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Biological Assay of Pumice Soil Fertility¹

ABSTRACT

The fertility of pumice soils is difficult to assess by laboratory analysis. A biological assay of growth responses yields more meaningful information. Four pumice soils common in central Oregon were assayed in the greenhouse using ponderosa pine as an indicator species.

A composite experimental design was used involving additions of N, P, K, Ca, and S. There were no responses to either K or Ca. Nitrogen appeared to be the most deficient nutrient element since it was the only one tested that gave large responses when added alone. Combinations of N and P and N and S gave better responses than N alone. Best growth resulted from addition of N, P, and S in combination. The experimental design used was very satisfactory for this type of assay, particularly in evaluating various nutrient interactions.

¹ Technical Paper No. 1806. Oregon Agr. Exp. Sta., Oregon State Univ., Corvallis, Ore. Portions of the material presented before Div. S-7 Soil Science Society of America, St. Louis, Mo., Nov. 29, 1961.

² Professor of Forest Soils, Oregon State University and Soil Scientist, Pacific Northwest Forest and Range Exp. Sta., respectively. Statistical analyses were made by the Oregon State University Statistical Service, Dr. Lyle A. Calvin in charge.

Received for publication April 20, 1964. Accepted for publication November 25, 1964.