Ustic

Abstract: It is important to know quantity of crop residue on the soil surface to maintain or to improve soil physical and chemical properties and to assess the soil's susceptibility to erosion. Our objective was to use remote sensing techniques to examine the potential for remotely differentiating among wheat residue quantities and bare soils. We used three soils of the northern Great Plains (Williams loam [fine-loamy, mixed Typic Argiboroll], Vanda Clay [fine-silty, mixed calcareous, frigid Ustic Torriorthents], and Lambert silt loam [finesilty, mixed calcareous, frigid Typic Ustorthents]) that had either dry or wet surfaces and 0, 33, 66, and 100% wheat residues covering the soil surfaces (...)

Abstract: A suite of Vertisols (clay-rich soils with high shrink-swell potential) were examined across a climosequence (climatic transect) in twelve soil pits from the Coast Prairie of Texas in order to determine if mean annual precipitation (MAP) exerts a control on the chemistry of these soils, and if the observed chemical trends are useful for interpreting paleoclimate records of paleoVertisols in the geologic record. The precipitation regime of the climosequence spans a range between 144 and 86 cm/year, with moisture regimes classified as udic, udic-ustic, ustic, and aridic-ustic, in a general northeast to southwest direction. Other soil-forming factors, such as soil age (<35–40 ka), parent material (fluviodeltaic Beaumont Formation of late Pleistocene age), landscape (low-relief coastal plain), and vegetation (prairie or mixed woody shrubs), are relatively constant across the climosequence. Climate-sensitive chemical proxies of MAP identified include dithionite citrate-extractable Fe (Fedith), acid oxalate-extractable Fe (Feoxal), CaCO3 equivalent (CaCO3equiv), S, and ammonium acetate-extractable Na, K, and Mg (Naacet, Kacet, and Mgacet, respectively), which vary across the climosequence because of differences in effective depths of leaching and intensity of wetting and drying cycles. These standard USDA wet-chemical climate proxies are related to bulk (oxide or element) chemistry of soils and paleosols measured using XRF, which supports the use of geochemical climate proxies for interpreting the paleoclimate records of paleoVertisols. Application of the chemical index of alteration minus potash (CIA-K) geochemical climofunction to late Mississippian paleosols from the Appalachian basin of the eastern U.S. demonstrates evidence for a shift from a lower to a higher MAP paleoclimate that is consistent with previous paleoclimate models and with observed morphological changes in the paleosols. We advocate actualistic research using bulk chemistry of soils and paleosols as a means of obtaining soil information useful for interpreting paleosols in the geological record.

Abstract: . Topsoil (0–20 cm) and subsoil (60–100 cm) properties are compared at agricultural and nearby natural vegetation sites in Sao Paulo State. Differences are related to land use and climate, in order to estimate soil carbon storage under various ecosystems and also to study the effects of high-input agriculture on the chemical composition of soils with low activity clays. Within each land use, organic carbon in the topsoil is most strongly related to clay + silt content. This relationship is stronger for cropped, short savannah (cerrado) and tall savannah (cerradao) sites than for semi-deciduous and evergreen forest sites. Losses of topsoil carbon with cropping can be predicted if the initial carbon and the clay+silt contents are known. The greatest carbon losses after long term cultivation occurred in forest mineral topsoils, ranging from 6% for perudic clayey soils to 37% for ustic sandy soils. No significant difference in carbon content was found between the paired savannah-cultivated sites. In most of the originally less fertile soils cation exchange capacity was greater in the cultivated topsoil (Ap) than in the topsoil under savannah or forest (A1), probably because of liming and phosphate fertilization. Most subsoils at agricultural sites show increases in exchangeable bases (mainly Ca) and base saturation, but no significant change in pH.