soil samples

Labs nationwide have seen soil samples with drops in potassium levels. While researchers say it is hard to pinpoint a reason, increasing sampling frequency could find other trends.

Nationwide, there has been a major trend in soil test results — a drop in potassium.

Andy Wycislo, an agronomist who works with Waypoint Analytical, said there is no identified root cause for why potassium levels are dropping over the last few years, and while some other nutrients have seen decreases over the past couple of years, this one stands out.

“There’s a number of potential reasons for it and we don’t really understand why,” Wycislo said.

“We’ve seen this potassium drop over the last four, five or six years, and farmers might take a sample for the first time in four years and see a massive drop in potassium and can’t explain it.”

Wycislo said it’s hard to give a good idea on regional soil tests due to the wide range of unnown variables. When labs receive soil for testing, they don’t know the full history of where it is coming from, whether that’s land with no-till practices and cover crops or land that receives anhydrous and full tillage every year.

The reason he feels confident in the overall drop in potassium is it isn’t just a one-lab situation. Wycislo said he’s discussed this issue with universities and other labs and they are seeing the same overall trends.

Potassium helps water and other nutrients pass through plant tissue, and is also associated with creating ATP which can regulate photosynthesis.

Daniel Kaiser, an Extension specialist with the University of Minnesota, said in an April article about managing potassium fertilizer that anyone looking to add the element back into the soil should focus on having the correct rate, adding it is especially important compared to applying at a specific time throughout the year.

One way to help monitor the situation is to have producers get more soil samples to create a clearer picture of the soil map and identify any problem areas in their fields much more quickly.

“Increase the frequency of sampling and increase the density of sampling and that will theoretically help them identify trends quicker, like this potassium problem,” Wycislo said.

“That also potentially helps them save money by putting the money in the right place.”

For those specifically monitoring the potassium in their fields, in his article Kaiser suggests getting samples done at the same time of year, as levels will change throughout the growing season.

“Potassium is different from other nutrients in that the soil test value is not static in the field over the growing season and can vary from fall to spring,” he wrote.

While it is hard to pinpoint trends for certain areas, Wycislo said overall trends appear to be down in most nutrient categories. He said some of the cause may be farmers renting ground for only a couple of years.

“There are times when growers might not necessarily fertilize how they should for the health of the crop because they only have the ground for a year or two,” he said.

“Some aren’t going to take the time and investment to build up the fertility which can take multiple years to get.”

Wycislo said there are some landlords who take time to mandate certain fertility levels in the ground, but from what he’s seen it isn’t very common.