Subsoiling, or deep tillage, could help solve some of the problems that farmers face growing wheat and soybeans in silt loam soil with a shallow clay pan — a common scenario on Arkansas' Grand Prairie.

Gary Huitink, an agricultural engineer for the University of Arkansas Cooperative Extension Service, says that while silt loam with a hardpan is ideal for rice, it's often too wet for wheat in the winter and too dry for soybeans and other crops in the summer.

Huitink and other scientists are studying the effects of subsoiling on wheat, soybeans and corn in rotation at the UA Pine Tree Branch Station in St. Francis County, Ark. He believes all three crops could benefit from subsoiling.

Huitink said the subsoiling study consists of five replications in a 6-acre plot. “Half of each replication is subsoiled and half is not. In each replication, soybeans follow wheat, then wheat is followed by corn.”

Roger Eason, director of the Pine Tree station, said subsoiling was done in the fall, while the soil was still dry, and then wheat was planted. Corn and soybeans were planted in the spring. The test plot was border irrigated using the UA computerized Irrigation Scheduling Program.

The wheat was harvested in June, and according to Huitink, the results were promising. “We got a 9-bushel advantage on the subsoiled half of the plots.”

Huitink says wheat benefits from fall subsoiling because “there's less moisture and more oxygen in the root zone during wet periods. The typical problem on these Prairie soils with a clay pan 4 to 6 inches underneath the surface is too much water. Yields can go from 70 bushels an acre to nothing because of standing water.

“Subsoiling improves surface drainage and fosters root growth.”

He said the jury is still out on just how much subsoiling silt loam with a pan will affect soybean and corn yields. Subsoiling does allow water to move downward into the soil profile. When the rains stop, that stored moisture comes in handy.

In the long run, all crops in the rotation will benefit from a buildup of organic matter in the soil. In the test plot, wheat, soybeans and corn are drilled into the previous crop's stubble.

“While half of the test plot is subsoiled, it's not tilled,” said Huitink. “We subsoil to open up the ground, but we want to leave as much residue as possible, and modern equipment allows us to do both.”

Eason added that the non-subsoiled part of the plot isn't tilled either. “We've had a lot of success on the station doublecropping wheat and soybeans and never tilling the ground. The biggest benefit from no-till comes from leaving the residue on the surface, although you may not realize the benefits for three or four crops.”