Research bearing fruit: The corner store procurement project

Background/Question/Methods

Global food demand is expected to double by 2050, while environmental impacts from agriculture are already at unsustainable levels. Urban agriculture can help meet food demand without compromising natural lands. It can also improve nutritional conditions and alleviate food insecurity for vulnerable urban residents. Here we report on the Corner Store Procurement Project, an urban agriculture project that combines research and community service. We tested how worm-composted (=vermicomposted) coffee grounds affect vegetable growth and nutrient content. Annual coffee consumption in the U.S. is over 100 L/person, and coffee grounds are generally not re-used. Although vermicomposting has been shown to increase concentrations of nitrogen (N) and other minerals in coffee waste, it is not clear how vermicomposted coffee increases crop growth relative to synthetic fertilizers, nor whether the fertilizer value of vermicomposted coffee depends on crop type. We conducted a greenhouse experiment where we compared effects of vermicomposting to those of synthetic fertilizer or uncomposted coffee grounds. In the service component of the project, we integrated the vegetables produced in the study to the Healthy Corner Store Initiative, a nutritional program run by the Minneapolis Health Department that encourages corner stores owners to stock more fruits and vegetables.

Results/Conclusions

Vermicomposting increased substrate N content from 2.31% to 3.51%. We had 4 treatments: RC=raw coffee grounds, VC1=vermicompost where N addition equaled that in the RC treatment. VC2= vermicompost where fertilizer addition equaled that in the RC treatment, and SYN= where 20-20-20 (NPK) synthetic fertilizer was added such that N addition equaled inorganic N addition in VC1. Vegetables in the study were leaf lettuce, mustard greens, collard greens, tomatoes, cucumbers, and potatoes. Compared to RC, vermicompost (VC1 and VC2) increased overall crop production by 827%; crop growth did not differ significantly between VC1 and VC2. Vermicomposting did not increase crop growth as much as synthetic fertilizer did. Vermicomposting effects on production also differed significantly among crop species (significant treatment-by-crop interaction).  Finally, vermicomposting did not increase crop N content as much as synthetic fertilizer did. Overall, these results suggest that vermicomposting growth and nutritional deficits (relative to synthetic fertilization) are crop specific.

Crops from the study were delivered regularly to participants in the Healthy Corner Store Initiative and were sold in stores. These deliveries may help urban store owners acquire small quantities of produce at affordable prices.