A soil is made up of three types of soil particles: sand, silt and clay. Each of these particles plays a vital role in the success of the infield skin. In order for the soil to provide ample support for athletic play, it needs to have the proper density of particles to fully stabilize the soil surface.
SAND — Its function in the infield soil is to provide structural stability. When sand is present in proper amounts and sizes, it creates “pore space” or “air space” and leaves room for the smaller particles of silt and clay. Because of its large particle size, sand should take up the majority of the volume in your infield soil.
Sand is usually divided into five sizes ranging from very fine to very coarse. For infield soils the majority of the sand should be in the medium to very coarse range. An infield soil with the proper volume and sizes of sand will remain stable — even in wet conditions. Infield soil with a large volume of fine and very fine sand will lack stability.
SILT — This is the soil particle that is sized between sand particles (larger) and clay particles (smaller). Because of this, silt helps to bind sand and clay particles together in a mix. However, excess silt can cause problems ranging from a greasy surface when wet to a very dusty infield when dry.
How much silt is needed? The ideal silt content is a ratio which is equal to or half the clay content.
CLAY — It represents the smallest particle size in an infield soil and it provides color and moisture retention. Not all clays are the same. It takes specific mineralogy of the clay in your infield for it perform properly. In general, higher clay content in a mix requires more maintenance.
How much clay is needed? The ideal clay content is a ratio that is equal to or 1 ½ times the silt content.
TO FIND THE SILT-TO-CLAY RATIO divide the % silt by the % clay, as reported in your soil test. Check the SCR Scale to judge how your infield soil measures up.
The ideal SCR range for any infield soil is between 0.5 and 1.0. Fields with an Elevated SCR (between 1.0 and 2.0) can often improve performance by adding a topdressing.
Soils with a High SCR (between 2.0 and 3.0) will definitely need to be amended to get to the idea range. Overall sand content and sand size distribution will also need to be adjusted in these fields. High SCR infield soils will typically be very slippery or greasy when wet, and very dusty when dry. Both of these conditions are due to excessive silt content in the infield soil.
Excessive SCR fields (above 3.0) are very high in silt and usually high in fine or very fine sand content as well. That combination of Excessive SCR and high fine to very fine sand content results in extremely unstable infield soils when wet.
Low SCR fields (below 0.5 SCR) are common in the southeast U.S., but are rare elsewhere. These fields typically suffer from either being too loose and sandy or they have too high a clay content which will cause chunking out on the infield skin.