manure

can horse manure be spread on to established grass
                                  thx
                                          Joe

yes.

If you put it on too thick, it will smother the grass. 

If it's too fresh, it might burn your grass (and annoy your neighbors)

Horse manure has more seed in it than most other manures because of the inefficient digestive systems horses have, so, if you have horse manure to use as compost, make sure it's totally composted before you use it.
  If it's not fully composted you'll have weeds all over the place with nice rich soil making them grow really swell!

I missed this, but I mix the fresh manure with plenty of water and spread on grass or even on gravel, grows fine grass.

I am playing with aquaponics but do not have the time to join another group of friends...I know that sounds bad but it is life. 

I am thinking of, what else but, horse manure in a hydroponics system.

Uh .... horse poop soup?

i agree that our experience shows it needs to be well composted to kill the weed seeds in it..but it also grows really great morels