Etter hvert som plantenæringen virker, blir næringsmangelen mindre alvorlig.

Etter hvert som is a fixed expression meaning something like as, as time goes on, or gradually as.

In this sentence, it shows that one thing changes progressively while another process is happening:

• Etter hvert som plantenæringen virker = as the plant nutrition/fertilizer takes effect
• blir næringsmangelen mindre alvorlig = the nutrient deficiency becomes less serious

A useful contrast:

• etter hvert on its own often means gradually or eventually
• etter hvert som introduces a whole clause: as ...

So here you should learn etter hvert som as a set phrase.

Normally, no. In this expression, som is part of the fixed conjunction etter hvert som.

It connects the two parts of the sentence and introduces the clause plantenæringen virker.

So:

• Etter hvert som plantenæringen virker = correct
• Etter hvert plantenæringen virker = not natural here

For learners, the safest approach is to memorize etter hvert som as one unit.

This is because Norwegian follows the V2 rule in main clauses: the finite verb usually comes in the second position.

Here, the whole subordinate clause comes first:

• Etter hvert som plantenæringen virker

That first clause takes the first position in the sentence. So in the main clause, the verb must come next:

• blir

Then comes the subject:

• næringsmangelen

So the order is:

• first element: Etter hvert som plantenæringen virker
• second element: blir
• then subject: næringsmangelen

If you put the main clause first, the word order becomes more familiar:

• Næringsmangelen blir mindre alvorlig etter hvert som plantenæringen virker.

That version means the same thing.

Here, virke means to work, to have an effect, or to take effect.

So plantenæringen virker means that the plant nutrition, nutrient treatment, or fertilizer is starting to do what it is supposed to do.

This verb is very common in Norwegian for things like:

• medicine: Medisinen virker = The medicine works / takes effect
• a method: Metoden virker = The method works
• treatment or fertilizer: Det virker = It works / has an effect

So this is not about working in the sense of having a job. It is about producing an effect.

Because blir shows change.

• er = is
• blir = becomes / gets

The sentence is describing a development over time: the nutrient deficiency is not simply in a state; it is becoming less serious.

Compare:

• Næringsmangelen er mindre alvorlig. = The deficiency is less serious.
  This states a condition.

• Næringsmangelen blir mindre alvorlig. = The deficiency is becoming less serious.
  This shows change.

Since the sentence contains etter hvert som, a gradual change is exactly what we expect, so blir fits very well.

Because Norwegian very often forms compound nouns as single words.

Here you have:

• plantenæringen = plante
  • næring
    • -en
• næringsmangelen = næring
  • mangel
    • -en

A few things to notice:

1. Compounds are usually one word in Norwegian
   Where English often writes separate words, Norwegian often joins them.

2. The definite article is added at the end

   • plantenæring = plant nutrition / plant nutrient supply
   • plantenæringen = the plant nutrition / the nutrient supply
   • næringsmangel = nutrient deficiency
   • næringsmangelen = the nutrient deficiency

3. The -s- in næringsmangel is a linking sound
   This is common in Norwegian compounds and does not always translate directly.

This is a very typical Norwegian word-building pattern.

The ending -en makes each noun definite:

• plantenæringen = the plant nutrition / the nutrient treatment
• næringsmangelen = the nutrient deficiency

Norwegian often uses the definite form where English might sound more general or less specific. In a technical or scientific context, the speaker may be referring to:

• the specific nutrient treatment being discussed
• the specific deficiency already identified in the context

So even if English might sometimes say something more general, Norwegian can naturally use the definite form here.

In other words, the sentence is probably talking about a known situation: the plant nutrition in question and the deficiency in question.

Mindre means less, and alvorlig means serious. Together, they mean less serious.

This is a comparative structure:

• alvorlig = serious
• mindre alvorlig = less serious
• mer alvorlig = more serious

Norwegian often forms comparisons with:

• mer = more
• mindre = less

So instead of changing the adjective itself, Norwegian often uses a separate word in front of it.

Examples:

• alvorlig = serious
• mer alvorlig = more serious
• mindre alvorlig = less serious

That is very similar to English.

Because the subject is singular:

• næringsmangelen = the nutrient deficiency

After verbs like være and bli, the adjective is predicative, and it agrees with the subject.

Here the subject is singular, so alvorlig is correct.

Also, this particular adjective can be a little deceptive because:

• singular: alvorlig
• plural/definite: alvorlige

So if the sentence were plural, you would see the difference more clearly:

• Næringsmanglene blir mindre alvorlige.
  = The nutrient deficiencies become less serious.

That makes it easier to see why alvorlig is right in your original sentence.

Yes. A very natural alternative is:

Næringsmangelen blir mindre alvorlig etter hvert som plantenæringen virker.

This means the same thing.

The difference is mainly one of structure and emphasis:

• Etter hvert som plantenæringen virker, blir næringsmangelen mindre alvorlig.
  This starts by highlighting the process over time.

• Næringsmangelen blir mindre alvorlig etter hvert som plantenæringen virker.
  This starts with the result or main point.

Both are good Norwegian. The first one is especially useful when you want to foreground the time/process relationship.