Dusty, Compost is easy to apply with a hydroseeder as long as you use a quality compost. Compost that is not completely composted and containing larger particals will clogg your spray nozzle. I suppose you could always get a bigger nozzle. It is also a heavy material and requires constant agitation to stay suppended or it will seperate from the water and settel to the bottom of the tank. It can also settel in you spray hoses and cause cloggs there as well. it is best to just mix what you are going to use at each site instead of just mixing a tank load and trying to spray several different sites. When you stop spraying the compost will settle in the hoses and can be pretty hard to unclogg. I have sprayed as much as 400lbs in a 500gal jet hydroseeder and could probably add a little more but I dont like fooling with cloggs so I dont take chances.