Gurpal S. ToorSoil & water quality
Portrait of Gurpal S. Toor
Gurpal S. Toor, Ph.D.Professor and Extension Specialist, University of MarylandFellow, Soil Science Society of America · Fellow, American Society of Agronomy

Gurpal S. Toor is a Professor and Extension Specialist in Nutrient Management and Water Quality at the University of Maryland, College Park, USA. His research examines nitrogen and phosphorus sources, transformations, and transport in agricultural and urban landscapes, combining field monitoring, isotope tracing, and biogeochemical analyses to identify nutrient pathways and evaluate practices that protect water quality. His Extension program translates research into guidance for land managers, communities, farmers, and policymakers.

More about Gurpal

His work on residential runoff, stormwater systems, and onsite wastewater links environmental processes with practical nutrient management. He contributes to Maryland initiatives that address nutrient losses and protect water quality in the Chesapeake Bay watershed. He earned his Ph.D. in environmental soil science from Lincoln University, New Zealand, and held faculty appointments at the University of Florida before joining Maryland. He has also served on the Board of Directors and Science Policy Committee of the American Society of Agronomy and the Soil Science Society of America.

Nitrogen · Phosphorus · Water

Chasing nutrients from land to water.

Our group studies how nitrogen and phosphorus move from the farms and cities where they are applied, through soils and shallow groundwater, into streams, bays, and lakes. The question that organizes the work is residence time: what a landscape stores, what it releases, and on what schedule.

Explore the research Latest news
Cutaway landscape at dusk: rain falls on a farm field and a town; nitrogen seeps down through soil layers into groundwater while phosphorus runs off the surface and out a drain pipe; both travel down a stream past monitoring points into a bay
HoursSeasonYearsDecades

Nitrogen and phosphorus leave farms and towns by surface runoff, tile drains, and groundwater, and reach the water in hours to decades. Illustration.

Now underwayDecoding dissolved organic nitrogen in cropping systems: what it is made of and where it goes New paper · STOTENDown the ditch, nitrogen and phosphorus part ways Viewpoint · ES&TUrban nitrogen policy should follow pathways, not the calendar In the fieldStorm-by-storm nitrogen and phosphorus monitoring in 15 small agricultural catchments

The program

Feeding people without fouling the water

Crops need nitrogen and phosphorus. Bays and lakes need far less of them. Most of what we apply to land is held in soils, ditches, and groundwater for hours to decades before it reaches water. Our group measures those stores and pathways, and turns the results into tools farmers and regulators use.

Cross-section from a farm through a town to a bay. Fertilizer, manure, and biosolids go onto fields. Phosphorus builds up in topsoil for decades; tile drains and ditches carry nutrients in days to seasons; nitrate moves through groundwater for years to decades; septic effluent seeps from homes; storm runoff reaches the bay in hours, where algal blooms and low oxygen result. Pins mark the three research lines.
Swipe to see the whole diagram →
The same nitrogen and phosphorus that grow a crop can take hours or decades to reach a bay. Conceptual diagram, not to scale.

In the field

Fifteen small agricultural catchments, storm by storm

From farms to the Chesapeake Bay. Stations at the outlets of small agricultural catchments measure flow and collect water every time it rains, across the three pathways water takes to leave agricultural farms: overland flow, tile drains, and open ditches.

15 small agricultural catchments, 5 to 140 acres7,400+ runoff and drainage samples in three years3 flow paths: overland, tile, ditch

A storm reaches the flume and runoff starts to pour through. Trail-camera clip.
Monitoring station at the outlet of a small agricultural catchment, with a flume, autosampler shelter, rain gauge, and solar panel beside a cornfield
Flume, autosampler, rain gauge, and solar panel at a catchment outlet.
Open drainage ditch running between green fields, with a monitoring structure in the water
An open drainage ditch, monitored where it leaves the field.
Runoff pouring through a flume at the edge of a field during a summer storm
Summer storm runoff leaving a field through the flume.
Close-up of a flume floor coated with sediment after a storm, with corn stalks behind
What a storm leaves behind: sediment on the flume floor.

Keeping the stations running

A station visit, sped up: cleaning the flume and servicing the autosampler.
Another visit, sped up: collecting samples and checking the data on a laptop.
Drainage water flowing through a water-control structure on a farm ditch, beside the monitoring station.
Four people at a monitoring station in a field: one in the station vault, one with a phone, one at a laptop with cables, and one watching
Installing a sensor at a monitoring station.

Research

Three questions along the way

Nitrogen and phosphorus can take years to decades to travel from farm fields to streams and bays. Held in soils, sediments, and groundwater and routed along slow, winding flow paths, they keep arriving long after practices change, which is why even well-run conservation programs can wait decades for cleaner water. Each line of our work follows one part of that journey.

Schematic of one storm: phosphate flushes early, nitrate dips and arrives late, and a concentration–discharge loop shows where nutrients were stored
PNLegacy nutrients

What controls the release of legacy phosphorus and nitrogen?

Decades of surplus fertilizer and manure sit in soils, ditch sediments, and groundwater. Our group measures how that legacy is released, storm by storm, in small agricultural catchments and drainage networks, and identifies the forms it is held in, from dissolved organic molecules to soil minerals.

Event-scale sensors · C–Q hysteresis · molecules to minerals: FT‑ICR‑MS, ³¹P NMR, P K‑edge XANES

Molecular makeup of dissolved organic N and P — Water Research 2022 Phosphate minerals in legacy-P soils by XANES — Chemosphere 2022
Schematic dual-isotope plot of nitrate showing source ranges for atmospheric nitrate, nitrate fertilizer, ammonium fertilizer, soil nitrogen, and manure and septic waste, with a denitrification arrow
NSources & transit

Where do nutrients in water come from, and how much is lost on the way?

Nitrate and water isotopes separate fertilizer, manure, and septic sources from what happens in transit. New work follows dissolved organic nitrogen, the form that nitrate measurements miss, from its molecular makeup to its fate in cropping systems.

δ¹⁵N, δ¹⁸O of nitrate · δ²H, δ¹⁷O, δ¹⁸O of water · molecular DON

Isotopes reveal nitrate sources in stormwater — Environ. Sci. Technol. 2016 Nitrate sources and transformation along farm ditches — Sci. Total Environ. 2026

News & field notes

From the field

All news
PaperSept 2026

Urban nitrogen policy should follow pathways, not the calendar

Seasonal fertilizer blackouts are an imperfect proxy for nitrogen export. This ES&T Viewpoint argues that policy should target sources, forms, storage pools, and hydrologic pathways.

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Read the story →
VideoField video

A storm reaches the flume

A trail camera at the outlet of one of our small agricultural catchments catches runoff starting to pour through the flume as a storm arrives.

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8-second clip
Paper2026

Nitrogen loss from agricultural land to water

Our new comprehensive review of how nitrogen moves from farmland to water: the pathways, the drivers, and what they mean for management. Advances in Agronomy 198.

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Read the paper →

Publications

Selected papers

A steady record from 2015 to today, including long-running collaborations in China, Croatia, and Chile. Every paper, with citations, is on Google Scholar.

127peer-reviewed papers
7,975citations
49h-index

Google Scholar, October 2026

Google Scholar

29 papers · hover near the top or bottom, use the arrows, or scroll inside the list

Teaching & mentoring

Training the people who manage nutrients next

Most of my teaching happens one-on-one, in the lab and the field, and in the certification courses where consultants and farmers learn the rules they will work under.

6Ph.D. students chaired or co-chaired
14M.S. students chaired
20graduate committees served on as a member
5postdoctoral researchers
8research scientists and professional track faculty
21undergraduate and high school researchers
Urban Soil and Water SystemsA course I designed and taught at the University of Florida for undergraduate and graduate students: 136 students over 12 offerings, with a mean student rating of 4.69 out of 5.
Six-lecture series in ChinaWater quality monitoring, nitrogen isotopes, climate effects on nutrient losses, phosphorus, organic wastes, and scientific writing, Northwest A&F University, 2023.
Teachers College AwardUF/IFAS, 2010.
Aerial view of a field crew beside a tractor and dump trailer on a hillside field, with farm buildings and silos behind
Setting up a field plot experiment with students and staff.

People

Where the group has gone

Former students, postdocs, and professional track faculty now work in universities, research centers, government agencies, and water utilities on three continents.

Two group members standing between two monitoring stations with autosampler housings, solar panels, and rain gauges, beside a pond and a harvested field
Two monitoring stations at a catchment outlet, each with an autosampler, solar panel, and rain gauge.
A group member holding a soil probe among tall corn, with an orange sample bucket
Sampling soil in a cornfield.
  • Charles BurgisPostdocAssistant Professor of Civil and Environmental Engineering, Villanova University
  • Jesse RadolinskiPostdocAssistant Professor, Arkansas State University
  • Shuiwang DuanProfessional track facultyUSDA Agricultural Research Service
  • Fajun SunProfessional track facultyProgram Manager, University of Maryland
  • Kelly HaydenProfessional track facultyPh.D. student, Stony Brook University
  • Casey GreufeProfessional track facultyNutrient management and water quality work in Iowa
  • Mary LuskPh.D. 2015Assistant Professor, University of Florida Gulf Coast REC
  • Mriganka DePh.D. 2015Associate Professor, Minnesota State University, Mankato
  • Ignacio Rodríguez-JorqueraPh.D. 2014Executive Director, Centro de Humedales Río Cruces, Universidad Austral de Chile
  • Manmeet WariaPh.D. 2011Senior Scientist, Orange County Water District
  • Jariani JaniPh.D. 2018Researcher, University of Malaya
  • Josefin Edeback-HirstM.S. 2015Senior Environmental Engineer, Hazen & Sawyer
  • Bethzaida (Betzy) ColonM.S. 2015Business Director and Environmental & Social Safeguards Specialist, Washington, D.C.–Baltimore area
  • Matthew JablonskiM.S. 2017Supervisor, South Florida Water Management District
  • Natasha DarreM.S. 2017NASA Kennedy Space Center

Extension & tools

Science that has to hold up in regulation and on the farm

A researcher explains a catchment monitoring station, with its flume and sampler shelter, to a group of farmers and agency staff at a field day
Field day at a small agricultural catchment monitoring station.
Phosphorus Management ToolLeading the field testing and revision of Maryland’s phosphorus risk index, the tool written into the state’s nutrient management regulations.
Certification trainingTeaching the nutrient cycles and soil testing lectures in Maryland’s Fundamentals of Nutrient Management course for new consultants and farmers.
U.S. Environmental Protection AgencyPresenting nutrient-flux data from small agricultural catchments at EPA modeling and agriculture workshops.
Farmer meetings and field daysNitrogen, phosphorus, and soil testing talks at winter agronomy meetings and field days from Garrett County to the Lower Shore.

Extension publications

Numbered soil samples in tins, from pale sandy soil to dark, carbon-rich soil

Maryland New Extension bulletin · September 2026

Measuring, modeling, and managing soil organic carbon in Maryland agriculture

Toor & Dorsey · University of Maryland Extension EB-2026-0828

We tested COMET-Farm, a widely used carbon decision tool, against measured soil organic carbon on 15 Maryland fields. Its default estimates missed by 18.8 tonnes of carbon per hectare on average; field-specific inputs cut the miss to 7.9, and both pointed the same way on carbon change in 13 of 15 fields. The advice: use the tool to compare management scenarios, not as a measurement of what is in the soil, and pair it with sampling, especially on poorly drained or manured fields.

Read the bulletin

Around the world

Nutrients and water are a global problem

Collaborations, appointments, and lectures in ten countries, with the most active partnerships in China, Chile, and Croatia.

Recognition & service

Fellowships, editing, and review

Recognition

  • 2025
    Fellow, American Society of Agronomy
  • 2023
    Fellow, Soil Science Society of America
  • 2023
    Research Excellence Award, University of Maryland
  • 2022–24
    Board of Directors, American Society of Agronomy
  • 2022
    Dean’s Grantsmanship Award, College of Agriculture and Natural Resources, UMD
  • 2021–22
    LEAD21 national land-grant leadership program
  • 2019–20
    Chair, SERA-17, the national working group on minimizing nutrient loss from the landscape
  • 2018
    Extension Award, Department of Environmental Science and Technology, UMD

Editorial and review service

  • Since 2019
    Academic Editor, PLOS ONE
  • Since 2020
    Academic Editor, Water
  • Since 2023
    Academic Editor, Scientific Reports
  • 2016–24
    Section Editor, Current Pollution Reports
  • 2009–14
    Associate Editor, then Senior Associate Editor, Journal of Environmental Quality
  • Reviewer
    114 manuscripts for leading journals, and 170+ grant proposals for USDA-NIFA, NSF, EPA, USGS, USDA-ARS, and USAID

Supported by

Funders and partners

Agencies, utilities, and grower organizations that have funded the work in Maryland and Florida.