EFFECTS OF NITROGEN SUPPLY ON THE GROWTH, YIELD COMPONENTS, AND DISTRIBUTION OF NITROGEN IN LINOLA

A glasshouse study was undertaken to evaluate the effects of nitrogen (N) supply on the vegetative growth, yield components and the distribution of N in Linola(TM) (low linolenic acid linseed). Nitrogen stress reduced the number of tillers (secondary basal stems) and fruiting branches per plant. Severely N-stressed plants produced only 20% of the dry matter of plants provided with an adequate N supply. The dry-matter harvest index of the shoot was negatively related to N supply. The main effect of N stress on yield components was a reduction in the number of capsules per plant; seed number per capsule and the 1000-seed weight were not altered by N stress. Nitrogen stress reduced seed and oil yields per plant through its effect on capsule production. Seed yield and seed oil percentage were reduced by excessively high levels of N supply. Concentrations of total N were highest in leaves and lowest in roots. There was little change in seed N concentrations in relation to N supply. Concentrations of nitrate-N (NO3-N) were higher in stems than leaves, and concentrations of both NO3-N and total N decreased in vegetative organs as the plants aged, irrespective of N supply. There were biphasic relationships between concentrations of reduced N and NO3-N in young plants. Leaves had the greatest proportion of the total amount of N in young plants, but seeds contained the major proportion in mature plants. Shoot N harvest indices ranged from 30 to 70%, and were inversely related to N supply. Depending on the N supply, plants accumulated from 57 to 76% of their final N content after flowering. Remobilization of N from senescing leaves ranged from 70 to 87%, and was highest for the most N-stressed plants. Nitrogen remobilization from the leaf canopy was estimated to provide only about 10% of the N accumulated by seeds. It was concluded that an adequate supply of N is required throughout the growth of a Linola crop, in the pre- flowering phase to support tiller and fruiting branch production, and post-flowering to sustain seed development.