Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2010
Publication Date: 9/1/2010
Citation: Treonis, A.M., Austin, E.A., Buyer, J.S., Maul, J.E., Spicer, L., Zasada, I.A. 2010. Effects of organic amendments and tillage on soil microorganisms and microfauna. Applied Soil Ecology. 46(1):103-110. Interpretive Summary: The addition of organic amendments, for example composts and plant materials, to soil is a sustainable agricultural practice that can control pests and maintain soil fertility while minimizing synthetic chemical inputs. There is increasing interest by farmers to utilize organic amendments in crop production systems. One of the problems with using organic amendments is that their effects on microorganisms, including those that play a role in nutrient cycling and pest regulation, are poorly understood. Therefore, University of Richmond and ARS scientists monitored soil microorganisms at different soil depths after the addition of organic amendments to soil with and without tillage. It was found that depth in the soil profile was a significant factor influencing the density of microorganisms, and that organic amendments had positive effects on most measured variables. The results are significant because they provide insights in how to promote the occurrence of microorganisms that provide important soil ecosystem services (pest suppression, nutrient cycling). Consequently, the results will be used by scientists developing more effective strategies for incorporating organic amendments into crop production systems.
Technical Abstract: The impact of organic amendment and tillage on the soil food web at two depths in a field experiment was investigated. Over a three-year period, field plots received seasonal organic amendments, and the amendments were either incorporated into the soil (tilled) or not (no-till) as part of a tomato:soybean:corn cropping system. Un-amended, control plots that were either tilled or no-tilled were also included. We found that depth in the soil profile was a significant factor influencing the density of microorganisms and microfauna. Regardless of treatment, the 0-5 cm depth contained higher abundances of bacterial and fungal PLFA biomarkers and microfauna (protozoa and nematodes) than the 5-25 cm depth. Organic amendment had positive effects on most measured variables, including organic matter, respiration, protozoan and nematode density, and the abundance of PLFA biomarkers for bacteria and fungi. DGGE analyses of bacterial rDNA fragments indicated that distinct bacterial communities were selected for among tillage and amendment treatments and depths. Enhancement of the decomposer microorganisms and microfauna in amended, tilled soils (0-5 cm depth) corresponded to a decline in the relative abundance of plant-parasitic nematodes. In control soils (0-5 cm depth), tillage reduced the relative abundance of fungal-feeding nematodes and increased bacterial-feeding nematodes, in particular nematode species contributing to the Enrichment Index. Future research evaluating the influence of agricultural management practices on soil microorganisms and microfauna should employ sampling schemes to account for stratification of resources.