By making a callback to a dropdown loses the style (if the first dropdown the form, if not so it's okay)
I put the code here:
$crud->callback_field ( 'id_provincia', array ( $this, '_callback_field_provincia' ) );
 // Ayudante de funciones de Filtrar DropDowns según el usuario logeado
function filter_dropdown($table, $id_table, $desc_table, $id_field)
{
 $this->db->select ( '*' );
 $this->db->from ( $table );
 $this->db->where ( $id_table, $id_field );
 $result = $this->db->get ();
 $data = $result->row ();	
 $html = '<div><select name="'.$id_table.'" class="chosen-select" data-placeholder="Selecciona '.ucwords($table).'" style="width: 200px;">';
 $html.= '<option value=""></option>';
 $html.= '<option value="'.$data->$id_table.'" >'.$data->$desc_table.'</option>';
 $html.= '</select></div>';
 return $html; 
 // retorna el selectbox filtrado
 }
	
 // Filtrar DropDowns según el usuario logeado
 function _callback_field_provincia($value = '', $primary_key = null)
 {   
 return $this->filter_dropdown('provincia','id_provincia','desc_provincia',$this->session->userdata('provincia'));
 }
before callback:

after callback:

Note: I'm using this library gc_dependent_select

 
                                 
             
                                                                                             
                                                                                                    