A model for evaluating differentiating characteristics of the Colo soils as mapped in the North Central Region

Abstract

<p>The Colo soil series (fine-silty, mixed, mesic Cumulic Haplaquoll) was studied as mapped 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. The majority of the Colo soil profiles studied (located on floodplains of streams of varying size) were collected at the type location for the Colo series in the county soil survey. Forty-seven soil profiles were described and sampled to determine selected physical, chemical, and mineralogical properties of the Colo soil. A limited amount of data for soils derived from alluvial sediments is available. This investigation studied one soil series and characterized the series as mapped, compared soil and landscape parameters relative to the Colo soil, and developed a model to better understand the genesis of soils derived from alluvial sediments in the NCR;Chemical and physical depth distributions of selected properties in some profiles indicated some degree of horizon differentiation. Clay depth distributions were either a straight line or a curve which increased systematically with depth to a maximum (illuviated zone) then decreased, indicating little particle size stratification. B/A and subsurface/surface (sub/sur) clay ratios ranged from 1.7 to .9. Total phosphorus (TP) and inorganic phosphorus (IP) depth distributions in many profiles had a zone of eluviation and illuviation indicating redistribution of phosphorus in the profile. This could be interpreted that the soils are on landforms that have been stable for some period of time. Total carbon (TC) content usually increased regularly with increasing depth. In some profiles the TC increased with depth to a maximum then decreased with increasing depth. Recent sediments with relatively low amounts of TC were present in the upper part of some profiles;Statistical model equations involving several physical, chemical, mineralogical, and landscape parameters as dependent or independent variables were developed. The statistical model developed with chemical and physical data for all observations that had the highest R('2) (.72) had TC as the dependent variable and TP, IP, organic phosphorus/total phosphorus and organic carbon/organic phosphorus as independent variables. Another model, significant at the 1% level, predicted the relationship of clay, TC, AVP (available phosphorus), and HION (hydrogen ion activity in moles/liter) to TP. Weighted averages of the physical and chemical data were also used in model equations. Models using other soil and landscape vairables such as the type of clay minerals present, longitude, latitude, climatic data, width of the floodplain, parent material, vegetation, and slope and erosion class of the associated upland soils were indexed to determine relationships among these variables;Clay mineralogical analyses indicated a dominance of interstratified clay minerals while montmorillonite, kaolinite-chlorite, and illite were minor clay minerals as interpreted from relative peak heights. The types of clay minerals did not change but relative peak heights did change with depth in the profile.</p>