| The split blot design was used for the experiment with sugarcane cultivars (GT 11 and GXB9) as the main plots, and nitrogen levels [application of 0 kg/ha (NO),150 kg /ha (N150),300 kg/ha (N300) urea, respectively] as the sub-plots. Both field and pot experiments were conducted respectively to study the nitrogen fixation ability of different sugarcane varieties, the effects of different nitrogen levels on the dry matter accumulation and distribution, nitrogen accumulation and utilization, agronomic traits, yield and quality in two sugarcane cultivars with different nitrogen fixation ability, in order to provide a reference for rational application of nitrogen fertilizer in sugarcane production. The main results are as follows.(1) The tillering rate and leaf chlorophyll relative content (SPAD) in sugarcane increased with the increase of nitrogen level, while the germination rate and growth rate were opposite. Under high nitrogen fertilization level, the germination rate was higher in GT11than GXB9, but the tillering rate was higher in GXB9 than GT11. At early growth stage, the growth rate was higher in GT11than GXB9. The SPAD was decreasing with the growth of sugarcane, and it was higher in GT11 than GXB9 at NO level.(2) Under 150 kg/ha urea level, the yield and yield components showed better in GXB9 than GT11. The levels of nitrogen fertilization had little effect on the quality of GXB9, but had a significant influence on the quality of GT11. The quality of GT11 showed the best at low nitrogen level, but decreased with the increase of nitrogen fertilization rates.(3) The highest plant biomass of variety GXB9 was found in the middle nitrogen level (150 kg/ha urea) treatment, but that of GT11 was found in high nitrogen level (300 kg/ha urea) treatment, and the total plant biomass was higher in GTl 1 that GXB9. At tillering and elongating stages, the dry weights of root, stem and leaf were the highest in the medium nitrogen treatment for both sugarcane cultivars, and the differences were very significant in different nitrogen levels. At mature stage, the biomass was the highest at high nitrogen level for the roots and leaves of both sugarcane cultivars. As the plant growth processed, the biomass allocation rate in root declined continuously, while that in stem and leaf increased and decreased respectively at elongation stage, and decreased and increased respectively at mature stage.(4) The total nitrogen accumulation in plant increased with the increase of the nitrogen fertilization level, and it showed a curve increase in GXB9, but a straight line in GT11. The nitrogen accumulation showed the highest in leaf, then stem, and the lowest in root. At processing mature stage, the nitrogen accumulation in stem of GTl 1 was higher in the low nitrogen level treatemt than the medium nitrogen treatment, for sugarcane variety GXB9, however, it was significantly different between the high and medium nitrogen treatments. The nitrogen accumulation in root was changed with sugarcane variety and growth stage.(5) Distribution of nitrogen from fertilizer was similar to that of the total nitrogen, which showed leaf> stem> root, and, the proportion in leaf increased while in root and stem decreased with growth regardless of varieties.(6) The total nitrogen utilization rate of sugarcane showed the lowest at elongation stage and the highest at mature stage, and that of root and stem showed the highest at elongation stage. With the plant growth, the proportion in leaf increased while that in root and stem decreased. Leaf showed the highest nitrogen utilization rate among the organs, stem the second, and root the lowest. The nitrogen utilization rates of whole plant, leaf and root all showed in the treatments N150> N300> N0, and that of stem was in two sugarcane cultivars, which showed higher at tillering stage for GXB9 and at mature stage foe GT11, respectively. Nitrogen use efficiency in different organs of GXB9 was decreased with growth at medium nitrogen level. |
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