NO3=>N2 is not going to be a large component in a planted tank.
As mentioned by Sean, O2 is going to change things for the substrate.
You can measure the amount of NO3 removed by this process by removing the plants and then measuring the NO3 loss without fish/critters etc by several doses of KNO3 to know values.
Then you can get the rate. I did this in the past with a flourite sub at 4 " deep. I did not find much decline over the course of a week, perhaps 2-4ppm.
Other substrates might perform better(higher rate).
If NO3 export is your goal and the plants in the tank cannot do the job enough, lower the fish load etc, or add more plants in a filtration section, they will remove far more NO3 than any anaerobic/anoxic bacteria will, aerobic organisms are about 18X more efficent at that than any DBS/substrate process.
Regards,
Tom Barr