Microbial biomass-C determined using CaCl2 and K 2SO4 as extraction reagents

Abstract

Microbial biomass-C [MBC] was determined by re-hydration [RHD] technique using two very similar salt solutions in dissociation potency (0.5 mol/l K 2SO4 [MBC-K] and 0.01 mol/l CaCl2 [MBC-Ca]) in forest, grassland, arable Cambisols [Inceptisols] and Podzols [Spodosols]. MBC-Ca ranged from 254 to 5076 mg/kg dry soil (1.2-4.0% of Corg). 114 soil samples were examined in the years 2002 and 2003. Organic C compounds extracted by 0.5 mol/l K2SO4 [EC-K] and 0.01 mol/l CaCl2 [EC-Ca] increased in sequence: (1) arable Cambisols (100%), (2) cut and grazed grasslands (547%), (3) forest mineral horizon AH 0-50 mm (783%) and (4) Norway spruce forest floor (2421%). The ratio EC-Ca/EC-K reached on average 62% and ranged from 48% to 74%. Correlation between EC-K and EC-Ca values is connected with soil organic matter status; the correlation was very close for Cambisols (r2 = 0.925), a medium correlation was found for forest floor (r2 = 0.380) and a weak correlation was observed for Podzols (r2 = 0.042). The correlation between MBC-K and MBC-Ca was very close in all cases: Cambisols (r2 = 0.811), Podzols (r 2 = 0.904) and forest floor (r2 = 0.496). The ratio between organic carbon and organic nitrogen in 0.01 mol/l CaCl2 extracts [EC-Ca/N ] could be declared as a new indicator for soil microbial association status.