Yield advantage and nitrogen fate in an additive maize-soybean relay intercropping system

Sustainable agricultural development is urgently required to satisfy future food demands while decreasing environmental costs. Intercropping can increase per-unit farmland productivity through a resource-efficient utilization. However, the fate of N in intercropping systems remains unclear. To study the yield advantages and the fate of N in additive maize-soybean relay intercropping (IMS) systems, we quantified crop yield, soil N transformation abilities, soil bacterial abundances, and the fate of ¹⁵N. This study was conducted using three planting patterns, namely, monoculture maize (Zea mays L.) (MM), monoculture soybean (Glycine max L. Merr.) (MS), and IMS, and two N application rates, specifically, no N and applied N (N₁, 45 and 135 kg N ha^-1 for MS and MM, correspondingly; and N for the IMS, which was the sum of the monocultures). Results showed that a higher per-unit farmland productivity and a lower land use intensity are attained in the intercropping system than in the corresponding monocultures. In addition, land equivalent ratio (LER) ranges from 1.85 to 2.20. Moreover, the fate of ¹⁵N showed that the N uptake and residual are the highest, whereas N loss in the IMS is the lowest among all planting patterns. Intercropping had an increased N use efficiency by increasing N utilization efficiency, rather than N uptake efficiency. The abundance of ammonia oxidizer and denitrifier indicated that IMS improves the structure of soil microorganisms. Furthermore, the transformation abilities of soil N denoted that intercropping strengthens ammonifying and nitrifying capacities to increase soil N residual while decreasing ammonia volatilization and N₂O emission. Finally, the greenhouse warming potential and gas intensity of N₂O were significantly lower in the IMS than in the corresponding monocultures. In summary, the IMS system provides an environmentally friendly approach to increasing farmland productivity.