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Effect of Sewage Sludge on Some Soil Physical Properties¹

ABSTRACT

Raw and digested sewage sludges, 5% by weight, were incorporated into a Beltsville silt loam soil. The soil-sludge mixtures were incubated at 15, 25, and 35C for 75 days. Periodic measurements were made on water retention, hydraulic conductivity, and aggregate stability. Adding sewage sludge shifted the water retention curve so that the water content at specific water potential values was higher, but the amount of water between –0.33 and –15 bars potential essentially remained the same as that of the original soil.

Addition of sewage sludge initially increased the saturated hydraulic conductivity. After 50 to 80 days, however, the hydraulic conductivity dropped to that of the original soil. Percent stable aggregates increased as a result of sludge addition. After 175 days, the percent stable aggregates averaged 28–35% for the sludgeamended soil, as compared to 17% for the original soil.

Key Words: waste • water retention • hydraulic conductivity • aggregate stability

¹ Contribution from the Agricultural Environmental Quality Institute, Agricultural Research Service, USDA, Beltsville, Maryland 20705.

² Research Soil Scientist.

Received for publication May 10, 1974.