-Farm News photo by Darcy Dougherty Maulsby
Soil erosion ruins the land’s ability to produce healthy crops. It has contributed to the collapse of numerous civilizations around the world throughout history, says Brian Dougherty with UnderstandingAG. The reason current rates of soil erosion are considered "tolerable" is because no one has to write a check for $50 per acre every year as an "erosion tax" while their soil disappears, Dougherty says.

With all the factors that go into producing high-yield crops, from seed selection to proper fertilization to weed control — what about controlling soil erosion?

“Now’s a key time to revisit the principles of soil health and think about what can be improved for future growing seasons,” said Brian Dougherty, who works with UnderstandingAG, a consulting group focused on regenerative ag for more productive, profitable, resilient farms.

That includes limiting soil erosion.

It’s estimated that the current global soil erosion rate is around 75 billion tons per year, said Dougherty, who spoke in Wall Lake this past summer about the value of regenerative ag practices that help curb soil erosion.

“Soil erosion has been one of the most persistent challenges humanity has faced since the advent of agriculture more than 10,000 years ago. Tillage and poor grazing practices were the main causes of land degradation historically. Mechanized agriculture has greatly increased the rate of erosion from cropland during the past century.”

-Farm News photo by Darcy Dougherty Maulsby
Soil was swirling dramatically around this tractor working in a west-central Iowa field in May 2024.

Soil erosion, which ruins the land’s ability to produce healthy crops, has contributed to the collapse of numerous civilizations around the world throughout history. This fascinating, sobering history is detailed in the book “Dirt: The Erosion of Civilizations” by David Montgomery.

“I highly recommend it if you’re inclined to think that we are now somehow immune to a similar collapse in agricultural productivity,” Dougherty said.

While previous generations of people would simply move on to a new piece of land when the soil lost its capacity to produce, that’s no longer an option.

“Land degradation is as severe as ever,” Dougherty said. “We’ve just masked the symptoms of lost topsoil and poor soil function with added fertility, pesticides and other technological and engineering fixes.”

Paying the “erosion tax”

-Farm News photo by Darcy Dougherty Maulsby
Soil from this central Iowa field was washing into the ditch in May 2024.

Determining the cost of erosion starts by assigning a value to soil. Let’s assume it’s possible to purchase more topsoil if the existing topsoil eroded away. One common way to put a value on soil is to determine how much fertilizer it would take to replace the lost nutrients.

“You can run a total nutrient digestion (TND) test on your soil to get a breakdown of what it contains,” said Dougherty, who calculated numbers from his family’s farm in northeast Iowa, which has silt-loam soil with just over 3% organic matter in the top 6 inches.

He created a spreadsheet to take the numbers directly from this test and calculate a value per ton of soil, based on average fertilizer prices in the past several years. To determine the cost of erosion, he used the Natural Resource Conservation Service’s (NRCS) tolerable soil loss, or “T” value of 5 tons per acre.

Soil-loss estimates are complex, because they depend on models to predict soil loss, Dougherty acknowledged.

“Despite the complexity, 5 tons per acre per year is a reasonable estimate for the Midwest,” said Dougherty, who added that actual erosion rates were likely much higher in 2024, due to heavy rainfall events earlier this year.

-Submitted photo
Brian Dougherty, who farmed for a number years in northeast Iowa, is part of UnderstandingAG, a consulting group focused on regenerative ag for more productive, profitable, resilient farms.

In his calculations, Dougherty put a small value ($20/ton) on soil carbon, plus he valued the major micronutrients. With an erosion rate of 5 tons/acre, this equates to a cost of about $50 per acre per year in lost nutrients.

“That $50 per acre per year is an alarmingly high number in my book,” Dougherty said.

The actual cost would be higher, he added, because the soil that erodes away comes from the very top of the soil profile, where organic matter and nutrient concentrations are highest. “The reason we consider this rate of erosion to be ‘tolerable’ is because no one has to write a check for $50 per acre every year as an erosion tax while their soil disappears,” Dougherty emphasized.

Avoid the death cycle of ag land degradation

Tackling the underlying cause of the “death cycle” of erosion and poor soil function means implementing soil-health principles.

“How we manage our farms is a choice,” Dougherty said. “There are economic, social and political barriers to change, but change we must. We as individuals, communities and societies can choose a better path forward.”

Soil can be managed in a way that improves the land over time. Adding a cover crop is one proven way to reduce erosion. Research shows that adding a cover crop to a row-crop field can reduce soil loss by about 60%, on average, Dougherty said.

What’s the value of this?

“Using a $30 to $50 per-acre estimate for the cost of erosion, the cover crop keeps $18 to $30 worth of nutrients in the field that would otherwise be lost,” said Dougherty, who noted that cover crops also provide an array of other soil-health benefits.

Water quality research from the Upper Midwest shows that a winter cereal rye cover crop reduces nitrate leaching by around 30%. This equates to a reduction in nitrogen loss of around 10 to 15 pounds of nitrogen per acre per year in a tile-drained field. Preventing this nitrogen loss is worth around $10 per acre (depending on nitrogen prices), if you didn’t have to repurchase what was lost, Dougherty said.

Nitrogen loss may not be noticeable year to year, just like soil erosion isn’t always noticeable in the short term, but farmers are indeed paying the cost of soil and nutrient loss in the form of higher fertility bills and lost yield, Dougherty said.

That’s why cover crops pay, he added.

“Adding the erosion reduction and nitrogen savings gives us a cover-crop value in the neighborhood of $25 to $40 per acre. We have to ask: Are cover crops really an expense, or are they actually a dividend-paying investment that saves money and improves soil productivity over time?”

Other practices that control soil erosion include less tillage, adding more biodiversity to the landscape, and incorporating livestock on the land, when possible. These are all principles of regenerative agriculture.

“Topsoil is rebuilt rather than eroding away in this system,” Dougherty said. “Only then can we reduce our reliance on expensive, supplemental inputs and technological ‘fixes’ that mask the symptoms but do not address the root causes.”

Regenerative ag means working with nature, not against it. It also means learning lessons from prior civilizations that collapsed under the weight of poor land management, Dougherty said. “The cost of soil erosion is something we cannot afford to ignore. Less erosion, less pollution, cleaner water, better food and a healthier environment full of life-sustaining diversity are invaluable.”