In his December 2022 newsletter titled Crop Soil News (at advancedagsys.com), Certified Crop Advisor Tom Kilcer firmly warned about how compaction forms in our fields, how it hurts yields and, importantly, how to avoid it.
Kilcer managed field crop demonstrations at the Cornell Research Farm in Valatie, NY, during his quarter-century Cooperative Extension career, plus another 15 years after that in “retirement.” He wrote that the yield loss associated with compaction and increased cost per unit of production are real.
Bigger tractors, even with more tires, and a do-or-die attitude of “we have to get this done now” have increased the size of wet areas in fields and turned even well-drained soils into something much less. With increasingly popular vertical tillage, farmers have been told they can go on the field any time and this practice will dry up wet soils. But, in fact, this results in tremendous compaction issues.
Kilcer mentioned one farm where he advised the operator that such practice “actually ripped the legs off of a deep tillage unit when they tried to remove the vertical tillage compaction. My research crop had only rooted two inches deep on that farm.”
He wrote that a common expectation when compaction is found is that frost heaving action will worry its way through the compacted material, as well as the plow pan in the next couple years. Then he gave an example of an alfalfa grass stand which, after 15 years, was still compacted.
The next all-too-common reaction is to chisel plow deeper to remove the layer. Quoting Kilcer again, “As you go below the operating level of the curve of the point, instead of loosening the soil you are pushing it forward, down and out the side, creating more lateral compaction.”
He further described very hard curved soil bricks – some of them slick and shiny – from trying to chisel deeper than the unit was designed for.
To properly break a compacted layer, he recommended a tillage tool designed to go a couple of inches deeper than the bottom of the compaction and lift it to the surface. A large curved shank or a narrow vertical leg could do the job. Unfortunately, he said, “farmers frequently get a deep tillage ripper and hook it to the biggest tractor and go out and blow a tremendous amount of diesel smoke and make a heck of a mess.”
In many cases the soil is left in worse condition than if it had not been deep tilled at all. His recommended approach is to mount a shovel holder on the deep tillage tool: “This is critical. Then rip for 100 feet and then stop and dig a hole to see if you are doing any good. If the deeper soil is too wet and plastic, stop, go back home and find something else to do instead. Continuing while the surface is being ripped and the deep layers are being laterally compacted is a waste of time and fuel.”
I first encountered a non-farm approach to lessening compaction issues when visiting the Jersey Shore as a teenager. I saw signs which read “10 PSI Max Tire Pressure.” I found out that normal tire pressure caused sand compaction, which increased the threat of shoreline erosion and made it more difficult for sea turtles to lay their eggs.
I addressed the subject in a column several months ago, when I checked out a video of tire pressure demonstration which took place at North Carolina’s Outer Banks. In that demo, a four-wheel-drive gets stuck, with its 60 PSI tires digging deeper and deeper into the sand. Then the truck’s tire pressure is reduced to 15 PSI. At that point the truck easily backs out of its ruts and effortlessly ascends a sandy slope.
The video narrator then compares the tire track widths of the two PSIs. The lower-pressure tire boasts a width 40% greater than that of the higher-pressure tire. He stressed that 15 PSI causes significantly less compaction than 60 PSI.
Switching back to hardcore cropsmanship, I’ll refer to work done by University of Minnesota agronomists. They state that soil compaction concerns have been growing in their state as annual precipitation and farm equipment size have increased significantly. Wet soils are particularly susceptible to compaction. Heavy equipment and tillage implements amplify damage to soil structure, decreasing pore space, further limiting soil and water volume.
Improving soil structure is the best defense against soil compaction. Well-structured soils hold and conduct the water, nutrients and air necessary for healthy plant root activity.
The UM agronomists defined soil compaction as taking place when soil particles are pressed together, reducing pore space between them. Heavily compacted soils contain few large pores, less total pore volume – and consequently a greater density. Compacted soils have a reduced rate of water infiltration and drainage because large pores are more effective at moving water downward.
In addition, the exchange of gases slows down in compacted soils, increasing the likelihood of aeration-related problems. While soil compaction does increase soil strength, i.e. the ability of soil to resist being moved by an applied force, a compacted soil also means that roots must exert greater force to penetrate the contacted layer.
These UM workers explain away one common soil compaction myth often believed in temperate climate states – that freeze/thaw cycles alleviate most soil compaction created by machinery. Although soils in the northern half of the country are subject to annual freeze/thaw cycles, with freeze depths of three feet or more, only the top two to five inches experience more than one freeze/thaw cycle per year.
The belief that freeze/thaw cycles loosen compacted soils may have developed years ago when compaction was comparatively shallow. At that time machinery weighed less and more grass and deep-rooted legumes were grown in rotation. The combination of heavy axle loads and wet soil conditions increase compaction’s depth in the soil profile.