Abstract
The distribution of different forms of N in desert soils collected at Nevada Test Site were examined. Soil profiles were sampled in 7.6-cm increments to various depths of which the maximum was 91.4 cm. Among the soil profiles examined, the different forms of N in the surface layer (0.0–7.6 cm) was always NO2-N (not detectable) < extract-able NH4,-N < NO3-N < fixed NH4 +-N < organic N. In the sublayers, some variations from this order of N forms occurred in that the extractable NH4-N was greater than NO3 -N with the presence of trace amount of NO2-N and/or the fixed NH4-N was greater than organic N. The amount of total N was the greatest in the surface layer and usually decreased very sharply in the second layer (7.6–15.2 cm). Below the second layer, the total-N contents generally varied slightly. In the surface layers, the total N was always accounted for primarily by organic N. Depending on the soil and the profile layer, the concentration of the total extractable inorganic N ranged from 0.00004 to 0.00586 percent by weight of oven-dry soil. Expressed as percentage of total N, the range was 0.33 to 16.17. The amount of fixed NH4+-N varied somewhat with different soils, but within any given soil profile, it generally varied slightly. The fixed NH4-N in the profiles collected in different areas and under different plant species ranged from 0.0028 to 0.0079 percent by weight. Expressed as percentage of total N, the range was 3.4 to 74.4. The exchangeable K concentration under the plant was 41 to 240 percent greater than in the bare soil. The higher exchangeable K plus the higher organic matter content was considered to cause the lower NH4-N fixation under the plant compared to its fixation in the bare soil. The distribution of different forms of N in desert soils collected at Nevada Test Site were examined. Soil profiles were sampled in 7.6-cm increments to various depths of which the maximum was 91.4 cm. Among the soil profiles examined, the different forms of N in the surface layer (0.0–7.6 cm) was always NO2-N (not detectable) < extract-able NH4,-N < NO3-N < fixed NH4 +-N < organic N. In the sublayers, some variations from this order of N forms occurred in that the extractable NH4-N was greater than NO3 -N with the presence of trace amount of NO2-N and/or the fixed NH4-N was greater than organic N. The amount of total N was the greatest in the surface layer and usually decreased very sharply in the second layer (7.6–15.2 cm). Below the second layer, the total-N contents generally varied slightly. In the surface layers, the total N was always accounted for primarily by organic N. Depending on the soil and the profile layer, the concentration of the total extractable inorganic N ranged from 0.00004 to 0.00586 percent by weight of oven-dry soil. Expressed as percentage of total N, the range was 0.33 to 16.17. The amount of fixed NH4+-N varied somewhat with different soils, but within any given soil profile, it generally varied slightly. The fixed NH4-N in the profiles collected in different areas and under different plant species ranged from 0.0028 to 0.0079 percent by weight. Expressed as percentage of total N, the range was 3.4 to 74.4. The exchangeable K concentration under the plant was 41 to 240 percent greater than in the bare soil. The higher exchangeable K plus the higher organic matter content was considered to cause the lower NH4-N fixation under the plant compared to its fixation in the bare soil. © Williams & Wilkins 1973. All Rights Reserved.