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Nitrogen- and Water-Use Efficiency of Several Cool-Season Grasses Receiving Ammonium Nitrate for 9 Years¹

Comparative information is needed on differences between grass species regarding dry matter production, root growth, water use, and response to N fertilization, as affected by both age of stand or years of N fertilization. The research reported here was conducted on a Temvik silt loam (fine-silty, frigid, mixed Typic Haploboroll) at Mandan, ND. Ammonium nitrate was surface broadcast at 0, 45, or 225 kg N/ha for 9 years on established stands of western wheatgrass [Pascopyrum smithii Rydb. (Love)], crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schult.], intermediate wheatgrass [Elytrigia intermedia (Host) Nevski], smooth bromegrass (Bromus inermis Leyss.), Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski], green needlegrass (Stipa viridula Trin.), and Garrison creeping foxtail (Alopecurus arundinaceus Poir). Dry matter production was usually greatest for E. intermedia. Production for B. inermis, P. smithii, and A. desertorum averaged 85 to 90% that of E. intermedia, and about 65 to 72% for the other species. Dry matter production for all species was generally doubled by 45 kg N/ha, and increased three-to fourfold with 225 kg N/ha. At 45 kg N/ha, N-use efficiency varied from an average of 51 kg dry matter per kg N for E. intermedia to 22 for Ps. juncea. Corresponding values at 225 kg N/ha dropped to 16 and 12 kg/kg N. Root dry weights were generally increased 50 to 100% by both N rates, but consistent differences among species were not evident. Annual water use was increased about 20 mm by fertilization, except in extreme drought years. Water-use efficiency (WUE) was also increased about threefold by fertilization, ranging from 22.6 kg/mm for fertilized E. intermedia to 3.2 for nonfertilized Al. arundinaceus. Water-use efficiency was highly correlated with dry matter production, increasing about 2.8 kg/mm for each 1000 kg/ha increase in production, with no effect of species, time, or N fertilization.

Key Words: Grasslands • Rangelands • Range fertilization • Root growth • Water use

² Research leader and soil scientist, USDA-ARS-USDA, Univ. Nebraska-Lincoln, (formerly at Mandan, ND).

Received for publication March 26, 1984.