Correlation of Environmental Factors with Nitrate Concentration in Meadow Plants

Abstract

Earlier studies of meadow forages in eastern Oregon have shown that fertilizer-N increased yields and N concentration. How much of the increased N was NOa-N or how variations in environmental factors affected the accumulation of NO3 in meadow plants is not known, Plots of native meadow were fertilized on March 31 with ammonium sulfate to provide nitrogen levels of 0, 110, 220, 440 kg/ha. Changes in air temperature; soil temperature at the 0-, 5, lo-, 20-, and 50-cm depths; luminous flux at canopy level, at 20 cm above ground, and at ground level; solar radiation over vegetation; and soil moisture content were monitored through the growing season. These data were statistically correlated with concentrations of NO3-N extracted from plant tissue. Herbage yields at the end of the growing season increased from 4,275 kg/ha without fertilizer to 9,782 kg/ha with 440 kg N/ha. Total-N concentration was highest (3.33%) on May 5 in herbage fertilized with 440 kg N/ha. As plants matured, concentration of total-N decreased by August 29 to 1.15% in plants receiving the 440 kg/ha rate and to 0.72% in unfertilized plants and was higher in the leaves than in the stems. Conversely, concentration of N03-N were lowest (lo-70 ppm) early in the season. Late in the growing season the N03-N level was lowest in the leaves and highest (1,060 ppm) in the stems. Correlation analyses indicated that soil-moisture content was the most significant environmental factor correlated with accumulations of N03-N, except for soil fertility as measured by increased fertilization rate. Luminous flux at ground level and air temperature were also contributing factors. Native plants commonly found on flood meadows of eastern Oregon are tolerant to long periods of flooding. These plants thrive under seasonally moist to saturated soil conditions, yet survive periodic droughts. With nitrogen(N) fertilization, these meadow plants generally have increased yields and increased N content of the herbage (Rumburg Author is range scientist, U.S. Dep. Agr.-SEA-Agr. Res., Crops Research Lab., Utah State University, Logan, 84322. Formerly at Oregon State University, Squaw Butte Agricultural Experiment Station, Burns, Ore. This study represents the cooperative investigation of the U.S. Dep. Agr.-SEA-Agr. Res. and the Agr. Exp. Sta., Oregon State Univ. Tech. Pap. No. 4915 of the latter. Manuscript received January 8, 1979. JOURNAL OF RANGE MANAGEMENT 33(3), May 198