Topdressing with compost in sports fields is a topic of debate, with many professionals decrying the practice as being inappropriate and unsanitary. The practice involves using large volumes of organic matter (i.e. topsoil) in order to promote the growth of healthy root systems for sports fields.
While the practice can be beneficial to certain applications, many other applications, such as application of rubber mulch, are not recommended due to the potential for increased moisture uptake, root rot, and root damage to young roots.
Topdressing with compost for organic grass maintenance is typically used in sports facilities that have dry fields. It is believed that the best times to top seed are late spring and early summer, when soil temperatures are high and moisture levels are low.
During these seasons, plant root systems from within the field are able to obtain most nutrients needed for successful sports field growth. Therefore, topdressing with compost is best done prior to the beginning of the sports season, when root systems in the soil are already established and ready for the large volume of nutrients provided.
The most common questions involving the preparation of compost are the benefits to the lawn and the risk of introducing harmful species to the compost. Studies conducted by the National Aerobic Management Association and National Wildlife Federation have concluded that there is no significant benefit to the lawn from composting.
Also, studies have found that while the majority of aerobic insects are killed during composting, a small number of those beneficial species are still introduced into the compost. The greatest risks associated with composting are the release of nitrates into the environment, whether through wetting or runoff from heavy rains, and the leaching of phosphates to the ground water supply.
Studies have also found that a significant amount of phosphorus and potassium are released into the environment from the application of organic compost as compared to the natural release from the earthworms. These two nutrients are used for various functions such as building up the soil’s fertility, providing plant food, improving root structure of the plant, and increasing the plant’s resistance to environmental stresses such as drought and heavy rainfall.
However, phosphates are a form of non-natural soil additive which may affect plant health, color and texture, and can encourage the growth of weed seeds. Potassium is commonly used as an agricultural fertilizer, but its release into the environment has been linked to the production of superweeds, a dangerous class of weeds that can sometimes spread rapidly to other fields within the lawn.