Infield Mixes, Vol. 2: What Makes Up a Mix?

What makes a good infield mix? You hear it all the time. “Our infield mix is a 70/30.” That is another statement that is echoed frequently in the industry.
One of the reasons why the Smart Turf blog was created was to shed light on many issues in sports turf. What makes a good infield mix typically is at the top of the list of questions. So, let’s get to the bottom of the matter.

First of all, for years building and maintaining baseball/softball infields was considered an art. What one groundskeeper thought was a great infield, another thought it was a horrible infield. The process was subjective and creative. How many times have you heard, “I’m looking for some black dirt.” Or, “I’m looking for some red clay.” Times are changing and the tide is turning to science. Why? Simply stated, when the process is a science, soils are tested, results can be predictable, and replicable.

The infield mix profile consists of three components. The deepest part of the profile is a compacted native soil that is 3-6 inches below the surface. Next, the base soil exists. The base soil is the “meat” of the infield. The material is usually imported, compacted firmly, and has surface drainage. (more on drainage in another upcoming blog) Finally, 1/8-1/4 in of topdressing rests on the surface much like mulch in a landscaping. (more on topdressing in another upcoming blog)

So, what makes a good mix? A good mix has many characteristics, but the most important ones include: traction, playability, and consistency. A mix should provide consistent traction, the ability for athletes to play the game without sliding/slipping around the infield. The infield should play consistently in a variety of weather conditions. How many time have you heard, “I hope it doesn’t rain, we will be shut down for 3 days!” When all the characteristics are achieved, the infield is considered a “balanced soil.”

Infield mixes have three components, sand, silt, and clay. Sand, the largest soil particle, provides the structural integrity of the infield. The targeted range is 58-75% and over 50% of the sand should be retained on the medium sieve. Silt, the second largest soil particle, acts as a bridge between the sand and the clay. 10-35% is the acceptable range. Clay, the smallest soil particle, provides the color of the mix and retains moisture. 15-35% is the acceptable range. The take home message on silt/clay is that the ratio of silt/clay (SCR – more on that later) should NEVER be higher than 1:1.

Does your infield become very tacky after a rain? Does your infield blow around during periods of dry weather? Is your infield too beachy? What are your sand/silt/clay percentages of your infield? Testing is the only way to know!

Play on!
--Jamie