How to make sysctl.conf effect?

I am sorry if this is not the right place to ask this question.
I am using freebsd amd64 7.2.
I cannot make more than 32768 directories in a folder. So I edited
/etc/sysctl.conf and added a line
vfs_ufs_dirhash_maxmem=67108864
when I do sysctl -a |grep mem, I saw the setting was correct.
But when I went into a directory and try to make more than 32768
subdirectories, it always was told me too many links. I have rebooted
many, many times. I even powered of the computer several times. I have
6G memory in the computer. And I even recompiled the kernel once. All
failed.
Could you please help me to give me some hints to activate the
/etc/sysctl.conf file.
Thanks a lot!

Fulan Peng