College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Evidence of Phosphate Mining and Agriculture Influence on Concentrations, Forms, and Ratios of Nitrogen and Phosphorus in a Florida River(MDPI, 2021-04-13) Duan, Shuiwang; Banger, Kamaljit; Toor, Gurpal S.Florida has a long history of phosphate-mining, but less is known about how mining affects nutrient exports to coastal waters. Here, we investigated the transport of inorganic and organic forms of nitrogen (N) and phosphorus (P) over 23 sampling events during a wet season (June–September) in primary tributaries and mainstem of Alafia River that drains into the Tampa Bay Estuary. Results showed that a tributary draining the largest phosphate-mining area (South Prong) had less flashy peaks, and nutrients were more evenly exported relative to an adjacent tributary (North Prong), highlighting the effectiveness of the mining reclamation on stream hydrology. Tributaries draining > 10% phosphate-mining area had significantly higher specific conductance (SC), pH, dissolved reactive P (DRP), and total P (TP) than tributaries without phosphate-mining. Further, mean SC, pH, and particulate reactive P were positively correlated with the percent phosphate-mining area. As phosphate-mining occurred in the upper part of the watershed, the SC, pH, DRP, and TP concentrations increased downstream along the mainstem. For example, the upper watershed contributed 91% of TP compared to 59% water discharge to the Alafia River. In contrast to P, the highest concentrations of total N (TN), especially nitrate + nitrite (NOx–N) occurred in agricultural tributaries, where the mean NOx–N was positively correlated with the percent agricultural land. Dissolved organic N was dominant in all streamwaters and showed minor variability across sites. As a result of N depletion and P enrichment, the phosphate-mining tributaries had significantly lower molar ratios of TN:TP and NOx–N:DRP than other tributaries. Bi-weekly monitoring data showed consistent increases in SC and DRP and a decrease in NOx–N at the South Prong tributary (highest phosphate-mining area) throughout the wet season, and different responses of dissolved inorganic nutrients (negative) and particulate nutrients (positive) to water discharge. We conclude that (1) watersheds with active and reclaimed phosphate-mining and agriculture lands are important sources of streamwater P and N, respectively, and (2) elevated P inputs from the phosphate-mining areas altered the N:P ratios in streamwaters of the Alafia River.Item Effects of On-Farm Dairy Manure Composting on Tetracycline Content and Nutrient Composition(MDPI, 2021-04-15) Schueler, Jenna; Naas, Kayla; Hurst, Jerod; Aga, Diana; Lansing, StephanieThis study quantified the potential of farm-scale composting to degrade antibiotics in dairy manure. The compost windrow, consisting of sick cow bedding from a 1000-cow US dairy farm, was managed using the dairy farm’s typical practices and monitored for tetracycline and nutrient composition. Samples were collected over 33 days, which was the time from compost pile formation to land application as fertilizer, and analyzed for solids, antibiotics, and nutrient content. Average tetracycline concentrations at the beginning of the study (452 ng/g DW) were lower than at the end of composting (689 ng/g DW), illustrating that antibiotic degradation was not greater than degradation of the compost solids. Total Kjeldahl nitrogen (TKN) increased from 15.3 to 18.4 g/kg during the composting period due to decreases in solids and likely inhibition of N-mineralization due to the presence of antibiotics. The results indicated that antibiotics were not completely degraded when using the farm’s compost pile management techniques, with antibiotics possibly impacting nitrogen transformation in the compost, which should be considered in nutrient management when using sick cow bedding. Additionally, the results showed that antibiotic degradation during farm-scale composting can vary from reported laboratory-scale due to differences in management, composting duration, and temporal conditions, illustrating the need for more extensive on-farm research including common farm practices and real-world conditions.Item Saltwater intrusion alters nitrogen and phosphorus transformations in coastal agroecosystems(2020) Weissman, Dani; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As sea levels rise, coastal regions are becoming more vulnerable to saltwater intrusion (SWI). In coastal agricultural areas, SWI is causing changes in biogeochemical cycling in soil and waterways. These changes are leading to the release of excess nitrogen (N) and phosphorus (P) from farm fields, which in turn can cause impaired water quality downstream. I explored the effects of saltwater intrusion on N and P concentrations of surface water and soil porewater on Maryland’s Eastern Shore in the Chesapeake Bay Watershed on three spatial and temporal scales: 1) a three-year field study through farmland and various surrounding habitats; 2) a one-month laboratory soil incubation study; and 3) a regional study of tidal tributaries (sub-watersheds) along Maryland’s Eastern Shore where I utilized 35 years of observational data on nutrient concentrations and salinity from the Chesapeake Bay Water Quality Monitoring Program. The results of the field and incubation studies suggest that SWI can cause a large release of N and P from the soils of coastal landscapes to downstream water bodies such as tidal creeks and marshes. However, the results of the regional study suggest that the relative magnitude of SWI-driven contributions of N and P to waterways as compared to other sources and drivers of N and P differ depending on the spatial and temporal scale considered. Defining mechanisms through which SWI spurs nutrient release from soils of agricultural fields and surrounding habitats as well as the magnitude of these processes is critical for quantifying N and P export in coastal watersheds. The results of these three studies can potentially be used to inform water quality models for individual tidal tributaries, which would allow for more targeted approaches to nutrient load reductions in sub-watersheds of the Chesapeake Bay and other watersheds globally.Item Evaluating Soil Phosphorus Dynamics over Time(2017) Lucas, Emileigh Rosso; Coale, Frank J; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agricultural nutrient management became mandatory in Maryland (MD) due to water quality concerns. Phosphorus (P) management is complex due to the stability of P in the soil, nutrient mass imbalance, and “legacy” P. To explore how potential P application bans impact historically manured fields, agronomic and environmental soil tests were conducted on plots treated with five manure-P rates, then no P applications, spanning 15 years. Mehlich-3 extractable P (M3P) declined slowly and then generally did not change during the last six years. Phosphorus saturation declined slowly or not significantly. Excessive P soils had sufficient P for crop growth in solution. Phosphorus saturation and M3P were compared in fifty sites across MD pre- and post- nutrient management planning. Results showed an increase in P concentration of Maryland agricultural fields. This response was logical, as better management would increase below-optimum P concentrations, and the regulations were not designed to draw down P.Item Evaluation of accuracy and sensitivity of the University of Maryland Phosphorus Management Tool and investigation of subsurface phosphorus dynamics in the Maryland Coastal Plains region(2015) Fiorellino, Nicole; McGrath, Joshua M; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phosphorus (P) loss from agricultural fields to surface water represents a major environmental challenge in agricultural nutrient management. To reduce P loading, areas where both P source and transport conditions are present must be identified and appropriate management practices implemented to reduce the source or break transport connectivity. The Maryland P Site Index (MD-PSI) was modified from a multiplicative structure to a component structure and renamed University of Maryland Phosphorus Management Tool (UM-PMT). In the UM-PMT, each component is the product of source, transport, and management factors specific to a P loss pathway. Our objectives were to evaluate the UM-PMT for accuracy, investigate soil conditions in ditch-drained agricultural systems, compare different methods for degree of P saturation (DPS) calculation, and compare numerical and categorical final scores of the multiple versions of the Maryland P loss risk indices. Agronomic soil samples were collected from fields across Maryland, and analyzed for P, aluminum (Al), and iron (Fe) concentration using multiple extractions, soil texture was determined, and degree of P saturation (DPS) was calculated using five methods. Deep soil samples were collected and analyzed similarly from three sites on Maryland's eastern shore. A poor relationship was identified between UM-PMT and modeled P loss data (R2=0.09), but the relationship improved with modifications to UM-PMT calculation (R2=0.97), which resulted in UM-PMT Version 2 (UM-PMT v.2). Soil Fe concentration was responsible for a large proportion of DPS at one sample location on the Eastern Shore, demonstrated through poor correlation between two methods for DPS calculation, including and excluding Fe concentration. Numerical differences existed between different methods for DPS calculation and these translated to differences in UM-PMT final score, particularly in the Lower Shore region. The UM-PMT v.2 categorized more fields as HIGH risk than MD-PSI but less than UM-PMT. Neither version of the UM-PMT was very sensitive to management factor input variables. Evaluation of tools like the UM-PMT for accuracy, sensitivity, and magnitude of change is necessary to understand potential economic and environmental impacts of implementing new indices as nutrient management tools.Item Utilization of Gypsum as a Filter Material in Agricultural Drainage Ditches: Impacts of Land Application on Soil Fertililty Conditions(2010) Grubb, Karen Lyn; McGrath, Joshua M.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agricultural drainage ditches can provide a direct connection between fields and surface waters, and some have been shown to deliver high loads of phosphorus (P) to sensitive water bodies. A potential way to reduce nutrient loads in drainage ditches is to install filter structures containing P sorbing materials (PSMs) including gypsum to remove P from ditch flow. One projected advantage would be the potential application of spent PSMs to agricultural fields to provide nutrients for crop production after the filter has lost its effectiveness. The study evaluated the feasibility of this strategy. Gypsum was saturated at two levels on mass basis of P, and applied to two soil types, a silt loam and a sandy loam and applied at both a high and low rate. The treated soils were incubated at 25° C, and samples were collected at 0, 1, 7, 28, 63, 91, 119, and 183 days after saturation.Item Forage Radish Cover Crop Effects on Mycorrhizal Colonization and Soil Test Phosphorus(2009) White, Charles Macaulay; Weil, Ray R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Forage radish (Raphanus sativus L. var. longipinnatus) and cereal rye (Secale cereale L.) cover crops were examined for their effects on arbuscular mycorrhizal colonization and P acquisition of a subsequent corn (Zea mays L.) silage crop. Soil test P following these cover crops was also measured in bulk soil collected at three depths in the surface soil and in soil sampled within 3 cm of forage radish tap root holes. Forage radish never decreased mycorrhizal colonization and rye sometimes increased colonization of the subsequent crop compared to growing no cover crop. The extent of colonization of corn roots by arbuscular mycorrhizal fungi was positively correlated with corn shoot tissue P concentrations. Slight vertical soil test P stratification in the bulk soil occurred following both forage radish and rye cover crops at some sites. A large increase in soil test P occurred within 3 cm of forage radish tap root holes.Item Agricultural Drainage Ditches: Soils and Implications for Phosphorus Transport and Retention(2005-12-13) Vaughan, Robert Edward; Needelman, Brian A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agricultural drainage ditches act as pathways for nutrients to local surface waters. Knowledge of ditch materials, the spatial variation and distribution of ditch soil phosphorus, is critical to effective ditch nutrient management strategies. Ditch materials from the University of Maryland Eastern Shore Research Farm in Princess Anne, Maryland were described and characterized using a pedological approach. The spatial variation of phosphorus was also investigated. The materials found within these ditches are natural soil bodies. Pedogenic processes operating in these soils include organic matter accumulation, structure formation, Fe oxidation and reduction, sulfuricization, sulfidization, and bioturbation. Soil phosphorus was well autocorrelated, and exhibited a high degree of spatial variation. Ditch soil phosphorus at depth ranged from 4 to 4882 mg kg-1 for total phosphorus, 4 to 4631 mg kg-1 for oxalate-extractable phosphorus, and 2 to 401 mg kg-1 for Mehlich-3 phosphorus. Future ditch management strategies should include a subsurface soils component.Item WATER QUALITY IN MANAGEMENT INTENSIVE GRAZING AND CONFINED FEEDING DAIRY FARM WATERSHEDS(2005-07-12) Gilker, Rachel Esther; Weil, Ray R.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dairy farm size has increased in the United States, while the profit margin has decreased. An alternative to confined feeding dairy farming is management intensive grazing (MIG), a grass-based system relying on rotational grazing for most of the herd's dietary requirements. Previous research has measured high levels of nitrate leaching under MIG, citing the liquid nature and high nitrogen (N) content of urine. However, this research included heavy N fertilizer applications or was conducted on monolith lysimeters with artificial leaching processes and did not accurately represent mid-Atlantic MIG dairy farms. Phosphorus (P) losses have typically been attributed to runoff and erosion but are now being ascribed to leaching as well. To measure the magnitude of N and P losses to groundwater, we sampled shallow groundwater and pore water on one confined feeding and two MIG-based Maryland dairy farms between 2001 and 2004. Transects of nested piezometers and ceramic-tipped suction lysimeters were installed in two watersheds on each farm. Two streams running through two of the grazed watersheds were also sampled to measure the effects of grazing on surface water. For three years, groundwater and surface water samples were collected biweekly and pore water was collected when conditions made it possible. Samples were analyzed for inorganic N and dissolved reactive P and were digested for determination of dissolved organic N and P, pools previously not considered major sources of nutrient loss. Seasonal mean nitrate concentrations under the grazed watersheds remained below the EPA maximum contaminant load of 10 mg L-1 with only two exceptions on the grazed watersheds. Mean nitrate concentrations in the four grazed watersheds ranged from 3 to 7.44 mg L-1. Nitrogen losses were closely correlated to farm N surpluses. Groundwater P concentrations exceeded the EPA surface water critical levels in all six watersheds. Geologic factors, rather than dairy farm management, played a large role in P losses. In all watersheds, substantial pools of dissolved organic N and P were measured in groundwater. Low nitrate losses under MIG as well as the environmental advantages inherent in a grass-based system make grazing a viable Best Management Practice.Item WATER AND NUTRIENT DYNAMICS IN CONTAINER-NURSERY PRODUCTION SYSTEMS(2004-04-30) Ristvey, Andrew George; Lea-Cox, John D; Plant Science and Landscape Architecture (PSLA)Water quality remains a predominant issue within the Chesapeake Bay watershed, and nutrient loading continues to undermine the progressive recovery of this ecosystem. Until recently, the ornamental plant industry has had little information to develop better management practices to increase the efficiency of water and nutrient applications. This research used an integrated approach to examine container- production systems, to develop recommendations to increase nutrient uptake efficiency and reduce runoff. A 40-month field study examined the effects of various cultural practices on irrigation and nutrient uptake efficiencies. Under cyclic scheduling, drip irrigation applied 3 to 4.5 times less water than overhead irrigation and had significantly less runoff when plants were spaced at low densities. While drip irrigation is significantly more efficient, overhead irrigation is more practical and economically feasible for most small container-nursery stock. Time Domain Reflectometry (TDR) was examined as an alternative to cyclic scheduling and when used with overhead irrigation, water applications were half that of cyclic irrigation scheduling. . This research simultaneously documented nitrogen (N) and phosphorus (P) dynamics by examining nutrient applications, uptake and leaching over the forty months. In most cases, N and P uptake efficiency and runoff was negatively affected by overhead irrigation, particularly when soluble nutrients were applied via fertigation and at low plant densities. Nitrogen and P efficiencies ranged between 10 and 30% and were dependent upon methods of irrigation and fertilization, plant density and water use. The use of both drip and TDR-scheduled overhead irrigation reduced nutrient runoff to half that of the overhead irrigation program Intensive spring nutrient uptake studies showed that N influences the total growth of Rhododendron (azalea) and P uptake is a function of P fertilization rate and growth, influenced by N rate. Moderate N rates maintained optimal growth, while total P was only required at 1/20 of this N rate. Periodicity in nutrient uptake suggests seasonal timing of fertilizers may increase N and P uptake efficiency. Novel management strategies in the area of irrigation, fertilization, and cultural practices should be adopted by the ornamental industry to improve upon low efficiencies and reduce nutrient pollution in our watersheds.