Mineral Fixation of Anhydrous NH3 by Air-Dry Soils
1962
Young, J. L. | Cattani, R. A.
Fixation of anhydrous NH₃ by the mineral fraction of air-dry samples from 65 horizons in 17 Pacific Northwest soils was investigated. Soils represented a wide variety of great soil groups. Nitrogen fixed from anhydrous NH₃ was compared to (a) nitrogen fixed from aqua-NH₃, (b) indigenous fixed NH₄⁺, and (c) NH₃ retention of the whole soil (organic and mineral fraction). Mineral fixation of anhydrous NH₃ varied greatly between soils and between horizons within individual profiles. Values ranged from 6 to 1015 ppm. N and appeared large enough to have possible practical significance in some soils. Though small in comparison to NH₃ retention, mineral fixation of NH₃ caused lattice collapse from 14Å. to 10Å. in some samples. Mineral fixation of anhydrous NH₃ by air-dry samples generally exceeded by severalfold the wet fixation of nitrogen from aqua ammonia. Ammonia retention ranged from 820 to 9190 ppm. N. Of the NH₃ retained, from 1 to 8% in the surface and from 2 to 31% in the subsurface horizons was fixed by the mineral fraction. Indigenous fixed NH₄⁺, found in all horizons, ranged from 17 to 125 ppm. N and comprised from 1 to 7.5% and from 2 to 42% of the total N in surface and subsurface horizons, respectively. From 11 to 89% and from 6 to 63% of the total mineral-fixed NH₃ in the surface and subsurface horizons, respectively, was previously satisfied by indigenous fixed NH₄⁺.
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