Cannot insert the value NULL into column 'NgoId', table 'CSR.dbo.tbl_student_term'; column does not allow nulls. INSERT fails. The statement has been terminated.

Here i am getting error for NgoId. But i don't want to Insert NgoId from here. It will take NgoId from the master table. Still i am getting error as in the title mentioned below.
Here is my insert code:-
SqlCommand cmd1 = new SqlCommand("Insert into tbl_student_term ( Student_id,term_title,term_description) values(@Student_id,@term_title,@term_description)", conn); // cmd1.Parameters.Add("@NgoId", SqlDbType.Int).Value = ddlNgoName.SelectedValue; cmd1.Parameters.Add("@Student_id", SqlDbType.Int).Value = ddlStudent.SelectedValue; //cmd1.Parameters.Add("@emailid", SqlDbType.NVarChar).Value = txtEmailId.Text; cmd1.Parameters.Add("@term_title", SqlDbType.NVarChar).Value = txttermtitle.Text; cmd1.Parameters.Add("@term_description", SqlDbType.NVarChar).Value = txttermdescription.Te ...