Install to NFS & boot from PXE

Installing and Using OpenWrt
1

need some help

i tried to boot a custom nfs client enabled kernel & mount a NFS share

pxe looks like

LABEL openwrtx86A
	menu default
	kernel ./openwrt/openwrt-x86-64-generic-initramfs-kernel
	#APPEND root=/dev/nfs nfsroot=192.168.20.99:/volume1/nfs/pxeWRT rw ip=dhcp init=/sbin/init
	#APPEND root=nfs:192.168.20.99:/volume1/nfs/pxeWRT rw ip=dhcp init=/bin
    	APPEND root=/dev/nfs nfsroot=192.168.20.99:/volume1/nfs/pxeWRT,nfsvers=4 ip=dhcp init=/sbin/init

but did not work so far

I also tried CONFIG_CMDLINE_FORCE

root=/dev/nfs nfsroot=192.168.20.99:/volume1/nfs/pxeWRT,nfsvers=4 ip=192.168.20.92::192.168.20.250:255.255.255.0::eth0:off rootwait

also no success

any ideas ?