Learn Spanish (Latin America): Normalmente, los cultivos se suelen revisar cada dos días. - Normally, the cultures are usually checked every two days.

Because this is a passive reflexive sentence, and the grammatical subject is the plural noun los cultivos. When you have a verb phrase made of a conjugated verb plus an infinitive, the conjugated verb must agree with the plural subject receiving the action.

Can I attach the se to the end of the infinitive instead?

Yes! You can say los cultivos suelen revisarse. When working with an infinitive, you always have the choice to put the pronoun before the conjugated verb (se suelen revisar) or attached to the infinitive (suelen revisarse). In both cases, suelen must remain plural.

How does soler work to mean "are usually checked"?

The verb soler followed by an infinitive is used to express that an action happens "usually" or "tends to" happen. When combined with the passive se, se suelen revisar translates literally as "they tend to be checked," which is the most natural way to say "they are usually checked" in Spanish.

Is it completely wrong to say se suele revisar los cultivos?