Critical Nitrogen Supply On Nitrogen Uptake and Utilization of Covered and Hulless Oats.

Nitrogen uptake and utilization in hulless and covered oat (Avena sativa L.) are not well documented. A greenhouse study was conducted to determine the critical timing of N supply on the growth, N uptake and partitioning using an ¹⁵N labeling approach. Plants grown in plastic pots were subjected to 5 N fertilization regimes: T₁ – Control, N supply from seedling to physiological maturity (PM); T₂ - N supply from seedling to flag leaf; T₃ - N supply from flag leaf to PM; T₄ - N supply from seedling to heading; and T₅ - N supply from heading to PM. Leaf chlorophyll content, plant dry matter (DM), and N uptake and accumulation were measured. Total plant DM was 21% greater for naked ‘VAO-2’ than for covered ‘Prescott’, while both genotypes produced similar grain yields. Varietal differences in total plant N were significant (P < 0.05) with average of 18% higher N content for VAO-2, but most of its accumulated N was in the vegetative components. For both varieties, N supply was more critical before heading than thereafter. Compared to the control, restriction of N supply from seedling to flag leaf stage significantly reduced spikelet number (28%) and grain yield (26%). Withholding N supply until heading reduced yield by up to 65% and N uptake by 75%. There was no yield reduction when N was withheld from flag leaf or heading to PM. Withholding N supply till FL increased ¹⁵N in the grain by 29.6%. For VAO-2, 31.2% of the total ¹⁵N was partitioned to the grain in T₃, compared to only 12.9% in T₁; while for Prescott, there was 11.4% more grain ¹⁵N in T₃ than in T_1.