EFFECTS OF N FERTILIZER ON TOTAL-N AND NO3-N CONTENT OF SIX GRASS SPECIES

Total-N and NO3-N content of forage were determined for six grass species — timothy (Phleum pratense L.); crested wheatgrass (Agropyron cristatum (L.) Gaertn.); intermediate wheatgrass (Agropyron intermedium (Host) Beauv.); stream-bank wheatgrass (Agropyron riparium Scribn. and Smith); bromegrass (Bromus inermis Leyss.); and Russian wild ryegrass (Elymus junceus Fisch.). The grasses were fertilized with ammonium nitrate in early spring and were sampled at four levels of applied N — 0, 185, 550, and 940 kg/ha — and at three stages of maturity — early heading, anthesis, and seed-set. Total-N and NO3-N increased in all grasses with increasing levels of N fertilizer; Russian wild ryegrass showed the greatest increase and timothy the least. As maturity advanced, total-N content decreased. Total-N contents were similar in crested wheatgrass, intermediate wheatgrass, and streambank wheatgrass. As maturity advanced, the NO3-N content of fertilized timothy, crested wheatgrass, and bromegrass decreased while that of Russian wild ryegrass increased. The NO3-N content of intermediate wheatgrass and of stream-bank wheatgrass was highest at anthesis. At 0 and 185 kg N/ha, the NO3-N content was well below the lethal level for ruminants, but at the two higher N fertilizer levels it often exceeded the lethal level. Timothy can be considered a low, Russian wild ryegrass a very high, and the other four grasses high, NO3-N accumulators.