Three techniques (buried bag, resin membrane, and cellulose disk approaches) for assessing the nitrogen-15 (15N) concentration of the soil N pool available to plants were evaluated by initiating buried bag N-mineralization, resin membrane, and cellulose disk incubations in coordination with the germination of two non-N2-fixing reference plants in four types of 15N-enriched soil. In turn, the incubation samples and reference plants were collected after 45 and 90 days for 15N analysis. The deviation from the reference plant 15N concentration averaged across all four soil types was least for the cellulose disk technique (3.8 ± 2.3 and 3.5 ± 3.8‰) followed by the buried bag (9.8 ± 5.5 and 4.5 ± 2.5‰) and resin membrane (38.4 ± 11.9 and 21.7 ± 1.6‰) techniques on days 45 and 90, respectively. Also, the linear relationships between soil 15N concentrations and corresponding cellulose disk and reference plant 15N concentrations had high coefficients of determination (average R 2 = 0.96 ± 0.03) and comparable slope and intercept parameters, whereas the linear relationships between soil 15N concentrations and corresponding buried bag soil and resin membrane 15N concentrations were not significant. Overall, the relatively new cellulose disk technique was considered to be the most reliable and practical (i.e., inexpensive and easy to employ) approach for assessing plant-available 15N concentrations in the relatively coarse textured and infertile soils used in this assessment.