Complementation drives higher growth rate and yield of wheat and saves nitrogen fertilizer in wheat and faba bean intercropping

Positive interaction between cereal and legume could drive high system productivity in intercropping. However, crop performance related to interaction between wheat and faba bean is unclear, and knowledge gap about the relationship among crop performance, N management, and specie-specie interaction still remains in intercropping. Two-year field experiments were implemented in 2014-2015 and 2015-2016, and two factors involving in planting patterns (wheat monocropped, faba bean monocropped, and wheat and faba bean intercropping) and N rates (N0, 0 kg N ha(-1) (the control); N1, 45 and 90 kg N ha(-1) for faba bean and wheat; N2, 90 and 180 kg N ha(-1) for faba bean and wheat; N3, 135 and 270 kg N ha(-1) for faba bean and wheat, repetitively) were studied in a randomized complete block design with three replicates. Growth parameters and species interaction indices for inter- and mono-cropped wheat and faba bean under different N rates were estimated and calculated during each growing season. The results showed that interspecies competition was dominant in intercropping during the time from sowing to 75 days after wheat and faba bean emergence which sometimes induced lower growth rate of intercropping faba bean (IB) relative to monocropped faba bean (MB) and resulted in poor intercropping biomass production. Intercropping wheat (IW) suffered less intraspecies competition as compared to monocropping wheat (MW) during mid- and late-growth stages. The maximum growth rate (R-max), maximum biomass production (A), and grain yield of wheat were increased by 19.4-27.8%, 6.7-7.1%, and 19.5-28.2%, respectively, when wheat was intercropped with faba bean relative to MW. Intercropping sustained high or equal A and R-max for wheat under reduced one half N fertilizers as compared to MW due to the interaction of planting patterns x N levels. Intercropping generated yield and biomass advantages (Land equivalent ratio (LER) > 1, relative crowding coefficient (IC) > 0) at harvest though both biomass and yield of IB were lower than those of MB. Lower K, LER, and relative completion intensity of wheat (RCIw) with N rates were found only in 2016. However, intercropping showed a potential of reducing 5-15% N fertilizer application but still increased wheat yield by 16-30%. In conclusion, wheat and faba bean performance in intercropping is regulated by both growth pattern and N levels. Complementation in intercropping during mid- and late-growth stages is beneficial for stimulating wheat growth, reducing N fertilizer application rate, and maximizing the system productivity.