Changing climate could flush more soil and fertilizers into water, experts say

BROOKINGS — Water management professionals say more soil and fertilizer will leave farms and enter the state’s waterways as climate change intensifies storms and droughts.

Experts from around the nation discussed the problem recently at the annual Eastern South Dakota Water Conference in Brookings. The Northern Great Plains can expect more heavy rains because of climate change, according to Lindsay Pease, a nutrient and water management specialist at the University of Minnesota.

“And those high-intensity rainfall events are some of the worst things for the field to experience in terms of nutrient loss. You can get a lot of surface runoff in a short amount of time,” Pease said.

Warmer winters could also cause underground drain pipes — known as drain tile — to flow with water more often. Farmers install drain tile to remove unwanted water from their fields.

More water running through drain tile means more fertilizers, like nitrogen and phosphorus, escaping soil.

“And so what today might not be a big impact on kind of an annual scale, over time could become more impactful both with nitrogen and phosphorus losses,” Pease said.

Paul Fixen, retired senior vice president of the International Plant Nutrition Institute, said farmers should optimize fertilizer application to make sure it’s just what they need, and no more.

“Because if it’s higher than it needs to be, and we run into one of these years where losses are amplified because it’s a wet year and lots of runoff, you’re going to lose more value from your soil,” Fixen said. “You’re also going to contribute to water quality degradation.”

Farmers should think of the landscape as a system and consider all the variables that may change, according to Heidi Peterson, vice president of agricultural research and conservation at the Sand County Foundation.

She said rising air temperatures may cause rising soil temperatures, which could change the nutrient mix in the soil. And that could necessitate changes in fertilizer applications.

“The adoption of conservation practices is going to be critical as we see the changes in temperature and more intense precipitation events,” Peterson said.

Precipitation on the Northern Great Plains grew 29% between 1998 and 2016, Peterson added. Last summer, Sioux Falls experienced its rainiest day on record when more than 5 inches of rain fell on Aug. 7.

Greater and more intense rainfall is pushing fertilizers from farms into the state’s streams, rivers and lakes, experts said at the conference.

Agriculture accounts for the majority of phosphorus in the state’s waterways, which leads to the kinds of algae blooms observed at Lake Mitchell, where city leaders are struggling with proposed solutions to clean the water.

But fertilizers don’t only enter waterways via surface runoff and water drainage.

Erosion along streams and rivers also puts large amounts of soil into the water, according to Garey Fox, head of the Department of Biological and Agricultural Engineering at North Carolina State University. He said the rate of erosion along streams is likely to increase as climate change causes more severe drought-flood cycles.

“If it’s a long dry period and you get these episodic flood events that are coming through, it’s easier to take away all that material that’s been sitting there,” Fox said.

More intense droughts could also cause problems with fertilizer management, according to South Dakota State University Extension Water Management Engineer John McMaine.

“Because what we’re counting on when we put down fertilizer, whether it be in the fall or in the spring, we’re counting on that crop being able to use that, which requires some moisture. Without it, that crop will not grow, and that crop will not use any of the nutrients that have been applied,” McMaine said. “And now if you have a storm come in, and the nutrients just sat there because the soil is dry, a big rain will just take the nutrient with the surface runoff.”