Cut Slope Composting: Field Trials and Evaluation

WTI teamed with the Reclamation Research Group to evaluate and optimize low compost application rates and determined best compost retention techniques that increase native vegetation establishment on steep highway cut slopes.

The purpose of this project is to expand the knowledge base and further refine the use of various materials and application techniques to increase the performance of compost at lower application rates that promote the establishment of native plants on steep cut slopes along highways.

Successful revegetation of highway right-of-ways following construction, reconstruction, and other disturbances of Montana Department of Transportation (MDT) lands requires creating environmental conditions conducive to the successful establishment and survival of reclamation plantings. Steep cut slopes present a challenge, given the difficulty to place salvaged soil with conventional equipment and retain soil on these areas. Standard practice is to hydromulch and broadcast seed; however, this is problematic on steep bare slopes, often resulting in marginal plant establishment related to low germination rates and seedling survival due to nutrient poor, rocky substrates characteristic of cut slopes. Poor vegetation establishment leads to increased erosion and sedimentation, occasional slope failure, and increased noxious weed growth. Unsuccessful revegetation has the potential to substantially increase maintenance costs in these areas. Roadside composting research done for MDT by the Research Reclamation Unit at Montana State University (MSU RRU 2007) established baseline compost application rates MDT uses to guide reclaiming steep slopes. The research used high compost application rates. New research is needed to optimize application rates using various compost materials and application techniques and increase the performance using less compost on steep slopes. Past research observed loss of applied surface compost from wind erosion prior to vegetation establishment. Compost stabilization techniques limiting wind erosion are required prior to widespread adoption of compost application on MDT steep cut slope. This research project will evaluate compost performance applied at rates less than the 1 to 2 inches applied in the 2007 research. This phase of the research will establish minimum quantity recommendations to be used on steep cut slopes and will evaluate the use of various materials and/or application techniques to prolong the period of time the compost remains on steep slopes.