The transport of plant nutrients in drainage waters from two steeply sloping, differentially fertilized, grassed watersheds located in western North Carolina was determined over a 4-year period. Watershed No. 1 has a drainage area of 1.89 ha, No. 2, 1.48 ha. The dominant slopes on both watersheds are 35 to 40%. During this period, watershed No. 1 received a total of 112-48-24 kg N-P-K/ha; watershed No. 2 received 448-192-24 kg N-P-K/ha.
Average annual measured N losses were 3.28 and 12.08 kg/ha for watershed No. 1 and watershed No. 2, respectively; NO3-N comprised 70% and 85% of the total N lost in discharge waters from the two watersheds. Total N lost over the 4-year period from each watershed was 6 to 10% of the fertilizer N applied.
Annual P losses were negligible, amounting to 0.15 kg/ha from watershed No. 1 and 0.27 kg/ha from watershed No. 2.
Measured K losses averaged 3.99 and 5.83 kg/ha annually; S losses were 1.92 and 2.54 kg/ha from watershed No. 1 and watershed No. 2, respectively.
Additional nutrient losses likely occurred because of deep seepage and an estimate of these losses was made.
Losses of all nutrients were highest during the winter and spring months. Concentrations of nutrients in discharge waters from watershed No. 2 were consistently higher compared with watershed No. 1. However, NO3-N concentrations exceeded 10 ppm on watershed No. 2 only once during the 4-year period.
The authors conclude from this study that steeply sloping pastures, judiciously fertilized, are not an important source of nutrients occurring in surface and ground waters.