SOMfractionation is a website guiding students and scientists on soil organic matter fractionation methods.

Fractionation is conducted to elucidate the fate of organic matter in the soil. This can have several purposes, such as understanding processes of soil organic carbon (SOC) stabilization, quantification of potentially labile SOC or short-term plant available macro-nutrients, quantification of environmental changes on long-term SOC sequestration or calibration and initialization of carbon turnover models. Based on specific research questions and views of SOC turnover and stabilization, a myriad of different fractionation schemes have been developed and performed during the last three decades. Fractionation of SOC is often aimed at separating the bulk SOC into fractions with varying turnover rates.

This website will introduce the most common physical, chemical and combined (physical+chemical) methods, provide detailed guidance on how they have to be performed in the lab and provide background information on the purpose of the fraction methods and their advantages and disadvantages. This website is related to the publication “Isolating organic carbon fractions with varying turnover rates in temperate agricultural soils – A comprehensive method comparison” (under review in Soil Biology and Biochemistry) in which 20 different fractionation methods were compared with regard to isolating fractions with distinct turnover rates.

The following methods were tested in the mentioned study, and are described in detail in the guidelines:

ClassIDnDisperionDensityOx/Ex/HydSizes
PhysicalAggregates Elliot30>53>250>2000
Aggregates Six30>53>250>2000
Particles Sanderman2HMP0>50>2000
Particles Rovira4Ultrasonic0>20>50>200>2000
Density Sollins121.6
Density Sollins25Ultrasonic1.6, 2, 2.4, 2.8
Density Golchin3Ultrasonic1.6
Aggregates+Density Six10HMP1.850>53>250>2000
Particles+Density Six4HMP, glass beads1.850>53>2000
Particles+Density Shaymukhametov5Glass beads20>20>1000
Particles+Density Diochon5Glass beads1.70>5>53>250>2000
Particles+Density Steffens5Ultrasonic1.80>20>2000
Particles+Density Balesdent5Glass beads10>50>200>2000
ChemicalOxidation Mikutta2NaOCl, HA
Hydrolysis Rovira4H2SO4
CombinedParticles+Extraction Soong5Glass beadsK2SO40>63>2000
Particles+Oxidation Leifeld3UltrasonicH2O20>20
Aggregates+Oxidation Six7HMPNaOCl0>53>250>2000
Particles+Density+Oxidation Zimmermann5UltrasonicNaOCl0>0.45>53>2000
Aggregates+Particles+Density+ Extraction Kaiser10UltrasonicNa4P2O70>0.45>53>250
with method class and ID, number of fractions isolated, dispersion method (HMP=hexametaphosphate), applied density [g cm-³], chemicals used for oxidation / extraction / hydrolysis (Ox/Ex/Hyd, HA=Hydrofluoric acid), and size ranges of the isolated particles or aggregates [μm]

The guidelines are open to grow. New methods, or methods that have not been applied within the SOMfractionation initiative can also be displayed. Please send an email to axel.don@  thuenen.  de if you want to suggest additional material to be published on this platform.