Herbage yield and nitrate concentration in meadow plants as affected by environmental variables.

Livestock losses from NO,, poisoning vary among locations. An understanding of the effect of environmental factors on NO,, 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 NO,, 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 NO:, than the other species. Herbage yields were higher in all plants grown for 45 days at 30°C than in those grown for 45 days at 15°C. Yields were also higher in plants grown with 42.0 W/m’ than they were in plants grown with 4.2 W/m? Concentrations of NO,, were highest when plants were grown in unsaturated soil, with 4.2 W/m2, and they increased with fertilization. The NO,, concentrations obtained could be toxic to cattle (lethal NO,,-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 NO,, concentrations were never high enough to be toxic, even when the plants were heavily fertilized. The incidence of livestock loss from nitrate poisoning varies among plant species and localities. While some species or types of forage are recognized as potentially dangerous at one location, they may never cause trouble in another location. Areas not previously identified as supporting dangerous types of forage have reported losses after cultural practices were changed or fertilizers were used. I hc author i\ ;1 range scientist. Crops Research Laboratory. Scwnce and Education Admlnlwatwn. U.S. Department of Agriculture. Logan. Utah X4322. The report involv~scooprrativc investigation by the Scicnccand Education Administratlon. L’. S. Dep. qgr. and the Oregon Agricultural Experiment Station. Oregon State C’nt\cr\lty. rechntcal paper no. 4x21 of the latter. The research was conducted by the author at the Squaw Butte Experiment Station. Burns. Oregon. Manuscript received July 20. 1978. JOURNAL OF RANGE MANAGEMENT32(5), September 1979 Nitrogen fertilizer is important for increasing forage yields where grasses are the dominant species. High rates of fertilizer N. however, increase the N content of these plants (Willhite et al. 1955; and Rumburg 1969, 1972). Cattle ingesting such high-N feeds may develop nitrate poisoning. The property of causing nitrate poisoning, however, is not limited to fertilized plants; poisoning can also occur when cattle graze environmentally stressed plants. Primary factors known to affect the accumulation of N in plants include nutrient supply, soil moisture level, temperature, light, soil type, herbicides, and disease (McKee I 962). Normally, the NO,, taken from the soil by plants is converted into ammonia, amino acids, protein, and other proteinaceous compounds. The N in herbage often is erroneously considered to be entirely in the proteinaceous forms. Environmental stresses that upset the photosynthesis-respiratory balance can, however, cause dangerous amounts of NO,, to accumulate in plant tissues (Deinum I97 I ; and Murata 1969). Rumburg ( 1972) observed that the concentration of N in herbage of species native to flood meadows of eastern Oregon increased rapidly after fertilizer was applied. It reached a maximum level in IO14 days then decreased gradually until the N concentration of the fertilized herbage equaled that of nonfertilized herbage. It is not known how much of the N in the herbage was NO:{-N, how long the NO,, persisted in the plants, or whether any species accumulated excessive amounts of NO,,. The object of this study was to determine the effects of variations in temperature, h-radiance, soil moisture content, and fertilizer rate on yield and NO,, accumulation in four species important in the flood meadows of eastern Oregon. Materials and Methods The study was conducted in a growth room where temperature, irradiance, and soil moisture were controlled in a4-phase experiment.