Using Chosen for select elements on add/edit form of jqGrid

I have jQGrid. Some of columns are edittype:"select".

{label:"Student",name:"student_id",index:"student_id",editable:true,edittype:"select",editoptions:{dataUrl:"../ajax/selects/select_student.php"}},

In my project the number of elements in selects become huge and this lead to usability drawbacks. I want to make selects in add/edit form more intelligent. For this purpose i try to use "chosen" plugin. So, i try this:

beforeShowForm: function() {
       $("#student_id").chosen();
}

In this example "student_id" is the id of select element on editform. but no effect. Select stay as usual select. Chosen functionality is not added. How can I have chosen to work on add/edit form for select elements?