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Use of Slow-Release N Fertilizers on Native Mixed Prairie¹

Although it is known that the native mixed prairie grasses will respond to N fertilization, little is known concerning the recovery and fate of different fertilizer N sources applied to this ecosystem. Possibly by using slow-release N fertilizers, changes in stands of the different grass species could be controlled in a manner that would improve productivity. Consequently, a 4-year field experiment was conducted at Mandan, North Dakota, to compare the effects of S-coated urea and ureaformaldehyde with ammonium nitrate on production of mixed native prairie vegetation. In general, all fertilizers at all rates of application decreased Boulettoua gracilis (blue grama) density, while Agropyron smithii (western wheatgrass) density generally increased at rates above 56 kg N/ha annually. Dry matter production from all rates of N application was greatest for ammonium nitrate and least for ureaformaldehyde, with intermediate production for the S-coated ureas. Fertilizer N recovery in harvested forage followed this same order. Assuming that about 100 kg fertilizer N was immobilized in grass roots, and that fertilizer N not accounted for in tops, roots, and soil inorganic N forms estimates gaseous losses, presumed gaseous losses varied from less than 10% of the amount of N applied as ammonium nitrate to about 60% for ureaformaldehyde. In general, the mixed prairie grasses used N from urea-containing fertilizers less efficiently than that from ammonium nitrate.

Key Words: Slow release fertilizer • N sources • Grassland fertilization • Fertilizer efficiency • Rangeland • Native species • Urea-containing fertilizers

² Soil scientist, USDA-SEA-AR, Lincoln, NE, formerly at Mandan, ND.

Received for publication September 1, 1978.