Incorporating analytical data and comments from:
N. Yoshinaga,
Department of Agricultural Chemistry, Ehime University, Matsuyama, Japan;
J.M. Kimble, T.L. Huscher and S. Samson,
USDA Soil Conservation Service, Midwest National Technical Center, Lincoln, Nebraska,
USA;
S. Shoji and I. Yamada,
Faculty of Agriculture, Tohoku University, Sendai, Japan.