Infield Mixes for Baseball and Softball Infields

Brad S. Fresenburg, Extension/Research Associate
University of Missouri Turfgrass Research Center

We are frequently asked what are the best infield mixes for good playability, traction, ball response and safety. It is difficult to create a universal formula as to how much sand and/or calcined clays to add, through tillage, to achieve the desired recipe. This difficulty results due to the existence of soils ranging in a wide array of sand, silt and clay compositions.

Amending infield soils is a bit of trial and error. However, we will give you a couple recipes as a final goal to achieve and some guidelines on how you can reach that goal.

Infield mixes across the country do vary slightly, but for the majority, we tend to see a trend in the composition of these mixes.

MIX #1:

  • 60 % sand of which,
    • 50% is composed of a round, uniform (masonry-type) sand
    • 50% is composed of sharp, angular, manufactured sand that is often used by city street departments for iced roads or by the highway department for crack and seal sand.

    The round sand shall be uniform, medium/coarse sand screened and washed meeting the following criteria:

    Fraction Size Name Sieve Diameter(mm) Allowable Range
    (% Retained on Sieve)
    Gravel >2.00 < 3%
    Very Coarse 1 mm - 2 mm < 7%
    Coarse 0.5 mm - 1 mm At Least 60% particles
    Medium 0.25 mm - 0.5 mm in this range

    The manufactured, angular sand shall be screened and washed meeting the following criteria:

    Fraction Size Name Sieve Diameter(mm) Allowable Range
    (% Retained on Sieve)
    Gravel >2.00 < 25 %
    Very Coarse 1 mm - 2 mm At Least 50 % particles
    Coarse 0.5 mm - 1 mm in this range
    Medium 0.25 mm - 0.5 mm < 15 %
    Fines < 0.25 mm < 3 %

  • 20 % silt: possibly from the existing soil.
  • 20 % clay: possibly from the existing soil. This totals 100%.

MIX #2:

  • 50 % sand of which,
    • 50% is composed of a round, uniform (masonry-type) sand
    • 50% is composed of sharp, angular, manufactured sand that is often used by city street departments for iced roads or by the highway department for crack and seal sand.

    Specifications for the sands are listed above.

  • 10% coarse calcined clay or infield conditioner.

    The calcined clay/infield conditioner shall be of the coarser material meeting the following criteria:

    Fraction Size Name Sieve Diameter(mm) Allowable Range
    (% Retained on Sieve)
    Gravel > 2.00 > 40 %
    Very Coarse 1 mm - 2 mm > 40 %
    Coarse 0.5 mm - 1 mm > 10 %
    Medium 0.25 mm - 0.5 mm < 0.5 %
    Fines < 0.25 mm < 0.1 %

  • 20 % silt: possibly from the existing soil.
  • 20 % clay: possibly from the existing soil. This totals 100%.

There are two approaches to creating the ideal infield.

The first is for projects that involve major renovations or new construction. Infield skinned areas can be subbed-out 4 to 6 inches in a renovation or new construction project, then back-filled with the proper mix manufactured with a blending machine at a sand plant. Not all sand plants are set up to do this, however, there are several (just call around) that blend sands for root-zone mixes utilized in golf course construction. These operations can blend infield mixes to the specifications outlined in this article. If this approach is used then the sand plant will need specifications for the silt/clay portions of the mix. These specifications are listed below:

The silt and clay content shall be obtained from a silty clay soil meeting the following criteria:

Sand 0 to 20 %
Silt 40 to 60 %
Clay 40 to 60 %

The second approach to amending an infield, skinned area is to add sands with or without calcined clay material/infield conditioner and till evenly to a depth of 4 inches. Some questions first need to be answered before adding these amendments to your infield. 1) What is the make-up of your infield? and 2) How much material do I need to add to achieve the desired mix?

  1. The make-up of your infield can be determine by taking a representative sample of the soil and submitting it to a soil testing lab for a particle size analysis (PSA). The PSA will breakdown the percentages of sand, silt and clay, plus classify your soil by name (EG: Loam, silty clay loam, etc.). By knowing the amounts of sand, silt and clay, estimates of each sand amendment needed, with or without calcined clay, can then be made. Sands estimated in a particle size analysis, are usually of the round-type and should pertain to that portion of the amended sands.
  2. Amount of sand required, will be dependent on the amount of sand determined in the PSA. If your sand content is around 30%, then the addition of sharp sand is only required. If your sand content is around 5 or 10%, then the addition of some round and sharp sand are required. Add sand an inch or two at a time, then till down to desired depth, level and roll to re-pack surface.

Sands delivered for amending infields are usually by 15-ton truckloads. Majority of your expense will be trucking. The key is to apply sands evenly over the infield soil and till uniformly with a roto-till/RotaDairon to the desired depth. Then sample the soil again for another particle size analysis to determine how closed you are to the desired mix. Adding more materials, tilling, leveling and rolling as necessary can make minor adjustments until the desired mix is achieved.

Finish off infields with topdressing of mid-size calcined clays or infield conditioners. Adding calcined clays or infield conditioners evenly over the surface of the skinned area can improve playability and water management (dust control and safety) when these materials are nail dragged into the top 1 or 2 inches. Recommendations vary from one manufacturer to another on the amount to use, however, 40 to 60 bags is usually a good start. The medium sized calcined clay should meet the following criteria:

Fraction Size Name Sieve Diameter(mm) Allowable Range
(% Retained on Sieve)
Gravel > 2.00 < 10 %
Very Coarse 1 mm - 2 mm > 80 %
Coarse 0.5 mm - 1 mm < 10 %
Medium, Fines < 0.5 mm < 1 %