element does not post data?

i have a form page and when i submit this form all inputs are posting successfully except this one:

**<input id="TC" class="form-control" name="kullanici_id" type="text" onchange="edit()" <?php if($this->data['kullanici_id']){echo 'readonly';} ?>  value="<?php echo $this->data['kullanici_id']?>">**

But why?