If you're sure you're very low in N, and can't add any P, there are "industrial-strength chemical fertilizers" that are all-N.
I have a big bag of urea (46-0-0, I think). Per pound of nitrogen, it is very cheap. However, it has to be the easiest thing in the world to over-do, and the most likely to burn plants if used to excess.
I'm far from sure I would recommend it, but if dissolved and diluted, it sure will add N to marginal soil. Much better to have rich organic soil with all nutrients present in slow-release organic form, if you can.
Excessive chemical fertilizers (especially high-N fertilizers) are kind of harsh on root hairs, leaves, soil microbes and probably worms. I rely on lots of dilution, and under-fertilization.
If you're interested, I'll look up the numbers suggested for safe application rates. Ideally, you would dissolve a little in a bucket, and then use a 20-1 dilution mixer/sprayer. Otherwise, dissolve a very little per gallon, and spread it with a watering can.
It might be safer for plant root hairs and soil microorganisms to dilute household ammonia (if you find a brand with no perfume or other additives). I don't know the numbers for safe dilution of ammonia.