Prueba esto
Código PHP:
Ver original$plant="SELECT nom FROM $users1";
echo "<tr><td>$row[0]</td>";
echo "<td>$row[1]</td>";
echo "<td>$row[2]</td>";
echo "<td>$row[3]</td>";
if($row["campo"]==""){
echo "<td><input type='text' name='cost[]'></td></tr>";
}else{
echo "<td>".$row["campo"]."</td>";
}
}