Abstract: The effects of different sowing time on the carbonnitrogen metabolism and yield of soybean cultivars with different maturity under wheatmaizesoybean planting pattern were studied. The results showed that early sowing caused reduction in the yields of three soybean cultivars; late sowing caused increase in the yield of earlymaturing variety (Zhechun No.3); sowing at earlymid June increased the yield of midmaturing variety(Ledou No.1) and the latematuring cultivar (Gongxuan No.1). The highest yield was obtained from Gongxuan No.1 in three soybean cultivars. The growth period of the latematuring cultivar (Gongxuan No.1) was the longest， and its symbiotic period of reproductive growth with maize could be shortened by adjusting sowing time， which could reduce the effect of shading stress on soybean during early growth stage and prolong soybeans single growth period. So the contents of soluble sugar， starch， nitrogen in leaf and stem， the activity of sucrose phosphate synthase(SPS) and glutamine synthetase(GS) in leaf were at a high level at each stage. Moreover， the change trend of carbonnitrogen metabolism in soybean plants was beneficial for high yield. In conclusion， the optimum combination of this experiment was Gongxuan No.1 and the sowing time from 15th June to 22nd June．

Key words: soybean, relayintercropping, sowing time, maturity, carbonnitrogen metabolism, yield