El compost incluye materia orgánica.

Because compost is treated as a masculine noun in Spanish, so it takes el.

A useful reminder:

• el compost = the compost

Spanish nouns have grammatical gender, and it does not always match any logical or real-world category. With borrowed words like compost, you usually just learn the gender together with the noun.

In Spanish, you do not always need the article where English might use the or some.

Here, materia orgánica is being used in a general, non-specific sense:

• El compost incluye materia orgánica.
• Compost includes organic matter.

This sounds natural in Spanish without la. If you said la materia orgánica, it could sound more like you are referring to a specific organic matter already known from the context.

Incluye is the third-person singular present tense of incluir (to include).

Conjugation:

• yo incluyo = I include
• tú incluyes = you include
• él / ella / usted incluye = he / she / it / you include

Since the subject is el compost, which is singular, Spanish uses incluye:

• El compost incluye... = The compost includes...

The written accent in orgánica shows where the stress goes:

• or-GÁ-ni-ca

It is the feminine singular form of orgánico.

The accent mark is important because Spanish spelling rules use accents to show pronunciation clearly. In this sentence:

• materia orgánica = organic matter

Both words are feminine singular, so they match.

Because adjectives in Spanish usually agree with the noun they describe in gender and number.

Here:

• materia is feminine singular
• so the adjective must also be feminine singular
• therefore: orgánica

Compare:

• material orgánico = organic material
• materia orgánica = organic matter

It is singular.

You can tell because:

• materia is singular
• orgánica is singular feminine to match it

Even though organic matter can refer to a mass or substance, Spanish treats materia here as a singular noun.

Yes. Contiene is also very natural here.

Both can work:

• incluye = includes
• contiene = contains

There is a slight nuance:

• incluye often suggests something is among the components or elements
• contiene focuses more on what is contained inside

In many practical contexts, both are acceptable.

A simple pronunciation guide for an English speaker is:

• El ≈ el
• compost ≈ kom-POST
• incluye ≈ een-KLOO-yeh
• materia ≈ ma-TEH-rya
• orgánica ≈ or-GA-nee-ka

A few useful pronunciation notes for Spain:

• c before a sounds like k: compost
• y in incluye sounds like a soft y
• the stress in orgánica is on GÁ

This is the most neutral and common Spanish word order:

• Subject + verb + object
• El compost
  • incluye
    • materia orgánica

That is the same basic order as in English:

• The compost includes organic matter

Spanish can change word order for emphasis, but this version is the standard, straightforward one.

Compost is used and understood, especially in environmental, gardening, and recycling contexts.

In Spain, you may also see related expressions such as:

• compostaje = composting
• abono orgánico = organic fertilizer
• compostador = composter / compost bin

So el compost is a perfectly useful word to know.

No, not normally.

In Spanish, common nouns and adjectives are not capitalized unless they begin a sentence. So:

• El compost incluye materia orgánica.

Only El is capitalized here because it starts the sentence.