Intercropping perennial aquatic plants with rice improved paddy field soil microbial biomass, biomass carbon and biomass nitrogen to facilitate soil sustainability

Agricultural intensification threatens the sustainability of agricultural and environmental quality by decreasing soil quality, reducing biodiversity, and increasing the risk of pest outbreaks. Intercropping has been developed, applied and practiced across the world over centuries, and it has been proven an effective way to increase plant community diversity, thus promoting both complementary and facilitative interactions among species. Here we conducted field experiments from August 2016 to November 2018. We used four important perennial plant species (e.g., Acorus calamus L., Canna indica L., Pontederia cordata L., Thalia dealbata Fraser) to monocrop and intercrop with rice and evaluate their effects on soil physicochemical and biological properties. Our results suggested that soils planted with A. calamus and T. dealbata led to higher total organic carbon (TOC, p < 0.001), total nitrogen (TN), dissolved organic carbon (DOC), moisture content (p = 0.019), and lower soil bulk density (SBD) compared with rice monocropping. Specifically, soil TOC, TN and moisture content in the A. calamus and T. dealbata monocropping systems were, 29.30 and 25.39 %, 15.41 and 25.38 %, and 12.12 and 23.08 % respectively higher than that in the rice monocropping system. We also observed significantly higher microbial biomass (p < 0.001), biomass carbon (p = 0.017), and biomass nitrogen (p < 0.001) and microbial diversity in A. calamus and T. dealbata monocropping and/or intercropping systems. Our results suggest that intercropping perennial plants, A. calamus and/or T. dealbata, in paddy fields for three years could significantly improve soil properties, concomitantly providing more beneficial habitats for microbes, and together, soil sustainability was complemented.