Impacts of Organic Soil Amendments on Runoff and Soil Ero- Sion under the Natural Rainfall Conditinos, Preliminary Re- Sults

Organic amendments such as composts and mulches have been shown to improve soil quality and reduce the impacts of stormwater runoff and soil erosion Previous studies using rainfall simulators have documented that runoff volumes and soil erosion can be significantly reduced when organic materials are added to the soil profile. The objectives of this study are to measure the changes in runoff and soil erosion under natural rainfall conditions in Georgia over a five year period and to determine the changes in soil carbon levels over time. Results from such measurements could be used to improve prediction technologies such as the curve number method and RUSLE type erosion models that engineers and designers use to account for soil erosion during construction as well as long term stormwater management. INTRODUCTION Every year thousands of acres of land are disturbed in a manner that promotes runoff, erosion of topsoil and loss of soil organic carbon. While these construction and development projects are required by law to control stormwater during the develop process, the long term changes in soil properties impact the surrounding environment for decades. Many studies have investigated the use of compost and other organic soil amendments to control runoff and soil erosion (Claassen, 2000; Faucette et al., 2004; Faucette et al., 2005; Hernando et al., 1989; Shiralipour and Aziz 1992). Almost all of these studies have been conducted using rainfall simulators and have only measured the changes for short periods of time (some have lasted up to one year). Since the primarily mechanism of soil improvement using organic matter is improved soil structure and higher infiltration rates (Mukhtar et al., 2004; Risse and Faucette, 2001), these studies, which often use very high rainfall rates, may be underestimating the effects of organic amendments by only considering the extreme events. Since the majority of rainfall events are small events (often less than 1 inch) of shorter duration, amended plots often produce little or no runoff compared to plots with little or no organic cover. Furthermore, organic amendments promote biological activity that improves soil structure and may allow for greater differences in infiltration rates over time. One primary goal of this project is to measure the changes in runoff and soil erosion under natural rainfall conditions in Georgia over a five year period. Results from such measurements could be used to improve prediction technologies such as the curve number method and RUSLE type erosion models that engineers and designers use to account for soil erosion during construction as well as long term stormwater management. Adding organic materials to the soil also sequesters carbon and could potentially be a method of combatting global warming. While there is considerable data on the fate of organic carbon under agricultural and forested conditions, very little data exists concerning the fate of carbon when added to disturbed soils under urban/suburban land uses such as grassed lawns. A secondary objective of this study is to observe long term changes in soil carbon levels under these conditions. This paper reports on the establishment of these plots and the preliminary results during the period from June 1 to December 2, 2010.