Role of Fungi in Stabilizing Aggregates of Sewage Sludge Amended Soils

Abstract

Abstract The effect of sludge amendment on the percentage of water‐stable aggregates (WSA) of five soils with different physical and chemical properties was studied in an incubation experiment. A 5% sludge addition to soil incubated at 25 °C increased the per cent of WSA after 30 d in all of the soils. Bactericides were added to soil‐sludge mixtures to assess the role of fungi in the aggregation process. Bactericide addition resulted in the suppression of bacterial growth and a concomitant proliferation of fungal hyphae. The WSA was highly correlated with water‐soluble carbohydrates in all of the soils, and with hyphal length in two loessial soils. This suggests that cementing by fungal carbohydrates is a relatively more important binding mechanism than physical entanglement by mycelium in WSA formation of sludge‐amended soils. By using a soil washing technique, it was determined that fungi involved in stabilizing aggregates were indigenous soil saprophytes which replaced the native sludge fungal flora.