Microbial biomass-C determined using CaCl₂ and K₂SO₄ as extraction reagents

Abstract

Microbial biomass-C [MBC] (1) arable Cambisols (100%), (2) cut and grazed grasslands (547%), (3) forest mineral horizon A H : 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 ma�er status; the correlation was very close for Cambisols (r 2 = 0.925), a medium correlation was found for forest floor (r 2 = 0.380) and a weak correlation was observed for Podzols (r 2 = 0.042). The correlation between MBC-K and MBC-Ca was very close in all cases: Cambisols (r 2 = 0.811), Podzols (r 2 = 0.904) and forest floor (r 2 = 0.496). The ratio between organic carbon and organic nitrogen in 0.01 mol/l CaCl 2 extracts [EC-Ca/N org ] could be declared as a new indicator for soil microbial association status.

Effect of K2SO4 concentration on extractability and isotope signature (δ13C and δ15N) of soil C and N fractions

“…() for mineral horizons of forest soils (0.01 m CaCl 2 extracted 3–7 times less C than 0.5 m K 2 SO 4 ). Smaller differences for the same solutions (0.01 m CaCl 2 extracted 50–70% of C extractable with 0.5 m K 2 SO 4 ) were found for more than 60 arable, grassland and forest soils in another study (Růžek et al ., ). All these findings can be explained with the increased desorption of organic matter because of the larger concentration of a competing sulphate anion in 0.5 m K 2 SO 4 solution.…”

“…Therefore, to obtain reliable and comparable data it is necessary to know how the extractant influences C and N extractability. It is well documented that water and different salt solutions release different quantities of organic C (Joergensen, ; Reemtsma et al ., ; Gregorich et al ., ; Haney et al ., ; Růžek et al ., ; Rennert et al ., ). However, only a few comparative investigations have studied the dependence of non‐microbial and microbial C solubility on the concentration of the same (K 2 SO 4 ) extractant (Tate et al ., ; Gregorich et al ., ; Haney et al ., ; Makarov et al ., ), and even less is known about the effect of K 2 SO 4 concentration on extractability of non‐microbial and microbial N (Bruulsema & Duxbury, ; Dijkstra et al ., ; Makarov et al ., ).…”

“…Labile forms of C and N are usually extracted from soils with either water or with different concentrations of salt solutions (Hart et al ., ; Reemtsma et al ., ; Růžek et al ., ; Pörtl et al ., ; Rennert et al ., ). A concentrated 0.5 M K 2 SO 4 solution is the classical extractant of microbial biomass C and N as well as non‐microbial C and N in the fumigation‐extraction method (Brookes et al ., ; Vance et al ., ).…”

“…A wide range of smaller K 2 SO 4 concentrations have been used to study labile C, N, δ 13 C and δ 15 N (Bruulsema & Duxbury, ; Gaillard et al ., ; Haney et al ., ; Pörtl et al ., ; Zareitalabad et al ., ; Makarov et al ., 2013a,b). Some authors have used 0.01 m CaCl 2 (Joergensen, ; Růžek et al ., ) or water (Gregorich et al ., ; Haney et al ., ).…”

Microbiological parameters of soil set aside before and after desiccation

“…-K 2 SO 4 extractable carbon (EC) -extraction with 0.5 mol/l K 2 SO 4 (Vance et al 1987, Růžek et al 2005). 8 days incubation ) -arylsulphatase activity (three repetition and control): 1 g fresh soil was incubated with 4 ml acetate buffer and with 1 ml p-nitrophenylsulphate for 1 hour in 37°C (control without 1 ml p-nitrophenylsulphate); before filtration 1 ml p-nitrophenylsulphate was added to the control and 25 ml distilled water were added to both variants; 6 ml filtrate were taken and mixtured with 4 ml 0.5 mol/l NaOH; colorimetric determination in 420 nm (Tabatabai and Bremner 1970) Following ratios were calculated: -(MBC/C org ) × 100 -(EC/MBC) × 100…”