Crop diversification improves the diversity and network structure of the prokaryotic soil microbiome at conventional nitrogen fertilization

Abstract Background Sustainable agriculture seeks to optimize the application of nitrogen (N) fertilizers to reduce adverse economic and ecological effects. Crop diversification has been proposed to increase the efficiency of N fertilization. An open question is how the soil microbiome responds to these beneficial practices. Methods In a field study we investigated the effects of mineral N fertilizer with a 0-control, a conventional amount of 150 kg N ha −1 and an excessive application of 250 kg N ha −1 on the soil microbiome within a diversified cropping system with oil radish and undersown ryegrass over a period of 2.5 years and a non-diversified control, both in rotation of potato, winter rye and maize. Results N-fertilizations and crop rotations altered the pH, but differences were less pronounced with the diversified system. Compared to the crop species and season, N fertilization and crop diversification had less influence on the abundance of soil bacteria, archaea and fungi. The crop diversification showed a much stronger effect on archaeal than on bacterial or fungal abundances, while the microbial carbon use efficiency correlated strongly with bacterial abundance. At the end of the growing seasons, crop diversification increased prokaryotic richness and Shannon diversity in response to N addition, with a greater increase in the conventional N. At conventional N supply, prokaryotic co-occurrence networks revealed a much denser and complex structure in the diversified system. Conclusions The diversified cropping system under conventional N application rates showed positive effects on the prokaryotic soil microbiome by increasing their richness, Shannon diversity, and promoting a more elaborated network structure.

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