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Dig down for better crop yields

Compaction can be a limiting factor, but you don’t know what you have until you see what’s under the surface.

Tom Kilcer

October 18, 2022

7 Min Read
farmer using a penetrometer to check soil compaction
FEEL THE LAYERS: Using a penetrometer, you can feel the layers of compaction that could be affecting your crop yields. Courtesy of Tom Kilcer

As you’re starting to wrap up combining for the season, right now is the best time to see if you have maximized yield.

Check for soil compaction as this can affect root depth and available water, and can severely limit availability to nutrients as the plants can’t get to them.

As farms and tractor sizes get bigger, we should remind ourselves that compacted soils, if not dealt with, can come and bite us in the backside.

Get your shovel out

Use a shovel to feel the compaction and to look at your roots’ growth and growth pattern.

The first layer you will see is the surface. Too much tillage, no surface residue and destroyed soil structure can leave the surface particles vulnerable to raindrop impact. The larger the drops, the greater the vertical speed of the rain — over 20 mph — and speed times mass equals the force that it hits the surface.

Multiple researchers have described this as small bombs exploding in horizontal shear that strips off and pulverizes the surface. With no protective cover and broken soil structure from excess tillage, the surface quickly becomes a soup of small particles that plug every pore in the surface. The soil acts like a kitchen linoleum floor that does not absorb water quickly.

This stops yield-producing rains from getting to the roots and seals out critical oxygen, thus the roots have trouble taking up nutrients and growing. And this is all because the top half-inch of the soil was destroyed before the growing crop could protect the surface.

The most fertile parts of the soil go first; the stones and subsoil stay behind. This is so common that some farms think of it as normal, but it is not and it will greatly affect your yields.

On the other hand, corn that has been strip-tilled or zone-tilled into winter triticale forage stubble has very little of this surface sealing. The stubble breaks the force of the raindrop impact, and the many hollow stems and dying roots underneath provide macropores that quickly absorb heavy rain and channel it to the roots of the next crop.

An added benefit is that the macropores from earthworms are protected and can absorb major amounts of rainfall without runoff or plugging. The same happens with fall-killed sods that are no-tilled in the spring.

Dig deeper

The next layer down you can often feel with a shovel or soil auger. As you dig, the soil breaks horizontally, and there are very few roots below. This is especially prevalent on fields that were chiseled or disked.

You can often feel the pan at 3-4 inches down. This is one-quarter the diameter of the disk. Tandem or offset disks move large particles to the surface and sift the fines down to the bottom of the disk layer.

Adding more insult to injury is the fact that the soil is often wetter as we go deeper, and the disk’s action smears a thin, root-limiting layer at the bottom. Therefore, in many cornfields, the stalk pulls out of the ground at 3 inches. There are few if any roots deeper than that, and many of the corn roots are growing horizontal, and are flattened and distorted.

A huge amount of plant photosynthesis is not going to yield by trying to force the root through compacted soil. The result is corn growing on one-third the volume that it could have, and you need even higher fertility to achieve full yield.

Tillage often hides this top layer destruction. On many farms, I’ve seen producers break up large blocks of soil on the surface layers to make brick and softball-size compacted blocks. This is not loosened, friable, well-structured soil.

Get to root causes

Finally, we get to why we were digging in the field: accessing root depth. I’ve been in many fields where we put the shovel in and thought we hit a stone in multiple spots that stopped at the 7- to 8-inch mark. There was no stone, but there was a roadbed of compacted soil that completely limited rooting depth.

The bottom of a chisel or moleboard plow can leave a compacted deep layer. I saw this in a chisel plow tillage study on silty clay soil. Heavy rains in August produced a perched water table on top of this layer and drowned or killed all the corn roots below 3 inches.

The crop looked great from the surface. But in many cases the deep compaction was made worse by spreading manure with a spreader that had too few axles for the load and too-high tire pressure to effectively support the weight.  

Tire pressure is surface compaction, axle load is deep compaction. Drag hose injectors can take a lot of that compaction weight off, but operating it when the soil is not dry will put a lot of that compaction back in.

Frost cannot not remove this compaction, nor can a perennial sod crop.

We had a 15-year timothy hayfield that showed compaction from a moleboard plow when it was originally plowed for seeding. The plow share marks could be seen and no roots went below 7 inches.

This field was plowed with a smaller tractor when the soil was still plastic at the plow shear layer.

After 10 years of no-till rotated alfalfa — corn on a gravel soil where the gravel bank was at the end of the field — we dug up the alfalfa roots. Each plant went down 8 inches. The taproot twisted and turned like a pig’s tail as it couldn’t get through the compaction.

On a pure sand field, we deep-tilled and then moleboard-plowed strips and planted corn. There were no roots below the 8-inch pan where we plowed.

At 12 inches, I could put my arm into the ground up to my elbow as the soil was very loose from the deep till, but the corn never reached that depth.

You can’t solve a problem if you don’t know the problem. This summer’s drought showed that you may have a problem. A simple computer hard soil analyzer (called a shovel for us old guys) can show if you do have a problem.

I did this at 9 a.m. with a farmer who I had to convince to take five minutes and check his field next to the house. He reluctantly agreed, thinking it was a waste of time. At 5 p.m., I told him I had to go home and make supper for the kids. He kept saying “one more field.” He then said that he learned more about his fields and cropping in one day of digging holes than he did at all our Extension meetings. That’s a compliment!

Right solutions

Once you find compaction, the initial reaction is to look for the biggest, deepest ripper, and a monster tractor to tear it all out. As research from New Zealand has found, without changes to the rest of your cropping system, this will be a complete waste of time.

Without knowing what’s going on underground, you may be doing more damage than good.

Lots of black smoke and lumps on the surface won’t improve anything. Running a chisel plow deeper than its designed depth will horizontally compact the soil.

As one farmer said to me, “Removing compaction is a process we have to figure out for our farm and our soils.” This was after a research trial that only grew on 3 inches of soil, and subsequent deep tillage ripped the shanks off the machine from the hard soil.

Improving fields takes strategic planning. It all needs to be done when the soil profile is dry enough to shatter.

One part of the process is to deep-till in fall (if dry) and immediately drill winter triticale as a winter forage. The massive roots will brace the soil, keeping them open to start the process of improving soil structure. If you haven’t done this yet, do it soon to maximize the time for tillers to grow, and to produce above- and belowground biomass.

Next spring, no-till a legume into the newly opened soil. It will continue to improve the soil structure until you are ready to rotate to no-till corn.

Another option is to strip-till corn into the triticale stubble.

The less trips it takes to get the crop in, the more you can wait for the right conditions to work or plant the field.

Kilcer is a certified crop adviser in Rutledge, Tenn., formerly of Kinderhook, N.Y.

About the Author(s)

Tom Kilcer

Tom Kilcer is a certified crop adviser in Kinderhook, N.Y.

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