| Abstrakt: |
The NO3‐N concentration of wheat, oats, rye, and barley forage was found to be a function of rate of N fertilization, P fertilization, and date of sampling. The crops were not very different with respect to NO3‐N accumulation, though barley and wheat appeared to accumulate more nitrates than rye or oats during periods of highest concentration. Nitrate‐nitrogen concentrations were highest in samples collected March 18 and 24 when the plants were in the “joint” or “preboot” stage of growth. Concentrations greater than 3,500 ppm were not uncommon in barley and wheat samples collected at these stages of growth, whereas oat and rye samples rarely exceeded 3,500 ppm. The NO3‐N concentrations rarely exceeded the potentially toxic level of 2,100 ppm when 90 kg/ha or less N was applied, a rate that is as high as is typically applied to dryland winter wheat. The NO3‐N concentration declined sharply after the March 24 sampling date and continued to decline through the April 13 sampling date. A slight increase in concentration appeared late in the season, especially in oats. The tendency for NO3‐N accumulation to be increased by a deficiency of P was also found. The concentration in wheat forage was reduced from 1,300 ppm to 300 ppm NO3‐N with the application of 15 kg/ha P. P rates beyond that necessary for maximum grain production did not further reduce the NO3‐N content of the forage. |
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