Effect of nitrogen rates on growth characteristics, yield and quality of autumn- sown sugar beet

In order to evaluate the effect of different N rates on yield components, the proportions of each part of the sugar beet plant such as leaf number, leaf area index, canopy expansion rate, and N uptake to total dry matter, were evaluated in autumn planting of 2004-2005 at Safiabad Agricultural Research Center, Dezful, Iran. Five rates of N fertilizer including 0, 60, 120, 180 and 240 kg/ha and two monogerm cultivars Shirin and Rasoul were evaluated in factorial experiment based on randomized complete block design with four replications. In terms of quantitative and qualitative characteristics, significant differences were observed between two years. In the first year of the experiment, N level had no significant effect on root yield, and both cultivars were placed in one group (average root yield of 93 t/ha), however, sugar percentage was influenced and the maximum value (13.7%) achieved in zero N rate. In the second year, root yield was influenced significantly by N rate and the maximum yield (80.9 t/ha) was achieved at 240 kg/ha N treatment, while sugar percentage was not influenced. In both years, no significant difference was observed among culti-vars for quantitative and qualitative traits. With further N application, the proportion of total biomass increased in petiole and crown and decreased in root, with no influence on leaf dry matter. N rates showed no significant difference in terms of leaf num-ber, leaf area index and complete canopy expansion in the first year of the experiment, whereas, in the second year, significant differences were observed among the treatments, so that increased N rate resulted in increaesed leaf number, leaf area index and the rate of complete canopy expansion. N treatments in the first year had no significant effect on N concentration in plant organs and the total rate of N taken up by the plant was 574 kg/ha. In the second year, N treatments influenced the rate of N uptake from the soil and the rate of N taken up at 0 and 240 kg/ha N fertilizer levels were 186 and 351 kg/ha, respectively.