Network-booting multiple RPi3 with Kodi

I want to boot multiple RPI3 with libreelec. At the moment i have one system runing raspian booting without problems.
i used the tutorial from the raspberry foundation but now i stuck because my raspberry is not finding the root-folder of libreelec. I think he is reading the kernel but then it ends with the recovery-console.

my cmdfile:
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=/dev/nfs nfsroot= rw ip=dhcp rootwait elevator=deadline

nfsroot= content:
bcm2708-rpi-0-w.dtb bcm2709-rpi-2-b.dtb bcm2835-rpi-a-plus.dtb bcm2835-rpi-zero.dtb cmdline.txt flash start.elf
bcm2708-rpi-b.dtb bcm2710-rpi-3-b.dtb bcm2835-rpi-b.dtb bcm2836-rpi-2-b.dtb config.txt kernel.img SYSTEM
bcm2708-rpi-b-plus.dtb bcm2710-rpi-cm3.dtb bcm2835-rpi-b-plus.dtb bootcode.bin distroconfig.txt LICENCE.broadcom
bcm2708-rpi-cm.dtb bcm2835-rpi-a.dtb bcm2835-rpi-b-rev2.dtb cmdline.old fixup.dat overlays

I dont know where it tries to mount the storage and the root-filesystem. at the moment the recovery-console only shows me that /dev is mounted.

Can someone help me?