Polthanee, Anan. 2001. “The Effects of Field Ridging and Flat-Field Planting on Growth and Yield of Three Legumes Grown Before Rice in the Pre-Monsoon Season of Northeastern Thailand”. Agriculture and Natural Resources 35 (1). Bangkok, Thailand:51-59. https://li01.tci-thaijo.org/index.php/anres/article/view/240320.