Reducing Phosphorus Runoff from Urban Landscapes
As cities develop, the natural vegetation (pervious areas) is replaced with roads, roofs, and pavements (impervious areas), thereby changing the water cycle by way of increased runoff and reduced groundwater recharge. This increased runoff rapidly carries contaminants, including phosphorus (P) and nitrogen (N), to nearby water bodies and leads to the deterioration of water quality.
Individual home lawns contribute small amounts of contaminants, but collectively they can contribute to water quality problems in downstream water bodies. For example, nutrient runoff from lawns, parks, and gardens results in an abundance of aquatic weeds and algae, degrade fish and wildlife habitats, and affect recreational uses of water.
Pervious areas can have a positive effect on water quality by slowing down and filtering runoff water, or they can contribute nutrients and exacerbate water quality problems. The effects depend on the management of fertilizer, water, and soil in the urban landscapes (including paved areas) around the residential areas.
Good fertilization, irrigation, soil management, and lawn maintenance practices are key to reducing the amount of N and P in urban runoff and protecting water quality.
How Does This Practice Work?
Phosphorus can be brought onto your property in fertilizer, soil amendments, pet waste, and other chemicals (for example, from washing cars).
Nutrients, such as P, are needed for root development in lawns and gardens; however, adequate P may already exist in your soil, depending on geology and previous management. Since P can have detrimental impacts on water quality, it should only be applied when it is necessary based on soil test results. Further, only use the recommended fertilizer amount; more is not better. Excess fertilizer not only wastes money but can damage water quality. To determine if your lawn needs fertilizer, take a soil test or consult with your local Extension office for advice. Do not apply P fertilizer if your soil test results is in the optimum or high ranges.
If P is needed, use slow-release forms of fertilizer to minimize runoff losses. Most plants, including lawns, require much less P than N. Consider buying N only fertilizer rather than a fertilizer blend that includes P when soil P is adequate. Set the fertilizer spreader on the setting no higher than recommended on the fertilizer bag or according to fertilizer rates recommended by your local Extension; if you are unsure where to set the spreader, put it on a low setting to avoid over-fertilizing. After application, water the fertilizer into the soil, but do not over-water and cause runoff.
Never apply fertilizer to sidewalks and driveways. If you accidentally get fertilizer on paved areas, sweep it up and return it to the lawn. Wash off fertilizer application equipment on the lawn, not on the sidewalk or driveway. Store all fertilizers in a safe, dry place.
Overwatering is not only wasteful but also causes nutrient runoff from the lawns. Most of the P is lost to runoff from the soil surface but can also leach through the soil below the root zone.
Install water-efficient sprinkler systems that are directed away from paved surfaces. Don’t water the pavement! Also, check your downspouts and redirect them from paved to pervious (vegetated) areas.
Water lawns on an “as-needed” basis, when it is dry, rather than on a calendar schedule. Watering a little bit every day is unnecessary and can lead to reducing water supplies and increasing the runoff of nutrients. Homeowners with automatic sprinkler systems should check the weather to assess landscape water needs. Turn off or reset sprinklers after rain or during periods of cool weather. Apply only enough irrigation water to meet plant needs.
In addition to irrigation management, other soil management techniques can improve infiltration and water-holding capacity, thus minimizing runoff and leaching of nutrients. The use of organic soil amendments such as aged manure or compost before planting can improve soil health. This will help develop soil with good infiltration and aeration. Further, these soil amendments contain nutrients, so reduce your fertilizer application accordingly.
Another good practice is establishing a ground cover or mulch on all bare soil areas. Mulching will help conserve moisture, protect roots, reduce weeds, and prevent the loss of soil and nutrients.
In compacted lawns, occasional aerating can be useful to encourage good rooting and water penetration. Maintain natural buffer areas where no fertilizer is applied between your property and any stream, lake or drainage way. Keeping any part of your property that borders surface water in dense, natural vegetation can help filter out nutrients that might be lost in runoff water.
Finally, appropriate plant selection and lawn maintenance decisions can reduce the need for fertilizer and water and minimize the potential for water contamination with nutrients. Select landscape plants that are native and/or well-adapted to the area and have low irrigation requirements. Mow grass up to 2-3 inches high regularly to keep the lawn healthy. If not composting, leave grass clippings on the lawn to recycle nutrients and partially supplement and reduce the need for fertilizers. A healthy lawn will soak more rainfall water and reduce the potential for runoff of water and nutrients.
Where This Practice Applies and Its Limitations
Specific recommendations are subject to local soil, climate, management, and local ordinances and regulations. However, the concepts described here apply to all of these scenarios and can be modified to accommodate local needs.
Following these practices will reduce P (and N) runoff from urban landscapes by reducing soil test P buildup and minimizing the potential for P loss. Combining good fertilization and irrigation practices, with proper soil and landscape management, will result in better quality lawns, lower water use for irrigation, and reduced runoff of nutrients, which will protect water quality in urban landscapes.
Cost of Implementing the Practice
Following the practices outlined here will save you money on fertilizer and water. Water use, soil amendments and mulches will vary in cost depending on the region and availability, and aeration costs will depend on whether you have your aerator or have to contract for this service.
Operation and Maintenance
The decisions these factsheet addresses are not made at once for the indefinite future. These decisions must be reconsidered every time fertilizer is applied, or irrigation takes place. Site-specific soil and climatic conditions and other factors will affect these decisions.
For Further Information
Contact your local soil and water conservation district, USDA-NRCS or Cooperative Extension Service office. To find your local USDA Service Center, visit https://www.nrcs.usda.gov/contact/find-a-service-center.
|Gurpal S. Toor
University of Maryland
Colorado State University
Retired- Colorado State University
Colorado State University
Editing and Design
NC State University
University of Tennessee
Toor, G., and T. Baudion. 2023. Reducing Phosphorus Runoff From Urban Landscapes. SERA17 Phosphorus Conservation Practices Fact Sheets. https://sera17.wordpress.ncsu.edu/reducing-phosphorus-runoff-from-urban-landscapes/