| Based on the problems of weak light environment,variety and density selection in soybean-maize strip intercropping after rapeseed harvest in southwest China,two varieties,three sowing dates and four densities were designed to carry out a three-factor split zone test.Two varieties with different of maturity periods,Nanxiadou25（ND25,intermediate-late maturing,multi-branched）and Qihuang 34（QH34,early maturing,less branched）were selected to the effects of sowing date（2021:S1:May17,S2:May 27,S3:June 6;2022:S1:May 10,S2:May 25,S3:June 9）and density(D1:81,000 plants hm-2,D2:101,000 plants hm-2,D3:140,000 plants hm-2,D4:171,000 plants hm-2)on the strip intercropping soybean light environment,the plant architecture,dry matter accumulation and distribution and yield formation.The results show that:1.Sowing date had a great effect on the growth period of soybean,but the density had no obvious effect.With the delay of sowing date,the whole growth period and symbiotic period of soybean were gradually shortened,and ND25 had a long recovery period after corn harvest.The time from the beginning of flowering to the beginning of podding of ND25 showed a decreasing trend with the delay of the sowing date,while the time from the beginning of flowering to the beginning of podding of QH34 showed almost no difference among the three sowing dates.2.Sowing date and density had significant effects on plant type shaping of soybean.With the delay of sowing date at the same density and the increase of density at the same sowing date,the plant height of ND25 and QH34 V5 increased,while the stem diameter,node number and branch number decreased.R5 stage density increasing both varieties of plant height and lodging rate rise,D4 compared with D1,S1,S2,S3 two years average ND25 lodging rate increased by 17.34%,16.18%and11.98%respectively,QH34 increased by 19.50%,21.19%and 27.47%respectively.Sowing date delaying,ND25 reduced plant height,lodging rate is lower,the same density of planting the S3 than S1,D1,D2,D3,D4 two years average lodging rate ND25 reduced by 9.45%,8.95%,12.32%and 14.80%respectively.The same density of sowing date delaying QH34 increase plant height,lodging rate increases,the S3sowing date compared with S1,D1,D2,D3,D4 two years average lodging rate increased by 15.42%,19.14%,20.57%and 23.39%respectively.The sowing date was delayed and the density increased,while the stem diameter,node number and branch number of ND25 and QH34 decreased gradually.The lodging rate of R5 ND25 and QH34 was 26.27%and 20.29%respectively.ND25 was more prone to lodging than QH34.Correlation analysis showed that the plant height of ND25 and QH34 had a significant positive correlation with lodging rate.Stem diameter was negatively correlated with lodging rate.There was a significant negative correlation between stem bending resistance and lodging rate.3.The effects of sowing date and density on photosynthetic characteristics of soybean differ.The same density of sowing date delayed,ND25,QH34 soybean V5inside the canopy light transmittance are reduced and R5 are gradually increasing,leaf area index in different periods are decreased.With the increase of density in the same sowing period,the light transmittance of ND25 and QH34 in different periods decreased and the leaf area index increased.At the same time,the photosynthetic potential of ND25 and QH34 increased gradually with the increase of density,and decreased gradually with the delay of sowing date.The photosynthetic potential of ND25 was much higher than that of QH34.Correlation analysis showed that the photosynthetic potential of ND25 and QH34 had a significant negative correlation with light transmittance,and the light transmittance had a significant negative correlation with leaf area index.4.With the delay of sowing date and the increase of density,the dry matter accumulation per plant in each period of ND25 and QH34 gradually decreased.Meanwhile,the average dry matter accumulation per plant in each treatment of ND25was 30.94 g plant-1,while that in QH34 was 14.05 g plant-1,and the dry matter accumulation per plant in ND25 was much higher than that in QH34.When the sowing date of the same density was delayed,the population dry matter accumulation of ND25 and QH34 showed a decreasing trend in each period,while the density of the same sowing date increased,showing an increasing trend.Among different varieties,the average dry matter accumulation of R5 ND25 and QH34 was 3574.41 kg hm-2and1641.95 kg hm-2respectively.The distribution ratio of ND25 and QH34 to stem increased with the increase of density in the same sowing period.When the sowing date of the same density was delayed,the ratio of ND25 to pod increased and QH34decreased.5.Sowing date and density significantly affected the yield composition of soybean,and the response of different varieties to sowing date and density was significantly different.With the same density,the seed number,effective plant number and contribution rate of branch yield increased gradually for ND25,but decreased gradually for QH34.The effective plant number of ND25 and QH34 increased with the increase of density in the same sowing period,while the contribution rate of grain number per plant and branch yield decreased.The contribution rate of each treatment to the average branch yield of ND25 and QH34 was 55.30%and 5.82%,respectively.The effective number of ND25 and QH34 increased and the number of grains per plant decreased with the increase of density in the same sowing period.For ND25,S3>S2>S1 and D1>D2>D3>D4,optimum yield was obtained with a yield of1752.89 kg hm-2at S3 and D1.For QH34,S1>S2>S3 and D3>D2>D1>D4,optimum yield was obtained with a yield of 1538.64 kg hm-2at S1 and D3.ND25early in six months,81,000 plants hm-2,early QH34 in mid-may,140,000 plants hm-2can obtain high yield.ND25 yield was positively and significantly correlated with the number of grains per plant and light penetration,while QH34 yield was positively and significantly correlated with the number of grains per plant and group dry matter accumulation.The yield of both varieties was negatively correlated with plant height and inversion rate.In summary,in soybean-corn strip cropping systems,appropriate late sowing of mid-late maturing soybean varieties can suppress early overgrowth,short shading time by taller crops and long recovery periods.It also has a suitable leaf area index and increased light transmission inside the canopy,improving the light environment in the lower and middle layers of the plant.There is a suitable plant shape,a reduced fall rate and a better yield and yield composition.Early sowing of early maturing varieties reduced the shade from corn in the middle and late stages,and had suitable plant shape and reduced lodging.At the same time,large leaf area index was beneficial to the synthesis of photosynthate.Meanwhile,the multiple branching varieties should be moderately sparse,and the few branching varieties should be moderately dense,which can improve the yield of soybean population through the coordination of main stem and branching. |
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