The quality of an athletic field is directly related to the drainage capability of the soil. How fast water drains into and through the soil (infiltration rate, KSat) is the best indicator of how many games can be played and how the field will react during a rain game. Ideally, fields should have a minimum infiltration rate of 1 inch/hr., but it is not uncommon to see soils with infiltration rates of 0.01 inches/hr or less. The infiltration rate of a soil is influenced by the soil texture and the level of compaction the soil is subjected to. Typically, sands do not compact as readily as finer soils like clay loams but they can get compacted if they are worked when wet or there is excessive traffic. Fields with low infiltration rates create very poor playing conditions. When wet, they turn to mud, when dry they turn to concrete. Turf plants will not grow in these soil conditions and so the field gets taken over by weeds like prostrate knotweed, clover, dandelions and Poa. Turf growth is so poor that nutrients are not taken up, so the turf becomes clorotic/yellow and does not recover from wear. Slow turf growth is also more susceptible to diseases like red thread and rust. Improving the infiltration rate of the soil is therefore the key to improving field conditions.
There are short term fixes to improve infiltration. These include using aeration equipment like a core aerator, spiker, deep-tiner or verti-drain. These machines punch holes in the soil, allowing water and gas to enter. After a period of a couple of weeks or less however, those holes seal over and the previous conditions return.
A long-term fix is to amend the soil with a material that improves the infiltration rate, namely sand. Applying 50 tons of sand to a field per year appears to be an effective rate. It is possible to apply higher rates of 60-100 tons, especially if the sand is applied in two increments (spring & fall). The sand is either applied alone or in combination with soil or compost. The soil &/or compost typically makes up 10-30% of the mix. Adding compost to the mix is a good way to get some organic material into the soil if it is lacking. A new study has just started at OSU, looking at compost types and mixes with sand. The aim it to identify rates and sources of compost that would improve field quality and playability under traffic. This study is being undertaken by MS student Marcela Munoz.
The ultimate goal of topdressing with sand is to achieve at least 70% sand by weight in the rootzone. At this point, the sand particles bridge, creating macropores and reducing particle density. Without a doubt, initiating a sand topdressing program significantly improves native soil field quality and longevity.
Twenty five years of research by Dr. Stephen Baker at STRI has shown that sand dressings, sand caps and sand-slit systems are all a major improvement to native soil alone. One of the main issues with starting a topdressing program is that a topdresser is needed to apply the material, unless an outside contractor is paid to make the application. Also, the program is not a “one time” occurrence, but must take place each year, ideally in conjunction with aeration, which will take time and money. However, in every instance where a sand topdressing program has been adopted, the results have been so dramatic and the fields have improved so significantly that school boards and administrators usually look for extra sources of funding to try to start topdressing programs on additional fields.
It may take a couple of years to see the benefits of dressing with sand. Obviously, the more sand applied, the faster the desired 70% by weight goal will be reached. It is not a good idea to apply more than 0.25 inch at any one time as the sand can be abrasive to both turf equipment and the grass, but two or three applications could be made each year, outside of the playing season. If there is money and manpower available, a new “fast-track” sand build-up system could be employed. This system was recently developed by Michigan State University and can be accessed through their website.
Posted by Pam Sherratt & John Street in the July 24 issue of Buckeye Turf newsletter, www.buckeyeturf.osu.edu