Common vetch intercropping with reduced irrigation ensures potato production by optimizing microbial interactions

Inner Mongolia is a major potato-producing region in China. Soil quality degradation and water deficiency limit the local potato industry. Legumes can improve soil fertility and moisture, an intercropping system of common vetch with reduced irrigation was established to achieve potato production and soil restoration considering the annual cultivation system in Inner Mongolia. A two-factor field experiment design was then used. The first factor was the plant pattern with two levels, namely, potato monoculture (M) and potato-common vetch intercropping (I). The second factor was the irrigation amount with two levels, namely, reduced irrigation (R) and conventional irrigation (C). qPCR and high-throughput sequencing were used to determine soil microbial abundances and communities. After two years of field experiments, reduced irrigation significantly (p < 0.05) reduced the aboveground biomass of common vetch by 36.06%. Reduced irrigation reduced potato quality by 11.87–31.37%, but intercropping compensated for this shortcoming. Compared with potato monoculture, common vetch incorporation into the soil significantly (p < 0.05) increased the soil water content and available nutrients, by 10.98% and 13.75–55.08%, respectively. Although intercropping significantly (p < 0.05) increased the abundance of bacteria and fungi, it did not change (p > 0.05) the abundance of protists. The Beta-diversity of fungi and protists were also affected (p < 0.05) by intercropping and irrigation, whereas the bacterial Beta-diversity did not change (p > 0.05). The network complexity and connection between protists and fungi under the IR treatment were higher than those under the MC treatment. Soil available nutrients and network topological indices such as edges linking protists to fungi were significantly positively correlated with potato production. Common vetch intercropping with reduced irrigation could ensure potato tuber yield and quality, and improve soil quality, our research provides a sustainable cropping system suitable for potato cultivation in Inner Mongolia.