Effect of crop management and sample year on abundance of soil bacterial communities in organic and conventional cropping systems

Abstract

Aims: To identify changes in the bacterial community, at the phylum level brought about by varied crop management.

Methods and results: Next-generation sequencing methods were used to compare the taxonomic structure of the bacterial community within 24 agricultural soils managed with either organic or conventional methods, over a 3-year period. Relative abundance of the proportionately larger phyla (e.g. Acidobacteria and Actinobacteria) was primarily affected by sample year rather than crop management. Changes of abundance in these phyla were correlated with changes in pH, organic nitrogen and soil basal respiration. Crop management affected some of the less dominant phyla (Chloroflexi, Nitrospirae, Gemmatimonadetes) which also correlated with pH and organic N.

Conclusion: Soil diversity can vary with changing environmental variables and soil chemistry. If these factors remain constant, soil diversity can also remain constant even under changing land use.

Significance and impact of the study: The impact of crop management on environmental variables must be considered when interpreting bacterial diversity studies in agricultural soils. Impact of land use change should always be monitored across different sampling time points. Further studies at the functional group level are necessary to assess whether management-induced changes in bacterial community structure are of biological and agronomic relevance.

Keywords: 16S rDNA; agriculture; bacterial community structure; conventional farming; diversity; metagenomics; microbial phylogenetics; organic farming; soil.