eiru_purchase_lines_total/views/purchase_order_form_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record id="inherit_purchase_order_form_view" model="ir.ui.view">
            <field name="name">Purchase Order</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="/form/sheet/notebook" position="after">
                    <group>
                        <group>
                            <field name="tot_purchase_qty" nolabel="0"/>

                        </group>
                    </group>
                </xpath>
            </field>
        </record>
    </data>
</openerp>