Tawin Krutkun, Samruay Krutkun, and Chamchan Vijarnsorn. “Development and Conservation of Soil Fertility of Cultivated Soils of the East Region of Thailand”. Agriculture and Natural Resources 25, no. 1 (March 31, 1991): 1–8. accessed September 18, 2026. https://li01.tci-thaijo.org/index.php/anres/article/view/241897.