1. Weiliang Yunshu Yu Weifei Shiyong, Longye Publishing House, Beijing, 1984 p. 103.
2. Trace Element in Plants, Elsevier Science Publishing Company, New York, 1984, p. 195.
3. Youji Shiji Yu Huatan Fenxi, Dizhi Publishing House, Beijing, 1985, p. 160.