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Livestock losses from NO3 poisoning vary among locations. An understanding of the effect of environmental factors on NO3 accumulation in meadow plants may aid in management of meadowlands to reduce these losses. Controlled studies were undertaken to determine the effect of soil moisture, temperature, irradiance, and soil fertility on the yield and NO3 concentrations in herbage tissue of slender sedge (Carex praegracilis W. Boott), beardless wildrye (Elymus triticoides Buckl.), Nevada bluegrass (Poa nevadensis Vasey ex Scribn.) and reed canarygrass (Phalaris arundinacea L.). Reed canarygrass consistently yielded higher and contained higher concentrations of NO3 than the other species. Herbage yields were higher in all plants grown for 45 days at 30 degrees C than in those grown for 45 days at 15 degrees C. Yields were also higher in plants grown with 42.0 W/ m2 than they were in plants grown with 4.2 W/ m2. Concentrations of NO3 were highest when plants were grown in unsaturated soil, with 4.2 W/ m2, and they increased with fertilization. The NO3 concentrations obtained could be toxic to cattle (lethal NO3- N level = 0.21%), especially when the plants were grown at 30°C in dry soils. When meadow plants were grown in saturated soil, the NO3 concentrations were never high enough to be toxic, even when the plants were heavily fertilized. This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020