Impact of Agricultural Management Practices on Mitigating Soil Phosphorus Loss: A multi-scale study

The widespread use of inorganic phosphorus (P) fertilizers has had a profound impact on the global P cycle, leading to increased crop yields but also contributing to P pollution in freshwater and coastal ecosystems. Canada, a world-leading agricultural producer, is facing water pollution challenges due to agricultural P losses, which not only affect water quality but also impact the economy. In addressing this challenge, many efforts have explored the effects of agricultural practices on sustainable P management. However, the outcomes have been somewhat controversial, likely due to variations in field design and experimental conditions. Furthermore, historical (residual) P from previous applications has garnered substantial attention in recent years due to its potential to sustain crop yields while mitigating P runoff. Despite this, a comprehensive national-scale assessment of its benefits for Canada remains unclear. My research endeavors to tackle the P pollution challenge in Canada by employing various methodologies. To begin, I conducted a meta-analysis to assess the efficacy of different agricultural practices in reducing soil P loss while considering their impact on crop yields. Our synthesis of field data suggests that conservation practices tend to be the most practical and effective approach for sustainable P management. Subsequently, I employed machine learning (ML) techniques to evaluate the effectiveness of conservation practices in mitigating P export from the Maumee River watershed to Lake Erie over the coming decades. The ML models indicate that additional practices may still be urgently required to address the ongoing P pollution in Lake Erie. Finally, I assessed the potential of reusing residual soil P to reduce P losses across Canadian agricultural land. Developing a P cycling model allowed me to analyze Canada’s P dynamics. Coupled with a soil P dynamics model, my findings suggest that using residual P could reduce mineral P demand in Canada. The Atlantic provinces, Quebec, Ontario, and British Columbia exhibit the highest potential for reducing P applications. Notably, the Atlantic provinces and Quebec are poised to experience the greatest reductions in runoff P loss with this strategy, while Ontario, Manitoba, and British Columbia may experience relatively lower reductions. In conclusion, my research contributes to safeguarding water ecosystems and achieving long-term P sustainability. It underscores the importance of considering residual soil P as a valuable resource and its potential role in mitigating P pollution

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