RickCorey said:
10 kilograms per square meter is the same as one gram per square cm. If that is "wet weight", I think the layer would be less than 1 cm deep (less than 0.4 inches). If it was dry weight, I'm guessing it would be around 1 inch deep.
In the Japanese study, the coffee grounds had a moisture content of 65%, so the 10 kg. would have meant 3.5 kg. of actual coffee grounds dry. The one I wasn't sure about was the Starbucks analysis of 2% N, because they said "On the basis of dry matter bulk density (452 lbs. per cubic yard), organic matter content (97.7%) and total nitrogen (2.28%), the estimated carbon/nitrogen ratio is about 24:1." So it sounds like those aspects were measured dry.
IMHO the bottom line is probably that if you are planning on adding a lot of coffee grounds at any one time it is better composted first. Another study on composted coffee grounds compared to other composts noted "The present study also showed that the composted coffee waste that had the highest C/N ratio (21.0) also had the lowest N mineralization degree among all the composts." This is from:
http://scialert.net/fulltext/?...
Another study noted: "......Therefore, the decomposition of the coffee residue is slower than that of other organic materials." That's in this one:
http://www.tandfonline.com/doi...
Cheryl, don't let this put you off using coffee grounds! The only aspect being considered is the length of time before coffee grounds start to release their nitrogen in a form that plants can use, and whether there is competition in the soil between microbes and plants for nitrogen to be used in the conversion process when it is added fresh.
This same question applies to pretty much all organic materials used as nitrogen sources because plants don't, for the most part, take up organic nitrogen. Instead they need soil microbes to convert the organic nitrogen into ammonium (mineralization) and then nitrate (nitrification), which are the forms of nitrogen that the plants can then use. If a material has a lot of carbon in comparison with nitrogen then the microbes will need extra nitrogen to decompose it, which can result in less being available for the plants. This is called immobilization, but it's not permanent, though, as when the microbes die their nitrogen can then be released.
I'm not sure if this helps or makes it sound worse!
