Understanding Possible Sources of Phosphorus Contamination
by Don Janssen, Extension Educator
Are lawns a significant source of nutrients to urban streams and lakes? The answer to this question appears to be "maybe." On the one hand, over-fertilization of home lawns has been frequently cited as an important and controllable nutrient source. On the other, turfgrass researchers report that well-tended lawns produce minimal runoff and nutrient movement. What are the nutrients with potential to pollute and what are some of their sources?
The primary nutrient found to cause the growth of algae and aquatic weeds in streams and lakes is phosphorus. Phosphorus movement from urban landscapes can be attributed to several sources including the physical movement of soil or organic debris (tree leaves, grass clippings, animal waste), the leaching or runoff of phosphorus from the soil, and direct movement of phosphorus from fertilizer that is applied to impervious surfaces. Phosphorus from properly applied lawn fertilizers is rapidly fixed or immobilized following application and will not run off the lawn.
It is common for phosphorus to be applied as a casual compliment for nitrogen rather than using a soil test to judge phosphorus requirements. As a result, phosphorus is often applied when a soil test would recommend no application. Soil testing should be used to determine phosphorus needs for home lawns and when soils test high for phosphorus, zero phosphorus fertilizers should be applied.
Never apply fertilizer to a hard surface such as sidewalks, driveways or streets. Sweep or blow granular fertilizers off all hard surfaces and back onto the lawn or into the gardens. Granular fertilizers washed off of these hard surfaces by rainfall and into storm drains eventually find their way to our streams and lakes.
Leaves and flowering parts of trees contain significant amount of soluble phosphorus. When these natural sources of phosphorus fall onto rooftops and get caught in rain gutters, the phosphorus will leach out of these plant parts and be channeled into storm drains and sewers. To prevent this, check and clean out rain gutters in the spring to remove flower parts and in the fall to remove leaves and seeds.
Phosphorus becomes chemically bound to soil particles. Once bound to clays, practically the only way phosphorus can move is if the soil particles are eroded and become suspended in storm water runoff. Prevent soil erosion by using mulch where soils are not fully covered by a dense plant ground cover.
Everyone has the potential to contaminate the streams and lakes. Knowing the sources of phosphorus contamination and how to prevent them will go a long ways toward enhancing our environment.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office