[Wonder Warthog]

"...and chemical fertilizers derived from petroleum. "

Pretty much all chemical fertilizers these days use natural gas to provide the necessary energy for their synthesis. You need the petroleum stuff to fuel and lube the machinery. (Note...former farm boy, born and raised).

[Mr Ramsbotham]

Pretty much all chemical fertilizers these days use natural gas to provide the necessary energy for their synthesis.

I was thinking of the raw material, but of course there's the energy factor in producing it. Bottom line: farming is energy-intensive.