Nitrogen and phosphorus flows in Ontario’s food systems

Abstract

Resource scarcity, energy requirements, and environmental pollution resulting from the production and use of nitrogen (N) and phosphorus (P) fertilizer have spurred an interest in a circular approach to nutrient management. An analysis of N and P flows in Ontario’s food systems was carried out to quantify relevant flows and stocks, evaluate alternative management scenarios and identify points of loss to the environment. The results showed that mineral fertilizers accounted for 42 % of N and 90 % of P inputs to Ontario’s food systems. Of the total amount of food produced, 153 kt-N/y ± 27 % and 28 kt-P/y ± 21 % in grain and oilseed were fed to animals. About 58 % (298 kt-N/y) and 29 % (15 kt-P/y) of the annual supply of N and P were lost to the environment. Major nutrient losses were from the crop production system, through erosion, contributing 35 % (103 kt-N/y ± 10 %) and 90 % (14 kt-P/y ± 51 %) of the total N and P lost. Over half of the N and P in the waste subsystem was disposed of in landfills or incinerators, where further N losses occurred through leaching and volatilization. Ontario’s reliance on inorganic fertilizer supply could reduce by 28 kt-N/y and 9 kt-P/y if the current waste diversion rates were to increase by 30 %. No single waste management scenario could effectively circularize N and P flows in Ontario’s food system. However, investment in new technologies might help to recover nutrients from manure and wastewater treatment systems efficiently.