Stratification of Soil Microbial Community in Acidified Soils of No-till Systems Reflects Aluminum Concentrations and Liming Efficiency.

As much as 40% of farmed lands globally suffer from soil acidification, however little is understood about the basic structure and function of the associated soil microbial communities in recently acidified (<40yrs) agricultural soils. Particularly little is known about the impact of long-term no-tillage soil management systems and the interaction of nutrient and pH stratification with soil microbial communities. Through the use of T-RFLP microbial community profiling in the Palouse soils of eastern Washington, we have begun to answer critical questions regarding the impact of no-till systems on soil acidity and the associated soil microbial communities.  Under two chemically distinct liming treatments (liquid CaCO₃ vs sugar-beet lime) we have assessed depth stratification within the soil microbial community in 2cm-increments in a wheat-garbanzo bean rotation. Results indicate strong vertical stratification in soil chemistry measures for the top 10 centimeters of the soil in all treatments. The pH of the soil increased significantly within the first 2 cm of soil for both lime applications but at no other depths, with the lowest pH occurring at the deep-band fertilizer zone 4-8 cm. Microbial community composition is significantly impacted by bioavailable Al concentrations, more so than pH or other measured chemical variables. This may suggest that liming success relies primarily on Al toxicity amelioration in these soils, but further work is necessary.