What are the atmospheric contents of Mars?

The Martian atmosphere is mainly CO2 and as Mars atmosphere is so thin it actually has about the same amount of CO2 in its atmosphere as earth. So there really isn�t alot there. There is even less nitrogen. And as nitrogen is essential to life this also means that humans can never settle on Mars. Because what are you going to eat considering that the Martian atmosphere doesn�t even have enough nitrogen to grow the gr on a golfcourse?