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. Water-intensive crops like canola may deplete phosphorus faster than wheat or barley, while climate change may also intensify the release of phosphorus, increasing pollution risks downstream.
