Phosphorus losses from sewage sludge disposed on a field: evidence from storm event simulations

Sewage sludge is used as fertilizer, owing to its nutrient contents. But li ttle is known about the consequences of sludge disposal on erosion intensit y and P losses from soil to runoff. This paper reports on a study of three simulated storm events (40 mm h(-1) during 30 min), performed on a field su pplied with liquid sludge (23 g L-1 of dry solid). The sludge phosphorus co ntent was 26.5 g kg(-1) of dry solid. The runoff and erosion intensity as w ell as the P losses were monitored during the experiment. The distribution of phosphorus on the soil surface, was investigated after the last simulati on. Sludge disposal reduced the total amount of runoff water collected duri ng the experiment from 290 m(3) ha(-1) to 134 m(3) ha(-1), it also decrease d the quantity of sediment exported from 1200 kg ha(-1) to 500 kg ha(-1) an d the total phosphorus loss from 2.7 kg ha(-1) P to 1.4 kg ha(-1) P. But, i t increased the average concentration of dissolved phosphorus in the overla nd flow from 0.15 mg L-1 P to 0.57 mg L-1 P. The distribution pattern of P and organic matter, on the soil surface, after the simulations, showed a he terogeneity induced by the runoff processes. This effect is increased by sl udge disposal.