Kevin Green with Dr. Pam Doolittle, Prof. Wayne Kussow and Robert McClain

UW-Madison Departments of Chemistry and Soil Science

Fertilizers have become a topic of great concern recently.  Some worry that too much of the phosphorus in fertilizers is carried off into lakes by rainwater.  Phosphorus can deplete surface water of oxygen, creating a eutrophic state:  uninhabitable to fish, but amenable to plant life, especially algae.  Scientists have usually suspected the sediment that runs off into surface water to be the main carrier of phosphorus, but studies have shown that sediment does not account for all the phosphorus being transported to our lakes.  This has led to the hypothesis that some phosphorus is leached from grass itself.  To find out if this is true, and to see whether different types of grasses leach different amounts of phosphorus, several miniature ecosystems were constructed in 2' by 2' by 1' wooden boxes, consisting of a "lake", a container for runoff collection, topsoil, and a layer of soil roughly one inch thick with grass.  Types of grass tested included low and high quality Kentucky Bluegrass, and low and high quality Creeping Bentgrass, both commonly found on golf courses and lawns.  An ecosystem with no grass, just topsoil, served as a control.  Results showed that the lakes in Bentgrass and high-quality ecosystems had higher phosphorus concentrations than the lakes in the Bluegrass and low-quality ecosystems.  Grass samples taken before and after runoff show that some phosphorus was leached from each type, but the amounts with respect to the type were not significantly different.