Abstract
•Delayed maize leaf senescence in maize-soybean relay-intercropping can increase the resource use efficiency.•Under narrow-wide-row planting pattern in maize-soybean relay-intercropping, maize yield is constrained.•Compared to the equal-row planting pattern, the narrow-wide-row planting pattern increased soybean grain-yield by 147%.•Overall, the total land equivalent ratio value of maize-soybean relay-intercropping in narrow-wide-row planting pattern was increased by 22% compared to the equal-row planting pattern.
Different planting pattern affects the leaf senescence of maize under intercropping systems, which regulate the grain yield of maize plants. In this study, we observed that a narrow-wide-row planting pattern in maize soybean relay intercropping system (MS) improved the leaf greenness and green leaf area, delayed the leaf senescence process in maize and increased the photosynthetic rate of maize leaves during the reproductive stages of maize in MS. In a three-year field experiment, soybean was relay-intercropped with maize under different planting patterns (1M1S, “50 cm + 50 cm” 1-row of maize and 1-row of soybean with an equal row distance of 50 cm; and 2M2S, “40 cm + 160 cm” narrow-wide-row planting pattern, where 2-rows of maize were planted in narrow rows, and 2-rows of soybean were planted in wide rows, and 60 cm distance was maintained between the rows of maize and soybean) of MS, and both planting patterns of MS were compared with sole cropping systems of maize and soybean.
Compared with 1M1S, planting pattern 2M2S significantly increased the number of green leaves (by 36%), leaf greenness (by 17%), and leaf nitrogen content (by 13%) at the dent stage (R5). The improved leaf nitrogen content in 2M2S at R5 significantly increased the green leaf area (by 16%, from 4170 cm2 plant−1 in 1M1S to 4960 cm2 plant−1 in 2M2S) of maize, indicating that leaf senescence of maize plants was delayed, which in turn significantly enhanced the photosynthetic rate of maize leaves at R5 by 57% in 2017, 75% in 2018 and 49% in 2019 than 1M1S. Overall, in 1M1S and 2M2S, relay-cropped maize produced 100%, and 89% of sole maize yield and relay-cropped soybean produced 27% and 66% of sole soybean yield, respectively. Importantly, compared to 1M1S, the decline of maize yield by 11% in 2M2S was compensated by a substantial increase in soybean yield by 147%, and 2M2S achieved the highest land equivalent ratio value of 1.54 compared to the land equivalent ratio value of 1.27 in 1M1S. Our results suggest that by selecting the appropriate planting pattern or stay-green maize hybrids, we can improve the land equivalent ratio of maize soybean relay intercropping system.