soil organic carbon analysis techniques
TRANSCRIPT
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