Pedogenesis along a Climosequence in Loess-Derived Soils of the Central Great Plains

Abstract

Understanding the pedogenic effects of average annual precipitation on loess-derived soils provides insight to past climate scenarios based on buried paleosols, as well as the ability to better predict future soil morphological changes due to projected climate forcings. This study explains variability in soil morphological properties in surface loess along a precipitation gradient in the Central Great Plains of the United States. Soil cores were collected from undisturbed portions of seven pioneer cemeteries to a depth of 50 cm across the transect spanning northwest Kansas into western Missouri. Pioneer cemeteries were selected due to the likely undisturbed nature of the soils in unused portions of the cemeteries. Soil cores were cut into 2.5-cm intervals, which were prepared and analyzed for bulk density (BD), color (CIELAB 1976 color space), organic carbon (OC) obtained from a modified Walkley-Black method, and aggregated and disaggregated particle-size distributions (PSD) from laser diffraction. The predictor variables--annual precipitation, depth, and PSD--were used in multivariate analyses to explain the distribution of the pedogenic indicators: color, OC, BD, and complexed organic carbon (COC). Lightness (L*), OC, BD, and COC--an indicator of soil physical quality--were all significantly explained by average annual precipitation. A proxy for microaggregation, geometric mean shift (GMS), was developed for this study deriving the difference between the geometric mean of the untreated and pretreated PSD results. Microaggregation occurred below an OC to clay ratio of 0.163 in the upper 50 cm of the loess-derived soils analyzed in this study. Among the morphological variables considered, COC had the highest coefficient of determination (R2 = 0.871) and BD was best explained by average annual precipitation. These findings indicate any future climate forcings resulting in precipitation changes may have an effect on soil physical quality of loess-derived soils.