Nitrogen (N)


Nitrogen is one of the primary plant nutrients that plays a major role in achieving the maximum economic yields from your production acres. Management of Nitrogen, and other essential nutrients, is part of a balanced fertility program. This can lead to increased efficiency and profitability for you.


Plants absorb Nitrogen in some of the greatest amounts of any essential nutrient. In order for a crop to achieve its maximum yield potential, Nitrogen and other macronutrients are needed in large quantities and must be in balance with other nutrients.


Since Nitrogen is easily lost, it is important to include a source of humates with every application of Nitrogen. Humates act as a chelator or "claw" to hold onto Nitrogen, as well as other nutrients in your soil, enabling a slow release of Nitrogen, making your nitrogen application more effective and more efficient.


Most farmers apply Nitrogen once, or maybe twice, in the growing season. The first application is often applied before seeds are planted. Even after germination, tiny seedlings cannot utilize even a fraction of what is applied so most of the Nitrogen is lost due to oxidation and other loss factors.


What happens to Nitrogen in your soil?


In order to manage your soil's Nitrogen, you must understand what happens to Nitrogen in the soil. About 98% of the Nitrogen in the soil is tied up in the organic matter and unavailable to plants. Only 2 – 3% is in the inorganic form of nitrate (NO3–) and the ammonium (NH4+) form that are available to plants. When levels of temperature, moisture, and oxygen are high enough, the organic matter that is holding the vast majority of Nitrogen can be broken down by microorganisms and released as inorganic Nitrogen into the soil. This process is called mineralization. An opposite process also occurs where microorganisms feed on inorganic Nitrogen. This process is called immobilization.


In healthy soil, both of these processes are taking place, simultaneously. When large amounts of crop residue, with high carbon and low Nitrogen content, are incorporated into the soil, immobilization can take place at such a rapid rate that levels of available Nitrogen become depleted. Later, the microorganisms will breakdown these residues and go through the process of mineralization. When this happens, the Nitrogen is, again, released into the soil and becomes available for plant growth.


During the process of mineralization, most of the organic matter is first converted to ammonium (NH4+). The process that breaks down the ammonium (NH4+) to nitrate (NO3–) by nitrifying bacteria is called nitrification. This process is very important because nitrate is readily available for use by crops and microorganisms. Nitrates are very mobile in the soil.


How is Nitrogen Lost?


Nitrogen is lost from the soil in several ways: plant uptake, immobilization by microorganisms, nitrates that move out with drainage water, and the loss of nitrates by denitrification. Denitrification occurs in flooded or saturated soils during periods of warm temperatures. In this state of depleted oxygen, microorganisms take oxygen from the nitrate (NO3–). Then, the Nitrogen escapes into the air as gas.


Denitrification is particularly evident in wet spots in corn fields where the plants are yellow and stunted. Applied Nitrogen can also be lost in several ways. Loss occurs when urea, applied to the surface, converts rapidly to NH3 and escapes into the air as ammonia gas. This can occur when adequate moisture, temperature, and the enzyme urease is present. To avoid this loss, it is wise to either incorporate the urea, or irrigate immediately. A urease inhibitor can also be utilized to reduce loss. Anhydrous ammonia can also be lost rapidly if the injection slot is not sealed.


Forms of Nitrogen Taken Up By Plants


Most plants absorb a majority of their Nitrogen in the form of nitrate (NO3–) and to a lesser extent the ammonium (NH4+) form. Plant growth seems to improve when a combination of ammonium and nitrate Nitrogen is taken up by the plant. Once inside the plant, the nitrate is transformed into NH4-N through energy provided by photosynthesis.


In alfalfa and soybeans, most of the Nitrogen is supplied by the Nitrogen fixation process performed by rhizobia and other symbiotic bacteria. This Nitrogen is fixed in the nodules on the roots of the plants. Presence of nodules does not mean that Nitrogen will be fixed. Healthy nodules are usually located on the primary root and are larger in size, elongated, form clusters, and have pink-to-red centers. The red color represents the presence of leghemoglobin, which means that the rhizobia are fixing Nitrogen in the nodules.


How Nitrogen is Used by Plants


Inside the plant, Nitrogen converts to amino acids, the building blocks for proteins. These amino acids are then used in forming protoplasm, which is used in cell division. These amino acids are also utilized in producing necessary enzymes and structural parts of the plant and can become part of the stored proteins in grain.


Nitrogen serves as the source for the dark green color in the leaves of various crops. This is a result of a high concentration of chlorophyl. Nitrogen, combined with high concentrations of chlorophyl, utilizes the sunlight as an energy source to carry out essential plant functions including nutrient uptake.


Chlorophyl is associated with the production of simple sugars from carbon, hydrogen, and oxygen. These sugars, along with their conversion products, play a role in stimulating plant growth and development along with higher protein content in the grain.


Nitrogen deficiency shows up in the yellowing or chlorosis of the plant leaves. The yellowing will start in the oldest leaves, and then will proceed to develop on younger leaves, if the deficiency continues. Plants will typically be shorter or stunted and grow slower than plants with sufficient Nitrogen. Nitrogen stress also reduces the amount of protein in the seed and plant. Tillering can also be reduced in small grains.


A Nitrogen deficiency can also affect the stand of crops as grain fill occurs. If a plant is deficient in Nitrogen, it will draw Nitrogen out of the leaves and stalk for grain fill. This will weaken the stalk or stem causing stand problems.


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