Environmental Science & Technology
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Item Managing Cover Crops for Better N Efficiency and Soil Health(2024) Stefun, Melissa; Weil, Ray; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Winter cover cropping is a major tool that agriculture can use to protect soil and water quality and mitigate climate change. Unlike farmland in the world at large, most Maryland cropland has seen little tillage disturbance and some level of cover cropping for decades. With that background, field experiments on two soils with contrasting textures at the Beltsville Facility of Central Maryland Research and Education Center tested the effects of cover crop management enhancements on nitrogen (N) leaching, soil health indicators, and cover crop N uptake over three years. Two cover crops (sole rye and a mixture of forage radish, crimson clover, and rye) were compared to a control where cover cropping was ceased. The cash crops were corn and soybean grown in rotation. With best nutrient management practices applied, suction lysimeter sampling at 90 cm depth from October through April showed low levels of N leaching in general, but NO3-N concentrations were significantly lower under cover crops. Overall mean concentrations of NO3-N were 2.20 mg N/L in the control but 0.43 mg N/L under cover crops. Additionally, soil water samples were digested to determine dissolved organic N (DON) which was found to make up between 44-60% of the total dissolved N in the leaching water. In additional experiments, a small fertilizer N application was made to cover crops to stimulate rapid deep rooting with the goal of accessing soluble N deep in the profile to increase N capture by more than the amount of N applied. The response to fall N fertilization failed to accomplish this goal and was not related to the surface soil NO3-N concentration as expected. In spring, cover crops were terminated on three dates from mid-April to mid-May and rye biomass doubled with each extra two weeks it was allowed to grow whether it was in the mix or alone. The effect of cover crops on soil health indicators was evident with increased soil permanganate oxidizable carbon, total soil carbon, lower bulk density, and greater aggregation. These experiments demonstrated that cover crops with enhanced management can have marked effects on an agricultural system already using sustainable practices.Item AUGMENTING SEQUENCING TECHNOLOGY FOR BETTER INFERENCE IN SOIL MICROBIOME ANALYSIS(2023) Epp Schmidt, Dietrich; Yarwood, Stephanie A; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The advent of DNA sequencing revolutionized the field of microbiome research. Many organisms, by virtue of their codependence and/or growth rate, are either impossible or extremely challenging to get into pure culture. Sequencing allows important taxonomic and phylogenetic information to be obtained independent of culturing. Development of the sequencing technology itself has allowed for high throughput workflow that has allowed low cost and extensive sampling of microbiomes across environments. The co-development of reference datasets for taxonomy and functional assignments, along with open-source bioinformatics pipelines has further empowered scientists to explore microbiomes in many environments. However, there are limitations to sequence data that have constrained the ecological inferences in microbiome research. One such limitation, the compositional nature of sequence data, has impeded our ability to make accurate inferences about the environmental drivers of taxon abundance and covariance across conditions. In this dissertation I explore the use of quantitative PCR in combination with sequencing techniques to generate “Quantitative Sequencing” data (QSeq) that mitigates the limitations of compositionality on inferences relating to taxon abundance and covariance across environmental gradients. In chapter 1, I reviewed key characteristics of the soil environment and sequencing as a mechanism for sampling. In chapter 2, I leveraged modeling, synthesis, and literature review methods to establish the questions and data characteristics that demand QSeq methodology. I show that even small amounts of variation in total abundance make determining the effects of environment (biotic and abiotic factors) on any given taxon unreliable without QSeq. In Chapter 3, I extend the logic of quantitative sequencing to improve metagenome prediction from PICRUSt2. Using data synthesis methods, accounting for 16S gene abundance consistently improved the accuracy of predicted functional genes. This was confirmed by high correlations between predicted and measured gene abundance (QPCR). There was however a large variation in prediction accuracy, likely due in part to database biases and in part to decoupling of bacterial function from taxonomy. In Chapter 4, I applied QSeq in the context of an experimental, long-term farming system that has large gradients in total abundance with depth, and I used QSeq to identify taxa that changed in abundance due to different farming system management and soil depth. Finally in Chapter 5, I used QSeq to identify putative N-fixing taxa that responded to glyphosate in four experimental farming systems. I show that the abundance of these taxa were decoupled from other effects of glyphosate on N-fixation in soybean across farming systems.Item DISTRIBUTION AND VARIABILITY OF CARBON STOCKS IN MID-ATLANTIC TIDAL MARSH SOILS(2022) Kim, Jordan; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal marsh wetlands have the capacity to store disproportionately large quantities of Cdespite their small areal extent. Good estimations of this “blue C” are now more critical than ever due to implications for the global C cycle and climate change, especially since C storage in tidal marshes has historically been understudied. In this study, we set out to measure, more accurately estimate, and conceptually model the C stocks in representative tidal marshes of the Mid-Atlantic region. We found that C storage differs significantly in marshes formed among various pedogeomorphic settings due to differences in pedogenic processes and soil morphology. Further, we have demonstrated that the mean C densities of particular soil materials can be used in conjunction with soil morphological descriptions to reliably estimate the C stocks in the absence of laboratory data. Finally, we augmented existing concepts of tidal marshes in the region by incorporating newly gained understandings of the spatial changes in morphology and C stocks across marshes within different pedogeomorphic settings.Item Monitoring and Predicting the Microbial Water Quality in Irrigation Ponds(2022) Stocker, Matthew Daniel; Hill, Robert L; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Small- to medium-sized farm ponds are a popular source of irrigation water and provide a substantial volume of water for crop growth in the United States. The microbial quality of irrigation waters is assessed by measuring concentrations of the fecal indicator bacteria Escherichia coli (E. coli). Minimal guidance currently exists on the use of surface irrigation waters to minimize consumer health risks. The overall objective of this work was to provide science-based guidance for microbial water quality monitoring of irrigation ponds. Spatial and temporal patterns of E. coli were evaluated in two Maryland irrigation ponds over three years of observations. Patterns of E. coli were stable over the three years and found to be significantly correlated to patterns of water parameters such as temperature, dissolved oxygen, turbidity, and pH. The EPA Environmental Fluid Dynamics Code model was used to evaluate the spatial 3D heterogeneity of E. coli concentrations within the ponds. Significant differences in E. coli concentrations by sampling depth were found. Spatial heterogeneity of E. coli within the pond also resulted in substantial temporal variation at the irrigation pump, which was dependent on the intake location. Diurnal variation of E. coli concentrations was assessed for three farm ponds. E. coli concentrations declined from 9:00 to 15:00 for each pond, but statistically significant declines were only observed in two of the three ponds. Dissolved oxygen, pH, and electrical conductance were found to be the most influential environmental variables affecting E. coli concentrations. To better describe the relationships between E. coli and the environmental variables, four machine learning algorithms were used to estimate E. coli concentrations using water quality parameters as predictors. The random forest algorithm provided the highest predictive accuracy with R2 = 0.750 and R2 = 0.745 for Ponds 1 and 2, respectively, in the multi-year dataset containing 12 predictors. Temperature, electrical conductance, and organic matter content were identified as the most influential predictors. It is anticipated that the recommendations contained in this dissertation will be used to improve microbial monitoring strategies and protect public health.Item ORGANIC MATTER SOIL AMENDMENTS, ANOXIC SOIL BIOGEOCHEMISTRY AND WETLAND RESTORATION(2021) Scott, Brian; Yarwood, Stephanie; Baldwin, Andrew H.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Organic Matter (OM) amendments are often used in wetland restoration – a practice required in Maryland and other states. This work summarizes a literature review and lab and field experiments to evaluate the consequences of OM amendment use. The literature review showed that although OM use is widely accepted, the evidence that they are effective is weak, and there can be negative effects. Transplanted topsoil is much more effective than allochthonous OM (e.g., manure). OM amendments were largely ineffective in a field study conducted on a mitigation wetland in Caroline County, MD, and negative consequences were possible, although composting the OM relieved negative effects. One example of ineffectiveness: OM is not needed to develop anaerobic conditions in saturated soil. While in some cases OM seems to be a benefit, as in aboveground biomass production, this is usually accompanied by a loss of diversity and it selects for undesired and invasive species. One of the negative consequences OM is the increased production of methane, a greenhouse gas, which became the focus of this work. Two lab microcosm studies and a field study revealed that rewetting dried soils (as in after mitigation wetland construction) immediately releases small amounts of methane, and methane sharply increases after about 7 weeks. Using OM affects methane production in two ways. First, overall methane production usually increases. Second, the time frame before there is a sharp increase in methane production is shorter, from ~7 weeks to as little as 1 or 2 weeks. These effects are somewhat reduced with composted OM. Using a Stable Isotope Probing microcosm study, the work also helped to identify the archaeal and bacterial taxa that are responsible for the sudden increase in methane. Methanosarcina is likely the primary taxa responsible for methane generation. Understanding the conditions that result in methane emanating from wetlands could lead to practices that reduce its release into the atmosphere, where it contributes to global warming. Methane is a more potent greenhouse gas than carbon dioxide, but is short lived, so controlling methane emissions can have a more immediate effect on climate change.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 Investigating the Effect of Management on Agricultural Organic Nitrogen Cycling and Alternative Nitrification Pathways(2021) Houde, Alyssa Wellman; Yarwood, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This project studied the influence of agricultural management strategies (such as tillage and fertilizer choice) on nitrogen (N) cycling pathways. Soil samples and leachate samples from a series of experimental plots at the Wye Research and Education Center were analyzed using a combination of traditional chemical N measures (DON, PMN, NOx, NH3, TN, and microbial biomass C & N) and novel mass spectrometry techniques (FT-ICR-MS) to characterize shifts in organic matter composition and quantity over time and under three different cover cropping regimes. Analysis of these samples indicate that the DOM (dissolved organic matter) composition of leachate changed significantly with increasing sampling depth. However further research is needed to fully investigate the potential impacts of cover cropping and time on soil and leached DOM and DON. Soil samples were also collected at the Farming Systems Project in Beltsville, MD and at several of the University of Minnesota’s Outreach farms. These samples were analyzed for their abundance of 16S, nirK, nirS, nxrA, and amoA AOB to characterize the nitrifying and denitrifying microbial communities under a combination of management strategies. While the findings were not significant, they indicate that fertilization and tillage may have an impact on the nitrification and denitrification communities.Item QUANTIFICATION OF WATER EXTRACTABLE PHOSPHORUS POOLS IN SOILS AND MANURES TO PREDICT PHOSPHORUS LOSS(2021) Roswall, Lauren T; Toor, Gurpal; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phosphorus (P) is an essential nutrient for sustaining plant, animal, and human health, but can be a pollutant in water bodies. In intensive animal agriculture regions globally, long-term manure application has led to an abundance of P in soils. Exploitation of finite reserves of P is concerning for the future of agriculture and water quality. This research investigates how better understanding the most labile pool of P in soils and manures, i.e., water-extractable P (WEP), can lead to better quantification and risk-assessment of P loss. High P soils were extracted using varying methodology to improve long-term P loss risk assessment. Poultry litter and products were added to a soil to understand how WEP-based application (WEP) affects the loss of dissolved P forms in runoff. We conclude that an accurate quantification of WEP in both soils and manures is needed to improve manure management and mitigate P loss to waterways.Item SUBAQUEOUS SOILS OF SOUTH RIVER, MARYLAND: SOIL-LANDSCAPE MODEL EVALUATION(2021) Park, Cedric Evan; Rabenhorst, Martin C; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The way soils form, their distribution on the landscape, and their interactions with their ecosystems must be understood if they are to be managed well. Our incipient understanding of subaqueous soils limits successful management, but recent research efforts have sought to address this problem. The goal of this study was to evaluate the protocols for describing, characterizing, classifying, and mapping subaqueous soils. To this end, a subaqueous soil-landscape model (Wessel, 2020) was used to predict the distribution of soils in South River, a western shore Chesapeake Bay subestuary. The soils of South River were surveyed, and the observed soils were compared to the predictions. The model provided significant positive guidance for mapping subaqueous soils, confirming that a pedological approach is useful in subaqueous settings. Pedological data were used to generate a subaqueous soils map for South River and make recommendations to refine the model. Protocols related to soil porewater halinity and mineralogy were also investigated.Item Sulfur Management to Enhance Yield and Protein Quality of Grain Legumes(2020) Rushovich, Dana Alison; Weil, Raymond; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sulfur (S) is an essential macronutrient and a key component in essential amino acids, methionine and cysteine (MET+CYS) that are the building blocks of protein. For a number of reasons, including difficulties in analysis for S, soil testing and fertility management has largely ignored this essential plant macronutrient. Trials were carried out over three years to evaluate the role of S fertility on the yield, seed S content, S yield and seed MET+CYS content of three types of grain legumes: double crop soybeans (Glycine Max), full season soybeans, and common dry beans (Phaseolus vulgaris). Sulfur fertility management significantly increased yield, seed S content, S yield, and seed MET+CYS content on low S soils. Additionally, four soil extractions were evaluated as potential methods to improve S fertility recommendations. Calcium phosphate extractions more accurately identified sites that had a yield or seed s content response to applied S compared to Mehlich 3 and Calcium Chloride.