Effects of Sludge Irrigation on Three Pacific Northwest Forest Soils

摘要

A sprinkler irrigation system developed for uniform applications of anerobically digested, municipal-industrial sewage sludge initially applied up to 5.8 mt/ha/wk. Reduced infiltration of sludge occurred due to physically blocking of soil pores, causing ponding of sludge in the micro-depressions. Sludge loading rates were decreased to 10, 20, 30 and 40 mt/ha/yr. The renovating capacity of forest soils for most suspended and dissolved constituents in sludge was very good (95 to 99+%). Optimum loading rates of 20 to 30 mt/ha/hr. of sludge show trends to increased surface soil total N, organic material and cation exchange capacity. Analyses for virus at all depths in the soil and from the soil solution at corresponding depths were negative, nor were human pathogens of the bacteria type isolated from the limited numbers of soils and soil solutions analyzed.