About

Owen Duckworth is a Professor and Director of Soil Science Graduate Programs in the Department of Crop and Soil Sciences at NC State University. His research focuses on the activity of microbes and their impact on the biogeochemical flow of nutrients and contaminants in the environment. His work primarily investigates the thermodynamics and kinetics of aqueous and interfacial reactions involving biogenic exudates, contributing to the understanding of the biogeochemical cycling of natural and anthropogenic species. Dr. Duckworth employs a multidisciplinary approach that combines traditional wet-chemical, field, and microbiological methods with modern spectroscopic, microscopic, genetic, and theoretical techniques. This integrated methodology aims to elucidate mechanisms and reaction pathways on molecular to macroscopic scales, advancing knowledge in soil and environmental biogeochemistry.

Research topics

• Chemistry
• Ecology
• Organic chemistry
• Biology
• Environmental chemistry
• Environmental science
• Agronomy
• Soil science
• Nuclear chemistry
• Geology
• Inorganic chemistry

Selected publications

• High‐Resolution Soil Total Phosphorus Mapping for the Conterminous USA Using Machine Learning

  Journal of Geophysical Research Biogeosciences · 2026-01-01

  articleOpen accessSenior authorCorresponding

  Abstract Accurate estimates of soil total phosphorus (TP) concentrations are essential for sustainable nutrient management, food security, and water quality protection. This study predicts and maps the spatial distribution of TP in the top 5 cm and C horizon of soils across the conterminous USA (CONUS) using data from the Geochemical and Mineralogical Data for Soils of the Conterminous United States. We compare the performances of random forest (RF) and inverse distance weighting (IDW) to model and generate soil TP predictions. The RF incorporates 19 predictor variables, including spatial coordinates, climate, soil properties, and topography, while IDW relies solely on coordinates and interpolates between soil TP observations. Models are evaluated using five‐fold cross‐validation. The RF models outperform the IDW models and explain 52% (RMSE = 0.22 log 10 mg kg −1 ) and 56% (RMSE = 0.26 log 10 mg kg −1 ) of the variance in soil TP for the top 5 cm and C horizon, respectively. As expected, both model types identify higher TP concentrations in the top 5 cm than in the C horizon, particularly in agricultural regions, reflecting anthropogenic influences. Furthermore, the RF‐generated maps show more realistic spatial patterns that capture the heterogeneity of the CONUS and avoid the bullseye patterns often characteristic of IDW‐generated maps. Additional insights from the RF models show that coordinates, soil texture, pH, and climate are top predictors of soil TP. Increased availability of variables, such as iron and aluminum, that can bind with phosphorus in soils, could improve RF model performance.

  PublisherOA PDFDOI

• Comparative dissolution of iron-bearing minerals by catecholate and hydroxamate siderophores under oxic and anoxic conditions

  Geochimica et Cosmochimica Acta · 2026-01-11 · 1 citations

  article
  PublisherDOI

• Why Does Overapplication of Phosphorus Fertilizers Occur: Insights from North Carolina Farmers

  Agriculture · 2025-03-12 · 2 citations

  articleOpen accessSenior author

  To minimize environmental damage, conserve global diminishing fertilizer reserves, all while maximizing food production, it is essential that farmers apply phosphate fertilizers at the optimal rate. The purpose of this study is to assess grower attitudes and behavior, with respect to proper application of phosphorus, and to investigate how certain exogenous factors might influence such applications. Data were analyzed from a survey conducted in North Carolina, USA, with 122 farmer participants. The findings reveal that annual phosphorus applications consistently exceed recommendations, which indicates overapplication, leading to economic inefficiency and environmental concerns. Overapplication is neither due to knowledge gaps in nutrient concentrations in the soil nor the lack of interest in soil sampling, as 99% of farmers submit soil tests as frequently or more frequently than every two years. Only 36% of growers indicated that they would not apply phosphorus if their soil report indicated that levels were sufficient, and that none was required. Additionally, overapplication is not strongly influenced by price effects, as only nine percent of growers abandoned applications in 2021, following a dramatic spike doubling fertilizer prices. The adoption of reduced phosphate fertilization will depend on strong local trusted technical assistance and continued extension education.

  PublisherOA PDFDOI

• Landscape Position and Burn Intensity Influence Heat-Induced Soil Chromium Contamination

  Environmental Science & Technology · 2025-11-25

  article

  Wildfires are increasing in extent and severity, posing a worldwide threat to human and environmental health. Fire-induced oxidation of Cr in soils can generate hexavalent chromium (Cr(VI)), a mobile and toxic Class A carcinogen, but the controls on Cr(VI) generation across landscapes are poorly constrained. Here, we use natural soil samples, laboratory experimentation, and spectroscopic analyses to simulate and quantify how burn intensity and landscape position drive Cr(VI) generation and mobility across an unburned serpentine soil toposequence in southwestern Oregon. Maximum Cr(VI) was generated in summit soils burned at 400 °C, and Cr(VI) concentrations decreased downslope. Although reactive secondary minerals generally transformed toward more ordered phases with increased burn intensity, Cr(VI) was mainly associated with poorly ordered (oxy)hydroxides that formed in soils between 200-600 °C. The availability of Cr and Cr(VI) was negligible in soils burned at 800 °C due to Cr incorporation into newly crystallized minerals. Column experiments revealed that Cr(VI) efflux from burned soils could persist at levels exceeding drinking water screening levels for up to two years after a wildfire event, depending on hillslope position. Overall, these findings demonstrate that both fire intensity and geomorphic context (e.g., degree of soil weathering) codetermine Cr(VI) risks to soil and water quality in postfire landscapes.

  PublisherDOI

• Predicting arsenic and manganese contamination in private well water with Machine Learning: An integrated analysis of geologic, well construction, and permitting data

  The Science of The Total Environment · 2025-11-18

  articleOpen access

  Exposure to arsenic (As) and manganese (Mn) through private well water is a pressing public health issue in North Carolina (NC). The goal of this study was to identify geologic, geographic, well construction, and water characteristics (e.g. pH) that are predictive of As and Mn concentrations in private wells. Data collected from over 700 private well water tests from Union County, NC, were analyzed, including thirteen variables spanning well construction and water characteristics that were joined with geologic and geographic features. These data were used to develop random forest (RF) and support vector machine (SVM) models to predict whether wells exceeded their respective maximum contaminant level (MCL) or health advisory level (HAL) (10 ppb for As; 300 ppb for Mn) using four different variable combinations (use cases). Major findings included that As and Mn contamination was prevalent with 18 % and 12 % of tested wells exceeding the MCL and HAL, respectively. Most algorithms across the use cases had generally high predictivity (AUC > 0.7). The top performing models used a linear kernel SVM that leveraged all thirteen variables for As (AUC = 0.80) and the geologic/geographic variables for Mn (AUC = 0.74). When classifying As concentrations, longitude, flow rate, pH, and land use were the most important predictors of contamination. When classifying Mn concentrations, casing depth, longitude, and latitude were the most important predictors. In conclusion, these findings can be used to inform the identification of private wells at-risk for metal contamination, prioritize intervention efforts for existing wells, and provide safer parameters for newly constructed wells. • Permitting data was collected from private drinking wells in Union County, NC. • 18 % and 12 % of tested wells exceeded the MCL and HAL for Arsenic and Manganese, respectively. • Most models were able to predict metal contamination in wells (AUC > 0.7). • Contaminated wells were mostly found on the east and were underlain with mudstone rock. • Casing depth and geology were top contributors to model predictivity.

  PublisherDOI

• Quantifying Summer Internal Phosphorus Loading in Large Lakes across the United States

  Environmental Science & Technology · 2025-05-20 · 4 citations

  article

  Internal phosphorus loading (IPL) can be a significant phosphorus (P) source in freshwater systems, often causing water-quality improvement delays. Despite its importance, IPL estimates are missing for many freshwater systems due to several large-scale measuring and modeling challenges. In this study, we develop a modeling framework to estimate summer anoxic sediment release rates (SRRs) for P in 5899 large lakes and reservoirs (surface area > 1.0 km2; mixing depth < maximum depth) across the contiguous US (CONUS). Our framework combines random forest models for bottom-water temperature (BT) and surface-water total P (TP) with a mixed-effects regression model for SRR, and it includes uncertainty propagation across these models. Our results indicate that mean summer SRR ranges from 1 to 37 mg/m2/day across CONUS lakes, with 31% of waterbodies having SRR > 10 mg/m2/day. Areas of high SRR are generally associated with high predicted surface-water TP, which is particularly common in agricultural areas. Uncertainties in SRR predictions are largely attributable to the random forest-based inputs and predictive error in the SRR regression. In relatively dry summers, IPL is likely to be higher than external loading in 26% of watersheds. Overall, our results reveal where IPL can be a critical factor in watershed nutrient management.

  PublisherDOI

• Degradation of catecholate, hydroxamate, and carboxylate model siderophores by extracellular enzymes

  PLoS ONE · 2025-08-19 · 3 citations

  articleOpen accessCorresponding

  Siderophores are low-molecular weight biomolecules with a high affinity for ferric iron (FeIII) that can impact plant and microbial growth. Although their formation and biology have been investigated in detail, little is known about the environmental fate of siderophores, including their potential reactions with common degradative enzymes, which may influence or hinder the ability to promote the uptake of Fe for plants and microbes. In this study, we examined the ability of the model extracellular enzymes phenol oxidase, protease, and horseradish peroxidase to degrade apo siderophores and FeIII siderophore complexes. The siderophores were selected to represent the natural diversity of siderophore structures: the bacterial triscatecholamide siderophore protochelin; the bacterial trishydroxamate siderophore desferrioxamine B (DFOB); and the synthetic carboxylate phytosiderophore analog proline-2'-deoxymugineic acid (PDMA). In general, apo siderophores were more susceptible to degradation, with some protection of the siderophore provided by FeIII complexation. Phenol oxidase reacted rapidly with protochelin, leading to 90% degradation of protochelin after 24 hours of reaction, which could be modeled by Michaelis-Menten kinetics. Peroxidases in the presence of H2O2 were also effective in the degradation of protochelin (80%) and, to a lesser extent, reacted with DFOB, leading to ~5% degradation. Control experiments showed that protochelin oxidation is caused primarily by H2O2 alone, even in the absence of the peroxidase enzyme. When bound to FeIII, the degradation of protochelin by phenol oxidase and DFOB degradation by peroxidase was reduced by ~50% and ~3%, respectively. No significant reaction was detected between PDMA and any of the three enzymes, supporting its proposed use for plant Fe fertilization.

  PublisherOA PDFDOI

• Impact of labile organic carbon and manganese oxide on chromium and vanadium subsurface mobility: evidence from laboratory incubation experiments

  Environmental Science Processes & Impacts · 2025-01-01

  article

  Dissolved organic carbon can facilitate the abiotic solubilization of chromium and vanadium from saprolite to groundwater.

  PublisherDOI

• Commercial compost amendments inhibit the bioavailability and plant uptake of per- and polyfluoroalkyl substances in soil-porewater-lettuce systems

  Environment International · 2024-03-29 · 13 citations

  articleOpen accessSenior author

  Compost is widely used in agriculture as fertilizer while providing a practical option for solid municipal waste disposal. However, compost may also contain eight per- and polyfluoroalkyl substances (PFAS), potentially impacting soils and leading to PFAS entry into food chains and ultimately human exposure risks via dietary intake. This study examined how compost affects the bioavailability and uptake of eight PFAS (two ethers, three fluorotelomer sulfonates, and three perfluorosulfonates) by lettuce (Lactuca sativa) grown in commercial organic compost-amended, PFAS spiked soils. After 50 days of greenhouse experiment, PFAS uptake by lettuce decreased (by up to 90.5 %) with the increasing compost amendment ratios (0–20 %, w/w), consistent with their decreased porewater concentrations (by 30.7–86.3 %) in compost-amended soils. Decreased bioavailability of PFAS was evidenced by the increased in-situ soil-porewater distribution coefficients (Kd) (by factors of 1.5–7.0) with increasing compost additions. Significant negative (or positive) correlations (R2 ≥ 0.55) were observed between plant bioaccumulation (or soil-porewater distribution coefficient) and soil organic carbon content, suggesting that compost amendment inhibited plant uptake of PFAS mainly by increasing soil organic carbon and enhancing PFAS sorption. However, short-chain PFAS alternatives (i.e., Perfluoro-2-methoxyacetic acid (PFMOAA)) were effectively translocated to shoots with translocation factors > 2.9, increasing their risks of contamination in leafy vegetables. Our findings underscore the necessity for comprehensive risk assessment of compost-borne PFAS when using commercial compost products in agricultural lands.

  PublisherDOI

• Tracing the Environmental Effects of Mineral Fertilizer Application with Trace Elements and Strontium Isotope Variations

  Environmental Science & Technology Letters · 2024-05-09 · 13 citations

  article

  Fertilizer utilization is critical for food security. This study examines the occurrence of trace elements (TEs) and Sr isotope (87Sr/86Sr) variations in phosphate rocks and mineral fertilizers from a sample collection representative of major phosphate producing countries. We show high concentrations of several TEs in phosphate rocks (n = 76) and their selective enrichment in phosphate fertilizers (n = 40) of specific origin. Consistent with the concentrations in parent phosphate rocks, phosphate fertilizers from the U.S. and Middle East have substantially higher concentrations of U, Cd, Cr, V, and Mo than those in fertilizers from China and India. Yet, fertilizers from China and India generally have higher concentrations of As. The 87Sr/86Sr in phosphate fertilizers directly mimic the composition of their source phosphate rocks, with distinctive higher ratios in fertilizers from China and India (0.70955–0.71939) relative to phosphate fertilizers from U.S. and Middle East (0.70748–0.70888). Potash fertilizers have less Sr and TEs and higher 87Sr/86Sr (0.72017–0.79016), causing higher 87Sr/86Sr in mixed NPK-fertilizers. Selective extraction (Mehlich III) of soils from an experimental agricultural site shows relative enrichment of potentially plant-available P, Sr, and TEs in topsoil, which is associated with Sr isotope variation toward the 87Sr/86Sr of the local utilized phosphate fertilizer.

  PublisherDOI

Recent grants

• Elucidating the Effects of Structure on the Redox Reactivity of Mycogenic Mn Oxide Nanoparticles

  NSF · $415k · 2014–2019

• CAREER: Assessing the Reactivity and Diversity of Neutrophilic Iron-Oxidizing Bacteria in Terrestrial Aquatic Environments

  NSF · $400k · 2013–2019

• Defining Critical Roles of Siderophore Structures in Environmental Trace Metal Cycling

  NSF · $297k · 2009–2013

Frequent coauthors

• Scot T. Martin

  Harvard University Press

  28 shared

• Garrison Sposito

  University of California, Berkeley

  25 shared

• John Bargar

  Environmental Molecular Sciences Laboratory

  22 shared

• Matthew L. Polizzotto

  University of Oregon

  17 shared

• James M. Harrington

  RTI International

  14 shared

• Megan Y. Andrews

  University of Southampton

  10 shared

• Detlef R.U. Knappe

  North Carolina State University

  10 shared

• Aziz Amoozegar

  North Carolina State University

  10 shared