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Opportunities and strategies to improve the sustainability of nitrogen and phosphorus use
Algren, Mikaela M.
Algren, Mikaela M.
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2021
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2023-04-14
Abstract
Over the past century, humans have dramatically increased levels of terrestrial reactive nitrogen and mobilized phosphorus through industrial fixation of nitrogen and phosphorus mining. These additional nutrient resources have enabled vital food production increases; industrially-fixed nitrogen and mined phosphorus now support around 50% of global food production. The problems with human manipulation of natural N and P fluxes lie in continuous losses of these nutrients from human systems: only about 17% of nitrogen and 20% of phosphorus used in agriculture is consumed by humans. Nutrient losses to the environment have a wide range of impacts, including contribution to global climate change, disruption of ecosystems in both coastal and inland water bodies, air pollution, and drinking water pollution. Additionally, phosphorus is a finite resource, and high-quality phosphate rock is becoming scarce.
To ensure sustainability of future bio-economies, nutrient-related impacts must be minimized. This thesis quantifies the nitrogen and phosphorus flows embodied in the production of United States (US) commodities and assesses the potential of phosphorus management strategies to reduce net phosphorus inputs to the contiguous US. Modeled commodity nitrogen and phosphorus flows show that inclusion of ethanol coproducts in animal diets reduces the nitrogen inputs associated with ethanol fuel, beef, and milk production, and total phosphorus inputs to the US are highly sensitive to animal dietary P intake. A materials flow analysis of US phosphorus demonstrated that over half of phosphorus inputs to the US economy were either landfilled or lost to the environment, primarily from crop farming and animal production systems. The strategies with the most potential for reducing US net phosphorus inputs were efficient manure utilization and widespread adoption of variable rate fertilization. Improving phosphorus digestibility in animal diets is also promising for reducing both P supplement demand and county-level excess manure phosphorus.
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