jQuery Grid Plugin - jqGrid

I got the following problem 
I want to send to PHP server nested json using ajax. I need this to send  cells that were edited and after save event all changed cells  will be send to server.

{item1:'one', 
item2:'eeee', 
item3:[{item31:'sdf', 
  item32:'sdfs'}] 

} 

My code: 
  $.ajax({ 
  url: "translation_edit.php", 
  type: "post", 

  data: {item1:'one',item2:'eeee',item3: 
[{item31:'sdf',item32:'sdfs'}]}, 
  success: function(data) { 
  alert('Success');}, 
  complete: function () { 
  alert('Complete'); 
  }, 
  error: function (xhr, ajaxOptions, thrownError){ 
  alert(xhr.valueOf()); 
  } 
  }); 

But result on server(PHP) is as follows: 
Array 
( 
  [item1] => one 
  [item2] => eeee 
  [item3] => [object Object] 
) 

My code on PHP server: 
<?php 
$handle = fopen("data.txt", "w"); 
fwrite($handle, print_r($_POST,true)); 
fclose($handle); 
?> 

How to get rid of [object Object] and get item31 and item32? 

Greetings 
Majkel