Overview

Decomposition is comprised of a series of interacting physical, chemical, and biological processes. In general, three major processes are involved in terrestrial decomposition: leaching, fragmentation, and chemical alteration. Leaching is a physical process through which ions (such as K+, Mg2+, and Ca2+) and small water-soluble organic compounds (such as sugars, amino acids, and amino sugars) dissolve in water and move out of the decomposed organic material. Leaching could happen even from green leaves still attached to the plants. These soluble materials move into the soil matrix where they are taken up by plant roots or soil microbes, adsorbed to soil minerals, or leached and transported through the soil column by water drainage. Leaching losses are greatest in environments with high precipitation and negligible in dry environments. Fragmentation is a physical process through which fresh detritus is broken down into smaller particles. During fragmentation, some chemical bases can break off from organic compounds thereby contribute to nutrient mineralization. Fragmentation also provides more fresh surfaces that can be used by microbial colonization thereby facilitating further decomposition. Biological factors are major contributors of litter fragmentation. Fragmentation is a byproduct of the feeding activities of larger animals and the direct product from the feeding of smaller organisms such as protozoan, potworm, and earthworms. Abiotic factors such as freeze-thaw and wetting-drying cycles can also facilitate litter fragmentation. Through chemical alteration, the final stage of the decomposition process, litter fragments are further broken down into simple organic and inorganic compounds. The complete decomposition, that is, the release of all the energy fixed in organic compounds, may take thousands of years if it happens at all. One of the most commonly known products of incomplete decomposition is fossil fuel, on which our modern societies heavily rely.

Organic matter Decomposition Inorganic material

Organic matter Decomposition Inorganic material

Figure 1 The process of decomposition and mineralization.

Carbon mineralization is about the same as carbon decomposition if we exclude the leaching process. Nitrogen (N) and phosphorus (P) mineralization, however, although related to decomposition, are distinct-processes. In particular, P mineralization is less-tightly linked to decomposition than N mineralization due to the chemical structure of P containing compounds. In fact, because the N atoms are directly bonded to carbon skeletons of organic matter (C—N), N is generally released as dissolved organic N (DON) in the breakdown of these skeletons, that is, in the course of the decomposition process (e.g., during fragmentation or chemical alteration). On the other hand, because P atoms can form ester linkages C—O—P, P can be released (i.e., mineralized) independent of the decomposition of organic matter, that is, with no breakdown of the carbon skeleton. N mineralization starts with the release of DON associated with decomposition. Both plants (through the mycorrhizal fungi associated with plant roots) and soil microbes can take up DON, although in most cases soil microbes outcompete plants for DON uptake. When microbial needs for DON are met, microbes break down the remaining DON using the energy released by the breakdown of the carbon skeleton and secrete NH^ to the surrounding soil matrix. This process is known as 'N mineralization'. When DON is insufficient to meet the microbial N requirement, soil microbes absorb additional N from the pool of inorganic N (e.g., NH|, NO^) in the soil solution, a process known as 'immobilization'. Immobilization also includes the removal of inorganic N from the soil solution by chemical fixation.

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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