Tekuté hnojivo dám do vody.

Because tekuté is an adjective agreeing with hnojivo.

• hnojivo is neuter singular
• in this sentence it is in the accusative (direct object)
• for many neuter singular adjectives, the nominative and accusative ending is -é

So:

• tekutý = base dictionary form, masculine
• tekuté hnojivo = neuter singular form matching hnojivo

Hnojivo is neuter.

A very common clue is the ending:

• nouns ending in -o are often neuter
• so hnojivo follows a very common neuter pattern

Because it is neuter, words agreeing with it also take neuter forms, such as tekuté.

It is in the accusative, because it is the direct object of the verb dám.

The sentence structure is basically:

• dám = I will put / I put
• co? = what? → tekuté hnojivo

For neuter singular nouns, the nominative and accusative are often identical, so hnojivo looks the same in both cases.

This is a very common Czech aspect question.

• dát is perfective
• dávat is imperfective

So:

• dám = I will put / I’ll place (one completed action)
• dávám = I am putting / I put habitually / I usually put

A key point: the present-tense form of a perfective verb usually has future meaning in English.

So dám is literally a present form, but it usually means something like:

• I’ll put
• I will add

If you said dávám do vody, it would suggest an ongoing or repeated action instead.

Because the preposition do requires the genitive case.

The noun is:

• voda = water

But after do, it changes to genitive singular:

• do vody = into water / into the water

So this is not optional word shape; it is required by the preposition.

Because Czech distinguishes between:

• movement into somewhere → do
• location in/inside somewhere → v / ve

So:

• do vody = into the water
• ve vodě = in the water

In your sentence, the fertilizer is being moved into the water, so do is the correct choice.

Czech word order is more flexible than English because cases show grammatical roles.

This sentence is grammatical, but starting with Tekuté hnojivo gives it a certain emphasis or topic-like feeling, something like:

• As for the liquid fertilizer, I’ll put it into the water.

A more neutral order in many contexts would be:

• Dám tekuté hnojivo do vody.

So the original word order is fine, but it is not the only possibility, and it may reflect context or emphasis.

Because Czech does not have articles like English a/an/the.

So hnojivo can mean, depending on context:

• fertilizer
• the fertilizer
• a fertilizer

And do vody can mean:

• into water
• into the water

Czech usually leaves this to context rather than using articles.

Because Czech usually does not need subject pronouns unless you want emphasis or contrast.

The verb ending already tells you the subject:

• dám = I will put

So já is unnecessary here.

If you did say Já dám tekuté hnojivo do vody, it would sound more emphatic, like:

• I’ll put the liquid fertilizer into the water.

A few useful points:

• dám has a long á, so it is pronounced longer than short a
• tekuté has stress on the first syllable: TE-ku-té
• Czech stress is almost always on the first syllable of the word
• the final -é is also a long vowel

Very roughly:

• dám ≈ daam
• tekuté ≈ TEH-ku-teh with the last vowel held a bit longer

The exact sounds are Czech sounds, of course, but those are the main things an English speaker usually needs to notice.

Yes. That is also correct.

Because Czech cases show the relationships between words, you can often rearrange the sentence. Different orders change the information focus:

• Tekuté hnojivo dám do vody. → focus on the liquid fertilizer
• Do vody dám tekuté hnojivo. → focus on where it’s going
• Dám tekuté hnojivo do vody. → often the most neutral, all-purpose order

So all of these can be correct; the best choice depends on context.