Coffee is an important agricultural product with substantial environmental impact. This impact would be reduced if the many by-products of coffee production could be repurposed. One abundantly produced by-product of the coffee roasting process, chaff, is generally discarded and deposited in landfills. Here, we use an urban agriculture setting to test whether this chaff can be useful as either a protective covering (mulch) or a soil amendment.
We conducted the study in experimental research sites at two community centers in lower-income neighborhoods in St. Paul, MN. Each site consisted of a grid of 32 1.8m-by-1.8m raised beds. We compared the effects of raw chaff vs. woodchips (a commonly used mulching material) as either a mulch or as a soil amendment in a fully factorial design. We also used a commercial coffee chaff pellet product as a positive soil amendment control. Our response variables were water retention, weed suppression, and agricultural product yield, and crop plant aboveground biomass. We grew a mixture of tomatoes, peppers, eggplant, and potatoes in each plot. We predicted that coffee chaff would be a comparable mulch and a superior soil amendment to woodchips. Plots were open to public visitors throughout the experimental period.
Results/Conclusions
We found that, overall, coffee chaff added as either a mulch or a soil amendment did not have a significant effect on water retention, weed presence, crop yield, or above-ground biomass compared to unamended control plots, woodchip plots, or commercial coffee chaff pellet plots. The fact that neither chaff nor the positive controls (woodchips) for mulching did not affect water retention likely reflects higher than average rainfall during the study period. The lack of effect on weed presence may reflect the regular plot maintenance that was required by the public presentation of the project. Lack of effects of soil amendments on yield may reflect the use of nutrient-rich compost in all plots that was also required for public presentation. Research is still needed in low soil nutrient and moisture conditions to determine whether coffee chaff can benefit urban agriculture in more marginal conditions. We also describe how our work reveals opportunities and challenges of conducting research in public urban spaces.