In general, high traffic athletic fields should have a root zone that will remain somewhat firm during times of high stress and/or above average play. To accomplish this preeminent goal, most field construction recommendations will refrain from suggesting an excessively sandy, or high sand fraction root zone. When breakthrough of the sod or grass layer does occur under high stress play periods, safer conditions will prevail if the underlying root zone has the firmness needed to allow the participants in athletic competition to continue their normal activities associated with the sport they are playing, i.e. cutting, turning, pivoting, accelerating, etc.

Most natural athletic surfaces that are constructed properly desire to accomplish a few basic ideas and concepts ensuring the maximum amount of quality usage. These concepts are listed below:

1. Proper drainage, whereby excessive moisture is either filtrated through the root zone, or surface drained to the outer limits of play.
2. The soil medium must be able to nurture growth of quality turf grass.
3. The soil medium must be able to retain limits within a spectrum of firmness for the integrity of the game played, yet not get to hard and rigid for the safety of the participants.

To this end, soil needs must be selected with care and with an eye for understanding the three general principles or properties that all soils are graded. The three components of any soil are: a) the soil’s texture-physical properties, b) the soil’s nutrient analysis- chemical properties and c) organic matter- biological properties.

A. Texture analysis- All soil is comprised of a sand fraction, a silt fraction, and a clay fraction. Sand, silt and clay are different sized materials, with sand being considerably larger than silt and clay. Clay is the smallest. Generally speaking, sand will help any soil drain more freely, because water finds it easier to translocate over, down and through larger particles. However, sand (larger fractions) is susceptible to shifting and unstable surface compaction. Think of running through dry sand at the beach. To build resistance and firmness in any soil matrix, a fraction of silt and clay must be part of any soil, or root zone, desiring to withstand competitive activity or excessive play.

Generally accepted texture analysis results giving this healthy mix of sand, silt and clay fall between these ranges:

a. sand- 60-75% fraction
b. silt- 15-25%
c. clay- 5-15%

B. Chemical analysis- Chemistry becomes important in any soil when the desire is to withstand and sustain plant growth. Most nutrient soil tests performed by the VA Tech Soils Lab, or any of the independent labs throughout the state and region, have ranges listed on each nutrient tested, whereby their opinion states that if the data falls within the historical ranges given, plants will have a much better chance at successful growth and life, than if it falls outside of the given ranges. On each soil analysis test, there are approximately10-15 nutrients that are tested- macro nutrients and micro nutrients. Both macro and micro nutrients are important to consider. Examples of macro nutrients are Phosphorous, Potassium, and Calcium. Examples of micro nutrients are Iron, Boron, and Copper. Also listed on the soils tests are the soil pH and quantities of Sodium in the soil, as well as the organic matter content- which we’ll discuss below.

Most native and constructed soils in Virginia do not have abundant salt to worry about, as our yearly rainfall and moisture amounts serve to flush undesirable sodium from our soils. pH, however, is something that should be closely watched and considered, as soil acidity and alkalinity can impact overall soil balance. For turfgrass sustenance and growth, most scientific recommendations suggest soil pH levels to fall in the range of 6.2-7.0. Soil chemical neutrality is set at a pH of 7.0. Historically, all varieties of grass used for athletic fields will perform better if their soil is slightly acidic, hence the recommended range.

C. Biological analysis- Soil biology is the third leg of the stool, so to speak, in considering a soil for athletic field renovation or construction. The levels and vitality of soil microbes present in any soil will be a factor in overall soil health. Beneficial fungi, bacteria, starches, and other very small microbes inhabit our native soils in varying numbers. In a 10 gram sample, there will/should be billions of soil microbes. These very small one cell organisms and other small critters are essential in helping much of the chemical component of soil function and react proactively to aid in the health of soil. The old adage is that, without bugs…your soil will never reach its potential.

Organic Matter is the building block to recommended levels of soil microbes. An organic matter test can be easily performed by a soil lab. In Virginia, native soils have organic matter levels ranging from 1-3%, which can give slightly below average to average levels of soil microbes. When organic matter levels reach four percent, you begin to experience the impact sufficient microbial activity can have on your soil health.

In choosing an appropriately tested soil for an athletic field renovation or construction project, other considerations should be levied before all data can be analyzed. First, where is the material coming from, and is it consistently mined from the same bank of base material? Many times, projects rely on material that is mined from different sources and locations. This can lead to inaccuracies in the soil’s overall physical, chemical, and biological make-up.

Additionally, care should be taken in deciding specifications for the sieve analysis of the chosen soil. Essentially a sieve analysis report will tell you the sizing of the material that is acceptable in construction. Most sieve specifications for athletic field renovation and construction, utilizing soil, should have 100% passing a 6mm or 3/8th inch screen. This will guarantee the elimination of larger stones and rocks in any ton that is delivered to the project site.

Another consideration is delivery of soil that is free from weed seed and undesirable contaminants. If soil is adversely contaminated by chemical waste, your soil report will highlight these factors. Weed seed is harder to control, in that, the only measure employed to be completely assured of weed free soil, is to have the material sterilized, i.e. heated in an oven whereby all weeds are cooked to an inert status. However, in doing so, understand that the sterilization of your soil will also kill many, if not all of the beneficial soil microbes present. The best choice in this regard is to choose a materials supplier that has clean soil to begin with and practices best known mining techniques to help ensure as little weed seed contamination as possible.

In choosing the depth of soil relating to an athletic field construction project, an understanding of root usage must be considered. In essence, soil is the medium that produces the life blood of plant growth. You must have a medium depth that supports the overall health of the plant being grown. In shallow soils, plants find it difficult over time, to extract the needed beneficial “life” they need to remain viable. In deep, physically, chemically, and biologically balanced soils this never will be a problem, as all life material is readily available. Yet there are cost factors to consider in any project, and it becomes economically prudent to find a depth that will not restrict plant growth, and, fall within budget allotments. To find this so called ‘sweet spot’, investigate average root development and growth of any of the desired plants being grown. For athletic field construction, either warm or cool season grasses grown in Virginia will have root development between 8-12 inches. Recommendations generally fall into this logical pattern.