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<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.