Comparamos la rotación de cultivos con la asociación de cultivos.

Comparamos is the 1st person plural form (we) of the verb comparar.

So grammatically it means we compare or, depending on context, sometimes we compared. The ending -amos tells you the subject is nosotros/nosotras even though that pronoun is not written.

Yes. With -ar verbs, the nosotros form of the present indicative and the preterite can look identical.

So comparamos can be:

• present: we compare
• preterite: we compared

Only context tells you which one is meant. In an isolated sentence like this, it is ambiguous. In many textbook or explanatory contexts, it will usually be understood as the present.

Because Spanish often drops subject pronouns when the verb ending already makes the subject clear.

Here, comparamos already shows we, so nosotros is unnecessary:

• Comparamos la rotación... = natural
• Nosotros comparamos la rotación... = also correct, but more emphatic

Spanish does this much more often than English.

Because both rotación and asociación are singular feminine nouns, so they take la:

• la rotación
• la asociación

Also, Spanish often uses the definite article with general concepts where English might not. So Spanish naturally says la rotación de cultivos rather than leaving the article out.

De cultivos is a general, category-style phrase: it means something like of crops / involving crops.

Spanish often uses a bare plural after de when talking about something in general:

• rotación de cultivos
• asociación de cultivos

If you said de los cultivos, that would sound more like you mean specific crops already known in the context.

So:

• de cultivos = crops in general
• de los cultivos = the specific crops

Because the normal pattern for compare X with Y in Spanish is:

comparar algo con algo

So:

• Comparamos la rotación de cultivos con la asociación de cultivos.

You may also encounter comparar algo a algo, but that usually has a more literary sense of likening one thing to another, not simply comparing two things side by side. For everyday use, con is the safest choice.

Not always, but here it is very natural and clear to repeat it.

The full phrase names two agricultural techniques:

• la rotación de cultivos
• la asociación de cultivos

You could sometimes shorten the second one if the context is obvious, but repeating de cultivos makes the comparison precise and avoids any doubt. In explanatory or formal language, that repetition is completely normal.

Because the sentence is talking about each one as a concept or method, not about multiple individual rotations or associations.

So Spanish uses the singular:

• la rotación de cultivos
• la asociación de cultivos

This is similar to English using singular abstract nouns in phrases like crop rotation.

Both words end in -n, so without an accent mark, Spanish would normally stress the second-to-last syllable.

But these words are stressed on the last syllable:

• ro-ta-CIÓN
• a-so-cia-CIÓN

That is why they need a written accent on ó.

A Spain-Spanish pronunciation would be approximately:

kohm-pah-RA-mohs la roh-tah-THYON de kool-TEE-bos kon la ah-soh-thyah-THYON de kool-TEE-bos

A few useful pronunciation points:

• comparamos → stress on -ra-
• rotación → stress on the last syllable
• asociación → stress on the last syllable
• In most of Spain, c before i/e sounds like th in think, so:
  • rotación has -thión
  • asociación also has that th sound

If you hear a Latin American pronunciation, that c sound is usually s instead.