Lawn fertilization 04-14-08

Proper fertilization is a key factor in keeping your lawn healthy and beautiful. However, there should always be a purpose for fertilization. Have you had soil analysis done of your lawn in the past three years to determine the nutrient and pH levels? Does the lawn need canopy, greater cover, enhanced root development, improved color, etc.? The turf species, how the lawn is used, the growing zone you are in, and the source of fertilizer used should all be considered in developing your lawn fertilization program.

There are many different types of fertilizers with varying amounts of the essential nutrients within them, but the three numbers marked on the bags represent the percentage of nitrogen, phosphorous, and potassium. Most turf grasses prefer a 4-1-2 or 4-1-3 ratio of N-P-K, so keep this in mind when selecting a turf fertilizer.

Even though plants, including lawn grasses, can’t tell the difference in elemental nitrogen once it becomes usable by the plant, there is a 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, do not give extended results, and may increase disease pressure.

Slow-release formulations contain at least a portion of the nitrogen source that is not immediately available. 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.

Many of the modern products contain quick-release nitrogen forms that have thin plastic, sulfur, or resin coatings that allow temperature and moisture to release them slowly. The main thing to remember is that all these slow release 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 April 14, 2008

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. wwells@ext.msstate.edu