This past year I’ve read several articles about using human urine as an organic fertilizer and although some people think it makes good sense to dump fermented urine on agricultural land by the ton, I have some experience with doing this and I don’t agree. In moderation, human urine can serve as a free high-nitrogen fertilizer. Overdone, you can poison your property with salt. I have additional concerns about antibiotics and prescription drugs making their way into my soil through urine, so if you want to offer a batch, I will decline. I know what’s in my urine but I don’t know what’s in yours. Possibly fermentation removes some of the hazardous byproducts the human body eliminates this way, but I doubt it removes them all.
Anyone growing up in Ozarks in the 1950’s knows what over-application of urine does to the soil Nothing grows there for years afterwards, so there’s obviously an overuse factor involved. In the days of pit toilets, men found their own places for the Number One, behind a barn or a convenient tree. Nothing grew there and the tree usually died. In cities, if you see tree trunks wrapped with fabric and surrounded by fencing, it’s because even dogs marking their territory regularly can peel the bark off a tree and kill it.
I’ve used fermented urine as liquid fertilizer only one time, in an apple orchard I took charge of in the Ozarks. Was only a few trees and they never produced much, so one winter I collected urine in empty plastic milk jugs and poured it around those apple trees, at the perimeter of the canopy, just to see what might happen. I’m guessing I poured about 15 gallons out, per tree, and tried to spread it out a bit instead of concentrating it in a small area. That next year those apple trees flourished and we had the best crop of apples the orchard ever produced. The following winter, those same trees died. Somehow I suspect that application of fermented urine had something to do with both events, the excellent harvest and the death of the trees. I would blame salt for the latter.
Currently I only use urine as a booster for my compost heaps, and I don’t overdo it. Decomposing urine creates a lot of ammonia, and that breaks down into ammonium nitrate and fuels the decomposition of tougher things like hay and wood debris. By the time I work this pile into my garden in the spring, most of the dangerous fumes will have converted to by-products plants can assimilate without damage. There will probably be some salt still in the mix, but a conservative use of urine will not poison the ground.
The safest alternative, if you are looking for a high-nitrogen fertilizer, is urea. Urea fertilizer
contains the main ingredient in urine without all the contaminants. Tilled into the soil immediately, the urea converts to ammonia and the ammonia converts to usable chemical compounds. If you only spread the urea on the ground, much of that potential fertilizer evaporates as ammonia gas and does the garden no good. Urea creates so much ammonia that it will kill weed seeds and vegetable seeds in the upper layers of the soil. It’s a good weed suppressant early in the year, but give the garden a few days to recover before you plant the crop you actually want. Successive feedings, in moderation, won’t harm mature plants if you till the urea in shallowly before watering.