The liquid fertilizer labeled 28-0-0 is one of the most common sources of nitrogen in agriculture and turf management, sold as a Urea Ammonium Nitrate (UAN) solution. This highly concentrated product delivers nitrogen in a readily available liquid form, making it popular for both broadcast and precision applications. Because liquid fertilizers are sold by volume (gallons) but their nutrient content is guaranteed by weight, determining the precise amount of actual nitrogen (N) in a single gallon requires a specific calculation.
Decoding the NPK Analysis
The series of three numbers—28, 0, and 0—on the fertilizer label is known as the Guaranteed Analysis, or NPK grade, which is standardized across the industry. The first number, 28, indicates that the product contains 28% nitrogen by weight. The subsequent zeros confirm that the product contains no phosphorus (P) in the form of phosphate (\(P_2O_5\)) and no potassium (K) in the form of potash (\(K_2O\)).
The 28% figure means that every 100 pounds of the product contains 28 pounds of actual nitrogen. This is a fundamental distinction, because the fertilizer is purchased by volume, but the analysis is based on weight. Therefore, knowing the total weight of one gallon is necessary to determine the weight of the nitrogen within it. The Guaranteed Analysis provides the first of two variables needed for the final nitrogen content calculation.
Determining the Density of Liquid 28-0-0
Since the nitrogen content is a percentage of the total weight, the next step is to establish the density of the liquid, which determines how much one gallon weighs. Density varies slightly based on the specific formulation and temperature, but 28-0-0 UAN solution is significantly heavier than water. Manufacturers commonly report the weight per gallon on the product label or safety data sheet.
The density for 28-0-0 UAN solution ranges from 10.5 to 10.77 pounds per gallon at standard temperatures. Using a common figure, such as 10.66 pounds per gallon at 60°F, provides a reliable average for calculation. This weight is the second variable, representing the total mass from which the 28% nitrogen is derived.
Calculating the Exact Nitrogen Content
The core calculation to find the pounds of actual nitrogen (N) per gallon combines the two variables: the total weight per gallon and the percentage of nitrogen. The formula is straightforward: \(\text{Weight per Gallon} \times \text{Percentage of Nitrogen} = \text{Pounds of N per Gallon}\). For the 28-0-0 product, the percentage must be converted to its decimal equivalent, which is 0.28.
Using the common average density of 10.66 pounds per gallon, the calculation is \(10.66 \text{ lbs/gal} \times 0.28 = 2.985 \text{ lbs N/gal}\). Based on the density range of 10.5 to 10.77 pounds per gallon, the nitrogen content will fall between 2.94 and 3.01 pounds of actual nitrogen per gallon. Many agricultural professionals simplify this figure, often rounding it to 2.9 or 3.0 pounds of nitrogen per gallon for quick field calculations.
Translating Nitrogen Weight into Application Rates
Knowing the precise pounds of nitrogen per gallon is necessary to determine the correct volume of fertilizer needed to meet a specific nutrient requirement. Most soil test recommendations and application targets are expressed in pounds of actual nitrogen per unit area, such as per 1,000 square feet or per acre. The calculated nitrogen content allows for the accurate conversion from the required weight of the nutrient to the necessary volume of the liquid product.
The formula for calculating the required application volume is: \(\text{Target Pounds of N} \div \text{Pounds of N per Gallon} = \text{Gallons of Product Needed}\). If the application goal is 1 pound of actual nitrogen per 1,000 square feet, and the fertilizer contains 2.985 pounds of N per gallon, the calculation is \(1 \text{ lb N} \div 2.985 \text{ lbs N/gal} = 0.335 \text{ gallons}\). This means that 0.335 gallons of the 28-0-0 solution must be applied to every 1,000 square feet to achieve the target rate.