# Help Calculating Fertilizer Program

buzzsaw8October 15, 2009

I've got a really small lawn 250 sqft and I'm trying to figure out a fertilizing program/schedule. Because money is tight, and I think the idea is kinda cool anyways, I plan on using urine. Lawn is TTTF.

So here's where I'm at so far, if there's any errors, suggestions, please let me know:

Fescue lawns require 4lbs of N per year @ 1000 sqft. Mine being 250 sqft would require 1lb/year.

I'm working under the assumption that urine is 10% N (I've read it's anywhere from 8% - 12%, so we'll go with the average of the two).

I'm also working under the assumption that urine weighs the same as water, roughly 16oz equals 1 lb.

So to get the required 1lb of N per year, I would need 10 x 16oz of urine, 160oz total.

160oz urine x .10 rate of N = 1lb N

Because urine is going to leach out of the soil quickly and I don't want to burn the lawn, I thought that 10 applications of 16oz of urine in a hose-end sprayer would be my best bet. I'd apply this monthly, except for July and August. I also mulch mow and put down compost in the Spring so that would cover the needed organic material.

Thoughts?

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bpgreen(5UT)

"I'm working under the assumption that urine is 10% N (I've read it's anywhere from 8% - 12%, so we'll go with the average of the two). "

Where have you found this number? Since urea is 46% N, you're saying that urine is about 1/3 urea. That seems unlikely.

"I'm also working under the assumption that urine weighs the same as water, roughly 16oz equals 1 lb. "

Umm. 16 oz of anything is 1 lb. If you mean 16 fl oz, that's a different story. Metrics use water, so I converted 16 fl oz to ml (same as g) and converted that to lbs. 16 fl oz of water is still pretty close to 1 lb (1.04317556 lb). Urine is denser than water, so 16 fl oz of urine would probably be a little heavier still.

If your assumptions on the nitrogen content of urine are correct, your calculations of amount of urine to use are probably close, but not quite right. But I am very doubtful that urine is 10% N.

October 16, 2009 at 2:10AM
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skoot_cat

For a 250sqft lawn Go out and buy a 50lb bag of SBM for less than \$20.00 and that should last you 2 years if you apply it @ 5-lbs per 250sqft.

October 16, 2009 at 10:21AM
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anubis_pa(z5 PA)

Wikipedia has urine as 95%, the remainder having urea as a part of it, so 10% may even be high if that's accurate info. I looked it up because my first thought was more that there's got to be a lot of variability in that percentage anyway.

October 31, 2009 at 12:00AM
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buzzsaw8

Thanks for the replies guys, I bought some SBM and will be using that along with twice yearly compost dressing

November 2, 2009 at 9:52PM
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featherhoof(zone 9)

Why not a compost tea?

November 8, 2009 at 9:47PM
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