KDSN RADIO News
Soil temperature is key for Iowa farmers to apply fertilizer
With the corn and soybean harvest winding down, many farmers are turning their attention to fertilizer.
Richard Roth, a nutrient management specialist with Iowa State University Extension, says the primary motivation for farmers to apply fertilizer in the fall is to spread out the workload.
Spring rainfall and muddy fields can narrow the window for applying fertilizer and planting seeds.
To prevent nutrients from washing into streams and rivers, Roth says timing is key.
“When it comes to fall nitrogen applications, there’s a lot of dos and don’ts,” Roth says. “The number one is the soil temperature, right? If your soil temperature is not below 50 degrees, you just shouldn’t be out there. That’s number one.”
Roth recommends farmers monitor the Iowa Environmental Mesonet’s (MEH-so-nets) soil temperature maps.
“Our goal when we apply nitrogen in the fall is to do it when the soil temperatures are below 50 degrees and on a downward trend,” he says. “The reason why we do that is because when you get below 50 degrees, microbial activity in the soil really drops off.”
When the soil is warm and moist, microbes convert ammonium into nitrate, and without living roots to absorb nitrate, it can easily move with water and accumulate downstream.
Between 25 and 50 percent of the total anhydrous ammonia fertilizer applied to fields across Iowa occurs in the fall, often to save time around spring planting.
(By Rachel Cramer, Iowa Public Radio)
