O adubo está pronto para usar.

O is the masculine singular definite article, meaning the.

So o adubo = the fertilizer.

Portuguese often uses articles more regularly than English. In this sentence, o adubo usually refers to a specific fertilizer already known from the context, such as the one you prepared or the one being discussed.

You could say just adubo in some contexts, but o adubo is the most natural choice when you mean a particular fertilizer.

Portuguese has two main verbs for to be: ser and estar.

Here, está is used because pronto describes a current condition or state: the fertilizer is now ready.

• está pronto = is ready
• é pronto would sound wrong here

A good way to think about it is:

• ser = identity, permanent characteristics, classification
• estar = condition, state, result

So O adubo está pronto means the fertilizer has reached the state of being ready.

Because adubo is a masculine singular noun.

In Portuguese, adjectives usually agree with the noun they describe:

• masculine singular: pronto
• feminine singular: pronta
• masculine plural: prontos
• feminine plural: prontas

So:

• o adubo está pronto
• a mistura está pronta
• os adubos estão prontos

Adubo usually means fertilizer in Brazilian Portuguese.

Depending on context, it can sometimes refer more broadly to something used to enrich soil, such as:

• fertilizer
• manure
• compost
• plant feed

But in a sentence like this, the most natural translation is usually fertilizer.

Literally, para usar means to use or for using, but in natural English it usually becomes:

• ready to use
• ready for use

So:

• O adubo está pronto para usar. = The fertilizer is ready to use.

This pattern is very common in Portuguese:

• água pronta para beber = water ready to drink
• comida pronta para servir = food ready to serve

Because after para in this kind of structure, Portuguese commonly uses the infinitive.

Pattern:

• para + infinitive

Examples:

• para comer = to eat
• para beber = to drink
• para plantar = to plant
• para usar = to use

So pronto para usar is a standard construction meaning ready to use.

The subject of usar is left general or understood from context.

In English, ready to use also leaves the user unspecified. Portuguese does the same.

So O adubo está pronto para usar means something like:

• the fertilizer is ready for someone to use
• the fertilizer is ready to be used

Portuguese often leaves this kind of subject unspoken when it is obvious or not important.

Yes. O adubo está pronto para ser usado is correct and means:

• The fertilizer is ready to be used

This version is a bit more explicit and passive.

Compare:

• pronto para usar = ready to use
• pronto para ser usado = ready to be used

In everyday Brazilian Portuguese, pronto para usar is usually shorter and more natural.

Not exactly.

• pronto para usar = ready to use
• pronto para uso = ready for use

Both can work, but para usar sounds more verbal and everyday, while para uso sounds a little more formal or technical.

So in normal speech, pronto para usar is very common.

A natural Brazilian pronunciation is approximately:

o ah-DOO-boo es-TAH PRON-too PA-ra oo-ZAR

A few helpful notes:

• o often sounds close to oo when unstressed
• adubo has stress on du
• está has stress on the final á
• pronto has a nasal sound in pron
• usar has a z sound: oo-ZAR

In casual Brazilian speech, para is often reduced to pra:

• O adubo está pronto pra usar.

Yes. In English, both are natural translations depending on context.

• ready to use sounds more everyday
• ready for use sounds a little more formal

The Portuguese sentence itself does not strongly force one or the other. It simply says the fertilizer is in a usable, ready state.

Yes, this is a perfectly natural sentence.

A very common spoken version would be:

O adubo tá pronto pra usar.

That is just a more informal pronunciation/spelling of:

• está → tá
• para → pra

So:

• O adubo está pronto para usar. = neutral / standard
• O adubo tá pronto pra usar. = informal / conversational