I don't think my method for growing cereal grass can be considered strictly hydroponic but it IS soil-free, i.e., I use a combination of Hoffman vermiculite and Hoffman Canadian sphagnum moss (it's chemical-free--you want to watch for that if you're planning to consume what you grow). I've also been using SeaStart kelp fertilizer which does a great job but given that I'm not using soil and rely on supplemental lighting, I wanted to try taking fertilizing up a notch. I use Handy Pantry grain and ran across AZOMITE (sorry, I don't have a small caps font) on their Web site. I liked what I read and on that basis, decided to give it a shot.
My growing trays are smaller than standard flats so I mix just a tablespoon of AZOMITE with my dry planting medium, after which I wet it down with my kelp solution (to which I now add 5 drops/pint of Nutri-Biotic Maximum GSE to help control mold). And it really did provide a boost--I'm growing gorgeous, healthy grass that's (I imagine) as full of juice as grass can be (which admittedly isn't much--it's grass, after all) and that's ready for harvest just over a week after I first soak the seeds for pre-sprouting.
My suggestion is that if you're looking for a second crop from grass that has already been cut, give it a watering containing a second dose of AZOMITE as the initial tablespoon is pretty much utilized by the first crop. Don't be afraid to combine AZOMITE with another safe, organic fertilizer such as SeaStart--they complement each other very nicely.
Wheatgrass is something of a pain to cultivate at home and AZOMITE has really contributed to my own success, in spite of my brown thumb. I can only imagine that it works equally well, if not better, on plants that aren't as fussy.