Nutrient Export from Agricultural Watersheds in the Piedmont and Coastal Plain, North Carolina

Abstract

Abstract. Nitrogen (N) and phosphorus (P) input and export rates were determined in six rural, predominantly agricultural watersheds located in the Piedmont and Coastal Plain regions of North Carolina. Water quality monitoring was conducted at the outlets for 2.3 to 8.0 years to determine the annual N and P export from each watershed. Total N and P input and export from five of the six watersheds were correlated, with only a no-till cropland watershed differing. The correlation showed that N and P exports increased by about 4.0% and 8.7%, respectively, of applied N and P for the range of applications rates, whereas dissolved N (NOx-N) export increased by 2.8% with increasing N application rates. Therefore, practices that reduce inputs, such as nutrient management, should result in similar percentage reductions in exports. The Small Watershed Nutrient Forecasting Tool (SWIFT) was used to forecast discharge, N, P, and sediment export from each of the six watersheds. For the no-till cropland watershed, the SWIFT-forecasted N and P export rates were more than 2.5 times those measured, while the sediment export rate was 72 times the measured value. Thus, these data showed that the SWIFT forecasts for N, P, and sediment export were poor for the no-till cropland watershed. For the pasture watershed, the SWIFT forecasts for N and sediment export agreed reasonably well with measured export; however, the forecasted P export was much less than measured. For the four mixed land use watersheds, the SWIFT forecasts for discharge, TN, and sediment were mostly greater than measured, and the forecasted TP export was less than measured for three of the four watersheds. Thus, as with many predicstion tools, SWIFT results must be used with caution. Keywords: Nutrient export, Nutrient management practice, Water quality monitoring.

Assessing the Agricultural Conservation Planning Framework toolbox in a Southern Piedmont landscape of the United States

“…Local experts listed conservation concerns in a 2020; USDA FSA 2021), with current conservation focused on pasture management, including exclusion fencing (ponds and streams), as well as stream crossings and filter strips. Exclusion fencing is the most currently accepted structural practice; research has shown nitrogen (N), phosphorus (P), and sediment reductions 20%, 47%, and 60%, respectively, when implemented in these watersheds (Line et al 2016(Line et al , 2019.…”

“…In comparison, ACPF placed approximately three times the number of conservation practices than that of the local experts in each watershed respectively. The use of contour buffer strips as an in-field practice was the most identified conservation practice by ACPF and placed in 75% of cropped fields; this is not a common practice in North Carolina partially because conservation tillage has been widely and successfully adopted with concomitant low sediment and nutrient loading (Line et al 2016(Line et al , 2019Schomberg et al 2020), but also because of the small field size (<5 ha). Between 2005 and 2019, only two contour buffer strips were installed in North Carolina (USDA 2021).…”