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Anhydrous Ammonia Compared to Ammonium Nitrate on Cool-Season Grasses¹

Nitrogen fertilization of perennial grasses would be more widely accepted in the humid temperate part of the USA if it were more profitable. Currently the total cost of injecting NH₃, anhydrous ammonia (AA), into sod is less than broadcasting ammonium nitrate (AN) but application technology and effects of AA on grasses are meager. These two N sources were compared in the field on deep-rooted grasses—bromegrass (Bromus inermis Leyss) (SB), reed canarygrass (Phalaris arundinacea L) (RC), tall fescue (Festuca arundinacea Schreb.) (TF), and orchardgrass (Dactylis glomerata L.) (OG)—and on Kentucky bluegrass (Poa pratensis L.) (KB), a shortrooted grass. Grasses were evaluated for seasonal and total yield, efficiency of N use, yo stimulation between AA rows, and injury from AA in a 2-year period (YR 1 + YR 2) after N fertilization of a Conover loam (Udollic Ochraqualfs; fine loamy, mixed, mesic). N was applied to the five grass sods only in the first year at rat,rs 112, 224, 448, and 896 kg/ha as surface-broadcast AN or AA injected 13 cm deep into sods at row spacing of 25, 51, 76, and 102 cm. AA was slower than AN in increasing yield: in YR 1, AA produced lower yields in the first and higher yields in the last cutting than AN; in YR 1, yields were lower with AA but, except at the lowest N rate, were higher with AA in YR 2. Total yields increased with higher rates of N and were similar at all rates with either N source on all grasses except KB which yielded more with AA than AN at the highest rate. First-year yields on all grasses plateaued at 224 kg N but increased with higher N rates in YR 2. Increasing AA spacing did not affect total yields but decreased yields in YR 1, particularly with KB, and increased yields in YR 2. Average yields in % were: SB-100, TF-86, RC-79, OG-75, and KB-56. RC was the most efficient user of N. We concluded that AA is a feasible and efficient N source on perennial cool-season grasses at rates up to 224 kg N/ha. Row spacings of 51 and 76 cm with special knives are suggested for shallow and deep-rooted grasses, respectively.

Key Words: Bromus inermis • Dactylis glomerata • Festuca arundinacea • Phalaris arundinacea • Poa pratensis • NH₃ • fertilization

² Graduate assistant (presently Senior Research Biologist, Monsanto Agricultural Products Co., St. Louis, MO 63166) and professor, Dep. of Crop and Soil Sciences, Michigan Agric. Exp. Stn., East Lansing, MI 48824.

Received for publication June 4, 1976.