Looks like a "many to many" relationship where you need at least three tables instead of two to properly record what you are doing here--and possibly more tables than that.
Invoices::InvoiceID = Applications::InvoiceID
FarmFields::FieldID = Applications::FieldID
In your portal to applications, you'd use a drop down of FieldID's and names to select a Field for each chemical application record. That way, you have a single portal where each row documents both what is being applied and to which field.