Improved summer pasture areas, such as at site S5, are planted in bahia grass (Paspalum notatum) and receive a springtime application of fertilizer to sustain adequate growth. For 15-20 years prior to 1987, phosphate-containing fertilizers were applied annually, or at least biannually, at rates of 34-45 kg P₂O₅ per hectare. Since 1987, only N-based fertilizers such as ammonium sulfate, ammonium nitrate, and calcium nitrate have been applied to these pastures. From 1986 to 2000, for example, ammonium sulfate fertilizer was applied annually or biannually at a rate of 56 kg per hectare. In contrast to fertilized site S5, unfertilized pasture areas, such as site 770 and managed winter pasture W4 (Figure 1), are less well drained and contain mostly native vegetation.

Site S5 is one of 8 adjoining plots of similarly improved summer pasture used for controlled testing of best management practices such as stocking rate and fertilization rate (Figure 1). Each plot is equipped with a flume and automated water sampling equipment designed to monitor runoff water quality during significant rainfall events. Runoff from these sites enters the adjacent Harney Pond Canal (Figure 1), a major drainage that flows into Lake Okeechobee.