A gallon of UAN-32 contains about 3.54 pounds of actual nitrogen. That number comes from two facts every fertilizer dealer knows: UAN-32 weighs roughly 11.06 pounds per gallon at 60 °F, and 32% of that weight is nitrogen. Multiply 11.06 by 0.32 and you land at 3.54. Simple as the math is, what you do with that number in the field involves quite a bit more, from calculating application rates per acre to managing the nitrogen losses that eat into what your crop actually gets.
Where the 3.54 Figure Comes From
UAN-32 is heavier than water. A gallon of plain water weighs about 8.34 pounds, but the dissolved urea and ammonium nitrate in UAN-32 push its density up to roughly 11.06 pounds per gallon. The “32” in the name means the solution is 32% nitrogen by weight, a figure printed on every spec sheet and guaranteed by the manufacturer. The math is just weight times percentage: 11.06 × 0.32 = 3.54 pounds of nitrogen per gallon. That 3.54 figure is the one you plug into every rate calculation you do.
Temperature matters slightly. Liquid fertilizer expands when it warms up and contracts when it cools down. The 11.06 pounds-per-gallon figure is measured at 60 °F, which is the standard reference temperature the industry uses. On a hot summer day the solution is a bit lighter per gallon; on a cold morning it is a bit heavier. For practical rate calculations the difference is small enough to ignore, but if you are calibrating equipment on a 95 °F afternoon and filling the tank on a 50 °F morning, the volume in the tank changes slightly even though the total weight of nitrogen stays the same.
How UAN-32 Compares to Other Liquid Nitrogen Solutions
UAN-32 is the most concentrated of the three common UAN grades, but it is not the only one. UAN-28 and UAN-30 are widely available, and the choice often depends on climate. Higher-concentration solutions have a higher salt-out temperature, meaning they can crystallize in cold weather. UAN-32 starts forming crystals at around 32 °F, which makes it impractical in northern states during early spring. UAN-28, with a salt-out temperature near 0 °F, handles cold weather much better.
The nitrogen content per gallon drops as the concentration drops:
- UAN-32: weighs about 11.06 lb/gal, delivering roughly 3.54 lb N per gallon.
- UAN-30: weighs about 10.86 lb/gal, delivering roughly 3.26 lb N per gallon.
- UAN-28: weighs about 10.66 lb/gal, delivering roughly 2.99 lb N per gallon.
If your nitrogen recommendation is 150 pounds of N per acre and you are using UAN-32, you need about 42.4 gallons per acre. Switch to UAN-28 and you need about 50.2 gallons for the same amount of nitrogen. That difference adds up across hundreds of acres in hauling, storage, and application time, which is one reason UAN-32 remains the preferred grade wherever the climate allows it.
The Three Forms of Nitrogen Inside the Solution
UAN-32 is not one chemical. It is a blend of urea and ammonium nitrate dissolved in water, and the nitrogen it contains arrives in three distinct chemical forms. Roughly half the total nitrogen is in urea form. About a quarter is ammonium nitrogen from the ammonium nitrate, and the remaining quarter is nitrate nitrogen, also from the ammonium nitrate. These three forms behave very differently once they hit the soil.
Nitrate is immediately available to plant roots. It is also the form most prone to leaching, because it carries a negative charge and moves freely with water through the soil profile. Ammonium holds onto soil particles and resists leaching, but soil microbes convert it to nitrate within days to a few weeks depending on temperature and moisture. Urea has to go through an extra step: the enzyme urease in the soil breaks it down into ammonium first, and then microbes convert that ammonium to nitrate. This staggered release is one of UAN-32’s practical advantages. You get some nitrogen the crop can use immediately, some that becomes available over the following week or two, and some that takes a bit longer. It is a built-in split application in a single pass.
Calculating Application Rates in the Field
Most rate recommendations are given in pounds of nitrogen per acre. Converting that to gallons of UAN-32 is straightforward: divide the recommended pounds of N by 3.54. If your soil test calls for 180 pounds of nitrogen per acre, that is 180 ÷ 3.54 = about 50.8 gallons per acre. For a 160-acre field, you would need roughly 8,130 gallons of UAN-32 total.
Sprayer calibration introduces a second calculation. You need to know how many gallons per acre your equipment is actually delivering and then adjust nozzle size, pressure, or ground speed to hit your target. A common approach is to set a carrier volume (say 15 gallons per acre of total spray solution) and then determine what proportion of that volume needs to be UAN-32 versus water or other tank-mix partners. When UAN-32 is the sole product, the carrier volume and the fertilizer volume are the same thing, but when you are blending it with herbicides or micronutrients, the math gets more involved. Keeping a notepad with your 3.54 pounds-per-gallon conversion handy prevents expensive errors.
One practical tip: UAN solutions are corrosive to many metals, especially brass and copper. Standard brass spray nozzles can degrade quickly. Stainless steel or polymer nozzles hold up better and maintain the consistent flow rate your calibration depends on.
Ammonia Volatilization and Surface Application Losses
Not all 3.54 pounds of nitrogen in that gallon make it to the root zone. When UAN-32 is surface-applied and not incorporated into the soil, the urea portion is vulnerable to ammonia volatilization. The enzyme urease converts urea to ammonium, and if that reaction happens at the soil surface rather than below it, some of the nitrogen escapes as ammonia gas into the atmosphere.
The good news is that UAN tends to lose less nitrogen to volatilization than dry urea under many conditions. Research on soils with pH below 7 found that urea lost about 21% of applied nitrogen as ammonia, while UAN lost only about 3.3%. The reason is partly that only half of UAN’s nitrogen is in the urea form to begin with, and partly that the liquid carrier helps move the urea into the soil more quickly than dry granules sitting on the surface. On alkaline soils with pH above 7, though, the advantage shrinks or even reverses, with UAN losses becoming comparable to or higher than urea losses.1Agrosystems, Geosciences & Environment. Soil properties that influence ammonia loss from surface‐applied, unincorporated urea‐based fertilizer
Soil pH is not the only factor. Warm temperatures, windy conditions, and dry soil surfaces all accelerate volatilization. If you are broadcasting UAN-32 on a hot, windy afternoon onto dry alkaline ground, you are setting up the worst-case scenario for nitrogen loss. Incorporating the solution with light tillage or irrigation, or applying it before a rain, dramatically reduces the problem.
Leaf Burn Risk with Foliar Application
UAN-32 is sometimes applied directly to crop foliage, either as a late-season nitrogen boost or as a carrier for foliar herbicides. The risk is leaf burn, and it is real. When concentrated UAN solution contacts leaf tissue, it damages epidermal cells through what appears to be rapid water loss. Within a couple of hours the leaf surface darkens, and by eight hours the epidermis can be desiccated and sunken, with visible lesions forming on the leaf surface. Under a microscope, the epidermal and mesophyll cells collapse and wrinkle as they lose moisture.2Agronomy Journal. Morphological and Anatomical Characterization of Leaf Burn in Corn Induced from Foliar‐Applied Nitrogen
The severity depends on rate, crop stage, and weather. Low rates diluted in plenty of carrier water cause minimal damage. High rates applied in hot, humid conditions can cause significant yield-reducing injury. A common guideline for corn is to keep UAN-32 foliar rates below about 15 to 20 pounds of nitrogen per acre when applying with flat-fan nozzles, and to apply during cooler parts of the day. Streaming nozzles, which produce coarser droplets that roll off leaves rather than coating them, reduce burn at a given rate. Mixing UAN with certain herbicides can make burn worse because the herbicide’s surfactant holds the solution on the leaf surface longer.
Using Inhibitors to Get More Out of Each Gallon
Because UAN-32’s nitrogen passes through multiple transformations in the soil, there are several points where you can slow the process down and reduce losses. Urease inhibitors block the enzyme that converts urea to ammonium, keeping the urea stable in the soil longer and reducing ammonia volatilization from the surface. Nitrification inhibitors slow the microbial conversion of ammonium to nitrate, which reduces both nitrous oxide emissions and nitrate leaching.
Pairing both types of inhibitors with UAN can be particularly effective. Research on injected UAN found that combining urease and nitrification inhibitors reduced both ammonia volatilization and nitrous oxide emissions simultaneously, avoiding the “pollution swapping” problem where controlling one gas pathway increases the other. Corn grain yields increased by about 7% compared with injected UAN alone when both inhibitors were used.3PubMed. Combining Urease and Nitrification Inhibitors with Incorporation Reduces Ammonia and Nitrous Oxide Emissions and Increases Corn Yields
The specific combination of inhibitors matters, though. Studies on maize in mollisol soils found that adding a urease inhibitor alone to UAN reduced ammonia emissions by 13% but actually increased nitrous oxide emissions by the same amount, essentially trading one loss pathway for another. A nitrification inhibitor alone cut nitrous oxide emissions by about 31% and boosted maize yield by over 21%, but it increased ammonia losses. Only certain paired combinations improved yields and reduced total nitrogen loss at the same time.4PubMed Central. The Combined Use of Liquid Fertilizer and Urease/Nitrification Inhibitors on Maize Yield, Nitrogen Loss and Utilization in the Mollisol Region The practical upshot is that inhibitors can make each gallon of UAN-32 go further, but picking the right products and combining them correctly takes some homework.
Nitrate Leaching and Why Application Rate Matters
The nitrate fraction of UAN-32 is plant-available from the moment it hits the soil, but it is also the fraction most likely to move below the root zone with percolating water. The urea and ammonium fractions eventually become nitrate too, which means leaching risk increases over time, especially in sandy or irrigated soils where water moves quickly through the profile.
Long-term field research has consistently shown that nitrate leaching increases with higher nitrogen application rates. In one multi-year study under supplementary irrigation, nitrate-nitrogen concentrations in the soil at every depth measured were significantly higher at 200 pounds of nitrogen per acre than at 100 pounds, and higher at 100 than at zero. The critical drinking-water threshold of 10 mg/L of nitrate-nitrogen was exceeded under all fertilized treatments at all depths studied.5Agricultural Water Management. Nitrate leaching assessment in a long-term experiment under supplementary irrigation in humid Argentina The largest leaching losses occurred during the growing season when irrigation volumes were highest, not during fallow periods as you might expect.
Split applications, where you divide your total nitrogen rate into two or more applications spread across the growing season, are often recommended to reduce leaching. The logic is that smaller doses applied closer to when the crop needs them should leave less nitrate sitting in the soil waiting to be washed away. In practice, research on irrigated sandy loam soils found that increasing the number of nitrogen splits did not significantly reduce area-based nitrate leaching compared with fewer splits, though pore-water nitrate concentrations were dramatically higher in all fertilized treatments compared with unfertilized controls.6Agrosystems, Geosciences & Environment. Impact of split nitrogen applications on nitrate leaching and maize yield in irrigated loamy sand soils of Northeast Nebraska Splitting may still make sense for other reasons, like matching nitrogen supply to crop demand during rapid growth stages, but it is not a guaranteed solution for leaching on every soil type.
Another approach is to combine UAN with a nitrification inhibitor, which keeps more nitrogen in the ammonium form and slows the conversion to leachable nitrate. Research has shown this can significantly increase ammonium and nitrate retention in the top eight inches of soil while reducing movement to deeper layers.7Field Crops Research. Urea ammonium nitrate solution combined with urease and nitrification inhibitors jointly mitigate NH3 and N2O emissions and improves nitrogen efficiency of summer maize under fertigation
How UAN-32 Stacks Up Against Anhydrous Ammonia
Farmers sometimes wonder whether the convenience of liquid UAN-32 costs them yield compared with anhydrous ammonia, which is 82% nitrogen and far more concentrated. Anhydrous ammonia requires pressurized tanks, specialized application equipment, and careful safety protocols because it is a compressed gas at room temperature. UAN-32 is a low-pressure liquid you can haul in a nurse tank and spray through standard equipment, which is a major practical advantage.
In terms of crop performance, side-by-side comparisons in corn have found that UAN with added inhibitors did not significantly improve yield or grain nitrogen recovery compared with anhydrous ammonia.8Soil Science Society of America Journal. Enhanced‐Efficiency Fertilizer Impacts on Yield‐Scaled Nitrous Oxide Emissions in Maize That is not a knock on UAN. Anhydrous ammonia is injected directly into the soil, which virtually eliminates volatilization loss and puts the nitrogen right in the root zone. When UAN is also injected or incorporated, the two sources tend to perform similarly at the same nitrogen rate. The yield difference, if any, usually comes down to placement and loss management rather than the nitrogen source itself.
The real tradeoff is logistical. Anhydrous ammonia delivers about 5.7 pounds of nitrogen per gallon (it weighs roughly 6.96 lb/gal at typical delivery conditions, and 82% is nitrogen), so you haul far less volume per acre. But the safety requirements, equipment costs, and limited application windows for anhydrous ammonia push many operations toward UAN-32 as the more flexible option, especially for in-season topdressing or fertigation through pivot irrigation systems. If you know your 3.54 pounds per gallon, manage your losses, and apply at the right time, UAN-32 is a highly effective nitrogen source with a much easier logistics chain.