A farm in the Palouse region, which includes parts of Eastern Washington.
A farm in the Palouse region, which includes parts of Eastern Washington.

Gary Wegner first noticed the problem in 1991, when a field on his family’s farm west of Spokane produced one-fourth the usual amount of wheat. His father and grandfather attributed the problem to farming on shallow soils, but Wegner decided to dig deeper. Lab tests revealed a surprising result: the soil had become acidic.

Wheat farmers are now seeing this problem across the inland Pacific Northwest. The culprit, as far as anyone can tell, is the abundant use of synthetic nitrogen to increase crop yields, a practice that has otherwise revolutionized production over the past half century. Over time, however, it has contributed to a soil health problem that has farmers worried about the future of farming in the Palouse.

“We’re riding the edge of a crisis,” says Paul Carter, an agronomist and the director of WSU Extension in Columbia County. “We can pretty well nail it down to the addition of nitrogen to our soils for crops. In 1940 or 1950, nitrogen was applied at five pounds per acre. Now, in some areas, we’re up to 100 or more pounds per acre.”

Pullman-based USDA soil scientist David Huggins agrees with Carter, describing soil acidification as a “quiet crisis.” Quiet, because it can be masked by other types of problems and because farmers haven’t tended to look for it. Quiet also because most people aren’t aware of the soil health challenges that farmers face today as a result of increasing pressure to produce more food.

But it is nonetheless a crisis. At stake is the sustainability of wheat farming in Washington. As the state’s third largest commodity crop, wheat represents $1 billion of the state’s $10 billion agriculture sector.

A race to the bottom

Soil pH, Huggins says, is a “master variable” that affects almost everything: soil microbes, plant diseases, the ability of plants to access nutrients in the soil, the effectiveness of herbicides and how long they take to break down in soil—all of which can have an effect on crop yield.

“We farmers have used lots of ammonia fertilizer and that use has increased faster than the yields have,” Wegner says. “Some farmers say it’s a race to the bottom. The more you put on to raise yields, the more you have a pH [acid] problem.”

If it gets bad enough, soil acidification can render land unsuitable for growing crops altogether. Farmers near Rockford, Wash., south of Spokane, have a hard time growing an economically sustainable crop of wheat because the soil there has become too acidic.

Thirty years ago, Bob Mahler, a soil scientist at the University of Idaho, decided to map the extent of the problem in northern Idaho and eastern Washington over time. He found that since the Green Revolution—which transformed the agricultural industry, resulting in greater wheat yields but requiring more ammonia-based nitrogen fertilizers—soil acidification had dramatically accelerated. Between 1960 and 1985, 65 percent of the soils in that region’s farmland became acidic.

Evidence unearthed by Carter in Columbia County suggests the issue has continued to get worse.

Paul Carter

When Carter arrived in Columbia County in 2005, a handful of farmers were concerned about acidic soil locally. But he began to suspect the problem was more extensive after talking with farmers in other parts of the Palouse.

To explore the issue, he convinced the Washington Association of Conservation Districts to fund a soil sampling study. Carter collected data from 76 farm fields across different rainfall zones in Columbia County and discovered that acidic soils were far more widespread than he had thought. 97 percent of the fields were acidic, with a soil pH below 6. In 89 percent of the fields, the soil pH in the top six inches of soil where seeds take root was even worse, below 5.2.

Most plants are happiest when the soil pH is 6.5. Lentils and peas, common rotational crops for wheat growers, start to get into trouble below 5.6, and wheat below 5.2. Below a pH of 5.0, enough naturally occurring aluminum in the soil is released that it can become toxic to plants, stunting root growth and resulting in yellowing plants that don’t thrive.

Changes in soil pH are exponential. When pH drops by a point, from 7.0 to 6.0, that’s a tenfold increase in acidity. Going from 7.0 to 5.0 is a 100-fold increase. Some of Carter’s soil samples were as low as 4.2, a nearly 1000-fold jump.

Restoring balance

Acidification is relatively easy to reverse with the addition of lime to the soil, which raises the field’s pH. In fact, Carter says, that’s just “about the only thing you can do.”

For farmers like Wegner and Chuck Schmidt of Rosalia, Wash., who have acidic soils, adding lime has been the go-to solution. But the practice comes with a downside: it’s expensive, and that presents a challenge when commodity prices are relatively low.

Depending on the quality of the lime and the amount applied, the price tag for liming a field can be over $400 an acre, according to Carter. For a typical 1,000- to 2,000-acre wheat farm, that adds up quickly.

“We don’t have a lot of options besides lime,” Huggins says. “But we haven’t quite figured out where to put it, how much, and what form to use.”

Knowing these things is critical to ensuring the liming is effective and economical. Simply broadcasting lime across a field doesn’t necessarily get it to the specific area where the soil is acidic, and any wasted effort and resources is a hit to the farmer’s bottom line. Therefore, Carter and Huggins are exploring new methods and equipment to boost the precision of the process.

Precision agriculture

“In the future,” Mahler wrote in 1985, “an even greater percentage of agricultural soils will require amendment with lime to produce optimum yields of wheat, peas, lentils, and alfalfa.”

The future is now.

It’s possible, Carter says, that farmers didn’t heed Mahler’s warning 30 years ago because soil acidification is not easy to recognize. “Farmers and agronomist who aren’t familiar with the problem are sure it’s something else,” he says, “a chemical that didn’t work right, or tolerance to herbicides, or that certain diseases are worse now.”

Growers in the Palouse haven’t typically tested for soil pH, Huggins says. And even when they have, the results may not have shown a problem, given the way soil traditionally has been sampled.

In response to growing issues, farmers and scientists like Carter and Huggins are now rethinking soil sampling techniques.  Accurate soil testing, sophisticated mapping, and the measurement of crop yields are the cornerstones of a new approach to farming called precision agriculture. It’s an approach that could help farmers be smarter about nitrogen use. In the long run, it could substantially lower costs, be easier on the soil ecology, and contribute to the overall sustainability of farming. Aided by technology like satellite mapping and remote sensing, precision agriculture allows farmers to apply inputs like fertilizer, pesticides, and lime only when and where they will have the most impact, instead of uniformly across a field.

Applying nitrogen for decades has created what ecologists call a brittle situation. Like a weakened immune system, it has decreased the capacity of the system to be resilient to stresses.

“We’ve gone through a golden age of resource use where we’ve relied on our soil’s natural capital and we’ve basically used a large portion of it up,” Huggins says. “Now, we have to pay much more attention to this resource [soil] in order to keep it functional. We really need to step up and address soil health, and get the word out that it’s important.”

Huggins believes an appreciation of soil health goes beyond farmers and soil scientists. “It goes along with people’s increasing interest and knowledge of where the food they eat comes from and how it is produced,” he says.

If the quiet crisis is to be averted, this interest is vital. Progress lies in raising awareness about the soil we rely on for our food, and in scientists and farmers working together to rebuild resilience into our soil systems.