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The California Nitrogen Assessment (CNA): Challenges and Solutions for People, Agriculture, and the Environment is the first comprehensive account of nitrogen flows, practices, and policies for California, encompassing all nitrogen flows—not just those associated with agriculture—and their impacts on ecosystem services and human wellbeing.


How California handles issues of nitrogen will be of interest nationally and internationally, and the goal of the assessment is to link science with action and to produce information that affects both future policy and solutions for addressing nitrogen pollution. The CNA also provides a model for application of integrated ecosystem assessment methods at regional and state (subnational) levels.

The CNA underwent rigorous scientific review and stakeholder review stages, which concluded in June 2015, and was published by the University of California Press in 2016.



Main Messages: Drivers of Nitrogen Flows in California

Forces affecting levels of agricultural production and fossil fuel combustion have been the dominant drivers of the nitrogen (N) cycle in California.

California’s agriculture ships a large share of its products to other states and regions of the world.
For 2009, almost 50% of production went to Europe and Canada, and another 27% to Mexico, China, and Japan. Long-term reduction of transportation costs and reduction of international trade barriers have increased access to international markets for California producers. Thus California carries a lot of the nitrogen burden for many non-Californians.

Over the last fifty years, world population doubled and global income quadrupled.
The resulting increase in global demand for food has been a fundamental driver of expansion of agricultural production in California.

Demand for many of California’s main agricultural exports (pistachios, almonds, rice, walnuts, and oranges) is driven by rising per capita incomes and perceptions of quality.
Accordingly, population growth of high-income countries and increases in household incomes in regions such as East Asia have been the dominant underlying drivers of demand for food and other agricultural commodities produced in California.

Long-term decline in nitrogen fertilizer prices resulted in a large increase in fertilizer use in California from the 1950s through the 1970s.
Thereafter, fertilizer prices were stable relative to the prices of crops until 2000. Fertilizer price increases between 2001 and 2011 have exceeded increases in crop prices.

California's population doubled over the last 50 years, while income more than doubled over the same period.
The growth of California’s economy has resulted in a growth in non-agricultural activities that generate nitrogen emissions, including fossil fuel combustion and wastewater creation. In addition, population and economic growth in California has increased non-agricultural use of resources such as land and water.

In comparison to the effects of economic growth on fossil fuel combustion or the increase in fertilizer use, policies targeting nitrogen pollution have had small effects on nitrogen flows in California to date.

The bottom line: short of catastrophe, demand side fundamentals driven by growth in population and income in the rest of the world suggest that nitrogen flows in California are unlikely to decrease and indeed are likely to continue to grow.

In short, California agriculture is unlikely to disappear; in fact, on balance, it seems more likely to continue growing. Moreover, while there is considerable uncertainty about future climate, water supply, energy prices, and labor costs, the history of innovation in California agriculture gives some tentative (but unproven) reasons to believe that technological change and other forms of adaptation will enable California agriculture to continue to grow in value and employment. As long as the direct benefits of the system are so big, it is not likely that the the attendant external costs (environmentally or socially) will be mitigated on their own. The main sources of uncertainty regarding the future balance of costs and benefits of nitrogen flows in California concern policy choices regarding trade and exchange rates determined in national and international policy arenas and regarding environmental and public health policies largely shaped within California.

Main Messages: California's Nitrogen Cycle

We document six activities that have and will continue to shape California's N cycle:

1) fertilizer use on croplands;
2) feed and manure management;
3) fossil fuel combustion;
4) industrial processes (e.g. chemicals, explosives, and plastics);
5) wastewater management; and
6) land use, land cover, and land management

Everyday actions of Californians radically alter the nitrogen (N) cycle.
Activities such as eating, driving, and even disposing of waste modify N stocks and flows, transferring N statewide and influencing N dynamics beyond California’s border. Six actions fundamentally change N cycling in the state. Each of these drivers has intensified since 1980.

Direct drivers catalyze specific N transformations and transfers between environmental systems. 
There are close relationships between a direct driver and the N cycle. Some direct drivers are much more important than others for specific impacts. Fertilizer use dominates nitrate (NO3−) leaching and nitrous oxide (N2O) emissions. Fuel combustion drives volatilization of nitrogen oxides (NOx). The spatial distributions of activities create distinct regional patterns of consequences (both benefits and costs).

Fertilizer use—inorganic and organic—represents the most significant N cycle modification. 
Sales of chemical N fertilizers have increased considerably since World War II and have risen by at least 40% since 1970, but consumption has leveled off in the past 20 years. Increases in agricultural productivity have been even greater. N fertilizer has been critical for the growth of California’s agricultural industry and rural economy. Despite progress, inorganic N fertilizer application rates (kg ha−1) increased an average of 25% between 1973 and 2005. Data show the majority of California crops recover well below half of applied N, with some crops capturing as little as 30%. Similar or even lower N recovery rates are found when organic N sources are used. Differences between the NUE in research trials at plot and field scale and statewide averages suggest there may be substantial potential for improvement in fertilizer management.

Until recently, manure management decisions were made without much regard to N consequences.
The breadth of techniques used, limitations in available information, and large variability among operations, especially for San Joaquin Valley dairies, make any conclusion about changes in manure management practices tentative. Surveys, however, suggest the recent adoption of manure management techniques helps manage nutrients more effectively. It is important to note that optimal manure N handling is the consequence of many processes and thus must be considered as a system.

Fuel combustion increased significantly, but emissions declined steadily since 1980.
Over the past 30 years, sales of diesel and gasoline fuel, size of the vehicle fleet (both passenger cars and heavy-duty trucks), and the number of stationary sources (e.g., energy production and industry) increased measurably, often doubling. Emissions however have been controlled by aggressive technology forcing regulations. This is most evident in the declining importance of the small vehicle fleet for NOx emissions by comparison to diesel engines.

Ammonia (NH3) is an ingredient in a variety of industrial products - including plastics, nylons, chemical intermediaries, and explosives. However, much of its use and related impacts are poorly documented.
In addition to the release of N compounds during production, the longevity of N-derived industrial products (varying from spatulas to counter tops) results in a latent pool of N in human settlements. Slow degradation means they are a long-term threat to human and environmental health. Industrial use may be as large as 55% of inorganic N fertilizer use annually.

About 77% of food N will enter wastewater collection systems and about 50% of wastewater is dispersed in the environment without N removal treatment. 
This includes wastewater treatment plants with limited nitrification, leakage from sewers, and wastewater infiltration systems. Recent attempts to control N pollution have increased the level of treatment practiced at municipal wastewater facilities throughout California. In 2008, nearly 50% of wastewater treatment facilities reported performing at least advanced secondary treatment and 20% performed tertiary treatment processes. On-site wastewater systems treat the wastewater of more than 3.5 million Californians, with approximately 12,000 new units installed each year. Despite relatively small potential N emissions, improperly sited or malfunctioning systems can cause N discharge hot spots.

Changes in land cover, land use, and land management fundamentally alter N cycling in ways only recently appreciated. 
Change can result from a shift in land cover or simply a change in the intensity of use; both have occurred in California. The net effect of urbanization and agricultural relocation/expansion has led to a 1% decrease in total agricultural land over the same time frame. This shift in land cover has been accompanied with an intensification of use. In croplands, the mix of crops produced has changed from relatively N extensive to N intensive species.  Field crops were still grown on 53% of cropland in 2007 (largely because of the land area dedicated to alfalfa) but this is a significant decrease from 74% in 1970. Simultaneously, the dairy cow population has doubled and the broiler population has tripled in conjunction with higher flock/herd size, concentrating N rich feed in California and amplifying manure N handling concerns. Change can result from a shift in land cover or change in intensity of use. Urbanization has caused agriculture to relocate, often to lands more marginally suited for these systems. The net effect of urbanization and agricultural relocation/expansion has led to a 1% decrease in total agricultural land between 1972 and 2000. This has been accompanied by an intensification of use. The mix of crops produced has changed from relatively N-extensive to N-intensive species. Field crops were still grown on 53% of cropland in 2007 (largely because of the land area dedicated to alfalfa), but this is a significant decrease from 74% in 1970. Simultaneously, the dairy cow population has doubled and the broiler population has tripled, concentrating N-rich feed in California and amplifying manure N handling concerns.

Main Messages: Nitrogen Mass Balance

New reactive nitrogen enters California largely in the form of fertilizer, imported animal feed, and fossil fuel combustion. While some of that nitrogen contributes to productive agriculture, excess nitrogen from those sources contributes to groundwater contamination and air pollutants in the form of ammonia, nitric oxides, and nitrous oxide. Understanding the major nitrogen contributors will help policy-makers and nitrogen users, like farmers, prioritize efforts to improve nitrogen use.

In addition to statewide calculations, the magnitude of nitrogen flows was examined for eight subsystems:

  • cropland
  • livestock
  • urban land
  • people and pets
  • natural land
  • atmosphere
  • surface water
  • groundwater

nitrogen flows


Synthetic fertilizer is the largest statewide import (519 Gg N yr-1) of nitrogen (N) in California.
The predominant fate of this fertilizer is cropland including cultivated agriculture (422 Gg N yr-1) and environmental horticulture (44 Gg N yr-1. However, moderate amounts of synthetic fertilizer are also used on urban land for turfgrass (53 Gg N yr-1).

Excretion of manure is the second largest N flow (416 Gg N yr-1) in California.
The predominant (72%) source of this N is dairy production, with minor contributions from beef, poultry and horses.A large fraction (35%)  of this manure is volatilized as ammonia (NH3) from livestock facilities (97 Gg N yr-1) and after cropland application (45 Gg N yr-1). However, there is limited evidence for rates of ammonia volatilization from manure.  While liquid dairy manure must be applied very locally (within a few kilometers of the source), the solid manure from dairies and other concentrated animal feeding operations can be composted to varying degrees and transported much longer distances (>100 km). However, because of the increased regulation of dairies in the Central Valley (see Chapter 8), it will soon be possible to determine what fraction of the dairy manure is used on the dairy farm compared to what is exported based on the nutrient management plans produced for each dairy.

Synthetically fixed N dominates the N flows to cropland. 
Synthetic fertilizer (466 Gg N yr-1)is the largest flow of N to cropland, but a large fraction of N applied in manure and irrigation water to cropland is also originally fixed synthetically.  On average, we estimated that 69% of the N added annually to cropland statewide is derived from synthetic fixation.  

The biological N fixation that occurs on natural land (139 Gg N yr-1) has become completely overshadowed by the reactive N related to human activity in California.
While this flow was once the major source of new reactive (i.e., biologically available) N to California, it now accounts for less than 10% of new imports at the statewide level. The areal rate (8 kg N ha-1 yr-1) representing the sum of all N inputs to natural lands, including N deposition, is an order of magnitude lower than either urban or cropland. 

The synthetic fixation of chemicals for uses other than fertilizer is a moderate (71 Gg N yr-1) N flow.
These chemicals include everyday household products such as nylon, polyurethane, and acrylonitrile butadiene styrene plastic (ABS).These compounds have been tracked to some degree at the national level (e.g., Domene and Ayres 2001).The true breadth and depth of their production, use, and disposal is poorly established.

Urban land is accumulating N.
Lawn fertilizer, organic waste disposed in landfills, pet waste, fiber (i.e wood products), and non-fertilizer synthetic chemicals are all accumulating in the soils (75 Gg N yr-1), landfills (68 Gg N yr-1), and other built areas associated with urban land (123 Gg N yr-1).

Nitrogen exports to the ocean (39 Gg N yr-1) from California rivers accounts for less than 3% of statewide N imports.
In part, this low rate of export is due to the fact that a major (45%) fraction of the land in California occurs in closed basins with no surface water drainage to the ocean.While concentrations of nitrate in some rivers can be quite high, the total volume of water reaching the ocean is quite low.

Direct sewage export of N to the ocean (82 Gg N yr-1) is more than double the N in the discharge of all rivers in the state combined.
Because of the predominantly coastal population, the majority of wastewater is piped several miles out to the ocean.A growing number of facilities (> 100) in California appear to be using some form of N removal treatment prior to discharge.

Nitrous oxide (N2O) production is a moderate (38 Gg N yr-1) export pathway for N.
Human activities produce 70% of the emissions of this greenhouse gas while the remainder is released from natural land.Agriculture (cropland soils and manure management) was a large fraction (32%) of N2O emissions in the state.

Ammonia is not tracked as closely as other gaseous N emissions because it is not currently regulated in the state.
While acute exposures to NH3 are rare, both human health and ecosystem health are potentially threatened by the increasing regional emissions and deposition of NH3. However, rigorous methods for inventorying emissions related to human activities as well as natural soil emissions are currently lacking.

Atmospheric N deposition rates in parts of California are among the highest in the country, with the N deposited predominantly as dry deposition.
The Community Multiscale Air Quality (CMAQ) model predicts that 66% of the deposition is oxidized N and 82% of the total deposition is dry deposition not associated with precipitation events.In urban areas and the adjacent natural ecosystems of southern California, deposition rates can exceed 30 kg N ha-1 yr-1, but deposition is, on average, 5 kg N ha-1 yr-1 statewide.

The atmospheric N emitted as NOx or NH3 in California is largely exported via the atmosphere downwind (i.e., east) from California.
Approximately 65% of the NOx and 73% of the NH3 emitted in California is not redeposited within state boundaries, making California a major source of atmospheric N pollution.  Further, atmospheric exports of N are more than 20 times higher than riverine N exports. 

Leaching from cropland (333 Gg N yr-1) was the predominant (88%) input of N to groundwater.
It appears that N is rapidly accumulating in groundwater with only half of the annual N inputs extracted in irrigation and drinking water wells or removed by denitrification in the aquifer.On the whole, groundwater is still relatively clean, with a median concentration ~ 2 mg N L-1  throughout the state. However, there are many wells in California that already have nitrate concentrations above the Maximum Contaminant Level (10 mg NO3−-N L−1). Because of the time lag associated with groundwater transport (decades to millennia), the current N contamination in wells is from past activities and current N flows to groundwater will have impacts far into the future.

The amount of evidence and level of agreement varies between N flows.
The most important sources of uncertainty in the mass balance calculations are for major flows with either limited evidence or low agreement or both.  Based on these criteria, biological N fixation on cropland and natural land, the fate of manure, denitrification in groundwater, and the storage terms are the most important sources of uncertainty.  

In many ways, the N flows in California are similar to other parts of the world.
In a comparison with other comprehensive mass balances -- the Netherlands, United States, South Korea, China, Europe, and Phoenix - California stands out in its low surface water exports and high N storage, primarily in groundwater and urban land. Further, when compared to these other regions of varying size, California has a relatively low N use on both a per-capita and, especially, on a per-hectare basis.

Mass balance pie chart
California statewide nitrogen mass balance for the year 2005: Imports, exports and storage. Numbers indicated on the chart are in thousands of tons of nitrogen.


Main Messages: Ecosystem Services & Human Wellbeing

Healthy food

Production of California livestock and agricultural crops has increased since 1980, accompanied by greater N fertilizer application.
Between 1980 and 2007, production of vegetables and melons, and fruits and nuts increased 128% and 17% respectively, reflecting shifts in the diet composition of the US population. To meet increasing demands for animal protein, feed crops was also one of the highest crop production categories, almost tripling over this period. Correspondingly, livestock production was on an increasing trend, with the average annual milk cow and heifer population doubling.

While N is indispensable in increasing the production of agricultural systems, much of the N applied is lost to the environment, resulting in a variety of impacts on atmospheric, terrestrial, and aquatic ecosystems.
The difference between the tonnes of N fertilizer applied and N harvested is on a decreasing trend for cotton since 1980. However, the estimated amount of N that is not taken up by crops is on a slightly increasing trend for vegetables, fruits and nuts. This corresponds to the amount of fertilizer applied by crop, with estimated application rates on many vegetable and fruit and nut crops having increased in recent decades, at the same time as the total acreage for these crops has also increased.

California’s agricultural sector is important to the state’s economy and also contributes significantly to the provision of food security for the United States and globally.
California’s agricultural economy is the largest in the US with over $37.5 billion in earnings in 2010, producing 21% of the nation’s dairy commodities and more than 50% of the fruits and vegetables. The state is also the largest producer of ornamental horticultural goods in the US with $2.3 billion in wholesale sales and $235 million in retail sales in 2009.

Clean drinking water

The concentration of nitrate in California’s surface water bodies seldom exceeds the federal maximum contaminate level (10 mg nitrate-N L-1).
As such, the use of surface water sources for drinking is generally considered low risk.

Nitrate levels in groundwater have increased over the past several decades, and in some parts of the state now exceed federal drinking water standards.
This trend is likely to continue due to the time lag between the loss of nitrogen (N) to the environment and its accumulation in aquifers.

People in agricultural areas, particularly those with domestic wells, are more likely to be exposed to high levels of nitrate in their drinking water than those in urban and suburban areas.
Groundwater from wells in the Tulare Lake Basin and Salinas Valley regularly exceed the federal MCL and an estimated 8.0-9.4% of residents (212,500 – 250,000 people) in these areas are “highly susceptible” to exposure to water in excess of 10 mg nitrate-N L-1.

For most adults, the amount of nitrate and nitrite consumed via foods is much greater than the amount consumed through drinking water. 
Infants given water or foods high in nitrate can develop “blue-baby syndrome”, a potentially fatal condition where their blood cannot transport oxygen.

The International Agency for Research in Cancer concluded that nitrate and nitrite are “probably carcinogenic to humans”.
Nitrate and nitrite can form nitrosamines, which are suspected to cause cancer. Consumption of nitrate and nitrite from all drinking water and food sources such as preserved meats is associated with stomach cancer in some studies.

Nitrate and nitrite can have positive effects on the body.
In some patients they are used to treat high blood pressure and reduce the risk of stroke.

Costs of treating nitrate contaminated drinking water can pose a significant financial burden on low-income households and the public and community water systems that serve disadvantaged communities.
While state-wide estimates of the cost to address nitrate in public and community water systems are needed, recent studies suggest that an increase in public and private funding on the order of $17 – 34 million per year over many decades will be needed to implement required nitrate mitigation projects for water systems in the Tulare Lake Basin and Salinas Valley.

Clean air

Nitrogen is a component of, or aids in the formation of, five known air pollutants including NOx, NH3, O3, PM2.5 and PM10.
Air pollutants have important impacts on the economy, the environment, and human health, and thus are regulated by state and federal agencies.

Major emissions sources include the combustion of fossil fuels in the transportation, energy generation and industrial sectors, as well as agricultural fertilizers and livestock.
Higher NOx concentrations tend to be measured in and around California’s urban areas and originate mostly from the transportation and industrial sectors. Concentrations of ground level O3, which is formed from emissions of NOx and volatile organic compounds (VOCs), are highest during the summer months in the South Coast, Bay Area and Central Valley regions. The majority of NH3 emissions come from livestock waste and N fertilizers, thus concentrations of NH3 tend to be higher in the southern part of California’s Central Valley.

Levels of PM2.5 and PM10 are highest in the South San Joaquin Valley and South Coast regions.
In the San Joaquin Valley, where livestock activities occur, NH3 is the dominant constituent of secondary particulate matter. In the urban areas of the South Coast, compounds formed from NOx make up a larger fraction of the particulate matter.

Air quality regulations and technological innovations have led to significant declines in NOx, O3, PM2.5 and PM10 over the past four decades.
However, much of the state still has air quality that fails to meet one or more of the standards set by national and state agencies to protect human health.

There are important racial disparities in exposure to air pollutants.
In the South Coast and San Joaquin Valley Air Basins, a larger percentage of the Black and Hispanic populations relative to White and other races are exposed to PM2.5 concentrations that are above the national ambient air quality standard (35 µg/m3).

Air pollutants are associated with many health problems.
These include difficulty breathing, reduced lung function, asthma, respiratory infections, chronic obstructive pulmonary disease, cardiovascular disease, overall deaths, and deaths due to specific respiratory and cardiac causes. In California, over 12,000 premature deaths per year from cardiopulmonary disease and ischemic heart disease are attributed to elevated PM2.5 levels. Studies suggest that the health damages in California associated with poor air quality are on the order of tens of billions of dollars per year.

Air pollution, particularly O3, has adverse effects on crop growth.
Yield losses ranging from 1 – 33%, depending on the sensitivity of the crop and level of exposure, can reduce revenues for agricultural producers and increase food costs for consumers. The overall economic impact of O3 on agricultural production in California is estimated to be on the order of hundreds of millions of dollars per year.

Climate regulation

Human activities that increase reactive N have numerous competing effects on the ecosystem and biogeochemical processes that regulate the Earth’s climate.
Some processes have net warming effects that exacerbate climate change, while other processes have net cooling effects that partially offset the prevailing trend of a warming climate.

Emissions of N2O have a long term warming effect on global climate change.
As the third most important greenhouse gas behind CO2 and CH4, N2O accounts for approximately 8% of total global and 3% of total statewide greenhouse gas emissions. The vast majority of N2O emissions emitted globally and in California come from agricultural sources (N fertilizers, livestock, N2-fixing crops), while fossil fuel combustion, sewage treatment and industrial sources are also minor sources.

N deposition and fertilization tends to have an overall cooling effect on climate by enhancing terrestrial C sequestration in plant biomass and soils.
Increased C sequestration due to N input has been documented for many forest, grassland, wetland and agricultural ecosystems in North America (24 - 177 kg C per kg N deposited per year), a trend which has also been observed in California.

The formation of O3 from NOx has both warming and cooling effects on the earth’s climate.
Increased ground-level O3 has adverse effects on plant photosynthesis and CO2 uptake, which decrease C sequestration by crops and natural vegetation. While estimates suggest that O3 decreases plant C sequestration by 14 -23% globally, more research is needed to quantify the extent of this impact in California. In contrast, O3 can also have a small cooling effect on climate by increasing the concentration of hydroxyl radicals (OH), which in turn reduce the lifetime and overall burden of CH4 in the atmosphere.

Atmospheric aerosols formed from NOx and NH3 have a short term cooling effect on climate by reflecting and scattering solar radiation and stimulating cloud formation and the albedo effect.
Since the formation of aerosols from NOx and NH3 are generally linked to different pollution sources (e.g., fossil fuel to NOx, livestock to NH3), the relative contribution of each pollutant and the chemical composition of resulting aerosols is likely to vary considerably across California’s landscape.

Estimates suggest that anthropogenic sources of N have a modest net-cooling effect on the Earth’s climate in the near-term (20 years), but a net warming effect in the long-term (100 years) as the prolonged effects of N2O dominate the radiative balance.
It should also be noted that the overall effects of N on the climate are relatively small compared to CO2 from fossil fuel combustion (8% globally, 3-4% in California).

Cultural Services

Human induced changes in the N cycle have numerous positive and negative effects on the cultural services that are provided to society through natural and working landscapes.
Key services influenced by reactive N include the aesthetic value, recreational value, cultural heritage values, and spiritual and religious values of certain landscape elements and characteristics.

Shifts between natural, agricultural and urban land uses all made possible through N fertilizers and fossil fuel, have significant impacts on the aesthetic appearance of both natural and man-made environments in California.
Studies suggest that most people prefer the visual appearance of environments along the following land use gradient: natural habitat > diversified agricultural > agricultural monoculture > urban > industrial.

Loses of N to aquatic and terrestrial ecosystems through runoff and air pollution have a number of adverse effects on recreational opportunities in California.
Recreational opportunities such as fishing, hunting, hiking and bird watching are diminished because N losses tend to promote ecologically harmful eutrophication and anoxia in surface water bodies, and increases in N deposition on native grassland and forest ecosystems. These changes in N availability generally reduce native biodiversity and subsequent recreational opportunities.

Agritourism, culinary travel and other rural recreational activities (e.g. vineyards, u-pick farms) are examples of some of the benefits of N fertilizer and fossil fuel use.
Recent research indicates that opportunities for agritourism have been expanding in recent years with numerous ancillary benefits for job creation and economic growth in California’s rural areas.

Excess N in the environment can have detrimental impacts on native species, biodiversity, and natural and working landscapes, thus diminishing their natural heritage value to society.
Many of these elements of our natural environment are prominent subjects of nature study, literature, and other aspects of our cultural heritage.

Many religious traditions consider important species, locations, or geographic features to be “sacred”.
To the extent that N impacts biodiversity and ecosystem change, the spiritual and religious value that people derive from these species and places may be diminished.

Shared cultural and spiritual values can also be a key source of motivation and inspiration for environmental stewardship.
While this potential exists, more work is needed to determine effective ways to couple local cultural and spiritual values with sound science and public policy.

Studies in this field rarely attach monetary (or even quantitative) values to cultural services.
Like much of the rest of the world, there is very little quantitative evidence for California on cultural services generally and even less on cultural services specifically linked to N flows. The authors have made an effort to include in the text all those cases where they have found quantitative evidence, which is presented along with appropriate use of controlled vocabulary regarding uncertainty. The authors believe this approach is preferable to omitting these important (yet difficult to quantify and monetize) considerations.

Main Messages: Future of Nitrogen Management in Agriculture



Four scenarios for nitrogen in CA, 2010-2030
Four scenarios for nitrogen in California, 2010-2030



Participants in stakeholder scenarios workshops identified the profitability of farming and environmental regulations as two of the most uncertain forces and important drivers affecting N management in California over the next two decades.


Based primarily on variations in these two attributes of profitability and regulation, stakeholders determined four potential futures for N in California agriculture.
The four scenarios are the following:

  1. End of agriculture:  Rising cost and declining competitiveness for California farmers, with mandates and regulation running ahead of technological capabilities to address N issues.
  2. Regulatory Lemonade: Good prices and strong competitiveness for California farmers, with strict mandates and regulations to control N tempered by flexible implementation to allow technological capabilities to catch up.
  3. Nitropia: Farming economics are favorable, and technological innovation spurs controls of N before there is need for regulation.
  4. Complacent agriculture:  Rising costs and declining competitiveness for California farmers, with incentives and regulation lagging behind technological capabilities to address N issues.

The four scenarios show that the environmental and human health impacts of agricultural N use could vary substantially depending on regulatory responses and the competitiveness of California’s agriculture industry in the global context.
The worst-case scenario, from the perspective of outcomes for agriculture, the environment, and human health, evolves from a combination of low agricultural competitiveness and low regulatory pressure to adopt better management practices and technologies, which leads to poor outcomes for the agricultural sector and mixed outcomes for the environment and human health. The two best-case scenarios in terms of outcomes involve high agricultural profitability, which stimulates investment in better management options, and either strict regulations that are rolled out in a flexible and timely manner or government policies and consumer-driven certification schemes that provide incentives for adoption, resulting in better environmental and human health outcomes.

The four scenarios collectively suggest that multiple pathways could lead to positive environmental and human health outcomes around N.
On the one hand, strict regulations can force more monitoring, information management, and technology adoption, as happens in Scenarios 1 and 2, while on the other hand, agricultural profitability, often driven by consumer demand and possibly price premiums for best management practices, can also drive industry investment in development and adoption of better practices, as in Scenario 3.

The scenarios suggest that the manner in which regulations are implemented can be as important as the actual extent of regulations, and that farm profitability can be both an enabler of better N management as well as an outcome of N management policies.
In Scenario 2, regulations are implemented with flexibility and with more advance notice and involvement from agricultural producers, allowing producers to maintain profitability while changing practices. In Scenario 1, rapid imposition of regulations decrease profitability and farmer buy-in, resulting in good environmental outcomes but poor economic outcomes for the farm sector. Differences in scenarios suggest that pro-active industry participation may help agriculture to adapt successfully to a highly-regulated environment.  Moreover, the scenarios suggest that farm profitability can also be an important driver or at least a critical precursor to innovation in N management, suggesting multiple feedback loops between regulatory policies, farm profitability and N management. 

None of these scenarios by themselves lead to sufficient improvement in groundwater quality to fully address human health concerns by 2030.
This shortcoming is primarily due to the fact that N leaches through the soil profile at very slow rates, often taking decades to reach the groundwater. Therefore, even if all agricultural N inputs were 100% ended in 2010, the N that had already been added in prior years would continue to accrue in groundwater in 20 years’ time. For this reason, regulation of agricultural N management alone is unlikely to fully address human health concerns in only 20 years, although it could improve the condition of groundwater over a longer time frame.

Responses: Technologies & Practices


stakeholder review 

Today, countless technologies and practices are available to optimize reactive nitrogen (N) use and change the way Californians interact with the nitrogen cascade.
Knowledge and tools to limit the introduction of new reactive N into the cascade; mitigate the exchange of Namong the bio-, hydro-, and atmospheres; and adapt to the increasingly N -rich environment are already widely available for agriculture, transportation, industry, water treatment, and waste processing. With current technology, we estimate that strategic actions could reduce the amount of reactive N in the environment significantly.

Limiting the introduction of new reactive N—through improving agricultural, industrial, and transportation N efficiency—is the most certain way to create win-win outcomes.
Increasing efficiency would decrease the amount of Nper unit activity (potentially decreasing costs) and decrease emissions. Fortunately, practices are available to increase fertilizer and feed N use efficiency for virtually every agricultural commodity. Our conservative estimate suggests gains in efficiency could result in an estimated 36 Gg less fertilizer N use yr-1 and 82 Gg less feed N demand yr-1 without compromising productivity. By comparison to agricultural practices, the efficacy of engineering solutions to increase efficiency is well established.

Because a single source category is generally responsible for the majority (>50%) of each N transfer among environmental systems, priorities to mitigate N emissions are clear.
These include: manure management (to reduce ammonia (NH3) to air), soil management (to reduce nitrate (NO3-) to groundwater), fertilizer management (to reduce nitrous oxide (N2O) to air), fuel combustion (to reduce nitrogen oxide (NOx) to air), and wastewater treatment (to reduce ammonium (NH4) to surface water). Though these activities are the most culpable, a diverse number of additional actions also contribute to these transfers and it will take a systemic perspective to reign in N emissions. Further, because reactive N is intrinsically mobile in the environment, a narrow focus on a specific mitigative action will have the tendency to cause secondary emissions, thereby simply transferring the burden oftentimes with more harmful environmental and human health outcomes.

Reactive N is already changing California’s air, water, soils, and climate, and dynamics of the N cascade dictate that further degradation will continue to occur for some time.

Moving forward, Californians will have to adapt systems and behavior to the new state of resources to maintain productivity, minimize exposure, and relieve further pressure on the environment.
Adaptation will be especially important as populations grow further and concentrations of reactive N in the environment increase. There is already a need to treat drinking water to the regulated level of safe NO3- (45 mg per L) in many parts of the state, with this need projected to increase in the future. Ozone, groundwater NO3-, and increased deposition may all cause changes in productivity and management.


Responses: Policies & Institutions

California’s long-term success in achieving environmental goals through regulation of the main sources of nitrogen pollution from combustion (tailpipes and smokestacks) is largely irrelevant to challenges of addressing numerous, spatially dispersed, highly variable, context-specific (“non-point”) sources of nitrogen pollution typical of agriculture.

Any successful strategy to reduce nitrogen emissions from agriculture must take a comprehensive approach to the most important forms of nitrogen leakage into the environment, particularly ammonia and nitrate, but also including nitrous oxide.
Effort to control any one alone, while neglecting the others, is very likely to be counterproductive—“solving” one problem can worsen others.

There have been apparent improvements in the ability of producers to implement the 4Rs of nutrient stewardship in crop production: right amount, right time, right place, and right form.
Overall, however, although technologies and practices that can reduce nitrogen pollution from agriculture certainly do exist, they typically are costly (in money and management) for farmers and ranchers; thus, voluntary adoption tends to be low.

It is well established that voluntary participation in best management practice (BMP) programs typically cannot achieve significant reductions in nitrogen pollution from agriculture.  

Dairy waste is a significant source of nitrogen pollution in California, both to water and to air. It is critical to develop and implement cost-effective polices to effectively reduce nitrogen pollution from dairy operations.
The California Dairy Quality Assurance Program plays an important role in helping dairies comply with existing regulations. While not a panacea by any means, this is an example of how a voluntary, largely information-based educational program can play a supporting role to other environmental regulations.

Even if policies somehow could perfectly control nitrate leakages from farms and dairies starting immediately, California will be living with the consequences of past nitrate leakages to groundwater for decades to come.
Thus, for communities where drinking water supplies are unsafe because of high nitrate concentrations, point-of-use treatment or some other approach will be needed in the short run in order to assure safe drinking water for all California communities.

There is very limited information on the magnitudes of economic benefits that would be achieved through reductions in nitrogen emissions.
For this reason it is currently not possible to estimate the economically efficient level of nitrogen emissions—the level that balances marginal benefits and costs—nor the relative efficiency of policy instruments. However, it is possible to compare policy instruments in terms of cost to achieve desired emission levels.

Over the longer term, five types of policy instruments appear to be most promising: emission standards, emission charges, tradable emission permits, abatement subsidies, and auction-based abatement contracts.
However, theory provides little guidance on which of these instruments would be most effective under specific circumstances. The general lack of evidence, rigorous experimentation, comparative study, or integrated assessment of the impact of alternative policy instruments for controlling nitrogen pollution from agriculture is a major barrier to development of sound policy.

Given the monitoring challenges presented by non-point source nitrogen pollution, and the importance of having adequate data to enforce pollution control policies, efforts should be made to develop the technologies and tools needed to acquire the necessary data and to appropriately model the movement of nitrogen in the environment.
Doing so facilitates the transition of nitrogen from a non-point source problem to a more manageable point source problem. In addition, existing data from the diversity of monitoring sites and programs already operated by state and federal agencies need to be made more accessible and integrated with each other. Comprehensive integration,
transparent protocols, and evaluation of uncertainty are key characteristics of an effective statewide platform.

This assessment concludes that integrated policy solutions are needed to take advantage of existing technology and to develop new technologies and practices necessary to transition California to a sustainable nitrogen future.
While a necessary step, design and implementation of an integrative strategy for nitrogen policy holds many challenges, including the need to fill key information gaps, address existing administrative rigidities, and identify conflicting policies.