I’m sure you’ve heard this before, but it bears repeating: keeping residue on your fields will save water and reduce fertilizer costs.

South Dakota farmers see a range of benefits from crop residue — corn stalks, soybean stems and wheat straw left after harvest — especially in a dry season.

It can be tempting to cut corn for silage or bale oat straw to feed to cattle when yields and feed supplies come up short. But there are major costs to removing residue, the South Dakota Soil Health Coalition recently pointed out.

In northeastern South Dakota near Twin Brooks, farmer Dave Kruger planted his soybeans on light, sandy ground and watched them burn up in last summer’s heat. Across the road, soybeans planted in the same sandy soils held on.

The difference was that the second field of beans grew through a thick mat of rye straw. It took another two to three weeks to see signs of heat stress, Kruger says.

Residue’s role in moisture retention is two-fold. It acts like a lid, keeping soil covered and moisture from escaping. It also helps build organic matter and carbon, which in turn increases the soil’s capacity for holding water.

Kruger is short on moisture again this year. Most of his farm has seen 10-11 inches of rain or snow since January — about 3-4 inches below normal. But Kruger’s crops continue to pull through.

“It definitely has helped it hold on and survive through drier spells,” Kruger said.

It wasn’t a great year for small grains in central South Dakota. Marvin Schumacher, who farms north of Pierre, had to abandon one of his oat fields because the grain just didn’t fill in the hot, dry summer.

But he left the failed oats instead of putting them up for hay. “I hate to remove residue anytime if I can help it. What you lose for residue doesn’t pencil out,” he says.

Some of the most concrete costs of removing residue come from the nutrients that must be replaced when straw and stalks are baled up and hauled away, the coalition points out.

A ton of dry harvested corn residue contains 17 pounds of nitrogen, 4 pounds of phosphorus, 34 pounds of potash and 3 pounds of sulfur, according to research from the University of Nebraska-Lincoln. At today’s fertilizer prices, each round bale of corn stalks would add up to $32.61 worth of fertilizer.

The nutrient values of wheat straw and soybean residue are a little less, with 1 ton of wheat or bean stubble at around $20 worth of fertilizer.

Those numbers align with what Kruger has experienced on his farm. He has four quarters of ground that have been managed with continuous light tillage. While most of his ground has been no-till since 1993, those acres serve as a good side-by-side comparison. When it comes to fertilizer, his no-till land saves him $20-30 per acre per year.

“I think that’s the result of building that organic matter,” he says. “When you take any of the straw or the residue, you’re just carrying more fertilizer off the fields.” 

Producers should consider the long-term impact of removing residue, says Dwayne Beck, who manages the Dakota Lakes Research Farm near Pierre. “When you take off residue and you don’t replace it, that’s a permanent thing. It takes a long time to recover from that,” he said.

Diverse Rotations Can Help

A lot of less-than-stellar corn crops are being cut for silage this year. That takes a lot of potential residue out of the mix.

A high-residue cover crop planted behind the silage cutters can stem those losses, Beck said. Cereal rye, triticale or winter wheat are good options.

He also urges producers who cut silage to consider changing their rotation if they were going to plant soybeans next year. Growing a high-residue crop would be more appropriate. Producers will have to factor in the nutrients they’ll miss out on and maybe apply some manure to bring some of that fertility back.

“You’ve turned a high-residue crop, corn, into a low-residue crop. With two low-residue crops in a row, it could cause some real issues,” Beck said. “The worst thing you can do to a piece of ground is to take the forage off year after year.”

According to Beck, the best rotations are made up of 80% high-residue crops such as corn, wheat and other cereal grains. That’s food for thought for your fields going forward.