"Sustainable fertilizer: Urine and wood ash produce large harvest"
"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."
Which backs up the work of this guy: http://e-terrapretarooftopexp.blogspot.com/
So you farmer types might want to set a terra cotta pot a discreet few steps out the back door and fill it with the ash from your wood stove. Modify as nature calls.