Fertilizer is an essential tool for farmers, especially those who grow America's largest cash crops, corn and soybeans. For corn growers, fertilizer accounts for about a third of their input costs.

But fertilizer prices are now spiking.

The U.S. Department of Agriculture estimated the three kinds of fertilizer have dramatically increased in price over the past year: anhydrous ammonia, 235%; urea, 149%; and liquid nitrogen, 192%.

"Researchers expect the spike in fertilizer prices to affect producer decisions," the USDA said.

[Read more: Fertilizer washes off Midwest farm fields and taints communities’ drinking water, poisons Gulf of Mexico]

The rising prices have already had some impact — one Midwest farmer told Investigate Midwest in December she decided to not plant corn on her 183-acre farm because the fertilizer prices were too high.

One explanation for the spike, experts said, was supply chain disruptions caused by the COVID-19 pandemic.

In the graphic below, the USDA uses the state of Iowa as a stand-in for the U.S. because of its importance to the nation's crop production.

Top image: Farmer Paul Jeschke holds up an ear of corn on his farm near Mazon, Illinois, on Aug. 20, 2015. photo by Darrell Hoemman, Investigate Midwest