Characteristics of the Colo Soil Series as Mapped in the North Central Region

The Colo soil series (fine-silty, mixed, mesic Cumulic Haplaquoll) was sampled and studied in areas mapped as Colo in the North Central Region (NCR). Within this broad geographic area, there are variations in climate, vegetation, parent material, relief, and time—the five soil-forming factors. This soil is mapped on floodplains of streams and in drainageways of various size. Forty-seven soil profiles from five states were described and sampled to determine selected physical, chemical, and mineralogical properties and the ranges of these properties in this series. The principal objectives of this investigation were to (i) study one soil series and characterize the series as mapped, (ii) compare Colo soil properties with associated upland soils, and (iii) develop a model to better understand the genesis of soils derived from alluvial sediments in the NCR. Depth distribution of selected chemical and physical properties in some Colo profiles indicated some degree of horizon differentiation. Clay, total phosphorus (TP), inorganic phosphorus (IP), and available phosphorus (AVP) depth distributions in many profiles had a zone of eluviation and illuviation, indicating redistribution of these constituents within the profile. One possible interpretation of the redistribution is that the soils are on landforms that have been stable for some period of time. Total carbon (TC) content usually decreased regularly with increasing depth. Clay mineralogical analyses indicated a dominance of interstratified clay minerals. Smectite, kaolinite-chlorite, and illite are minor clay minerals in these soils as interpreted from relative peak heights. For most profiles, clay mineralogy was similar with increasing depth. Statistical model equations involving several physical, chemical, and mineralogical parameters, as dependent or independent variables, were developed.