Wiwat Ingkapradit และ Surapol Chatuporn. (2005) The Effects of Long Term of Ammonium sulphate Application on Properties of Paddy Soil and Rice Yield at Suphanburi Rice Research Centre in both Dry and Wet Seasons. <i>Thai Agricultural Research Journal</i>, <i>23</i>(1), 2-20.Wiwat Ingkapradit และ Surapol Chatuporn. "The Effects of Long Term of Ammonium sulphate Application on Properties of Paddy Soil and Rice Yield at Suphanburi Rice Research Centre in both Dry and Wet Seasons". Thai Agricultural Research Journal 23 (2005):2-20.Wiwat Ingkapradit และ Surapol Chatuporn. The Effects of Long Term of Ammonium sulphate Application on Properties of Paddy Soil and Rice Yield at Suphanburi Rice Research Centre in both Dry and Wet Seasons. Department of Agriculture:ม.ป.ท. 2005.