Buffer Effects on Runoff and Dissolved Organic Carbon Loss in a Corn-Soybean Rotation Using a Paired Watershed Approach.

Dissolved organic matter (DOM) plays several important biogeochemical roles in terrestrial and aquatic ecosystems including the mobilization and transport of nutrients and pollutants. Cropping, tillage or conservation practices, including buffer strip installation, may affect runoff and losses of dissolved organic carbon (DOC), a measure of DOM. While many studies show a reduction in pollutant transport in buffered systems, buffer strips can be a source of DOC and may contribute to surface water pollution. The objectives of this study were to compare runoff (m³ ha^-1) and DOC loss (kg ha^-1) as influenced by grass and agroforestry buffer strips using a paired watershed approach. The study consisted of three small agricultural watersheds located in northeast Missouri planted to a maize (Zea mays L.) – soybean [Glycine max (L.) Merr.] rotation using no-till. Grass buffers and agroforestry buffers were installed at 36 m intervals along the contour in two watersheds while the third watershed served as a control. Runoff and DOC were measured during a six-year calibration period (1991 – 1997) prior to installation of the buffers and for a nine-year treatment period (1997 – 2006). The grass buffer strips significantly decreased runoff by 8.4% during the treatment period while the agroforestry buffer system exhibited no significant change in runoff. Loss of DOC was not significantly affected by either type of buffer installation. Additionally, no significant difference in runoff or DOC loss was found between crops (maize and soybeans) or between seasons (growing and fallow). These results indicate that grass buffer systems are effective at reducing runoff losses and that the buffer strips do not contribute to DOC contamination of surface waters.