Chances are they use an ammoniacal source for at least part of the nitrogen. A very, very little bit of ammonia, especially in the form of ammonium can be okay in a planted aquarium since it is the preferred form of N for plants. ADA, Tropica, Seachem all use an ammoniacal source in their N supplements. Being what you're looking at is for agricultural purposes I would imagine it has a lot of ammonia, relatively speaking anyway, along with who knows what else. Of course, if you can find everything that's in it and how much then you can decide if it's safe for your use. I think it's easier and not that costly in the long run to use those products that are a known - ADA, Seachem, Tropica or dry salts such as KNO3, KH2PO4, K2SO4, etc.