The decline of pH over time in the first and third phase suggested that drying of soil with sunlight is a major factor controlling the decrease in pH. Drying also enhances soil aeration that along with an optimum temperature range accelerates nitrification as nitrifying bacteria are almost exclusively aerobic microorganisms (Avnimelech and Ritvo, 2003). As a consequence, nitrification releases H+ to the soil, causing a decrease in pH (Hargreaves, 1998).