Nutrient and Sediment Losses from Cropland and Pastures: A Paired Watershed Approach in NC.

A paired watershed study was implemented in nutrient-impaired watershed, Jordan Lake, which is representative of agricultural and soil systems of the piedmont region.  The objective of this North Carolina study was to quantify the effectiveness of agricultural conservation practices typical of the region.  Two pairs of watersheds were used; one pair focused on pasture and hay land uses, while the other focused on cropland. All four watersheds were first order streams that were often dry.  They were continuously monitored and storm-event, flow-proportional samples were collected and analyzed for nutrients (total phosphorus (P), total Kjeldahl nitrogen (N), ammonia N, total N, nitrate-N) and sediment.  Baseflow stream samples were collected when there was flow and sampled for e-coli and dissolved P.  Flow and rainfall were also obtained during storm events in order to compare pollutant export loads. Land use data were collected yearly.   The pasture pair of watersheds was monitored for approximately 8 years and treatment included nutrient management and exclusion fending.  For the pasture–treatment watershed, the export rate of TKN, NOx-N, and TN were approximately the same during the pre- and post-treatment periods, while the NH3-N, TP and TSS export rates decreased pre to post. The cropland pair of watersheds was monitored for approximately 6 years.  As the treatment watershed was  in long-term conservation tillage, the only treatment applied was N management on corn as no N was applied to soybeans and wheat N rates were appropriate.  We were not able to demonstrate a difference in nutrient losses.