Stratospheric ozone is destroyed catalytically by nitrogen oxides originating from N2O produced by denitrifying bacteria at the surface of the earth. Concern has been expressed that major perturbations in N2O production will result by the beginning of the 21st century because of increased use of industrially produced fertilizers. It is pointed out here that the reservoir of fixed nitrogen is so large that the time required to produce a significant increase in N2O production from denitrification is probably many hundreds of years.