http://jsbin.com/nivocijofi/edit?html,js,output

<div id="content">
<tr>
<td><br>
<label for="po">PO Number</label>
<br>
<input name="po" value="" autocomplete="off" required/>
</td>
</tr>
<tr>
<td><br>
<label for="kind">Material Name And Type</label>
            
            
           
           
           
<label for="qty">Quatity</label>
<br>
<input id="kind4" class="custom" name="kind[]" required/>
   
<input name="qty[]" value="" autocomplete="off">
</td>
</tr>
</div>
<tr>
<td><br>
<input type="button" id="more_fields">
</td>
</tr>

function add_fields() {
var d = document.getElementById("content");
d[removed] += "<tr><td><br/><label for='kind'>Material Name And Type<label/><?php echo $aku; ?><label for='qty'>Quatity<label/><br/><input id='kind4'class='custom'name='kind[]' required/><?php echo $aku1; ?><input name='qty[]'value=''autocomplete='off><td/><tr/>";
}