Phosphorus in Canadian Agriculture
For many years, phosphorus has been a staple in Canadian agriculture, helping deliver the core nutrients crops need to establish, grow, and thrive.
However, phosphorus runoff can occur due to snowmelt and seep into waterways, leading to the degradation of water quality due to excessive growth of aquatic plants and algae. Learn more in this CTV News article, “Researchers mapping phosphorus runoff hot spots in Lake Winnipeg“.
However, it has been found that adding humic acids to soil can be effective at reducing phosphorus runoff.
We reached out to our Soil Synergy Production Manager, Bernier Coto, and he explained how this works in detail.
Why Phosphorus Is Lost During Snowmelt
“Phosphate, commonly used in agricultural soils, is one of the least utilized elements in crop nutrition. In most soils, sources of soluble phosphorus bind to other elements, forming insoluble compounds that are not readily available to plants. The problem is that phosphorus is fixed in the soil’s clays in an insoluble form. So, why is phosphorus lost during snowmelt?”
“Most of the phosphorus lost during snowmelt is not dissolved phosphate, but particulate phosphorus bound to clays. Therefore, if the soil is more stable and less eroded, fewer particles are washed away. This means less particulate phosphorus reaches rivers and lakes because meltwater infiltration is improved.”
The Role of Gypsum and Magnesium Sulfate in Reducing Runoff
“How can this be achieved? This is where the application of agricultural gypsum (CaSO₄·2H₂O) and Epsom salts (magnesium sulfate MgSO₄·7H₂O) comes into play. Through two mechanisms, they help reduce phosphorus (P) loss in agricultural soils during snowmelt and, therefore, decrease freshwater pollution. They also improve soil structure and reduce erosion. The calcium (Ca²⁺) in gypsum and the magnesium (Mg²⁺) in magnesium sulfate flocculate or aggregate clay particles. This increases the size of soil aggregates and reduces surface runoff and particle transport during snowmelt.”
Why Humic Acids Are Essential for Phosphorus Management
“However, by applying these two amendments, we also indirectly cause greater phosphate fixation and, therefore, less uptake of this element by the crop. However, we generate a larger phosphorus reserve, and this is where humic acids come into play. Thanks to their complex structure of carboxylic compounds, humic acids create a balance among these soil compounds, making phosphorus much more available to microorganisms and plants.”
How Humic Acids Improve Soil Structure and Reduce Erosion
“But humic acids also play a role in soil structure formation. Remember, this is the natural way soil is formed. Humic acids have many negative functional groups (carboxyls –COO⁻ and phenols –O⁻). These groups can trap dissolved phosphorus, forming “humus-P” complexes, retaining phosphorus that would otherwise be washed away by surface water. They also trap phosphorus-binding cations, such as Ca²⁺, Mg²⁺, Fe³⁺, and Al³⁺. This creates “bridges” that keep phosphorus bound to soil organic matter, resulting in less free phosphorus in meltwater.”
How Humic Acids Reduce Particulate and Colloidal Phosphorus Loss
“Humic acids act as a natural adhesive for clay and silt particles, helping to increase aggregate stability, reduce surface sealing, and improve spring infiltration. This decreases runoff and the transport of phosphorus-bound particles, resulting in less surface erosion and reduced phosphorus loss. Much of the phosphorus lost in spring is not present as dissolved phosphate, but as colloidal phosphorus, composed of very fine particles that are easily moved. Humic acids stabilize these colloids and reduce their mobility.”
The Microbiological Role of Humic Acids in Phosphorus Availability
“We have analyzed the contribution from a chemical and physical standpoint, but another possible effect is microbiological. It is well known that phosphorus assimilation by plant roots, as well as its availability, is closely linked to microbiology. Many bacteria and fungi significantly influence the utilization of elements, as does the soil formation process itself, both chemically and physically. When the thaw begins, humic acids activate the dormant soil microbiology, thus contributing to better phosphorus stabilization and improved utilization in fertilization programs.”
An Integrated Strategy to Reduce Phosphorus Loss
“In summary, the best strategy for this phosphorus loss problem should include a combination of humic acids with agricultural gypsum (calcium sulfate) and Epsom salts (magnesium sulfate).”
Contact Soil Synergy to learn how humic products can elevate your fertilizer program and soil performance.
