Prior year legumes, but not history of crop rotational diversity, increase microbial carbon use efficiency across a soil-climate gradient

Authors: BOWLES, TIMOTHY - University Of California Berkeley; MOOSHAMMER, MARIA - University Of New Hampshire; GRANDY, A. STUART - University Of New Hampshire; GEYER, KEVIN - Allegheny College; CALDERON, FRANCISCO - Oregon State University; CULMAN, STEVE - Oregon State University; DEEN, BILL - University Of Guelph; DUNFIELD, KARI - University Of Guelph; Jin, Virginia; Lehman, Richard; Osborne, Shannon; Schmer, Marty

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2026
Publication Date: 6/16/2026
Citation: Bowles, T., Mooshammer, M., Grandy, A., Geyer, K., Calderon, F., Culman, S., Deen, B., Dunfield, K., Jin, V.L., Lehman, R.M., Osborne, S.L., Schmer, M.R. 2026. Prior year legumes, but not history of crop rotational diversity, increase microbial carbon use efficiency across a soil-climate gradient. Soil Biology and Biochemistry. 221. Article 110230. https://doi.org/10.1016/j.soilbio.2026.110230.
DOI: https://doi.org/10.1016/j.soilbio.2026.110230

Interpretive Summary: This study evaluated the effects of crop rotation on soil microbial activity and composition and its links to soil carbon storage in long-term agricultural soils. Using five long-term studies in the Central US and Canada, authors tested whether crop diversity or crop type affected microbial growth and respiration. Crop rotation complexity did not impact microbial growth and respiration, but microbial biomass was higher and respiration was lower whenever a legume rotation preceded corn. Variation in soil microbial properties were more heavily influenced by geographic variation than crop rotation and there was no clear connection that microbial changes were responsible for previously reported increases in soil carbon.

Technical Abstract: Soil microbial carbon use efficiency (CUE) is the proportion of carbon (C) that is taken up by microbes and allocated to biomass, relative to microbial respiration, an important parameter governing the formation of soil organic carbon. We hypothesize that increased CUE could explain high soil C in agricultural systems with diversified cropping rotations, which do not necessarily have higher C inputs or reduced soil disturbance, i.e. traditional drivers of soil C. Across five long-term experiments, crop rotational diversity increased microbial biomass C but did not affect microbial CUE or its components, with site-level effects overriding the influence on CUE. Microbial CUE was higher when the crop grown the year prior was a legume vs. a grain, though soil C did not differ. Observations of higher soil C in more diverse rotations thus likely result from mechanisms other than increasing microbial CUE.