Paweena Kirttrakolkal และ Ampan Bhromsiri. (2008) Chemical Fertilizer Management for Head Lettuce in the Northern Highland. <i>Thai Agricultural Research Journal</i>, <i>26</i>(3), 275-290.Paweena Kirttrakolkal และ Ampan Bhromsiri. "Chemical Fertilizer Management for Head Lettuce in the Northern Highland". Thai Agricultural Research Journal 26 (2008):275-290.Paweena Kirttrakolkal และ Ampan Bhromsiri. Chemical Fertilizer Management for Head Lettuce in the Northern Highland. Department of Agriculture:ม.ป.ท. 2008.