Wheat-clover intercropping can induce positive Plant-Soil Feedback with minimal impact on soil physical properties

Sustainable intensification of crop production plays a pivotal role in achieving food security while reducing negative environmental impacts. Based on their physiological complementarity, legume-cereal intercropping could be used to achieve this objective. However, its effects on plant performance, soil edaphic factors and microbial communities are still not fully elucidated. In this study, clover-soft wheat intercropping with an additive design under two N fertilization levels (normal vs reduced) was tested for its effect on crop performance and soil fertility in a one-year field trial. Different plant morphological parameters and yields were evaluated at two times to determine interspecies interactions. Physical properties of soil were evaluated along the profiles. Rhizosphere and bulk soil were sampled to determine their chemical and microbiological properties. A qPCR approach, starting from the total soil DNA, was used to quantify the abundance of microbial phylogenetic markers and functional genes (N and P cycling). Intercropping had limited effects on plant morphological parameters, but system performance was strongly increased (Land Equivalent Ratio>1). A possible suppression of Cuscuta sp. infestation by wheat has also been observed. The physical properties of soil were not affected by the tested factors. Similarly, physicochemical properties were not significantly different between the two niches, except for soil humidity in one case. Fungi were the microbial group most affected by the plant species, as clover increased their abundance in the rhizosphere. The tested factors had different impacts on ammonia-oxidizing bacteria and diazotrophic prokaryotes. The limited effects of the tested factors might be due to high soil fertility. Reducing N fertilization by 30% in intercropping did not induce negative effects because of its positive Plant-Soil Feedback. Therefore, soil diazotrophs may regulate N availability for other microbial groups. Overall, the results indicate that wheatclover intercropping can be a valid tool for the sustainable intensification of crop production in the Mediterranean climate and has great potential for ameliorating the ecological environment of soil microbial communities.