Soybeans Today January 2001

Subsoiling boosts brothers' soybean and wheat yields

by Rich Maples

Brandon and Justin Veach had the perfect field for subsoiling: Tunica silty clay soil with a hard pan created by years of continuous tillage. The field had never been subsoiled or deep tilled before.

Dave Freeze, a Mississippi County agent for the Cooperative Extension Service, University of Arkansas, saw it as a perfect opportunity to see if subsoiling would increase the Veach brothers' soybean yields. Freeze and U of A Agricultural Engineer Gary Huitink asked the Veachs to take part in a subsoiling study financed by Arkansas Soybean Promotion Board.

"In September of '98, Justin subsoiled half of a 20-acre field and left the other half unsubsoiled," says Freeze. "It hadn't rained in 45 days. The field was bone dry. Running the shanks 18 inches deep, with 40 inches between the shanks, he pulled up huge chunks."

According to Huitink, you want to see clay break into chunks when you're subsoiling. "That indicates that the soil is hard and compacted. If the clay is soft and flows real smooth, you don't need to subsoil.

"When you subsoil, you open up big voids. The idea is to store water during the winter. Then when it's dry in the summer, the stored moisture will carry the crop longer."

Justin Veach says rain helped melt down the clods a little, but the soil had to be disked behind the subsoiler before wheat could be planted. "It was pretty rough," he recalls.

When the wheat was harvested in June 1999, the subsoiled side of the field averaged 74 bushels, compared to 33 bushels on the non-subsoiled side. Freeze says, "The subsoiled side was next to a ditch and had a little elevation, which helped increase yields, but we're certain that subsoiling gave us a 20-plus bushel response.

"When we harvested soybeans following wheat in 1999, we ruled out the ditch effect by recording yields down the middle of the field," notes Freeze. "Where the subsoiled ground and the non-subsoiled ground met, you could see a 6-inch difference in plant height. And there was a big difference in yields."

The subsoiled side of the dryland field averaged 30 bushels per acre, 11 bushels more than the non-subsoiled side.

"Soybean prices in '99 were about $5 to $5.25 a bushel, so you're talking about a difference of $55 or more per acre," says Huitink. "It costs about $15 an acre to subsoil. That's the cost of tractor operation Ð pulling the subsoiler and smoothing out the ground for planting. Every other input is the same."

Freeze says when April-planted Group IV soybeans were harvested on the test field in September 2000, they averaged 43 bushels per acre on the subsoiled side and 33 bushels on the side that wasn't subsoiled. Plants on the subsoiled side were 9 inches taller.

Brandon Veach says subsoiling helps two ways. "When you get a heavy rain, you don't have near as much standing water. And subsoiling makes the soil like a sponge. It holds more water and retains it longer."

His brother, Justin adds, "On the subsoiled ground, you get the water where you want it, inside the soil instead of being lost to evaporation."

Freeze says the Veachs' field was one of three subsoiling demonstration sites he established in Mississippi County during the fall of 1998. "We had another field that was Tunica silty clay. It got a 5-bushel per acre response. We also had a field that was Sharkey clay, which is a much deeper clay. We got no response on that field. Zero."

Huitink recommends that subsoiling be done every other year. "You always want to subsoil when it's dry. If it's wet, you can subsoil the third year.

"If you're going to plant full season beans, try to subsoil in September or early October. There's usually a dry period."

He says the winter rains will help melt down the soil. "When there's a dry spell in January or February, you can come back in and smooth it down with a field cultivator. You want to stay off the field as much as possible to avoid compaction."

Justin Veach says, "We usually minimum till our wheat-beans. The less tilling you do, the more moisture you leave in the soil."

Subsoiling isn't suitable for all the Veachs' fields, but they intend to subsoil all they can where subsoiling can help."

Soybeans Today January 2001
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