Peer Review of Teaching Benchmark Portfolio for Soil 477/877: Great Plains Field Pedology

Pedology is a field that focuses on soil morphology, genesis, classification, and mapping. Students in pedology must learn to be keen observers, who are able to accurately evaluate the characteristics of the soil. This portfolio focuses on efforts to improve students’ skills at describing soil color, texture, and morphologic features

Distribution and Properties of Vesicular Horizons in the Western United States

Vesicular horizons are thin (usuallycm) surface or near-surface horizons characterized by the predominance of vesicular porosity. Th ey are widespread in arid and semiarid lands, occurring on every continent and covering 156,000 km2 of the western United States. Vesicular horizons have critical implications for management due to their role in controlling surface hydrology and dust mobilization. Th is study evaluates the distribution and varia-tion in expression of vesicular horizons across the western United States using the soil databases available from the USDA. A vesicular horizon index (VHI) that incorporates vesicular horizon thickness and the size and quantity of vesicular pores was developed using soil descriptions from a published chronosequence study. Th e VHI was applied to descriptions from the soil survey databases to evaluate vesicular horizon expression across the western United States. Vesicular horizons were better expressed (higher VHI) in the Central and Northern Basin and Range com-pared to the Mojave and Sonoran Basin and Range. Th is may be due to diff erences in temperature regime or to larger areas of playas in the Central and Northern Basin and Range that serve as sources of dust that forms the par-ent material for vesicular horizons. Th e median VHI was highest in the Aridisols and Mollisols compared to other soil orders. No signifi cant relationship was found between VHI and soil textures. Vesicular horizons are widely distributed in western United States and occur across a wide range of soil types and soil-forming environments

Analysis of vesicular porosity in soils using high-resolution X-ray computed tomograpy

Vesicular horizons are common at the surface of arid and semiarid soils and play a critical role in regulating infiltration. Most methods for examining pore morphology in the vesicular horizon involve physical sectioning of the sample and individual measurement of pores, which is time-consuming and provides an incomplete view of the pores. The objectives of this study were to (i) develop methods for the classification and characterization of pores in the vesicular horizon using high resolution X-ray computed tomography (HRXCT) and (ii) use these methods to examine the distribution of pores within vesic-ular peds. Three intact peds were scanned by HRXCT and examined using Blob3D software. A subset of pores from the first scan were observed and used to develop a classification tree model based on quantitative parameters of pore shape. Five major pore classes were found: equant vesicles, non-equant vesicles, individual vughs, connected vughs, and planar voids. All pore types decreased in size with increasing depth in the samples; however, the trend in quantity of pores with depth varied between pore types. In the ped with the least vesicular porosity, there was an increase in size and decrease in number of all pore types between the ped interior and exterior, a pattern which was reduced in the peds that were more dominantly vesicular. The application of HRXCT in this study shows how pore shape and size can be quantified within the vesicular horizon and reveals considerable variation of these characteristics within and between peds

Distribution and Properties of Vesicular Horizons in the Western United States

Vesicular horizons are thin (usuallycm) surface or near-surface horizons characterized by the predominance of vesicular porosity. Th ey are widespread in arid and semiarid lands, occurring on every continent and covering 156,000 km2 of the western United States. Vesicular horizons have critical implications for management due to their role in controlling surface hydrology and dust mobilization. Th is study evaluates the distribution and varia-tion in expression of vesicular horizons across the western United States using the soil databases available from the USDA. A vesicular horizon index (VHI) that incorporates vesicular horizon thickness and the size and quantity of vesicular pores was developed using soil descriptions from a published chronosequence study. Th e VHI was applied to descriptions from the soil survey databases to evaluate vesicular horizon expression across the western United States. Vesicular horizons were better expressed (higher VHI) in the Central and Northern Basin and Range com-pared to the Mojave and Sonoran Basin and Range. Th is may be due to diff erences in temperature regime or to larger areas of playas in the Central and Northern Basin and Range that serve as sources of dust that forms the par-ent material for vesicular horizons. Th e median VHI was highest in the Aridisols and Mollisols compared to other soil orders. No signifi cant relationship was found between VHI and soil textures. Vesicular horizons are widely distributed in western United States and occur across a wide range of soil types and soil-forming environments

Analysis of vesicular porosity in soils using high-resolution X-ray computed tomograpy

Vesicular horizons are common at the surface of arid and semiarid soils and play a critical role in regulating infiltration. Most methods for examining pore morphology in the vesicular horizon involve physical sectioning of the sample and individual measurement of pores, which is time-consuming and provides an incomplete view of the pores. The objectives of this study were to (i) develop methods for the classification and characterization of pores in the vesicular horizon using high resolution X-ray computed tomography (HRXCT) and (ii) use these methods to examine the distribution of pores within vesic-ular peds. Three intact peds were scanned by HRXCT and examined using Blob3D software. A subset of pores from the first scan were observed and used to develop a classification tree model based on quantitative parameters of pore shape. Five major pore classes were found: equant vesicles, non-equant vesicles, individual vughs, connected vughs, and planar voids. All pore types decreased in size with increasing depth in the samples; however, the trend in quantity of pores with depth varied between pore types. In the ped with the least vesicular porosity, there was an increase in size and decrease in number of all pore types between the ped interior and exterior, a pattern which was reduced in the peds that were more dominantly vesicular. The application of HRXCT in this study shows how pore shape and size can be quantified within the vesicular horizon and reveals considerable variation of these characteristics within and between peds

The Impact of Sampling Methodology on Soil Bulk Density Measurement by the Clod Method

The clod method is a widely used and accurate bulk density method. However, its use is limited to sampling from soil pits. This study was conducted to: 1) determine whether clods collected from cores provide similar bulk density measurements to those collected from soil pits and 2) evaluate the impact of various clod bulk density methods on carbon stock calculation. Clods were collected from soil pits, 5.1 cm soil cores, and 8.9 cm soil cores. Three-dimensional laser scanning was used to measure the volume of the soil clods before and after oven-drying and bulk density was calculated as the dry mass of the clod divided by volume. Of 24 horizons sampled, 17 showed no significant effect of sampling method (core vs. pit) on dry bulk density. The error introduced by collecting clods from a core was small enough that it had no significant effect on carbon stock (p = .683). However, the moisture at which clods were scanned did have a significant effect on carbon stocks (p = .002 to 0.016). Data from the study suggest that collecting clods from soil cores introduces minimal error, but attention should be given to the moisture state at which clod volume is determined

Strange Stones of Skull Creek: Basalt Glacial Erratics and Omars in Eastern Nebraska

We describe unusual stream- reworked glacially transported rocks (erratics) from a locality 50 km east of the limit of all pre- Illinoian (pre- 190 ka) Pleistocene glaciations in the central USA. Almost all these erratics consist of the igneous rock basalt, and of those, the vast majority have at least one fl at, smooth face. Some have two or more such faces that meet at obtuse angles along one or more well- defi ned, straight edges. We attribute these features, as well as laminations, plumose marks, and other features, to columnar jointing in ancient lava fl ows and shallow intrusions. Th e most likely source of these erratics is the Lake Superior region. Aft er the Laurentide Ice Sheet deposited them, the erratics experienced at least one episode of erosion and deposition in local stream sediments as the regional landscape evolved during the Middle Pleistocene to Holocene times. Before it found its way into Skull Creek, one of the basalt erratics was polished and reshaped as a ventifact by sediment- laden Pleistocene winds as it lay exposed on an ancient land surface. We also found four examples of omars: very distinctive erratics that eroded from outcrops in Hudson Bay and transported 2,100 km into the study area

Soils of the Central Nebraska Loess Hills and Central Loess Plains

Understanding soil systems that characterize a region is critical to natural resource management. However, the knowledge gained through intensive study of local soil systems, which takes place annually as part of collegiate soil judging contests, is often poorly preserved for future use. In this study, field descriptions and laboratory data for 16 soil profiles described for the 2019 Region 5 Soil Judging Contest were used to characterize the soil system of the Central Nebraska Loess Hills and Central Loess Plains. Three landscape components of this soil system were analyzed: the loess uplands and rainwater basins, the transitional zone, and bottomlands. Rainwater basins exhibit increasing clay, clay films, and melanization compared to surrounding uplands. The transitional zone between the upland and bottomlands exhibits fining and aging of parent material with increasing elevation, resulting in increased prevalence of clay films, lower pH relative to parent material, and melanization. The bottomlands exhibited subtle variations in texture of the alluvium resulting in differences in expression of melanization, effervescence, pH, and redoximorphic features. Patterns observed within this soil system are well explained by existing pedogenic theories and demonstrate the unique interplay between soil-forming factors characteristic of this region of the Great Plains

Manganese-coated IRIS to document reducing soil conditions

Iron-coated indicatorof reduction in soils (IRIS) devices have been used for nearly two decades to help assess and document reducing conditions in soils, and official guidance has been approved for interpreting these data. Interest in manganese (Mn)-coated IRIS devices has increased because Mn oxides are reduced under more moderately reducing conditions than iron (Fe) oxides (which require strongly reducing conditions), such that they are expected to be better proxies for some important ecosystem services like denitrification. However, only recently has the necessary technology become available to produce Mn-coated IRIS, and the need is now emerging for guidance in interpreting data derived from Mn IRIS. Ninety-six data sets collected over a 2-yr period from 40 plots at 18 study sites among eight states were used to compare the performance of Mn-coated IRIS with Fe-coated IRIS and to assess the effect of duration of saturation and soil temperature as environmental drivers on the reduction and removal of the oxide coating. It appears that the current threshold prescribed by the National Technical Committee for Hydric Soils for Fe-coated IRIS is appropriate for periods when soil temperatures are warmer (\u3e11 °C), but is unnecessarily conservative when soil temperatures are cooler (5–11 °C). In contrast, Mn-coated devices are particularly useful early in the growing season when soil temperatures are cool. Our data show that when using a threshold of 30% removal of Mn oxide coatings there is essentially 100% confidence of the presence of reducing soil conditions under cool (\u3c11 °C) conditions

The effects of nitroxyl (HNO) on soluble guanylate cyclase activity: interactions at ferrous heme and cysteine thiols

It has been previously proposed that nitric oxide (NO) is the only biologically relevant nitrogen oxide capable of activating the enzyme soluble guanylate cyclase (sGC). However, recent reports implicate HNO as another possible activator of sGC. Herein, we examine the affect of HNO donors on the activity of purified bovine lung sGC and find that, indeed, HNO is capable of activating this enzyme. Like NO, HNO activation appears to occur via interaction with the regulatory ferrous heme on sGC. Somewhat unexpectedly, HNO does not activate the ferric form of the enzyme. Finally, HNO-mediated cysteine thiol modification appears to also affect enzyme activity leading to inhibition. Thus, sGC activity can be regulated by HNO via interactions at both the regulatory heme and cysteine thiols