Knowing the specific gravity ( density) of fluid fertilizers is very important for accurately applying the correct rate of fluid crop nutrients. So where can we find a table or chart that presents the densities of various fluid fertilizers and blends? While there is information detailing the characteristics of common fluid fertilizers, we need to keep in mind that this information provides typical values only and will vary depending on such things as the raw materials used, impurities in the product, temperature, storage conditions and other factors. These ‘table values’ are ballpark values only – they should be checked for your specific product. Also, there are an infinite number of fluid blends that can be made from common fluid fertilizers – and there are no ‘table values’ for these individual blends. The density of each blend should be determined.
How can density be measured in the field? The best way is to use a hydrometer. A hydrometer is an instrument typically made of glass that measures the specific gravity of fluids. If a hydrometer is not available, a simple method is to fill any container with water and weigh it – taking into account weight of container. Then repeat with the liquid fertilizer and compare its weight to the weight of the water. By comparing these weights you can determine the specific gravity and hence the density of the liquid.
Specific Gravity of Fertilizer = Weight of fertilizer / Weight of water
Density of Fertilizer (lbs/gal) = Specific Gravity of fertilizer X 8.34
For example –-> assume a 5 gallon pail of water weighed 42.7 pounds after subtracting out the weight of the pail. When filled with 28% UAN, the weight of the fertilizer was 53.4 pounds.
Specific Gravity of UAN = 53.4 / 42.7 = 1.28
. Density of UAN = 1.28 x 8.34 = 10.67 lb/gal