Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2008
Publication Date: 9/2/2008
Citation: Jangid, K., Williams, M.A., Franzluebbers, A.J., Sanderlin, J.S., Reeves, J.H., Jenkins, M., Endale, D.M., Coleman, D.C., Whitman, W.B. 2008. Relative impacts of land-use, management intensity and fertilization on microbial community structure in agricultural systems. Soil Biology and Biochemistry. 40:2843-2853. Interpretive Summary: Soil supports human life and is alive with soil organisms, most of which are microscopic bacteria and fungi. Healthy soil requires a wealthy diversity of microorganisms. Very little is known about how long-term agricultural land management affects the composition and genetic diversity of bacteria and fungi in soil. A collaborative research effort among scientists at the University of Georgia, Mississippi State University, and USDA-ARS’s J. Phil Campbell Sr., Natural Resource Conservation Center in Watkinsville Georgia investigated the role of typical long-term land management systems on soil microbial diversity in a typical soil of the Piedmont region of Georgia. Management systems were broiler litter versus inorganic fertilizer application in each of conventionally tilled cropland, hayed pasture, and grazed pasture. A forest stand planted in the mid 19th century served as a control area. Soil bacterial diversity was greater under pasture systems than under forest, suggesting that forage, fertilizer applications, and cattle grazing increased the diversity of soil microorganisms. Conventionally tilled cropland with inorganic fertilizer had a similarly low diversity of soil microbes like the forest. Broiler litter application had a positive influence on nutrient accumulation and soil microbial activity and diversity. Conservation agricultural systems with wise use of animal manure improved soil quality by increasing the number and type of soil microorganisms. Since greater diversity of soil microorganisms is accepted as an indicator of high soil quality, these results can be used by action agencies such as USDA-NRCS to foster soil quality improvement on much of the nation's 125 million acres of pastureland and 430 million acres of cropland.
Technical Abstract: Effects of agricultural land management practices on soil prokaryotic diversity have not been well described. Soil microbial communities under three agricultural management systems (conventionally tilled cropland, hayed pasture, and grazed pasture) and two fertilizer systems [inorganic fertilizer (IF) and poultry litter (PL)] were compared to that of a >50-year-old forest near Watkinsville, Georgia. Community DNA was extracted from soil in winter and summer, and the community composition and diversity were assessed using 16S rRNA gene clone libraries for bacteria and using phospholipid fatty acid (PLFA) analyses for bacteria and fungi. LIBSHUFF analysis of the libraries indicated that soil bacterial communities were different among all seven treatments. However, those from the forest were clearly distinct from the others. Hierarchical linear modeling of taxa abundance within the agricultural soils revealed that the effect of fertilizer was more dramatic than land use or season. Of the 14 taxonomic groups tested, fertilizer source influenced the abundance of seven, whereas land use and season influenced the abundance of only five and three, respectively. Specific associations between operational taxonomic units and land uses were also noted. Multivariate nonmetric multidimensional scaling of the mol % PLFA confirmed that the forest soil communities were different from the agricultural soil communities. Fungal mass was more abundant in the forest soil, and bacteria were more abundant in agricultural soils. In addition, soil bacterial communities under cropland were different than those under pasture. Fertilizer source also had a large effect on PLFA community structure, whereas season did not. The PLFA analysis reflected many of the same trends detected in the 16S rRNA gene analysis. However, some of the differences reflected by PLFA analysis may be a result of physiological responses to changing soil environment rather than a reflection of the community structure per se. Community-level differences correlated to differences in soil biochemical and chemical properties, such as mineralizable C and N and extractable nutrients. Agricultural land management practices, especially fertilizer source, significantly influenced the composition of soil microbial communities.