The pamphlet I linked is also interesting re storage and application: do not apply directly, but near the roots in a shallow trough, and cover immediately, b/c the nitrogen will volatilize out in the ammonia:
Because of the high pH, coupled with the high ammonium concentration of urine, there is a risk of losing N in the form of ammonia to the air. As long as the collection and storage chambers are sealed and the contact of the urine with air is reduced to a minimum, neither losses of nutrients nor changes in their availability can occur (JÖNSSON 2004).
Yes, Rebecca, I've burned smaller and younger plants too. Though the other posters are also right, I've applied and not burned anything many times. There is a grey area that I'd rather avoid by aging the pee.
It's an interesting idea to try and normalize such traditional fertilizing practices: even if I don't know the humans providing the fertilizer, I'd rather eat produce raised thusly than made with the Haber-Bosch process...figuratively (literally?) eating natural gas and coal.
Further, the SSWM writes: "If urine is used for crops that are eaten by people other than the urine producer,
it should be stored beforehand for 6 months. " Good dog, who has time for that. Why are they so exercised about flowjolais nouveau?
This 2001 paper from the Swedish Institute for Infectious Disease Control, republished by the WHO, is generally pretty interesting, discussing history, sociocultural perceptions, practices around the world and plenty of hard science, but here's a TLDR b/c permies already know pee is good and pee separation also = good:
"The pathogens traditionally known to be excreted in urine are Leptospira interrogans,
Salmonella typhi, Salmonella paratyphi and Schistosoma haematobium (Feachem et al.
1983). "
HOWEVER: "...It can be concluded that pathogens that may be transmitted through urine are rarely
sufficiently common to constitute a significant public health problem and are thus not
considered to constitute a health risk related to the reuse of human urine in temperate
climates. ... Furthermore, the inactivation of urinary excreted pathogens in
the environment reduces their ability for transmission." Yay!
Aging is good because it raises the pH: "At pH 6 most of the bacteria had a better survival than at pH 9. The reduction of bacteria at high
pH-values may be an effect partly of the pH and partly of the presence of ammonia."
And the attached handy table.
UPSHOT: Unsurprisingly, your own or familiar pee is fine applied direct. Minimize air contact to retain nitrogen. If uncertain of source, age 1 mo at 20deg C. If you are afraid of lawsuits and crazy risk-averse, age 6 mo at 20deg C. If you must use pee from elderly homes, hospitals and day cares (not advised), age 6 mo at 20deg C. (lol)
IF YOU HAVE ACIDIC SOILS, AGING THE URINE IS GOOD because the pH goes up to 9. I think the biochar folks in the northern Olympic Peninsula like Norm Baker and Francesco Tortorici have it right: a bucket of biochar that you pee in til it's full doesn't just release N slowly from the biochar matrix, but it buffers our region's acidic soils. Biochar alone only fleetingly lowers pH, but I bet aged-pee biochar has amazing results as Norm avers in his test gardens.
Additional reading.
Useful if you want to know exactly what chemicals constitute our pee,
here, in 1971, NASA (USA's National Aeronautics and Space Administration) published a report on composition and concentration of human urine. ("In space, nobody can hear you pee.") A tacit acknowledgement that you drink the water you bring, and that the Haber-Bosch process will not be available on the new frontier.