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On-Farm Bioconversion Of Organic Wastes Into Fertility Inputs For Sustainable Agriculture
Olson, Noah E.
Olson, Noah E.
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Organic wastes from agricultural and human sources represent substantial but underutilized nutrient resources. In agriculture, hemp production for cannabidiol (CBD) generates large volumes of residual biomass (i.e., stalks and leaves) that are often left to decompose in piles, burned, or landfilled despite containing many essential plant nutrients. This practice is not only damaging to the environment and economically costly, but also forfeits opportunities for nutrient recovery. Converting hemp residues into organic fertilizers could reduce reliance on external inputs while improving farm sustainability and profitability. However, the high lignin content of hemp stalks resists decomposition which poses a significant barrier for on-farm recycling.
Sustainable nutrient recovery from human excreta also remains a major challenge. Expanding populations have overburdened wastewater treatment infrastructure leading to routine discharges of untreated sewage during heavy rains or system failures. The influx of nutrients into waterways degrades water quality, contributes to eutrophication, and threatens human health. Furthermore, the land-application of sewage sludge, intended to close the human waste stream loop, introduces per- and polyfluoroalkyl substances (PFAS) and other synthetic contaminants into agricultural soils, creating long-term environmental health risks. Composting toilets such those developed by Clivus Multrum offer a sustainable alternative to conventional wastewater treatment by capturing and stabilizing nutrients at the source. The resulting compost and leachate could serve as low-cost, renewable fertility inputs, but regulatory constraints in the United States have limited scientific evaluation of their agronomic potential.
This dissertation evaluates three complementary approaches for converting organic residues and human waste into soil amendments with the overall goal of assessing their effects on soil health, plant growth, and disease. The first study tested cannabis-specific microbial inoculants for the semi-anaerobic digestion of hemp stalks. Within three weeks, residues were transformed into a compost-like product that increased root:shoot ratios of hemp CBD plants and suppressed the growth of fungal pathogen Rhizoctonia solani. The second study explored companion cropping gourmet “winecap” mushrooms (Stropharia rugosoannulata) with hemp CBD as a method to recycle hemp biomass in-field. Winecap inoculation accelerated residue decomposition beyond the rate of waste generation and reduced lesion nematode abundance. Mushrooms generated as a byproduct could serve as an additional revenue source for farmers. The third study examined Clivus Multrum composting toilet leachate as a liquid fertilizer in greenhouse and field trials. Leachate applications matched synthetic and vermicompost fertilizers in promoting plant growth and forage yield, did not support Escherichia coli survival, and had no nontarget impacts on root microbiomes.
Collectively, these findings demonstrate that microbial digestion, mushroom companions, and composting toilets offer practical pathways for transforming agricultural and human wastes into resources that improve soil health, enhance crop productivity, and reduce reliance on external inputs. Future work should explore how these approaches can be scaled and integrated into existing agricultural systems to provide sustained environmental and economic returns while fostering soils suppressive to disease.
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2025
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