PHOSPHORUS IN WATERS FROM SEWAGE-SLUDGE AMENDED LYSIMETERS

In surface waters, phosphorus (P) concentrations exceeding 0·05 mg liter-1 may cause eutrophic conditions. This study was undertaken to measure total P concentrations in runoff and tile drainage waters from land receiving either inorganic fertilizer or anaerobically digested sewage sludge. Total P was measured in runoff and tile drainage waters during 2 years of sample collections from instrumented, large-scale lysimeters planted to corn (Zea mays L.). During the 3 years prior to monitoring P concentrations, six of the lysimeter plots had been amended with anaerobically digested sewage sludge which supplied 5033 kg P per ha. Additional sludge applications supplied 1058 and 1989 kg P per ha during the first and second years of monitoring operations, respectively. Another six lysimeters were annually treated with fertilizer which included P applications amounting to 112 kg ha-1. For years 1 and 2, respectively, annual losses from lysimeters treated with sewage sludge were 4·27 and 0·35 kg P per ha in runoff and 0·91 from 0·91 and 0·51 kg Per P per ha in drainage waters. Parallel annual losses of P from lysimeters treated with superphosphate were 2·15 and 0·17 kg ha-1 in runoff and 0·53 and 0·35 kg ha-1 in tile drainage waters. Sludge applications did not significantly change absolute soil contents of organic P, but did decrease the per cent of total P present in organic forms. Sludge and soil, respectively, contained 21 and 36% of their total P contents in organic forms. In sludge and soil about 85 and 64% of their respective total inorganic P contents were associated with the Al and Fe fractions. Sludge applications significantly increased soil contents of P in the saloid (water-soluble plus P extracted with 1 N NH4Cl), Al, Fe and reductant soluble P fractions, but contents of Ca-bound P were not changed. Total P contents of the soil below a depth of 30 cm were not affected by sludge incorporated to a depth of about 15 cm by plowing. © 1990.