If possible that would seem ideal, however we don't exactly have tons of excess fossil fuel free methane just sitting around waiting to be used, atleast compared to the absolutely massive amount of fertilizer we need to produce to feed farmland. And if you are eliminating the fossil fuel from production, you might as well eliminate the methane component too and produce hydrogen on-site from water.

The main problem is just the energy cost because ammonia and urea both contain an ass ton of energy, 90% of which is coming from the the fossil fuel sourced methane. 1% of total world electrical production already goes into fertilizer production, and eliminating the fossil fuel component increases energy requirements near 10x over.

I had understood that e.g. landfill methane capture was this promising new (and cheap) idea that people just aren't executing because of a lack of political will. Is it not so straightforward?