Yes. Nat gas -> ammonia -> urea. Theres some efficiencies that vary by site but its a hundred year old process of a true commodity. The price per therm _is_ the input.

Was listening to a fertilizer analyst the other day. She thought corn:urea was the better comparison. Nitrogen is the cost of marginal yields. And corn:urea shows the farmer being squeezed between their commodity output price and the required input cost. At some point its just not cost effective to grow corn, so you go soy, and reduced supply should pish up future prices. Oh look! More commodity price inflation pressure!