June 15, 2021

Jones: What a shovel test can reveal about your soil

When was the last time you grabbed your favorite shovel or spade and took a walk through your fields? A simple shovel test can reveal several things about soil that you may want to take into consideration this year and looking forward.

I challenge you to take a few moments this spring or summer to investigate your soil’s health. Here are a few tips for when you go out.

Pick a day when the soil is not too dry or too wet. Soil moisture can influence some of the physical properties of soil observed during your shovel test, so we want the soil to be moist, not saturated or bone dry.

As you push your shovel into the ground, notice how it feels. Check multiple spots in the field, some with residue present and some areas of bare soil, to see if it feels different.

Do you hit a hardpan layer? If so, at what depth? Hardpan layers are indicative of compaction beneath the surface, which can negatively influence your crops’ ability to establish roots and take up water and nutrients.

Excessive or repetitive tillage may cause hardpan layers to form over time, though we also often see compaction on the end rows of fields where wheel traffic frequently occurs. It is also possible for compaction to occur in your no-tillage fields, especially in the first few years after transitioning to no-till.

Lift up a shovel full of soil. How does it look? A plate-like structure running horizontally through the soil could be another sign of compaction and poor aggregate stability.

Aggregate formation occurs when soil particles bind together in clumps of various sizes; roots, earthworms, fungi and other microorganisms all contribute to aggregate formation.

When soils have good aggregate stability, they can hold more water and air, resist erosion and compaction and provide more pore space and channels for root growth. A soil with good aggregate stability should break up into clumps when you gently squeeze it, and it may even look like cottage cheese.

Do you see any earthworm activity in your soil? Seeing zero or very few earthworms after digging around in different areas of your field may mean your field is not attractive to them. This could be due to regular disturbance of their habitat, the soil, through tillage, or even lack of residue for them to feed on.

As mentioned earlier, earthworms are key players when it comes to aggregate formation. They can also do some “tillage” for you by pulling residue into their burrows to eat and by creating channels that roots and water can later follow.

If your field is experiencing compaction issues, you want to improve your soil’s aggregate stability, or you wish you had more earthworms, consider planting cover crops. Cover crop species with a tuber and taproot, like daikon radish, are generally able to drill through compacted layers.

It is not recommended to plant a brassica like daikon radish by itself, so pair it with a grass species like cereal rye, annual ryegrass, or oats. Their fibrous root system can also assist with breaking up compaction and forming soil aggregates. Earthworms enjoy munching on the residue and the protection it provides from predators.

Changes will not occur immediately, but over time, I encourage you to go back out with your shovel and notice the changes and improvements in your soil.

Jennifer Jones is a University of Illinois Extension watershed outreach associate.