Environmental Science & Technology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2748
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Item Extending the Cover Crop Growing Season to Reduce Nitrogen Pollution(2021) Sedghi, Nathan; Weil, Ray R; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Maryland currently has the highest rate of cover crop use in the United States. The Cover Crop Program, started as an initiative to clean nutrients from the Chesapeake Bay, has made it a common practice to plant a cereal cover crop after cash crop harvest in fall, and kill it several weeks before cash crop planting in spring. In Maryland, this practice does not allow enough growing time with warm conditions for optimal cover crop growth. Planting earlier in fall and killing a cover crop later in spring could improve soil N cycling. We hypothesized that interseeding into a cash crop in early fall, and delaying spring cover crop termination could increase cover crop biomass, carbon accumulation, and nitrogen uptake and decrease nitrate leached. We tested these hypotheses over four years with five field experiments, consistently using a brassica-legume-cereal cover crop mix. We evaluated the relationships between cover crop planting date and fall cover crop N uptake and reduction in nitrate leaching. In spring, we tested termination timing effects on cover biomass C and N, soil mineral N concentration, soil moisture, and corn yield. We tested multiple dates for broadcast interseeding cover crops into standing soybean cash crops. We partnered with farmers on Maryland’s Eastern Shore to test if our methods are feasible at a realistic scale. We measured nitrous oxide emissions to test if our recommended cover crop practice has the negative drawback of increasing emissions of nitrous oxide, a powerful greenhouse gas. The nitrate leached under late drilled and early interseeded methods were comparable under conditions which favored late drilling, but interseeding outperformed drilling when there was adequate rainfall for seed germination. The result was lower nitrate porewater concentrations under early planted cover crops. Nitrous oxide emissions increased slightly with cover crops relative to no cover crop, but the increase was negligible when compared to the nitrous oxide produced from applying N fertilizer. Our research showed that extending the cover crop growing season of a brassica-legume-cereal mix has multiple environmental benefits and few drawbacks.Item 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.Item 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.Item FATE AND TRANSPORT OF NITROGEN AT A DEEP ROW BIOSOLIDS APPLICATION HYBRID POPLAR TREE FARM(2012) Maimone, Diana; Felton, Gary K; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study evaluates deep row applied biosolids as a nutrient source for hybrid poplar trees grown on a gravel mine reclamation site in Brandywine, Maryland from November 2003 to April 2009. The study included biosolids application rates of 386, 773, and 1,159 dry Mg/ha (172, 345, and 517 dry ton/ac.) and hybrid poplar tree densities of 0, 716, and 1,074 trees/ha (0, 290, and 435 trees/ac.). Soil water samples taken from suction lysimeters located 15 - 120 cm (6 - 48 in.) vertically below the biosolids were analyzed for total ammoniacal-nitrogen (TAN) and nitrate-nitrogen (NO3-N). The majority (96.3%) of NO3-N values were less than EPA drinking water MCL of 10 mg/L. No NO3-N values within the tree plots exceeded 2 mg/L. The TAN concentrations increased with application rates, but decreased with distance from the biosolids, except there was no difference between 60 cm (24 in.) and 120 cm (48 in.).Item EVALUATION OF BASE LINERS TO REDUCE NITROGEN AND SALT LEACHING FROM POULTRY LITTER STORAGE STOCKPILES TO THE UNDERLYING SOIL - A FIELD COLUMN STUDY(2011) Baranyai, Vitalia; McGrath, Joshua M; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agriculture has been linked to the eutrophication of the Chesapeake Bay. The Delmarva Peninsula is an intensive poultry producing region, where poultry litter (PL, mix of manure and bedding material) is often stored in outdoor stockpiles. Continued development of management practices is required to achieve environmentally sound PL storage. This study evaluates base liners placed between the bottom of the pile and the soil to reduce nitrogen (N), potassium (K) and sodium (Na) movement from PL stockpiles after 15 and 91 days of storage. Six conically shaped stockpiles were established with five PVC pipe columns placed in the soil under each pile. The soil surface in each column was covered with one of five treatments: alum, gypsum, lime, plastic, or control (no material). Nitrogen, K and Na concentrations increased between 15 and 91 days of storage. Ammonium losses under alum and lime treatment were not different from the control. Alum created adverse conditions by dropping the pH to 3.8. After 91 days of storage, the surface 10 cm of the soil was severely salt affected: under alum, gypsum, lime and control the conditions became moderately to strongly saline. Plastic was most effective in preventing N, K and Na leaching to the soil.Item Fate and Transport of Nitrogen at a Deep Row Biosolids Application Hybrid Poplar Tree Farm(2006-08-10) Buswell, Carrie Ursula; Felton, Gary K; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study focused on a gravel mine reclamation site using biosolids in deep rows as a nutrient source and hybrid poplar trees as the stabilizing crop. Biosolids application rates of 481, 962, and 1443 dry Mg/ha and tree densities of 0, 716, and 1074 trees/ha and controls (0 dry Mg/ha - 0 trees/ha) were studied. Total nitrogen, ammonium, nitrite and nitrate in soil water samples from pan and suction lysimeters under and around the biosolids rows were evaluated. Total nitrogen was predominantly in the form of ammonium. Ammonium concentrations in more than half the samples were above 100 mg/L, reflecting the average biosolids concentration of 2,300 mg/kg. No significant differences (a = 0.05) were determined between application rates or tree densities, but ammonium concentration significantly decreased with distance below the biosolids row. Nitrite and nitrate nitrogen concentrations were predominantly non-detects or less than 1 mg/L, indicating that nitrification was not occurring.