EFFECT OF N SOURCE, AND RATE OF N, P AND K ON THE AMMONIUM, AMINO, AND AMIDE NITROGEN LEVELS IN VEGETATIVE TISSUE OF BARLEY GROWN IN HYDROPONIC CULTURE

Vegetative tissue of barley (Hordeum distichon L.) cultured on 100 ppm ammonium-N contained a high level of ammonium-N and showed severe toxicity symptoms and markedly reduced yield, particularly when associated with the low (10 ppm) K rate. When K supply was increased to 100 ppm, the ammonium level decreased significantly although the concentration was still much higher than that in tissue supplied with 100 ppm of N from either ammonium-nitrate or nitrate source. Insufficient K supply also resulted in accumulation of amino- and amide-N in the tissue, the highest proportion of the water-soluble N fraction occurring as amino-N. The incorporation of ammonia into amide-N as a main detoxication process failed to explain the decrease of ammonium level in barley tissue supplied with an increasing rate of K. In general, the effect of P on the ammonium-, amino-, or amide-N level was not as large as that of K. Increasing the rate of P from 10 to 100 ppm caused an increase in the ammonium concentration in plants supplied with 100 ppm ammonium-N.