LONG-TERM SWINE LAGOON EFFLUENT APPLICATIONS ON COASTAL BERMUDAGRASS .1. YIELD, QUALITY, AND ELEMENT REMOVAL

Swine (Sus scrofa domesticus) confinement systems that use anaerobic lagoons for waste collection in the humid regions require effluent removal during the year. Land area adjacent to the hog facility frequently becomes the site for continuous effluent distribution. The objective of this experiment was to determine the effect of long-term application of swine lagoon effluent to 'Coastal' bermudagrass [Cynodon dactylon (L.) Pers.] on dry matter yield, stand persistence, and nutrient concentration and removal. Effluent loading rates of low (L), medium (M), and high (H) approximating 335, 670, and 1340 kg of N ha-1 yr-1, respectively, were evaluated for 11 yr beginning in 1973 through 1983. The experiment was a randomized complete block with three replicates. Dry matter yields in Year 11 were altered by effluent loading rates with greater production from the M (19.0 Mg ha-1) or H (19.6 Mg ha-1) compared with the L (13.1 Mg ha-1). Although fluxes in stands occurred, they recovered completely as indicated by these yields. Higher concentrations of N, P, K, Mg, Cl, and Zn were present in forage in 1983 compared with 1973. Calcium was unchanged and Cu, Fe, and Na were less. In vitro dry matter disappearance of the forage was similar among loading rates (0.634) in 1983 and greater than in 1973 (0.553). Concentrations of NO3-N were higher in 1978 (1.14 g kg-1) compared with 1973 (0.87 g kg-1), but highest concentrations occurred in 1983 (1.57 g kg-1). By 1983, NO3-N concentrations of forages from the H loading rate approached or exceeded the toxic threshold in all summer harvests. Only the H loading (1340 kg ha-1) caused unstable stands and eventually produced forage that had NO3-N concentrations potentially toxic if fed as the sole ration to ruminants. Further, it resulted in disproportionally greater quantities of elements - especially N, P, K, Cl, and Na - that remained in the soil environment to become potential soil and soil-water pollutants.