The rice lacks salt.
To my understanding I translated the above sentence into
El arroz escaso de sal.
However, it turned out to be incorrect as I was practicing the spanish grammar. The correct answer turned out to be
El arroz está escaso de sal.
I did not get much sense either when I tried to translate this sentence to English as it would be something like
The rice is lack of salt.
So I would like to know what role does 'esta' plays in above sentence? And why the sentence would be incorrect without the use of it?