Alfalfa/maize intercropping has comparable productivity and lower environmental impact than nitrogen fertilizer application

Abstract Background and Aims Due to the unique biological nitrogen fixation of legume crops, intercropping maize with legume/grass crops such as alfalfa becomes an effective way to reduce exogenous nitrogen fertilizer inputs. This study aimed to determine whether intercropping could be compared to nitrogen fertilizer application and identify potential differences. Methods The trial was laid out in the field since 2015 in a randomized complete block design. Treatments included maize monocropping without nitrogen (N0M) and with nitrogen (NM), maize/alfalfa intercropping without nitrogen (N0IM). In autumn 2019, crop and rhizosphere soil samples were collected to determine yield, rhizosphere soil properties and microbial indicators. Results Results demonstrated that N0IM and NM treatments had the similar effect on the enhancement of maize yield and yield composition factors and the improvement of soil physicochemical properties related to nitrogen and kalium. Additionally, NM treatment significantly increased the Chao1 and ACE indices by 28.1% and 29.49%, while the N0IM treatment significantly increased the Shannon index by 1.90%. The NM and N0IM treatments had significantly different pathways for increasing maize yield. Both NM and N0IM treatments increased the relative abundance of assimilatory nitrate reduction. And the N0IM treatment increased nitrogen fixation as well. At the same time, NM significantly increased nitrogen dissimilation by 23.98% and intercropping significantly increased denitrification by 12.81%. Conclusion Intercropping can be considered comparable to nitrogen fertilizer application in terms of yield and yield composition factors, rhizospheric soil physicochemical properties. Moreover, intercropping was found to be more conducive to the stability of rhizospheric soil bacteria and more environmentally friendly.