السماد في التربة.

It is naturally read as a complete sentence in MSA, especially with the period.

Arabic often makes a full sentence without a present-tense verb to be. So this is a nominal sentence:

• السماد = the topic / subject
• في التربة = the comment / predicate

So the structure is basically:

• the fertilizer
  • in the soil

In English you need is, but in Arabic you normally do not use a separate word for is in the present tense.

It is understood, not spoken.

In present-tense nominal sentences, Arabic usually leaves out is / am / are. So:

• السماد في التربة = The fertilizer is in the soil
• not because Arabic forgot the verb, but because this is the normal grammar pattern

If you wanted a past-tense version, then Arabic would normally use a verb, for example a form meaning was.

Because الـ is the Arabic definite article, equivalent to the.

So:

• السماد = the fertilizer
• التربة = the soil

A few useful points:

• الـ is attached directly to the noun in writing
• it is not written as a separate word like English the
• a noun with الـ is definite
• definite nouns do not take tanwīn

So both nouns here are definite.

في is the preposition meaning in.

Its main grammar effect here is that the noun after it becomes genitive. So if you fully vowel the sentence, you get:

• في التربةِ

That final -i sound on التربةِ shows the genitive case.

So the structure is:

• في = preposition
• التربةِ = noun governed by the preposition

That final letter is tāʾ marbūṭa: ة.

It is very common at the end of nouns, especially feminine nouns. In this word, it is part of the normal spelling of تربة.

Its pronunciation changes depending on context:

• in pause, it is usually pronounced like -a or -ah
  
  • التربة → at-turbah
• when connected in full grammar pronunciation, it can sound like -at or -ati
  
  • after في: في التربةِ → fi t-turbati

So English speakers often hear both the -a(h) sound and a t sound in different situations.

Here, الـ is pronounced differently from how it is written because both س and ت are sun letters.

That means the ل sound of الـ is assimilated to the next consonant.

So:

• السماد is pronounced as-simād
• التربة is pronounced at-turbah or at-turbati in connected reading

Important:

• the ل is still written
• but in pronunciation, you do not really hear it here
• instead, the next consonant is doubled

If fully vowelled, you would normally see a shadda on the sun letter.

A fully vowelled version would be:

السِّمادُ في التُّربةِ

The case endings are:

• السِّمادُ → nominative -u
• التُّربةِ → genitive -i because it follows في

So grammatically:

• السمادُ is the mubtadaʾ (the topic/subject of the nominal sentence)
• في التربةِ is the khabar (the predicate), and inside it التربةِ is genitive after the preposition

In normal everyday writing, these short vowels are usually omitted.

The structure is:

• noun
• • prepositional phrase

More traditionally:

• السماد = مبتدأ (mubtadaʾ)
• في التربة = خبر (khabar)

So Arabic is doing a topic + comment structure:

• The fertilizer → what about it?
• In the soil → that is the information being given about it

This is a very common and useful Arabic pattern.

A careful full reading would be approximately:

as-simādu fi t-turbati

A more pause-based reading, which is also very common, would sound more like:

as-simād fī t-turbah

Why the difference?

• in careful grammatical reading, final case vowels are pronounced
• in pause, final short vowels are often dropped
• ة at the end is then heard as -ah

So both styles are useful to recognize.