first u have to inhert hr.applicant class in py file : 1)

from osv import osv, fields
class hr_applicant(osv.osv):
       _inherit = "hr.applicant"
      _columns = {
          'field1' : fields.char('name', size=246),
      }

and then u have to inherit hr.applicant form / tree view in xml file

2)

 <record model="ir.ui.view" id="crm_case_form_view_job">
        <field name="name">Jobs - Recruitment Form</field>
        <field name="model">hr.applicant</field>
        <field name="arch" type="xml">
          <field name="inherit_id" ref="crm.crm_case_form_view_job"/>
          <form string="Jobs - Recruitment Form" version="7.0">
                     <field name="field1"/>
         </form>
        <field>
 </record>

thanks