Turf

Using Compost as a Soil Amendment (Post-Construction Soil BMP)

Compost is the product resulting from the controlled biological decomposition of organic materials that has been sanitized through the generation of heat and stabilized to the point that it is beneficial to plant growth. It is an organic matter resource that has the unique ability to improve the chemical, physical, and biological characteristics of soil.

Key Considerations

Healthy, undisturbed soils provide important stormwater management functions including efficient water infiltration and storage, adsorption of excess nutrients, filtration of sediments, biological decomposition of pollutants, and moderation of peak stream flows and temperatures. In addition, healthy soils support vigorous plant growth that intercepts rainfall, returning much of it to the sky through evaporation and transpiration. Common development practices include removal of topsoil during grading and clearing, compaction of remaining soil, and planting into unimproved soil or shallow depths of poor quality imported topsoil. These conditions typically produce unhealthy plants that require excessive water, fertilizers and pesticides, further contaminating runoff.

To maintain the natural soil qualities, impacts to undisturbed soils should be avoided and minimized during the construction process. When impacts are unavoidable and soils have been compacted or otherwise disturbed, compost can be used as an amendment to regain some of the characteristics of undisturbed soils.

Figure of Comparison of Soil Infiltration after Compaction (from John Barten, Three Rivers Park District)

Figure 1 shows the effect that compaction of soils has on infiltration of water into sandy and clay soils. Uncompacted sandy soils will infiltrate up to 12 inches of water per hour. When compacted, the infiltration rate decreases to 1 inch or less per hour or a 90% reduction in the infiltration of water. Uncompacted clay soils are able to infiltrate up to 9 in per hour. However, when compacted, the infiltration rate drops to less than a ½ inch per hour or a 95% reduction in the infiltration of water. This illustrates how compacted soils contribute a significantly greater volume of runoff to the storm water system. Later discussion shows how compost can help to off-set the effect of compaction.

Establishing soil quality and depth regains greater stormwater function in the post development landscape, provides increased treatment of pollutants and sediments that result from development and habitation, and minimizes the need for some landscaping chemicals, thus reducing pollution through prevention. Establishing a minimum soil quality and depth is not the same as preservation of naturally occurring soil and vegetation. However, establishing a minimum soil quality and depth will provide improved onsite management of stormwater flow and water quality.

Benefits:

Compost can be used as a soil amendment to:

• Increase infiltration
• Reduce runoff
• Improve soil porosity
• Increase soil moisture holding capacity (reduce water demand of lawns and landscaping)
• Reduce erosion
• Absorb certain pollutants (increase cation exchange capacity)
• Reduce fertilizer needs
• Reduce pesticide and herbicide needs

Both yard – leaf compost and the manure compost could be used for turf applications. However, if using manure compost, the fertilizer application may need to be adjusted downward so as to not over fertilize the turf and inadvertently create nutrient runoff.

Compost maturity is another important factor. Using compost that has been properly aged as a post-construction soil amendment promotes healthy root and plant growth and will prevent damage to turf and plantings. When immature compost is applied to soils it continues to decompose and the process of decomposition robs nitrogen from the plants and stunts plant growth, possibly even killing the plant.

To facilitate the creation of consistent compost products throughout the United States, the U.S. Composting Council (USCC) created the Seal of Testing Assurance Program (STA). This voluntary program requires participating compost facilities to perform a uniform set of tests on their compost products. Composters who are STA participants are required to furnish test information to compost buyers. This gives the purchaser of the compost the agronomic information needed (such as pH, particle size and test results from a number of other parameters) to successfully use the compost.

Turf Establishment or Incorporation in Soil as an Amendment

When purchasing compost to be used for turf establishment or incorporation into soil as a post-construction ===3.1. Application Guidelines===efits of naturally occurring soil and vegetation. Compost amended soils will improve on-site stormwater management and reduce long term operation and maintenance costs for off-site water treatment best management practices. Developing a Soil Management Plan is an important first step in minimizing and mitigating impacts to native soils and maximizing onsite stormwater management benefits.

The goal in amending compacted soils with compost is to reach or exceed the stormwater management ben

In areas where remaining topsoil or subsoil will be amended in place, it is important that, at a minimum, certain soil quality and depth improvements are achieved, as follows: : For soils in planting areas, a minimum dry weight organic matter content of 10% is recommended. For soils in turf areas, a minimum dry weight organic matter content of 5% is recommended. Soil pH should range from 6.0 to 8.0 or match the pH of the original topsoil (WDOE, 2005).

Soil Quality: Within the construction limits, a minimum, uncompacted depth of 12 inches is recommended (Kunz and Jurries, 2001, WDOE, 2005). In high traffic areas, a minimum uncompacted

depth of 18 inches is recommended. Table 1 summarizes how to achieve these depths in planting areas and turf areas.

Depth

portant to use a compost product that fits the specific situation. In Minnesota, compost is made from a variety of feed-stocks, including yard and leaf debris, residential or commercial food residuals, and animal manure. Each type of feedstock produces a slightly different compost. Examples would be, a yard and leaf compost is low in nutrients (N-P-K) and the particle size is generally a little more coarse than a manure compost which is higher in N-P-K and has a finer, more uniform particle size. These are important factors, as a yard - leaf compost would be more appropriately used when applying compost to a project site that is close to a water source. In addition, yard – leaf compost is more coarse and is a better choice for a blanket, filter sox or berm to control erosion.

When amending disturbed soils with compost, it is im

Comparison of Soil Infiltration after Compaction (from John Barten, Three Rivers Park District)