A Buffer For Acid Requirement Determination Of Soils.

High soil pH can be a problem to grow acid-loving plants such as blueberries, azaleas and many others optimally.  The causes of high soil pH are overliming, free Ca/Mg carbonate parent materials and/or high concentrations of OH^-, HCO3^- and CO₃^-2.  Even though there are many proven materials that will reduce soil pH, there is a lack of a rapid method to determine the amount of acidifying materials that can be applied to soil to lower the pH. The objective of this study was to develop a rapid laboratory method that will determine the amount of acid needed to lower a soil pH to a target value.  Ten mL soil samples were equilibrated with 10 mL of H₂O and water pH was measured.  Then, 10 mL of either dilute NH₄CH₃COOH + KH₂PO₄ + NH₄F, H₂SO₄, FeSO4 or (Al)₂(SO₄)₃, were added to the same soil samples and pH was measured in 20 mL of H₂O and buffer (1:1) solutions.  Each buffer solution was evaluated for reproducibility, sensitivity and stability. A simple equation analogous to soil lime requirement methods was developed that determined the amount of acid needed to lower soil pH to a target value.