Land Use Data: Understand It Before Making Water Quality Rules.

Like many impacted coastal waters, environmental rules were created to reduce nitrogen (N) loading by 30% and maintain phosphorus (P) loss levels in the Tar-Pamlico River Basin in North Carolina.  Agriculture’s contribution to nutrient loading in the basin was based on models, and no agricultural data was collected before the rules were designed. A one-time statistically valid area-frame sampling was applied to agricultural fields in the Tar-Pamlico River Basin to collect a baseline of cropping systems, soil types, and currently used best management practices. This sampling was much more detailed than current USDA-agricultural statistics. Best management practices included buffers, water control structures, cover crops, and conservation tillage.  It was found that most counties had low use of cover crops, but a substantially greater use of conservation tillage (50% or more).  One county had few buffers next to stream or ditches, while another had almost 100%; most are buffered at greater than 50% of the stream or ditch corridors.  Water control structures consisted of more than 25% of the agricultural acreage in some counties, where they can be installed. Nitrogen fertilizer rates were frequently lower than the recommended rate, and therefore, N losses were lower than expected. Soil erosion was modest (7.8 t ha^-1 yr^-1 (3.5 t ac^-1 yr^-1)), and potential off-site loss of P from agricultural fields was also low (< 1.12 kg ha^-1 yr^-1 (<1.0 lb ac^-1 yr^-1)).  Generally, the survey found that producers in the Tar-Pamlico River Basin are minimizing environmental impact of nutrient and soil losses from agricultural fields.  Surveys, such as these, should be done prior to rule making to better inform the decision making process and target conservation practices to the areas with the greatest need.