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
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.