Substrate-induced respiration of a sandy soil treated with different types of organic waste

A sandy soil was amended with different types of sewage sludge (digested, dried, and composted) and pig slurry. The composted sludges displayed higher organic-matter stability (39-45%) than only digested sludge (26-39%) or digested + dried sludge (23-32%). The microbial biomass of the dried sludge was undetectable. Digested and composted sludges and pig slurry displayed microbial biomasses (12492-13887 μg g-1, 1221-2050 μg g-1, and 5511 μg g-1, respectively) greater than the soil (108 μg g-1). The wastes were applied at seven doses, ranging from 10 to 900 g kg-1. Soils were incubated for 28 days. Substrate-induced respiration (SIR) was measured for 12 consecutive hours on day 1 and on day 28. The results showed that SIR increased with the dose of organic amendment. However, SIR decreased when moderate doses of pig slurry or high doses of digested + dried sludge were tested. The possibility of using this inhibition as an ecotoxicological indicator is discussed. © Taylor & Francis Group, LLC.