【Objective】 The aim of this study is to investigate the effect of weak light on the leaf structure and photosynthetic characteristics of northern and southern soybeans, and further to screen shade tolerant soybean varieties for maize-soybean relay intercropping. 【Method】 Ten soybean varieties were selected as materials, including five main varieties from the north and five main varieties from the south. Normal light and weak light were set to analyze the effects of weak light on plant growth, leaf structure, and photosynthetic characteristics when the third compound leaf of soybean was fully exposed （V4 stage）. Principal component analysis was used to evaluate the shade tolerance of soybean seedlings. 【Result】 A total of 10 soybean varieties were selected as materials, including 5 main varieties from the northern and southern regions. Normal light and weak light conditions were set to analyze the effects of weak light on plant growth, leaf structure, and photosynthetic characteristics of soybeans at the fully exposed third trifoliate leaf stage （V4 stage）. Principal component analysis was used to evaluate the shade tolerance of soybean seedlings.The results showed that under weak light conditions, soybeans exhibited varied physiological changes. To adapt to weak light conditions, the average plant height of both the northern and southern soybean varieties significantly increased by 101.19% and 125.04%, respectively. The average total leaf area decreased by 4.26% and 0.25%, respectively （P<0.05）. The leaf thickness of the northern and southern varieties decreased significantly by 15.62% and 36.18%, respectively. The palisade tissue thickness decreased by 19.53% and 34.26%, respectively, and the spongy tissue thickness decreased significantly by 17.02% and 25.74%, respectively. Both the stomatal density of the northern and southern soybeans decreased under weak light conditions. Specifically, the stomatal density of the northern and southern soybeans decreased by 35.56% and 26.34%, respectively, while the stomatal aperture decreased by 14.85% and 70.75%, respectively. The stomatal area of the northern soybeans significantly increased by 6.30%, while the southern soybeans showed a significant average decrease of 12.53%. Under weak light conditions, the decrease in P_n, G_s, and T_r in the northern varieties was significantly higher compared to the southern varieties, with an increase of 3.71%, 15.19% and 11.52%, respectively. The C_i of the northern soybeans decreased by 20.95%, while the southern soybeans showed an average increase of 8.63% under weak light conditions.Based on the principal component analysis, Jinyi 59 and Zheng 59 in the northern soybeans, and Nanong 88-48 and Nan 41 in the southern soybeans exhibited stronger shade tolerance, making them suitable for corn-soybean intercropping. 【Conclusion】 Different soybeans have different responses to weak light environment. In this experiment, the differences in response of northern and southern soybeans to weak light mainly lie in the stomatal structure and quantum transfer of Photosystem.

【Objective】 The effects of different shade degrees and light recovery on photosynthetic physiology of different soybean varieties were clarified, in order to provide theoretical reference for shade design of maize-soybean relay strip intercropping field and breeding of shade-tolerant soybean varieties. 【Method】 Two different shade-tolerant soybean materials were selected in this study： Nandou 12 （shade-tolerant） and Jiuyuehuang （shade-intolerant）. Four treatments were set up： S0 （normal light）, S1 （30% shading）, S2 （50% shading）, and S3 （70% shading ）, the effects of different shading degrees and light recovery on morphological traits, photosynthetic characteristics, antioxidant metabolism and osmotic adjustment substances of soybean were studied. 【Result】 The results showed that the stem diameter, leaf area, biomass, net photosynthetic rate, stomatal conductance and transpiration rate of the two soybean materials decreased significantly under shading, and decreased with the increase of shading degree. The main stem length and intercellular carbon dioxide concentration increased with the increase of shading degree. Compared with the S0, the SOD activities of Nandou 12 S1 and S2 treatments increased significantly by 20.4% and 43.6%, the POD activities of S2 and S3 treatments increased significantly by 14.71% and 25.61%, and the SOD activities of Jiuyuehuang S2 and S3 treatments increased significantly by 61.9 % and 43.19%. POD activity did not change significantly except that S1 decreased significantly. After light recovery, the stem diameter, biomass and photosynthetic parameters of the two soybean varieties were recovered in different degrees. In the second week after light recovery, the SOD activity of Nandou 12 was significantly higher than S0 only in S3 treatment, while that of Jiuyuehuang was higher than S0 in each treatment. In addition, the SS content of Nandou 12 in S1 and S2 treatments was higher than that of JS1 and JS2 in Jiuyuehuang, and the difference was significant. 【Conclusion】 The above results showed that shade stress could affect the morphology, photosynthetic characteristics, antioxidant metabolism and osmotic adjustment substances of soybean, but there were significant differences in the response of different varieties to different shade conditions. Because of its higher photosynthetic rate and smaller decrease in soluble sugar and soluble protein content, Nandou 12 has stronger shade resistance and faster response in the process of light recovery. The results of this study can provide a theoretical reference for the cultivation and selection of shade-tolerant soybean under maize-soybean relay strip intercropping.

【Objective】 The objective of this study is to create the ideal plant type of soybeans and maize, and thus to provide theoretical support for the application of synergistic chemical control technology in soybean-maize strip compound planting. 【Method】 In this experiment, the soybean-maize strip intercropping system was used as the object, and the two-factor split-plot experimental design was adopted. The effect of five plant growth regulators, namely PD（30% paclobutrazole·methylpiperium）, SD（30% uniconazole·methylpiperium）, PP333（15% paclobutrazole）, S3307 （5% uniconazole）, DPC（25% methylpiperidium）, on agronomic traits and yields of soybeans and maize, were studied under the two spraying stages T1 （soybean first flowering stage）, and T2 （soybean branching stage and first flowering stage）. 【Result】 With regard to agronomic traits, compared with CK, the plant heights of soybeans and maize treated with PD in T2 decreased by 34.30% and 5.03%, respectively. The soybean stem thickness treated with PD and the maize stem thickness treated with S3307 increased by 9.10% and 3.97%, respectively. The first internode length, average internode length and lodging rate of soybeans treated with PD decreased by 13.58%, 34.91% and 72.78%, respectively, and the number of branches increased by 97.33%. In terms of leaves, the leaf area indices of soybeans and maize decreased by 4.43% and 2.13% respectively after PD treatment in T2. The SPAD of the leaves of maize increased by 2.97%, while the SPAD of the leaves of soybeans treated with S3307 increased by 21.80%. In terms of yield, in T1, the valid number of soybeans treated with PD and PP333 and the grain number per plant of maize were higher than those per plant of CK8.20% and 2.56%, respectively, under the treatment of PD and PP333 and the yield of soybeans treated with SD increased by 22.10%. In T2, the grain number per plant and 100 grain weight of soybeans increased by 12.57% and 7.97% respectively, the 1 000 grain weight and yield of maize treated with SD and PD increased by 6.22% and 13.32%, respectively, and the system yield of PD treatment was the highest, with an increase of 14.50%. 【Conclusion】 Under the two spraying periods, the five plant growth regulators reduced the plant height of the two crops and the lodging rate of soybeans and increased the yield. In particular, the spraying of paclobutrazole·methylpiperium once at the branching stage and the first flowering stage of soybean can better reduce the height and control the overgrowth, and increase the system yield.

【Objective】 This paper was conducted to investigate the effects of different exogenous sucrose concentrations on photosynthetic physiological characteristics and yield of soybean under corn-soybean strip cropping. 【Method】 A two-factor split-zone design was used with shade-tolerant soybean "Nandou 25" and compact maize "Denghai 605" as materials. The main zone factors are the cropping patterns： strip intercropping（MS）, strip set（IS） and monocropping（SS）, and the secondary zone factors are the concentration of exogenous sucrose： 0% （CK）, 1.0% （T1） and 1.5% （T2）, with aims to investigate the effects of foliar spraying of exogenous sucrose on photosynthetic physiological characteristics and yield of soybean at flowering stage under the soybean-corn strip cropping pattern. 【Result】 During the R2 period, exogenous sucrose at T1 concentration significantly increased leaf area in the upper, middle and lower canopy of soybean by 28.55%, 22.97% and 70.22% in the IS mode compared to CK, and by 25.07%, 26.09% and 16.42% in the MS mode compared to CK, respectively. During the R4 period, in the middle layer of the MS model, soybean leaf P_n increased significantly by 33.87% and 45.02% in the T1 and T2 treatments, respectively, as compared to CK. In the SS model, T1 and T2 treatments significantly increased soybean leaf starch content in the upper and middle layers by 29.02% and 29.14%, respectively, as compared to CK; T1 and T2 treatments reduced the soluble sugar content of soybean leaves and promoted the transfer of soluble sugars from stems and leaves to pods at the later stage. The T1 and T2 treatments significantly increased the number of pods, grains per plant and yield of soybean IS model soybean by 42.50%, 31.35%, 28.34% and 43.78%, 38.50% and 33.79% respectively compared to CK; in MS mode, number of pods per plant, number of grains per plant and yield were significantly increased by 60.65%, 54.52%, 74.17% and 52.80%, 58.47% and 71.45% under T1 and T2 treatments, respectively, as compared to CK. In SS mode, number of pods per plant, number of grains per plant and yield were significantly decreased by 19.06%, 15.79% and 21.20% and 21.20%, 19.46% and 11.63%, respectively, under T1 and T2 treatments, as compared to CK, 11.50% and 21.20%, 19.46% and 11.63%, respectively. 【Conclusion】 The exogenous sucrose increased the chlorophyll content of soybean leaves, increased leaf area, increased photosynthetic rate, alleviated the low light stress caused by shade, improved photosynthetic characteristics, promoted soluble sugar production, starch synthesis and thus yield increase, and the best treatment was T1 in MS mode. Both T1 and T2 in the SS model resulted in lower yields.

【Objective】 This paper aims to clarify the configuration of high yield and high efficiency bandwidth and maize density of strip intercropping of fresh corn and fresh soybean in southwestern China. 【Method】 In this study, two fresh corn varieties with great difference in plant height were selected, and three fresh corn density levels of 37 500 ,45 000 ,52 500 plants/hm² were set under the bandwidth of 200 and 240 cm in 2018. In 2019, the density level was optimized by removing the lowest density and increasing 60 000 plants/hm². The effects of bandwidth and corn density on population yield and matter accumulation of different types of fresh corn and soybean strip intercropping were studied. 【Result】 With the increase of fresh corn density, the population yield increased at first and then decreased. Among them, the dwarf type intercropping population reached the maximum at 200 cm,52 500 plants/hm² and 240 cm,52 500 plant/hm², and the tall culm type intercropping population was at 200 cm,52 500 plants/hm² and 240 cm,45 000 plant/hm². With the increase of fresh corn density, the population matter accumulation and grain dry matter distribution ratio of fresh corn reached the highest at the density of 52 500 plants/hm². Under 200 cm bandwidth, the matter accumulation of tall culm type and dwarf type increased by 7.60% and 6.24% respectively, while under 240 cm bandwidth, the two varieties increased by 5.33% and 6.36%, respectively. The results of correlation analysis indicated that the effective panicle number of maize and soybean grain weight were the key factors to regulate population yield in dwarf population, while they were corn grain weight and soybean grain weight in high stalk population. 【Conclusion】 In this banded intercropping population, under two different bandwidths, the best density of fresh corn is 45 000~52 500 plant/hm². Under this density, the intercropping population increases material accumulation, distribution to grains, and ultimately increases population yield.

【Objective】 This study aims to uncover the fungal growth inhibition and control efficacy of the strain IRHB 47 from soybean rhizosphere on soybean root rot, and provide some references for the control of root rot.【Method】 Plate dual culture method, seed soaking wit bacterial suspension, and pot experiments were used for detecting the mycelial inhibition effects, application safety, disease control efficiency and environmental tolerance. Morphologial characteristics of colony combined with phylogenetic analysis based on 16S rDNA sequence were used for clarifying its taxonomy.【Result】 The strain IRHB 47 had the fungal growth inhibition effects on five Fusarium species causing soybean root rot including F. oxysporum,F. graminearum, F. asiaticum, F. solani and F. fujikuroi with the inhibition rate of 51.04%-70.40%. And meanwhile it also displayed good antagonistism against nine agricultural pathogenic fungi like Botrytis cinerea, Selerotium rolfsii, Pyricularia oryzae. Pot experiment array showed that IRHB 47 application through either seed soaking or irrigation at the seedling growth significantly decreased the disease index of soybean root rot caused by F. oxysporum and promoted its survival of soybean seedlings. Analysis of 16S rDNA sequence showed that IRHB 47 was identified as Streptomyces virginiae and was gram positive bacteria. Furthermore, this strain not only had strong stress tolerance under low nutrients （6.25% LB） and wide pH condition （pH 5-10） but also produced Protease and Caseinase to induce plant immunity. 【Conclusion】 This study indicates that Streptomyces virginiae IRHB 47 has big potential to be explored as one biocontrol bacterium of soybean root rot because of wide fungal growth inhibition effects and strong stress tolerance.

【Objective】 The aim of this study to explore the effects of different nitrogen （N） levels and sweet maize//soybean intercropping patterns on soil aggregate stability and organic carbon （C） content in sweet maize, aiming to provide a scientific basis for optimizing the sweet maize//soybean strip intercropping system, and thus achieving N fertilizer reduction and efficiency increasing, and promoting C sequestration in agricultural ecosystem. 【Method】 In this study, a long-term field experiment was conducted to investigate the effects of N levels （N0-no nitrogen, N-reduced nitrogen dose of 300 g/hm² and N2-conventional nitrogen dose of 360 kg/hm²） and planting mode （SS-sweet maize monocropping, S2B3-sweet maize//soybean 2∶3 intercropping and S2S4-sweet maize//soybean 2∶4 intercropping） on sweet maize yield, soil aggregates and organic C content. 【Result】 Nitrogen application significantly increased sweet maize yield but reduced the land equivalent ratio （LER） by 11.30%-14.59% and 9.66%-10.73% for N1 and N2, respectively. Notably, there was no significant difference of sweet maize yield and LER between N1 and N2. Nitrogen application promoted the decomposition of large macroaggregates （>2 mm） into small macroaggregates （0.25-2 mm）, which significantly reduced the stability of sweet maize soil aggregates, as well as organic C content of bulk soil and aggregates, and the organic C contribution rate of large macroaggregates. In general, intercropping had no significant effect on soil aggregate stability, and soil organic C content of bulk soil and aggregates. However, the S2B3 treatment appeared to improve the stability of sweet maize soil aggregates compared with other treatments. Furthermore, when no N was applied, soil organic C content in S2B3 was increased by 10.48% （P<0.05） compared with SS. 【Conclusion】 Nitrogen application significantly reduced soil aggregate stability and organic C content in sweet maize//soybean intercropping system, reduced N application and S2B3 intercropping showed the potential to improve soil aggregate stability and organic C sequestration, and meanwhile ensure the stable sweet maize yield.

【Objective】 The aim of this study was to investigate the photosynthetic physiological characteristics of soybean under different intercropping row ratios of maize/soybean, clarify the soybean yield, land equivalent ratio and interspecific competitiveness of different modes, for screening suitable maize-soybean intercropping mode in Guangxi region. 【Method】 In this experiment, maize （Bama pearl yellow） and soybean （Guichun 15） were used as experimental materials, and maize monoculture, soybean monoculture and six intercropping treatments were set up as follow： maize/soybean row ratio 4:4 （M4S4）, 2:4 （M2S4）, 3:3 （M3S3）, 2:3 （M2S3）, 2:2 （M2S2） and 1:2 （M1S2）. 【Result】 Compared with monoculture soybean group, the relative chlorophyll content of M2S3 and M2S4 treatments increased by 9.26% and 7.90% respectively, and the leaf area index decreased by 16.12% and 3.3% respectively. The net photosynthetic rate, transpiration rate, and stomatal conductance decreased in varying degrees, but intercellular CO₂ concentration increased significantly. The population yields of M2S3 and M2S4 treatments were 3 504 kg/hm² and 3 467 kg/hm² respectively, which increased by 22.43% and 21.14% respectively compared to monoculture soybean, and also increased by 17.39% and 16.15% yields compared to monoculture maize. The land equivalent ratios of M2S3 and M2S4 treatments were 1.21 and 1.20, but the interspecific relative competitiveness was -0.58, which was weaker than M4S4 and M3S3 treatments. 【Conclusion】 Overall, the practice of soybean/maize M2S3 and M2S4 intercropping can effectively reduce the shading effect of maize on soybean, which could improve the optimal utilization of land resources, and increase the total yield of the system.