We've long known that we need more nitrogen. One idea is to use ammonia asteroids, which do double duty as a greenhouse gas ... http://www.users.globalnet.co.

We've long known that we need more nitrogen. One idea is to use ammonia asteroids, which do double duty as a greenhouse gas ... http://www.users.globalnet.co.uk/~mfogg/zubrin.htm http://www.users.globalnet.co.uk/~mfogg/zubrin.htm