jQuery Forum

Hi guys,
Please, everybody can help me with my linked select. I use Codeigniter and jquery. Now i just try to get the string of data by received value from first form (year). The value is received properly but i have problems with that i can`t post this value to my controller`s function. In the future I will try to integrate this string to the second form but now is necessary to solve the first thing. Where is an error? What i do wrong?

View:

1.     <div class="form-order">
           <?php echo form_label('Journal year') ?></br><p></p>
           <?php echo form_dropdown('journal_year',$j_years, set_select('journal_year'), 'id="year"'); ?>
       </div>
   
       <div class="form-order">
           <?php echo form_label('Journal Volume/Number') ?></br>
           <?php echo form_dropdown('journal_volume', set_select('journal_volume'), ' id="volume"'); ?></br>
       </div>
   
   <script type="text/javascript">
   function populateYears() {
        var year = $('#year').val();
        $.post("journal/_get_journal_volumes()", {'year' : year},
        function(data) {
           alert(data.j_volumes);
        }, "json");
   }
   
   $(document).ready(function() {
           
           populateYears();
           $('#year').change(function() {
               populateYears();
           });
   });
   </script>

Controller`s function

1.       public function _get_journal_volumes(){        
2.        $year =$this->input->post('year');
             $this->db->where('journal_year', $year);
           $this->db->order_by('journal_volume, journal_issue','asc');
           $journal_volumes = $this->db->get('journals');
           $j_volumes = array();
           foreach($journal_volumes->result_array() as $journal_volume){
               $j_volumes[$journal_volume['journal_id']] = "Volume ".$journal_volume['journal_volume']." / Issue ".$journal_volume['journal_issue'];
           }
           echo json_encode($j_volumes);
           }