Optimizing Compost Application Rates for Vegetation Health, Maximal Stormwater Infiltration, & Runoff Quality

Soils disturbed by roadway construction often exhibit reduced soil porosity, precipitation storage capacity and infiltration rates, thereby yielding increased surface runoff. Poor performance of vegetation in these locations also leads to long-term aesthetic and erosion problems. Research has demonstrated that tillage can be used in conjunction with compost to improve soil conditions on disturbed, pervious areas. This year, NCDEQ formally recognized soil improvement as a stormwater best management practice (BMP). The soil improvement BMP has potential advantages to NCDOT with respect to lowering the cost of regulatory compliance while also contributing to goals such as beautification of the right-of-way via healthy landscape plantings, wildflower beds, and permanently stabilizing eroding areas caused by poor soil conditions. Given the broad applicably of soil improvement as a BMP throughout NCDOT’s transportation network, it is important to optimize soil improvement specifications to ensure the lowest-cost effective solution is achieved. There has been very little research to specifically determine optimal compost application rates to concurrently improve stormwater infiltration and/or storage, limit potential for offsite losses of nutrients and metals, and aid in timely vegetation establishment. These are all potential benefits of soil improvement BMPs, and the addition of compost at a proper rate is anticipated to be the most costly consideration for BMP implementation. The proposed research is designed to determine optimum compost amendment rates for soil improvement BMPs in North Carolina. The project will include a series of complimentary activities: (1) A literature review on the performance of compost amendments, application rates and pollutant transport mechanisms. (2) Laboratory assessment of the effects of compost amendment rate on hydraulic properties of North Carolina soils. (3) Bench-scale testing of nutrient and metal losses from compost/soil blends in leachate waters at target amendment rates. (4) Greenhouse testing of vegetation establishment and performance with compost amendment at target incorporation rates. (5) Field evaluation of optimized compost amendment rate effects on runoff water quantity and quality, infiltration, and vegetation establishment. (6) Development of recommended specifications for optimizing compost amendment rates for soil improvement BMPs.