Apple-Soybean Mixed Stand Increased Fine Root Distribution and Soil Water Content with Reduced Soil Nitrate Nitrogen

In dryland agroecosystems, intercropping fruit trees with legumes is often an important option for maintaining and improving soil N quality and fertility. The relationships of fine root length density (FRLD), soil water content (SWC), and soil NO3--N content (SNC) in agroforestry systems is essential for optimal orchard management. Our objective was to understand the temporal and spatial dynamics of FRLD, SWC, and SNC in an apple-soybean intercropping system and competition between species for ecological niches. We established an orchard with soybean and apple, including monoculture apple (MA), monoculture soybean (MS), and apple-soybean intercrop (AS) treatments. We collected data on the distribution of FRLD, SWC, SNC, and productivity under the MA, AS, and MS from 2020 to 2021. This study showed that AS had more FRLD compared to MA, and intercropping apple (IA) FRLD increased at 20-60 cm soil depth at 50 and 100 cm from the tree and decreased at 0-40 cm soil depth at 150 and 200 cm from the tree. Intercropping increased the SWC of the system and decreased the SNC, and the effect of intercropping was concentrated in the soybean cover area. The competition between apple and soybean reached its maximum at soybean seed filling stage, with competition occurring mainly at 100 cm from the tree and at 0-20 cm soil depth. Intercropping affected soybean growth and also reduced soybean yield with a land equivalent ratio = 1.45. By understanding the dynamics of subsoil resources in the apple-soybean intercropping system and interspecific competition, we can provide a theoretical basis for exploring the potential of sustainable intensification of agroforestry systems.

Automated summary

Interplanting fruit trees with legumes is a valuable approach for maintaining soil nitrogen quality and fertility in dryland agroecosystems. This study examined the dynamics of fine root length density (FRLD), soil water content (SWC), and soil nitrate-nitrogen content (SNC) in an apple-soybean intercropping system to optimize orchard management. The results showed that intercropping increased FRLD and SWC, while decreasing SNC, with the effect mainly observed in the soybean cover area. Interspecific competition between apple and soybean was highest during soybean seed filling stage, primarily occurring at a distance of 100 cm from the tree and at a soil depth of 0-20 cm. Intercropping negatively affected soybean growth and yield, with a land equivalent ratio of 1.45. This study provides a theoretical basis for exploring sustainable intensification of agroforestry systems by understanding subsoil resource dynamics and interspecific competition in apple-soybean intercropping systems.