Evaluation of Phosphorus Transport by Surface Runoff From Field Receiving Long-Term Dairy Manure Applications and Occurring in a Karst Landscape.

Agricultural runoff is considered to be the leading source of non-point source pollution and, thus, is the leading source of water quality impairment in the United States. The main water quality issue associated with agricultural runoff is accelerated eutrophication of surface waters. The objective of this study was to characterize the P forms transported by surface runoff from an agricultural field that has received long-term applications of liquid dairy manure. Furthermore, this study quantifies the input of the dairy manure constituents from the field application. With these data, it is possible to determine the amount and form of P that is lost from these areas via runoff. The P lost can be transported to surface waters, or the P can be transported to groundwater through sinkholes that are indicative of karst landscapes. This study took place in an east Tennessee watershed. This study utilizes three 70 ft. length x 20 ft. width (21m x 6 m) bermed plots to collect the runoff for a representative area in a field that has received long-term applications of liquid dairy manure. The runoff is collected at the base of the plots with a series of three five-gallon (19 L) plastic buckets with flow dividers for each plot. This collection system is capable of representing 3005 gallons of runoff water. The runoff collected is then analyzed for dissolved reactive phosphorus (DRP), total P (TP), total dissolved P (TDP), and particulate P (PP). Preliminary results show that the majority of P leaving the field is associated with the PP. However, the amount of sediment associated with the runoff ranges from 0.06 to 5.43 lbs acre^-1. DRP is the fraction of P that is considered to be immediately biologically available, and the DRP ranges from 0.045 to 0.60 mg L^-1.