Timing and level of nitrogen supply affect nitrogen distribution and recovery in two contrasting oat genotypes

Human diets containing oat ( Avena sativa L.) grain offer health benefits resulting in an emerging interest in oat improvement. Information on nitrogen (N) uptake, distribution, and use efficiency (NUE) in oat is limited. A greenhouse study using a 15 N‐labeling technique was conducted to determine the responses of two contrasting oat genotypes to timing and level of N deficiency. Hulled oat cv. Prescott and hulless cv. AC Gehl were grown in soil‐mix pot culture with five N treatments applied through modified Hoagland solutions. Differences in 15 N accumulation, 15 N distribution, plant N originating from the labeled source, and NUE between the contrasting cultivars, were examined for each N strategy. Level of N deficiency and timing of N supply of 15 NH 4 15 NO 3 greatly affected 15 N distribution, the origins of plant N, and the amount of 15 N recovered in the plant. When N was supplied from seedling emergence to maturity (T 1 ), AC Gehl accumulated 61% more 15 N in the shoots, but 46% less 15 N in the grain than Prescott (0.43 vs. 0.80 mg plant –1 ), indicating that AC Gehl was less effective in producing grain yield than Prescott as AC Gehl produced greater total dry matter (DM). Withholding N supply until flag‐leaf stage (FL) increased 15 N in the grain of both cultivars by 29.6%, resulting in the highest NUE. In most cases, there were larger portions of plant N derived from the labeled source for AC Gehl than for Prescott. Our results suggest that greater NUE in the newly released AC Gehl was associated with N accumulation in the vegetative tissues. It is concluded that genotype improvement of hulless oat should be focused on enhancing N‐translocation efficiency.