Diethyl aminoethyl hexanoate (DA-6) and planting density optimize soybean growth and yield formation in maize–soybean strip intercropping

The exogenous plant growth regulator, diethyl aminoethyl hexanoate (DA-6), in combination with suitable varieties and planting densities, is important to increase yield in the maize soybean strip intercropping system. To identify the role of DA-6 in mitigating high-density stress and increasing yield, we conducted a two-year field experiment examining changes in branching architecture and other yield traits of soybeans in maize–soybean strip intercropping systems. In the planting system, two soybean cultivars (ND: Nandou 25 and QH: Qihuang 34) were grown under three planting densities (D1: 102,000 plants ha −1 , D2: 130,000 plants ha −1 , D3: 158,000 plants ha −1 ) with DA-6 treatments (DA0: water control; DA60: 60 mg L −1 ; DA100: 100 mg L −1 ). Applying DA-6 at 60 mg L −1 at the fourth trifoliolate leaf stage increased soybean yield, with QH yield rising by 22.4 % and 29.5 % at D3 density, and ND yield by 29.5 % and 30.0 % at D2 density in 2022 and 2023, respectively, compared with D1 under DA0. DA-6 improved photosynthesis in both varieties under D2 density, with DA60 increasing ND canopy photosynthetic rate by 15.1–16.4 % and QG by 9.1 %–20.6 % over two years. In ND, DA-6 enhanced branching, raising the leaf area index by 37 %, branch number from 3.6 to 4.7 per plant, and total pod number by 19.7 %. In QH, yield grains were mainly due to a 17 % increase in the number of stem pods and a 6.5 % improvement in hundred-grain weight. In the maize soybean strip intercropping system, QH achieved a high yield by forming a high-density (D2 to D3) main stem pod, and ND by combining moderate density (D1 to D2) with DA-6-induced branching.