Decomposition, stages decay

Fig. 1. Generalized a—time plot summarizing characteristic kinetic behaviour observed for isothermal decompositions of solids. There are wide variations in the relative significance of the various stages (distinguished by letter in the diagram). Some stages may be negligible or absent, many reactions of solids are deceleratory throughout. A, initial reaction (often deceleratory) B, induction period C, acceleratory period D, point of inflection at maximum rate (in some reactions there is an appreciable period of constant rate) E, deceleratory (or decay) period and F, completion of reaction.

The auto-decomposition of lead tetraacetate in acetic acid, which normally occurs at reflux temperature , can be studied at 50 °C in the presence of sodium acetate The principal products of both the uncatalysed and catalysed decompositions are acetoxyacetic acid and carbon dioxide. The kinetic order of the normal decay of Pb(IV) is complex and evidence was obtained that oxidation of products is significant after the earliest stages. The evidence indicates that slow, simple homolytic breakage of lead tetraacetate to give Pb(OAc)3- and AcO-does not occur but that the solvent plays an integral part, e.g. 

Soil organic matter is a product of the decay of plants and animals. It usually includes a large number of things in various stages of decomposition. Most plant and animal materials break down rapidly at first, then more slowly as the easily decomposed parts disappear. All of these plant and animal residues are collectively referred to as organic matter. The fraction of organic matter in a relatively advanced state of decay, now decaying only slowly, may be referred to as humus. 

Figure 2.1 Pig (Sus scrofa L.) cadaver in the bloated (a) and advanced decay (b) stage of decomposition on the soil surface of a pasture near Mead, Nebraska. Cadavers were 8 weeks old and approximately 40 kg at the time of death. Cadavers were placed on the soil surface within 30 minutes of death. Arrow indicates location and direction of maggot migration. (See color insert following p. 178.)...

Figure 2.4 Putative postputrefaction fungi (Coprinus sp.) in association with a pig (Sus scrofa L.) cadaver in the advanced decay stage of decomposition 28 days after death.

Decomposition is complex.40 Decomposition rates were measured between 194° and 216°C in terms of the gas evolved. Four stages could be distinguished (1) initial rapid decomposition, (2) slow reaction, (3) extremely rapid decomposition in which approximately two thirds of the material react, (4) a short, slow decay period. The major part of the residue is Pb02, with some PbCl2. No perchlorate is formed. The reactions, therefore, probably are... 

The solution for specific cases is greatly simplified when one of the reactions (87) or (88) is much slower than the other and thus controls the initiation rate. [In radical polymerizations, this is usually reaction (87).] We know, of course, that reaction (87) can be reversible, that R° can decay by secondary decomposition to R j (the reactivity of which generally differs from that of R°), and both reactions can only be a part of a much more complicated set of interactions, especially in ionic and coordination polymerizations. An exact kinetic analysis must be based on a proved scheme with identified intermediate transition states and products, and a knowledge of the rate constants and of the rates of various initiation stages. Such a complete and complex analysis does not yet exist. 

Detrital processing can be thought of as a continuum from fresh litter to stabilized SOM (Agren and Bosatta, 2002). At different stages in this continuum, the relative importance of each of these environmental and biological factors that have been identified as controlhng decomposition dynamics will likely vary. The initial stages of mass loss are characteristically most affected by climate, resource quality, and, when abundant, soil macrofauna. The physical soil environment also needs to be considered as an important control on the turnover of more humified SOM in the mineral horizons. It is also evident from this literature review that observed correlations between decay rates and decomposition factors are often attributable to both the direct effects of that factor on microbial metabolism and to the indirect interactions with other factors. 

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