Investigating the short term impact of organic amendments on sweetpotato rhizosphere bacterial communities in south central alabama organic farms

Background/Question/Methods

Agricultural practices impact many important properties of soil ecosystems.  In particular, organic farming has become an attractive alternative to conventional methods of production, but there is limited information on its impact on soil rhizosphere microbial communities and their function. Most rhizosphere community research has been directed at crops such as alfalfa, soybeans, and tomato; however there is limited research available about the sweetpotato rhizosphere bacterial communities and their impact on sweetpotato developments. The objective of this study is to assess the impact of organic amendments on organic carbon, pH, enzyme activity, and bacterial community composition in the sweetpotato rhizosphere and detect if there are any relationships between rhizosphere bacterial communities, enzyme activity, soil pH, and organic carbon. A field experiment was conducted to evaluate the impact of organic amendments and fertilizers (poultry litter, Megabloom [fish protein]) on the soil microbial community and selected soil parameters in the rhizosphere’s of four sweetpotato cultivars (J6/66, NCC-58, BH, and TU). Rhizosphere soil samples were collected at harvest and analyzed for soil pH, soil organic carbon content (SOC), soil gDNA, and selected soil enzyme activity. 

Results/Conclusions

Significant main effect was found between the sweetpotato cultivar and organic amendments where the soil pH in treatments and sweetpotato variety with BH variety untreated soils had significantly higher pH than other treatments, and the fish fertilizer had significantly lower pH in the TU variety. Fertilizer had no significant (P<0.05) impact on SOC but cultivars did with soils from Whatley/Lortan rhizosphere having lower SOC than other cultivars. Plots that received fertilizer and organic amendments had significantly higher enzyme activity compared to the control plots, but there was no difference among amendments, while cultivar had no significant effect on the enzyme activity (P<0.05). Fertilizer had a significant impact on bacteria at every taxonomic level (P<0.05), with substantial impacts to the Proteobacteria at the phylum and class levels. These results indicate that soil bacterial communities in organicly amended soils may be affected by the soil organic carbon content and the plant nutrients that are available in those amendments.