PO 37: Describe the long-term change in soil pH from applying N

Nitrification or the conversion of ammonium N to nitrate N produces acidity:

2 NH₄⁺ + 4 O₂ → 2 NO₃^- + 4 H⁺ + H₂O

2 H⁺ are produced for every N in the ammonium-N form (NH₄⁺).  This reaction occurs regardless of the source of the NH₄⁺.  This acidity is often the largest single source of acidity in fertilized agricultural soils.

The net amount of acidity created when N fertilizer is applied depends on other reactions that occur with the fertilizer.  The acidity created by different fertilizer materials is summarized below, as is the lb CaCO₃ required to neutralize the acid.