Paper No. 11
Presentation Time: 11:15 AM
CONTROLS OF CA AND MG YIELDS IN SMALL AGRICULTURAL WATERSHEDS, COSHOCTON, OHIO
Gains in riverine concentrations of Ca and Mg ions in large watersheds that are dominated by agricultural landuse types have been largely attributed to the application and dissolution of liming materials. More work, however, is needed on small-scale watersheds to assess the relation between these ions and their response to hydrologic changes associated with landscape conversion. While applications of lime may act as sources of Ca and Mg, a loss of baseflow may act as a sink. Between 2003 and 2009, yields of Ca+Mg were determined from six (<39 ha) watersheds at the USDA North Appalachian Experimental Watershed, Coshocton, Ohio where the residual soils are primarily derived from sandstone and shale bedrock. Selected watersheds include a long-term, no-till cornfield (40+ years), a tilled and a recently tilled (<3 years) cornfield, an unimproved pasture, a forest (>70 years), and a mixed-use site composed of forest, pasture, and cornfield. The three cornfield watersheds had no baseflow and were only sampled during storm runoff. Additionally, three of the watersheds were limed including the tilled and recently tilled cornfields and the mixed site. The unlimed forest had the greatest overall Ca+Mg yield (183 kg ha-1 a-1) and the no-till cornfield yielded the least (1 kg ha-1 a-1). The forest had the highest (0.37 kg ha-1 mm-1) and no-till cornfield lowest (0.12 kg ha-1 mm-1) ratio of yield to discharge. Mean stormflow Ca+Mg yields were greatest from a limed and tilled cornfield (97 kg ha-1 a-1). This cornfield, and the limed mixed-use watershed, also had the greatest ratio of yield to discharge during stormflow. Clearly, the greater baseflow of the forested site contributed to its overall elevated Ca+Mg yield with respect to other landuse types, yet storm events released Ca+Mg. Therefore, careful attention is needed to determine to what extent Ca+Mg yields respond to surface chemical applications versus changes in contributions of surface runoff and baseflow.