Siripaiboon, Chantana, and Pornpimol Chaiwanakupt. 1999. “Evaluation fo rDinitrogen fixation and Yield of Soybean Cultivars under Conditions of Zero and Conventional Tillage by 15N Technique”. Thai Agricultural Research Journal 17 (2):116-28. https://doi.org/10.14456/thaidoa-agres.1999.12.