Controlling area blank in purchase requisition triggered from S.O.

Hello Experts,

I have two different purchase reqisition triggered from two different sales order. When I checked the account assignment for both purchase requisition, G/L account determined is the same for both purchase reqisition. However, Controlling area determined in one purchase requisition and in another purchase requisition it is blank. Request you to help me how to trace why co area is blank in one purchase requisition.

Thanks and Regards,

Dharmendra Verma