In moisture excess regions, irrigation of lagoon effluent to land is generally required to prevent water pollution from lagoon overflow. However, the land area receiving lagoon effluent then becomes a potential nonpoint source of pollution, especially if effluent is applied at high rates. The quantity and quality of rainfall runoff were determined for six years from plots of ‘Coastal’ bermudagrass on typical Coastal Plains soils that received weekly irrigations of swine lagoon effluent during the growing season. Three application rates supplied an average of 335, 670, and 1340 kg N ha-1 yr-1; 90, 180, and 360 kg P ha-1 yr-1; and 200, 400, and 800 kg Cl- ha-1 yr-1. The soil crop characteristics promoted high infiltration of rainfall and the plots were not irrigated during the nongrowing season, when runoff is usually highest. Thus, both runoff volume and nutrient mass transport were low, but nutrient concentrations were relatively high compared with typical concentrations in cropland runoff. Average annual arithmetic mean concentrations ranged from 7 to 13 mg L-1 for total N and from 3 to 6 mgL-1 for total O for the three treatments. Treatment differences were usually significant for the high-rate treatment, but not significant between the low- and medium-rate treatments. For this soil-crop system, NO3- -N movement to groundwater and P accumulation in the soil for the high- and medium rate treatments would likely be of more concern than the pollution of rainfall runoff.
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