Optimal N Application Improves Interspecific Relationship, Productivity and N Utilization in Wheat/Faba Bean Intercropping

We assessed the effects of various N levels on interspecific interaction and faba bean N utilization and yield in wheat/faba bean intercropping system. The field experiments involved three cropping systems (faba bean monocropping, wheat monocropping, and wheat/faba bean intercropping) and four N levels (0, 45, 90, and 135 kg·ha⁻¹). The results showed that N fertilization significantly increased the competitive ratio (CR_F) and aggressivity (A_F) values in the early growth stage of faba bean (F), and faba bean was dominant in the middle and late growth stages of intercropping (CR_F>1, A_F>0). The grain yield of faba bean reached the maximum at the 45 kg·N ha^-1 level. The land equivalent ratio (LER) of wheat/faba bean intercropping system was greater than 1, which indicated that their intercropping had yield advantages over the monocropping. Compared with faba bean monocropping, wheat/faba bean intercropping produced significantly more faba bean grain yield and biomass than the relative area; and its agronomy efficiency of fertilizer N (AE_N) and partial N productivity (PFP_N), and the N fertilizer equivalent ratio (NFER) were all significantly greater than 1, indicating that intercropping can save N fertilizer. The N rate of 45 kg·ha⁻¹ was found to optimize interspecific interactions and increase productivity of wheat/faba bean intercropping system.