Environmental Science & Technology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2748

Browse

Now showing 1 - 3 of 3

Nitrogen dynamics in cover crop-based no-till corn
(2014) Poffenbarger, Hanna Jane; Weil, Ray R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Legume/grass cover crop mixtures and sidedress subsurface band manure application are two approaches to improving nitrogen (N) use efficiency in a cover crop-based no-till corn (Zea mays L.) system. The objectives of this study were to: 1) quantify cover crop biomass and N content in response to different hairy vetch (Vicia villosa Roth)/cereal rye (Secale cereale L.) sown proportions, 2) evaluate the effects of cover crop species proportions and pelletized poultry litter (PPL) application method on residue decomposition, and 3) model the spatio-temporal dynamics of soil inorganic N as influenced by different cover crop residues and subsurface band-applied PPL. Results suggest that cover crop mixtures can accumulate as much biomass as a cereal rye monoculture and as much N as a hairy vetch monoculture, and have decomposition patterns intermediate between those of monocultures. Subsurface band PPL application provided a localized N source that did not influence decomposition of surface mulches.
NITROUS OXIDE EMISSIONS IN COVER CROP-BASED CORN PRODUCTION SYSTEMS
(2016) Davis, Brian Wesley; Needelman, Brian A; Mirsky, Steven B; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Nitrous oxide (N2O) is a potent greenhouse gas; the majority of N2O emissions are the result of agricultural management, particularly the application of N fertilizers to soils. The relationship of N2O emissions to varying sources of N (manures, mineral fertilizers, and cover crops) has not been well-evaluated. Here we discussed a novel methodology for estimating precipitation-induced pulses of N2O using flux measurements; results indicated that short-term intensive time-series sampling methods can adequately describe the magnitude of these pulses. We also evaluated the annual N2O emissions from corn-cover crop (Zea mays; cereal rye [Secale cereale], hairy vetch [Vicia villosa], or biculture) production systems when fertilized with multiple rates of subsurface banded poultry litter, as compared with tillage incorporation or mineral fertilizer. N2O emissions increased exponentially with total N rate; tillage decreased emissions following cover crops with legume components, while the effect of mineral fertilizer was mixed across cover crops.
Urea Hydrolysis in Soil Profile Toposequences: Mechanisms Relevant to Nitrogen Transport and Water Quality
(2014) Fisher, Kristin A.; James, Bruce R.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Urea 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 (r2 = 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.