Este fertilizante es nuevo.

Because fertilizante is a masculine singular noun, and the demonstrative has to agree with it.

• este = this, for masculine singular
• esta = this, for feminine singular

So:

• este fertilizante
• but esta planta

Even though fertilizante ends in -e, it is still masculine.

In Spanish, noun gender is not always obvious from the ending. While many masculine nouns end in -o and many feminine nouns end in -a, nouns ending in -e can be either masculine or feminine.

So with fertilizante, you simply have to learn that it is masculine:

• el fertilizante
• este fertilizante
• un fertilizante nuevo

A good habit is to learn new nouns together with their article, for example el fertilizante rather than just fertilizante.

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

Since fertilizante is masculine singular, the adjective must also be masculine singular:

• nuevo = masculine singular
• nueva = feminine singular
• nuevos = masculine plural
• nuevas = feminine plural

So:

• Este fertilizante es nuevo.
• Esta fórmula es nueva.
• Estos fertilizantes son nuevos.

Spanish has two verbs that both can mean to be: ser and estar.

Here, es is from ser, and it is used because nuevo is describing a characteristic or quality of the fertilizer: it is new.

• es nuevo = it is new

For many learners, this is a very common question because English only has one verb, to be.

In this sentence, ser is the normal choice.

Sometimes yes, but it does not mean exactly the same thing.

• es nuevo usually means it is new
• está nuevo can suggest it is in like-new condition or it looks new

So if you are simply identifying it as a new fertilizer product, es nuevo is the better choice.

Because este already works as a determiner, like this in English.

In Spanish, you normally do not say:

• el este fertilizante ❌

You say:

• este fertilizante ✅

The same happens in English:

• this fertilizer ✅
• the this fertilizer ❌

Yes, if the context is clear.

• Este fertilizante es nuevo. = full version
• Este es nuevo. = This one is new.

Spanish often leaves out repeated information when it is obvious. If you are pointing at different products, Este es nuevo sounds very natural.

Modern standard Spanish normally writes demonstratives like este, ese, aquel without an accent mark.

So in current spelling:

• este
• ese
• aquel

Older materials may sometimes show éste, but that is now generally avoided.

In standard Peninsular Spanish, the z is pronounced with the th sound from English think.

So fertilizante in Spain sounds approximately like:

• fer-tee-lee-THAN-te

Also, the c before e or i has that same sound in most of Spain.

The stress is on:

• fertiliZANte
• NUEvo

Why?

• fertilizante ends in a vowel, so without an accent mark it is normally stressed on the second-to-last syllable
• nuevo also ends in a vowel, so the stress is also on the second-to-last syllable

The normal and natural word order is:

• Este fertilizante es nuevo.

Spanish does allow word order changes for emphasis or style, but Nuevo es este fertilizante sounds unusual in everyday speech.

For a learner, the safest pattern is:

demonstrative + noun + verb + adjective

So:

• Este fertilizante es nuevo.

The plural is:

• Estos fertilizantes son nuevos.

Here everything changes to plural:

• este → estos
• fertilizante → fertilizantes
• es → son
• nuevo → nuevos

This shows how Spanish words often agree with each other in number.

Yes, but the meaning changes slightly.

• este fertilizante = this fertilizer (near the speaker)
• ese fertilizante = that fertilizer (near the listener or a bit farther away)
• aquel fertilizante = that fertilizer over there (farther away)

So este is chosen when the fertilizer is close to the speaker or being presented as this one here.