bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time Domains for Early‐Time and Steady‐State Pressure Infiltrometer Data
Authors: Groenevelt P. H. , Odell B. P. , Elrick D. E. 
Published: July 2010

AbstractThe determination of the field‐saturated hydraulic conductivity, Kfs, using a Guelph Pressure Infiltrometer, typically relies on the establishment of steady‐state flow. For media with very low values of Kfs, such as the compacted clay liners of landfills, the establishment of steady‐state flow may take months. It then becomes opportune to rely on early‐time observations of infiltration to infer Kfs. The time domain in which early‐time data analysis is valid can, for the first time, be delineated by equating the flux from both the early‐time and steady‐state flow expressions. This new delineating boundary value will be indicated by tcr. This will be the critical time at which the early‐time behavior gradually transits into the steady‐state time domain. There is, however, a time zone around tcr in which neither the early‐time analysis nor the steady‐state analysis is appropriate, as flow is neither purely dominated by capillary forces nor gravitational forces. Results of tcr delineations are presented as a function of two field and clay liner parameters: Kfs and Δθ, the change in volumetric water content between initial and field‐saturated conditions. Graphical interpretation reveals the existence of the inversely proportional relationships: critical time vs. Kfs and critical time vs. applied pressure head. Also evident is the directly proportionate response of the critical time to change in Δθ. We find that the present form of the critical time expression can be reduced to previous formulations concerning characteristic times. We offer these derivations as proof of the validity of this new critical time parameter.
Mechanisms of Nickel Sorption on Pyrophyllite: Macroscopic and Microscopic Approaches
Authors: Scheidegger André M. , Sparks Donald L. , Fendorf Mark 
Published: July 2010

AbstractRetention of heavy metal ions on soil mineral surfaces is a crucial process for maintaining environmental quality. A thorough understanding of the sorption mechanisms of heavy metals on soil mineral surfaces is therefore of fundamental importance. This study examined Ni(II) sorption mechanisms on pyrophyllite. The removal of Ni from solution was studied as a function of pH (pH = 5–8.5), initial Ni concentration (1 × 10−4 to 1 × 10−2 M), and ionic strength (0.01–1 M). The data suggest that Ni sorption behavior can be divided into two distinct pH regions. In the lower pH region (i.e., pH <7), relative Ni sorption increased with decreasing ionic strength and initial Ni concentration. The adsorption maximum at pH = 6 was significantly higher than the cation‐exchange capacity (CEC) at the same pH. Based on these findings, we propose that both specific and nonspecific adsorption are involved. In the higher pH region (pH >7), nickel sorption becomes slow and does not seem to be affected by the ionic strength and the initial Ni concentration. We employed high‐resolution transmission electron microscopy (HRTEM) to ascertain whether any alteration in the surface structure of pyrophyllite could be detected after reaction with Ni at pH >7. Surface deposits, not present on untreated samples, were found. At low Ni sorption densities, surface precipitation seems to occur preferentially along the edges of the particles. Based on the HRTEM findings, and on results from a previous x‐ray absorption fine structure spectroscopy (XAFS) study, we hypothesize that the formation of a mixed Ni‐Al hydroxide phase on the pyrophyllite surface is responsible for the sorption behavior above pH 7.
Landscape and Seasonal Patterns of Nitrous Oxide Emissions in a Semiarid Region
Authors: Corre M. D. , van Kessel C. , Pennock D. J. 
Published: July 2010

AbstractAs a prerequisite for quantification of annual N2O emissions at a regional scale, this study was conducted to determine the landscape‐scale patterns and seasonal fluctuations of N2O emission and to demonstrate the linking relationships between large‐scale controllers and proximal factors of N2O emission. An area of the Black soil zone of central Saskatchewan, Canada, was stratified into three main textural areas: clay loam, fine sandy loam, and sandy. Within each textural area, representative sites were selected based on land use: unfertilized and fertilized cropland, fallow, pasture, and forest sites. A consistent landscape‐scale pattern of N2O emission was observed; footslope positions had higher N2O fluxes than shoulder positions. The role of topography is attributed to its strong influence on the hydrologic and pedologic processes in the landscape, which, in turn, regulate the soil factors controlling N2O emission at the microscale level. The seasonal fluctuation of N2O emission was influenced by precipitation. Pulses of activity were observed during summer, after rainfall events following N fertilizer application, and during spring thaw. At the regional scale, the sandy area had lower N2O emissions than the fine‐textured areas. The general order of N2O evolved among the land uses was forest < pasture < fallow ≈ unfertilized < fertilized cropland. Our results showed the importance of developing spatially based, predictive relationships between N2O emission and its controlling factors. Linking these relationships with large‐scale integrative variables, such as soil texture and land use, provides a means for extrapolating N2O fluxes from landscape to regional scale.
Denitrification in Soil Profiles beneath Grassland and Cultivated Soils
Authors: Sotomayor David , Rice Charles W. 
Published: July 2010

AbstractThe denitrification potential of subsoils and aquifers must be characterized to assess the ultimate fate of soil N. This experiment was conducted to study changes in the subsurface distribution and activity of denitrifying bacteria as a result of cultivation. We examined soil profiles for their capacity (N addition) and potential (N + C addition) to denitrify as well as for denitrifying bacterial numbers in a Reading silt loam (fine, mixed, mesic Typic Argiudoll) soil under grassland and cultivation. Denitrifying enzyme activity was undetectable throughout the subsurface of soil profiles at both sites. Overall, the cultivated site had significantly higher NO−3 concentrations, denitrifier populations, and denitrification potential. Denitrifying bacteria were stratified in the vadose zone at the prairie site, with lowest numbers and lowest denitrification potential occurring at the interface of the water table. Although C addition enhanced denitrification at this site, the profile was not nearly as limited by C as that of the cultivated site. The results demonstrated that increased N inputs and cultivation during approximately 50 yr changed the denitrifying population and denitrification potential in the vadose and saturated zones of soils.
Nitrification and Coupled Nitrification‐Denitrification Associated with a Soil‐Manure Interface
Authors: Nielsen Tommy Harder , Nielsen Lars Peter , Revsbech Niels Peter 
Published: July 2010

AbstractNitrification and denitrification in soil often occur in close proximity so that a substantial part of the NO−3 formed by nitrification afterwards diffuses to the anaerobic denitrification zone where it is reduced to N2. The stable N isotope based isotope pairing method was used to study nitrification and coupled nitrification‐denitrification associated with a manure hot‐spot in soil contained within a diffusion chamber. During the 3‐wk incubation period, a very active nitrification zone developed within 0.7 to 1 mm from the aerobic‐anaerobic soil‐manure interface, and within this thin zone, all NH+4 liberated from the manure was oxidized. The short distance between the nitrification zone and the anaerobic manure facilitated coupled nitrification‐denitrification, which turned out to be the main sink for liberated inorganic N with maximum rates of 140 nmol N‐N2 cm−2 h−1, thereby removing 90% of the inorganic N liberated during the incubation period. The applicability of the isotopic pairing method was verified by using variable concentrations of 15NO−3 and by selectively inhibiting nitrification with acetylene. The change in 14NO−3 profile following addition of acetylene was simulated by a diffusion reaction model to obtain estimates of the underestimation of denitrification by use of the commonly used acetylene blockage technique. Incubation periods with acetylene of 1, 3, 6, and 12 h reduced the coupled nitrification‐denitrification rate to 46, 25, 16, and 10%, respectively, of the original rate, and use of the acetylene technique for determining denitrification in manure‐amended soils thus cannot be recommended.
Mycorrhizae, Phosphorus Absorption, and Yield of Maize in Response to Tillage
Authors: McGonigle Terence P. , Miller Murray H. 
Published: July 2010

AbstractMaize (Zea mays L.) in the early season in no‐till (NT), compared with conventional tillage (CT), has reduced dry matter due to cooler temperatures near the seed, in spite of increased plant P absorption caused by more effective mycorrhizae in the less‐disturbed soil. We grew maize under NT and CT in a soil with 1.6 mg kg−1 NaHCO3‐extractable P, adding 0, 25, 50, or 100 kg P ha−1. A rotary cultivator (ROTO) soil‐disturbance treatment gave plots more severe disturbance than CT, and a no‐till hand‐plant (NTHP) treatment gave plots with minimal soil disturbance. Early season P uptake and mycorrhizal colonization were stimulated in the NT and NTHP treatments. The reverse was true for shoot dry mass. Early season responses to tillage treatments were the same at each of the fertilizer rates. Yields increased with increasing fertilization. At all rates of P, yields with the CT and ROTO treatments were similar to each other, as were yields with the NT and NTHP treatments. At low soil‐P fertility, NT and CT gave similar yields. However, at and above 50 kg P ha−1, yields in CT exceeded those in NT by 1000 kg ha−1. We expect that under P‐limiting conditions, NT could give increases in yield over CT, or similar yields could be achieved in NT and CT but at lower soil‐P availability in NT, but only if the early season growth depression in NT can be overcome.
Comparison of Models Describing the Vertical Distribution of Wind‐Eroded Sediment
Authors: Sterk G. , Raats P. A. C. 
Published: July 2010

AbstractFor the study of field wind erosion, detailed observations of windblown sediment transport in the field are needed. The objective of this study was to determine the best method to quantify the mass of wind‐blown material moving past a fixed point during four storms. Twenty‐one Modified Wilson and Cooke (MWAC) sediment catchers were installed in a pearl millet [Pennisetum glaucum (L.) R. Br.] field in the Sahelian zone of Niger, on a sandy, siliceous, isohyperthermic Psammentic Paleustalf. Each catcher trapped materials at seven heights between 0.05 and 1.00 m. The vertical profiles of measured horizontal mass fluxes were described by two different models, a three‐parameter power function and a five‐parameter combined model, which is a combination of an exponential function and a power function. For all four storms, both models described accurately the mass fluxes between 0.05 and 0.26 m, but fitted mass fluxes at 0.50, 0.75, and 1.00 m deviated from measured fluxes. Deviations were 21.1, 45.2, and 60.6% for the power function and 12.4, 18.5, and 38.0% for the combined model. Mass transport rates were calculated by integrating the mass flux profiles across height. The differences in calculated mass transport rates were small, but because of the better fit, the combined model was preferred. Correcting for the trapping efficiency of the MWAC catchers (0.49) and multiplying by the storm duration resulted in total mass transport values, which are equal to the mass of soil passing a strip of 1‐m width perpendicular to the mean wind direction. The average mass transport values were 102.7, 15.5, 31.8, and 149.8 kg m−1, respectively, for the four storms.
Exchangeable Hydrogen Explains the pH of Spodosol Oa Horizons
Authors: Ross Donald S. , Bartlett Richmond J. , David Mark B. , Lawrence Gregory B. 
Published: July 2010

AbstractThe chemistry of extremely acid Oa horizons does not conform to traditional pH, Al, and base saturation relationships. Results from two separate studies of northeastern U.S. forested soils were used to investigate relationships between pH in water or dilute salt solutions and other soil characteristics. In Oa horizons with pH below 4, soil pH in dilute CaCl2 solution was correlated with exchangeable H+ measured either by titration (r = −0.88, P = 0.0001, n = 142) or by electrode (r = −0.89, P = 0.0001, n = 45). Exchangeable H+ expressed as a percentage of the cation‐exchange capacity (CEC) was linear with pH and showed similar slopes for data from both studies. For all samples, pHw = 4.21 − 1.80 × H+/CEC (R2 = 0.69, n = 194). The reciprocal of the H+/CEC ratio is base saturation with Al added to the bases. Because of the low pH, exchangeable Al does not appear to behave as an acid. Exchangeable H+ remains an operationally defined quantity because of the difficulty in separating exchange and hydrolysis reactions. In a variety of neutral‐salt extractants, concentrations of H+ were correlated with 0.1 M BaCl2‐exchangeable H+ (r > 0.91, P = 0.0001, n = 26) regardless of the strength of the extract. Nine successive extractions with 0.33 mM CaCl2 removed more H+ than was removed by single batch extractions with either 1 M KCl or 0.1 M BaCl2 (average H+ of 70, 43, and 49 mmol kg−1, respectively for 26 samples). The data showed little difference in the chemical behavior of Oa horizons from a variety of geographical sites and vegetation types.
Cation and Nitrogen Contents of Organic Matter Determine Its Soil Liming Potential
Authors: Pocknee Stuart , Sumner Malcolm E. 
Published: July 2010

AbstractThe effect of organic matter addition to soil in relation to soil pH changes is not well understood. Organic matter additions to soil have been reported to both increase and decrease soil pH. An investigation of the effects and mechanisms involved was undertaken. Plant materials of different types were incubated with an acid Cecil topsoil (clayey, kaolinitic, thermic Typic Kanhapludult) (pHKCl 4.01) in a glasshouse experiment at rates equivalent to 50 and 200 Mg ha−1 (dry mass). Soil pH was measured with time and increases of up to 4 pH units were observed followed by attainment of a steady state at or above the original soil pH, depending on the type of organic matter added. The final pH was well correlated with the amount of basic cations present in the organic matter (r2 = 0.92). The initial short‐term fluctuations in pH were due to mineralization and nitrification of the N added in the material. A separate factorial study using simple organic sources of Ca (calcium gluconate) and N (β‐alanine) supported this contention. The short‐term organic liming effect stemming from N transformations is strongly dependent on the kinetics of the organic matter decomposition, which are, in turn, biologically mediated. Decomposition of Ca‐containing organic molecules was shown to have an effect on pH analogous to that of mineral lime (CaCO3).
Suitability of Sunn Hemp as an Alternative Late‐Summer Legume Cover Crop
Authors: Mansoer Zulfadli , Reeves D. Wayne , Wood C. Wesley 
Published: July 2010

AbstractThe tropical legume ‘Tropic Sun’ sunn hemp (Crotalaria juncea L.) may have potential as an alternative legume cover crop or as forage for cattle in southern temperate regions. This study determined dry‐matter production, chemical composition, and N release from sunn hemp residue under conventional and no‐tillage systems as might be used in corn (Zea mays L.) production. Sunn hemp was sown in mid‐August and mowed in early December on a Norfolk sandy loam (fine‐loamy, siliceous, thermic Typic Kandiudult) and a Lucedale fine sandy loam (fine‐loamy, siliceous, thermic Rhodic Paleudult) in Alabama (1991–1992). Mesh bags were used to determine residue decomposition and N release. Average dry‐matter production was 5.9 Mg ha−1 9 to 12 wk after planting. At mowing, residue N content averaged 126 kg ha−1. Residue overwintered on the soil surface until early April. During the first 4 wk following mowing, N release from residue was 50%. In April, N remaining in overwintered residue was only 38% of that after mowing in December (45 kg N ha−1). Nitrogen release from residue during the subsequent corn growing season was 13% in no‐tillage and 43% in conventional tillage. Sunn hemp produced sufficient dry matter to cover and protect the soil from erosion and provided sufficient N to benefit a succeeding summer crop. In addition, forage quality of leaves was suitable to provide late summer and fall grazing. Sunn hemp has potential to be managed as an alternative to winter legume cover crops in warm temperate regions.
Herbicide Losses in Runoff from Conservation‐Tilled Watersheds in a Corn‐Soybean Rotation
Authors: Shipitalo M. J. , Edwards W. M. , Owens L. B. 
Published: July 2010

AbstractSoil and nutrient losses are tolerable when corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are grown in rotation on steep slopes in northern Appalachia if conservation tillage is used and a rye (Secale cereale L.) cover crop follows soybean harvest. Herbicide losses and concentrations in runoff resulting from this rotation, however, may be unacceptable. Therefore, runoff from two chiseled and two no‐till watersheds was monitored for 4 yr to determine the effect of this cropping sequence on losses of four commonly used herbicides: alachlor [2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl) acetanilide], atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine], linuron [3‐(3,4‐dichlorophenyl)‐1‐methoxy‐1‐methylurea], and metribuzin [4‐amino‐6‐(1,1‐dimethylethyl)‐3‐(methylthio)‐1,2,4‐triazin‐5(4H)‐one]. The spectrum of weeds controlled by linuron is similar to that of atrazine and their losses were compared to determine if substitution of linuron for atrazine would decrease herbicide loss in runoff. As a percentage of applied chemical, average losses were small with atrazine (0.31%) > linuron (0.20%) > metribuzin (0.14%) > alachlor (0.05%). At times, however, herbicide concentrations may be a concern. Atrazine concentrations consistently exceeded the lifetime Health Advisory Level‐Maximum Contaminant Level (HAL‐MCL) of 3 µg L−1 in the first few runoff events after application. In addition, atrazine was detectable in runoff during soybean years, at times above the HAL‐MCL. Average linuron loss was significantly less (P ≤ 0.05) than that of atrazine and linuron was rarely detected in runoff following corn harvest or during soybean years. The 2 µg L−1 MCL for alachlor was only exceeded during the first few events after application, whereas metribuzin concentrations never exceeded the HAL of 200 µg L−1.
Predicting Rainfall Erosivity in Honduras
Authors: Mikhailova E. A. , Bryant R. B. , Schwager S. J. , Smith S. D. 
Published: July 2010

AbstractIso‐erodent maps can be used in soil conservation planning to identify regions with high rainfall erosive potential. This study was conducted to determine the significance of elevation in predicting the rainfall erosivity index (R) in addition to the average annual precipitation and to develop an iso‐erodent map for Honduras. With previously calculated R‐factor values for eight climatic stations in Honduras, a regression relationship was established for estimating the rainfall erosivity index as a function of average annual precipitation and elevation with R2 of 0.972. This regression model was used to estimate the rainfall erosivity index for each of the 344 Honduran climatic stations without calculated rainfall erosivity indices. Due to the limited number of data points and their geographic clustering, the best estimates of mean rainfall erosivity indices were for stations with average annual precipitation in the range from 831 to 1313 mm and elevation between 360 and 1080 m. A provisional iso‐erodent map of Honduras at a scale 1:1 000 000 was compiled in Arc/Info format, using a basemap obtained from the digital chart of the world. Iso‐lines for the 95% prediction intervals for new rainfall erosivity indices are displayed on the map to show the accuracy of the new estimates. Elevation was found to be highly significant in predicting the rainfall erosivity in addition to the average annual precipitation. Data from Costa Rica, Sri Lanka, and the southeastern USA supported this finding.
Characterizing the Structure of Undisturbed Soils
Authors: McCoy E. L. , Cardina J. 
Published: July 2010

AbstractSoil structure is often viewed as the spatial heterogeneity of component soil properties. To explore a method for determining this heterogeneity, we examined the use of spectral analysis to discern the periodic spatial variance in depth series measurements of penetration resistance and oxygen diffusion rate (ODR) in undisturbed soil cores. Mean power spectra of penetration resistance residuals for 105 moldboard‐plowed (MP) and 109 no‐tillage (NT) cores had peaks at a frequency of 0.031 cycles mm−1. The NT treatment, however, averaged 0.71 higher loge power across the frequency range of 0 to 1.0 cycles mm−1. Harmonic analysis related this to increased aggregate strength in the NT treatment. Mean power spectra of detrended ODR data from 96 MP and 95 NT cores had peaks across the frequency range of 0.017 to 0.025 cycles mm−1. The NT treatment again averaged 0.78 higher loge power across the frequency range of 0 to 0.125 cycles mm−1. Geometric mean aggregate diameters showed tillage‐induced differences of 6.8 mm for the MP and 10.8 mm for the NT treatments. The mean frequencies corresponding with maximum power for the individual spectra were not different between tillage treatments or between the independent penetrometer and ODR methods, yielding aggregate diameters of 15.3 mm. The absence of tillage‐induced aggregate diameter differences from analysis of penetration resistance and ODR data, as contrasted with the observed aggregate diameter differences from sieving, suggests that sieving may not precisely reflect the in situ aggregation of soils.
Compositional and Functional Shifts in Microbial Communities Due to Soil Warming
Authors: Zogg Gregory P. , Zak Donald R. , Ringelberg David B. , White David C. , MacDonald Neil W. , Pregitzer Kurt S. 
Published: July 2010

AbstractMicrobial decomposition processes are typically described using first‐order kinetics, and the effect of elevated temperature is modeled as an increase in the rate constant. However, there is experimental data to suggest that temperature increases the pool size of substrate C available for microbial respiration with little effect on first‐order rate constants. We reasoned that changes in soil temperature alter the composition of microbial communities, wherein dominant populations at higher temperatures have the ability to metabolize substrates that are not used by members of the microbial community at lower temperatures. To gain insight into changes in microbial community composition and function following soil warming, we used molecular techniques of phospholipid fatty acid (PLFA) and lipopolysaccharide fatty acid (LPS‐OHFA) analysis and compared the kinetics of microbial respiration for soils incubated from 5 to 25°C. Substrate pools for microbial respiration and the abundance of PLFA and LPS‐OHFA biomarkers for Gram‐positive and Gram‐negative bacteria differed significantly among temperature treatments, providing evidence for a shift in the function and composition of microbial communities related to soil warming. We suggest that shifts in microbial community composition following either large seasonal variation in soil temperature or smaller annual increases associated with global climate change have the potential to alter patterns of soil organic matter decomposition by a mechanism that is not considered by current simulation models.