Single textbox for all rows in a grid on one form

[bolaabola]

Hello,

Description:
I have a table with columns: id, name, date.
And a form to enter data into the table. This form has a table element (grid) to enter new rows and one textbox at the top:

Question:
How can I make that textbox to specify date for all new rows in the table element (grid)?

This is simply to avoid typing the same date in all rows. Form is used only to enter new data, so it doesn't show previous data.

Thanks.