Agricultural sector is different from economic sector in the way research is conducted.

In the noun phrases agricultural sector and economic sector, you mention specific sectors – agricultural and economic. It is obvious that you are not talking about the bananas sector and the pornography sector.

If you mention a noun and both you and your reader know exactly which noun you’re talking about, then you must use the definite article – ‘the’.

In the photo that accompanies this post, there are two puppies. If you say you want the light-coloured puppy, you use ‘the’, because it is clear both to you and to your listener exactly which puppy you want!

It’s the same when you’re talking about sectors:

• The agricultural sector is different from the economic sector in the way research is conducted.

Admittedly, identifying the main noun in a noun phrase becomes challenging with longer phrases. For example, can you identify the main noun in the following highlighted phrase? Answers in the comments section below! 🙂

• I sometimes experience difficulties with the less obvious and more subtly nuanced aspects of article use in unnecessarily complicated academic writing.

Incidentally, an English native speaker would probably use the name of the sector without labelling it ‘sector’:

• The agricultural sector is different from the economic sector in the way research is conducted.

This ‘labelling’ of nouns is discussed further in a previous post.