You have an awful lot of batches there, a million polygons shouldn't be a problem for average hardware. Are you running in debug mode by chance? What are your system specs?
my system spec:
athlon xp 1950mhz
gf 7600gt 256mb
but on better pc fps still low.
maybe i need another height function? Can you give me advice?
What's your FPS without grass?
Are you compiling in debug or release mode?
What's the limit of far distance of drawing grass and impostors?
There is no hard distance limit that I'm aware of.