EFFECTS OF VARYING NITROGEN SUPPLY AT DIFFERENT GROWTH-STAGES ON NITROGEN UPTAKE AND NITROGEN PARTITIONING EFFICIENCY IN 2 WHEAT CULTIVARS

The objective of this work was to determine the effect of N availability upon N uptake and nitrogen partitioning efficiency and its relationship with %N in the grain in two wheat cultivars, differing in their grain protein content. Plants were grown in a nutrient solution with 2 nitrogen levels, 200 ppm (H) and 40 ppm (L). Four treatments were imposed: HH, HL, LH and LL. Nutrient solution exchange was done at maximum floret number. Plants were harvested at terminal spikelet stage, maximum floret number, 10 days after anthesis and maturity. Nitrogen content, N uptake and N distribution at maturity were significantly affected by N supply. Nitrogen content in the grain was similar in both cultivars, but varied significantly between treatments and decreased as follows: LH; HH; LL and HL. In both cultivars a low leaf %N was observed in HL 10 days after anthesis, which suggest early N utilization and its premature depletion, resulting in a low %N in the grain. Total %N in the plant, for both cultivars was higher in HH and LH than other treatments. When N availability was high during the whole crop cycle (HH), N distribution to the ear was improved. It is concluded that late N availability is necessary to achieve high %N in the grain. On the other hand if high and initial N availability is not maintained, %N in the grain decreased in a significant way. © 1990 Kluwer Academic Publishers.