Impacts of Intercropping Row Patterns on the Heterogeneity of the Light Environment and Photosynthetic Product Production in Maize Canopy

This study aimed to elucidate the effects of maize–soybean intercropping patterns on canopy light heterogeneity, light use efficiency, and yield formation in maize rows, and to identify an intercropping configuration suitable for mechanized operations in the black soil region along the foothills of the Greater Khingan Range, so as to enhance regional agricultural productivity.

Field experiments were conducted during 2023-2024 in the black soil region along the eastern foothills of the Greater Khingan Mountains (Arong Banner, Inner Mongolia, China), using maize (Yinongyu 12) and soybean (Dongsheng 19) as test cultivars. The canopy light environment of maize was visualized. Six maize–soybean intercropping configurations were established, including two rows maize–two rows soybean (2M2S), four rows maize–four rows soybean (4M4S), four rows maize–two rows soybean (4M2S), six rows maize–six rows soybean (6M6S), six rows maize–four rows soybean (6M4S), and six rows maize–two rows soybean (6M2S), and differences in canopy structure, light-use characteristics, and yield formation were systematically evaluated.

(1) The 4M4S configuration exhibited the most favorable canopy structural characteristics due to enhanced light penetration in marginal rows and improved light conditions within inner rows, followed by 2M2S. Consequently, light-use efficiency and leaf photosynthetic rate during the tasseling–silking and grain-filling stages were significantly higher under 4M4S and 2M2S than that under the other intercropping treatments. (2) Maize yield under 4M4S did not differ significantly from that under 2M2S, whereas soybean yield was significantly higher under 4M4S, leading to the highest land equivalent ratio (LER), reaching 1.61 and 1.60 over the two years. LER values for the remaining treatments ranged from 1.31-1.56 and 1.28-1.53, respectively. Moreover, owing to better compatibility with agricultural machinery and lower operational costs, 4M4S achieved the highest benefit–cost ratio (6.61), exceeding those of other treatments by 7.39%-32.28%.

The upper canopy layer (L160 and L200) was identified as a key functional zone regulating photosynthesis in intercropped maize, with pronounced gradient differentiation in the relationships among canopy structure, photosynthetic performance, and yield across spatial row positions, where marginal rows exhibited the strongest advantage. Mantel analysis further revealed a strong coupling between light environmental structure and photosynthetic efficiency, forming a continuous pathway of “light acquisition–photosynthetic conversion–yield formation”. Owing to enhanced marginal effects and improved light distribution within inner rows, maize yield under the 4M4S configuration did not differ significantly from that under the conventional 2M2S pattern, whereas soybean yield was significantly increased (P<0.05), resulting in the highest land equivalent ratio and a greater benefit–cost ratio. Therefore, in the black soil region along the eastern foothills of the Greater Khingan Mountains, the 4M4S intercropping system represented an effective strategy to simultaneously enhance productivity and economic returns while facilitating fully mechanized cultivation and promoting sustainable agroecosystem development.