Optimizing planting geometry in sorghum–soybean systems: asymmetric row spacing improves resource use efficiency and crop adaptation in semi-arid environments

This study (2023–2024) assessed soybean (Glycine max L.) cultivated as a monocrop or intercropped with sorghum (Sorghum bicolor L.) adopting three planting configurations: alternate-row intercropping (App1), asymmetric-row intercropping (App2), and soybean monoculture (App3). Morphological, physiological, yield, and seed oil-quality parameters were assessed using multivariate analyses and multi-criteria decision-making methods. In the two years studied, App 3 tended to achieve the greatest shoot and root biomass, pod production, and cumulative oil content, emphasizing its excellence in overall productivity. App 1 showed low reproductive output, declining from 68.00 to 47.83 pods plant⁻¹, with pod weight increasing only from 21.29 to 32.00 g across years. However, intercropped soybean recovered in the second year: shoot weight increased from 8.16 to 66.47 g in App 1 and from 14.89 to 58.92 g in App 2. Root fresh weight also improved markedly, especially in App 2 (4.14 to 19.33 g), indicating stronger below-ground resource capture in 2024. Oil composition shifted toward higher oleic acid under intercropping, with App 1 increasing from 21.73% (2023) to 28.84% (2024). Nonetheless, Asymmetric intercropping (App 2) shown enhancement in the second year, especially in photosynthetic efficiency and oil quality (increased oleic acid content). In contrast, alternate-row intercropping (App 1) typically diminished output due to intensified competition, although there was some rebound in aboveground biomass in the second year. The overall performance was evaluated using WSM, AHP, and Fuzzy TOPSIS, with all methodologies designating 2024-App3 as the superior option, followed by 2023-App 3 and 2024-App 2. While monocropping exhibited greater performance overall, the positive trajectory of asymmetric intercropping suggests its potential as a viable option in semi-arid environments when row spacing is appropriately adjusted.