Fixation of Ammonia by Organic Soils
1961
Burge, W. D. | Broadbent, F. E.
Ammonia fixation in organic soils of varying carbon content was found to be linearly correlated with percent carbon. In the presence of oxygen 1 molecule of ammonia was fixed per 29 atoms of carbon, and 1 for every 45 atoms of carbon in the absence of oxygen. Treatment of these organic soils with ammonia usually resulted in decreased capacity to retain barium and cupric ions, but the amount of ammonia fixed bore no quantitative relation to the decrease in cation retention. Blocking hydroxyl groups in soil organic matter by treating with dimethyl sulfate decreased the capacity of the organic matter to fix ammonia, indicating that these groups are involved in the fixation reaction. Aldehyde groupings are apparently not involved. Formation of amides through the action of anhydrous ammonia on carboxylic esters may play a minor role in ammonia fixation. A tracer experiment showed that fixed ammonia is slowly made available to plants.
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