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Infield Soils and Topdressings – A Geological Perspective

Baseball and softball fields are unique playing surfaces. In “hard-surface” sports (volleyball, basketball, tennis) the game is played on firm, solid materials which aren’t readily eroded even when they are outdoors (Fig. 1). Other outdoor sports (soccer, football, lacrosse) are played on grass. The roots of the grass stabilize the soil much like rebar or wire mesh helps to stabilize concrete. The green tissue above the ground also shields the soil from erosion by water and wind. On a baseball or softball field, there is no vegetation to protect the soil from being displaced by the elements or by players’ cleats. While this seems obvious, we’ll discuss below why it’s an important concept in field construction and maintenance.

infield 1

Figure 1. Baseball and softball fields are more susceptible to erosion than other sports surfaces, which are either impermeable or covered with turfgrass. 

Crown erosion

At H&K Sports Fields we constantly preach the importance of a proper “grade” (slope) on an infield. It doesn’t take much: we grade infields at 1% slope or less- but having a slope to the field ensures that excess water will exit the skin thanks to gravity. Unfortunately Mother Nature doesn’t want soil to be placed this way! After a field is built, normal use tends to displace material in the high-traffic areas. In addition, the elements act on an infield 24 hours a day, 365 days a year- slowly but surely carrying soil away with the wind and the rain.

Without grass or other vegetation to protect the soil, the crown wears away until the higher areas are leveled and the entire surface becomes relatively flat- with the exception of low-lying depressions which form around the bases and other high-traffic areas. This is particularly true on totally-skinned infields because the high point of the field has no grass on it. In geology, surface topography which has been worn flat is called a peneplain (Fig. 2, left). I have observed very degraded softball fields where the entire field is within 1.5” of level (minus the aforementioned wear areas, which quickly fill with standing water). Without a crown or other slope, water can sit in the low spots for days (Fig. 2, right). Geologically speaking, the soil erosion happens quickly- within just a few years. But in our normal concept of time this is still slow and occurs too gradually to notice with the naked eye. This gradual removal of material means when it comes time to re-grade, new infield soil must be added to replace what was lost since the previous renovation.

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Figure 2. Left: A landscape-scale “peneplain,” showing relatively flat topography with lakes and ponds. Right: A skinned softball field on which the positive surface grade which has worn away, leaving a nearly flat surface with low spots in the high-traffic areas.

Infield soil composition

The physical makeup of an infield soil is a hefty topic- one which warrants its own article. However it is worth mentioning that the percentages of sand, silt, and clay in the mix certainly affect the longevity of an infield’s grade. Fields with too much sand and too little cohesive clay tend to erode mostly via rainfall- meaning lip buildup will be especially serious on these fields. Infields with too much silt tend to become very dusty. Silt is lighter than sand, so it can be carried far away by the wind and completely disappears from the field. After a few years, high-silt fields are usually very low and require quite a bit of imported material to correct the grade.

Topdressing materials

An infield topdressing provides several benefits, one of which is slowing degradation of the infield crown. The individual particles of a topdressing material are larger and heavier than those of infield soil, so it takes more energy from a gust of wind or a raindrop to move them around. During heavy rainstorms, the topdressing helps to shield the infield from raindrop impacts and prevents the base soil from washing away. The topdressing material may still move to some degree; however because it is loose and free-flowing it can easily be re-distributed with a screen drag or level board.

infield figure 3

Figure 3. Typical infield topdressing material (left) is much coarser material than infield soil (right). The larger particles are less susceptible to erosion than fine-textured soil.

Lip buildup

A dense stand of grass is one of the world’s best erosion controls. Turfgrass is planted along agricultural fields, riparian buffer areas, and urban landscapes to reduce the loss of nutrients and sediment. Unfortunately for baseball field managers, the ability of grass to slow runoff and trap sediment is also the source of our biggest headache- lip buildup. As water flows across the infield, it carries with it small amounts of infield soil and topdressing. When the water reaches the grass, it loses some of its kinetic energy. As the water slows down, it can no longer carry the sediment with it, so the soil drops out of suspension and into the turf canopy. Over time, the soil builds up and creates a mounded ridge or “lip” which prevents water from flowing off the skin and into the grass. On fields which receive little maintenance, I have seen lips as large as 8” tall and 10 ft wide! Lip buildup will occur on every field that has a positive surface grade, so regular edging is an important maintenance practice. Improper dragging procedures are another common cause of lip buildup, so be sure to stay at least 12 inches away from all turf edges when dragging.

infield figure 4

Figure 3. Typical infield topdressing material (left) is much coarser material than infield soil (right). The larger particles are less susceptible to erosion than fine-textured soil.


  1.  Although we intentionally build baseball and softball fields with a minor slope, the forces of nature slowly erode the crown unless the field is highly maintained.
  2. Infield soil and topdressing are gradually carried away by wind and rain, so more soil must be periodically imported to be sure the field stays at the proper grade. This is referred to as the infield “being low.”
  3. Grass is a highly efficient sediment trap, meaning lip buildup is inevitable without both proper dragging procedures and periodic edging.
  4. The use of infield topdressing can help preserve the integrity of the grade along the base infield mix by shielding it from the elements. The topdressing layer also creates a buffer between the players’ cleats and the soil below.
  5. A baseball or softball field is a dynamic surface! Understanding the natural forces which act on our fields helps us understand how to build, renovate, and maintain better infields.

For more information on infield soils and topdressings, contact H&K’s Evan Mascitti at evan@HKSportsFields.com.