Using a Penetrometer for Improved Soil Health
What is a Penetrometer?
A penetrometer, or soil compaction tester, is a device used for detecting soil compaction in the field. A simple-looking tool, a penetrometer is used to measure the amount of resistance it takes to move through, or penetrate, the ground. A good penetrometer ranges in price from $300 to $400, is built to last a number of years, and should more than return on your investment provided its used to help develop and implement strategies to reduce soil compaction.
Using your Penetrometer
In order to understand the nature of a field, farmers typically test a lightly trafficked area of the field with a penetrometer to establish a baseline, before moving onto taking measurements in the field. Obviously, the more measurements are taken in the field, the greater understanding of what’s happening beneath the soil’s surface a farmer will have. A good rule of thumb is to take a reading every 100 to 150 feet, or three to four readings per acre.
Measuring Soil Health
It’s recommended that farmers use a penetrometer when the field is at its water holding capacity (a few days after the soil has been thoroughly wetted). Spring is an ideal time to test because typically the entirety of the field is properly moisture-laden for testing. Testing in too-wet or too-dry conditions can result in inaccurate readings. A penetrometer can move too easily in muddy soil, leading a farmer to underrate a potential problem. Alternately, overly dry soil can increase resistance, perhaps giving the impression of a problem that doesn’t exist.
“overly dry soil can increase resistance, perhaps giving the impression of a problem that doesn’t exist”
Penetrometers measure the amount of pressure it takes to move the instrument through the ground in pounds per square inch (psi). Ideally, farmers want their penetrometer to measure between 100 psi and 200 psi. Readings over 300 psi indicate the soil is compacted and roots will have difficulty growing. In soil that measures under 100 psi, you may have to adjust your planter to pack soil over your seed or there may not be enough contact between the seeds and the soil for good germination.
Two Types of Soil Compaction
Soil compaction comes in two forms—surface and subsurface. Because surface compaction occurs in the top layer of the soil, it’s easier to both diagnose and fix. Surface compaction often takes shape as a hard, plate-like crust on top of the soil and can commonly be alleviated with normal tillage, strip tillage, or, for no-till operations, by direct seeding or including forage in the crop rotation.
Identifying subsurface compaction, sometimes called a plow pan or hardpan, is more difficult. A penetrometer allows farmers to understand if their subsoil is compacted, and, if so, at what depth is it occurring. For conventional-tillage operations, a heavy-duty cultivator or deep ripper with spikes set to just below the hardpan (measured via the penetrometer) can be used to break up the compaction. No-till operations can turn to taproot and fibrous-rooted crops—sometimes called “biological ripping”— to remedy the plow pan problem.
How We Roll
One of the easiest ways to minimize compaction in the field is to reduce traffic in the field when it’s wet and most susceptible to compaction. Another sound method for reducing soil compaction is to use the lowest acceptable tire pressure. We're committed to offering a low-pressure tire solution for every piece of equipment that enters the field, whether it’s a tractor, sprayer, combine, grain cart, or transport truck. Our AgriFlex line of IF/VF tires are capable of carrying the same load as a conventional radial tire with 20% (IF) and 40% (VF) less pressure. They can also carry 20% (IF) and 40% (VF) more weight than a comparable radial at the same inflation pressure.
One of our customers who’s having success using a penetrometer and Alliance AgriFlex tires is Wisconsin farmer Patrick McHugh. While we’d love to tell you how Patrick is improving his yields, ensuring healthy soils, and protecting the future of his farm, it’s so much better to hear it from Patrick himself, so check out the embedded video. If you’re inspired by Patrick’s story, contact your local dealer or rep to start putting Alliance tires to work on your farm.