na-adjective, noun
Describes soil or land that is naturally rich and good for growing crops. Also used figuratively for a fertile mind or creative environment.
この地域の土壌は非常に肥沃だ。
The soil in this region is very fertile.
肥沃な土地で作物がよく育つ。
Crops grow well on fertile land.
豊か is a broader term for abundance, wealth, or richness in general, while 肥沃 specifically refers to soil fertility.
Compound of 肥 (ひ, 'fertilizer, manure') and 沃 (よく, 'fertile, rich'). Both kanji contribute the meaning of fertility.