The settlement of organic soils can be caused by the decomposition of the organic fraction without any change in the effective stresses in a given soil profile. Are there any new techniques for estimating the settlement of organic soils due to reduction in organic content?
Spectroscopic analysis of soils does give a precise fingerprint of soil structure as a function of chemical structure. Interpretation however is unavoidably pH dependent: the same chemical structure at pH 5.5 will not have the same fingerprint as at pH 7.5. Soil decomposition mechanisms will include oxidative and/or reductive processes, and if one balances any redox reaction, there is always a change in pH: H+ ions are either created or consumed. So in effect if does not return to the starting pH, the accounting of what is happening during soil decomposition is biased and correspondingly results are less reproducible and less self consistent than what one may desire.
Solving the soil decomposition measurement chemically requires extracting the components without adding to the decomposition in the process. The attached article by Dr. Heighton demonstrates if one protects soil from further oxidation and then maximized chemical reduction [in this case using Sodium Borohydride], both the amount and the chemical decomposition of the actual functional groups in soils can be monitored over time. Reduction often correlates with the loss the oxygen component in soils, e.g. humic substances. The loss of the nitrogen components in soils, e.g. fulvic substances follows a different chemical pathways form those without nitrogen components.
If you have any further question, please feel free to ask.
Kind regards,
Walter.
Just thought of one important thing I had forgotten. Carbohydrate soil degradation as oxidation is forming CO2 [and also forming H2O from burning H component in soils]. The chemical composition of soils however also changes from CH2-CHOH going to CH=CH resulting chemically in the loss of water. It is an rearrangement process, not an oxidation reaction even though water is produced. The reductive process results in an increasing number of double bonds. The increased number of double bonds also results in conjugation and extended conjugation which in turn is responsible for the fluorescence often present in soils.
Specific H-C=C-H sites can have high affinity for / complex soil metal ions such as ferric and ferrous salts. Historically, analyzing the composition and decomposition of soil samples has bee a bear, and sometime more often than not a grizzly bear or more than one grizzly bear.
Dr. Heighton's manuscript is the evidence of what one can know about soil structure when the organic wet-chemistry portion and modern instrumental techniques (including Raman spectroscopy) are both done with equal rigor.
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