Analysis of alternative soil amendments from coproduction processes at the nexus of food, energy, and waste management

Kimberley E. Miller, Dillman Delgado Paredes, Toby A Adjuik and Sarah Davis, Voinovich School of Leadership and Public Affairs: Environmental Studies Program, Ohio University, Athens, OH, Toby A Adjuik, Biosystems & Agricultural Engineering, University of Kentucky, Lexington, KY

Background/Question/Methods
Healthy soils are dependent on management decisions made at the nexus of food, energy, and waste management systems. Soil amendments that make use of organic wastes from local communities are particularly relevant to resilient systems. To determine their relative efficacy as fertilizers and soil amendments for an advanced bioenergy crop grown in marginal soils, we applied anaerobically-digested food waste, hydrothermally-treated food waste digestate, and an inorganic nitrogen (urea) to mature stands of Miscanthus x giganteus and measured crop yield, soil nutrient status, and greenhouse gas flux. We tested the effect of these same treatments on heterotrophic soil greenhouse gas emissions in laboratory soil incubations. We also applied raw brewery wastes (brewer’s spent grains and trub) to farm plots of kale (Brassica oleracea) and measured the impact on soil health. In a greenhouse pot experiment, we applied inorganic fertilizers (nitrogen as urea, triple phosphate, and a combination of the two) and hydrothermally-treated septage to Spinacea oleracea, Miscanthus x giganteus, and Agave americana and measured soil and plant responses relative to an unfertilized control.

Results/Conclusions
Our work indicates that carbon-rich materials like brewery and agricultural wastes can improve the physical conditions of the soil (in both marginal lands and organically-managed agricultural soils) and results in greater micronutrient concentrations. We have also found that anaerobically-digested food waste and hydrothermally-treated food waste digestate and septage are effective fertilizer products when compared to traditional, inorganic fertilizers. When compared with reference soils and those treated with a common nitrogen fertilizer (urea), we found that applications of hydrochar created from anaerobically-digested food waste did not negatively impact crop yields but did increase soil organic matter and nutrient contents (p < 0.05). Hydrochar-treated soils resulted in decreased soil CO2 emissions to the atmosphere throughout the growing season following application (p < 0.05) from field plots, and decreased CH4 emissions from soils incubated in the lab (p < 0.05). In the pot experiment, Miscanthus x giganteus plants grown in hydrochar-treated soils had an increased photosynthetic capacity, as well as higher leaf nitrogen content, compared with those treated with urea. These results suggest promising future possibilities for coproduction systems that include organic waste management for soil health and fertilizer products. Coproduction systems require cooperation and strategic planning, and soil health can function as a common goal that unites people from farmers to city engineers in an effort to plan for sustainable communities now and into the future.