Plants, including our lawn grasses, can’t tell the difference in elemental nitrogen once it becomes usable by the plant. However, there is considerable difference in the types of fertilizer sources and their release time or availability of nitrogen to the plant. Nitrogen fertilizer sources are classified as either “readily available” or “slow release”.
Products such as ammonium nitrate, urea, and ammonium sulfate are very water-soluble and become available very quickly. The advantages of such fertilizer sources are that they are generally less expensive per pound of actual nitrogen and plants respond very quickly following an application. Disadvantages are that they have greater burn potential, have a greater risk of leaching, and do not give extended results.
Many lawn fertilizers are characterized as slow-release formulations. These fertilizers primarily contain nitrogen sources that are not immediately available to the turf. The oldest slow-release products are natural fertilizers such as compost, cottonseed meal, sewage sludge and manures, which release their nitrogen as the microorganisms in the soil break them down. Some sources combine urea with formaldehyde and many of the more modern products contain quick-release nitrogen forms that have thin plastic, sulfur, or resin coatings that allow water to dissolve them slowly.
The main thing to remember is that all these products will release their nitrogen over a longer period of time and provide more uniform vegetative growth to the turf without the potential of turf injury from over fertilization. The initial costs of these products are generally higher, but they perform much longer and reduce flushes of growth that encourage disease attack.
Published March 28, 2005
Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. firstname.lastname@example.org