Circular nutrients for supplying phosphorus and closing urban to rural nutrient cycles in organically managed cropping systems
Year: 2021
Type: dissertation
Abstract: Phosphorus (P) nutrition is vital for crop growth and yield, but the global P cycle is broken. The current system is linear, with P entering the food system as fertilizer mined from rapidly depleting phosphate rock reserves, and leaving the food system via food and human wastes entering landfill or waterways. Excess P from urban wastes contributes to eutrophication and toxic algal blooms in freshwater bodies. Meanwhile, P deficiency can limit yields, particularly on organic farms which often have negative P balances. Improved recycling of P from urban areas onto farmland is essential for food system sustainability, reducing reliance on non-renewable mined P, diverting harmful P from waterbodies, and improving crop yields by eliminating P deficiency. Urban recycled (circular) P fertilizers are understudied compared to manure and conventional P fertilizers. This thesis evaluated three circular nutrient sources for their capacity to supply P and improve yields on a P-depleted soil of the Canadian Prairies. Frass is the excreta of black soldier fly (Hermetia illucens) larvae fed a diet of urban pre-consumer food waste. Digestate is the product of anaerobic digestion of urban food processing waste. Struvite is a phosphate mineral precipitated from municipal wastewater streams. Frass, digestate, and struvite were compared with monoammonium phosphate (MAP), a soluble conventional P fertilizer, compost, a common organic amendment, and an unfertilized control. In a wheat (Triticum aestivum) experiment replicated in two years, frass, MAP, compost, and digestate increased P uptake and improved grain yields compared to the control. In an alfalfa (Medicago sativa) based forage experiment monitored over two growing seasons, all nutrient sources improved P uptake and yield compared to the control in the second growing season. In a pot experiment using Italian ryegrass (Lolium multiflorum), where adequate nitrogen (N) was supplied to remove any N effect of the amendments, all nutrient sources improved P uptake and yields compared to the control. All three circular nutrient sources showed the potential to supply P and improve yields in some organic cropping systems, with the degree of improvement varying depending on crop and nutrient source. These circular nutrient sources have the potential to play an important role in recycling P from urban areas to farmland.
Source: Mspace (University of Manitoba)
Author: Jessica Nicksy
Language: English
Subfield: Waste Management and Disposal
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W3164962614