The Influence of Climate on the Development of Soil Structure.

Soil structure affects soil water holding capacity, infiltration, evaporation, and the exchange of gases. Despite this importance, little is known about the role that climate has on the development of the shape, size, and grade of soil structure. This lack of understanding is, in part, due to the categorical and qualitative nature of soil structural data. The goal of this research, therefore, was to examine the development of soil structure along multiple climosequences of the conterminous USA. We chose a subset of samples from the National Cooperative Soil Survey (NCSS) Soil Characterization database, which contains laboratory data and field-derived information (e.g., depths, structure, rock fragments, pores, root distributions, and landform properties), to create the climosequences used in this study. Because the initial structure of these data files was prohibitively complex, we linked the information from both the field and laboratory, cleaned and filtered these data, and put them into an easily accessible form for further analyses. In addition, structural information was transformed from categorical descriptions to quantitative ratio scales using geometric values for each of the common ped type classes. Ped size was calculated using the geometric mean diameter of the structure size class recorded for each horizon and grade was placed on an ordinal scale ranging from structureless to strongly structured conditions. In addition, the dataset was combined with the USFS Ecoregions of the US and the Parameter-Elevation Regressions on Independent Slopes Model to add both climatological and ecological information. This merged and cleaned dataset is known as the University of Kansas Research Dataset of Soils (KURDS) and contains >94,000 observations. We used a variety of exploratory multivariate approaches to examine relationships within this dataset. The results from this work shed light on how soil structure responds to climatic gradients at both near surface and subsurface soil depths.