The soil pH is determined by the concentration of which ions?

The soil pH is determined by the concentration of which ions?

• A. hydrogen and nitrogen
• B. phosphorus and gypsum
• C. calcium and phosphates
• D. hydroxyl and hydrogen

Answer: (D)

Soil pH is determined by the hydrogen ion activity in the soil solution. In water, hydrogen ions and hydroxyl ions are linked by the autoionization of water, with the product [H+][OH−] = Kw. This means the balance between hydrogen ions (which lower pH and increase acidity) and hydroxyl ions (which raise pH and increase basicity) sets the soil’s overall pH. In other words, the acidity or alkalinity you measure comes from how many hydrogen ions are present, with hydroxyl ions reflecting the opposite end of the same equation. Other nutrients or compounds, like nitrogen, phosphorus, calcium, or gypsum, influence soil chemistry and nutrient availability, but the pH itself hinges on hydrogen and hydroxyl ion concentrations.

Soil pH is determined by the hydrogen ion activity in the soil solution. In water, hydrogen ions and hydroxyl ions are linked by the autoionization of water, with the product [H+][OH−] = Kw. This means the balance between hydrogen ions (which lower pH and increase acidity) and hydroxyl ions (which raise pH and increase basicity) sets the soil’s overall pH. In other words, the acidity or alkalinity you measure comes from how many hydrogen ions are present, with hydroxyl ions reflecting the opposite end of the same equation. Other nutrients or compounds, like nitrogen, phosphorus, calcium, or gypsum, influence soil chemistry and nutrient availability, but the pH itself hinges on hydrogen and hydroxyl ion concentrations.