Losing six inches of topsoil could cost farmers more than $6,600 in nutrients and organic matter, according to a new analysis by North Dakota State University (NDSU) researchers.
Topsoil is the most fertile layer of a soil, rich in microbial activity and essential for crop production. When it erodes, thousands of dollars’ worth of nutrients and organic matter erode with it.
NDSU researchers’ findings showed that the cost of direct nutrient loss and nutrient loss due to organic matter loss totals over $1,100 for every inch of lost topsoil, or $6,600 for a 6-inch layer.
These numbers show that soil erosion is an economic issue, not just an environmental one, said Naeem Kalwar, NDSU soil health specialist at the Langdon Research Extension Center. “Protecting topsoil from erosion is crucial,” Kalwar said. “That layer is where farmers plant seed, and it is responsible for feeding the world.”
Soil erosion, which is the loss of soil sediments or material, can happen due to wind, water and tillage. Tillage can worsen wind- and water-related erosion by loosening the soil. When topsoil erodes into roadside ditches, it pollutes the drinking water for humans and livestock.
“Farmers, ranchers and landowners will eventually have to pay to replace those nutrients,” said Kalwar.
Kalwar set out to determine the value of an inch of topsoil in terms of replacing lost crop nutrients and organic matter. Researchers collected a 6-inch-deep sample of topsoil that had eroded into a roadside ditch from an adjoining field and sent it to a soil testing laboratory for a comprehensive fertility analysis. Results showed appreciable quantities of essential plant nutrients and a significant amount of soil organic matter.
After calculating the cost of replacing the nitrogen, phosphorus, potash, sulfate-sulfur and iron present in the lost 6 inches of soil through commercial fertilizers, researchers determined the replacement cost to be $2,541.22, or $423.54 for every inch of lost topsoil.
In addition, replacing nutrients associated with organic matter loss added another $4,141.73, or $690.28 per inch. Combined, the total cost is $1,113.82 per inch, or $6,682.95 for six inches.
While fertilizers can replace nutrients, rebuilding soil organic matter could take decades, even with the adoption of best management practices. A study at the NDSU Carrington Research Extension Center determined that soil organic matter increases by 1% after 27 years of consistent livestock manure applications. Based on that rate, replacing the 5.7% of organic matter lost from six inches of topsoil could take approximately 154 years, or nearly two lifetimes.
“Preventing erosion is far more cost-effective than trying to rebuild the soil,” said Kalwar. “Simple practices like reduced tillage and cover crops can save thousands over time.” — NDSU Extension
