EFFECT OF NITROGEN SUPPLY ON THE SEED SET OF SPRING WHEAT AND BARLEY

Abstract

Applications of NO3-N increased seed set of wheat grown under hot, moist conditions. An attempt was made to determine whether this improvement in seed set was due to improvement in plant nutrition or to NO3 poising the soil Eh above that at which phytotoxic ethylene is produced. Two pot experiments were carried out in a controlled environment chamber at diurnal temperatures 27/12 °C and slightly above field capacity. NO3-N or NH4-N with N-Serve ® were applied to Manitou wheat at rates of 45, 90, 135, and 180 kg N/ha in the first experiment, and to Manitou wheat and Conquest barley at rates of 23, 45, 90, 180 and 360 kg N/ha in the second. N-Serve successfully maintained the nitrogen in the NH4 form throughout the experiment. In both experiments, the seed set of the primary and secondary florets of wheat was directly proportional to the NO3-N rate. Wheat plants fed NH4-N exhibited significantly higher seed set than the NO3-N-fed plants at the low nitrogen rates. Seed set of lateral spikelets of barley was unaffected by rate, but the NH4-N-fed plants tended to produce slightly higher seed set. Ethylene was not detected in any of the soils. Since NH4-N corrected the seed set problem even at low levels of nitrogen, it was concluded that poor nitrogen nutrition and not the production of soil ethylene was responsible for poor seed set of wheat.