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Urea Hydrolysis in Soil Profile Toposequences: Mechanisms Relevant to Nitrogen Transport and Water Quality

dc.contributor.advisorJames, Bruce R.en_US
dc.contributor.authorFisher, Kristin A.en_US
dc.date.accessioned2015-02-05T06:37:54Z
dc.date.available2015-02-05T06:37:54Z
dc.date.issued2014en_US
dc.identifierhttps://doi.org/10.13016/M2GK64
dc.identifier.urihttp://hdl.handle.net/1903/16095
dc.description.abstractUrea has been linked to harmful algal blooms in surface waters, but numerous studies of its hydrolysis in agricultural soils have concluded that urea does not persist long enough to be transported to surface waters. This paradox in the published literature may be explained by our lack of knowledge regarding the soil chemical conditions that affect microbial urease activity in surface and subsurface horizons of soil profiles that lie between agricultural fields and surface waters, particularly in sandy Coastal Plain regions. Laboratory studies were conducted to determine the most influential soil chemical characteristics predicting rates of urea hydrolysis in six Maryland soils. Soils were sampled from both the A and B horizons of toposequences consisting of an agricultural field, a grassed field border, and a transitional zone adjacent to surface waters. A pH-adjustment experiment identified soil C and N as important predictors of urea hydrolysis. Analysis of microbial community composition and ureC genes across a toposequence found the greatest abundance of bacteria, fungi, and ureC genes in riparian A horizon soils, despite inhibitory conditions of low pH, low field-sampled moisture content, and high extractable metal concentrations. The high carbon content of A horizon riparian soils likely mediated these toxic characteristics. Of particular note was the significant correlation between ureC genes and rate of urea hydrolysis (r<super>2</super> = 0.82), indicating that the presence of this gene may be useful as a biomarker for predicting rates of urea hydrolysis in other soils. An investigation into the effects of added C revealed that diverse soil C compounds influenced urea hydrolysis differently. In a 24 hr incubation, ascorbic and gallic acid acted as pro- and antioxidants with both enhancement and inhibition of hydrolysis, depending upon concentration, whereas benzoic and cinnamic acids likely enhanced hydrolysis as a result of being metabolized by soil microorganisms. A better understanding of the mechanisms controlling urea hydrolysis in diverse soils will help researchers and policymakers formulate defensible recommendations related to urea fertilizer and animal waste application so that urea-N can be efficiently used by crops and urea movement across the landscape and into surface waters can be minimized.en_US
dc.language.isoenen_US
dc.titleUrea Hydrolysis in Soil Profile Toposequences: Mechanisms Relevant to Nitrogen Transport and Water Qualityen_US
dc.typeDissertationen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.contributor.departmentEnvironmental Science and Technologyen_US
dc.subject.pqcontrolledSoil sciencesen_US
dc.subject.pqcontrolledAgronomyen_US
dc.subject.pqcontrolledMicrobiologyen_US
dc.subject.pquncontrolledcarbonen_US
dc.subject.pquncontrolledmicrobialen_US
dc.subject.pquncontrollednitrogenen_US
dc.subject.pquncontrolledsoilen_US
dc.subject.pquncontrolledtoposequencesen_US
dc.subject.pquncontrolledureaen_US


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