Plant Growth Regulators Increase Soybean Yields by Delaying Leaf Senescence in Maize (Zea mays L.)-Soybean [Glycine max (L.) Merr] Relay Strip Intercropping System

Background: The shading caused by maize inhibited the growth of soybean, reduced the yield of soybean under maize-soybean relay strip intercropping system. To investigate whether foliar spraying different types of plant growth regulators could improve the growth and yield of intercropped soybean.Methods: A field experiment was conducted in 2018 to evaluate the effect of foliar spraying 6BA (6-benzylaminopurine), S3307 (uniconazole) and DTA-6 (diethyl aminoethyl hexanoate), at the soybean beginning flowering stage, on the growth and yield of three soybean varieties (i.e., Nandou 25 (ND25), Gongqiu 8 (GQ8) and Guixia 3 (GX3)).Result: The leaf area index of three soybean varieties were highest in DTA-6 at 35 days after spraying (DAS) and no significant difference (p less than 0.05) were observed among three plant growth regulators. The chlorophyll a and chlorophyll b content under 6BA and DTA-6 treatments were significantly higher than CK and S3307 at 35 DAS. The activities of antioxidant enzymes (i.e., SOD (Superoxide dismutase) and CAT (Catalase) and antioxidant substances (i.e., GSH (Glutathione) were increased after spraying 6BA, S3307 and DTA-6 in three soybean varieties at 35 DAS. Independent soybean varieties, foliar spraying 6BA, S3307 and DTA-6 increased the soybean yield, pods per plant, 100-grains weight and grain per plant and the effect of DTA-6 (60 mg l -1) treatment were best than others.