Pyrosequencing reveals profiles of soil bacterial communities after 12 years of conservation management on irrigated crop rotations

Potato and sugar beet, which are widely grown in southern Alberta, may degrade soil quality because they return little C to the soil, and their harvesting methods cause soil disturbance that increases erosion risk. To reverse these effects, a 12-yr study was established to evaluate soil conservation (CONS) management systems for rotations that included potato, sugar beet, dry bean and wheat. These systems, comprising addition of feedlot manure compost, reduced tillage, diverse crop rotations and use of cover crops, were applied to 3- to 5-yr crop rotations. They were compared with conventional (CONV) management systems that did not have any of the CONS practices. In the final year of the study, pyrosequencing was used to determine differences in soil bacterial community profiles between the two systems (CONS vs. CONV) in wheat rhizosphere and bulk soil. Thirteen phyla were observed, and the most abundant were Proteobacteria (39.6%), Actinobacteria (19.1%) and Acidobacteria (14.9%). Soil bacterial a-diversity increased under CONS relative to CONV management. However, whereas the relative abundances of Bacteroidetes and Firmicutes were greater under CONS than CONV management, the reverse was observed for Acidobacteria and Gemmatimonadetes. Proteobacteria were also more abundant under CONS than CONV management, but only in bulk soil. The community structures of the bacterial communities were in agreement with the differences in relative abundances. These differences were consistent with the ecological classification of soil bacteria as copiotrophic or oligotrophic. Therefore, CONS management systems altered the soil bacterial community profiles and increased the productivity of these soils.