I couldn't find any precise information regarding used coffee grounds, so I'll just drop this here....
Eurofins Viljavuuspalvelu Oy is a company that does pretty much all the lab testing of soil samples here in Finland, and they have tested, just for the kicks of it, used coffee grounds the same way they would any soil. I have attached the results in picture. You should pick out all the info from there even if it is not in English. Or I can type them alse here.....
Edit: Unfortunately they didn't test Nitrogen, but from the conversation where I found this I gathered that most of the nitrogen nitrates have leached away while making the coffee, and the rest (not much) will come available after the bacteria have started their processes. If anyone has more definitive information about the N-values in used coffee grounds, do tell!
Every morning I make the short walk out the door with my coffee pot and coffee grounds to the compost pile. Sometimes even in my nightgown! I love that it is high in magnesium because this is a mineral that is sorely lacking in many people's diet. Thank you for sharing the composition. I do believe I have read that the grounds break down and release the nitrogen once the soil organisms eat it!
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I looked that up and found the reason given for no numbers is because they vary so sharply. Perhaps it has to do with roast, degree of use, water temp, time fermenting following use, etc. Like you, I wasn't satisfied and went to test. Infact, I used to mix used coffee with a little milk. Well, the pH was alright, but the N-value was way too low. So then I went to fish emulsion. Too stinky and also dangerous if you don't wash thoroughly after. So, then I moved to something safer, high in nitrogen and cheaper: pee. I still have to finish off the emulsion (why waste?). The plants like that too and honestly, sometimes I'm just out of pee, but when I can I try to fertigate with diluted pee. And it is, in my opinion, since it is deluted and uptaken, less stinky than emulsion too. Supposedly it's also an animal deterrent, but I have yet to see that magical property. The coffee grounds go right into the compost pile now and compost is said to be semi predictably about 5-5-5, slow release.
One of the best nitrogen tests is actually done in a Kjeldahl apparatus then titrated to find how much ammonium is present.
As you found out, most of the N that is in coffee beans ends up in the cup you drink. There is a fair amount that remains tied up in other compounds that don't leach into the brew but are released as bacteria, fungi and molds do their work on the remaining grounds.
Spent Coffee Grounds also have a fair amount of acidity which is why they work well on ant hills and also why slime molds love to grow on them.
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