I own a commercial hydroponic greenhouse. I also grow outside using the fertigation method, or drip to waste. I was mentored by David Hill, who now works for Canna International. He is from S. Africa, and was the State field rep for all the farms in Kenya, and S. Africa until he moved to the U.S. with his American bride. this info will shed some light on the use of nitrogen in the event that any of you want to delve into mixing your own. 
There are 3 types of Nitrogen.
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Nitrate: Readily available to the plant. This is why we use Calcium Nitrate, and Potassium Nitrate in our professional hydroponic solutions. Nitrate is the main Nitrogen source (over 90%) for all soluble nutrients for hydroponics.
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Ammonical: (sp.?) This form is used in a very small % in Foxfarm, for instance. In my hydroponic solutions I get this from adding M.A.P. Mono Ammonium Phosphate It takes bacteria and microbes to turn this from insoluble to soluble. IN hydroponics, it has to be in water above 80 degrees to make it soluble and it can still take days to become available.
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Urea: This is a form of Nitrogen used in soil applications. It has a 2 step process to change it from Urea to Ammonia to Nitrogen. So we do not want to use this in hydroponics. I have seen it in some blends but, only about 33% will become soluble, so it is a waste of time.
As far as Foxfarm. The only blend they have that can be used in hydroponic systems is the hydroponic blend of Grow Big, and Big Bloom, I think. You can check their website for the hydroponic series.
Organic blends use organic forms of Nitrogen. Guano, and Worm castings are the most common. the issue with using these organic forms of Nitrogen is that 67% of the weight of material used is going to stay unsoluble. This can equate to the issues some growers have when choosing an Organic hydroponic nutrient system.
my reference materials are from my 12 year old notes. Joe (The chemist) at Vereen’s Fertilizers; And my buddy, “Max” (Head product specialist at Foxfarm)