Isotopic Labeling of Soil Nitrate Pools Using 15N-Nitric Oxide Gas

Document Type


Journal/Book Title/Conference

Soil Science Society of America Journal



Publication Date


First Page


Last Page



In N cycling studies, soil NO3 pools are typically labeled by adding solutions containing 15NO3. The associated increase in moisture may perturb the system and preclude measurement of N-cycle processes in relatively dry soils. This study examined the feasibility of using 15N-NO gas to label soil NO3 pools without addition of water. Soil samples (ashed, oven dry, or with soil water potentials ranging from −3.7 to −0.2 kJ kg−1 [1 MPa = 1 kJ kg−1]) were exposed to various quantities of NO gas (0–600 mg NO-N kg−1 soil). Maximum recovery of NO-N in soil NO2 and NO3 pools occurred after <2 h of exposure to the gas and ranged from ≈ 40% for moist soil samples to >90% in ashed soil. Relative increases in either NO2 or NO3 depended on the initial NO concentration and the soil treatment. In general, higher soil moisture resulted in higher NO2/NO3 ratios. Within 20 h of addition of 15NO, almost all of the NO2 was converted to NO3; however, a small amount was also converted to NH+4 and organic N. These results demonstrate that 15NO can be used to label soil NO3 pools without addition of water. Depending on the objectives of the study, however, it may be necessary to monitor the enrichment of a variety of other soil N pools as well.

This document is currently not available here.