NITROGEN-UTILIZATION IN N-LIMITED BARLEY DURING VEGETATIVE AND GENERATIVE GROWTH .2. METHOD FOR MONITORING GENERATIVE GROWTH AND DEVELOPMENT IN SOLUTION CULTURE

Growth of barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum) under N-limitation was investigated in solution culture, with special emphasis on the generative growth stage. Three different regimes for limiting nitrate-N availability while keeping other elements in surplus were employed. In the 'high, decreasing nitrogen' (HN) treatment, the relative nitrogen addition rate (RA) was maintained at 0.08 d-1 until the ears started to develop and was then decreased stepwise to, finally, RA 0.005 d-1. In the 'low, decreasing nitrogen' (LN) treatment, plants received 45% of the nitrogen added in HN. In the 'constant nitrogen' (CN) treatment, RA was held constant at 0.0375 d-1. Cumulative nitrogen additions at termination of the experiment (day 147 after sowing) were 192, 179 and 87 mg plant-1 for HN, CN, and LN cultures, respectively. Nitrogen availability limited nitrogen acquisition in all treatments except in the CN culture at plant ages above 110 d. Stepwise decrease of RA largely synchronized transitions in developmental stages in the different cultivars and nitrogen regimes (HN and LN), and eventually yielded plants that were close to completing their life cycle. Normal maturation was not obtained in the CN treatment. The HN and LN treatments were used for formal analysis of post-anthesis growth. A sigmoid function was fitted to growth data and from this, organ weights and nitrogen concentrations at maturity (defined as cessation of growth) were derived. The two modern cultivars, Golf and Mette, clearly outperformed the more primitive cv. Laevigatum in terms of allocation of nitrogen to ears, particularly in the LN culture. The stepwise decrease of RA appears suitable for studies of post-anthesis growth and nitrogen relations in barley, with regard to both genotypic variation and variation caused by differences in cumulative amounts of nitrogen added.