Phytolith Size Characteristics Between Udolls and Ustolls

To test a phytolith size‐annual rainfall relationship hypothesis, the sizes of opaline phytoliths from four Oklahoma soils were compared. Opaline phytoliths form in intimate association with plant cells and the variation of plant cell size with moisture stress forms the theoretical basis for the hypothesis. The soils sampled were St. Paul, a Typic Argiustoll; Zaneis and Vanoss, Udic Argiustolls; and Fitzhugh, a Typic Argiudoll. Opaline phytoliths were isolated from the 5–20µ, 20–35µ, and 35–50µ soil fractions. The relative amounts of phytoliths in these size fractions in the upper 10 cm of each soil was used to measure their size variation among soils. Phytoliths were further characterized by shape in each soil. Distribution of phytoliths with depth was also noted. There was a higher incidence of the 5–20µ phytoliths in the Ustoll than in the Udoll (66.9% vs. 53.2%) and a correspondingly higher percentage of 35–50µ phytoliths in the Udoll compared to the Ustoll (14.8% vs. 4.4%). The Udoll‐Ustoll intergrades contained intermediate quantities of the 35–50µ phytoliths but not of the 5–20µ and 20–35µ phytoliths. It was concluded that the hypothesized relationship seemed to exist with further work required to understand the relationships in the intermediate areas. Such a relationship would be a very useful tool in paleosol and paleoclimate studies.