Thoughts on acidification of soils by nitrogen and sulfur fertilizers

Some crops, like blueberries, require a pH of 4 to 5. Irrigation of acid‐loving crops with alkaline water can raise pH and cause micronutrient deficiencies. Diseases like citrus greening (Huanglongbing) are more severe at higher soil pH values. Application of acidifying fertilizers to lower soil pH may therefore benefit crop growth in such instances and release calcium from calcareous soils to remove sodium. Therefore, a good understanding of the processes involved and the amount of acidification from various fertilizer materials is needed. We show with an anion–cation balance of recent plant uptake data that the alkalinity released from plant uptake of nutrients alone gave a value of 2 kg CaCO 3 equivalents of alkalinity per kilogram of N uptake, in close agreement with Association of Official Analytical Chemists values of 1.8. We also provide equations and calculations and a summary table that allows a user to compare the acidifying capacity of commonly available N and S fertilizers.