Effects Of Population Structur Optimization On Yield Formation Of Summer Soybean In Wheat Stubble

Soybean is an important economic crop that provides high quality oil and protein,and is becoming increasingly important in national food security.At Present,there is a gap between China’s soybean yields and those of developed countries,and the total yield is low,with insufficient self-sufficiency and an outstanding contradiction between supply and demand,so there is an urgent need to increase soybean yields and total production.Soybean is a group crop and the group structure can be adjusted according to different planting methods.Therefore,it is important to study the differences in soybean group structure characteristics under different soybean planting methods and analyze its yield formation pattern,which is important for soybean canopy group optimization and tapping soybean yield potential.This study was conducted at the Xinxiang Integrated Experiment Station of the Institute of Crop Science,Chinese Academy of Agricultural Sciences for two consecutive years from 2018 to 2019.The experiment was arranged with three planting methods,including three parts:planting density test,row spacing configuration test and planting uniformity test.The planting density test was conducted with Zhongzuo XA12938and Zhonghuang13 as the test varieties,with 13.5×10⁴（D1）,18×10⁴（D2）,22.5×10⁴（D3）,27×10⁴（D4）,31.5×10⁴（D5）and 36×104 plants/hm2（D6）planting densities;the row spacing test was conducted with Zhongzuo XA12938 as the test variety,with 18×10⁴and27×10⁴plants/hm²planting densities.The row spacing test was conducted with Zhongzuo XA12938 as the test variety,with two planting densities of 18×10⁴and 27×10⁴plants/hm²and three spacing configurations of 20 cm+60 cm,40 cm+40 cm and 20 cm+40cm;the planting uniformity test was designed with Zhongzuo XA12938 as the test variety,with two planting densities of 18×10⁴and 27×10⁴plants/hm²and two spacing configurations of equal and unequal spacing.The results of the study are as follows:1.Planting density trials:Yields increased with planting density and then decreased,with the maximum yield of Zhongzuo XA12938 occurring at treatment D5(5000.45 kg hm^-2)and gradually stabilizing as planting density continued to increase,and the maximum yield of Zhonghuang13 occurring at treatments D4(4477.90 kg hm^-2)and D5(3935.30 kg hm^-2)for two years,respectively.The maximum LAI for Zhongzuo XA12938 and Zhonghuang13 was 7.06 and 6.26,respectively;with increasing planting density,soybean LAI entered high values（>4）earlier,from 47.0 d（D1）to 31.0 d（D6）after emergence for Zhongzuo XA12938,and from 54.6 d（D1）to 32.9 d（D6）after emergence for Zhonghuang13;Zhongzuo XA12938 at increasing density to the D2 treatment,the LAI>4can be maintained for more than 40 d at increasing densities to the D2 treatment,while Zhonghuang13 reaches more than 40 d only at D4 or higher densities;the Zhongzuo XA12938 LAI decreases less（47.4%）than B（56.9%）at mid to late soybean reproduction（R5-R7）;The dry matter accumulation of the population was enhanced with the increase of planting density,and the enhancement of high density treatment was significant,and there were differences in the extent of increase among varieties.The proportion of dry matter in reproductive organs at maturity tended to increase and then decrease with increasing density.Grey correlation analysis revealed that plant height and effective pods per unit area were strongly correlated with yield in Zhongzuo XA12938,while effective grains per unit area and height of centre of gravity were more highly correlated with yield in Zhonghuang13.The photosynthetic capacity of individual plants decreases with increasing planting density,Zhongzuo XA12938 has a high basal photosynthetic capacity and performs more consistently;In the canopy light interception performance,the canopy light interception rate in the critical period was 4.90%higher in Zhongzuo XA12938 than in Zhonghuang13.The SPAD increased with increasing density,and the highest values appeared earlier to the R3 stage in the high density treatments(31.5×10⁴and 36.0×10⁴plants hm^-2),in addition to the longer duration of high SPAD values in Zhongzuo XA12938;In the chlorophyll fluorescence characteristics,the maximum net photosynthetic rate was 30.46 and 24.34μmol CO₂·m^-2·s^-1for Zhongzuo XA12938 and Zhonghuang13 respectively,and the decrease in net photosynthetic rate with increasing planting density was smaller for Zhongzuo XA12938（17.73%）than for Zhonghuang13（22.51%）,with Zhongzuo XA12938 showing an advantage in net photosynthetic rate at all densities.Variety Zhongzuo XA12938 shows the production advantages of a sparse canopy,strong green holding of leaves in the late reproductive period and stable photosynthetic capacity in the high density treatment.It can reduce the stress of dense planting and give full advantage to the plant type in the composition of dense planting groups.2.Row spacing configuration trials:When increasing the density of planting was matched with different row spacing configurations,there was a yield difference（8.58%）between the 40 cm+40 cm（S2）and 20 cm+60 cm（S1）row spacing treatments under high density treatment.The increased row spacing（S1 treatment）improved the yield performance of this variety of soybean under high-density conditions,both by changing the row spacing configuration,further increasing the yield potential of high-density planting,saving germplasm resources and improving management efficiency;dense planting with different row spacing configurations increased the photosynthetic capacity and material synthesis capacity of the high-density planting group,improving yield potential.Increasing the row spacing（S1 treatment）significantly increased the leaf area index of the soybean population,with the maximum leaf area index at a row spacing configuration of 20 cm+60 cm（S1）,which was more effective under high-density planting conditions;The 20 cm+60 cm row spacing（S1）increased the dry matter accumulation of the population,forming a significant increase at the R6 stage,compared to the 40 CM（S3）and 20 CM+40 CM（S2）row spacing populations.Increasing the planting density further increased the dry matter accumulated by the group and reduced the difference between the row spacing treatments;the 20 cm+60 cm row spacing（S1）increased the light penetration in the middle of the canopy of the soybean group.The 20 cm+60 cm row spacing（S1）increased the light penetration in the middle of the canopy of the soybean population.The row spacing treatment reduced light transmission in the high density group,but increased the difference in mid-canopy light transmission,and changing the row spacing configuration improved mid-canopy light transmission more significantly in the high density group.3.Planting evenness configuration test:Denser planting can alleviate the negative effects of uneven planting.Yield was increased by 8.8%at equal spacing compared to non-equal spacing under conventional density conditions and by 9.3%at higher densities.The high and stable photosynthetic rate value of soybean plants under spaced planting conditions is an advantage over non-equally spaced planting,as it reduces light leakage in the field and allows full use of light.The higher density of equidistant planting increases the variability of the indicators,and the higher the planting density,the higher the requirement for uniformity of the population.