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 NO3- 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-, 10-, 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 NO3- N were lowest (10-70 ppm) early in the season. Late in the growing season the NO3- 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 NO3- N, except for soil fertility as measured by increased fertilization rate. Luminous flux at ground level and air temperature were also contributing factors.