Received for publication May 30, 1972. Published with the approval of the Director of the Colorado State University Experiment Station as Scientific Series Paper No. 1728. This work was supported in part by materials and grant-in-aid funds from Geigy Agricultural Chemicals, Ardsley, New York 10502, and Rayonier, Incorporated, New York 17, New York. Leonardite, sold as Aqua Humus, was supplied by American Humates, Inc., Dallas, Texas.
The author acknowledges with sincere appreciation the advice and assistance of J.S. Williams and Forest Nelson, Statisticians, Colorado State University, Fort Collins.