You could call Dean Sponheim an accidental conservationist.

Well, at least initially, anyway.

In 1999, Sponheim was frustrated that every year he had to replant a big chunk of a field that wasn't well tiled. "I was looking for a system where I didn't have to work it in the spring," he said.

Sponheim ended up building the machine he wanted, attaching a strip-till unit to an old planter bar. In the fall, he tilled an 8-inch strip in each row of the field that he could plant into the next year. "I didn't even put fertilizer in the strip," typical "with true strip-tilling," he said.

But he liked how it worked.

The strip is "raised a little bit," Sponheim said. "It dries out and warms up faster in the spring. It's amazing what that does, even in wet muck ground. ... It works really, really well."

A couple of machines later, he and a neighbor started strip-tilling acres for their neighbors. "Most people thought we were nuts," he said. "We just played around with it for a few years. ... We did a lot of modifications."

Now Sponheim uses two machines to strip till 6,000 acres for neighbors, a business that's grown from about 500 acres in the early days.

Sponheim said he and his son, Josh, will spend about 600 hours this fall doing the custom work after they've finished harvesting their own corn and soybeans. They also sell DuPont Pioneer seed and provide variable rate planting and fertilizer prescriptions for their customers.

Variable-rate, or precision farming, allows farmers to use yields, nutrient tests and other data to determine exactly how much seed and fertilizer they need to grow a crop, potentially changing as they move equipment across a field.

Sponheim, who strip-tills both corn and soybean acres, has become a believer in the conservation practice that leaves most of the crop residue on the field to help build organic matter. It also reduces erosion and keeps fertilizer from moving from the soil.

Sponheim's experimentation with strip-tilling has led to other conservation practices, including strip-cropping — eight rows each of alternating corn and soybeans.

He believes strip-cropping, an old practice that's gaining new popularity, allows for better use of nutrients, and it gives nature an opportunity to build better yields. Sponheim said the soybeans allow more sunlight and air to flow through the field.

"If you have an 80-acre field of corn, it becomes a sauna in there," he said. "There's hardly any air moving in the corn when it's tasseling ... but if we open it up with bean strips, now all of a sudden we've reduced the temperature of that cornfield tremendously."

Sponheim said the yields on the outside corn rows are up to 35 percent higher than the inside rows. And the soybean yields are the same, or slightly better, than with "block cropping."

Sponheim also is testing strip-cropping four rows of alternating corn and soybeans. "It makes every row an outside row."

And strip cropping better enables cover crops such as cereal rye to grow. Many farmers have the cover crop seeds flown over corn and soybean fields before they're harvested.

Sponheim, who's testing different cover crop varieties and application methods, sees the over-winter crop as an "insurance policy," allowing him to tap the nitrogen and phosphorous that the corn and soybean crops may not have used.

Cover crops use the nutrients as they grow, releasing them for corn and soybeans the next year as they decay.

Sponheim has come a long way from 15 years ago, when he first started strip-tilling. Back then, he moldboard plowed "fence to fence."

"If there was a single corn stalk standing up, you did an awful job of plowing," he said, cringing now, thinking about the erosion it caused. "I remember springs when we had black water running down the ditches. It was terrible."

Sponheim believes strip-tilling, precision farming and other changes better position his farm, and those of his neighbors, for extreme weather conditions.

Keeping more stalks, husks and other crop residue on the land is improving the soil health, enabling it to better hold moisture needed during droughts, and keep nutrients from leaving fields during heavy rains, he said.

"I have two grandsons ... and we want to leave something for them," Sponheim said.