Changes in fluxes of N and P in water draining a stand of Scots pine treated with sewage sludge

The soil drainage water chemistry of a mature Scots pine stand was studied following an operational-scale addition of sewage sludge. A 1.33 ha experimental area at Monaughty forest, northeast Scotland was treated with 200 m(3) ha(-1) of anaerobically digested sewage sludge. Approximately 400 kg ha(-1) of nitrogen (N) and 200 kg ha(-1) of phosphorus (P) were applied in the sludge treatment. The hydrological balance and fluxes of nitrogen and phosphorus in throughfall and soil drainage water (O-1, O-2 and B-s soil horizons) over the short (3 month) and longer-term (17 month) period after application are compared with untreated areas. immediate increases in soluble ammonium (NH4) and phosphate (PO4) were apparent within the organic soil horizons and PO4 in the B-s horizons of sludge-treated areas. This observation was attributed to the direct leaching of nutrients contained within the original liquid phase which constituted 95% (by volume) of the sludge. The late initially resulted in autumn application of sludge which contained only small amounts of nitrate (NO3) (<0.05 kg N ha(-1)) limited additional mineralisation and consequently little N leached as NO3. Over the longer 17 month period the total fluxes of both N and P from sludge-treated areas remained greater than those of the untreated areas with significant losses as NO3 being detected from the organic and B-s horizons. However, total fluxes of N and P measured in the soil drainage water from the lowest soil horizon, over the whole study period represented 2.5 and <1%, respectively, of the total N and P applied as sludge. (C) 2000 Elsevier Science B.V. All rights reserved.