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Compost to Reduce Runoff and Lawn Fertilizer Use By Mark Carroll, Ph.D., University of Maryland
New
residential lots can be among the most challenging areas on which to establish turf. Poor soil chemical and physical conditions, combined with lessthan-optimal seeding times, can result in low-density lawns. Poorly established lawns increase the potential for runoff from landscape areas and drive some new homeowners to use more lawn fertilizer than homeowners residing in older, more mature developments. Improvement of poor-quality soils is often accomplished by amending soil with compost prior to turfgrass establishment. High-volume additions of compost alleviate soil compaction, improve the water-holding ability of the soil and reduce runoff by improving soil infiltration. The key to improving soil physical properties is to ensure that a large amount of organic matter is added into the soil and that heavy equipment is kept off the site (especially when the soil is wet) after incorporation of the compost. A typical recommendation for amending soil with compost is to spread 1" (or 3 cubic yards per 1,000 ft2) of material over the soil prior to incorporating it. Recognition that adding more than this amount will improve the infiltration capability of most fine-textured soils has led some states and municipalities to recommend that soils be amended with 2" or more of compost to reduce stormwater losses from the site. For example, the Virginia Stormwater Management Handbook recommends that 2" to 4" of compost be incorporated into the top 6" to 10" of soil to
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reduce runoff from compacted soil sites where turf is to be established. In areas where the lawn will receive runoff from impervious surfaces (such rooftop downspouts or adjacent paved areas), higher rates of compost and deeper rates of incorporation are recommended. In Pennsylvania, the guidance provided in the state’s Stormwater Best Management Practices Manual for infertile, non-compacted soils is to mix one part compost with two parts soil. Most rototillers can till soil to a depth of only 5" to 6".
Thus, if one were to follow the Pennsylvania guidelines, 1.6" to 2" of compost would be spread over the soil surface prior to incorporation to reduce stormwater runoff. We measured runoff losses from a silt loam soil amended with 2" compost at our turf farm as part of a National Fish and Wildlife Foundation-funded project and found that these plots had about 50% less runoff when compared to plots that were not amended with compost prior to establishment (Figure 1).
7 TF Lawn Compost Ammended Soil TF + MC Lawn
6 5 4 3 2 1 0
2013
2014 Year
Figure
1
Cumulative runoff expressed as a percent of total precipitation for six events that generated runoff in 2013 and eight events that generated runoff in 2014. Plots were either amended with 2" of yard-trimmings compost to depth of 5" and seeded with a lawn seed mixture containing 95% tall fescue (TF) and 5% microclover (MC), or simply rototilled, leveled and seeded with 100% tall fescue. The compost-amended plots were not fertilized during the study. The tall fescue plot received 3.0 lbs. N/1,000 ft2 per year using urea and sulfur-coated urea after establishment.