Microbial biomass and activity down the soil profile after long-term addition of farmyard manure to a sandy soil

Abstract

Long-term application effects of cattle farmyard manure (CM) without and with biodynamic preparations (CMBD) on basal respiration, 0.5 M K2SO4 extractable C and the relationships of microbial biomass C (MBC) estimates by chloroform fumigation extraction (CFE) and substrate-induced respiration (SIR) were evaluated down to 1 m depth. The contents of total N, K2SO4 extractable C and MBC-CFE declined with depth from 0–25 to 90–100 cm by −82, −47 and 86%, respectively. The contents of these three soil properties were always 17% lower in the mineral fertilization (MIN) treatment than in the CM and CMBD treatments. However, these differences were not always significant. The MBC-SIR/CFE ratio varied around 1 and did not show a significant depth gradient, due to the strong layer-to-layer variation within each treatment, although this ratio was generally 25% lower in the subsoil than in the topsoil. The metabolic quotient qCO2, i.e. the ratio of basal respiration to MBC, was positively affected by the MBC-SIR/CFE ratio, soil pH and K2SO4 extractable C and negatively by total N. Long-term application of farmyard manure, especially in the CMBD treatment, resulted in a subsoil microbial community with a more efficient use of SOC and glucose.