Inspired by something I heard in Collapse, I did some research and found this article on the use of ash and urine to revive your soil.
Results of the first study evaluating the use of human urine mixed with wood ash as a fertilizer for food crops has found that the combination can be substituted for costly synthetic fertilizers to produce bumper crops of tomatoes without introducing any risk of disease for consumers. The study appears in the current issue of ACS’ Journal of Agricultural and Food Chemistry, a bi-weekly publication.
In the study, Surendra Pradhan and colleagues point out that urine, a good source of nitrogen, has been successfully used to fertilize cucumber, corn, cabbage, and other crops. Only a few studies, however, have investigated the use of wood ash, which is rich in minerals and also reduces the acidity of certain soils. Scientists have not reported on the [combination] of urine and wood ash, they say.
Read the article in its entirety here.