| A specific line of flue-cured tobacco, F1-35, was bred and released by ourselves in Longyan tobacco production area. The field experiment was conducted to study the effects of nitrogen application rate, planting density and its manner on leaf area index (LAI), field microclimate, agronomic straits, yield components, and chemical composition in a new fragrance style line of flue-cured tobacco, F1-35. For this purpose, the parameters such as leaf area index of tobacco, illumination intensity and vertical air temperature of trial field were determined, and the data comparison was made, in turn to further determine the optimal planting density and nitrogen application rate for the incorporation into theoretical basis of high yield and good quality cultivation techniques, thereby to fully manifest the yield and quality potential of the newly released line of flue-cured tobacco, F 1-35, The results were as follows:1. Experiment of nitrogen application rate:variance analysis showed that at rosette, vigorous, and flattened stages, leaf area index, plant height, and leaf number available in tobacco F1-35 were significantly different under different nitrogen treatments, showing that they were decreased all like the tendency of B4> B3> B2> B1. At vigorous and flattened stages of tobacco, the light intensity was significantly decreased in middle-lower parts of plant and plant or row and row as nitrogen application rate was increased. The vertical air temperature changes in tobacco field was different from the treatments of nitrogen application rate, detecting time and vertical height. It was found that the vertical air temperature in the field was increased with the increase of nitrogen application rates at 8:00 and 18:00. Reverse was true at 12:00 and 14:00. It was also found that at 8:00-12:00, the vertical air temperature in the field tended to increase with the increase of vertical height. The maximum temperature in the field was detected at 14:00, and appeared at the active surfaces (65cm) outside the canopy of tobacco under all N treatments, and the maximum air temperature in the field of tobacco was the highest under B1 treatment, followed by B2, B3, and B4 treatments.The results of the leaf chemical composition analysis from the comparison test of different nitrogen application treatments showed that increasing tendency was found in the contents of total sugar, reducing sugar and total potassium in the leaves of tobacco F1-35 with increase of N supplies in the range of 75～105kg/hm2 treatments. However, the total sugar and reducing sugar contents in the leaves of tobacco F1-35 were decreased at N supply of 120 kg/hm2. Comparison test of N supplies showed that the contents of the total sugar and reducing sugar in the leaves of tobacco were B3> B2> B1> B4 treatment. It was also found that the contents of nicotine, and total nitrogen in the leaves of tobacco were increased with N supply increasing in the range of 75～120kg/hm2 treatments, showing B4> B3> B2> B1 in order.The results also showed B4 treatment, highest yield, but lower quality. At the treatments of B1 and B2, the growth of F1-35 tobacco plants turned to be weak, and this led to short plant, small leaves, low dry matter weight and earlier flowering in some tobacco plants due to reduced N supply. At B3 of N supply, the growth of the tobacco plants turned to be better, the leaves of the crop plants can get to mature and yellow color, the plant height was 108.0 cm, the number of leaves was 18.1, the proportion of top and middle grades of tobacco leaf reached to 93.0% and the yield and its economic value were 2320kg/hm2 and 38605 yuan/hm2 under this treatment. It was also found that under B3 treatment, the quality of the tobacco leaves was also better, showing that 31.8% in total sugar content of tobacco leaves,13.65 in ratio of sugar to nicotine contents, a moderate nicotine content and a coordinated internal chemical composition with faint fragrant style in tobacco leaves, suggesting that N supply at 105 kg/hm2 can be recommended in practical use, especially at the middle grade of soil fertility.2. Experiment of planting density:variance analysis showed that the leaf area index was significant at rosette, vigorous, and flattened stages of tobacco plants under the treatments of different plant densities with 4 levels, the leaf area index was decreased with the plant spacing increasing (i.e. with the plant density decreasing) within the range of 45～55cm.Further analysis showed that the light intensity between plant and plant, or row and row were significant in the different treatments of plant density, showing increasing tendency in A4> A2> A3> Al. The changes in the vertical air temperature in tobacco field were different from the plant spacing at the vigorous and flattened stages of tobacco plants. The vertical air temperature in tobacco field was increased with plant spacing decreasing, and it was the highest at 8:00 and 18:00 in A1 treatment. The vertical air temperature was increased with plant spacing increasing and it was increased with the testing height increasing in the field at 8:00 and 12:00. The maximum temperature appeared at the active surfaces (65cm) outside the canopy of tobacco plants under all treatments of plant densities at 14:00, and the vertical air temperature was the highest detected in A4 treatment followed by A3,A2,and A1 treatments. The results also showed that the effects of different plant densities on the contents of total sugar and reducing sugar in the leaves of tobacco F1-35 were A2>A3>A1>A4 in order, and the effects on the contents of nicotine and total nitrogen in tobacco leaves were A4>A1>A2> A3. It was also found that the growth of tobacco plants was better in Al treatment, showing that the plant was higher, and the leaf area index was the largest, thereby leading to decreased light intensity in the field, and increased senescence of leaves in lower parts of tobacco plants. This in turn resulted in reduced yield and its quality with a poor coordination of the internal chemical composition. The present study also suggested that A4 treatment, the growth of tobacco plant was slower in early stage, but turn to be fast in late stage, performing that the upper leaves including the first and second leaves from the top were larger and thicker due to higher uptake of N elements from applied fertilizer in soil, consequently reduced yield and its output under A4 treatment than any other treatments, the similar result was also observed in A3 treatment. The result suggested that plant spacing should be appropriate controlled in the 45-50cm,A2 treatment can be considered as a recommended measure in practical use. The treatment can receive a good result including optimal light and temperature condition in the field, and higher contents of total sugar (31.6%) and ratio of sugar to nicotine contents (13.67)... |
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