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From the Fields

Q: Why is phosphorus immobile in soil?

A: In general, phosphorus is immobile in soil due to the chemical bonds a phosphate ion can form. Phosphorus from commercial fertilizer and soluble phosphorus in the soil — phosphate — is either present as H2PO4¯ or HPO4¯2 when the soil pH is near neutral. These are the forms of phosphorus that are plant available and can be taken up.

However, the oxygen that surrounds phosphorus in the phosphate ion allows for chemical bonds with other nutrients and soil clays depending on the soil pH. Phosphate readily binds with iron, aluminum, and manganese in soil solution and on iron/aluminum oxide surfaces when the pH is acidic (below 7), and phosphate binds with calcium or calcium carbonate surfaces when the pH is alkaline (above 7). The result is insoluble compounds. Therefore, phosphorus is rendered immobile and unavailable to plants.

Check out this related story on how soil pH affects phosphorus availability to determine optimum soil pH ranges for crop production.

Cristie Preston, PhD
Nutrien | Senior Agronomist

From the Fields

Q: How does potassium help plants regulate moisture?

A: To put it simply, potassium regulates the opening and closing of plant stomata. Stomates are the pores on plant leaves that allow for gas and water vapor exchange.

When plants have adequate potassium, the guard cells swell and allow for complete closure of the stoma opening. However, when plants are potassium deficient, these guard cells do not function properly and moisture can escape.

Adequate potassium fertilization is essential for crops, specifically those under drought stress. When moisture is limiting, potassium is pumped out of the guard cells and the pores will close tightly, thus allowing for the conservation of water. Otherwise, plants would be more susceptible to drought.

Stoma Open

Cristie Preston, PhD
Nutrien | Senior Agronomist