Growers in North Carolina have begun to notice that wheat tends to be taller and to produce larger heads in response to sub-soil slits from previous crops, but whether the practice is really improving yields has been up for debate.

North Carolina State Extension Associate Georgia Love put the question to a test last year at the Moore Brothers Farm near Maxton, N.C.

“The Moores were set up with their DMI on 40 inches, so we checked it on 40 inches and on 20 inches, and compared the results with a chisel plow and with no deep tillage,” Love says.

DMI is a type of vertical cultivator, which is sold under a number of trade names.

Vertical tillage refers to systems where soil disturbance is confined to soil movement mostly in the upward direction and/or confined to a slot or strip where the next crop rows are to be planted using strip-tillage implements or coulter-based implements that perform full width tillage.

The fields tested on the Moore farm are sandy to very sandy. It’s not the kind of land on which most growers would plant corn, and is better suited to soybeans and wheat. It has a significant hard pan and is technically a Norfolk loamy sand, with a high sand percentage, Love says. 

Also, previous research has indicated that soils with less sand and a high clay layer do not respond to deep tillage, so it’s important to know your soil type before doing any form of deep tillage. 

The DMI in this test was run at 12-14 inches below the soil surface, just enough to break the hard pan without bringing up acidic clay.

The lowest yield came on the check plots with only 46 bushels of wheat per acre. Love stresses that this is marginal land and high wheat yields were not expected. Using a chisel plow increased yields by four bushels per acre. The 20-inch DMI increased yields by 11 bushels per acre and the 40-inch DMI by nearly 9 bushels per acre.