| In order to improve the seasonal planting system of alfalfa in Changjiang-Huaihe Area, an experiment was conducted at an agricultural science institute in Nanjing city of Jiangsu province from September2010to June2011. And a less fall dormancy alfalfa cultivar Victoria was used in this trail to study the effect of sowing dates and nitrogen application on growth characters, yield and its components, quality and photosynthetic characteristics of alfalfa. The results showed as follows:1. The effects of sowing dates and N-fertilizer application on growth characters showed that with the mode of sowing in autumn and twice-cutting in spring, different sowing dates had significant effects on growth characters. In the aspect of stem number, stem diameter, especially plant height, shoot number, as well as growth rate, the sowing date on September6and September18got the advantage over other sowing dates. The result also showed that nitrogen fertilizer had a limited influence on alfalfa growth, and the treatments with nitrogen application rates of120kg/hm2got the best performance. The regeneration process of Alfalfa requires more N-fertilizer, so fertilization in stage can both increase the amount of nitrogen utilization and promote the growth of alfalfa.2. Sowing dates and N-fertilizer had significant effects on FMY and DMY of alfalfa at different cutting time. The total dry matter yield had reduced from1.88×103g/m2to0.77×103g/m2with the sowing date delayed. Growth characters of alfalfa were increased significantly with N application. Among different nitrogen treatments, alfalfa yield in descending order, followed by N120> N180> N60. In which the total dry matter yield in N120treatment was higher than N60and N180treatments,8.89%and3.52%respectively. There was a positive interaction effect of sowing dates and N-fertilizer application on alfalfa yield, and the treatment with120kgN/hm2and sowing date of September6treatment was the optimal combination, in which the forage yield was2.02×103g/m2.3. Sowing dates had significant effects on CP and ADF content, but less effects on IVDMD and NDF content. In general, the content of crude proteins was increased, and the content of ADF was decreased with the sowing date delayed. Compared with other sowing dates, September6treatment had the highest CP content which was20.75%at first and19.35%at second cutting time. The treatments with nitrogen application rates of120kg/hm2can improve the CP, IVDMD content and decrease ADF content of alfalfa at fist cutting time. However, it had less affect on them at second cutting time and NDF at both twice cutting times.4. By measuring the photosynthesis of alfalfa at different growth stage, founding that the rate of dry matter was "S" shaped curve, and diurnal changes of photosynthetic rate showed a single peak curve with the peak value appearing around ten o’clock. Daily changing trend in Pn was completely the same as Gs and Tr, but Ci had the opposite trend. The maximum photosynthetic rate was reached at120kg N/hm2, which was1.68umolCO2·m-2s-1and1.2umolCO2-.m-2s-1higher than60kgN/hm2and180kgN/hm2treatments, respectively. Besides, the transpiration rate, stomatal conductance and intercellular CO2concentration at120kg N/hm2were slightly above the other two treatments as well.5. All results above revealed that, plant height, shoot number and crop growth rate were important factors to affect dry matter yield, which would be the target characters of alfalfa for seasonal utilization. Therefore, selection for less fall dormancy alfalfa cultivars with target characters in conjunction with agronomic and management measures could contribute greater biomass in a short-time. |
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