Soil organic carbon analysis techniques

By Group VI

Soil Organic Carbon analysis

Techniques

Forms of carbon (1) elemental (2) inorganic (3) organicIn most soils (with the exception of calcareous soils) the majority of C is held as soil organic carbon (SOC).

SOC

more accurately known as the carbon stored within soil.

is a complex and varied mixture of materialsis part of the soil organic matter (SOM)used as an indicator of SOM presence in a soil or

sediment) is an essential part of any site characterization.

Soil carbon or soil organic carbon (SOC)

soil organic matter (SOM) is used to describe the organic constituents in the soil

soil organic carbon refers to the C occurring in the soil in SOM.

SOC/ SOM

Soil carbon is stored in a number of fractions with widely varying chemistry and stability.

These soil carbon fractions can be converted to the greenhouse gas carbon dioxide, and comprise: rapidly decomposable raw pieces of plants and micro-organisms that lasts for days or weeks

Background

Measuring carbon in soils is increasingly important world-wide due to its conversion to the greenhouse gas, carbon dioxide

Managing global climate change.

Importance

QUALITATIVE METHODS

SEMI-QUANTITATIVE METHODS

QUANTITATIVE TECHNIQUES

ANALYTICAL METHODS FOR

TOC DETERMINATION

Two methodsnuclear magnetic resonance (NMR) spectroscopy

diffuse reflectance infrared Fourier transform (DRIFT)

QUALITATIVE METHODS

Measuring the characteristic energy absorbed and re-emitted or dispersed by atomic nuclei Advantage no extraction of organic matter

is needed. However, these are expensive and time-consuming

NMR spectroscopy

Carbon compounds are identified by assignment of the main infrared absorption bands to the bonds being stretched or deformed at that particular frequency. Both inorganic and organic forms rapid and inexpensive

DRIFT spectroscopy

Two primary methods:loss-on-ignitionhydrogen peroxide

digestion

SEMI-QUANTITATIVE

METHODS

heated destruction of all organic matter in the soil or sediment.

ceramic crucible (or similar vessel)

3500 and 440oC

loss-on-ignition (LOI) method

through oxidation. concentrated hydrogen

peroxide (30% or 50%) Temperature: 900C

Hydrogen peroxide digestion method

no universal conversion factor Conversion

factors ranges 1.724 to as high as 2.5

Conversion factor

destructive non-destructive techniques

The destructive techniques the most common techniques

QUANTITATIVE TECHNIQUES

Three basic principleswet oxidation followed by

titration with ferrous ammonium sulfate or photometric determination of Cr3+

wet oxidation followed by the collection and measurement of evolved CO2

dry combustion at high temperatures in a furnace with the collection and detection of evolved CO2

The destructive techniques

Wet Chemistry Techniques for the determination of Total Organic Carbon.Two phases: sample extractionsample quantitation.

Conti..

Dry Chemistry Techniques Two phases: sample combustionsample quantitationCO2 is quantitated by titrimetric, gravimetric,

manometric, spectrophotometric, or gas chromatographic techniques.

are typically cited as total carbon techniques

Conti..

This technique:Involves inelastic neutron scattering and bears

mentioning can be performed in situ. is based on the detection of 4.44 MeV gamma

rays that result from the bombardment of carbon atoms with 14 MeV neutrons and the subsequent emission of gamma rays from the excited carbon.

The gamma rays are then detected, quantified, and converted to % C content.

Drawbacks is currently under development requires a radioactive neutron generator be

used and taken to the field for analysis

Non-Destructive Techniques

Near-infrared (NIR) and

Laser Induced Breakdown Spectroscopy (LIBS)

Other techniques

rapid and non-destructive involves diffuse-

reflectance measurement in the near infrared region

1000 - 2500 nm depend on the number

and type ofchemical bonds in

thematerial being analysed

NIR Techniques

to predict various soil properties including C and N content in soils

Is recognized as a practical indicator

tool to measure soil health and their basic characteristics

Advantages

is based on atomic emission spectroscopy

A laser pulse is focused on a (soil) sample, creating high temperatures and electric fields that break all chemical bonds and vaporize it into a white-hot gas of atomic ions known as micro plasma

The resulting emission spectrum is then analyzed using a spectrometer covering a spectral range from 190 to 1,000 nm.

Laser Induced Breakdown

Spectroscopy

Root respiration is a direct release of photo synthetically-fixed C,

root exudation is a process through which photosynthetic ally-fixed C enters the C pool in the soil.

Root respirationAnd

Root exudation

14C labeling is used to investigate microbial respiration of root exudates.

14C Labeling

a Plexiglas chamber, an air supply and dispensing system,

14C02 generating and infrared gas analyzer loop

two air mixing fans

Labelling apparatus