In the previous issue of the H&K Maintenance Minute we discussed the drainage of infield skin areas. But drainage is also a common problem on the grass portions of a field. If muddy conditions are present, the field becomes unsafe and can warrant cancellation of games and practices. The cause of most drainage problems are fairly predictable. First we’ll briefly review surface drainage. Then we’ll examine ways to help water move into the soil more quickly.
As with skinned infields, surface drainage is the first concern on grass areas. The field must be sloped at a minimum of 1% so that excess water will flow off the field. Even if the general grade is correct, any small undulations in the surface will cause water to “pocket” and form puddles. Sometimes these low spots can be corrected by topdressing with a thin layer of high-quality topsoil. If done a few times per year this practice can disperse the water and allow it to flow along the grade. Larger undulations will require removal of the vegetation and re-shaping of the field contours.
Figure 1: Puddles often in the low areas of a field during rain events. These water pockets are common on high-wear portions of the field, such as soccer goal mouths or the center of a football field.
When sloped properly, excess water will run off the field. However, wet conditions may still persist if the soil is overly compacted. Soil compaction is probably the number one problem on athletic fields of all types. As pore space is squeezed out of the soil by players and equipment, water encounters great difficulty in moving through the profile. Aerification is the best practice to relieve compaction without complete tillage. A great upgrade to the aerification process is a topdressing of compost. By spreading compost over the field prior to aerification, organic matter can be incorporated into the holes when you drag the cores back in. The addition of organic matter will help build soil structure. Soil structure is the binding of small silt and clay particles together into larger aggregates. These aggregates act like sand-sized particles, which restores pore space to the soil and improves infiltration and percolation.
Figure 2: Applying a thin layer of compost prior to aerification will condition the soil to provide better soil structure and more porosity.
Figure 3: Soil structure is key to ensuring proper drainage on native soil fields.
Soil compaction is inevitable on any field receiving frequent usage. A more expensive but highly effective strategy to combat soil compaction is the installation of a sand cap. By repeatedly spreading small amounts of sand over the field, a layer of coarser material is built over the native soil. The grass slowly migrates upward through the material, so there is no need to re-establish the turf. The benefit of a sand cap stems from the inherent porosity of sand- even under the compactive forces of field usage, sand will retain large pores which help transmit water rapidly. Installing a sand cap can help reduce the risk of your field being ruined by just a single “mud bath” game, because it can be played on shortly after (or even during) a heavy rainfall. It is essential to use the correct type of sand- unfortunately, most construction or masonry sands from your local quarry are not suitable for athletic fields. Once established, the maintenance costs for this type of field are higher since it requires removal of aeration plugs and maintenance applications of sand topdressing.
Figure 4: This profile of a sand-capped field shows the layer of coarser-textured sand overlying the finer-textured native soil.
One final practice that warrants mention is the attempt by some field managers to till sand into their fields. This practice is not recommended unless your field already contains over 70% sand (very rare in Wisconsin). While sand by itself does drain well, tilling sand into fine-textured soil is akin to adding 3 or 4 marbles to a jar of flour. Imagine water flowing through this jar- unless the marbles are touching each other (“bridging”), the flour will simply fill in all the space around the larger marbles, preventing water from flowing through the jar. To dilute the fine soil sufficiently, so much sand would be required that it would make more sense to completely excavate the native soil and install a sand-based rootzone.
Figure 5: Tilling sand into a native soil field is unlikely to provide a significant benefit, just as adding only a few marbles to a jar of flour has little effect on the jar’s pore space.
Remember, surface drainage is always the first priority- any attempts to improve drainage must first include a proper surface grade. Next, consider ways to reduce soil compaction- aerification along with compost topdressing is one; the installation of a sand cap is another. Our third and final installment on drainage will focus on installed drain systems for grass areas! To inquire about drainage considerations at your facility, contact H&K’s Evan Mascitti at evan@HKSportsFields.com.