Every year we receive questions about using soil aerators on pastures to improve forage yields. And every year we give out the same answer which is, based on research tests comparing aeration to other inputs, aeration does not pay.  The research does not show that forage yield increases will justify the cost of running the equipment over the field.  In spite of this, we still have producers who claim that aeration has improved the forage yields of their pastures.  Even though the research does not show that aeration is justified, I cannot say that this is not happening because we don't have aeration research on all soil types and under all circumstances. With this in mind, let's look at some of the reasons people claim aeration should work and discuss how aeration might affect the pasture environment.

Compaction: compaction is the process where, due to high traffic from heavy machinery or animal traffic, the soil becomes pressed together so tightly that water and air has difficulty penetrating the soil surface, roots may also have a hard time penetrating the soil to great depths and air movement is restricted by the tight soil. Compaction is normally only a problem on soils that have large components of clay or loam in the soil. An aeration study conducted on a Silt soil and a fine sandy loam soil in Mississippi conducted from 1991 to 1995 showed no improvement of soil penetration tests or moisture contents in the upper 24 inches of the soil when comparing aerated plots verses non aerated plots at either site. This indicates that either compaction on heavily grazed areas is not a factor or natural processes reduce any compaction effects to the point that the aerators show no effect.

Southeast Oklahoma is blessed by many diverse soil types. Many have a large component of sand in their make up. These sandier soils by their nature do not compact easily due to the large irregular shape of their soil particles. Clay soils, on the other hand, have the ability to compact when heavy equipment or heavy animals constantly move over the same piece of soil on a regular basis.  Even though these soils can become compacted, environmental and biological factors will loosen this soil over time. An example of this is when a clay or loam soil dries out, it tends to crack to great depths, and in essence, is aerating itself due to the shrinking and swelling. Likewise, when a wet soil freezes in the winter it will fracture due to the freezing and thawing which also aerates the soil in upper 6 to 12 inches of the surface. Plants, due to root growth, also aerate the soil in their own way. A healthy, well fertilized bermudagrass plant will send roots as deep as 36 inches. As the plant matures, over time, older roots will die and be replaced by new growth. As these dead roots decompose, they leave channels in the soil allowing air and water infiltration. This in effect aerates the soil.

Renovation: Another argument for pasture aeration is that the bermudagrass becomes root bound in the "compacted" soil and that by disturbing the soil the plants will begin to grow more rapidly. In fact, any time you disturb the crown of a grass plant you will cause it some injury. Those plants that are not injured will use the nutrients and water that the injured plant would have used to make its growth. This may appear as a rejuvenation of the bermudagrass stand but does it increase the yield? A field study was conducted in 2001 on a verdigris silt loam soil in Craig County Oklahoma comparing doing nothing verses disking verses running an aerator. Also, included were the same three treatments, with the addition of proper fertilization. There was no statistical difference in yield between the disking and aerating, (they affected the Bermuda grass stand the same).  Doing nothing resulted in an increase in yield of 735 lbs per acre over disking or aerating.  In other words, as far as yields go, it was better not to do any type of tillage. When proper fertility was added to the equation it made no difference whether you aerated or not. The addition of the fertilizer increased grass yields for the year more than 5,000 lbs per acre on the do nothing plots. Aeration plus fertilizer did not improve yields over just fertilizer alone. Similar findings were reported in 1998 from a 3 year study on fertility and aeration done in Pontotoc County in Oklahoma. At this location, the highest yielding treatment was with 200lbs/ac of nitrogen and adequate phosphorus with "No Aeration". The three year average yield for this treatment was 5,400 lb/acre. This compares to the exact same fertility treatment that had spring aeration applied and only yielded 5,100 lbs/acre. Both of these studies show that proper soil fertility goes a lot farther in renovating poor bermudagrass stands than does aeration.  In fact, both point to the possibility of aeration reducing grass yields in the first year after treatment when compared to doing nothing.

This same theme tends to be consistent with all the research studies I have been able to find. The two Oklahoma trials, an aeration trial from Purdue University in Indiana, an aeration trial in Wisconsin and two aeration trials done at Mississippi State University.  All six of the trials showed no increase in forage yield that could be attributed to the use of a pasture aerator, and in those studies that had a fertility treatment as a comparison, the addition of proper soil fertility showed the largest increases in pasture production whether aeration was used with the added fertilizer or not.

None of these six trials showed that to the use of a pasture aerator resulted in increased forage yield and, in those studies that had a fertility treatment as a comparison, the addition of proper soil fertility as a treatment produced the largest increases in forage production whether aeration was used with the added fertilizer or not.

One instance where I did present aeration as a possible option was in a thin stand of Midland 99 bermudagrass.  Midland varieties tend to get tall and not spread as well as other varieties.  In this situation, an aeration or disking pass could help force the Bermuda to spread and thicken up.   This suggestion was made in conjunction with fertility recommendations.

If you have any other questions about aeration please come by 14001 Acme Rd. Shawnee, call (405) 273-7683, or email kyle.robinson@okstate.edu<mailto:kyle.robinson@okstate.edu>