Tropical agricultural land management in fl uences on soil microbial communities through its effect on soil organic carbon Soil Biology & Biochemistry

We analyzed the microbial community that developed after 4 years of testing different soil-crop man- agement systems in the savannah e forest transition zone of Eastern Ghana where management systems can rapidly alter stored soil carbon as well as soil fertility. The agricultural managements were: (i) the local practice of fallow regrowth of native elephant grass ( Pennisetum purpureum ) followed by biomass burning before planting maize in the spring, (ii) the same practice but without burning and the maize receiving mineral nitrogen fertilizer, (iii) a winter crop of a legume, pigeon pea ( Cajanus cajan ), followed by maize, (iv) vegetation free winter period (bare fallow) followed by maize, and (v) unmanaged elephant grass-shrub vegetation. The mean soil organic carbon (SOC) contents of the soils after 4 years were: 1.29, 1.67, 1.54, 0.80 and 1.34%, respectively, differences that should affect resources for the mi- crobial community. From about 290,000 sequences obtained by pyrosequencing the SSU rRNA gene, canonical corre- spondence analysis showed that SOC was the most important factor that explained differences in microbial community structure among treatments. This analysis as well as phylogenetic ecological network construction indicated that members of the Acidobacteria GP4 and GP6 were more abundant in soils with relatively high SOC whereas Acidobacteria GP1, GP7, and Actinobacteria were more prevalent in soil with lower SOC. Burning of winter fallow vegetation led to an increase in Bacillales, especially those belonging to spore-forming genera. Of the managements, pigeon-pea cultivation during the winter period pro- moted a higher microbial diversity and also sequestered more SOC, presumably improving soil structure, fertility, and resiliency.