EVERGREEN ECOAG 2005 - Soil Organic Matter (52 pages)

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Soil Organic Matter



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Soil Organic Matter

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Pages:
52
School:
Evergreen State College
Course:
Ecoag 2005 - ECOLOGICAL AGRICULTURE

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Soil Organic Matter Martha Rosemeyer January 20 2006 Ecological Agriculture Cornerstone of organic agriculture Organic matter content of soil is the most single important Rodale vs Sir Albert Howard Is adding organic matter is sufficient or need to pay attention to minerals as well Why important Soil quality the capacity of the soil to function to sustain plant and animal productivity maintain or enhance water and air quality and support human health and habitation depends on quality and quantity of soil organic matter Three times more C in soil than in world s vegetation Important in global warming Outline The C cycle C in soil pools Management of SOC Questions BW CH 12 SOM can naturally vary from 1 to 47 What is soil organic matter SOM Originates from plant tissue primarily and animal secondarily soil and above ground as well as microbial Three parts 1 Living plant animal and soil organisms 2 Dead roots and other identifiable residues detritus 3 non identifiable amorphous and colloidal materials humus Contains carbon Plant tissue Rapid decomposition Sugar starch and simple proteins Hemicellulose Cellulose Fats and waxes Lignins and phenolics Slow decomposition Elements Figure 12 2 Decomposition Carbon compounds oxidized to CO2 Essential plant nutrients mineralized immobilized depending on each element Resistant compounds formed fulvic and humic acids Organic decay process through time Microbial respiration peaks as microbes use up easily degradable substrates Figure 12 3 Small resident pop n of active organisms autochthonous Fresh material stimulates group of inactive opportunistic zymogenous organisms Microbial pop n at peak is 1 6 of SOM Priming effect stimulates breakdown of resistant microorganisms Mineralization due to death of microbial pop n due to lack of substrate and predation N S from protein breakdown Carbon can be chemically protected humus or physical protection with clay Factors controlling decomposition and mineralization Environmental conditions



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