Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/29/2010
Publication Date: 8/15/2010
Citation: Zerzghi, H., Brooks, J.P., Gerba, C.P., Pepper, I.L. 2010. Influence of long-term land application of class B biosolids on soil bacterial diversity. Journal of Applied Microbiology. 109:698-706. Interpretive Summary: Land application of biosolids occurs on an annual basis on approximately less than 1% of the available agricultural land in the US. However, little is understood of the overall influence of this organic residual on soil microbial quality over an extended period of time. This study was conducted in Arizona on controlled cotton plots in which annual applications of Class B biosolids have occurred for 20 years. Following the final application, surface soil samples (0-1 ft) demonstrated that the microbial population was not adversely affected. The overall microbial quality of the application sites yielded an increase in diversity of the represented bacterial types. Many members of these bacterial groups were similar for both control and biosolids applied soils indicating no demonstrated adverse effect. Overall, increasing the microbial quality of agricultural soils can be construed as a positive effect of this process.
Technical Abstract: This project evaluated the influence of annual land applications of Class B biosolids on soil bacterial diversity monitored over a 20 year period. Each annual land application was followed by a cotton crop. The study was initiated in 1986 at the University of Arizona Marana Agricultural Center, 21 miles north of Tucson, Arizona. The final application of biosolids was in March 2005, followed by growth of cotton from April through November 2005. Surface soil samples (0-30cm) were collected on December 2005, nine months after the final biosolids application, and analyzed for soil bacterial diversity. Replicated plots included control (unamended) soil and biosolid amended plots. The influence of land application on soil bacterial diversity was evaluated using 16S rRNA clone libraries. In the current study, bacterial diversity was not adversely impacted after 20 years of land application when evaluated through cloning and sequence analysis of bacterial 16S rRNA. In fact, the results showed that the known total number of identifiable species increased in the high rate biosolid plots, when compared to control (no biosolid) plots. The results from the Ribosomal Database Project II (RDP II) 16S rRNA gene sequences analysis showed that both soils had a broad phylogenetic diversity comprising more than four major phyla including: Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Firmicutes. Soil bacterial community members were similar to those normally found in arid southwestern soils. Overall, the data show that bacterial diversity was either unimpacted or enhanced following 20 years of land application of Class B biosolids.