SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: https://read.dmtmag.com/i/34725
FieldScience | Dr. Tom Samples, Dr. John Sorochan and Adam Thoms Are you getting the most from your granular nitrogen fertilizers? N ITROGEN (N) is the essential mineral nutrient required in greatest amounts by turfgrasses. Although more than 78% of the air we breathe is N2, turfgrasses are unable to capture it from the atmosphere so many researchers, chemists and fertilizer manufacturers spend considerable time and effort every year developing granular N-containing fertilizers for turf. Some of these are homogenous, with granules having an equal amount of nutri- tion. Others are blends of several nutrient sources or carriers. Depending on how it is formulated, a fertilizer may release N very quickly or for an extended period of time. Since energy is required to convert atmospheric N to ammonium and nitrate, the forms that turfgrasses use, the cost of fertilizers increases as energy and fuel costs rise. Knowing how much N a turfgrass requires, how long N is available after a fer- tilizer is applied, the factors that affect how N is released and the physical proper- ties of a fertilizer helps sports turf managers make informed decisions when purchasing and applying granular fertilizers. The N requirement of cool- and warm-season turfgrasses varies among species. Bermudagrass and Kentucky bluegrass usually need more N per growing month than tall fescue and perennial ryegrass. For example, bermudagrass and Kentucky bluegrass usually require from 0.5 to 1.5 lb. of N per 1,000 sq. ft. per growing month, and tall fescue and perennial ryegrass, from 0.4 to 1 lb. of N per 1,000 sq. ft. per growing month. This information is helpful when developing a fertilization program and budget. The N requirement of cool- and warm-season turfgrasses varies among species. Bermudagrass and Kentucky bluegrass usually need more N per growing month than tall fescue and perennial ryegrass. The chemical properties of the N carrier(s) in a fertilizer influence how, and the rate at which, N is released. Physical properties such as the size and uniformity of granules influence the ballistic properties, and may also affect N release. If the granules contain an herbicide, their size and uniformity may directly influence herbicide coverage and performance. >> Figure 2. UREA Prills. Figure 3. Granular Ammonium Sulfate. Figure 4. Monoammonium Phosphate. CHEMICAL PROPERTIES Highly Water-soluble N Carriers. There are two groups of highly water-soluble N carriers. Inorganic (containing no carbon) salts are synthetic, dry and solid materi- als formed as N from the air reacts with other materials. Urea, unlike the inorganic salts, is a quickly available, synthetic-organic (containing carbon) N carrier. It is made by reacting carbon dioxide with anhydrous ammonia under high pressure (e.g., 3000 psi) and temperature (~350 de- grees F). Water is removed dur- ing this process and a molten N-containing substance is con- verted into small, hollow prills (Figure 2) or solid granules. Inorganic salts like ammo- nium sulfate (Figure 3), cal- cium nitrate, diammonium phosphate (DAP), monoam- monium phosphate (MAP, Fig- ure 4) and potassium nitrate 8 SportsTurf | July 2011 www.sportsturfonline.com By Top left image: Grass image © istockphoto.com/cloki. Nitrogen fertilizer image © istockphoto.com/sb-borg.