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Native Fixed Ammonium in Hawaiian Soils¹

ABSTRACT

Native fixed ammonium was found to range from 0 to 585 ppm. Volcanic ash soil horizons generally had a lower fixed ammonium content (4 to 178 ppm) than those from basalt (0 to 585 ppm). There was a general decrease of fixed ammonium concentration with depth in most of the profiles, this pattern of decrease being more pronounced in basaltic soils than in ash soils. Native fixed NH₄-nitrogen as a fraction of total nitrogen in individual horizons varied from 0 to 32.9%. This fraction was generally much greater in the basalt soils than in the ash soils. The soils did not show any definite pattern in the profile as to the relative amount of nitrogen present as native fixed ammonium. There was a highly significant relationship between native fixed ammonium and total K₂O and percent mica in both ash and basalt soils. This relationship, however, does not apply to young, partially weathered soils containing primary potassium-bearing minerals. The difference between organic C/organic N and organic C/total N ratios was generally greater in basaltic soils than in ash soils.

¹ This paper is part of a thesis submitted by the senior author to the Graduate Division of the University of Hawaii in partial fulfillment of the M.S. degree requirements. Approved by the Director of the Hawaii Agr. Exp. Sta. as Technical Paper no. 912. Supported in part by Western Regional Research Project no. W-31. Presented before Div. S-2, Soil Sci. Soc. Amer. at Stillwater, Okla., Aug. 24, 1966.

² Formerly Research Assistant and Associate Professor of Soil Science, respectively, Department of Agronomy & Soil Science, University of Hawaii.

Received for publication October 2, 1967. Accepted for publication March 27, 1968.