Stability of organic matter

The rate of organic residue decomposition in soils and related environments is ultimately controlled by its biological stability, which is a function of the following four main factors, namely, (i) its biochemical recalcitrance, (ii) the biological capability and capacity of the environment, (iii) decomposition rate modifiers (e.g., temperature, moisture, exposure time) and (iv) physical protection mechanisms (Baldock et al., 2004). Recent studies have shown that the physical protection mechanisms, such as the spatial inaccessibility of organic matter in soil micropores, are the most important factors in controlling the stability of organic matter in soils (Mikutta et al., 2006 von Liitzow et al., 2006). 

Source Adapted from von Ltitzow, M., Kogel-Knabner, I., Ekschmitt, K., et al. (2006). Stabilization of organic matter in temperate soils mechanisms and their relevance under different soil conditions—a review. Eur. J. Soil Sci. 57,426-445, with permission from Wiley-Blackwell. 

Figure 14.5. Fatty acids patterns of soils under long-term monoculture, (a) Lipid extract of soil under maize, unfertilized, after derivatization with tetramethylammonium hydroxide determined by conventional gas chromatography/mass spectrometry (GC/MS) in comparison to direct, in-source pyrolysis-field ionization mass spectrometry (Py-FIMS) without derivatization (Jandl et al., unpublished), (b) Py-FIMS of lipid extract of soil under rye, farmyard manure (FYM) treatment, compared to solid extraction residue, both directly measured without derivatization. Reprinted from Marschner, B., Brodowski, S., Dreves, A., et al. (2008). How relevant is recalcitrance for the stabilization of organic matter in soils Journal of Plant Nutrition and Soil Science 171, 91-110, with permission from Wiley-VCH.

The stability of organic matter in soils formed from rhyolitic or andesitic ash has long been noted and has been attributed to the formation of complexes between organic matter... 

Sewage becomes offensive due to its own instability together with the objectionable concentration of suspended materials. In addition, the potential presence of disease producing organisms makes sewage dangerous. Removal or stabilization of sewage matters may be accomplished in treatment works by a number of different methods or by a suitable combination of these methods. 

The presence of organic matter or other reducible material also markedly affects the thermal stability of nitrates and the use of KNO3 in gunpowder has been known for centuries (p. 645). 

Soil physical properties most likely to be altered by biomass burning are soil structure, soil wettability, and clay mineralogy (Table HI) (43). The destruction of organic matter results in losses of soil structure, increases in bulk density, diminished aggregate stability and decreases in macropore space (44). 

Simple organic molecules such as small carboxylic acids (oxalate, acetate, malonate, citrate, etc.), amino acids and phenols are all ligands for metals. Such compounds may all occur as degradation products of organic matter in natural waters. The complexes formed are typically charged hydrophilic complexes. The stability of the metal complexes with these ligands is, however, moderate in most cases. Model calculations including such compounds at realistic concentrations indicate that their effects on speciation are relatively small [29],... 

Biochemical Oxygen Demand (BOD) The amount of oxygen required by bacteria stabilize decomposable organic matter under aerobic conditions. 

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