jQuery Grid Plugin - jqGrid

I want to add a field to a form which is not created automatically by the colModel.  How do I do this.

I have a form with

colModel:[
          {name:'ID',index:'machine_ID', width:36, align:"right", width:50, align:"right",
                editable:true, editrules:{required:true}},
          {name:'experiment',index:'experimentType_ID', 
                editable:true, editrules:{required:true}},
          {name:'data',index:'metadata', width:260, align:"left",
                editable:true, edittype:"select", editrules:{required:true}, editoptions:{value:"one:one;two:two"}}
          ]

and I have tried

beforeShowForm: function(formid){
      $("#detailGrid").html("<input type='text' name='moreData' value='test'/>";

}

And i have tried

onInitializeForm: function(formid){
       $("#detailGrid").html("<input type='text' name='moreData' value='test'/>";
 }

but no luck.

Thanks