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Soils and Tree Nitrogen

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Organic forms of nitrogen on any site are usually locked into complex and tightly held compounds. Most of these organic forms of nitrogen are unavailable for tree use. Tree-available and uptakable forms of inorganic nitrogen are primarily ammonium (NH4+) and nitrate (NO3-). Note it is possible for organic nitrogen forms like urea and free amino acids to be taken up by trees to a limited degree. Between unusable organic nitrogen forms and tree-preferred inorganic nitrogen forms, lie many soil organisms (almost exclusively bacteria). These bacteria use whatever nitrogen source is accessible to live and, in the process, transform nitrogen into another form. 

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Community and Urban Forestry
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