Maize-soybean relay strip intercropping system has developed and popularized in the southwestern China that has minimum soil water loses and high water productivity.Early studies have suggested that the field microenvironment exhibits changes for soybean plant,especially for the light and water conditions.Soil moisture contents followed the trend in the order: maize row < maize-to-soybean row < soybean row in maize and soybean intercropping system.Therefore,we hypothesized the water imbalance conditions in the field under maize-soybean relay intercropping system,and these water imbalance conditions could activate the various water deficit stress mechanisms in the soybean plant.In order to test this hypothesis,imbalance water deficit was produced by dividing the roots of two soybean cultivars under two independent solution and soil culture experiments.The following four treatments include 0% PEG as a control(0%: 0%),2% PEG per liter on side A and 0% PEG per liter on side B(2%A: 0%B),,6% PEG per liter on side A and 0% PEG per liter on side B(6%A: 0%B),and 4% PEG per liter on side A and 6% PEG per liter on side B(4%A: 6%B)were used in solution culture experiment and following six treatments include 100% of the field capacity on both sides of roots(100%A: 100%B),100%: 50% field capacity on both sides of root(100%A: 50%B),100%: 0% field capacity on both sides of root(100%A: 0%B),50%: 50% field capacity on both sides of root(50%A: 50%B),50%: 0% field capacity on both sides of root(50%A: 0%B),0% field capacity on both sides of root(0%A: 0%B)were used in soil culture experiment,respectively.The morphophysiological and metabolic responses of soybean were determined.The results showed that genotypes,duration and amount of the stress determined the severity of the effects of a split-root drought.In solution culture experiment,increased polyethylene glycol-6000(PEG)levels significantly decreased the photosynthetic rate,stomatal conductance,transpiration rate and chlorophyll content.Increased PEG levels led to a more abundant generation of reactive oxygen species(ROS),particularly in drought susceptible cultivar C-103.Soybean seedlings activated the antioxidant defense system.The activities of superoxide dismutase(SOD),catalase(CAT),ascorbate peroxidase(APX)and glutathione reductase(GR)increased except peroxidase(POD)with increase in PEG levels.However,in soil culture experiment,split-root drought had dominant effects on yield and yield related parameters as the drought level increased.However,little moisture imbalance did not affect the yield per plant in drought resistant cultivar Nandou-12.Well moisture treatments showed the maximum concentration of starch,sucrose and total soluble sugar in leaves at R5 stage,and biomass accumulation and distribution at maturity.Conversely,the concentration of free proline accumulated as the level of drought increased under split-root drought stress.Moreover,the results regarding metabolic response also showed significant differences between cultivars and drought levels.Split-root drought induced protein accumulation in both soybean cultivars.By contrast,the isoflavones declined throughout with increasing the split-root drought levels.The concentration of aglycone,β-glucoside,malonyl glycosides and acetyl glycosides decreased 94,40,45 and 75 %,respectively in drought susceptible cultivar C-103 under treatment T6 when compared with treatment T1.Under well moisture treatments T1,T2 and T3,interestingly drought resistance cultivar Nandou-12 induced slight increase in the aglycone by 65,102 and 112%,β-glucoside by 37,46 and 52 %,malonyl glycosides by 73,78 and 81 % and acetyl glycosides by 47,77 and 74 %,respectively.In addition,split-root drought stress significantly increased oleic acid concentrations but decreased linoleic acid and linolenic acid concentrations,as the availability of water decreased.From results,we concluded that moisture imbalance induced by split-root approach could be helpful to improve yield and quality of soybean additionally with water saving benefits.However,continuing studies about physiology,metabolism and molecular level will help to understand the mechanisms operating in split-root stress grown plants.