In fact, palm oil plantations cover huge hectares of land which often requires a significant amount of workforce to pick the heavy oil palm fruit.
Words like amount and number are used to communicate statistics, as in the amount of electricity, the number of deaths, etc. The same is true of workforce:
Note that you only need one statistics word – amount OR workforce. Workforce, measured here in millions of people, is all you need.
Indonesian scholars often run into similar problems with the words unemployment and population, especially in IELTS Task 1 writing:
For similar analysis, Indonesians in particular might be interested to read this post focusing on unemployment in IELTS task 1 writing, and this post looking at vocabulary for talking about workers.