EFFECTS OF NITROGEN SUPPLY ON GROWTH AND NITROGEN UPTAKE BY MISCANTHUS-SINENSIS DURING ESTABLISHMENT

The effect of nitrogen (N) supply on growth and N uptake of Miscanthus sinensis during the establishment was determined. Seven different N a ddition regimes were compared in a nutrient solution experiment. In th e treatments N111 (severe deficient), N222 (moderate deficient), N333 and N444 (optimal for maximum growth) different N concentration ranges were held constant during the entire growing season. In the treatment s N144, N414 and N441 plants were subjected to low (1) N concentration in one of three experimental periods, whereas the N concentration was high (4) in the other two periods. Depending on the N demand of the p lants, N concentrations were adjusted to 250-5000 mu M (N1), 500-1000 mu M (N2), 1250-2500 mu M (N3) and 2500-5000 mu M (N4) when the N conc entration in the N222 treatment had dropped below 100 mu M. The other elements in the solution were replenished according to the estimated e lement ratios in the plants. As a reference the potassium concentratio n in the solution was measured regularly. During the first year plants with a non-limited N supply (N444) produced new tillers and increased the length of individual tillers until the end of the growing season. This resulted in a 48% shoot dry matter increase late in the growing season between August and October and a linear increase of cumulative N uptake between July and October. Limited N supply during the entire growing season (N111, N222) caused lower shoot yields but rhizome and particularly root dry weights were less affected. Significant final yi eld losses were also observed when the N supply was limited only durin g the first 7 weeks of growth (N144). By contrast, final shoot yield w as hardly affected when the plants were exposed to limited N supply ov er a period of > weeks at the end of the growing season (N441). In the second year regrowth of shoots in spring was affected by the previous year's N supply, since five weeks after the beginning of regrowth, sh oot dry matter was significantly positively correlated with N contents in rhizomes and shoots in the previous October. Our results show, tha t N supply at the beginning of the growing season has a major effect o n final yield in the first establishment year of M. sinensis. However, from the second year on, the capacity of N reserves in rhizomes and r oots affects spring growth much more than current N supply.