| Southwest China is one of the most heavily populated agricultural regions of China,where crops rotation and intercropping are main cropping patterns,such as wheat-maizesoybean relay strip intercropping system.In wheat-maize-soybean relay strip intercropping system,Soybean is planted in the wide-rows between the maize and the vegetative growth duration of soybean and the reproductive growth period of maize overlap throughout approximately nine to ten weeks between the sowing of soybean and the harvesting of maize.However,the frequency and amount of rainfall during the co-growth duration(CGD)vary which resulted in interspecific interaction which changes the morphological characteristics of soybean crop.The vegetative and flowering durations are the crucial growth stages where severe environmental conditions and interspecific interactions negatively affect the initial growth of soybean plants.It is reported that if the differences among sowing time(CGD)between intercrops are larger,the larger size difference can occur within the early and late emerging plant,which results in the disproportionate distribution for resource capturing(soil and light),which can reduce yield differences between sole and intercrop.In maize and soybean relay strip intercropping(MSICS),selection of optimum sowing time(ST),phosphorus(P)applications and row spacings(RS)are the important factors which decide the CGD and interspecific interactions between intercrop species.In this study,different experiments were conducted to assess the effects of interspecific interactions in different ST of soybean(CGD),RS and P application and their effects on plant biomass,P uptake,and yield in MSICS.In this study,we conducted different studies from 2016-2018 at two different locations.In both experiments,we selected different sowing time(CGD),with different P levels or row spacing.The CGD were selected ST1,90 days of CGD;ST2,70 days of CGD;ST3,50 days of CGD.The P levels were P0 and P60(0 and 60 kg P ha-1).Three-row spacings were RS1,180+20 cm(180 cm wide soybean rows(WSR)and 20 cm narrow maize rows(NMR)),RS2,160+40(160 cm WSR and 40 cm NMR),and RS3,140+60 cm(140 cm WSR and 60 NMR)in MSICS.In this study changing the sowing times significantly altered the PAR transmittance at the top of soybean canopy in MSICS.The 50 days of CGD increases the PAR transmittance by 44% with P levels,and 20% within different RS,respectively,as compared with 70 days of CGD,in addition we observed the longer the co-growth duration,lower the PAR transmittance at the top of soybean was in MSICS.Results showed that P application and row spacings increase the photosynthetic characteristics of soybean(PC)in different sowing time.Soybean in 50 days of CGD increased photosynthetic rate(Pn)by 3% and 10%,stomatal conductance(Gs)9% and 13%,transpiration rate(Tr)11% and 12%,and intercellular CO2 concentration(Ci)8% and 12%,at R4 in two different locations,respectively in MSICS.In MSICS,significant variations for LAI of maize and soybean were also measured,maximum LAI were noted with P60 in P levels in both crops,and RS2 for maize and while soybean LAI was higher in RS1 under 50 days of CGD during the study.Furthermore,different sowing times show variation in PC and LAI under sole crops,and PC and LAI were always higher as compared with MSICS.Particularly,LAI and PC increased as PAR transmittance increased in MSICS.Similarly,above and belowground plant biomass significantly affected by P levels and row spacings within different sowing times.The P at 60 kg ha-1 increased soybean above and belowground plant biomass by 13.5% and 13.9% in SI,and 12.2% and 10.3 in SS,and it increased the maize above and belowground biomass by 13.9% and 11.6% in MI,and 14.6% and 13.8% in MS,respectively,as compared with P0 at R6 growth stage.Furthermore,50 days of CGD in MSICS and ST2 in SS,considerably increased the plant biomass of soybean and the average highest plant biomass of soybean was reached at the R6 growth stage.Similarly,50 days of CGD in MSICS,significantly increased the above and belowground plant biomass of MI in different row spacings.Relative to 70 days of CGD in MSICS at R6 growth stages,soybean and maize plants under 50 days of CGD had accumulated 12.4% and 11.4%,and 14.6% and 13.8% more above and belowground plant biomass.In MSICS,RS1 increased above and belowground plant biomass of soybean(SAPB and SBPB)at R4,and R6 growth stages by 16.7% and 19%,and 20.8% and 17.5% in comparison with RS3.Whereas,as compared to RS1 the above and belowground plant biomass of maize(MAPB and MBPB)increased by 5.8% and 10%,and 11.7% and 12% at R2 and R6 in RS2 under MS,respectively.In addition,above and belowground P uptake was changed with growth stage.In MSICS,applying of P at 60 kg ha-1 increased the above and belowground P uptake of soybean(SAPU and SBPU)by 21.9% and 21.4%,and 19.9 and 19.0% at R4 and R6,and above and belowground P uptake of maize(MAPU and MBPU)was increased by 8.7% and 7.6%,and 9.5% and 9.3% at R2 and R6 growth stages more P than P0.Differences among sowing time treatments revealed that plant under 50 days of CGD in SI and ST2 in SS with 60 kg ha-1(P60),had accumulated 38% and 14% SAPU and SBPU 19% and 16% more P at R6 than ST1 treatment.Similarly,in MSICS,more MAPU and MBPU and SAPU and SBPU were noticed in 50 days of CGD in changing row spacings.In MSICS,RS1 increased SAPU and SBPU by 16% and 17% in comparison with RS3,and RS2 increased MAPB and MBPB by 13% and 12% at R6 in comparison with RS1,in 50 days of CGD,respectively.In this study P application and row spacings with changes in ST also affected the crops yield and interspecific competitions.In MSICS,50 days of CGD reduced the aggressivity and competitive-ratio of maize(AGM and CRM)crop by 44% and 45%,and 10% and 6%,and it increased soybean competitive ratio by 11% and 5%,respectively,as compared with 70 days of CGD at two locations.Consequently,reduced AGM and CRM,increased the maize and soybean grain yield in 50 days of CGD by 12% and 13%,and 8% and 20% respectively,as compare to 70 days of CGD,thereby increased the total yield and LER at two locations by 12.7% and 11.3%,and 9.8% and 5.0%,respectively during the study seasons.We concluded that changing the ST and RS,with optimum P application in MSICS changed the interaction intensity between maize and soybean.The most important reason that farmers are interested in MSICS is the higher LER in this system.The better RS(160+40 cm)and better P levels in 50 days of CGD significantly reduce the maize competition and enhanced soybean competitive ability,while the earlier sowing time of soybean(90 and 70 days of CGD)increased the maize competitive ability during the CGD with soybean and reduced the TY and LER.In this study,crops higher economic return and increased yield production in an MSICS system were coordinated with higher APB,BPB,APU,and BPU by row spacings(RS),P application and sowing time(ST).This study also reported that in MSICS,50 days of CGD for growing soybean is the best approach to minimize the shading effect of maize on soybean at critical stage,i.e.,flowering because total number of flowers in soybean set the total number of pods,while shading at this stage considerably decreased the yield and yield components of soybean under MSICS.To the best of knowledge,this study is the first time reported the effects of different sowing time(co-growth duration)on interspecific interaction in MSICS.Further,we concluded that,system productivity of MSICS not only depends on biological performance but it is also associated with interspecific interactions(complementarity or facilitation),and interspecific interactions can be changed by the determination of proper RS of each crop and optimum P(nutrient)application with altered ST under MSICS.This study can be helpful in improving the farmer’s practices under MSICS,and it could be a reliable support for many similar kinds of intercropping systems. 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