Learn Italian: Meno pesticidi si usano, più la terra è sana. - The fewer pesticides are used, the healthier the soil is.

In English, you say 'the fewer... the healthier...'. In Italian, you never use definite articles before the comparative words in these correlative clauses. You just use meno (fewer) and più (more) directly. The literal structure is 'Fewer pesticides are used, more the soil is healthy.'

Why doesn't meno change to match the plural noun pesticidi?

When più and meno act as adjectives meaning 'more' or 'fewer/less', they are invariable. They never change their endings to match gender or number, unlike words such as tanto or poco (which would become pochi pesticidi).

Why is the verb usano in the plural form?

This uses the passive si (si passivante). Because the action is happening to a plural noun (pesticidi), that noun becomes the grammatical subject of the sentence. Therefore, the verb must be plural to match it, translating to 'pesticides are used.'

Could I change the word order in the second half to più sana è la terra?

Yes, Italian word order is quite flexible in these structures. You can say più la terra è sana, più è sana la terra, or più sana è la terra. Keeping the standard subject-verb-adjective order, as shown in this sentence, is very common and natural.