Proceedings of a Workshop

Reducing the Health Impacts of the Nitrogen Problem

Proceedings of a Workshop—in Brief

INTRODUCTION

Nitrogen fertilizer is used extensively in the United States to maximize crop yields. As an essential nutrient to plant growth, nitrogen is a critical input to enhance agricultural productivity. However, excess nitrogen can leach into soil and water and contaminate drinking water sources with nitrate, a water-soluble chemical compound of nitrogen. Too much nitrate consumption can pose a health risk. Users of public drinking water supplies and private wells in areas surrounded by farmland are particularly vulnerable to exposure to nitrate in their drinking water.

The workshop Reducing the Health Impacts of the Nitrogen Problem, held over five weekly virtual sessions from January 28 to February 25, 2021, provided a venue to discuss opportunities for reducing exposure to nitrate from agricultural sources in drinking water. More than 50 experts with backgrounds in agriculture, public health, economics, policy, engineering, water, social science, and other fields shared their perspectives through presentations and moderated discussions. The discussions touched on algal blooms and other issues related to excess nitrogen in the environment, but they were not the focus of the workshop. The workshop concentrated on reducing exposure by mitigating or eliminating nitrogen leaching into ground and surface waters from agricultural production systems, not on the downstream removal of nitrogen from drinking water systems or private wells.

The workshop was organized by the Workshop Planning Committee on Reducing the Health Impacts of the Nitrogen Problem as part of the Environmental Health Matters Initiative (EHMI),¹ a program that spans the major units of the National Academies of Sciences, Engineering, and Medicine to facilitate multisector, multidisciplinary exchange around complex environmental heath challenges. Thomas Burke, Johns Hopkins Bloomberg School of Public Health, and EHMI steering committee chair, opened with an overview of EHMI. Given the initiative’s focus on identifying opportunities to mitigate environmental threats to human health, the workshop’s structure was designed to highlight priority areas for intervention by different actors and specific actions that can be taken in these areas.

This Proceedings of a Workshop—in Brief provides the rapporteurs’ high-level summary of the topics and suggestions for potential actions to address challenges surrounding human exposure to nitrate from agricultural sources through drinking water, as discussed at the workshop itself. Additional details and ideas can be found in materials available online.² This document highlights potential opportunities for action, but these should not be viewed as consensus conclusions or recommendations of the National Academies.

Workshop planning committee chair Catherine Kling, Cornell University, summarized the impetus for the workshop. Nitrogen is applied to vast swaths of farmland across the United States with a goal of improving crop yields (see Figure 1). Excess nitrogen that is not taken up by plants flows through soil and drainage systems, ultimately reach-

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ing drinking water sources (see Figure 2). While there is a dearth of data quantifying the amount of nitrogen contamination in drinking water sources or tracing it back to specific farms, Kling described the overall problem as akin to “millions of small, drippy faucets that, unfortunately, are all directly channelized through hydrology into our waters.” The health impacts to people exposed to nitrogen in drinking water (where it exists in the form of nitrate) are not fully understood. Nitrate exposure is known to cause methemoglobinemia, or “blue baby syndrome,” a dangerous blood condition primarily affecting infants less than 6 months old, leading the U.S. Environmental Protection Agency to set a maximum contaminant level (MCL) of 10 mg/L for public drinking water under the Safe Drinking Water Act (SDWA). However, there are gaps in existing federal regulations that potentially leave many Americans at risk of exposure. The SDWA regulates public water providers but does not cover the estimated 43 million people who use private wells. The Clean Water Act regulates water pollution from industrial point sources, but most agricultural activities are exempt from these regulations. There are also recent studies that suggest that drinking nitrate-contaminated water at levels below 10 mg/L over a long period of time can have adverse health effects, such as cancer. Against this backdrop, individuals and organizations in industry, academia, government, and the nonprofit sector have explored technologies, policies, and practices to reduce nitrogen leaks and contamination, but little progress has been made, Kling said. Through an open discussion of various approaches and their economic, social, and legal contexts, the workshop sought to identify opportunities to break through critical barriers and inform future directions.

UNDERSTANDING NITROGEN CONTAMINATION

Mary Ward, National Cancer Institute, summarized the state of the science on the health effects of nitrate exposure via drinking water and dietary sources. Studies indicate the highest concentrations of nitrate are found in private water sources in heavily farmed areas, though these sources are not well monitored because they are not regulated.³ Since the 1940s, studies have provided strong evidence that drinking nitrate-contaminated water, even for a short period, can cause methemoglobinemia.⁴ This evidence is the basis of the current MCL of 10 mg/L in public water sources. In addition, more recent studies suggest that drinking nitrate-contaminated water over a long period of time could lead to cancer, adverse reproductive outcomes, and other health effects at contaminant levels below 10 mg/L.⁵ When ingested, nitrate is converted into nitrite by bacteria in the mouth and subsequently into carcinogenic n-nitroso compounds (NOCs) later in the digestive tract. Beyond methemoglobinemia, the strongest evidence for a relationship between drinking water nitrate ingestion and adverse health outcomes is colorectal cancer, thyroid disease, and neural tube defects. To further elucidate these and other potential health outcomes, Ward said research is needed to examine a wider range of exposure levels (including chronic exposure at levels between 5 and 10 mg/L); clarify the relationship between nitrate ingestion and NOC formation in the body at concentrations below the MCL; understand how the microbiome and other factors may influence the conversion of nitrates after ingestion; and investigate how nitrate may interact with co-occurring water contaminants that are also ingested.⁶ She stressed the need to include the users of private wells—who have been excluded from many previous studies and who likely suffer the worst impacts of nitrate contamination—in future research efforts.

How much nitrogen is leaching through the soil and subsequently contaminating drinking water sources? While the exact amount is unknown, the geographic breadth of row crop and animal production in the United States and results of drinking water tests point to a problem of enormous scale. Matthew Helmers, Iowa State University, described how the nitrogen challenge has grown and spread across the United States, exacerbated by a shift in crop agriculture toward corn and soybeans exclusively and away from crop rotations that include oats and hay and from land used for livestock pasture. The shift to corn and soybeans has reduced the amount of land with vegetative cover

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during the year, leaving upper Midwest soil bare and vulnerable to nitrogen leaching during high precipitation events in the spring. The change also means the use of nitrogen inputs is widespread across a landscape and concentrated at particular times of the year. At the same time, tile-drained landscapes, particularly prevalent in the upper Midwest, have fundamentally altered the hydrology of millions of acres, delivering excess nitrogen directly to streams. Helmers posited that, in the absence of large-scale changes and increased crop diversification, the flow of nitrogen into water is likely to continue to grow in the coming decades as climate change brings more spring precipitation to these areas.

Nitrogen leaks from farms into the environment at many points along the agricultural pipeline. Eric Davidson, University of Maryland Center for Environmental Science, described how knowledge of where those leaks and inefficiencies exist can inform more targeted and effective mitigation strategies, including engineered solutions to control the fate of surplus nitrogen lost to ecosystems.⁷ For example, the CAFE Framework,⁸ which integrates information about the cropping system, the animal-crop system, the food system, and the ecosystem, provides useful insights into the inputs, efficiencies, and leaks of various forms of nitrogen at different scales of analysis.

Nitrate contamination is present in a significant and growing number of U.S. water systems. Craig Cox, Environmental Working Group, presented an analysis of 2016–2017 average nitrate levels in about 50,000 community water systems across the United States, which showed that 129 systems serving about 116,000 people had nitrate at or above the MCL of 10 mg/L. More than 1,700 systems serving more than 5.5 million people had nitrate at or above 5 mg/L. While this is below the MCL, some studies have suggested that long-term exposure to nitrate at this level could potentially cause health problems, as Ward noted in her presentation. Ninety-eight percent of the water systems with nitrate at or above 5 mg/L served communities of 25,000 or fewer people and were concentrated in rural counties with crop and animal agricultural production. Looking closer at the 10 states in which most of those communities were located, another analysis found that about one-quarter of the 4,000 water systems reviewed saw a significant increase in the presence of nitrate from 2003 to 2017. Eighty percent of the communities with an upward trend had small or very small water systems. Noting that the costs of removing nitrate from water are likely prohibitively high for most of these communities, Cox suggested mitigation efforts should focus on prevention rather than treatment of nitrate contamination.

Why is so much nitrogen applied in U.S. agriculture? Kenneth Cassman, University of Nebraska–Lincoln, spoke about the role of nitrogen fertilizer in food, fiber, and fuel production from agriculture. Growers see a direct relationship between the amount of nitrogen applied and agricultural yield; ceasing nitrogen inputs can dramatically reduce yield. Alternative approaches to provide the same level of global crop production without nitrogen are limited and have their own environmental and human costs. Cassman posited that the overarching goal should be to optimize nitrogen use so that nitrogen is applied at the level needed and at the appropriate time in the production calendar to achieve a high yield but without applying so much that the excess leaches, uncontrolled, into soil and water. However, a lack of usable, on-the-ground data poses a critical challenge. Without knowing exactly how much nitrogen a field needs—or how much it is leaching—at a given point in time, it is extremely difficult to achieve this balance. Steve Hoffman, In Depth Agronomy, likened the farmers’ challenge to driving across the country without a gas gauge. He said it is imperative to ensure the crop has adequate nitrogen for the duration of the growing season but difficult to know exactly how much nitrogen is available and being taken up by the plant given the impacts of weather, soil health, and other factors. “If you can’t estimate what the soil is providing for the crop during the crop growth period, the tendency always is to apply a bit more than you need as an insurance policy,” Cassman noted.

To address this fundamental challenge, Cassman said a national research agenda is needed to better understand how to balance production and environmental quality, including adequate research and development funding to provide robust tools farmers can use to evaluate their nitrogen losses. This includes not only direct measurements of nitrogen but also high-quality, real-time information about weather and soils, which affect the need for nitrogen application and the fate of excess nitrogen. To make progress, he urged an interdisciplinary, multisectoral approach. Bonnie Keeler, University of Minnesota, emphasized it was also important to not only have better information about the social costs of excess nitrogen, including the health impacts caused by contaminated drinking water, but also to understand how that information would influence decisions about how and where to invest to address the problem.

OPPORTUNITIES TO REDUCE NITROGEN INPUTS INTO WATER SOURCES

Participants discussed technologies and practices that can potentially reduce the amount of nitrogen that makes its way into drinking water sources. Focusing specifically on tile drainage systems, Jane Frankenberger, Purdue University, presented 10 evidence-based strategies for reducing nitrogen losses,⁹ and other speakers offered examples and ad-

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ditional strategies to curtail nitrogen leaching by reducing the need for nitrogen application, better retaining nitrogen after it is applied, or capturing excess nitrogen before it can flow downstream.

Modifications to the Cropping System

Recommendations for nitrogen use often center around the “four Rs”: applying the right source of nitrogen, at the right place, at the right time, and at the right rate. While this is a useful framework for optimizing nitrogen use, Frankenberger noted that incentives to maximize yield and profit mean that the nitrogen application rate that is “right” or economically optimal for farmers is likely not optimal for reducing nitrogen loss, creating a tension that is at the heart of the nitrogen problem.

Many solutions to reduce nitrogen inputs focus on improving the ability for growers to “spoon-feed” nitrogen to their crops. Rod Weimer, Fagerberg Farms, reported that adopting drip irrigation on his onion farm allowed better control over nitrogen application with far less runoff, reducing water use by 30 percent and reducing nitrogen fertilizer use by up to 40 percent while maintaining a high-quality crop and yield. However, he noted that installing a drip irrigation system can be costly and may not be feasible for many farms without government support.

Altering the mix of plants on the field can reduce the amount of nitrogen that leaves the farm. Alejandro Plastina, Iowa State University, discussed how cover crops, which cover the soil between plantings of annual cash crops, can improve water quality and soil health, reduce erosion, and potentially reduce nitrogen losses. Despite these benefits, however, only a tiny fraction of Midwestern farms use cover crops, largely because they are not profitable for most farmers in crop-only production agriculture. Hoffman noted that farmers are becoming more amenable to incorporating cover crops and growing a more diverse mix of crops overall (e.g., growing barley in addition to corn and soybeans) as they become more concerned about soil health and more willing to experiment to find cover crops or small grains that work in their rotations and in their geographic environments. Several participants noted that the reintegration of crop and cattle production would help make cover crops more economically feasible by replacing some feed costs with cover crop forage and also reduce the need for nitrogen inputs.

Another option is to farm perennial crops. As an example, Steve Culman, The Ohio State University, described Kernza, a perennial wheatgrass that produces edible seed, could be used as forage, and can be grown with far less nitrogen fertilizer than annual wheat.¹⁰ It has a much deeper and more extensive root system than wheat and therefore captures more nitrogen. However, adoption of Kernza is limited at this time, largely due to low yields, a decline in productivity over time, and a lack of markets.

Lisa Schulte Moore, Iowa State University, discussed how prairie strips, sections of diverse perennial vegetation situated between crop fields, can substantially reduce nitrogen losses where shallow groundwater interacts with the prairie root zone. Prairie strips can also reduce erosion and support beneficial fauna such as pollinators and, at roughly $7 per treated acre, represent one of the most cost-effective conservation practices, especially when they are created on unprofitable regions of a farm.¹¹

Another option is to replace traditional synthetic nitrogen fertilizer with alternative sources of nitrogen. Daniel Nocera, Harvard University, discussed how his team effectively turned microbes into a slow-release fertilizer that directly injects nitrogen into the root system while also sequestering carbon. Once the microbial system is established in the soil, it can be maintained with drip irrigation and dramatically cuts the need for synthetic fertilizer. Leif Fixen and Ben Wickerham, The Nature Conservancy, discussed opportunities to develop a market value for livestock manure to better integrate livestock and crop production systems, particularly in the Midwest. Emerging technological approaches can improve the nutrient balance, remove water, allow for easy storage, and support precision application of manure-based fertilizer, though Fixen said further refinements to the supply chain are needed to overcome challenges such as the cost of storage and transportation to make this approach economically viable on an ongoing basis.

Modifications to the Drainage System

Controlling drainage water can reduce the amount of nitrogen that flows downstream.¹² For example, Frankenberger described how adjustable water control structures can be placed in the drainage system to reduce the amount of water drained during times of the growing cycle when drainage is less important. However, she noted that this strategy incurs installation costs and requires time for operation and maintenance. A more hands-off approach is to reduce the drainage intensity by spacing drainage pipes farther apart or placing them closer to the soil surface. This may not be

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an attractive option in areas where climate change is expected to bring increased precipitation, however, as growers in these areas are likely to increase their emphasis on ensuring adequate drainage.

Drainage water can also be captured and recycled in order to re-apply lost nitrogen to the same field later in the growing season, allowing farmers to achieve the same yield while applying less nitrogen overall. In tile-drained systems, this requires taking land out of production in order to construct a reservoir, which can create hurdles in terms of cost. Jim Schepers, University of Nebraska–Lincoln, discussed how in-field irrigation strategies are being leveraged to reduce nitrogen waste and loss in Nebraska. Where excess nitrogen flows into aquifers and then stays near the top of the water, it is possible to irrigate with the nitrogen-rich water at the top of the aquifer. However, for this approach to be feasible, he noted that farmers need better sensors to determine when the crop is close to needing more nitrogen.

Edge-of-Field Practices

Frankenberger described a variety of approaches implemented at the edge of the field that can help to reduce the amount of nitrogen that leaves the farm. Although most of these strategies require taking land out of production and many have no yield benefit, for some farms it is feasible to convert areas that are not profitable anyway, helping to mitigate cost barriers. Constructed wetlands, two-stage ditches,¹³ and saturated buffers¹⁴ are options that can not only increase denitrification but also reduce drain flow and increase plant uptake of nitrogen. Denitrifying woodchip bioreactors, simple trenches filled with woodchips, can enhance the natural biological process of denitrification.

Precision Approaches to Farming and Conservation

Several speakers discussed emerging technological solutions that could help growers manage nitrogen inputs and implement conservation measures in a way that is responsive to the on-the-ground reality of their farm. Bruno Basso, Michigan State University, described how sensors and digital tools can be used to precisely characterize how particular areas of a farm perform over time. Such tools can help growers apply the right amount of nitrogen to the areas where it will have the biggest payoff, or alternatively, inform conservation measures in areas that are more vulnerable to nitrogen surplus or that are unprofitable to farm.

Kit Franklin, Harper Adams University, described how high-resolution surveys of soil texture can be combined with lower-resolution information on soil chemistry and yield maps to understand baseline conditions on a farm, while in-growth sensing approaches based on spectral analysis (using satellite data, drones, or tractor-mounted sensors) can deliver insights into plant health and nitrogen needs in real time. David Lee, Booz Allen Hamilton, discussed how the U.S. Department of Energy’s SMARTFARM program¹⁵ aims to model nitric oxide and other greenhouse gases using technologies such as in-field microneedles for nitrogen monitoring. Ana Arias, University of California, Berkeley, described her team’s work to develop biodegradable sensors that could be spread across a field for continuous monitoring of nitrogen, water, and other variables. Karl Rockne, National Science Foundation, spoke of advances in using plants as sensors to better understand the bioavailability of nitrogen in soil.

APPROACHES TO INCREASE THE ADOPTION OF NITROGEN-CONSERVING PRACTICES

The public health and environmental dangers of nitrogen contamination have been known for decades, and a plethora of approaches has been proven to reduce nitrogen losses. So, why has nitrogen leaching continued to pose a problem? Participants discussed key barriers to the adoption of nitrogen-conserving practices, along with lessons learned from efforts in government, industry, and the nonprofit sector.

Motivating Change

Participants discussed what is needed for growers to adopt conservation practices, in terms of both willingness and feasibility. Linda Prokopy, Purdue University, said that background factors are an important starting place and include characteristics of the farmer, characteristics of the farm, and contextual factors like climate, commodity prices, and policies. These factors, combined with the characteristics of a given conservation practice, influence farmers’ perceptions and in turn feed into attitudes and norms—heavily influenced by the trusted individuals in a farmer’s orbit—and farmers’ perceived level of control over the actions required to adopt the practice. The intention to adopt a practice influences behavior but is mediated by the farmer’s actual level of control over the practice. Other factors, such as financial incentives and knowledge, are often a necessary part of the pipeline from awareness to action but are not in and of

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themselves sufficient to drive change, Prokopy noted. While the drivers of behavior are reasonably well understood up to the point of adoption, she said further research is needed to understand what motivates a farmer to continue using the practice in the future, especially after any initial incentives are terminated.

Farmers are not merely motivated by economic gain; many are intrinsically motivated to support a healthy environment. Rochelle Krusemark, Krusemark Farms, said that in her experience, farmers see themselves as stewards of the land and have a strong drive to retain and improve their soil and efficiencies in order to pass productive farms on to the next generation. Healthy, well-maintained soils, she noted, produce higher yields and better quality products while retaining nutrients better, thus requiring fewer inputs. The increasing adoption of no-till and low-till practices, nutrient and water management strategies, and precision technology for more efficient use of inputs speaks to many farmers’ desire to make U.S. agriculture a global leader in sustainability, she said. Economic drivers are important, as well. Richard Wilkins, Delaware Farm Bureau, pointed to a tension between consumer perceptions and the realities of today’s agricultural sector. While some consumers have expressed a desire for less “science” in the food production system (exemplified in the criticism of advanced plant breeding methods and the use of synthetic pesticides and fertilizers), applying the latest scientific advances is critical, in his view, to the ability to optimize food production and allow farmers to minimize the resources required for each unit of production. He cautioned that increasing regulation in agriculture could lead to even more consolidation and vertical integration in the food and agriculture system.

External motivators can be used to overcome barriers. Kurt Waldman, Indiana University, discussed how certification and supply chain standards can motivate change by rewarding producers for desired practices. This began in the 1970s with a proliferation of “eco-friendly” certifications and expanded to scorecards and public campaigns in the 1980s. More recent years have brought an emphasis on multistakeholder initiatives focused on continuous improvement toward more sustainable practices (e.g., by giving farmers tools for analyzing the environmental outcomes of their practices compared to industry averages). The idea behind all of these efforts is to create a de facto rule to drive the adoption of certain practices through consumer demand for products that comply with them. However, several factors limit the likely impact of these approaches in the context of nitrogen use. One is that demonstrating compliance depends on the ability to collect high-quality, farm-level data and then transmit them all the way through the supply chain. This is especially challenging given that some of the major crops that contribute to nitrogen contamination, such as corn and soybeans, are often consumed indirectly as part of processed food or animal products and are therefore “invisible” in the end product that the consumer encounters, Waldman noted.¹⁶ Plastina pointed out that food labels and certifications can be confusing to consumers and may not truly increase demand, especially given that there are already so many. Another key issue is a lack of incentives; Waldman said many farmers and retailers are reticent to undertake the work required to implement, document, and communicate about their practices unless there is a clear reward for doing so, or a clear cost for not doing so.

Paying for Change

Most nitrogen-conserving practices impose some cost. Wendy Graham, University of Florida, said that ultimately the consumer will need to pay more for food in order to support the changes required to make the agriculture system more sustainable; other participants argued that this is not generally seen as a viable option. Schulte Moore suggested that a nationwide “willingness to pay” study could shed light on the degree to which the public is willing to pay for environmental benefits that farms could provide to society, whether through increased food prices or government subsidies. If a price increase for consumers is not an option, it is necessary to find other opportunities to make a business case for adopting changes, said Jenny Ahlen, Environmental Defense Fund (EDF). Where farmers have a direct relationship with buyers, buyers can incentivize change. She pointed to corporate initiatives by Walmart, Smithfield Foods, Campbell Soup Company, and others as examples of supply chain–based efforts to reduce agricultural inputs and emissions. While the EDF has focused on how to get funding and incentives into the right hands, she noted that many of its efforts have failed due to a lack of economic viability. She suggested the farming community should advocate for the programs and funding that will make implementing changes more feasible for producers.

Another option is to pay producers directly for implementing desired practices. Leah Palm-Forster, University of Delaware, described how conservation auctions can be an efficient approach for connecting land managers with buyers willing to pay them to implement certain management practices. Buyers can be private individuals or groups, regulated entities, or government. Growers can be paid for either practices or outcomes. In theory, auctions provide a platform for reducing the cost of conservation by creating competition among land managers and selecting who can provide the most value per dollar spent. In practice, however, transaction costs can make auctions less cost-effective,

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particularly if participation is low. They require a significant amount of organization and education, and evaluating their benefits also requires time and resources, Palm-Forster noted.

Rockne noted that farmers are in a good position to provide ecosystem services, such as habitat for pollinators and game species. So far such services have been undervalued economically, but they provide a possibility to compensate farmers for a product that addresses the nitrogen problem and provides environmental and recreational benefits.

It is also possible to focus rewards and incentives related to the end of the pipeline by focusing on water quality. Kurt Stephenson, Virginia Polytechnic Institute and State University, discussed how a water quality trading system could provide a way to achieve this but cautioned that this approach would make only a trivial impact under the current circumstances. The degree to which such a system actually reduces nitrogen contamination depends on the ability to set a nitrogen cap below current levels. It also depends on the balance of entities that are regulated and thus motivated to adopt changes (or trade credits for others to do so) versus entities that are not regulated and not willing to adopt practices in exchange for some reward. To make a dent, Stephenson said such systems would need to incentivize trading among a large and diverse array of nitrogen contributors including agricultural entities that are not currently regulated as point sources, urban stormwater systems, and others.

Lessons from Policies and Programs

Most government efforts to control pollution fall into two main categories: incentives and regulations. Steven Wallander, U.S. Department of Agriculture’s Economic Research Service, discussed federal programs seeking to incentivize nitrogen conservation, focusing on two in particular: the Environmental Quality Incentives Program and the Conservation Stewardship Program. While a broad range of policy approaches can potentially have an impact, Wallander stressed that the success of any program is highly dependent on its ability to target the farmers, places, and practices where it can make the most difference. This can be challenging, however, as uptake depends not only on the eligibility rules and design for a particular program, but also on the decisions and behaviors of all of the stakeholders involved. Kling commented that federal and state policies are largely not well targeted or designed to address the scale and breadth of the problem. Overall, Wallander said that federal funding has mostly been devoted to programs that encourage cover crops, nutrient management, and conservation tillage, while less funding has gone to programs that promote riparian buffers, manure management, and other strategies. To design effective policies that link payments to outcomes, he said it is important to consider additionality (the degree to which farmers would adopt the practice irrespective of subsidies), direct impacts of the practices, and the degree to which the adoption of a given practice leads to the joint adoption of other practices or decisions.

Schepers noted that Nebraska’s natural resources districts have taxing authority, and the funds are used to improve on-farm water management. Farmers pay $3 an acre, which supports the purchase of equipment such as soil-water sensors, buried pipelines, and drip irrigation. One district also has the authority to restrict fall fertilizer application and require annual reports of soil and water testing, amount of nitrogen applied, irrigation amount, and yield. Schepers suggested this model could be a possibility for supporting programs to improve nitrogen management.

Mark Lubell, University of California, Davis, discussed the option of regulating nitrogen contamination from farms as point-source pollution. Three programs represent examples of this approach: California’s Irrigated Lands Regulatory Program (ILRP), the Everglades’ Agricultural Area Best Management Practices program, and the European Union’s Nitrates Directive. California’s ILRP takes a hybrid approach combining collaboration and regulation. Under this program, farmers must join coalition groups or register individually with the regional water board and submit documentation such as a farm evaluation plan for protecting surface and groundwater, their plan for irrigation and nitrogen application, and their actual yearly amount of nitrogen applied. It also requires producers to monitor nitrates in domestic wells on irrigated parcels and inform residents of exceedances. While the program currently does not impose nitrogen limits, it lays the groundwork to potentially do so in the future. Studies of farmer adoption of nitrogen-conserving practices since the program started reveal that cost and uncertainty—primarily regarding impacts to yield and return on investment—are important barriers to adoption.

Many programs have used collaborative approaches to increase farmers’ access to critical information they need to adopt nitrogen-conserving practices. Carrie Vollmer-Sanders, The Nature Conservancy, shared how the 4R Nutrient Stewardship Certification Program¹⁷ increased the adoption of these practices by certifying crop advisers—who have direct relationships and established rapport with farmers—to assist farmers with implementation. Because the “right” source, place, time, and rate of nitrogen application varies from place to place, she stressed that standards for 4R guidance should be location specific. She also urged a holistic approach that not only focuses on direct fertilizer application but also incorporates conservation practices such as reduced tillage, buffer strips, and cover crops. Greg La-Barge, The Ohio State University, discussed opportunities for improving the information sources farmers use to assess

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when nitrogen fertilizer is needed, including tools for calculating the optimal nitrogen application rate,¹⁸ extension services that connect farmers with specialists, and approaches to quantify water quality impacts of their practices. While farmers have many potential sources of information for monitoring the health of plants and soils, he noted that consistency among them is important to influence decision making. Several participants stressed the need for improved nitrogen monitoring capabilities in order to address the role of risk and uncertainty as a barrier to practice adoption. Better data could provide feedback to show farmers the impact of their actions and also potentially allow programs to offer guarantees as an insurance policy in case a practice does not have the expected impact. Cassman suggested a collaborative approach to giving farmers greater access to useful data, such as through a large, anonymized database that enables farmers to compare their performance to others with similar conditions. Such a system could also act as a collection of “thousands of field experiments” running each year, helping to build the evidence base for which practices yield the best payoff under given land, climate, and market conditions.

The Floridan Aquifer Collaborative Engagement for Sustainability project,¹⁹ presented by Graham, focuses on increasing the adoption of best management practices, which have been shown to allow farmers to reduce nitrogen application by about one-third without affecting yield. The project uses biophysical models to shed light on tradeoffs involved in different practices. The researchers are also developing economic modeling tools to help farmers balance environmental benefit with economic feasibility. The project uses a participatory modeling process to keep its research grounded in the growers’ needs and priorities and to facilitate stakeholder engagement. Building on this theme of collaboration, Roger Wolf, Iowa Soybean Association, described how the Iowa Soybean Association has advanced conservation goals and best practices to improve water quality at the watershed scale in Iowa using a coalition-based approach. Examples include the Middle Cedar Partnership Program, which connects upstream and downstream stakeholders in the Cedar River watershed to address community priorities such as flooding, and the Agriculture’s Clean Water Alliance, which brings agriculture retailers together around a shared mission to reduce nutrient loss, build healthier soils, and improve water quality in the Raccoon River and Des Moines River watersheds. To build successful coalitions, he said it is essential to have leadership, supportive policies and programs, and associated funding. It is also important to build on shared resources and values while using research, tools, and processes to derive measurable outcomes and impactful results.

Several speakers suggested that the nitrogen problem simply cannot be addressed by incremental fixes to the existing food and agriculture system, but instead will most likely be driven by disruptive changes, such as transformative shifts in consumer preferences, revolutionary new technologies, or the overhaul of current policy structures. Thomas Hertel, Purdue University, reminded participants that interventions to change behavior need to be designed beyond just the local scale. The nitrogen problem is influenced by policies and programs related to biofuels, crop insurance, and trade, among others. Tweaking the application of nitrogen will not mitigate the problem in a meaningful way if the fundamental economic drivers of the current production system are not considered. Frankenberger noted that a lack of accountability for externalities, such as environmental and public health consequences, within the agricultural system perpetuate unsustainable practices. To increase accountability, however, will require a clearer understanding of the benefits that can be derived from various practices, she noted.

The nitrogen problem is also inextricably linked to other issues, including climate change and phosphorous pollution, which may help drive some sweeping changes that address multiple issues, several speakers noted. Rockne and Hoffman both emphasized the need for a systems approach that integrates the management of nitrogen with that of phosphorus and carbon. Hoffman suggested that nitrogen-conserving practices could be paired with emerging carbon credit systems to drive the adoption of practices that bring multiple environmental benefits. To do this effectively, he stressed that a systems approach is needed to understand the full picture of how various practices affect both nitrogen use efficiency and greenhouse gas emissions because it is possible that some nitrogen-conserving practices could reduce nitrogen leaching while potentially increasing the emissions of nitrous oxide, a greenhouse gas.

SUMMARY

The workshop provided a venue for discussing the drivers behind, and opportunities to address, nitrate contamination of drinking water from agricultural sources in the United States. While numerous known practices can help farmers reduce nitrogen use and improve nitrogen uptake, thereby reducing downstream nitrogen contamination, barriers such as cost, uncertainty, and poorly targeted incentives have prevented the widespread adoption of these practices. Participants shared many ideas for moving forward, summarized in Table 1.

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TABLE 1 Potential Actions Suggested by Individual Workshop Participants to Understand and Address the Nitrogen Problem

* Actors have been inferred where attendees did not explicitly identify actors.

NOTES: This table lists potential actions attributed to individual workshop participants in the text above, grouped by similarity, as topics were discussed from different angles at different points during the workshop. This table does not include all of the actions mentioned by participants. These actions are not consensus conclusions or recommendations of the National Academies.

DISCLAIMER: This Proceedings of a Workshop—in Brief was prepared by Kara Laney and Anne Johnson as a factual summary of what occurred at the workshop. The statements recorded here are those of the individual workshop participants and do not necessarily represent the views of all participants, the workshop planning committee, the Environmental Health Matters Initiative committee, or the National Academies of Sciences, Engineering, and Medicine.

REVIEWERS: To ensure that this Proceedings of a Workshop—in Brief meets institutional standards of quality and objectivity, it was reviewed in draft form by Steve Hoffman, InDepth Agronomy; Matt Liebman, Iowa State University; Jennifer McPartland, Environmental Defense Fund; Linda Prokopy, Purdue University; Amy Pruden, Virginia Tech; and Mary Ward, National Cancer Institute. The review comments and draft manuscript remain confidential to protect the integrity of the process.

Workshop planning committee members are Catherine L. Kling (NAS) (Chair), Cornell University; Elena Austin, University of Washington; James N. Galloway (NAS), University of Virginia; Jerry L. Hatfield, U.S. Department of Agriculture-Agricultural Research Service (retired); Rajiv Khosla, Kansas State University; Jennifer McPartland, Environmental Defense Fund; and Robyn S. Wilson, The Ohio State University.

Members of the Environmental Health Matters Initiative committee are Martha E. Rudolph (Co-Chair), Colorado Department of Public Health & Environment (retired); Jonathan M. Samet (Co-Chair), Colorado School of Public Health; Thomas A. Burke, Johns Hopkins Bloomberg School of Public Health; Darrell Boverhof, The Dow Chemical Company; George P. Daston, Procter & Gamble Company; Ana V. Diez Roux (NAM), Drexel University Dornsife School of Public Health; Estella M. Geraghty, Esri; Lynn R. Goldman (NAM), The George Washington University Milken Institute School of Public Health; Daniel S. Greenbaum, Health Effects Institute; Gavin Huntley-Fenner, Huntley-Fenner Advisors; Philip R. Johnson, The Heinz Endowments; Beth Karlin, See Change Institute; Jennifer McPartland, Environmental Defense Fund; Devon C. Payne-Sturges, Maryland Institute for Applied Environmental Health at the University of Maryland School of Public Health; and Amy Pruden, Virginia Tech.

Liaisons of the Environmental Health Matters Initiative committee are Francie Abramson, Target; John Balbus, National Institutes of Health (NIH)/National Institute of Environmental Health Sciences (NIEHS); Linda Birnbaum, NIH/NIEHS; Patrick Breysse, Centers for Disease Control and Prevention; Wayne Cascio, U.S. Environmental Protection Agency; Elizabeth Cisar, U.S. Environmental Protection Agency; David Dyjack, National Environmental Health Association; Zach Freeze, Walmart; Richard Fuller, Pure Earth; Carlos Gonzalez, National Institute of Standards and Technology; Al McGartland, U.S. Environmental Protection Agency; Ansje Miller, Health & Environmental Funders Network; Gary Minsavage, Exxon-Mobil Corporation; Surili Patel, The Metropolitan Group; Geoffrey S. Plumlee, U.S. Geological Survey; Katherine Robb, American Public Health Association; John Seibert, U.S. Department of Defense; Robert Skoglund, Covestro; Joel Tickner, Green Chemistry & Commerce Council (GC3); Juli Trtanj, National Oceanic and Atmospheric Administration; and Jalonne White-Newsome, Empowering a Green Environment and Economy, LLC.

The Environmental Health Matters Initiative, under which this workshop was organized, has been supported by the Gordon and Betty Moore Foundation through Grant GBMR8014, the National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, under Contract No. HHSN263201800029I, the Centers for Disease Control and Prevention, ExxonMobil, Target Corporation, U.S. Environmental Protection Agency, and Walmart Foundation, as well as the National Academy of Sciences Cecil and Ida Green Fund and the National Academy of Sciences George and Cynthia Mitchell Endowment for Sustainability Science. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.

The Environmental Health Matters Initiative committee dedicates this proceedings to Dr. Deborah L. Swackhamer, a member of the committee until her passing in April 2021. Dr. Swackhamer was a supremely accomplished scholar and educator, whose work in the field of public health was unparalleled. She devoted much of her time to the work of the National Academies, and this workshop would not have been possible without her vision and her commitment to protecting water quality for all.

Suggested citation: National Academies of Sciences, Engineering, and Medicine. 2021. Reducing the Health Impacts of the Nitrogen Problem: Proceedings of a Workshop—in Brief. Washington, DC: The National Academies Press. https://doi.org/10.17226/26328.

Division on Earth and Life Studies

Copyright 2021 by the National Academy of Sciences. All rights reserved.