SOIL MICROBIAL BIOMASS AND MICROBIAL ACTIVITY IN SOILS TREATED WITH HEAVY-METAL CONTAMINATED SEWAGE-SLUDGE

Soil microbial biomass carbon (C(mic)) and respiration were measured i n soils from two long-term field experiments with recent sewage sludge applications. A moderately contaminated sludge was applied as receive d from the sewage treatment plant and after additional metal contamina tion. Generally, the low metal sludge had beneficial effects on C(mic) and on the soil microbial activity. Higher heavy metal contamination of soils resulted in a substantial decrease in C(mic). The ratio C(mic )/C(org) even decreased when low metal sludge was applied. Soil respir ation and especially the respiration per unit biomass (qCO2) increased with increasing amounts of heavy metals. Concomitantly the contributi on of fungi to soil respiration increased. Judging from these results the qCO2 appears to be a sensitive indicator of effects that are resul ting from the effects of heavy metals on the soil microflora.