ajax function returns [OBJECT OBJECT] [closed]

Good morning guys. I have a problem.

I have created a function to get results in the Onchange of a select via ajax

The problem is that in this input 'qtde' is printing the following msg [OBJECT OBJECT]

Someone knows what's wrong with me?

follow the code = >

function setqtde(obj)
 {
   var item = obj.value;
   $.ajax({
    url:BASE_URL+"estoque/pegaqtde",
    type:'GET',
    data:{valor:item},
    dataType:'json',
    success:function(json)
    {

      document.getElementById("qtde").value = json;
    }
  });
 }