Nutrient fluxes from a soil treatment process for pig slurry

The effects of pig slurry applications to a hydrologically isolated field t reatment plant (at Solepur) were studied over a period of eight years. Thir ty repeated doses, averaging 160 m(3) ha(-1) were applied from April to Oct ober of each year (1991-1995), to reach a total application of 4930 m(3) ha (-1). All slurry samples were analysed for their total solids (TS), macronu trient (C, N, P, K, Ca) and micronutrient (Cu, Zn) content. In total, 284 t onnes of total solids (57 t TS ha(-1) yr(-1)), 115 tonnes of carbon (23 t C ha(-1)yr(-1)), 24.5 tonnes of nitrogen (4900 kg N ha(-1) yr(-1)), 7964 kg of phosphorus (1593 kg P ha(-1) yr(-1)), 16 518 kg of potassium (3304 kg K ha(-1) yr(-1)), 183 kg copper (37 kg Cu ha(-1) yr(-1)) and 266 kg zinc (53 kg Zn ha(-1) yr(-1)) were applied to the soil. Thus, this site provides an opportunity to assess the balance and to examine the long-term behaviour of nutrients under conditions of intensive land application of pig slurries o r similar effluents. The main nutrient fluxes through the soil-water system were determined for each element. Over 40% of the total carbon applied was retained by the soil . About 25% of the slurry nitrogen applied remained in the soil profile and 12.5% was leached through the drainage water as nitrate. Most of the slurr y phosphorus applied was retained in the soil profile either as P-Dyer extr actable (83%), or as total soil phosphorus (112%); < 0.01% was found in the drainage water. Forty-three per cent of the potassium applied in the slurr y was recovered from the soil profile and 15% was recovered in the drainage water. Most of the copper (62%) and zinc (74%) applied in the slurry remai ned in the soil as EDTA extractractable forms; very low percentages (0.05% and 0.6% respectively) were found in the drainage water.