Uniconazole, 6-Benzyladenine, and Diethyl Aminoethyl Hexanoate Increase the Yield of Soybean by Improving the Photosynthetic Efficiency and Increasing Grain Filling in Maize–Soybean Relay Strip Intercropping System

Abstract

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. We conducted a sequential field experiment in 2018 and 2019, with foliar spraying of uniconazole (S3307), 6-benzyladenine (6-BA), diethyl aminoethyl hexanoate (DA-6) and water (CK) on soybean at the anthesis stage. Results showed the value of leaf area index, and chlorophyll (a + b) content, and net photosynthesis rat of soybean leaves were highest under DA-6 and significantly higher than CK at 56 day after spraying (DAS). Foliar spraying 6-BA, S3307 and DA-6 increased the activities of superoxide dismutase (SOD), peroxide (POD), and catalase (CAT) of soybean leaves at 35 and 56 DAS. The soybean aboveground dry matter weight and the dry matter accumulation after flowering stage was highest under DA-6 treatment, and the dry matter transportation ratio and the proportion of dry matter in pods were highest under S3307 treatment. The value of maximum grain filling rate (Vmax) and mean grain filling rate (Vmean) of soybean were highest in S3307, while the value of active grain filling period (D) was highest in DA-6. The hundred-grains weight was highest in S3307, then followed by DA-6 and S3307. The pods per plant in DA-6 were significantly higher than in 6-BA and S3307 and increased by 25.4% and 32.9% compared to CK in 2018 and 2019, respectively. Foliar spraying DA-6 (60 mg L−1) has a better effect on increasing the physiological function and photosynthetic capacity of leaves, leading to improving the grain filling process and increasing the yield of relay-intercropped soybean.