wikipedia is hardly an authoritative source, but it will suffice here!
"Nitrogen fertilizers are often made using the Haber-Bosch process (invented about 1915) which uses natural gas (CH4+) for the hydrogen and nitrogen gas (N2) from the air at an elevated temperature and pressure in the presence of a catalyst to form ammonia (NH3) as the end product. This ammonia is used as a feedstock for other nitrogen fertilizers, such as anhydrous ammonium nitrate (NH4NO3) and urea (CO(NH2)2)."
A TOTALLY different thing to "heating and drying"!
