Think you’ve avoided soil compaction on your farm? Kitty O’Neil believes most farms have some level of compaction and many farmers don’t even know it.
Speaking at the recent North American Manure Expo, O’Neil, statewide ag climate resiliency specialist at Cornell Cooperative Extension and an original member of Cornell’s Climate Smart Farming Extension team, said that “soil compaction is one of the aspects of soil health we don’t talk about enough.”
“It’s quite severe in every field. Healthy, well-structured soil is the goal,” she added.
Preliminary results of O’Neil’s research indicate that soil compaction is more severe in fields that consistently yield below the farm average compared with areas that consistently yield above the farm average.
The problem is that compaction squeezes the pore spaces in the soil so that its denser. That’s bad because instead of the natural nooks and crannies that hold long-term the water and nutrients plants need, these resources wash away.
She also said that compacted soil reduces air, gas exchange and water infiltration. These problems can happen at the surface, tillage zone, below the tillage zone or in all three areas.
As compacted soil remains saturated longer than healthier soil, O’Neil said this can cause increase denitrification loss and reduce nutrient use efficiency but increase greenhouse gas emissions. Compaction can also restrict root exploration, causing lower potassium and phosphorus uptake. O’Neil said this can lead to lower crop yields and productivity.
Why compaction happens is easy to see.
“We’ve been tilling 150, 200 years,” O’Neil said. “It’s a long time. We have very weak soil structure. We have decades of plow pan development with pressure going down. Our equipment has gotten larger, which is more pressure. Even raindrops at terminal velocity can smash the soil. We have poor structure, compacted soil with higher bulk density.”
To diagnose compaction, O’Neil encouraged farmers to probe their fields, looking at different locations in each field and looking at patterns of yield. Preventing compaction is ideal because reversing it is so difficult.
Some of the best ways to prevent compaction are by establishing perennial crops, using cover crops and protecting the surface.
Large equipment and improperly inflated tires contribute to soil compaction. Photo by Deborah J. Sergeant
O’Neil also said to avoid traveling on or working in wet soil. “Stay out of fields when the soil’s moisture is too high,” she said, “but that’s easier said than done.”
Reducing the load per square inch of ground contact is also important. O’Neil recommended increasing the number of axles and wheels; using tracks over tires where practical; and inflating tires to the proper level. The bigger the footprint of the tires, the fewer pounds per square inch and thus a lower risk of compaction.
“Carry a pressure gauge in all tractors and trucks and check tires regularly,” she said. “Compare with recommended pressures and top off tires as needed. Keep road tires and machinery off the field.”
She mentioned a farm that invested in on-field tire inflation/deflation equipment. The farm paid off that investment within a season by saving so much money on tires while also benefiting from reducing the risk of compaction.
O’Neil advised using controlled traffic farming (CTF), which includes restricting traffic to fewer laneways and across fields and avoiding diagonals and random driving across fields. The most conscientious CTF methods requires matching equipment widths and wheel spacing across the farm; however, O’Neil acknowledged that is not practicable for all farms.
“Begin to think about this when purchasing or replacing equipment,” she suggested.
Improving soil health can also reduce compaction. O’Neil encouraged adding organic matter, protecting the surface from raindrop impacts with residues and cover crops and keeping cover crops on for extended periods of time.
“Cover crops for four to six years can build new pores and channels and reduce compaction,” O’Neil said.
It’s not clear yet if the effects of improving soil health penetrate to the subsoil. “It provides little relief, but it’s temporary,” O’Neil said. “It’s variable and you lose any effect within a couple years.”
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