Long-term management drives divergence in soil microbial biomass, richness, and composition among upper Midwest, USA cropping systems

Highlights

• Cropping systems had distinct effects on soil microbial communities.

• Fungal and bacterial biomass were highest in pasture and lowest in continuous maize.

• Fungal richness but not diversity was affected by cropping systems.

• A soil chemical gradient explained some bacterial compositional differences.

Abstract

Long-term, systems-based experiments have previously demonstrated how different cropping systems change soil physiochemical properties and, less commonly, soil microbial communities. These long-term experiments allow for isolating the effects of management on soil microbial communities by minimizing variability in soil type, climate, and short-term effects of management intra-annual variability, and thus are able to inform best practices for regional cropping systems. In this study we address whether soil microbial communities are uniquely affected by upper Midwest US cropping systems’ management in a 26-year-old trial and examined how well microbial community responses to management track observed changes in soil physiochemical properties. We found that microbial biomass was highest in continuous pasture, lowest in continuous corn, and intermediate in alfalfa-based dairy forage rotations for both fungi and bacteria. Fungal taxonomic richness exhibited the same trend, but bacterial richness did not differ among cropping systems. Microbial community composition differed significantly among the cropping systems but could not be further explained by physical or chemical differences linked to particular management practices. We conclude that upper Midwest U.S. cropping systems cultivate distinct soil microbial communities, justifying further research on proximate drivers that cause the observed patterns and the consequences of altered microbial communities.