The biggest fertilizer is ammonia. It's made from nitrogen that comes from the air and hydrogen that comes from methane. Conveniently, methane can be burnt to c

The biggest fertilizer is ammonia. It's made from nitrogen that comes from the air and hydrogen that comes from methane. Conveniently, methane can be burnt to create the high temperature environment in which the reaction must take place. The other major fertilizer is potash. It is mined, but can also be extracted from underground brines, both natural and those produced from water pumped into deep wells and brought back up. If you took away the methane, you could heat the reactor electrically and produce hydrogen from water. It would be more expensive and use more energy, but it would work. Although potassium is a nonrenewable resource it is not likely to run out any time soon.