Response of Nitrogen Uptake and Partitioning to Critical Nitrogen Supply in Oat Cultivars

Nitrogen uptake and partitioning in 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. Plants grown in plastic pots were subjected to five N fertilization regimes: (i) control, N supply from seedling to physiological maturity (PM); (ii) N supply from seedling to flag leaf; (iii) N supply from flag leaf to PM; (iv) N supply from seedling to heading; and (v) 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 with 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%. No yield reduction occurred when N was withheld from flag leaf or heading to PM. Although naked VAO‐2 accumulated more N than Prescott under the same conditions, partitioning of N to the grain in VAO‐2 was less efficient.