light texture, with poor aeration due to high humidity, it is very important to add most of the nitrogen fertilizer after the soil dries. If nitrogen is introduced before sowing – the main nitrogen potential is lost due to denitrification.
For sandy soils, part of the nitrogen may be added with a herbicide or starting fertilizer. The part needs to be introduced before the phase of maximum nitrogen intake (as discussed above).
The amount of nitrogen washed out depends on the properties of the soil and the ability to hold water. Improving the structure of the earth, undoubtedly reduces the amount of washed nitrates. When macro-pores are developed, water can enter the ground by gravity, moving through the pores vertically downward, and spreading horizontally. The washout takes place on the capillaries. Capillary motion of water tolerates soluble nitrate.
The standard estimate of washed nitrate can be calculated using the following formula:
d = 100a / Pv, where d is the wash depth, Pv is the capacity (water absorption capacity), and – the amount of washing water. For example, if the water-absorbing ability of the loam is 46% and 2.5 cm of water moves along the root zone, then the nitrate moves to a depth of 5.5 cm. In sandy soils with a half-watering capacity, nitrate is washed to a depth of 2 times more – 11 cm.
Denitrification is a microbial process by which anaerobic soil bacteria (bacteria capable of living without air oxygen) utilize (recycle) oxygen nitrate (NO3) to maintain their living processes. The denitrification process is the transformation of the finished stock of nitrate into various forms of nitrogen, which can be lost in the atmosphere. The denitrification process can be represented by the following scheme: 2NO3 → 2NO2 → 2NO → N2O → N2
Different soil enzymes are accompanied by each step indicated. Soil bacteria produce enzymes. Denitrification occurs in the absence of oxygen and a sufficient amount of CO2 and NO3-. The gaseous forms of nitrogen are NO, N2O and N2.
In order to reduce potential nitrogen losses due to denitrification, it is necessary to synchronize the time of nitrogen input with the phase of maximum nitrogen consumption. If nitrogen fertilizers have to be introduced into the phase of maximum nitrogen consumption, you can use nitrification retardant, to restore nitrogen from fertilizer to nitrate.
Consumption and removal of nitrogen by crops
In the process of vegetation, nutrients are spent on the formation of leaves, grains, stalks, etc. The amount of nitrogen fertilizer that a plant needs depends on the yield and amount of nitrogen that is applied to the crop.
Table 1: Nitrogen Extraction with Crop em>
|Vintage||Unit of measurement per hectare||Take nitrogen (pounds)|
|Corn||Grain (kg/ha)||0.6-0.9 td>|
|td>||Straw (kg/ha) td>||0.3-0.5|
|Wheat||Grain (kg/ha)||0.85-1.2 td>|
The use of nitrogen is used to show how much it is brought out of the soil by culture. The requirement for nitrogen is the amount of nitrogen consumed by the plant to grow leaves, stems, roots and grains. Sludge residues contain residual nitrogen. This `organic nitrogen` will be released `after some time. However, for No-Till, you need to add a few nitrogen fertilizers for faster nitrogen processing in an affordable form. Only 3-4 years later, nitrogen from cultivating residues after rotting becomes available. In consequence of this fact will be taken into account when decreasing the dose of nitrogen fertilizers. Leguminous crops use in the majority and `own` nitrogen, which may be available for trace not legume crops.
Table 2. Nitrogen Credits
|The last legume harvest||Loans for nitrogen kg/ha|
That is, the value of the loan can be deducted from the total number of required nitrogen fertilizers.
In this paper, the function of nitrogen, as fertilizer and as a nutrient for plants, is considered. Nitrogen is needed to grow a healthy and high-quality crop. The amount of nitrogen that needs to be contributed depends on many factors such as: residual nitrate in the soil, past / true harvests of legumes, nitrogen consumption by culture, yield potential, immobilization of slurry residues with nitrogen fertilizers, degree of mineralization of nitrate, organic matter of soil, price of grain , protein level, protein level and other indicators of quality of the crop.
The effectiveness of nitrogen fertilizer application may be higher when the nitrogen source is properly selected. There are many effective ways to apply nitrogen fertilizers. Based on the time, equipment and other components, the best method of making – that’s what we can do at all. Typically, nitrogen, injected into the ground, is the most effective method than other methods of making. However, all other input methods work well. The article presents several indicators for nitrogen losses during washing, denitrification and weathering.
The use of nitrogen fertilizers increases, while when using No-Till, the following is observed: if the residue remains on the surface of the earth, the level of organic matter may decrease initially, although in the future it will necessarily increase. This is due to the release of nitrogen. Leaving on the surface of the earth the crop residues, we thus retain moisture for the future harvest. Use this additional capacity or not – depends on you only.