Nitrogen in Lawn Fertilizers

Daniel Gill, Koske, Thomas J.  |  5/20/2005 1:29:16 AM

Lawns need a dozen or so soil-supplied nutrients for adequate growth. Of those applied, nitrogen (N) is required in greater amounts. Nitrogen creates more growth, a sturdy plant and good color, but it also creates a softer, unhealthy growth if used in excess.

Most lawn foods sold are predominantly N, 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. It is provided in several fertilizer forms. 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 was applied as.

Nitrogen fertilizers are usually classified in two ways: inorganic vs organic N 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 quickly take up the applied N and respond with growth and color. They have a greater potential for salt burn and greater potential for leaching away. This 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; 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 or to a certain degree. The result is that N is released from the prills slowly.

Natural organics release N slowly based on microbial degradation to the available N forms. Temperature and moisture affect microbe 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.

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