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Soil Genesis in a Natrargid-Haplargid Complex in Northern Montana¹

ABSTRACT

Classical theory of the genesis of Natargids (solonetz) involves the upward movement of sodium from a water table. Examination of 24 pedons representing four Soil Series developed in glacial till on the Northern Great Plains (Montana) suggests that Natrargids (solonetz and solodized-solonetz) and Haplargids (soloth) can develop in the absence of a water table. The four soils occur as a complex on "panspot" rangeland with the soloth and solodized-solonetz on microknolls and the solonetz in microdepressions. The panspot soils have significantly (p = 0.01) greater B horizon clay contents than associated non-panspot soils. X-ray diffraction analyses indicate decomposition of smectite inherited from the parent material in the sola of all soils. Solonization of the panspots is driven by reduced infiltration and subsurface water movement in response to matric and osmotic potential gradients. Panspots occur over high points in the till-shale boundary where the wetting front penetrates into the salty, calcareous till. Movement of sodium upwards from the shale contact results in dispersion of the panspot B horizon. Natric horizon development causes reduced infiltration and subsurface interpedon translocation of water, salts, and amorphous materials.

¹ Contribution from the Montana Agric. Exp. Stn., Montana State Univ., Bozeman, MT 59717, J. no. 1318; and the Wyoming Agric. Exp. Stn., Univ. of Wyoming, Laramie, WY 82071. Supported in part by the USDI-Bureau of Land Management through Interagency Agreement MT950-IA9-1442.

² Former Assistant Research Soil Scientist, Dep. of Plant and Soil Science, Montana State Univ., Bozeman, now Assistant Professor of Soil Science, Univ. of Wyoming, Laramie. Former Graduate Student, Dep. of Plant and Soil Science, Montana State Univ., Bozeman, now Soil Scientist, Montreal Engineering, Calgary.

Received for publication July 12, 1982. Accepted for publication July 1, 1983.