Alfalfa and maize intercropping enhances soil nematode structure and food web complexity in low-nitrogen soils

Abstract

Soil nematodes play key roles in soil ecosystem processes and functions. Although agricultural practices such as intercropping and nitrogen (N) fertilization are known to have a strong influence on soil nematodes, less is known about the responses of the soil nematode community to the combined effects of intercropping and N fertilization. This study was conducted to test whether the intercropping of maize and alfalfa can enhance the nematode community and quantified the effects of intercropping and N fertilization on nematode abundance, diversity, and metabolic footprints compared with soils under monoculture systems. An experiment involving maize and alfalfa was conducted in a 2 × 3 factorial completely randomized block design with four replications. The factors consisted of two N levels, namely, no N fertilization and N fertilization (225 kg N ha−1 yr−1), and three cropping modes: monoculture maize, monoculture alfalfa and maize intercropped with alfalfa. The results showed that, compared with the monoculture systems, intercropping increased total nematode and omnivore–predator abundances but reduced herbivore abundance. The total nematode biomass and metabolic footprint of omnivores and predators significantly increased in the intercropping treatments, regardless of N fertilization. The soil food web in the intercropping system without N fertilization was mature, structured, and enriched, as indicated by high maturity, structure and enrichment index values. However, all these effects decreased in the monoculture treatments, particularly after N fertilization. These results indicated that, compared with the monoculture systems, maize/alfalfa intercropping in low-N soil can improve the structural complexity of the soil food web. The observed complexity was attributed to the high soil moisture content, soil organic carbon and total N under the intercropping and low-N conditions. Therefore, this study provides a promising way to improve soil health and ecosystem stability, revealing that alfalfa intercropping in low-N soils can improve resource flow in the soil food web through the increase in total nematode biomass and the metabolic footprints of nematodes.