| The experiment used Yudou No.1 and Zhechun No.3 as experimental material was carried out on 2013 May 22 to August 23 at the experimental farm of Southwest University. With randomized block experiment, the experiment adopted a total of three density levels and two nitrogen treatment, research on soybean growth and development at different reproductive period and micro environmental factors under the specific environment of high temperature in Chongqing, the results showed that:Density treatment had no significant effects on plant height, stem diameter and the number of branches in seeding stage; Nitrogen treatment had no significant effect on plant height and stem diameter, and had significant influence on the number of branches, the number of branches under nitrogen treatment of soybean Yudou No.1 and Zhechun No.3 were 58%, 22% higher than non nitrogen treatment respectively. During the full bloom stage, the stem diameter, branch number were significantly decreased with the increase of the density, the plant height increased with the increase of the density; The plant height, stem diameter and branch number of Yudou No.1 and Zhechun No.3 under nitrogen treatment were significantly higher than those under non nitrogen treatment; The plant height of Yudou No.1 treated by nitrogen treatment under LD、MD、HD were 0.3%, 4.6%, 9.6% higher than those under non nitrogen treatment while the percent of Zhechun No.3 were 3.1%, 7.9%, 10%; The stem diameter of Yudou No.1 treated by nitrogen treatment under LD、MD、HD were 19.4%, 14.4%, 16.7% higher than those under non nitrogen treatment while the percent of Zhechun No.3 were 18.2%, 26.2%, 23.5%; Comparison among cultivars showed that the plant height of Yudou No.1 was higher than Zhechun No.3, and the stem diameter and branch number of Zhechun No.3 was higher than that of Yudou No.1. In seed filling stage, the above indexes showed similar trends between different density and nitrogen treatments, and still achieve significant level.In seedling stage, the effects of different planting density on root growth and nitrogen fixation ability of soybean were not significant; The root length, root nodule number, dry weight, hemoglobin content, and total nitrogen fixing enzyme activity of soybean were inhibited under nitrogen application, the reduction range of the 2 varieties was 9%-17%, 16%-36%, 11%-22%, 26%-30%, 10%-13%, respectively; Nitrogen treatment on soybean root average diameter, root volume, root surface area has a significant role in promoting, the increase rate was 4%- 16%. 20%-41%, 15%-25%;There was a significant positive correlation between nodule total nitrogenase activity and nodule hemoglobin, nodule number, nodule dry matter accumulation, and showed a significant negative correlation with average root diameter, root surface area, root volume. During the period of full bloom and seed filling stage, the root growth and nitrogen fixation ability decreased with the increase of density; Nitrogen fertilization significantly promoted the growth of soybean root and the ability of nitrogen fixation; Nodule total nitrogenase activity and root length, root surface area, root average diameter, root volume, nodule dry weight, nodule hemoglobin was positively correlated.The root shoot ratio of the soybean decreased gradually with the growth stage pushback. In seeding stage, there’s no significant difference for the dry matter accumulation and root shoot ratio of soybean between different densities; The root shoot ratio of Yudou No.1 under nitrogen treatment was 7.6% higher than that under non nitrogen treatment while the root shoot ratio of Zhechun No.3 under nitrogen treatment was 8% lower than that under non nitrogen treatment. In full bloom and seed filling stage, the dry matter accumulation of underground and aboveground decreased with the increase of density while the root shoot ratio increased with density increasing; The root shoot ratio of Yudou No.1 and Zhechun No.3 were significantly decreased compared with those under non nitrogen treatment.The leaf area index grew rapidly from seeding stage to full bloom stage while grew slowly from full bloom stage to seed filling stage, which appeared an apparent “S” growth curve. The photosynthetic rate, transpiration rate, stomatal conductance and chlorophyll content of soybean showed a single peak trend which increased firstly and then decreased with the growth stage pushback. In seeding stage, density and nitrogen treatment had no significant effects on photosynthetic rate, transpiration rateand stomatal conductance; The chlorophyll content of Yudou No.1 and Zhechun No.3 were 3.4%, 3.6% higher than those of non nitrogen treatment respectively. The leaf area index of high density population under nitrogen treatment was significantly higher than that of medium density and low density, and the leaf area index of the same variety had no significant difference under non nitrogen treatment; There were significantly positively correlated between photosynthetic rate and transpiration rate, stomatal conductance, chlorophyll content, leaf area index, stem diameter, branch number while the photosynthetic rate and the plant height was negatively correlated, but not significant. During the full bloom stage, the photosynthetic rate, transpiration rate, stomatal conductance and chlorophyll content were significantly decreased with the increase of the density, the leaf area index increased with the increase of the density; Nitrogen fertilization could increase the leaf area index and chlorophyll content of soybean plants, and then increase the photosynthetic rate of soybean leaves of 2 varieties of soybean, its growth rate was 5.8%-9.4%, 2.8%-7.2%, 4.1%-7.9%, respectively; The leaf photosynthetic rate and stomatal conduction, chlorophyll content was significantly positively correlated while there’s no significant positive correlation between the leaf photosynthetic rate and transpiration rate, stem diameter, branch number of soybean; The leaf photosynthetic rate and soybean plant height, leaf area index was not significantly negative correlated. In seed filling stage, the indexes above showed similar trends between different treatments, and still achieve significant level; Comparison among cultivars showed that the chlorophyll content and photosynthetic rate of Yudou No.1 was higher than Zhechun No.3, and the leaf area index of Zhechun No.3 was higher than that of Yudou No.1.Different density and nitrogen treatments in Soybean group light intensity distribution and transmittance showed a trend of increasing from the bottom of the canopy to the top of the canopy. As for the light strength and light transmittance rate, difference among different treatment mainly concentrated in the middle layer, and decreased with the increase of the density. Canopy light distribution and light transmission rate with nitrogen treatment is less than non-nitrogen treatment. Relative humidity in soybean group and leaf temperature increased with the increase of the density, relative humidity in soybean Population and leaf temperature with nitrogen treatment is higher than non-nitrogen treatment. The change of the temperature in soybean group is opposite to the relative humidity in soybean group and the temperature of the blade. The temperature in soybean population and relative humidity, leaf temperature were negatively correlated at each of the three different growth stage while there’s extremely significant positive correlation between relative humidity and leaf temperature. The leaf temperature and relative humidity were negatively correlated with the light transmittance of each layer. The photosynthetic rate of soybean leaves was not significantly positively correlated with the light and effective radiation intensity at the middle and upper layers of soybean, and significantly positively correlated with the population temperature; the photosynthetic rate and relative humidity were not significantly negatively correlated while the leaf temperature showed significant negative correlation with the photosynthetic rate.The number of pods per plant, single plant grain number and 100-grain heavy decreased with the density increased, and the biological yield increased with the density increased. The economic yield and economic coefficient increased first and then decreased with the increase of density, and reached the peak value at the medium density level. Nitrogen treatment increased the pod number per plant, grain number per plant, 100 seed weight and economic yield. The biological yield under nitrogen treatment increased with the density increased, the growth rate of economic yield reached the maximum at the level of medium density. Soybean yield per plant was positively related to photosynthetic rate, chlorophyll content, stem diameter, branch number, root shoot ratio, root length, root diameter, root volume, root table area, nodule hemoglobin content, total nodule nitrogenase activity, grain number per plant, pod number, 100 grain weight while there were an negative correlation between yield per plant and leaf area index, plant height at full bloom stage.In this experiment, Yudou No.1 and Zhechun No. 3 in medium density(16*104 plants/hm~2) density and applied nitrogen 20kg/hm~2, the yield reached maximum, respectively 2549kg/ hm~2, 2514 kg /hm~2. |
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