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Aerification
by James A. McAfee, Ph.D. Associate Professor and Extension Turfgrass Specialist Texas A&M Research & Extension Center at Dallas

While soil aerification is a common practice on sports fields and golf courses, its practice is less often used by homeowners and commercial properties. In my 25 plus years of experience working with the predominately clay soils in Texas, it has been my experience that most home lawns and/or commercial properties also benefit from aerification. Benefits of aerification include: decrease in soil compaction, increased levels of soil oxygen, decrease in toxic soil gases, improved water infiltration and drying of water logged soils.

Without question, the biggest benefit from aerification is increased soil oxygen levels. Some soil scientist call oxygen the forgotten plant nutrient. Most individuals are aware of the importance of plant nutrients such as nitrogen, phosphorus, potassium, etc., but forget that the three most important plant nutrients are carbon, hydrogen and oxygen. Carbon and oxygen are taken up by the leaves for photosynthesis in the form of carbon dioxide. Plants take up hydrogen and oxygen as water. What is rarely understood is that plant roots also need oxygen for growth and nutrient uptake. Plant roots take up oxygen and give off carbon dioxide just as animals do when breathing. So, where does the soil oxygen come from? It comes from the soil air, which originates from the air above it. Soils must be able to “breath” in and hold enough oxygen in the soil for roots to grow and function properly.

Under ideal conditions, soils should contain approximately 50% minerals, 25% oxygen (soil air) and 25% water. In compacted soils, minerals become 70%, soil water 25% and soil air 5%, while in water logged conditions, minerals are 50%, water 45% and soil air 5%. In both of these conditions, soil air becomes a limiting factor, thus reducing the roots ability to actively grow and to take up plant nutrients and water. In soils with limited soil air, the turfgrass root system will be found growing in the very top part of the soil. Turfgrass growing in soils with limited oxygen will not respond to fertilizer applications because there are fewer roots to absorb the nutrients. Lack of oxygen also prevents the roots from making the energy needed for nutrient uptake. In addition, soil microorganisms need oxygen to recycle some of the important soil nutrients needed by the plants.

The most effective method to increase soil oxygen levels is aerification. Aerification will open up the soil and allow air from above to enter the soil. It will also allow some of the toxic gases that accumulate in the soil to escape. The most effective time to aerify is when the turfgrass root system is at its peak growth period. For the warm season turfgrasses such as bermudagrass, this will be in late spring through early summer months and for the cool season turfgrasses such as tall fescue, this will be in the fall. While these are the ideal times to aerify for the different turfgrasses, it should be noted that the turfgrass root system will respond to aerification anytime the roots are actively growing. Another important time to aerify is prior to overseeding warm season turfgrasses in the fall with a cool season grass for winter color. Aerifying thirty days prior to overseeding will help prepare a better seedbed for the cool season grasses.

For best results, use an aerifier that will penetrate down into the soil at least three to four inches deep. When aerifying, it is important to produce at least 10 to 20 holes per square foot. While this seems like a lot of holes, 10 to 20 holes per square foot will only impact about 10% of the actual soil surface. In order to produce this number of holes per square foot, it will probably be necessary to aerify the turf in two different directions.

Besides increasing soil oxygen levels, another major benefit of aerification is increasing the infiltration rate of water into our heavy, clay soils. Most clay soils have a very low infiltration rates, thus resulting in water run-off during irrigation and/or rainfall events. It has been estimated that as much as 30% or higher of water applied through irrigation runs off the turf site. By opening up the soil through aerification, the percent of moisture moving into the soil will be greatly enhanced. With the major concern over available water for our turf and ornamental sites in the future, increasing the efficiency of water applied to turf can be considered a major benefit.