| Abstrakt: |
Fixation of anhydrous NH3by 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 NH3was compared to (a) nitrogen fixed from aqua‐NH3, (b) indigenous fixed NH4+, and (c) NH3retention of the whole soil (organic and mineral fraction). Mineral fixation of anhydrous NH3varied 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 NH3retention, mineral fixation of NH3caused lattice collapse from 14Å. to 10Å. in some samples. Mineral fixation of anhydrous NH3by 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 NH3retained, 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 NH3in the surface and subsurface horizons, respectively, was previously satisfied by indigenous fixed NH4+. |
