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The Composition of the Silt Fraction as Related to the Development of Soils From Loess
Author(s) -
Springer M. Elsworth
Publication year - 1949
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1949.036159950013000c0083x
Subject(s) - loess , soil water , silt , citation , composition (language) , library science , environmental science , geology , computer science , soil science , philosophy , linguistics , geomorphology , paleontology
PROFILES of five loessial soils from northwest Missouri were used to relate the chemical composition of the silt fraction from the solum and its underlying loess to soil development processes. The composition of the silt fraction within the horizons of a soil depends upon the nature of the parent material and the type and degree of weathering. Accordingly as this composition differs from that of the material from which the soil developed, some of the changes with soil development may be interpreted. The soil survey of Holt County, Missouri, revealed that the soil types derived from loess lie in bands roughly parallel to the bluff. The order, starting at the bluff, is Hamburg silt loam, Knox silt loam, Marshall silt loam, brown phase, Marshall silt loam, and Sharpsburg silty clay loam (Fig. 1). The loess is deepest at the bluff, and shallower as the distance from that point increases. It ranges in depth from the 60 to 100 feet under Hamburg to the 7 to 11 feet in the Sharpsburg area. The native vegetation was prairie on all soils except Knox and part of the Hamburg, where mixed hardwoods were found at the time of first settlement. The topography of these soil types ranges from hilly on the Hamburg to undulating for the Sharpsburg. However, through selection of the sites similar topography was found on all except trie Hamburg for collection of representative samples for study. Holt County is bounded on the west and south by the Missouri River. The Missouri River flood plain with a width of 5 to 10 miles was the main source of loess from which the soils were developed. Transportation by wind and deposition occurred mainly during the Peorian substage. Holt County is in a region of prairie soils. The climate is continental subhumid. The average annual precipitation is 35 inches, with 26 inches falling from April to September inclusive. The average annual temperature is 53° F, with a January average of 26° F and a July average of 78° F. Evaporation exceeds precipitation as indicated by Transeau (8) who shows a precipitation-evaporation ratio of 0.6 to 0.8. Sample profiles of the soils developed under these conditions were chosen. Studies of the general morphological features, pH, mechanical composition, and chemical composition of the silt were made. Where so many factors of soil formation were constant, it seemed probable that in these predominantly silty soils critical studies of the silt fractions should contribute to the knowledge of soil development. HISTORICAL