LONG-TERM SWINE LAGOON EFFLUENT APPLICATIONS ON COASTAL BERMUDAGRASS .2. EFFECT ON NUTRIENT ACCUMULATION IN SOIL

Application of effluent from animal manure lagoons to cropland is an effective method of utilizing the nutrients in the effluent and minimizing groundwater and surface-water pollution. The objective of this study was to determine the effect of land application of effluent from a swine (Sus scrofa domenticus) manure lagoon on selected soil chemical properties at the end of an 11-yr study. Effluent was applied at rates to supply approximately 335, 670, and 1340 kg of N ha-1 yr-1 to 'Coastal' bermudagrass [Cynodon dactylon (L.) Pers.] on a Paleudult soil from 1973 through 1983. Soil cores taken to a depth of 210 cm were analyzed for H2O-extractable NO3-N and Mehlich 1-extractable P and cations. Nitrate-N concentrations (1-5 mg kg-1) with the two lower rates were similar to concentrations where no effluent was applied. At the high effluent rate, NO3-N concentrations were elevated, particularly in the subsoil, and 540 kg NO3-N ha-1 was present in the profile. Phosphorus increased with loading rate and at the high rate, P concentrations (450 mg kg-1) in the 0- to 15-cm zone was 10 times the level above which no response to P fertilization would be expected. Potassium concentration increased with loading rate throughout the profile. Magnesium accumulation was inversely related to effluent loading rate in the 0- to 15-cm zone, but accumulation in the subsoil was directly related to loading rate. Comparison of profile nutrient distributions at the high rate for Years 6 and 11 showed no appreciable accumulation of NO3-N during the period. Accumulation of other nutrients during this 5-yr period was P, 210%; K, 200%; Ca, 140%; Mg, 60%; and Na, 10% as compared with Year 6. Soil pH was decreased by the high effluent rate but did increase from 4.2 at Year 6 to 5.0 at Year 11 due to the increased rate of application of basic cations during that period. The high rate poses a groundwater pollution hazard because of the large quantity of NO3-N present in the profile. In previous years, appreciable NO3-N was also present at the medium rate, but NO3-N was low at this rate in Year 11. The high P concentrations in the surface soil increase the potential for runoff transport of P, which might pose a surface-water pollution problem.