Biosolids and tillage practices influence soil bacterial communities in dryland wheat

Authors: Schlatter, Daniel; PAUL, NARAYAN - Washington State University; SHAH, DEVENDRA - Washington State University; SCHILLINGER, WILLIAM - Washington State University; BARY, ANDY - Washington State University; Sharratt, Brenton; Paulitz, Timothy

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2019
Publication Date: 4/1/2019
Citation: Schlatter, D.C., Paul, N.C., Shah, D.H., Schillinger, W.F., Bary, A.L., Sharratt, B.S., Paulitz, T.C. 2019. Biosolids and tillage practices influence soil bacterial communities in dryland wheat. Microbial Ecology. 78(3):737-752. https://doi.org/10.1007/s00248-019-01339-1.
DOI: https://doi.org/10.1007/s00248-019-01339-1

Interpretive Summary: Biosolids are by products of sewage treatment plants, the solid material left over. High in nitrogen, it is being increasingly used by wheat farmers in the dryland cropping systems areas as a fertilizer, being trucked over from the Seattle area. The purpose of this study was to examine the effects of the biosolids on bacterial communities in the soil, in conjunction with the use of an undercutter. The undercutter is a low-disturbance tillage implement to reduce soil erosion from wind, by keeping more crop residue on the surface. This study showed that biosolids have long-term effects on bacterial communities, much larger than the undercutter effect. There were some bacterial communities that were coming from the biosolids (gut and sewage bacteria), and some that were in the soil that colonized the biosolids as a food source. We did not detect Salmonella or Clostridium perfingens in the biosolids or soil amended with the biosolids. These are two indicators of human pathogens.

Technical Abstract: Organic amendments and conservation tillage practices are important for reducing soil erosion and improving soil health. Class B biosolids are being used in dryland wheat (Triticum aestivum L.) production in eastern Washington as a source of nutrients and to increase soil organic matter, but little is known about the effects on bacterial communities and the potential for harboring human pathogens. We explored the impacts of biosolids or synthetic fertilizer in combination with conventional (disk) or conservation (undercutter) tillage on soil bacterial communities. Communities were characterized from biosolid aggregates and soil after the second application of biosolids in 2015 and before and after the second application of biosolids in 2016, using high-throughput amplicon sequencing. Communities were also characterized from biosolids prior to application in 2016. PCR was used to test for the presence of Salmonella and Clostridium perfingens. Biosolids application significantly affected bacterial communities and the effect was apparent where biosolids had been applied three years earlier. Bacteria in the families Clostridiaceae, Norcardiaceae, Anaerolinaceae, Dietziaceae, and Planococcaceae were more abundant in the fresh biosolids, biosolid aggregates, and soils treated with biosolids. OTUs from Turcibacter, Dietzia, Clostridiaceae, and Anaerolineaceae were highly abundant in biosolid aggregates in the soil, and likely originated from the biosolids. In contrast, Oxalobacteriaceae, Streptomyceteaceae, Janthinobacterium, Pseudomonas, Kribella, and Bacillus were in low levels in the fresh biosolids, but high levels in biosolid aggregates in the soil, and probably originated from the soil to colonize the substrate. Tillage had only minor effects on bacterial communities. Salmonella and C. perfingens were not detected in any biosolid or soil samples. Biosolid amendments to soil have profound effects on bacterial communities both by introducing gut- or digester-derived bacteria and by enriching potentially beneficial indigenous soil populations.