Immediate impacts of soybean cover crop on bacterial community composition and diversity in soil under long-term sugarcane monoculture for applied soil ecology

Authors: Mula-Michel, Himaya; White, Paul; Hale, Anna

Submitted to: PeerJ
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2023
Publication Date: 8/22/2023
Citation: Mula-Michel, H.P., White Jr, P.M., Hale, A.L. 2023. Immediate impacts of soybean cover crop on bacterial community composition and diversity in soil under long-term sugarcane monoculture for applied soil ecology. PeerJ. 11.Article 15754. https://doi.org/10.7717/peerj.15754.
DOI: https://doi.org/10.7717/peerj.15754

Interpretive Summary: Sugarcane (Saccharum spp.) yields decline when the crop is grown for many consecutive years without crop rotation. This long term monoculture reduces soil health by negatively impacting soil nutrients, infiltration and drainage, and the types of soil microorganisms that live in the soil. This in turns leads to declining cane and sugar yields for growers. The objective of this research was to evaluate changes in soil microbiology when a soybean crop was grown in a usual sugarcane monoculture field. The soybean crop was grown during the normal fallow period, between the termination of the old sugarcane crop (December-February) and the new sugarcane crop planting (August). Bacterial DNA was extracted from the soil surrounding sugarcane and soybean roots, and from a non-vegetated, fallow area nearby. Substantial changes in bacterial diversity was observed in the soybean treatment, when compared to the sugarcane or fallow samples. Use of soybean cover-crop fostered bacterial diversity and community structure change. This indicates cover crops could have a restorative effect and potentially improve soil health associated with long-term sugarcane monoculture, without competing for sugar production land.

Technical Abstract: Sugarcane (Saccharum spp.) yield decline results from long-term monoculture practices. Changes in cropping management (e.g. the use of cover crops) can improve soil health and productivity. The impact of a soybean cover crop on bacterial populations on land previously under long-term sugarcane monoculture was determined. Near full length 16S rRNA gene sequences among sugarcane monoculture (30+ y), soybean rhizospheres, and fallow bulk soil were compared. An increase in soil bacterial diversity with the soybean cover crop was demonstrated in each the diversity indices measured (rarefaction, chao1, Shannon, reciprocal simpson). Acidocateria, Proteobacteria, Bacteriodetes and Planctomycetes were the most abundant bacterial phyla across the three management systems. Relative abundances of minor phylotypes (unclassified bacteria, Firmicutes, Gemmatimonadetes, Cyanobacteria, Nitrospirae, Candidate_divisions: OP10,TM7,OP11) were significantly different among management systems. Non-metric multidimensional scaling analysis showed distinct groupings of bacterial OTUs (97% identity) according to management system. Use of soybean cover-crop fostered bacterial diversity and community structure change. This indicates cover crops could have a restorative effect and potentially address reduced soil health associated with long-term sugarcane monoculture.