Fill DropDownList According to Conditions

Hi All,
I am using VS05 + c#. In my application i have filled data from Databse and bind to DropDownList .This data is come from my master table ie.CropMaster. If user want to fill Any crop in that master at that time i have given i link for that master form.
I want when user click on link for CropMaster which is present on User.aspx and redirect to that page ie.CropMaster.aspx and fill CropName
at that time the The crop which is filled in master should automatically bind to DropDownList which is Present on User.aspx .
Inshort i want to fill DropDownList for CropName On User.aspx whenever user fill CropName in CropMaster.
How can i do this?

Thanks in advance. ...