Complementarity for nitrogen use in maize/faba bean intercropping with inoculation

Intercropping with legumes is beneficial for crop nitrogen (N) uptake, but the mechanism behind efficient N uptake in intercropping is not well understood. Therefore, this study aimed to measure the effect of crop diversity on N uptake in intercrop and to assess the mechanisms contributing to diversity effects.

The N uptake on equivalent area basis was determined during 2012 to 2014 using a long-term experiment established in 2009 including faba bean/maize intercropping and corresponding monocultures. Complementarity effects (CE) and selection effects (SE) were calculated to assess N complementarity/facilitation and dominant species effects.

Faba bean/maize intercropping had 17.6% greater system N uptake than weighted means of two monocultures. The fertilizer-N rate required to achieve the maximum total N uptake was 300 kg N ha^–1 without inoculation and was 225 kg N ha^–1 with inoculation. Similar results were observed for biological N fixation of faba bean. Enhanced N uptake from intercropping compared with monoculture was strongly and positively correlated with the CE, but not correlated with the SE. In addition, N fixation accounted for approximately 20% of the positive CE in faba bean/maize intercropping.

N complementarity and/or facilitation drove the increased N uptake in faba bean/maize intercropping. The results highlight the role of applying microbial inoculants to increase crop N uptake while reducing reliance on fertilizer N especially in newly reclaimed desert soils, and may also be useful for guiding the design of intercropping systems with complementary traits for efficient N use.