Nitrogen Within Plants
Nitrogen is a significant component of several important plant and animal metabolic functions making it one of the basic building blocks for all living things. It plays a vital role in protein synthesis, photosynthesis, DNA, and many other important life functions. Nitrogen is found in the backbone of all amino acids which are grouped together to form protein. Without nitrogen, photosynthesis, a process by which plants convert solar energy into chemical energy, would not exist.
Organic and Inorganic Forms
Nitrogen within the soil exists in two forms: organic and inorganic.
Organic nitrogen consist of amino acids and plant and animal residues. Generally, nitrogen in the organic form is not readily available to plants and must to converted by the microorganisms to ammonium and nitrate, a process called mineralization. However, research has shown that plants can uptake organic nitrogen compounds that are present in the soil but the amount of organic nitrogen contributing to the plant’s nutrition is unknown (Hodge et al., 2000; Näsholm et al., 2009).
Inorganic nitrogen consist of ammonium (NH4+) and nitrate (NO3–) and are readily available to the plant. With the ammonium ion carrying a positive charge, it binds tightly to the cation exchange complex within the soil making it virtually non-leachable. The negatively charged nitrate ion cannot bind to soil solids making it leachable and only existing in dissolved soil water (Nitrogen, 2018a). However, NH4+ is quickly converted to NO3– (nitrification) via soil bacteria, and under optimum soil conditions results in a minimal loss between nitrogen forms.
Natural sources of nitrogen that can be incorporated into the soil include atmospheric nitrogen, bacterial fixation, legume fixation, and manure.
Soil microbes can fix nitrogen that is supplied to the soil via rainfall or gas. Nitrogen (2018a) suggests that the heat generated by lightning during a thunderstorm produces NO3– from the combination of nitrogen and oxygen gases and is then washed out by precipitation. The quantity of added atmospheric nitrogen is dependent on thunderstorm activity and can vary from 5-10 lbs. N/acre up to 20 lbs. N/acre annually (Nitrogen, 2018a; Nitrogen, 2018b).
Nitrogen-fixing bacteria, such as Azotobacter spp., play a vital role in the reduction of atmospheric nitrogen into ammonia. This particular genus of bacteria is capable of fixing approximately 3.67 lbs. N/acre/year (Kizilkaya, 2009). In order to fixate nitrogen from the atmosphere, these bacteria need a significant amount of organic matter (i.e. carbon) to be effective. According to Dobereiner (1969), bacteria fix between 12 and 30 mg nitrogen per gram of carbon source resulting in microbes requiring 33 to 83 lbs. of carbon per acre to fixate 1 lb. of nitrogen, in nitrogen free soil and under optimum conditions. However, it is highly unlikely that soil will ever be void of nitrogen and yearly residual plant material provides recycled organic matter back into the soil.
Legume plant species have a symbiotic relationship with bacteria such as Rhizobium that also convert atmospheric nitrogen gas. Rhizobium infect the roots of the legume plant and form nodule growths where fixation occurs. Once the bacteria meet their nitrogen requirement, any extra nitrogen that was fixed is released for the plant to utilize. Good et al., (2004) suggest that biological fixation of nitrogen by legumes accounts for 44 million tons of soil nitrogen annually. As a result, legumes with increased nodules do not frequently respond to additional nitrogen (Nitrogen, 2018b). Once the legume is harvested, the remaining nodules provide nitrogen for succeeding crops. Data has shown that warm season crops following a good stand (2-4 plants/ft2) of alfalfa, sweet clover, red clover, soybeans can receive a nitrogen credit up to 80, 60, 40, and 40 lbs. N/acre, respectively (Nitrogen, 2018aksu).
Lastly, farmers have long utilized manure as a source of fertilizer. However, the nutritive value of manure is dependent on animal species, nutrient composition of feed fed to animals, method of manure storage, and application.
Plant Nitrogen Uptake
Approximately 93-100 million tons of nitrogenous fertilizers are applied annually to soil worldwide and predicted to increase to 265 million tons by the year 2050 (Tilman et al., 1999). People’s et al., (1995) estimated that 50-70% of this applied nitrogen is lost in the plant-soil system, however the plant’s ability to capture nitrogen is dependent on soil type, environment, and species (Masclaux-Daubresse et al., 2010). It has been generalized that plants residing in low pH soils tend to take up more ammonium ions compared to nitrate in plants residing in higher pH soils (Maathuis, 2009). However, as previously stated, nitrification of ammonium occurs rapidly resulting in the majority of nitrogen uptake occurring as nitrate.
Nitrogen uptake occurs at the root level. With nitrate being negatively charged and leachable, it moves freely toward plant roots when water is absorbed. By contrast, the positively charged ammonium ion can interact strongly with soil minerals and be 50-500-fold less mobile then nitrate (Forde and Clarkson, 1999). The plant root contains two transporter systems, low-affinity transport system (LATS) and high-affinity transport system (HATS), that coexist to uptake nitrate and ammonium from the soil and distributes nitrogen throughout the plant. When the soil nitrogen concentration is high, the plant relies on LATS for nitrogen uptake and HATS when the soil nitrogen concentration is low (Masclaux-Daubresse et al., 2010). An extensive root system is essential for unrestricted uptake of nitrogen. If roots become restricted because of soil type or compaction, symptoms of nitrogen deficiency can occur regardless of nitrogen quantity present in the soil.
Inorganic Fertilizer Sources
There are four types of major nitrogen fertilizer materials today which include urea, urea-ammonium nitrate solution (UAN), anhydrous ammonia, and ammonia nitrate. The choice of fertilizer source to utilize is dependent on the set up of each operation. While leaching and denitrification cannot be directly controlled, reducing the potential of their occurrence can be controlled through appropriate timing of fertilizer application. Uptake of nitrogen in corn is minimal until approximately 35 days after emergence when a spike in corn growth occurs. Research suggests that 50-90% of required nitrogen to be applied as a side-dress when corn is approximately 10-20 inches tall (Beegle and Durst, 2017).
Urea, a byproduct of ammonia manufacturing, is produced by the addition of two molecules of ammonia (NH3) and carbon dioxide (CO2). Because of it’s chemical makeup, urea contains 46% nitrogen, the highest analysis of a dry nitrogen source providing efficient shipping and storage (Nitrogen, 2018a). Urea is water soluble allowing it to move easily within soil until it is hydrolyzed into ammonium by the urease enzyme. This process can take 2-10 days depending on factors such as soil temperature, moisture, and urease concentration (Nitrogen, 2018a). As previously described, ammonium is quickly converted to nitrate within the soil. Application of urea is vitally important as improper application can result in the release of 30% or more of ammonia (Beegle and Durst, 2017). If applied to the surface, incorporation via rain or cultivation must occur within 24-48 hours is necessary to reduce the volatilization potential.
Urea ammonium nitrate solutions are mixtures of urea, ammonium nitrate, and water. The combination of the two nitrogen sources results in a more soluble product than either of the two alone. There are two common grades of UAN available are 28-0-0 and 32-0-0 containing 28% and 32% nitrogen, respectively. Within UAN solution, approximately 50% of the nitrogen comes from urea and the remaining 50% from ammonium nitrate. This results in 75% ammonium forming nitrogen and 25% nitrate nitrogen being applied to the soil (Beegle and Durst, 2017).
Anhydrous ammonia (NH3), containing 82% nitrogen, is an efficient and widely utilized source of nitrogen fertilizer. Ammonia is a gas at atmospheric pressure, must be handled with equipment designed for NH3, and must be injected into the soil at a recommended depth of 7 inches for row crops prior to planting (Nitrogen, 2018a). Once in the soil, NH3 reacts with water to produce hydroxide and ammonium ions which can be absorbed or converted to nitrate. However, nitrification ceases if soil temperatures are below 50°F resulting in ammonia bound to soil particles until the soil temperature increases.
Ammonia nitrate (NH4NO3) typically contains 34% nitrogen, half of the total nitrogen coming from ammonia and half nitrate. It is completely soluble making it an excellent nitrogen source. However, manufacturing of ammonia nitrate is declining in the US due to environmental considerations (Nitrogen, 2018a).
Here at High Brix Agronomy, we offer molasses-based solutions for agronomic applications with strategies designed to reduce nitrogen inputs for the best economic and environmental results. The addition of molasses-based products to crop ground will provide nutrition for soil microbes and stimulate activity, stabilize nitrogen within solution to reduce leaching and volatilization, and serve as a chelating agent and increase the mobility and ultimately the availability of nutrients to plants.
N-Forcer is a cane molasses blend that provides energy to feed the soil microbes. Providing food for the microorganisms to utilize results in proliferation and growth of the entire microbial population. The increased growth of the nitrogen fixing bacteria specifically is critically important in converting atmospheric nitrogen into nitrogen that is readily available for the plant. Having an increase in available nitrogen results in happier, healthier plants. When N-Forcer is combined with an inorganic nitrogen fertilizer source (UAN), a synergistic effect occurs. The N-Forcer acts to stabilize the available nitrogen within the soil resulting in a reduction of denitrification of the ammonia nitrogen and soil leaching of the nitrate nitrogen. This ensures that the plant has greatest opportunity at absorbing the available nitrogen. The current recommendation for N-Forcer is 0.5 gallon/acre with row starter, and 1-2 gallons/acre strip, drip, knife, or foliar.
UNS is a molasses-based blend developed to provide an alternative to UAN. It provides additional energy to the soil for increased microbial growth as well as an available nitrogen source for the plants. The combination of the molasses and nitrogen results in a more stabilized product resulting in less soil leaching than traditional UAN. UNS also aids in the stabilization of soil pH by reducing nitrification, conversion of NH4+ to NO3–, which results in less hydrogen in the soil. This product is safe to be mixed with most post-emergent crop chemicals making it a convenient product to add into your regimen.
Stalker NT is a molasses, enzyme product designed to aid in the degradation of crop stubble, specifically corn residue. It is specifically designed to be sprayed onto the residue at harvest to help decompose debris. If residue is not removed from the field via grazing livestock or physical removal by baling, Stalk NT will help reduce over-wintering of disease and insects that reside in residual corn stalks. Degradation of crop residue is magnified when debris is mulched or mildly tilled as it increases the interaction between enzymes and available organic matter in the residue and involves the already soil existing microorganism into the degradation process. This will create a more active organic soil structure that is beneficial to next years crop. Degradation of crop stubble by Stalker NT can also be enhanced with the addition of humates and additional nitrogen. Current recommendations for Stalker NT is to spray at a rate of 1 gallon/acre.
Sweet Green and Sweet Green Plus are our lawn and turf care products. Similarly to the products available for crops, Sweet Green provides readily available energy, i.e. sugar, but to your lawn. This helps the plant to build energy and protein reserves for times of stress from drought, disease, and insects. By providing additional energy for the soil, the microbes are able to utilize soil nitrogen more efficiently resulting in an increase in nitrogen uptake. An increase in nitrogen uptake by the plant results in more nitrogen to incorporate into chlorophyll producing a greener stand of grass. Sweet Green Plus provides the same sugar benefits as Sweet Green with the addition of 18% nitrogen. For maximum results, apply every 21 days.
To conclude, nitrogen is vitally important to the livelihood and success of your crop. Plants uptake nitrogen in the form of ammonium and nitrate which can come from an inorganic fertilizer source, atmospheric nitrogen, or fixation/mineralization from soil microorganisms. For microbes to produce nitrogen they consume a significant amount of carbon. With the utilization of High Brix Agronomy products, we are supplying additional carbon, via molasses, to the soil microbes resulting in an improved soil microbial population and increased crop yield.
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