How to add row below header row in gridview

<asp:GridView ID="ItemGv" runat="server" AutoGenerateColumns="false" CellPadding="4"
                        ForeColor="#333333" ShowFooter="true" Visible="False" Width="843px" OnRowCreated="ItemGv_RowCreated">
                        <Columns>
                            <asp:TemplateField HeaderText="ItemNo">                            
                                <ItemTemplate>
                                    <asp:TextBox ID="itemNotb" runat="server"></asp:TextBox>
                                    <asp:RequiredFieldValidator ID="itemnorv" runat="server" ControlToValidate="itemNotb"
                                        ErrorMessage="*"></asp:RequiredFieldValidator><br />
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Description">
                                <ItemTemplate>
                                    <asp:TextBox ID="desctb" TextMode="MultiLine" Width="500px" Height="40px" runat="server"></asp:TextBox>
                                    <asp:RequiredFieldValidator ID="descrv" runat="server" ControlToValidate="desctb"
                                        ErrorMessage="*"></asp:RequiredFieldValidator>
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Qty">
                                <ItemTemplate>
                                    <asp:TextBox ID="qtytb" runat="server"></asp:TextBox>
                                    <asp:RequiredFieldValidator ID="qtyrv" runat="server" ControlToValidate="qtytb" ErrorMessage="*"></asp:RequiredFieldValidator>
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="UnitPrice" Visible="true">
                                <ItemTemplate>
                                    <asp:TextBox ID="upricetb" runat="server" AutoPostBack="true" OnTextChanged="upricetb_TextChanged"></asp:TextBox>
                                    <asp:RequiredFieldValidator ID="uprv" runat="server" ControlToValidate="upricetb"
                                        ErrorMessage="*"></asp:RequiredFieldValidator>
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Total Amount">
                                <ItemTemplate>
                                    <asp:TextBox ID="amounttb" runat="server" ReadOnly="true"></asp:TextBox>
                                    <asp:RequiredFieldValidator ID="amountrv" runat="server" ControlToValidate="amounttb"
                                        ErrorMessage="*"></asp:RequiredFieldValidator>
                                </ItemTemplate>
                                <FooterStyle HorizontalAlign="Right" />
                                <FooterTemplate>
                                    <asp:Button ID="ButtonAdd" OnClick="ButtonAdd_Click" runat="server" CausesValidation="false"
                                        Text="Add New Item" />
                                </FooterTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField ShowHeader="False">
                                <ItemTemplate>
                                    <asp:LinkButton ID="LBDelete" runat="server" CausesValidation="false" CommandName="deleteRow"
                                        OnClick="LBDelete_Click" Text="Delete"></asp:LinkButton>
                                </ItemTemplate>
                            </asp:TemplateField>
                        </Columns>
                    </asp:GridView>