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The amount of applied nitrogen that is subsequently recovered in crop plants is usually less than 50%. This lack of recovery is mainly due to nitrogen losses by ammonia volatilization, nitrate leaching, surface runoff, and denitrification.
Nitrogen use efficiency (NUE) can be improved through soil and crop management practices. The objective is to get more nitrogen into the crop, less into the environment.
Various products are available in the market place that may potentially reduce nitrogen losses and improve NUE. Improved NUE helps improve crop yields, reduce production costs, and maintain environmental quality.
These products provide a specific benefit for a specific amount of time. They are beneficial if the product remains effective during the duration of loss conditions. If loss conditions do not occur, they may only be an expense to the user. Producers often use these products to push fertilizer application timing and spread workloads rather than to improve NUE.
This Crop File has information about additives and products that may enhance fertilizer nitrogen efficiency.
¶ A. Inhibitors and Stabilizers
- Control nitrogen transformations.
- Slow conversion from stable form to susceptible form.
- Help retain nitrogen in root zone for improved crop uptake.
- Loss protection from days to few weeks.
- Urease inhibitors
- Reduce urease enzyme activity.
- Urease is catalyst for hydrolysis reaction that splits urea molecule (CO(NH2)2) into ammonia (NH3) and carbon dioxide (CO2) molecules.
- Slow conversion of urea to ammonia.
- Reduces ammonia volatilization rate from surface-applied dry urea or urea-ammonium nitrate solutions (UAN).
- Sometimes used with manure.
- Nitrification inhibitors
- Prevent conversion of ammonium (NH4+) to nitrite (NO2-) and nitrate (NO3-).
- Suppresses Nitrosomonas bacteria populations.
- Nitrosomonas metabolize ammonium to nitrite.
- Nitrobacter metabolize nitrite to nitrate.
- Thiosulfates
- Are fertilizer products.
- May inhibit both nitrification and urease activity.
- Co-polymers
- Claim to inhibit both nitrification and urease activity.
- May “bind” compounds involved in conversion processes.
- Reduce losses by physically protecting soluble nitrogen forms from exposure to loss mechanisms.
- Slow-release fertilizers
- Uncoated, slowly available compounds.
- Synthetic organic compounds.
- Controlled release fertilizers
- Coated water-soluble fertilizers.
- N-(n-butyl) thiophosphoric acid triamide, NBPT (Agrotain™, many others)
- Is urea-like compound.
- Proven beneficial by research.
- Off-patent product, many retail sources.
- NBPT mechanism is to lock onto urease enzyme binding sites.
- Competes with nickel ions and carbamate group for active sites on urease enzyme.
- Prevents enzyme from reacting with urease.
- Acts like bent key stuck in lock, preventing lock from opening.
- NBPT itself has little or no activity.
- Must be converted to NBPTO.
- N-(n-butyl) phosphorictriamide, oxygen analog of NBPT.
- Applied to surface of dry urea or mixed with UAN solution.
- Slows ammonia loss for 7 to 10 days.
- Occasionally up to 14 days.
- NBPT degrades more rapidly in acidic soilsShorter time of inhibiting activity.
- Most beneficial with high-loss potential conditions:
- Broadcast-applied fertilizer to be left on surface for more than 2 or 3 day.
- High rates of stubble or surface residue.
- Alkaline or calcareous soils.
- Little or no benefit if conditions allow time to absorb ammonia.
- Incorporating tillage occurs within two days.
- At least 0.50 inches of rain or irrigation occurs within two days.
- Applied to bare soil with pH of 6.0 to 6.5.
- Active ingredient in proprietary product (ANVOL™), recently introduced.
- Product contains both NBPT and duromide
- Duromide is reaction product of NBPT.
- Has longer molecular chain than NBPT.
- Has longer inhibition period than NBPT alone.
- Duromide converts to NBPT; NBPT converts to NBPTO.
- Duromide persists longer than NBPT or NBPTO.
- Is synergistic effect with combination of NBPT and duromide.
- Less affected by acidic soil conditions than NBPT.
- N-(n-propyl) thiophosphoric acid triamide
- Used in combination with NBPT (Limus
- 16.9% NBPT, 5.6% NPPT
- 2-chloro-6-[trichloromethyl] pyridine (nitrapyrin) is proven product.
- Has been studied and commercially used since the late-1960’s.
- Used with anhydrous ammonia (N-Serve™) and with UAN solution and manure (Instinct™).
- Has bacteriostatic effect.
- Suppresses Nitrosomonas populations.
- Reduces loss potential from nitrate leaching and/or denitrification.
- Temporarily prevents nitrification step.
- Affects conversion of ammonium to nitrite.
- N-Serve™ Injected directly into soil with anhydrous ammonia stream.
- Ratio of nitrapyrin to anhydrous ammonia influences degree of nitrification.
- Can stabilize nitrogen for six to eight weeks in warm soil.
- May persist longer in cold soils.
- Is corrosive to certain fertilizer equipment components.
- Instinct™ is encapsulated nitrapyrin formulation.
- Is mixed directly with UAN solution or manure.
- Is impregnated on to dry fertilizer.
- Fertilizer can be left on soil surface for 7 to 10 days.
- DCD, dicyandiamide (or cyanoguanidine).
- Contains about 67% nitrogen.
- Was examined as fertilizer source in early 1900’s.
- Can be toxic at excess rates.
- Has bacteriostatic effect.
- Suppresses Nitrosomonas populations.
- May stabilize nitrogen for four to ten weeks.
- Activity is generally shorter than nitrapyrin.
- Active ingredient in proprietary product (CENTURO™), introduced recently.
- Is single compound.
- Reaction product of ammonia, DCD, formaldehyde, and urea.
- Are formulated as commercial fertilizer materials, commonly mixed with UAN.
- Ammonium thiosulfate, ATS
- (NH4)2S2O3; 12-0-0-26% sulfur
- Potassium thiosulfate, KTS
- K2S2O3; 0-0-25-17% sulfur
- Calcium thiosulfate, CaTS
- CaS2O3; 0-0-0, 6% calcium, 10% sulfur)
- Thiosulfate is “reducing agent”.
- Thiosulfate compounds have many industrial applications.
- Soil applied thiosulfate quickly converts to tetrathionate (S4O62-) which subsequently converts to sulfate (SO42-).
- Produces acidity when sulfur is oxidized.
- ATS affects nitrification and urea hydrolysis.
- Due to presence of both tetrathionate and subsequent acidity.
- Affects both steps of nitrification; ammonium to nitrite and nitrite to nitrate.
- Can slow urea hydrolysis, especially if UAN fertilizer droplet size is large and soil is relatively dry.
- ATS not expected to perform as well as other inhibitor products.
- Thiosulfate ion decomposes rapidly.
- Mineralization complete in about one week under warm soil conditions (> 60°F, > 15°C).
- Mineralization may take two to three weeks under cooler soil temperatures.
- Requires thiosulfate rate equivalent to 25 ppm S.
- Broadcast 16 gallons ATS per acre (assumes 6-inch soil incorporation depth.
- Apply 2.5 gallons ATS in band, regardless of band spacing.
- “maleic itaconic co-polymer calcium salt” (Nutrisphere™)
- 30% to 60% formulation (pH 2.5 to 5) to be sprayed on dry fertilizer.
- 40% formulation (pH 1 to 2) to be mixed with liquid fertilizer.
- Co-polymer is highly negatively charged.
- “Polymers” are large chain-like molecule made up of smaller, single molecules called “monomers”.
- Some polymers are made up of single type of monomer.
- “Co-polymers” made up of different monomers.
- Manufacturer claims co-polymer binds metal ions.
- i.e., copper (Cu2+) ions necessary for nitrification.
- i.e., nickel (Ni2+) ions necessary for urease activity.
- Laboratory studies show no nitrification or urease inhibiting properties.
- Some field studies do show yield response, especially when banded with liquid formulation.
- Responses may not be due to co-polymer activity.
- Could potentially bind beneficial metal ions (i.e., zinc or iron).
- Acidity reduces nitrification rate.
- 40% liquid formulation has pH of 1 to 2; may slightly inhibit nitrification.
- Group of urea formaldehyde-based fertilizers (UF fertilizers).
- Protects nitrogen by delaying availability.
- Largely used as horticultural products - professional turf, etc.
- Are comprised of short-chain and long-chain polymers of methylene urea.
- Manufactured by reaction of formaldehyde, CH2O with urea, CO(NH2)2.
- Produces “polymer, i.e., chain-like molecule.
- Urea units progressively linked with methyl units, CH22+.
- e.g., 2 urea units + one 1 methyl unit = methylene diurea, NH2C(=O)NH-CH2-NHC(=O)NH2
- e.g., 3 urea units + 2 methyl units = methylenetriurea, NH2C(=O)NH-CH2-NHC(=O)NH-CH2-NHC(=O)NH2
- Triazone (S-tetrahydrotriazone)
- Used for foliar and soil application on commercial vegetable and fruit crops.
- Produced by reacting urea, formaldehyde, and ammonia.
- Has a closed-ring structure.
- Low-volatile, stable slow-release nitrogen source.
- Has low plant toxicity/burning potential.
- IBDU
- Reacting urea with isobutyraldehyde instead of formaldehyde, yields isobutylidene diurea.
- NH2C(=O)NH-CH(CH (CH2)2)-NHC(=O)NH2
- About 90% of IBDU nitrogen is water-insoluble.
- Products are often mixtures of “quick-release” urea and “slow-release” UF products.
- Slow release characteristics depend on percentage of and length of long-chain polymers.
- After application, polymer chains gradually broken apart by biochemical reactions into individual urea units, then can be converted to nitrate form.
- Longer chains reduce nitrogen solubility and slow sown release rate.
- Release rate affected by environmental conditions.
- Often used for turf or landscape; very limited used in agronomic crops.
- Methyl-urea based products often labeled for foliar application.
- Have lower burn potential when compared to urea alone sue to slow-release characteristics.
- Have some use in horticultural applications.
- Are claims of ten-fold (or similar) efficiency for foliar application rates vs. soil applied rates.
- Claim is unproven in agronomic research results.
- Fertilizer cost of methyl-urea fertilizers are often prohibitive at rates equal to traditional fertilizers.
- Application rates should be comparable to traditional nitrogen fertilizers.
- Substituting lower rates for recommended nitrogen rates has not successfully improved crop yield or quality.
- Are coated water-soluble fertilizers.
- Coatings are applied to conventional fertilizers.
- Sulfur-and polymer-coated urea are common agronomic products.
- Coated mixed fertilizers often used in horticultural production (e.g., Osmocote™)
- Provides physical barrier against nutrient exposure to environment.
- Inhibits ammonia volatilization by separating urease enzyme from urea fertilizer.
- Inhibits nitrification by separating nitrogen fertilizer from nitrifying bacteria.
- Nitrogen availability depends primarily on destruction of coating.
- Urea dissolves/diffuses through breakdown of coating or imperfections.
- Physical breakage.
- Biological oxidation.
- Sulfur-coated urea (SCU)
- Insoluble sulfur coating plus protective overcoat applied to urea.
- Release rate determined by:
- thickness of coating.
- environmental conditions.
- Release is slow, but uncontrolled.
- Not widely used.
- Coating cost is high relative to fertilizer cost of the N fertilizer.
- Polymer-coated urea (e.g., ESN™)
- Polymer coatings applied to soluble fertilizer
- Proven effective by field research.
- Polyurethane, polyolefin used as coatings.
- Inhibits urease contact with urea fertilizer.
- Nitrogen released by diffusion through coating.
- Release rate determined by:
- polymer chemistry
- coating thickness
- coating process
- temperature
- Release can be highly controlled.
- Can be designed to match plant uptake.
- Can allow higher urea rates to be placed with small grain seed at planting.
- Injury risk is greater:
- in drier soils
- in sandy soils.
- in alkaline or calcareous soils
- at higher N rates
- Mixture of calcium polymer with penetrant buffer (e.g., NZone™)
- Ca-aminoethylpiperazine
- Uses include inhibition of corrosion, epoxy curing, surface activation, asphalt additive
- Ca-heteropolysaccharides
- Contains two or more different monosaccharide (single-sugar) units.
- Alkylarylpolyoxyethylene glycol
- Compound used to buffer spray adjuvants.
- Not proven effective in research studies.
Goos, R.J.. Nitrogen Fertilizer Additives, Which Ones WorkI? North Central Extension-Industry Soil Fertility Conference. 2011. Vol. 27. Des Moines, IA November 16-17, 2011. pg. 5-15.
Franzen, D. 2011. Nitrogen Extenders and Additives for Field Crops. Pub. SF-1581. North Dakota State University8 pg.
Blaylock, A. 2007. The Future of Controlled-Release Fertilizers. Presented at 2007 International Nitrogen Conference, Oct 1-5, 2007, Costa do Sauipe, Brazil. http://www.ipni.net/article/IPNI-3072 accessed 17Apr2019.
Nelson, K.A. 2018. Pronitridine Nitrification Inhibitor with Urea Ammonium Nitrate for Corn. Journal of Agricultural Science. 10:16-26.
Guodong Liu and Jeffrey Williamson 2016 What Is Urea-Triazone Nitrogen?2 Publication #HS1233 http://edis.ifas.ufl.edu/hs1233 accessed 19Apr2019
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