Phosphorus is essential for growing crops, but managing it is a balancing act. Too little phosphorus reduces crop yields; too much can wash into rivers and lakes, triggering harmful algal blooms. Around the world, scientists report conflicting trends: some regions are losing phosphorus, while others are accumulating excess amounts (Peñuelas et al., 2013; Liu et al., 2021). Monireh Faramarzi, lead researcher at the University of Alberta’s Watershed Science and Modelling Laboratory (WSML), explains that in cold regions such as the Canadian Prairies, soil nutrient dynamics are highly complex, as snow cover, frozen soils, and spring melt strongly influence how nutrients move through the landscape.

Faramarzi and her research collaborators across Canada and beyond, including lead author Yinlong Huang of the WSML, investigated this paradox across the Red Deer River Basin (RDRB), a major canola-producing region of the Prairies covering approximately 47,000 km² (Figure 1). Faramarzi explains that the region “has been reported to experience earlier snowmelt, frequent soil freeze–thaw cycles, and increasingly extreme climatic events.” To help address these challenges, her team used an advanced environmental modelling approach to track changes in soil phosphorus from 1993 to 2016, examining how these changes relate to climate, crop growth, soil characteristics, snow dynamics, and water conditions across the 17 counties of the RDRB.

Key findings:

The study results revealed that despite similar overall fertilizer application rates, the 17 counties in the RDRB did not behave uniformly. Instead, three long-term trends of soil phosphorous emerged: some counties gained phosphorus over time, some lost it, and others remained in balance (Figure 2). Fertilizer application alone could not explain these differences, as soil moisture was the dominant factor driving variations across counties.

In drier areas, canola crops were less able to take up fertilizer phosphorus, leading to its accumulation in the soil (Figure 2, left). In wetter areas, crops took up more phosphorus, leading to depletion or stable levels (Figure 2, right and middle). Climate warming over the past decade added another influence as earlier snowmelt and more frequent winter freeze–thaw cycles increased phosphorus release from soils across all regions, leading to greater phosphorus export through runoff in recent years (Figure 3). However, these winter export processes were insufficient to offset phosphorus accumulation in dry counties.

Implications for local, real-life scenarios:

Climate change is expected to increase the frequency of drought and unusually wet conditions, adding new challenges and complexity to agriculture. For example, crops respond differently to changes in moisture, temperature, and higher levels of carbon dioxide, which affects their growth and how they absorb phosphorus from the soil. As a result, Faramarzi’s study has important implications:

1. Dry counties are often perceived as posing lower risk for downstream waterways because phosphorus stays in the soil, but extreme events (rapid snowmelt or heavy rainfall) can release accumulated phosphorus, especially from topsoil and through frequent freeze-thaw cycles. In wetter regions, soil fertility can decline if phosphorus losses are not carefully managed.
2. Crops use different amounts of water, which can affect how soil phosphorus retains or mobilized. For example, water-intensive crops like canola may use up more phosphorus than crops like wheat or barley. Choosing the right crops can help manage phosphorus accumulation and depletion patterns. 

How is this study be helpful to local stakeholders?

Overall, this study shows that in cold agricultural regions like the RDRB, water availability and crop choice, rather than fertilizer alone, determine the long-term fate of soil phosphorus. This means the same fertilizer strategy can have different effects depending on local moisture conditions and crop types. As climate change alters weather patterns, managing water, crops, and nutrients together is essential for protecting both crop yields and freshwater ecosystems.

Acknowledgment: This research was funded by the Alberta Innovates-Agriculture Funding Consortium and Natural Sciences and Engineering Research Council of Canada Discovery Grant awarded to Dr. Faramarzi.

Reference to the study’s published article:

Huang, Y., Qi, J., Mezbahuddin, S., Dyck, M., MacKenzie, M. D., Faramarzi, M. (2026). Effects of soil moisture and winter hydrologic processes on soil phosphorus accumulation and loss in canola croplands of cold-region watersheds. Science of the Total Environment. DOI: https://doi.org/10.1016/j.scitotenv.2025.181051

References cited in the first paragraph:

Peñuelas, J., Poulter, B., Sardans, J., Ciais, P., Van Der Velde, M., Bopp, L., Boucher, O., Godderis, Y., Hinsinger, P., Llusia, J., Nardin, E., Vicca, S., Obersteiner, M., Janssens, I.A. (2013). Human-induced nitrogen-phosphorus imbalances alter natural and managed ecosystems across the globe. Nature Communication.

Liu, J., Elliott, J.A., Wilson, H.F., Macrae, M.L., Baulch, H.M., Lobb, D.A. (2021). Phosphorus runoff from Canadian agricultural land: A cross-region synthesis of edge-of-field results. Agricultural Water Management.