Imam dovoljno krompira.

• Imam = I have
• dovoljno = enough
• krompira = a genitive form of krompir, meaning potato / potatoes

So the whole sentence means I have enough potatoes.

Because here dovoljno is being used as an indeclinable quantity word, meaning enough.

Compare:

• Imam dovoljno krompira. = I have enough potatoes.
• Krompir je dovoljan. = The potato / potatoes are sufficient.

In the first sentence, dovoljno talks about quantity, so it stays dovoljno.
In the second, dovoljan is an adjective agreeing with a noun.

Because after quantity words like dovoljno, Serbian normally uses the genitive form of the noun.

That is why you get:

• dovoljno krompira
• mnogo krompira
• malo krompira
• puno krompira

So even though the basic dictionary form is krompir, after dovoljno it becomes krompira.

Krompire is a different form, usually the accusative plural.

You would use that form in sentences like:

• Vidim krompire. = I see the potatoes.

But in Imam dovoljno krompira, the noun is not a regular direct object by itself. It is part of a quantity expression with dovoljno, and that expression requires the genitive: krompira.

Formally, krompira can match more than one genitive pattern, so learners often get confused.

The important practical point is this: after dovoljno, you use krompira. In meaning, the sentence naturally comes across as enough potatoes.

With food words, Serbian often talks about an unspecified amount rather than clearly separating singular and plural the way English does.

Because Serbian often drops subject pronouns when they are already clear from the verb form.

• Imam already means I have
• so ja is usually unnecessary

That makes Imam dovoljno krompira the most natural neutral version.

Yes, absolutely.

Adding ja is possible, but it usually adds emphasis, contrast, or a more explicit tone.

For example:

• Ja imam dovoljno krompira, ali on nema.
  I have enough potatoes, but he doesn’t.

So:

• Imam dovoljno krompira. = neutral
• Ja imam dovoljno krompira. = more emphatic

Yes. Serbian word order is fairly flexible.

The neutral order here is:

• Imam dovoljno krompira.

But you may also hear:

• Dovoljno krompira imam.
• Krompira imam dovoljno.

These alternatives are more marked and usually shift the focus or emphasis.

A learner should usually stick with Imam dovoljno krompira first.

A rough pronunciation guide is:

• Imam ≈ EE-mahm
• dovoljno ≈ doh-VOHL-nyoh
• krompira ≈ krom-PEE-rah

A few notes:

• lj in dovoljno is a single Serbian sound, similar to the lli in million for many English speakers.
• Stress is not usually written in normal Serbian spelling, so listening to native audio is very helpful.

You say:

• Nemam dovoljno krompira. = I don’t have enough potatoes.

Here nemam is the negative form of imam.

Yes, but it is not exactly the same.

• Imam dovoljno krompira = I have enough potatoes
  This clearly focuses on sufficiency.

• Imam dosta krompira = I have quite a lot of potatoes
  This often focuses more on a large amount.

Sometimes dosta can feel close to enough, but if you specifically want the idea of sufficient, dovoljno is the clearest choice.