Positive effects of increasing crop diversity in land use on soil microbial biomass, enzyme activity and bacterial community composition

A rotation of summer tobacco–winter barley–next summer maize (T-B-M) has been suggested by Chinese government programs as an alternative land use practice to replace the conventional tobacco–fallow monoculture (T) and tobacco–barley succession (T-B) management systems. Crop yield in each crop system was recorded from 2010 to 2016 and routine and 454 pyrosequencing approaches were used to evaluate the effects of these cropping systems on organic matter, enzyme activity, and bacterial biomass and community composition within the same soil type. Tobacco leaf yields, barley grains, organic matter, microbial biomass, and enzyme activity (urease, neutral phosphatase, invertase and dehydrogenase) in the soil increased with crop species (but differences were not significant for dehydrogenase activity between T and T-B, and for neutral phosphatase activity between T-B and T-B-M). Indices of richness and diversity of soil bacterial communities also increased as the number of 16S rRNA gene sequences and bacterial phylotypes in the soil increased. The presence of many different bacteria in a soil system may prevent excess reproduction of any single pathogenic bacterium and subsequently reduce the risk of large-scale disease spread. All cropping soils were dominated by Proteobacteria, Acidobacteria, Actinobactria, Bacteroidetes, and unclassified bacteria. Of the 20 predominant bacteria, 13 were commonly found in all soils studied, whereas only four to five were unique in each of the soils examined. This suggests that the presence of those bacteria was more influenced by soil properties than cropping systems in a period of land use.