SEEDLING VIGOR AND NITROGEN USE EFFICIENCY OF MOROCCAN WHEAT AS INFLUENCED BY LEVEL OF SOIL-NITROGEN

One of the characteristics that can help wheat (Triticum aestivum L.) plants escape late season drought in the semiarid areas of Morocco is early stand establishment and adequate vigor. Little is known about th e effect of nitrogen (N) on early seedling vigor in wheat. The objecti ve of this study was to determine how N supply affects early root and shoot growth, N partitioning between the two parts and N use efficienc y of seedlings. To reach this objective, three spring wheat cultivars were grown in pots in a growth chamber under N conditions which were l ow, adequate and high. Data showed that optimum N rates increased shoo t and root growth but high N concentrations reduced their dry matter a ccumulation and inhibited root elongation. The cultivars tested behave d differently. 'Nesma', an older cultivar, produced 60% more dry matte r and accumulated 93% more N in the shoot and root than the newer cult ivars 'Merchouch 8' and 'Saada'. Because of its high N uptake, 'Nesma' probably reduced soil N concentration at the root zone and avoided th e negative effect of high N concentration on root growth. Although, 'N esma' performed better and produced more dry matter, it used N less ef ficiently than the other two cultivars. From this study, we can conclu de that use of optimum N rates at time of seeding will result in quick er establishment and higher vigor of wheat seedlings. However, excessi ve N supply may retard seedling growth. The cultivars that produce mor e seedling dry matter with greater N accumulation are not necessarily the ones that use N more efficiently.