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At least 613 records · Page 34Linked to original sources

USGS1992

Relating results from earthworm toxicity tests to agricultural soil

The artificial soil tests of the European Economic Community and of the Organization for Economic Cooperation produce data relating earthworm mortality to pesticide concentrations in soil under laboratory conditions. To apply these results to agricultural soils it is necessary to relate these concentrations to amounts of pesticide applied per area. This paper reviews the relevant published literature and suggests a simple relation for regulatory use. Hazards to earthworms from pesticides are suggested to be greatest soon after application, when the pesticides may be concentrated in a soil layer a few millimeters thick. For estimating exposure of earthworms, however, a thicker soil layer should be considered, to account for their movement through soil. During favorable weather conditions, earthworms belonging to species appropriate to the artificial soil test have been reported to confine their activity to a layer about 5 cm. If a 5-cm layer is accepted as relevant for regulatory purposes, then an application of 1 kg/ha would be equivalent to 1-67 ppm (dry) in the artificial soil test.

Book chapter↗

USGS1991

Calcic, gypsic, and siliceous soil chronosequences in arid and semiarid environments

We studied three soil chronosequences in the western USA to compare the development of calcic, gypsic, and siliceous soils through time. We compared calcic soils from the Silver Lake playa, southeastern California, gypsic-calcic soils from the Kane Fans in Big Horn County, Wyoming, and siliceous-calcic soils from Forty-mile Wash in southwestern Nevada. In these areas, carbonate, gypsum, and opaline silica appear to be derived primarily from eolian additions and, in advanced stages typical of old soils, are dissolved and precipitated as diagnostic calcic or petrocalcic, gypsic or petrogypsic, and duripan soil horizons. These three precipitates produce somewhat similar morphologic characteristics through time. Morphological stages progress from discrete coatings under clasts, to matrix and around clasts, to significant coatings of clasts and cementation of matrix, to laminar caps above plugged horizons in cases of carbonate and silica. Significant differences among the three soil types include development of color, change of pH, and the depth to which the precipitates begin to accumulate. The tops of gypsic horizons occur below the tops of calcic horizons in simple leaching regimes; the depth to the tops of siliceous horizons is more closely related to the presence and development of argillic horizons.

Conference Paper↗

USGS2008

Soil sail content estimation in the Yellow River delta with satellite hyperspectral data

Soil salinization is one of the most common land degradation processes and is a severe environmental hazard. The primary objective of this study is to investigate the potential of predicting salt content in soils with hyperspectral data acquired with EO-1 Hyperion. Both partial least-squares regression (PLSR) and conventional multiple linear regression (MLR), such as stepwise regression (SWR), were tested as the prediction model. PLSR is commonly used to overcome the problem caused by high-dimensional and correlated predictors. Chemical analysis of 95 samples collected from the top layer of soils in the Yellow River delta area shows that salt content was high on average, and the dominant chemicals in the saline soil were NaCl and MgCl 2 . Multivariate models were established between soil contents and hyperspectral data. Our results indicate that the PLSR technique with laboratory spectral data has a strong prediction capacity. Spectral bands at 1487–1527, 1971–1991, 2032–2092, and 2163–2355 nm possessed large absolute values of regression coefficients, with the largest coefficient at 2203 nm. We obtained a root mean squared error (RMSE) for calibration (with 61 samples) of RMSE C = 0.753 ( R 2 = 0.893) and a root mean squared error for validation (with 30 samples) of RMSE V = 0.574. The prediction model was applied on a pixel-by-pixel basis to a Hyperion reflectance image to yield a quantitative surface distribution map of soil salt content. The result was validated successfully from 38 sampling points. We obtained an RMSE estimate of 1.037 ( R 2 = 0.784) for the soil salt content map derived by the PLSR model. The salinity map derived from the SWR model shows that the predicted value is higher than the true value. These results demonstrate that the PLSR method is a more suitable technique than stepwise regression for quantitative estimation of soil salt content in a large area.

Canadian Journal of Remote Sensing↗

USGS2013

Monitoring restoration impacts to endemic plant communities in soil inclusions of arid environments

Soil inclusions are small patches of soil with different properties than the surrounding, dominant soil. In arid areas of western North America, soil inclusions called slickspot soils are saltier than adjacent soil and support different types of native vegetation. Traditional sagebrush restoration efforts, such as using drills to plant seeds or herbicides to control invasive vegetation, may damage sensitive slickspot soil and supporting vegetation. USGS scientists David Pyke and Scott Shaff and collaborators monitored slickspot size and cover of endangered slickspot peppergrass for two years to see if they were affected by the application of the herbicide glyphosate or by a minimum-till drill in the Snake River Plain, ID. The researchers examined the use of aerial photographs versus on-the-ground measurements and concluded that slickspot sizes were not affected by these treatments. Remote sensing using aerial photographs proved a useful method for mapping slickspot soils.

International Journal of Agriculture & Biology↗

USGS1990

Soil-vegetation correlations in selected wetlands and uplands of North-Central Florida

Vegetation on four hydric and two nonhydric soils series in north-central Florida was sampled as part of a national study examining the correspondence between wetland vegetation and soils. The wetland character of the vegetation was estimated by weighted average calculations using published wetland indicator values for individual plant species. The weighted averages produced an ordering of plant communities in general agreement with the hydric character of the soils. However, the two nonhydric soils has weighted average scores slightly below 3, normally considered the lowest end of the range of nonhydric vegetation. There was no clear or consistent effect of fire management on the weighted average scores. Vegetation strata (herbaceous, low shrub, tall shrub, and trees) were generally similar in weighted average values, with the wettest of the hydric soils tending to be low in all strata and the nonhydric soils tending to be high in all strata. However, strata differed considerably in the specific values for a single soil and in the specific rank ordering of soils in different strata.

Report↗

USGS1990

Synthesis of soil-plant correspondence data from twelve wetland studies throughout the United States

This report synthesizes the information collected for the U.S. Fish and Wildlife Service in a series of 12 studies designed to describe the relation between soils and vegetation in wetlands located in 11 States throughout the United States. Results of the study demonstrated almost complete agreement between hydric soils and hydrophytic vegetation. However, agreement between nonhydric soils and nonhydric vegetation was not as high because most nonhydric soils lay adjacent to the wetland boundary. There was some evidence that various vegetation layers describe the hydrophytic nature of the vegetation differently than others. Herbaceous species seem to reflect current hydrologic conditions while trees may reflect past hydrologic conditions. Wetland indicator categories for some plants listed in the Fish and Wildlife Service national list of plant species that occur in wetlands may need to be reevaluated as additional data become available. Similarly, soils listed in the Soil Conservation Service hydric soils of the United States list should always be verified in the field prior to assigning them to a hydric category. While wetland hydrology is the critical factor determining wetlands, the use of soils and vegetation are frequently adequate for designating wetland conditions.

Report↗

USGS2018

Increasing soil organic carbon to mitigate greenhouse gases and increase climate resiliency for California

Rising air temperatures are projected to continue to drive up urban, agricultural, and rangeland water use, straining both surface and groundwater resources. Scientific studies have shown that managing farms, ranches, and public lands to increase soil carbon can increase soil waterholding capacity and increase hydrologic benefits such as increased baseflows and aquifer recharge, reduced flooding and erosion, and reduced climate-related water deficits. Coincident improvements in forage and crop yields are also indicated, while simultaneously sequestering carbon, reducing atmospheric greenhouse gases and mitigating climate change. This study was developed to consider the multiple benefits of increasing the organic matter content of soils across California’s working lands. Study results indicate that a one-time ¼” application of compost to rangelands can lead to carbon sequestration rates in soils that are maximized after approximately 15 years, and more than offset greenhouse gas emissions stimulated by the compost addition for at least five decades longer. Modeled increases in total soil organic matter of 3% enhanced hydrologic benefits across 97% of working lands, and reduced climate change impacts. Economic valuation indicated all benefits increasing over time, demonstrating a large potential for the California carbon market to support incentives in regionalizing the impacts in the coming decades. Socioeconomic and related land use pressures pose barriers to implementing management practices to increase soil organic matter by driving conversion of rangeland to urban or to more greenhouse-gas emission intensive agriculture. Results can be effectively used with land use change scenarios to identify where on California’s working lands hydrologic benefits of soil organic matter enhancement coincide with development risk, highlighting counties in California in which there may be resilience to climate change when strategic soil management and land conservation are combined.

California↗

USGS2002

Nitrogen fixation in biological soil crusts from southeast Utah, USA

Biological soil crusts can be the dominant source of N for arid land ecosystems. We measured potential N fixation rates biweekly for 2 years, using three types of soil crusts: (1) crusts whose directly counted cells were >98% Microcoleus vaginatus (light crusts); (2) crusts dominated by M. vaginatus , but with 20% or more of the directly counted cells represented by Nostoc commune and Scytonema myochrous (dark crusts); and (3) the soil lichen Collema sp. At all observation times, Collema had higher nitrogenase activity (NA) than dark crusts, which had higher NA than light crusts, indicating that species composition is critical when estimating N inputs. In addition, all three types of crusts generally responded in a similar fashion to climate conditions. Without precipitation within a week of collection, no NA was recorded, regardless of other conditions being favorable. Low (<1°C) and high (>26°C) temperatures precluded NA, even if soils were moist. If rain or snow melt had occurred 3 or less days before collection, NA levels were highly correlated with daily average temperatures of the previous 3 days ( r 2 =0.93 for Collema crusts; r 2 =0.86 for dark crusts and r 2 =0.83 for light crusts) for temperatures between 1°C and 26°C. If a precipitation event followed a long dry period, NA levels were lower than if collection followed a time when soils were wet for extended periods (e.g., winter). Using a combination of data from a recording weather datalogger, time-domain reflectometry, manual dry-down curves, and N fixation rates at different temperatures, annual N input from the different crust types was estimated. Annual N input from dark crusts found at relatively undisturbed sites was estimated at 9 kg ha –1 year –1 . With 20% cover of the N-fixing soil lichen Collema , inputs are estimated at 13 kg ha –1 year –1 . N input from light crusts, generally indicating soil surface disturbance, was estimated at 1.4 kg ha –1 year –1 . The rates in light crusts are expected to be highly variable, as disturbance history will determine cyanobacterial biomass and therefore N fixation rates.

Biology and Fertility of Soils↗

USGS2014

Soil respiration patterns and controls in limestone cedar glades

Aims Drivers of soil respiration ( R s ) in rock outcrop ecosystems remain poorly understood. We investigated these drivers in limestone cedar glades, known for their concentrations of endemic plant species and for seasonal hydrologic extremes (xeric and saturated conditions), and compared our findings to those in temperate grasslands and semi-arid ecosystems. Methods We measured R s , soil temperature ( T s ), volumetric soil water content (SWC), soil organic matter (SOM), soil depth, and vegetation cover monthly over 16 mo and analyzed effects of these variables on R s . Results Seasonally, R s primarily tracked T s (r 2 =0.77; P < 0.01); however R s was depressed during a summer drought. SOM was highly variable spatially, and incorporating SOM effects into the R s model dramativally improved model performance. Both shallow soil and sparse vegetation cover were also associated with lower R s . Conclusions Soil depth, SOM, and vegetation cover were important drivers of R s in limestone cedar glades. Seasonal R s patterns reflected those for mesic temperate grasslands more than for semi-arid ecosystems, in that R s primarily tracked temperature for most of the year.

Plant and Soil↗

USGS2017

Enhanced precipitation promotes decomposition and soil C stabilization in semiarid ecosystems, but seasonal timing of wetting matters

Aims Changing precipitation regimes in semiarid ecosystems will affect the balance of soil carbon (C) input and release, but the net effect on soil C storage is unclear. We asked how changes in the amount and timing of precipitation affect litter decomposition, and soil C stabilization in semiarid ecosystems. Methods The study took place at a long-term (18 years) ecohydrology experiment located in Idaho. Precipitation treatments consisted of a doubling of annual precipitation (+200 mm) added either in the cold-dormant season or in the growing season. Experimental plots were planted with big sagebrush ( Artemisia tridentata ), or with crested wheatgrass ( Agropyron cristatum ). We quantified decomposition of sagebrush leaf litter, and we assessed organic soil C (SOC) in aggregates, and silt and clay fractions. Results We found that: (1) increased precipitation applied in the growing season consistently enhanced decomposition rates relative to the ambient treatment, and (2) precipitation applied in the dormant season enhanced soil C stabilization. Conclusions These data indicate that prolonged increases in precipitation can promote soil C storage in semiarid ecosystems, but only if these increases happen at times of the year when conditions allow for precipitation to promote plant C inputs rates to soil.

Plant and Soil↗

USGS2005

Effects of coal-bed methane discharge waters on the vegetation and soil ecosystem in Powder River Basin, Wyoming

Coal-bed methane (CBM) co-produced discharge waters in the Powder River Basin of Wyoming, resulting from extraction of methane from coal seams, have become a priority for chemical, hydrological and biological research during the last few years. Soil and vegetation samples were taken from affected and reference sites (upland elevations and wetted gully) in Juniper Draw to investigate the effects of CBM discharge waters on soil physical and chemical properties and on native and introduced vegetation density and diversity. Results indicate an increase of salinity and sodicity within local soil ecosystems at sites directly exposed to CBM discharge waters. Elevated concentrations of sodium in the soil are correlated with consistent exposure to CBM waters. Clay-loam soils in the study area have a much larger specific surface area than the sandy soils and facilitate a greater sodium adsorption. However, there was no significant relation between increasing water sodium adsorption ratio (SAR) values and increasing sediment SAR values downstream; however, soils exposed to the CBM water ranged from the moderate to severe SAR hazard index. Native vegetation species density was highest at the reference (upland and gully) and CBM affected upland sites. The affected gully had the greatest percent composition of introduced vegetation species. Salt-tolerant species had the greatest richness at the affected gully, implying a potential threat of invasion and competition to established native vegetation. These findings suggest that CBM waters could affect agricultural production operations and long-term water quality.

Wyoming↗

USGS2006

Alteration of soil microbial communities and water quality in restored wetlands

Land usage is a strong determinant of soil microbial community composition and activity, which in turn determine organic matter decomposition rates and decomposition products in soils. Microbial communities in permanently flooded wetlands, such as those created by wetland restoration on Sacramento-San Joaquin Delta islands in California, function under restricted aeration conditions that result in increasing anaerobiosis with depth. It was hypothesized that the change from agricultural management to permanently flooded wetland would alter microbial community composition, increase the amount and reactivity of dissolved organic carbon (DOC) compounds in Delta waters; and have a predominant impact on microbial communities as compared with the effects of other environmental factors including soil type and agricultural management. Based on phospholipid fatty acid (PLFA) analysis, active microbial communities of the restored wetlands were changed significantly from those of the agricultural fields, and wetland microbial communities varied widely with soil depth. The relative abundance of monounsaturated fatty acids decreased with increasing soil depth in both wetland and agricultural profiles, whereas branched fatty acids were relatively more abundant at all soil depths in wetlands as compared to agricultural fields. Decomposition conditions were linked to DOC quantity and quality using fatty acid functional groups to conclude that restricted aeration conditions found in the wetlands were strongly related to production of reactive carbon compounds. But current vegetation may have had an equally important role in determining DOC quality in restored wetlands. In a larger scale analysis, that included data from wetland and agricultural sites on Delta islands and data from two previous studies from the Sacramento Valley, an aeration gradient was defined as the predominant determinant of active microbial communities across soil types and land usage. ?? 2005 Elsevier Ltd. All rights reserved.

Soil Biology and Biochemistry↗

USGS2016

Long-term reactive nitrogen loading alters soil carbon and microbial community properties in a subalpine forest ecosystem

Elevated nitrogen (N) deposition due to increased fossil fuel combustion and agricultural practices has altered global carbon (C) cycling. Additions of reactive N to N-limited environments are typically accompanied by increases in plant biomass. Soil C dynamics, however, have shown a range of different responses to the addition of reactive N that seem to be ecosystem dependent. We evaluated the effect of N amendments on biogeochemical characteristics and microbial responses of subalpine forest organic soils in order to develop a mechanistic understanding of how soils are affected by N amendments in subalpine ecosystems. We measured a suite of responses across three years (2011–2013) during two seasons (spring and fall). Following 17 years of N amendments, fertilized soils were more acidic (control mean 5.09, fertilized mean 4.68), and had lower %C (control mean 33.7% C, fertilized mean 29.8% C) and microbial biomass C by 22% relative to control plots. Shifts in biogeochemical properties in fertilized plots were associated with an altered microbial community driven by reduced arbuscular mycorrhizal (control mean 3.2 mol%, fertilized mean 2.5 mol%) and saprotrophic fungal groups (control mean 17.0 mol%, fertilized mean 15.2 mol%), as well as a decrease in N degrading microbial enzyme activity. Our results suggest that decreases in soil C in subalpine forests were in part driven by increased microbial degradation of soil organic matter and reduced inputs to soil organic matter in the form of microbial biomass.

Soil Biology and Biochemistry↗

USGS2005

Mineralogy and arsenic mobility in arsenic-rich Brazilian soils and sediments

Background. Soils and sediments in certain mining regions of Brazil contain an unusually large amount of arsenic (As), which raises concerns that mining could promote increased As mobility, and thereby increase the risks of contaminating water supplies. Objectives. The purpose of t his study was to identify the most important factors governing As mobility in sediments and soils near three gold-mining sites in the State of Minas Gerais, Brazil. Methods. Surface and sub-surface soil samples were collected at those sites and characterized by chemical and mineralogical analyses. Oxalate (Feo) and citrate-bicarbonate-dithionite (Fed) iron contents were determined by atomic absorption spectroscopy (AAS). Arsenic mobilization was measured after incubating the samples in a 2.5 mM CaCl2 solution under anaerobic conditions for 1, 28, 56, 84, or 112 days. The solution concentrations of As, Fe, and Mn were then measured by inductively coupled plasma-mass spectrometry (ICP-MS) and AAS, respectively. Results and Discussion. Results indicated that As mobilization is largely independent of both the total As and the Feo/Fed ratio of the solid phase. Soluble As is roughly controlled by the Fe (hydr)oxide content of the soil, but a closer examination of the data revealed the importance of other highly weathered clay minerals and organic matter. Large amounts of organic matter and a low iron oxide content should favor As leaching from soils and sediments. Under reducing conditions, As is mobilized by the reductive dissolution of Fe and/or Mn oxides. However, released As may be readsorbed depending on the sorptive properties of the soil. Gibbsite is particularly effective in adsorbing or readsorbing As, as is the remaining unreduced fraction of the iron (hydr)oxides. Conclusion and Outlook. In general, low soluble As is rel ated to the presence of gibbsite, a large amount of iron oxides, and a lack of organic matter in the solid phase. This has environmental significance because gibbsite is thermodynamically more stable than Fe oxides under anaerobic conditions, such as those found in waterlogged soils and lake sediments. ?? 2006 ecomed publishers (Verlagsgruppe Hu??thig Jehle Rehm GmbH), D-86899 Landsberg and Tokyo.

Journal of Soils and Sediments↗

USGS1993

An improved method for quantifying soil macroporosity

Quantitative information on macroporosity is needed to predict water flow and solute transport in field soils. A method was developed for determining the number, shape, and size distribution of soil macropores. Horizontal serial sections sawed from paraffin-impregnated soil cores were photographed under ultraviolet (UV) light. Anthracene, mixed with the paraffin, fluoresces a bright bluish white under UV light and provides a sharp contrast between the soil matrix and the paraffin-filled pore space. Section photographs were converted to 256 level, grey-scale digital images using a flat-bed scanner. Image processing was used to classify each pixel in a digital image as pore space or soil matrix, to group the pore space pixels into pores, and to measure the area and perimeter of each pore. The method was able to measure pores with an equivalent radius ≥85 µm. Macroporosity in soil cores sampled form a tillage path and from an adjacent, undisturbed (notill) region was quantified. Tillage sections contained, on the average, 9.4 macropores/cm 2 with an equivalent macroporosity of 8%, while no-till sections contained 0.8 macropores/cm 2 with an equivalent macroporosity of 0.3%. Computed intrinsic permeabilities for tillage sections that included macropore information were significantly larger than values computed using micropore information alone, suggesting that macropores must be included in permeability calculations when the number of macropores is large. The developed method should be useful for quantifying macroporosity in nonskeletal soils.

Soil Science Society of America Journal↗

USGS2004

Pedogenic silica accumulation in chronosequence soils, southern California

Chronosequential analysis of soil properties has proven to be a valuable approach for estimating ages of geomorphic surfaces where no independent age control exists. In this study we examined pedogenic silica as an indicator of relative ages of soils and geomorphic surfaces, and assessed potential sources of the silica. Pedogenic opaline silica was quantified by tiron (4,5-dihydroxy-1,3-benzene-disulfonic acid [disodium salt], C 6 H 4 Na 2 O 8 S 2 ) extraction for pedons in two different chronosequences in southern California, one in the San Timoteo Badlands and one in Cajon Pass. The soils of both of these chronosequences are developed in arkosic sediments and span 11.5 to 500 ka. The amount of pedogenic silica increases with increasing duration of pedogenesis, and the depth of the maximum silica accumulation generally coincides with the maximum expression of the argillic horizon. Pedogenic silica has accumulated in all of the soils, ranging from 1.2% tiron-extractable Si (Si tn ) in the youngest soil to 4.6% in the oldest. Primary Si decreases with increasing duration of weathering, particularly in the upper horizons, where weathering conditions are most intense. The loss of Si coincides with the loss of Na and K, implicating the weathering of feldspars as the likely source of Si loss. The quantity of Si lost in the upper horizons is adequate to account for the pedogenic silica accumulation in the subsoil. Pedogenic silica was equally effective as pedogenic Fe oxides as an indicator of relative soil age in these soils.

California↗

USGS2010

Soil organic carbon stocks in Alaska estimated with spatial and pedon data

Temperatures in high-latitude ecosystems are increasing faster than the average rate of global warming, which may lead to a positive feedback for climate change by increasing the respiration rates of soil organic C. If a positive feedback is confirmed, soil C will represent a source of greenhouse gases that is not currently considered in international protocols to regulate C emissions. We present new estimates of the stocks of soil organic C in Alaska, calculated by linking spatial and field data developed by the USDA NRCS. The spatial data are from the State Soil Geographic database (STATSGO), and the field and laboratory data are from the National Soil Characterization Database, also known as the pedon database. The new estimates range from 32 to 53 Pg of soil organic C for Alaska, formed by linking the spatial and field data using the attributes of Soil Taxonomy. For modelers, we recommend an estimation method based on taxonomic subgroups with interpolation for missing areas, which yields an estimate of 48 Pg. This is a substantial increase over a magnitude of 13 Pg estimated from only the STATSGO data as originally distributed in 1994, but the increase reflects different estimation methods and is not a measure of the change in C on the landscape. Pedon samples were collected between 1952 and 2002, so the results do not represent a single point in time. The linked databases provide an improved basis for modeling the impacts of climate change on net ecosystem exchange.

Soil Science Society of America Journal↗

USGS2012

Strategies for soil quality assessment using VNIR gyperspectral spectroscopy in a western Kenya Chronosequence

Visible and near-infrared reflectance spectroscopy (VNIRS) is a rapid and nondestructive method that can predict multiple soil properties simultaneously, but its application in multidimensional soil quality (SQ) assessment in the tropics still needs to be further assessed. In this study, VNIRS (350–2500 nm) was employed to analyze 227 air-dried soil samples of Ultisols from a soil chronosequence in western Kenya and assess 16 SQ indicators. Partial least squares regression (PLSR) was validated using the full-site cross-validation method by grouping samples from each farm or forest site. Most suitable models successfully predicted SQ indicators (R 2 ≥ 0.80; ratio of performance to deviation [RPD] ≥ 2.00) including soil organic matter (OM LOI ), active C, Ca, cation exchange capacity (CEC), and clay. Moderately-well predicted indicators (0.50 ≤ R 2 < 0.80; 1.40 ≤ RPD < 2.00) were water stable aggregation (WSA), Cu, silt, Mg, pH, sand, water content at permanent wilting point (Θ pwp ), and field capacity (Θ fc ). Poorly predicted indicators (R 2 < 0.50; RPD < 1.40) were EC, S, P, available water capacity (AWC), K, Zn, and penetration resistance. Combining VNIRS with selected field- and laboratory-measured SQ indicator values increased predictability. Furthermore, VNIRS showed moderate to substantial agreement in predicting interpretive SQ scores and a composite soil quality index (CSQI) especially when combined with directly measured SQ indicator values. In conclusion, VNIRS has good potential for low cost, rapid assessment of physical and biological SQ indicators but conventional soil chemical tests may need to be retained to provide comprehensive SQ assessments.

Western Kenya↗