Gaseous nitrogen losses from15NH4+that was exogenously applied to desert surface soils which were then incubated under aerobic conditions for 35 days at constant 25% moisture reached 81% with plant material added and 75% without an exogenous carbon source. At a decreasing moisture regime, the respective values were 79% and 87%. The losses were attributed to denitrification and, partially, to dissimilatory N2O release during nitrification. Ammonia volatilization reached a plateau after 4 days, did not exceed 5% of the total15NH4+added, and was significantly higher in the plant interspace soils than in the canopy soils.