A question about resource fields

Hi all,

I've noticed a difference in total production between my own capital city, and a village of someone I sit for. I was hoping someone could explain what may be causing the difference.

I have increased all 4 woodlots in my capital to level 10 which produce a total of 960 units (200units x 4 fields x 20% bonus from lvl 4 sawmill). My friend has done the exact same, but his total production is 1200.

The only things that are not equal is that:
1) I am Roman and he is Teuton.
2) My village is my capital, and his is 2nd village.

Any answers/possible ideas would be appreciated.

AJB

He uses gold or has an oasis.

Thanks VAO for your answer. I am double checking with my sitting partner (Lincoln from Flank).

Yes it is because he is using gold. Thanks