Optimized planting time and co-growth duration reduce the yield difference between intercropped and sole soybean by enhancing soybean resilience toward size-asymmetric competition

Selecting optimum planting time (PT) in maize-soybean relay intercropping system (MSRI) is important to obtain higher intercrop yields because planting time decides the co-growth duration and competitive ability of intercrop species in MSRI. However, little is known on how planting time (co-growth duration) changes the interspecific interaction resulting in a seed-yield difference between intercropping and sole cropping system. Therefore, this field study was initiated to determine the effects of changing co-growth duration on competitive interactions, growth, and yield of intercrop species under MSRI. The sole soybean and relay-cropped soybean were planted on PT1(15-20 May, 90 days of co-growth duration in MSRI); PT2(5-10 June, 70 days of co-growth duration in MSRI); and PT3(25-30 June, 50 days of co-growth duration in MSRI) to generate different size-asymmetric competition between component crops in MSRI. Results showed that sole soybean produced the mean highest (2.93 t/ha) seed yield under PT2, and the mean lowest (2.51 t/ha) seed yield under PT1. However, in MSRI, PT(3)increased the soybean yield by 29.1% and 13.3% compared to PT(1)and PT2, respectively. The PT(3)also increased the maize yield by 7.4% and 2.9% than PT(1)and PT2, respectively, and it reduced the yield differences of maize and soybean between relay intercropping and sole cropping systems. In MSRI, decreased co-growth duration promoted the soybean plants to achieve the higher crop growth rate, and biomass accumulation, which ultimately improved the soybean resilience toward size-asymmetric competition created by maize plants. Furthermore, as compared to PT(1)and PT2, planting time PT(3)significantly increased the competitive ratio (by 10.1% and 17.3%, respectively) of soybean plants. Overall, the PT(3)achieved the average highest land equivalent ratio of 1.63, which is significantly higher than PT1(by 12.3%) and PT2(by 10.6%). In conclusion, this study implied that in MSRI, the determination of proper soybean planting time (co-growth duration) is one of the most critical factors to reduce the competition between the intercrops and to obtain higher crop yields.