For nearly two decades, Abe Sandquist has used every marketing tool he can think of to sell the back end of a cow. Poop, after all, needs to go somewhere. The Midwestern entrepreneur has worked hard to woo farmers on its benefits for their crops.

Now, facing a global shortage of commercial fertilizers made worse by Russia's invasion of Ukraine, more U.S. growers are knocking on his door. Sandquist says they're clamoring to get their hands on something Old MacDonald would swear by: old-fashioned animal manure.

"I wish we had more to sell," said Sandquist, founder of Natural Fertilizer Services Inc, a nutrient management firm based in the U.S. state of Iowa. "But there's not enough to meet the demand."

Some livestock and dairy farmers, including those who previously paid to have their animals' waste removed, have found a fertile side business selling it to grain growers. Equipment firms that make manure spreading equipment known as "honeywagons" are also benefiting.

Not only are more U.S. farmers hunting manure supplies for this spring planting season, some cattle feeders that sell waste are sold out through the end of the year, according to industry consultant Allen Kampschnieder.

"Manure is absolutely a hot commodity," said Kampschnieder, who works for Nebraska-based Nutrient Advisors. "We've got waiting lists."

Sky-high prices for industrial fertilizer are projected to reduce American farmers' corn and wheat plantings this spring, according to U.S. government data. That further threatens global food supplies as domestic wheat inventories are the lowest in 14 years, and the Russia-Ukraine war is disrupting grain shipments from those key suppliers.