Photosynthetic performance and yield of intercropped maize and soybean are directly opposite under different intercropping ratios and maize planting densities interactions

Maize-soybean intercropping, a sustainable intensification practice, has been extensively studied. However, systematic research on how maize planting density and crop allocation patterns influence yield-related photosynthetic mechanisms in intercropping systems is scarce. This study conducted a two-year field trial during the 2022 and 2023 planting seasons to evaluate the effects of intercropping ratios (M4S4: four rows maize to four rows soybean; M2S2: two rows maize to two rows soybean) and maize planting densities (D1: 45 000 plants ha^-1, D2: 52 500 plants ha^-1, D3: 60 000 plants ha^-1) on photosynthetic performance and yield of maize and soybean, with monoculture as controls.

Compared to monoculture, the two-season average of maize under M2S2 at D2 density showed the most significant increase (9.63-64.92%) in leaf area index, SPAD value (relative chlorophyll content), photosynthetic parameters (net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration), light interception, photochemical quenching and maximum quantum efficiency of PSII photochemistry, and the most significant decrease (13.11-31.23%) in penetration (Pr), reflectance (Re) and non-photochemical quenching (NPQ), resulting in a 58.80% maize yield increase. Conversely, the two-season average of soybean indicators in intercropping exhibited opposite trends to maize, with the worst performance at D3 under M2S2, increasing Pr, Re, and NPQ by 19.99-46.86%, and decreasing other photosynthetic parameters by 6.70-33.23%, with soybean yield decreasing by 36.03%.

Conclusively, intercropped maize with a similar monoculture density of 52 500 plants ha^-1 under the M2S2 intercropping ratio produced the optimal photosynthetic performance and yield, with results opposite in intercropped soybean. Therefore, this intercropping ratio and planting density are recommended for sustainable maize production. © 2025 Society of Chemical Industry.