Ammonia (NH3) reacts with nitric acid or sulfuric acid in the atmosphere and contributes to the formation of fine particulate matter. It is mainly produced by application of nitrogen fertilizer and livestock manure to the arable soil. Volatilization of NH3 could decrease with application of acidic amendments such as iron sulfate (FeSO4) through decreasing soil pH. This study was conducted to determine an optimum application rate of FeSO4 to reduce NH3 volatilization and maintain crop productivity in arable soil. Iron sulfate was applied at the rates of 0, 50, 100, and 200 kg Fe ha-1. Cabbage (Brassica rapa L.) was planted on April 8th 2020 and harvested on June 10th 2020. The NH3 gas was collected using static chamber (300 mm in length and 120 mm diameter) method. Cumulative NH3-N volatilization decreased significantly with increasing application rate of FeSO4. It decreased by ca. 21% at 200 kg Fe ha-1 of FeSO4. Soil pH decreased significantly with increasing application rate of FeSO4. A decrease in cumulative NH3-N volatilization with FeSO4 was mainly attributed to decrease in soil pH. Cabbage yield did not decreased with increasing application rate of FeSO4. The maximum cabbage yield was 7.10 Mg ha-1 and cumulative NH3-N volatilization decreased by 10.2% from 28.4 kg ha-1 63 days-1 to 25.8 kg ha-1 63 days-1 with 110 kg Fe ha-1 of FeSO4 application. Cumulative NH3-N volatilization from soils amended with different rates of FeSO4