Changes in the biodiversity of microbial populations in tropical soils under different fallow treatments

Favorable cropping systems that promote residue retention would normally lead to increased soil carbon storage. Experiments were conducted to test the hypothesis that soil carbon of different fallow management practices influences more the microbial biomass carbon and activity than the microbial community structure. Also, the distribution of the major microbial grouping in soil is influenced by how much carbon is sequestered in soil. Soils were sampled from the Kpeve Agricultural Experimental Station (KAES) in the Volta Region in Ghana. The treatments involved T1 - maize followed by fallow elephant grass that is burnt before planting, T3 - maize followed by pigeon pea fallow, T4 - maize followed by bare fallow, T7 - fertilized maize followed by elephant grass fallow, FR - forest reserve (unmanaged native vegetation). As the soil sequestered carbon, there was a corresponding increase in the microbial biomass carbon. The treatment effects were significantly different (p < 0.007). Correlation between biomass carbon and soil organic carbon was significant (r = 0.63*). Treatments with the least amount of carbon sequestered showed the least microbial activity. Significant relationship existed between dehydrogenase activity and the soil organic carbon (r = 0.683*). The phospholipid fatty acid (PLFA) analysis was used to assess the effect of different soil management practices on biodiversity of soil organisms. Differences in carbon sequestered in the treatments affected the percentage PLFA compositions of the various treatments, thus affecting the distribution. The amount of carbon sequestered in soil significantly influenced the proteobacteria (p < 0.001) and actinomycetes populations (p < 0.028). Thus, soils with high carbon storage showed high proteobacteria population and vice versa but the actinomycete population showed no particular trend with soil carbon. Diversity of the microbial community as assessed by the Shannon-Weiner Diversity Index showed no significant differences in treatments even though T4 had the highest diversity and FIR the least diversity. The terminal Restriction Fragment Length Polymorphism on the soil DNA samples showed that the bacterial species' richness was greatest in T1 and T4. The most dominant bacterial groups were found in T1 and FR. Evenness was greatest in T7. We conclude from this study that the different fallow management practices influence the microbial biomass carbon and microbial activity. Secondly, the distribution of the major microbial grouping in soil is influenced by carbon stored in soil. (c) 2008 Elsevier Ltd. All rights reserved.