Bacterial diversity in agricultural drainage ditches shifts with increasing urea-N concentrations

Authors: Klick, Sabrina; PITULA, JOSEPH - University Of Maryland Eastern Shore (UMES); COLLICK, AMY - Morehead State University; MAY, ERIC - University Of Maryland Eastern Shore (UMES); Pisani, Oliva

Submitted to: FEMS Microbiology Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2024
Publication Date: 4/12/2024
Citation: Klick, S.A., Pitula, J.S., Collick, A.S., May, E.B., Pisani, O. 2024. Bacterial diversity in agricultural drainage ditches shifts with increasing urea-N concentrations. FEMS Microbiology Ecology. 10/1093. https://doi.org/10.1093/femsec/fiae057.
DOI: https://doi.org/10.1093/femsec/fiae057

Interpretive Summary: Agricultural drainage ditches are targets for management because they receive excess chemicals and fertilizers from crop fields and connect to nearby surfaces waters of the nearby watershed. The use of urea fertilizers has raised concerns for water quality and the occurrence of harmful algal blooms in downstream coastal waters. Certain levels of urea have been associated with the toxicity and prevalence of certain algal bloom species. However, no information is known about how excess urea concentrations influence the microbial communities and nitrogen cycling activities in the drainage ditches bordering crop fields. The purpose of this study was to determine if there was an environmentally relevant level of urea that impacts the composition and nitrogen cycling activities of microorganisms in the drainage ditches bordering cornfields (spring fertilization) and soybean fields (no fertilization). Research was carried out using a combination of a field study and laboratory mesocosm experiment to investigate bacterial community and N cycling activity responses to high urea-N concentrations. Results showed that urea-N concentrations above 0.09 mg N L-1 leads to significant shifts in bacterial diversity in agricultural drainages and forest environments Additionally, fertilization of corn fields alters the bacterial community in adjacent drainage ditches when compared to the bacterial community observed in ditches next to unfertilized soybean fields. The results from this study can be used to inform management and future research aimed at reducing nitrogen transport downstream when implementing best management practices used to manipulate microbial communities in agricultural drainage ditches.

Technical Abstract: Urea-based fertilizers applied to crop fields can enter surface waters of adjacent agricultural drainage ditches and contribute to nitrogen (N) loading to nearby watersheds. Management practices applied in drainage ditches promote N removal by the microbial communities, but little is known about the microbial diversity in these ditches and the impacts of excess fertilizer from crop fields. In 2017, drainage ditches next to corn and soybean fields, and a reference forest site, were sampled to determine if fertilizer application and high urea-N concentrations alters bacterial diversity and urease gene abundances. A mesocosm experiment was paired with a field study to determine which bacterial groups respond to high urea-N concentrations. The bacterial diversity in the ditch next to corn fields was significantly different from the other sites. The bacterial orders of Rhizobiales, Bacteroidales, Acidobacteriales, Burkholderiales, and Anaerolineales were most abundant in the ditch next to corn and increased after the addition of urea-N (0.5 mg N L-1) during the mesocosm experiment. The results of our study suggests that urea-N concentrations >0.09 mg N L-1 can lead to shifts in the bacterial communities of agricultural drainage ditches, which is higher than the concentrations associated with algal blooms in downstream coastal environments.