Phosphorus is crucial for crop growth. But too little can lower crop yields, and too much can lead to pollution downstream. Studies show that some soils are losing phosphorus, while others are accumulating and leaking into waterways, says watershed researcher Monireh Faramarzi.
“This creates confusion about what is actually happening in farm landscapes,” she says, especially in areas with frequent freeze/thaw cycles.
Faramarzi and her collaborators, including lead author Yinlong Huang of the Faculty of Science, have now discovered that moisture has a greater effect than fertilizer alone on phosphorus levels in soil.
The researchers tracked soil moisture, temperature and snowmelt in the canola-growing Red Deer River Basin for almost three decades. Despite similar amounts of fertilizer use, some areas gained phosphorus, but others lost it or stayed in balance, which pointed to moisture as the key determinant.
In drier areas crops absorbed less phosphorus, causing it to accumulate in the soil, whereas in wetter areas crops took up more, leading to depletion or a steady balance.
“This means fertilizer alone is insufficient for phosphorus management; soil moisture and crop choice also matter,” says Faramarzi. “Where moisture is not limiting, water-intensive crops like canola may deplete soil phosphorus faster than wheat or barley. Climate change could further alter phosphorus release, with consequences for both crop productivity and downstream pollution risks.”
This research was funded by grants from the Alberta Innovates Agriculture Funding Consortium and the Natural Sciences and Engineering Research Council of Canada.