Sirichai Arayarungsarit. (1991) An evaluation of phosphorus balance of Upper Huai Fa Pah watershed after long-term monocropping of maize. Mahidol University,:ม.ป.ท.Sirichai Arayarungsarit. 1991. An evaluation of phosphorus balance of Upper Huai Fa Pah watershed after long-term monocropping of maize. ม.ป.ท.:Mahidol University,;Sirichai Arayarungsarit. An evaluation of phosphorus balance of Upper Huai Fa Pah watershed after long-term monocropping of maize. ม.ป.ท.:Mahidol University, 1991. Print.