Thomas J. Koske | 7/2/2005 2:17:37 AM
Lawns need a dozen or so soil-supplied nutrients for adequate growth. Of those applied, nitrogen (N) is required in higher amounts, according to LSU AgCenter horticulturist Dr. Tom Koske.
Nitrogen creates more growth, a sturdy plant and good color, but also creates a softer, unhealthy growth if used in excess.
Koske says most lawn foods sold are predominantly nitrogen, but plants should have a proper balance of nutrients for sustainable growth and health. The ideal balance depends on the type of grass and specific soil needs. A soil nutrient analysis (soil test) can give you this assessment.
"Nitrogen is, however, the chief nutrient and controller of plant growth in average soils," Koske states, adding, "It is offered in several fertilizer forms."
Nitrogen fertilizers are usually classified in two ways: inorganic vs organic and slow-release vs soluble (or readily available N).
Inorganic N is a salt that is usually manmade and processed. Organic N has carbon (C) associated with it and may be either manmade like urea or a natural organic like manure.
The dissolution or release rates may be quick release (soluble, readily available) or slow release (water insoluble, WIN). Soluble fertilizers are cheaper per pound of N and allow the plant to take up the applied N quickly and respond with growth and color. They have a higher potential for salt burn and higher potential for leaching away. These factors can shorten the greening results.
Most synthetic turf fertilizer blends are made with part of their N in a slow-release form. The soluble N portion gives a quick green-up for the first two weeks, and the controlled-release portion kicks in after that time to spread the feeding longer.
Slow-release synthetic organics are a prill (pellet) of urea that is coated with inhibitory chemicals, plastics, sulfur, resin and or wax. These coatings block or limit moisture access to the soluble urea for a period of time or to a certain degree. The result is that N is slowly released from the prills.
Natural organics slowly release N based on microbial degradation to the available N forms. Temperature and moisture affect the microbe's activity and thus affect N availability.
Slow-release N and products with this component cost more, but usually perform better. They provide N over a longer time, more efficiently to support steady growth. This growth comes with less salt burn and no flush of soft growth.
Soluble N fertilizers can be used equally well as slow release, but must be applied in lower amounts and more often for the same growth response. Expect soluble fertilizers to last three to four weeks and slow release to last six to eight weeks.
Plants almost completely take up only the nitrate form of N and/or the ammonium form of N. This is true no matter what substance the N is applied as.
Koske recommends contacting an extension agent in your parish LSU AgCenter office to learn more about lawn fertilizers. For related topics, click on the Lawn and Garden link at the LSU AgCenter Web site, www.lsuagcenter.com.