Schematic representation of different maize-soybean planting patterns.

A, B, C and D represent the general layout of 2M2S (40 cm + 160 cm; maize narrow-wide row planting, i.e., the relay intercropping combination of two crop strips with a total width of 200 cm, consisting of two rows of maize and two rows of soybean with 40-cm row width for maize and soybean, and 60-cm spacing between the adjacent rows of maize and soybean), 1M1S (100 cm; with width of one meter strip, i.e., one row of maize and one row of soybean with 50-cm spacing between the adjacent rows of maize and soybean), M (70 cm; with equal row configuration in one strip for maize row to maize row arrangement) and S (50 cm; with equal row configuration in one strip for soybean row to soybean row arrangement), respectively. 2M2S and 1M1S are intercropping system, M and S are sole cropping system of maize and soybean, respectively. The red film placed at the middle of maize and soybean leaves for one day from 6:00 am to 20:00 pm was used for the measurement PPFD as shown in the figure.