Mexico’s wheat fields help feed the world. They’re also releasing a dangerous greenhouse gas.

CIUD OBREGÓN, Mexico — In the foothills of the Sierra Madre mountains, the carcasses of starving cattle rotted in a bone-dry reservoir. Useless fishing nets hung on dusty fences. Rowboats were stranded in the sand.

Down on the valley floor, Rafael Parra bent to the work of feeding the world — and unintentionally warming it.

A layer of chalk-white fertilizer had been scattered on the barren ground. Tractors had cut long furrows in the dry and crumbling soil. The wheat seeds would not be planted for days, but it was time to release the laughing gas.

Story continues below advertisement

Story continues below advertisement

Parra plunged one end of an old, plastic tube into an irrigation canal, generating the suction that sent water gurgling into the drought-parched earth. It was a low-tech, gravity-fed form of irrigation used for generations here in the Yaqui Valley, a storied breadbasket of Mexico.

“That’s all there is to it,” he said.

Parra, like many farmworkers here, was not fully aware of the invisible consequences of his work. But scientists who have studied this valley for decades know that in these precise moments and conditions — when water mixes with nitrogen fertilizer, and when no crop is in the ground to absorb it — huge surges of nitrous oxide gas are released into the atmosphere.

Rafael Parra uses a shovel to allow water to flood a fertilized furrow in a field where wheat will be planted near Pueblo Yaqui in Sonora. Yaqui Valley farmers scatter heavy doses of fertilizer on bare ground, irrigate and wait for days or weeks before planting. In these wet conditions, soil microbes break down a compound called nitrate in a process that unleashes nitrous oxide into the air.

About this series The world has pledged to cut greenhouse gas emissions in the coming decades, but there are many ways to slash emissions immediately. In the fourth installment of our series, Invisible, The Washington Post examines how over-fertilization in Mexico results in a surge of nitrous gas that scientists and the government are grappling to understand. The world has pledged to cut greenhouse gas emissions in the coming decades, but there are many ways to slash emissions immediately. In the fourth installment of our series, Invisible, The Washington Post examines how over-fertilization in Mexico results in a surge of nitrous gas that scientists and the government are grappling to understand.

The world’s climate conferences and pledges have done nothing to change a basic and dangerous fact: Concentrations of major greenhouse gases in the atmosphere continue to rise. And what happens each fall in this valley underscores how difficult it is to even track these emissions accurately, let alone stop them.

Emerging scientific evidence suggests that Mexico’s emissions of nitrous oxide are significantly underestimated — emissions may be double or even quadruple what the country reports. It’s a problem that the Mexican government acknowledged to The Washington Post for this story.

As a contributor to climate change, nitrous oxide remains a mysterious villain, crudely measured and less-studied than carbon dioxide and other greenhouse gases. But it has caused 6.5 percent of the world’s current warming, and its concentration in the atmosphere is growing at an accelerating rate, surpassing even some of the worst projections. The gas is 265 times more powerful than carbon dioxide in heating the atmosphere over a period of 100 years. It depletes the planet’s ozone layer. And it lingers in the air for more than a century.

Last year, atmospheric concentrations of nitrous oxide showed a record-high increase, according to the National Oceanic and Atmospheric Administration.

The families who grow wheat in the Yaqui Valley run some of the most sophisticated, large-scale commercial operations in the country — the type of highly productive, heavily irrigated agricultural system essential for feeding billions of people. The bulk of their crop is durum wheat, which is exported by cargo ship to countries in Africa and Latin America for foods such as pastas and couscous. The rest is kept local for breads and tortillas.

The problems with the over-fertilization found here, in the world’s 10th-largest greenhouse gas emitter, are also common for the developing world. Wheat farmers in the Yaqui Valley apply about 300 kilograms of nitrogen onto every hectare of land they cultivate — primarily by scattering urea pebbles onto the soil before planting and later pumping anhydrous ammonia gas into the irrigation water once the wheat starts growing. That rate of nitrogen use is 50 percent higher than what is allowed by law in parts of Germany. Britain prohibits fertilizing before planting in vulnerable areas — a common practice in the valley.

“Indeed, these rules do not exist in Mexico,” Juan Gabriel León Zaragoza, a spokesman for Mexico’s Agriculture Ministry, said in a statement to The Post. “In part because these types of regulations are difficult to enforce, especially considering the size of our country compared to European countries.”

Story continues below advertisement

Story continues below advertisement

Without regulation, the fight against nitrous oxide pollution is left to people such as Iván Ortiz-Monasterio, a 63-year-old agronomist from Cuernavaca who has spent his career trying to convince farmers to use nitrogen more efficiently. Research by Ortiz-Monasterio and his colleagues has shown how farmers in the Yaqui Valley often use roughly double the amount of fertilizer necessary and that much of the excess nitrogen was being lost to the environment.

Over decades working in the valley, the soft-spoken scientist developed an intimate knowledge of the financial and cultural pressures that encourage wheat farmers to apply too much fertilizer — even when they could save money and pollute less.

“For the farmer, the cost of fertilizing too much is less than the cost of fertilizing too little,” Ortiz-Monasterio said. “That’s because they are not taking into account the environmental cost.”

Recent research by Ortiz-Monasterio and others also suggests the problem is far worse than is generally known. They have found that as farmers add more and more fertilizer, the resulting emissions begin to grow by disproportionate amounts, increasing on an exponential curve. The research has become a key clue that could help explain the huge gaps that exist between the amount of nitrous oxide that countries — including Mexico — claim to emit, and what atmospheric studies find.

This was not a problem that Norman Borlaug — an American expat who became the Yaqui Valley’s most famous farmer — contemplated when he began, in the years after World War II, to experiment with varieties of wheat in the Sonoran fields. The discoveries that the Iowa-born plant pathologist made would help end famines in South Asia, win him a Nobel Prize and launch the “green revolution,” which spread high-yielding varieties of wheat and rice throughout the developing world.

A statue of Norman Borlaug, an American expat who became the Yaqui Valley’s most famous farmer, stands amid wheat at the entrance of the International Maize and Wheat Improvement Center (CIMMYT), the agricultural research station where the Nobel Peace Prize-winning agronomist once worked.

But Borlaug also left a legacy of heavy reliance on synthetic fertilizers, which have become increasingly problematic as the world warms. There is growing evidence that the over-application of fertilizers — particularly in developing nations with growing agricultural industries such as Brazil, India, China and Mexico — is a central driver accelerating the nitrous oxide emissions that contribute to climate change.

“It’s just the ultimate story of unintended consequences,” said Marci Baranski, an expert on greenhouse gas emissions and author of a forthcoming book about Borlaug and the green revolution.

At the renowned agricultural research station where Borlaug once worked, Ortiz-Monasterio and other scientists have spent decades documenting the environmental damage that excess nitrogen can cause for the air and water. The station is the International Maize and Wheat Improvement Center, known by its Spanish initials, CIMMYT. Starting in the 1990s, they began taking emissions measurements — using simple PVC chambers at ground level, extracting the gas with syringes. The results shocked them.

“They were the highest that anybody had seen in the world at that point,” said Stanford University ecologist Pamela Matson, who has conducted extensive research in the Yaqui Valley. “It was mind-blowing how large those emissions were.”

‘Something big is pouring out of that bay’

Ciudad Obregón was built for farming. The streets are grid-straight and extra-wide to accommodate the convoys of diesel-powered cargo trucks passing through to fields and ports. Cylindrical silos and sprawling wheat depots line the valley that spans a half-million acres amid a network of irrigation canals connected to three reservoirs.

The canals are what allowed the southern tip of the Sonoran Desert to become an agricultural powerhouse. In the early 1900s, a pair of Los Angeles-based entrepreneurial brothers, W.E. Richardson and Davis Richardson, developed them, attracting investors for their vision of a railroad-connected, farming boomtown by advertising “the most fertile irrigated land on earth” and selling parcels for $25 an acre. The Indigenous Yaqui people who lived there first would fight bloody battles with the Mexican army as they lost control of rights to the Yaqui River in a water conflict that lingers to this day.

A truck driver waits on a May night to deliver wheat to Ferropuerto de Sonora, a cargo transportation company. The families who grow wheat in the Yaqui Valley export much of their crop to countries in Africa and Latin America.

Borlaug landed in the valley in the 1940s as an agricultural adviser for the Rockefeller Foundation while the farmers around him were beset by a fungus known as stem rust. His success during his career established the Yaqui Valley as an international hub for agricultural science.

“This became a mecca for investigators who wanted to improve wheat,” said Pedro Figueroa Lopez, an agronomist who recently retired after a career in wheat improvement with the Mexican government. “And people have come from many countries. And they still come here.”

Ortiz-Monasterio now works out of a building on one of the city’s main thoroughfares: Boulevard Dr. Norman E. Borlaug. His office at CIMMYT is fronted by a bronze statue of Borlaug standing amid sprigs of wheat.

Iván Ortiz-Monasterio, the principal scientist at CIMMYT, stands inside a cooler where seeds from 150,000 types of wheat from around the world are stored as genetic resources for researchers.

In some ways, Ortiz-Monasterio’s work mirrors that of his predecessor, who died in 2009. Like Borlaug, Ortiz-Monasterio is part scientist, part unofficial diplomat, traveling widely and teaching ways to grow wheat. But their differing messages point to an underlying tension.

Borlaug’s mission was yield. He wanted wheat grains to be more bountiful, hardier and more adaptable to places around the world. His great innovation was to go shorter, developing what was known as semi-dwarf wheat whose stems would not bend under the weight of larger grains. In the 1950s and ’60s, those Mexican seeds were introduced in India, Pakistan, China and elsewhere, allowing rapid expansions of food production that staved off hunger for millions of people.

In the countries where Borlaug worked, nitrogen rates were low and heavy fertilization was central to his message. When the Indian government in the 1960s wanted to spread its fertilizer supplies evenly throughout the country, Borlaug opposed that, arguing that the focus should be on “tremendous yield increases” in certain commercially farmed areas that could be “heavily fertilized and properly watered.”

Story continues below advertisement

Story continues below advertisement

Since then, global nitrogen fertilizer use has risen sharply, growing from about 10 million metric tons in 1960 to 111.6 million metric tons projected in 2022, according to the Food and Agriculture Organization of the United Nations. Farmers in the Yaqui Valley have followed suit. Surveys by CIMMYT over the decades show that average nitrogen use has risen roughly sixfold since 1960.

For decades Ortiz-Monasterio has fought an uphill battle to bend that curve downward. Trained at the University of Illinois, he joined CIMMYT in 1989 and soon began collaborating with Stanford scientists, including Matson, who would win a MacArthur Foundation fellowship, known as a “genius” grant, in 1995.

Then as now, Yaqui Valley farmers would scatter heavy doses of fertilizer on bare ground, irrigate and wait for days or weeks before planting. In these wet conditions, soil microbes break down a compound called nitrate in a process that unleashes nitrous oxide into the air.

The discs of a fertilizer spreader spin and scatter a mix of urea and phosphorous fertilizer across a dry field in early November. A mix of urea and phosphorous fertilizes a dry field where wheat will be planted near Pueblo Yaqui.

“The big pulses of nitrogen follow that perfect condition, where there’s no plants taking nitrogen up, there’s lots of it available in the soil, and microorganisms are using it for their own energy sources,” Matson said.

One of her graduate students at the time, Michael Beman, began investigating how the excess nitrogen seeped through drainage canals into Bahía del Tóbari and other outlets to the Sea of Cortez in northwestern Mexico. Using satellite imagery between 1998 and 2002, Beman and colleagues discovered algae blooms up to 220 square miles large that followed just days after the periodic irrigations in the valley.

This part of the ocean has naturally low levels of nitrogen, Beman said, so bursts from the farmlands are having an outsize impact.

Satellites can measure phytoplankton by using algorithms to calculate the concentration of chlorophyll based on the colors in the water. Gene Feldman, a NASA oceanographer and an expert on ocean color remote sensing, reviewed imagery from satellites off the coast of the Yaqui Valley at The Post’s request. He noted that average chlorophyll concentrations in the month of November, when the first fertilization and irrigation occurs in the wheat cycle, appear to be “significantly higher” than in the month prior, according to data between 2002 to 2021 from the MODIS instrument aboard NASA’s Aqua satellite.

A shoebox-size satellite that NASA began using this year, called the SeaHawk, also captured a portion of the Bahía del Tóbari this November, after irrigation in the valley. Elevated chlorophyll levels could be seen stretching far out to sea, which Feldman described as “remarkable.”

“It sure as heck looks like something big is pouring out of that bay,” he said.

A village is surrounded by wheat fields in the Yaqui Valley. After irrigation or rains, runoff flows from the fields through a network of drains into the Sea of Cortez. An irrigation canal provides water to the fields around the Yaqui Valley. The valley spans a half-million acres amid a network of irrigation canals connected to three reservoirs. When the nitrogen-rich runoff from wheat fields reaches the Sea of Cortez, algae blooms spread through the water. A satellite image from November provided by Planet Labs PBC shows the green hues from chlorophyll in the algae.

This proliferation of phytoplankton can drive down oxygen levels in the water creating “dead zones” where sea life cannot survive.

“If there’s an overstimulation of phytoplankton because of excess nutrient runoff, it’s not going to be a good thing,” Feldman continued. “If I happen to be a clam that can’t move, I’m dead. And if I’m a crab or a snail and I can’t get out of the way fast enough, I die.”

In this image taken by NASA’s SeaHawk satellite, superimposed on a map of the region, elevated chlorophyll levels can be seen near Isla Huivulau following irrigation and fertilization in the area around Villa Juarez in November. “Anything above green is a lot,” explains Gene Feldman, a NASA oceanographer.

The outflows also prompt what’s known as “indirect” emissions of nitrous oxide, which can surge in low-oxygen conditions. Scientists suspect that governments are badly underestimating how much nitrogen gets released downstream of agricultural operations. In the Midwestern United States, another over-fertilized nitrous oxide hot spot, research by Timothy Griffis and his colleagues at the University of Minnesota found such emissions could be three times more than typical estimates.

“If you only measure it from the fields, you’re only getting part of the story,” said Keith Smith, an expert on nitrous oxide at the University of Edinburgh.

A 2019 study of agrochemical pollution in the valley’s waterways found elevated levels of mercury, lead and chromium in the sediments flowing from the drainage canals into the Bahía del Tóbari and in the fish and mollusks found there. Earlier research has also documented widespread contamination by pesticides such as DDT and related chemicals in samples of blood and breast milk of people living in the area.

Story continues below advertisement

Story continues below advertisement

The fishermen of Paredón Colorado, a beachfront village along Bahía del Tóbari, live with the fertilizers, pesticides, tractor tires and other farming detritus that flush out of the canals, and they are familiar with the costs of this pollution. They say the chemicals have depleted populations of fish and shrimp.

“The pesticides, the herbicides, the fertilizers, all of it flows into the sea. And all of it affects us,” said Manuel Diaz Lopez, a 68-year-old fisherman and member of the village cooperative. “Everything pours off the shore and the species die.”

“I remember when I was 10 years old, the boats would come back with 200 kilos of shrimp. Now, they’re getting 10 or 20 kilos in a day.”

José Antonio Salido, 38, and his father, José Maria Salido, 64, untangle fish from their nets on the dock of Paredón Colorado after a fishing trip.

An exponential rise in emissions

In the absence of detailed field measurements, Mexico and many other countries, mostly in the developing world, use a crude calculation to quantify the amount of nitrous oxide they release into the atmosphere. They estimate that 1 percent of nitrogen fertilizer applied becomes nitrous oxide — a default “emissions factor” set by the U.N.’s Intergovernmental Panel on Climate Change (IPCC) in 2006.

But recent scientific models suggest those estimates are not in line with reality. In major food-producing countries, researchers have found large gaps between reported nitrous oxide emissions and those calculated by atmospheric models, including in Mexico, Brazil and India.

The discrepancy between Mexico’s reported nitrous oxide emissions and what’s in the atmosphere 162 k 747 k 451 k Atmospheric models Yearly N ₂ O emissions reported by Mexico 2015 Note: Atmospheric measurements come from three inversion models: Copernicus Atmosphere Monitoring Service, NASA’s GEOS-Chem and Geoscientific Model Development’s TOMCAT chemical transport model. Mexico’s nitrous oxide emissions come from Mexico’s National Institute of Ecology and Climate Change (INECC).

The country’s emissions could be up to 4.6 times higher than what it has acknowledged in the past, according to a study done by Philippe Ciais of France’s Laboratory of Climate and Environmental Sciences, along with several colleagues.

Hanqin Tian, a researcher at Auburn University who specializes in nitrous oxide, reviewed Mexico’s emissions for The Post. He analyzed independent data sets that track emissions by countries and “process-based models,” which track nitrogen in its various forms as it makes its way through Earth’s ecosystem. This analysis, too, suggests Mexico’s agricultural emissions of nitrous oxide are too low in the country reports.

Mexico’s Agriculture Ministry acknowledged its numbers probably are an undercount.

One of the reasons for this “apparent underestimation” in Mexico’s last official report to the United Nations was a reliance on the calculation set by the IPCC that assumes a linear relationship between fertilizer use and emissions, said León Zaragoza, the Agriculture Ministry spokesman.

He said more nuanced calculations, involving fertilizer dose and farmland surface area, were used in a 2019 government estimate. But in that update, the country’s reported emissions only rose by approximately 4 percent.

As for why some analyses produce much higher emissions totals, León Zaragoza noted, “nonlinear modeling yields emission data higher than linear ones.”

Ortiz-Monasterio’s research helps explain some of the disparity. In a 2018 paper, he and several colleagues documented that when doses of fertilizer are increased, nitrous oxide emissions begin to rise along an exponential curve.

“As long as you’re applying under what the crop needs, the emissions are mild,” he said. “It really jumps up once you start applying more than the crop needs.”

Growing plants need only so much nitrogen before they’re sated. Then the microbes, which had previously been competing with the plants for their nutrients, begin to feast. Scientists have documented this in field studies by adding more and more nitrogen to plots of cropland and measuring the resulting emissions.

Story continues below advertisement

Story continues below advertisement

The exponential rise “always coincides with the point at which there is so much nitrate that the plant growth won’t be stimulated any more,” said Philip Robertson, an agricultural scientist at Michigan State University who has worked with Ortiz-Monasterio analyzing the Yaqui Valley.

The warming climate makes things worse. Hotter temperatures, especially during the non-growing season, accelerate the microbes producing nitrous oxide. Drought conditions can also stunt plant growth leaving more fertilizer unused.

In a 2019 study, Rona Thompson of the Norwegian Institute for Air Research and her colleagues measured nitrous oxide in the air in spots around the globe, combined with atmospheric models to map how winds move the gas. They calculated that the true emissions factor could be nearly twice as high as the 1 percent set by the IPCC.

“If you use just a global default emissions factor everywhere, you will underestimate the [nitrous oxide] emission, especially in areas where there is very intense nitrogen fertilizer usage,” Thompson said.

These results help explain the rapidly increasing concentration of nitrous oxide that has been measured in the atmosphere in recent years.

Storage tanks hold anhydrous ammonia gas at the offices of a farming association in Villa Juárez. The gas, a common fertilizer, is injected into soil or pumped into irrigation water to fertilize wheat fields in the Yaqui Valley.

‘Low fertilizer, low production’

Fernando Esquer Rochin leaned against his pickup truck and watched the dust rising behind the weathered, blue Ford tractor. He is a supervisor at Agrocasa, the fertilizer supplier and part of the agricultural consortium called Grupo Cajeme that farmed parcels throughout the valley. These farmers had generations of experience but still relied on relatively rudimentary tools — with none of the satellite-monitored, laser-guided technologies used by competitors in wealthier countries.

But Rochin knew what happened when fertilizer was spread unevenly — ugly islands of yellow marring a sea of green wheat — and his job was to make sure Carlos Antonio Gaxeola and the other young farmworkers used enough fertilizer, and that the tractor scattering it followed a straight line.

“There isn’t money for a GPS,” he said.

That November morning, Gaxeola had signed the receipt for a delivery of 10,070 kilos of fertilizer, enough to cover 20 hectares. They were using a mixture that was typical for the valley: four parts urea, which looked like small, white hailstones, and one part phosphorous, a grayish pebble. The farming associations buy fertilizer in bulk from brokers who arrange for its delivery from major exporters such as China and Russia and it arrives in August on container ships in port towns such as Topolobampo.

The quantity that the workers applied amounted to 200 kilos of nitrogen per hectare — more than CIMMYT researchers considered advisable in a year. And this was just the first fertilization of the season.

Nitrous oxide emissions were not high on Rochin’s list of worries. The valley had endured two years of crippling drought, so extreme that local authorities the month before had sharply restricted planting corn — an important secondary crop for the valley, and lately the most profitable one — because reservoir levels had fallen so dramatically.

Gaxeola, 22, had shown up that morning with a goose egg on his forehead after being jumped in a bar fight the night before. It was not uncommon, he said, to see convoys of narcos in pickup trucks roaring down these rural roads. The local gangs would steal whatever they could — tractors, tires, even the massive tanks of anhydrous ammonia fertilizer marked with warnings “peligro” and “gas tóxico”— if left in the fields too long. Fertilizing needed to be quick.

“Many of our partners, because of the insecurity that we’re living through right now, prefer to do all the fertilizing before planting,” Rochin said.

Rochin had seen other farmers experiment with reducing nitrogen through organic practices, manures, infrequent tilling — and he found them lacking. The Yaqui Valley had been industrially farmed for a century and the soil was depleted. To him, using less fertilizer wasn’t an option.

“For the environment, it would be less harmful, but yield would be very low,” he said. “Low fertilizer, low production.”

Wheat is sold by the ton and so yield — the weight of the grains that gets harvested — is the ultimate priority for those who make their living from the land. Even small declines in the weight of wheat can turn profit into loss. Farmers and agronomists are continuously crossbreeding varieties to find wheat that weighs more, needs less water and is resistant to disease.

A worker operates a combine harvester to cut wheat at a plantation in Benito Juárez in Sonora state in May. Rufino Barreras Anaya arranges wheat grains as they fall from the combine harvester.

During the first week of May, as the harvest was in full swing across the valley, a few dozen farmers, agronomists and government researchers gathered under a white tent at the edge of a wheat field to learn what their future might hold. A thresher was harvesting samples of the newest genetic strains. The atmosphere of the annual test was festive — tacos were served on flour tortillas, and young women with clipboards and straw hats tallied results on an easel.

The experimental varieties had been developed by CIMMYT scientists and the tests were conducted by Agriculture Ministry officials to precise specifications. Each type of seed was planted in 12 rows that were 444 meters long and separated by 80 centimeters. The grains were harvested and weighed for all to see, so farmers would trust the outcome. It would be years before any of the seeds would become widely used across the valley, but the results that day were promising.

“These are better than the varieties we have,” said Alberto Borbón-Gracia, a government researcher. “And by a lot.”

It was a rare bit of good news amid increasingly dire conditions for those trying to make a living off the land. The record-breaking drought fanning wildfires and emptying reservoirs across the American West have been just as painful for Sonora. On the ranches in the hills above the Yaqui Valley, thousands of cattle have died of starvation or been slaughtered prematurely as grasses shriveled in the heat.

Three decades ago, it was common for farmers to harvest two crops per year — soybeans in the summer and wheat in the winter. There is no longer enough water for that. So the soybeans, which helped absorb nitrogen that might otherwise be lost, were phased out.

“The principal worry we have is drought,” said Álvaro Bours Cabrera, the head of the largest farming association in the valley, which produces a quarter of Sonora’s wheat. “We’ve always battled against years with shortages of water. But we are seeing those more continually, frequently.”

Members of the Union of Rural Production Societies of Southern Sonora (USPRUSS) gather in early May at a field in Villa Juárez to measure the results of a new type of wheat seed.

Wheat needs a certain number of cold nights in the winter to thrive. But those lows have softened over time. Between 1960 and 2019, minimum temperatures in the growing season of January to March rose 1 degree Celsius. This resulted in farm yields that were 7 percent lower than they otherwise would have been, according to a recent study.

During the wheat testing event, Juan Manuel Cortés-Jiménez helped record the results. He has watched farmers struggle to adapt to a changing climate over the past 37 years as an investigator with Mexico’s Agriculture Ministry.

He bristled at the notion that Mexican farmers could be blamed for emissions when major emitters are not fixing the problem, or when leaders such as former U.S. president Donald Trump are dismissing climate change entirely.

“What’s going to happen with the world if the principal producers of greenhouse gases say that climate change is a lie? What signal does that send?” he said. “For people who don’t read scientific journals, if they hear the Americans say there’s no problem with this. Why do we have to do something about it down here?”

Carlos Rodríguez Pacheco, 60, the insurance fund manager of USPRUSS, explains the GreenSeeker handheld sensor, which measures a wheat plant’s chlorophyll levels and recommends an optimal amount of nitrogen.

The next generation of farmers

In 2002, Ortiz-Monasterio and colleagues at Oklahoma State University introduced farmers to an innovation called a GreenSeeker — a handheld sensor that measures a wheat plant’s chlorophyll levels and recommends an optimal amount of nitrogen.

For eight years, the state and federal government helped fund the program, paying for technical advisers to take measurements and make fertilizer recommendations. Over that period, farmers working on a total of 48,000 hectares of land signed on. It seemed a rare win-win: The tool added $1.8 million to farmers’ profits, while cutting greenhouse gas emissions by 9,600 tons of carbon dioxide equivalent, akin to taking 2,000 cars off the road, according to an analysis of the program by RTI International, a nonprofit research group.

But in 2015, after a year in which low wheat prices and unusually bad weather hammered profits, farm associations pulled financial support for the GreenSeeker program, and public funding dried up as well. If farmers wanted sensor readings, they had to pay. Participation plummeted.

Story continues below advertisement

Story continues below advertisement

Now, only a handful of farmers still use the sensor. In the offices of one farming association, its GreenSeeker is stored next to the toilets, an unused relic.

“It sounds incredible, but it’s true,” said Bours, the farming association president. “A program that could help the producer save a lot and we’re not taking advantage of it.”

Credit bureaus haven’t helped. For many farmers to secure loans and insure their crops, they must over-fertilize. Bours acknowledged that his association still encourages over-fertilization, even with fertilizer prices “out of control,” as a way to minimize risk.

“They are afraid it will be a lost year, a bad harvest. And that means losing a whole year of income,” said Jose Alfonso Salido, a third-generation farmer who has worked with Ortiz-Monasterio using sensors affixed to drones to measure the color of wheat and its nitrogen needs. “The biggest problems we have is that farmers don’t want to worry — with too much fertilizer, they can relax, but it’s not what the plant needs.”

“As one farmer told me, ‘I put on 180 units of nitrogen as fertilizer,’ ” Ortiz-Monasterio said. “ ‘And later, I added 60 more as a tranquilizer.’ ”

On some parcels of his land, Luis Arturo Amaya, 48, practices low-till and organic techniques instead of relying on heavy doses of synthetic fertilizer. Amaya, a third-generation farmer, uses alternatives to synthetic fertilizer whenever possible.

Luis Arturo Amaya is one of the few farmers who still uses the GreenSeeker sensor to find the optimal level of fertilizer. His grandfather helped Borlaug reproduce wheat seeds for his experiments. His father worked with Ortiz-Monasterio and other CIMMYT scientists.

Amaya, 48, approaches his work managing 300 hectares with a tinkerer’s curiosity and an appreciation for science. And until Mexico’s government regulates fertilizer use, the process used by this third-generation farmer may be the only viable way toward lowering nitrous oxide emissions.

“Do you smell that?” Amaya asked. “That’s chicken dung.”

Amaya uses alternatives to synthetic fertilizer when possible, including “gallinaza,” which leaves a coating of white feathers over the dirt. He practices low-till and organic techniques that require less nitrogen. He takes soil samples for laboratory analysis. On some plots, Amaya experiments with rare varieties of wheat, including one from the time of the Spanish missions in the 17th century, and another common in the valley before Borlaug arrived.

Unlike others who stubbornly pursue yield, Amaya’s goal is to maximize margin. Particularly in years like this, with fertilizer prices twice as high as last year, he looks for any chance to cut costs. Yet even for him, a farmer attempting to sell to niche markets of restaurants and artisanal bakers, these alternatives cannot wholly replace synthetic fertilizers due to cost and manpower.

Story continues below advertisement

Story continues below advertisement

“After working all these years trying to transfer this one technology, that’s when I realized that we need policy,” said Ortiz-Monasterio. “If we really want to make a change, we need policy.”

Mexico’s populist president, Andrés Manuel López Obrador, who once campaigned on relocating the Agriculture Ministry to the Yaqui Valley, cut federal subsidies to farmers here when he took office, further eroding federal influence on their planting and fertilization decisions.

His administration “has decided to support with incentives the poorest farmers in Mexico, who had been left unattended,” said León Zaragoza, the ministry spokesman. “The high-input farmers of the Yaqui Valley do not fall into this category.”

Instead of subsidies or regulation, León Zaragoza said that federal funding supports CIMMYT and other organizations so they can try to convince farmers to adopt the sensors, drones and other technology for more efficient nitrogen use.

“There is excessive use of nitrogen fertilizers in wheat production in the Yaqui Valley,” León Zaragoza said. These farmers “should apply less nitrogen fertilizer and that is why we have supported institutions such as CIMMYT for the development of diagnostic tools.”

And so Ortiz-Monasterio will continue to spread the gospel of efficient nitrogen. His goal is not a fertilizer ban, but rather better management: applied in the right amount, at the right time, so the plant gets what it needs and not more.

He hopes he’ll find the next generation more attuned to the contamination in the water supply, the algae in the Sea of Cortez and the invisible dangers of nitrous oxide.

“It’s very difficult to change the mind of a 60-year-old person who’s been farming for the last 40 years, and pretty much thinks he knows everything,” he said. “The guys who are willing to adopt these changes are the younger guys who are replacing their parents. They’re a lot more open to change.”

A crack in the drought-parched earth separates wheat furrows at a Benito Juárez plantation of USPRUSS Chairman José María Osorio Alatorre.

Mooney reported from D.C.

About this story Editing by Dayana Sarkisova. Graphics editing by Monica Ulmanu. Graphics by Naema Ahmed. Photo editing by Olivier Laurent. Photography by Luis Antonio Rojas. Video editing by Jackie Lay. Design editing by Matthew Callahan. Design and development by Garland Potts. Copy editing by Melissa Ngo. Project editing by Trish Wilson. Project management by Julie Vitkovskaya.