Q. I need help finding an article about mathematics in agriculture prior 500 B.C.E

Begin my narrowing your search from the entire ancient world to maybe 1 or 2 locations, perhaps ancient Greece, Egypt, India, or China.

I recommend checking a variety of locations for this sort of question:

EBSCO e-books
JSTOR
AGRICOLA
Academic Search Complete

You can actually go into something like Academic Search Complete and do your search and then go to the top next to where it says "Searching: Academic Search Complete" and click "Choose databases". You can add multiple databases or even all of them to search simultaneously.