Jodi Dejong-Hughes digs deep into her soil research as a University of Minnesota Extension educator. In-field soil pits are one of her favorite teaching tools for revealing to farmers the importance of deep soil structure – and the and the importance of soil management. Her message is twofold: What occurs on top can either enhance soil structure, the root zone and root systems, or it can create long-term, yield-defeating damage. If you want a higher crop yield, soil management is vital.
Soil pits shed new light on the mysteries of the underground. “It’s what’s underground that product everything on top,” explains DeJong-Hughes. “If you don’t have the right soil structure below, I don’t care what genetics you put on top-you’ll decrease your yields. When we open a soil pit we really are searching for ideal root health.”
She emphasizes to farmers their most dangerous demons down below-such things as poor nutrient, air and water movement are the result of competition, tight crop rotations, aggressive tillage, erosion, release of carbon and consistently saturated ground due to poor drainage. DeJong-Hughes offers practical ideas on how to vanquish those demons.
“We’re really not talking about huge changes, either, to a farmer’s field practices. The point is that you can’t raise a successful crop unless the roots can get down to where they can explore the soil profile and take up nutrients from perhaps as far down as 1.5 to 2 feet below the surface.”
Constructing the the perfect pit
Excavation of a soil pit basically requires a backhoe or a skid loader. A workable pit generally is the width of the digging bucket and crosses four rows of crop to a depth of 4 feet.
At that depth, the layers of various soil in the profile are clearly visible, as is the plant root system. A pit must be spacious enough for several people to enter for a dose-up look at the profile.
A bright August morning brings several Minnesota farmers to a freshly dug pit in a cornfield on the Granite Falls, Minn., farm of Howard Gatchell Jr. and his son Dorian, who is an agronomist at a local elevator company. DeJong-Hughes uses the edge of the pit as her podium as she scratches away at the soil with a knife to help make her points. The soil profile in this pit features healthy com root systems and at least a foot of mellow, black loam topsoil under which lays a deep yellow layer of day.
The first thing she points to are the earthworm burrows. “Earthworms are our best friends down here,” she tells the crowd, noting that by working over thousands of pounds of soil per acre every year, worms help keep the rich loams here mellow and porous. Porosity is the key to ensuring good nutrient, air and water movement.
“Tillage is the No. I enemy of soil structure. Compaction is an enemy of good structure, and good soil structure is your No. I defense against compaction,”she says. Dejong-Hughes then explains exactly what good soil structure is and how it is achieved.
Healthy soil gives a farmer deeper, darker soil, and it’s easier to plow or till, reducing fuel costs. It requires less fertilizer, additionally reducing input costs. It will have stronger resistance to insects or disease. Good soil sponges up and holds more water, but also dries out quicker. Ultimately, crop yields are maximized.
When DeJong-Hughes talks about good soil structure, she means it has increased porosity. The soil crumbles easily into BB-sized aggregate, rather than clumping into clods that inhibit nutrient movement and root growth. Coming up against cloddcd, restrictive soils, roots ta kc a horizontal escape route rather tha1n delving deep into the underground.
Crumbling aggregate, mellow a1nd loose, enhances air exchange, improves drainage capability, while improving water-holding capacity and root growth. Porosity reduces soil crusting and bulk density (clodding) of the soil and slows erosion.