Typically, when mounting NFS directories on OS X, a password is required. This is problematic if you want them to automatically mount on startup. To get around this, you can edit the sudoers file on OS X.
Open the sudoers file
$ sudo visudo
Add the following line to the bottom of the file.
%admin ALL=(ALL) NOPASSWD: /sbin/mount_nfs
important: make sure you add this as a new rule. Do not overwrite any of the default rules that are already in the file.