bluuebunny/crossref_metadata_2025 huggingface dataset:
Work Organization and Health Among Immigrant Women: Latina Manual Workers in North Carolina
Authors: Arcury Thomas A. , Grzywacz Joseph G. , Chen Haiying , Mora Dana C. , Quandt Sara A.
Published: January 2014

Objectives. We sought to describe work organization attributes for employed immigrant Latinas and determine associations of work organization with physical health, mental health, and health-related quality of life.

Methods. We conducted a cross-sectional survey with 319 employed Latinas in western North Carolina (2009–2011). Measures included job demands (heavy load, awkward posture, psychological demand), decision latitude (skill variety, job control), support (supervisor control, safety climate), musculoskeletal symptoms, mental health (depressive symptoms), and mental (MCS) and physical component score (PCS) health-related quality of life.

Results. Three fifths reported musculoskeletal symptoms. Mean scores for depression, MCS, and PCS were 6.2 (SE = 0.2), 38.3 (SE = 0.5), and 42.8 (SE = 0.3), respectively. Greater job demands (heavy load, awkward posture, greater psychological demand) were associated with more musculoskeletal and depressive symptoms and worse MCS. Less decision latitude (lower skill variety, job control) was associated with more musculoskeletal and depressive symptoms. Greater support (supervisor’s power and safety climate) was associated with fewer depressive symptoms and better MCS.

Conclusions. Work organization should be considered to improve occupational health of vulnerable women workers. Additional research should delineate the links between work organization and health among vulnerable workers.
Parental Incarceration and Child Mortality in Denmark
Authors: Wildeman Christopher , Andersen Signe Hald , Lee Hedwig , Karlson Kristian Bernt
Published: January 2014

Objectives. We used Danish registry data to examine the association between parental incarceration and child mortality risk.

Methods. We used a sample of all Danish children born in 1991 linked with parental information. We conducted discrete-time survival analysis separately for boys (n = 30 146) and girls (n = 28 702) to estimate the association of paternal and maternal incarceration with child mortality, controlling for parental sociodemographic characteristics. We followed the children until age 20 years or death, whichever came first.

Results. Results indicated a positive association between paternal and maternal imprisonment and male child mortality. Paternal imprisonment was associated with lower child mortality risks for girls. The relationship between maternal imprisonment and female child mortality changed directions depending on the model, suggesting no clear association.

Conclusions. These results indicate that the incarceration of a parent may influence child mortality but that it is important to consider the gender of both the child and the incarcerated parent.
Suicidal Ideation Among Community-Dwelling Adults in the United States
Authors: Han Beth , McKeon Richard , Gfroerer Joe
Published: January 2014

Objectives. We examined the prevalence and correlates of past-year suicidal ideation among US community-dwelling adults.

Methods. We examined data from 183 100 persons aged 18 years or older (including 9800 sampled adults with past-year suicidal ideation) who participated in the 2008–2011 National Survey on Drug Use and Health. We applied descriptive analyses and pooled and stratified (by age and major depression) multivariate logistic regression models.

Results. The prevalence of past-year suicidal ideation among younger adults (6.6% among those aged 18–25 years and 4.0% among those aged 26–49 years) was higher than was that among adults aged 50 years or older (2.5%). The prevalence of suicidal ideation was high among adults with major depression (26.3%), adults with both major depression and substance use disorder (37.7%), and adults who received mental health treatment but perceived unmet treatment need (33.5%).

Conclusions. Many risk and protective factors of suicidal ideation are dynamic and vary by age or major depression. These results have important implications for developing specific suicide prevention strategies that help screen, assess, and treat suicidal adults at the earliest possible time.
Medical Marijuana Laws and Suicides by Gender and Age
Authors: Anderson D. Mark , Rees Daniel I. , Sabia Joseph J.
Published: January 2014

Objectives. We estimated the association between legalizing medical marijuana and suicides.

Methods. We obtained state-level suicide data from the National Vital Statistics System’s Mortality Detail Files for 1990–2007. We used regression analysis to examine the association between medical marijuana legalization and suicides per 100 000 population.

Results. After adjustment for economic conditions, state policies, and state-specific linear time trends, the association between legalizing medical marijuana and suicides was not statistically significant at the .05 level. However, legalization was associated with a 10.8% (95% confidence interval [CI] = −17.1%, −3.7%) and 9.4% (95% CI = −16.1%, −2.4%) reduction in the suicide rate of men aged 20 through 29 years and 30 through 39 years, respectively. Estimates for females were less precise and sensitive to model specification.

Conclusions. Suicides among men aged 20 through 39 years fell after medical marijuana legalization compared with those in states that did not legalize. The negative relationship between legalization and suicides among young men is consistent with the hypothesis that marijuana can be used to cope with stressful life events. However, this relationship may be explained by alcohol consumption. The mechanism through which legalizing medical marijuana reduces suicides among young men remains a topic for future study.
Associations Between Driving Performance and Engaging in Secondary Tasks: A Systematic Review
Authors: Ferdinand Alva O. , Menachemi Nir
Published: January 2014

We conducted a systematic review and meta-analysis of the literature examining the relationship between driving performance and engaging in secondary tasks. We extracted data from abstracts of 206 empirical articles published between 1968 and 2012 and developed a logistic regression model to identify correlates of a detrimental relationship between secondary tasks and driving performance.

Of 350 analyses, 80% reported finding a detrimental relationship. Studies using experimental designs were 37% less likely to report a detrimental relationship (P = .014). Studies examining mobile phone use while driving were 16% more likely to find such a relationship (P = .009).

Quasi-experiments can better determine the effects of secondary tasks on driving performance and consequently serve to inform policymakers interested in reducing distracted driving and increasing roadway safety.
Change in Walking and Body Mass Index Following Residential Relocation: The Multi-Ethnic Study of Atherosclerosis
Authors: Hirsch Jana A. , Diez Roux Ana V. , Moore Kari A. , Evenson Kelly R. , Rodriguez Daniel A.
Published: January 2014

Objectives. We investigated whether moving to neighborhoods with closer proximity of destinations and greater street connectivity was associated with more walking, a greater probability of meeting the “Every Body Walk!” campaign goals (≥ 150 minutes/week of walking), and reductions in body mass index (BMI).

Methods. We linked longitudinal data from 701 participants, who moved between 2 waves of the Multi-Ethnic Study of Atherosclerosis (2004–2012), to a neighborhood walkability measure (Street Smart Walk Score) for each residential location. We used fixed-effects models to estimate if changes in walkability resulting from relocation were associated with simultaneous changes in walking behaviors and BMI.

Results. Moving to a location with a 10-point higher Walk Score was associated with a 16.04 minutes per week (95% confidence interval [CI] = 5.13, 29.96) increase in transport walking, 11% higher odds of meeting Every Body Walk! goals through transport walking (adjusted odds ratio = 1.11; 95% CI = 1.02, 1.21), and a 0.06 kilogram per meters squared (95% CI = −0.12, −0.01) reduction in BMI. Change in walkability was not associated with change in leisure walking.

Conclusions. Our findings illustrated the potential for neighborhood infrastructure to support health-enhancing behaviors and overall health of people in the United States.
Mean Residence Time of Kaolinite and Smectite‐Bound Organic Matter in Mozambiquan Soils
Authors: Wattel-Koekkoek Esther J. W. , Buurman Peter
Published: January 2014

To gain understanding about the process of global warming, it is essential to study the global C cycle. In the global C cycle, soil organic matter (SOM) is a major source and sink of atmospheric C. Turnover times of C in these soil organic compounds vary from hours to thousands of years. Clay minerals can stabilize SOM through the formation of organo‐mineral bonds. The aim of this research was first, to determine the mean residence time (MRT) of organic matter that is bound to different clay mineral surfaces, and second, to explain the variance in the measured MRTs using multilinear regression. We especially studied organic matter that is bound to kaolinite or smectite. We analyzed the 14C activity of organic matter in the whole and heavy clay‐size fraction of kaolinite‐ and smectite‐dominated soils from N'Ropa, in northern Mozambique. The soils originated from natural savanna systems and bamboo forest. We assumed that C inputs and outputs are in equilibrium in such soils, so that the 14C age equals the MRT of the organic C. For both kaolinite‐ and smectite‐dominated soils, the organic matter in the whole and heavy clay‐size fraction and extracts had a fast turnover (400–500 yr on average). The MRT of kaolinite‐bound organic matter did not differ significantly from that of smectite‐bound organic matter. Multiple linear regression indicates that the effective cation‐exchange capacity (ECEC) is the main factor to explain variance in the MRT of the extracted SOM. These results agree with previously found trends in organic matter turnover of kaolinite and smectite‐associated clay.
Perched Water Table Responses to Forest Clearing in Northern Idaho
Authors: Rockefeller S. L. , McDaniel P. A. , Falen A. L.
Published: January 2014

Many forested soils of northern Idaho containing fragipans and seasonal perched water tables (PWTs) have been cleared for agricultural use. However, little information exists on the direct effect of canopy removal on PWTs in these soils. We compared PWTs in soils where forest canopy had been removed with those in adjacent soils with intact canopy. Study sites were selected such that both cleared and forested treatments occurred within the same soil map unit. Perched water table levels in shallow wells were monitored weekly or biweekly from November to June or July for 3 yr. Results indicate that canopy removal substantially affects both average height and duration of seasonal PWTs. Average PWT levels were 6 to 107% higher under cleared treatments, with greatest increases observed when seasonal precipitation was close to long‐term averages. Seasonal PWTs developed 2 to 8 wk sooner under cleared treatments compared with forested treatments. Additionally, it took as much as four months before PWTs in the forested treatments reached an equivalent height as those in the cleared treatments. At one study site, the average volume of perched water in the cleared treatment was 7.5 cm greater than that in the forested treatment over the period of episaturation. Results suggest that land‐use interpretations based on duration and proximity of a seasonal PWT to the soil surface may need to be adjusted when vegetation cover is altered. It may also be appropriate to distinguish between cleared and forested phases of fragipan‐containing soil series when developing hydrologic interpretations.
Conversion from a Sycamore Biomass Crop to a No‐till Corn System
Authors: Devine Warren D. , Mullen Michael D. , Tyler Donald D. , Houston Allan E. , Joslin John D. , Hodges Donald G. , Tolbert Virginia R. , Walsh Marie E.
Published: January 2014

Agricultural lands may be used to produce short‐rotation woody crops (SRWCs) for fuel or fiber, but the effects of SRWCs on soils are poorly understood. In this study, a SRWC was integrated with an annual row crop system in a row crop–SRWC–row crop rotation. The objective was to document the effects of the woody crop on soil total C, N, inorganic N, and aggregate stability after the site was returned to row crop production. Soybean [Glycine max (L.) Merr.] was followed by 4‐ and 5‐yr rotations of American sycamore (Platanus occidentalis L.), followed by no‐till corn (Zea mays L.) (SY4C and SY5C, respectively). Continuous row crops (soybean converted to corn) served as a control (SBC). Four rates of broadcast NH4NO3 were applied to corn. The study was in southwestern Tennessee on a Memphis‐Loring silt loam intergrade (fine‐silty, mixed, active, thermic Typic Hapludalfs–fine‐silty, mixed, active, thermic Oxyaquic Fragiudalfs). During 3 yr of post‐sycamore corn production, increases in soil total C concentration below a 2.5‐cm depth were attributed to the sycamore crop. After fertilization of first‐year corn at 73 and 146 kg N ha−1, soil inorganic N concentrations were lower in the SY4C than the SBC system from 0 to 2.5 cm. Mean weight diameter (MWD) of water‐stable soil aggregates at depths of 2.5 to 15 cm was greater for the SY4C than the SBC system. Four‐ and 5‐yr sycamore rotations significantly affected chemical and physical properties of an agricultural soil.
A Variable‐Volume TDR Probe for Measuring Water Content in Large Soil Volumes
Authors: Souza C. F. , Or D. , Matsura E. E.
Published: January 2014

Management of favorable conditions for plant growth within partially wet soil volumes under drip irrigation presents a measurement challenge. Typically, soil water status is determined from a single point measurement or several point measurements within the wet volume requiring various assumptions for quantitative interpretation of total water available for irrigation decisions. We propose a new coaxial time domain reflectometry (TDR) probe capable of measuring the total soil water storage within well‐defined soil volumes (referred to as the variable volume coaxial probe, VVCP). The measurement volume is contained between an array of stainless steel conductors embedded in the soil and arranged in a coaxial configuration with variable spacing. The average water content in the spacing between the inner and outer circular arrays of conductors is determined from travel time analysis of VVCP waveforms. Laboratory and field tests of the VVCP established that waveforms and travel time analyses resulted in dielectric permittivities and water contents similar to those obtained with standard three‐rod TDR probes. For uniform distribution of soil water VVCP measurements were independent of conductor spacing or soil volume. Variable volume coaxial probe‐determined water balance within a partially wet soil volume was in excellent agreement with the amount of water applied from a point source indicating accurate and integrative volumetric measurement.
Water and Redox Conditions in Wetland Soils—Their Influence on Pedogenic Oxides and Morphology
Authors: Fiedler Sabine , Sommer Michael
Published: January 2014

For wetland soil studies, it would be desirable to estimate soil redox status and its effect on element translocations based on diagnostic redoximorphic features. However, their identification and interpretation is often complicated and require a regional calibration. This study was conducted (i) to determine the relationship between water table and redox potential (EH), (ii) to investigate their influence on mass balances of pedogenic Mn‐ and Fe‐oxides and soil morphology, and (iii) to evaluate the use of soil color to identify redox status in hydromorphic soils. Three representative geomorphic units were chosen from low relief positions in the cool‐humid Allgäu (Germany): an alluvial plain and two pond margins. Within each unit two paired study sites were established along a wetness gradient. Thus in six wetland soils (Aquepts) groundwater level (GWL) and EH were measured over 1 yr. Monitoring results were presented as (i) percentage of time of water saturation, (ii) percentage of time the EH is <170 mV (onset of Fe‐oxide reduction), and (iii) related to static soil properties (mass balance of pedogenic oxides). Both, GWL and EH were linearly correlated (r2 = 0.88) and indicated increased Fe mobilization with increasing duration of saturation. Thus, higher Fe losses occurred with increasing duration of EH < 170 mV, whereas no correlation existed between Mn and the duration of reducing conditions. Calculation of Mn and Fe mass balances indicated losses of both elements within the pedons when reducing conditions were located near the surface (<10 cm). However, no losses were detected when the reductive conditions occurred at depths >50 cm. The element redistribution induced by soil redox conditions was reflected by the soil color index of subsoil horizons (C2h), within a sensitive range between 6 and 12. It was shown, that this index is an adequate tool to delineate wetland soils according to the duration of water saturation and Fe‐reducing conditions. It could be concluded that C2h may be used as a proxy to estimate the intensity of water/redox conditions.
Minimizing Drift in Electrical Conductivity Measurements in High Temperature Environments using the EM‐38
Authors: Robinson D. A. , Lebron I. , Lesch S. M. , Shouse P.
Published: January 2014

The EM‐38 is a noninvasive instrument, commonly used for monitoring salinity, mapping bulk soil properties, and evaluating soil nutrient status. Users in the Southwest USA have observed as much as 20% “drift” in the measurement of bulk soil electrical conductivity (ECa) with this instrument. This drift has usually been ignored or compensated for by statistical procedures. We performed laboratory and field experiments to determine if the drift is due to calibration instability of the instrument or to heating of the instrument by the sun. In laboratory experiments, after a warm‐up period, the instrument provided constant readings in the range 25 to 40°C; above 40°C the response of the instrument was unpredictable. In field experiments, where we placed the EM‐38 in a fixed location we observed an unexpected response at air temperatures below 40°C. Temperature sensors in different locations on the instrument demonstrated that temperature differences between the instrument's transmitting and receiving coils and the control panel (CP) were as great as 20°C. As the instrument is temperature compensated from this CP, erroneous compensation occurred when the instrument was placed in direct sunlight. In this study, we demonstrate that differential heating of the EM‐38 is one cause of drift and erroneous bulk electrical conductivity measurement; shading the instrument substantially reduced this problem, effectively extending the reliable working temperature range by minimizing drift.
Millimeter‐Scale Spatial Variability in Soil Water Sorptivity
Authors: Hallett P. D. , Nunan N. , Douglas J. T. , Young I. M.
Published: January 2014

Recent evidence suggests that reduced water infiltration may be linked to small scale microbial and/or chemical processes that cause subcritical water repellency. We measured water sorptivity on the surface of a large intact block of soil (0.9 m wide, 1.3 m long, 0.25 m deep) taken from a grassland site and examined the effects of surface elevation and water repellency on water sorptivity at the millimeter scale. The soil block was partially dried to 0.22 mm3 mm−3, appeared to wet readily, and is not severely water repellent at any water content. Water sorptivity varied from 0.1 to 0.8 mm s−1/2 across the sampling grid with a coefficient of variation (CV) of 0.57. Water repellency, determined by comparing water and ethanol sorptivities, also varied considerably (CV = 0.47). Geostatistical analyses of water sorptivity and repellency measurements found little evidence of spatial autocorrelation, suggesting a high degree of local variability. These data were compared to larger scale measurements obtained with conventional infiltrometers under tension conditions (40 mm contact radius), and ponded conditions (37 and 55 mm radius rings) where macropores influence infiltration heterogeneity. Larger scale tension infiltrometer measurements were less variable with a CV of 0.22, whereas ponded infiltrometer measurements were more variable, CV > 0.50, presumably because of the influence of macropore flow. Data collected on surface elevation showed that ponded infiltration but not tension infiltration was influenced by surface topography. The results suggested that repellency can induce levels of spatial variability in water transport at small scales comparable to what macropores induce at larger scales.
Characterizing Nonrigid Aggregated Soil–Water Medium Using its Shrinkage Curve
Authors: Braudeau Erik , Frangi Jean-Pierre , Mohtar Rabi H.
Published: January 2014

The properties of the soil–water medium are presented in the literature independent of its internal organization and operation. The objective of this study is to develop and test a conceptual model that used a continuously measured shrinkage curve (SC) to describe the functional organization of the soil–water medium. In this model, two functional porosities (micro and macro) are delineated and quantified by the SC. In addition, the equilibrium for four functional water pools is represented and parameterized by the SC. A set of eleven parameters was found necessary to model the seven phases of the SC and to describe the corresponding soil hydrostructural changes. A method to accurately obtain the parameters of this model by a specific analysis of the continuously measured SC is demonstrated. Examples of continuously measured and modeled SCs according to the pedostructure model (PS) are presented and discussed.
Controlled‐Suction Period Lysimeter for Measuring Vertical Water Flux and Convective Chemical Fluxes
Authors: Kosugi K. , Katsuyama M.
Published: January 2014

Unsaturated infiltration of rain and irrigation water and convective chemical transport processes in the vadose zone are poorly understood. This is partly due to the traditional techniques used to sample unsaturated soil water. This study evaluated the performance of a recently developed controlled‐suction period lysimeter in the field for more than 400 d. The lysimeter consists of two tensiometers and a porous plate connected to a suction system. The soil matric pressures immediately above the horizontally buried porous plate, and at the same depth in the natural soil profile, are measured at 3‐s intervals. The water extraction period is controlled so that the readings of the two tensiometers match. The lysimeter was installed at a depth of 30 cm in a sparse forest. The soil was sandy loam classified as Cambisol. The lysimeter maintained the soil moisture condition in the sampling profile similar to that in the natural soil profile. The mean absolute difference between the two tensiometers was 4.1 cm, with the mean relative difference of 3.5%. Water extraction by the lysimeter did not cause appreciable convergence or divergence in the soil water flow. The water loss due to evapotranspiration (ET) estimated from the water‐sampling rate was similar to the evaporation rates measured using water‐filled pans and the ET rate estimated by the Thornthwaite method, considering the reduction because of drought. In addition to the water flux, convective fluxes of dissolved silica, nitrate, and ammonium were quantified. As a result, the controlled‐suction period lysimeter has great potential to provide quantitative information on water and solute transport in the vadose zone.
Measurement of Soil Water Content with a 50‐MHz Soil Dielectric Sensor
Authors: Seyfried Mark S. , Murdock Mark D.
Published: January 2014

The Hydra Probe1 is a relatively inexpensive and widely used soil water content (θ, m3m−3) sensor. It measures both the real (εr) and imaginary (εi) components of the complex soil dielectric constant at 50 MHz. Our objectives were to: (i) determine the accuracy and precision of Hydra Probe dielectric measurements, (ii) establish an electrical conductivity limit for Hydra Probe measurements, (iii) document effects of soil type and temperature, and (iv) relate these results to much more thoroughly studied relationships established for time domain reflectometry (TDR). We evaluated Hydra Probe εrmeasurement precision and accuracy in air, ethanol, butanol, and water. Electrical conductivity effects were established in a series of aqueous KCl solutions. Effects of soil type on calibration were evaluated with four soils. Temperature sensitivity was tested in air, oven‐dried, and nearly saturated soil. Each test was performed with three sensors. We found that, in fluids, the sensors were accurate (εrwithin 0.5), precise (coefficient of variation [CV] < 1%), and that inter‐sensor variability was generally low except in KCl solutions with electrical conductivities >0.142 S m−1(0.01M). There was a strong correlation between θ and εrfor all soils tested but the θ–εrrelationship varied with soil. Deviations of measured θ–εrfrom the Topp equation increased in magnitude with εi, which may be the key to more general calibrations. Temperature effects on εrwere negligible in oven dry soils and different for each soil when nearly saturated. The largest temperature effect relative to 25°C was ±0.03 m3m−3In general, it appears that differences between Hydra Probe and TDR measurements are related to differences in soil dielectric properties at the measurement frequencies of the two instruments.
Neural Networks Prediction of Soil Hydraulic Functions for Alluvial Soils Using Multistep Outflow Data
Authors: Minasny B. , Hopmans J. W. , Harter T. , Eching S. O. , Tuli A. , Denton M. A.
Published: January 2014

Indirect methods for prediction of soil hydraulic properties play an important role in understanding site‐specific unsaturated water flow and transport processes, usually via numerical simulation models. Specifically, pedotransfer functions (PTFs) to predict soil‐water retention have been widely developed. However, few datasets that include unsaturated hydraulic conductivity data are available for prediction purposes. Moreover, those available employ a variety of measurement techniques. We show that prediction of soil‐water retention and unsaturated hydraulic conductivity curves from basic soil properties can be improved if hydraulic data are determined by a single measurement method that is consistently applied to all soil samples. Here, we present a unique dataset that consists of 310 soil‐water retention and unsaturated hydraulic conductivity functions, all of which were obtained from the multistep outflow method. With this dataset, neural networks coupled with bootstrap aggregation were used to predict the soil‐water retention and hydraulic conductivity characteristics from basic soil properties, that is, sand, silt, and clay content, bulk density (ρb), saturated water content, and saturated hydraulic conductivity. The prediction errors of water content were about 3 to 4% by volume. Unsaturated hydraulic conductivity predictions improved significantly when a so‐called performance‐based algorithm was utilized to minimize residuals of soil hydraulic data rather than hydraulic parameters. The root mean squared of residuals for predicted values of water content and unsaturated hydraulic conductivity were reduced by about 50% when compared with predicted hydraulic functions using a published neural networks program Rosetta Results from a sensitivity analysis suggest that the hydraulic parameters are mostly sensitive to sand content and saturated water content.
Root Growth and Nitrate Uptake of Three Different Catch Crops in Deep Soil Layers
Authors: Kristensen H. L. , Thorup-Kristensen K.
Published: January 2014

Catch crops can reduce NO3 losses from leaching, but little is known about the importance of deep rooting for the efficiency of NO3 depletion. In a field experiment, we investigated the N uptake and root growth of three types of catch crops using minirhizotrons (glass tubes of 70‐mm o.d.) reaching 2.4 m. Our purpose was to evaluate minirhizotron methodology and the importance of deep rooting in the ability of catch crops to take up NO3 from deep soil layers. Nitrogen uptake was studied over a 6‐d period at the end of October by injection of 15NO3 at four depths in the ranges: 0.4 to 1, 0.5 to 1.4, and 1 to 2.5 m under Italian ryegrass (Lolium multiflorum Lam.), winter rye (Secale cereale L.), and fodder radish (Raphanus sativus L. var. oleiformis Pers.), respectively. The root depth of the three species were 0.6, 1.1, and more than 2.4 m, respectively. No 15N was taken up from placements below root depth, and linear relationships were found between root density and 15N uptake from different depths. Residual soil NO3 of 18, 59, and 87 kg N ha−1 was left under fodder radish, winter rye, and ryegrass, respectively. The measurements obtained with the minirhizotron method were highly relevant for evaluating N uptake from different soil layers, and root depths of the catch crops were important for N depletion. Knowledge about root growth and N uptake in deep soil layers may be utilized when designing crop rotations with improved N use efficiency. Where N has been left by a preceding crop and leached to deeper soil layers, it may be recycled by deep‐rooted catch crops.
Soil pH Effects on Nitrification of Fall‐Applied Anhydrous Ammonia
Authors: Kyveryga Peter M. , Blackmer Alfred M. , Ellsworth Jason W. , Isla Ramon
Published: January 2014

Soil temperature at the time of application has been the primary factor used to predict rates of nitrification and assess the risks associated with losses of N applied in the fall as anhydrous ammonia in the Corn Belt. We report studies assessing the importance of soil pH as a factor affecting nitrification rates and losses of this N before corn (Zea MaysL.) begins rapid growth in June. Data were collected in a series of field studies conducted during 4 yr. Anhydrous ammonia was applied in the fall after soils had cooled to <8°C, and soils were sampled before corn plants emerged in the spring. Soil pH ranged from <6.0 to >7.5. Significant relationships between soil pH and percentage nitrification were observed each year. Means of measurements made in mid‐April (when planting begins) indicated 89% nitrification of fertilizer N in soils having pH > 7.5 and 39% nitrification of this N in soils having pH < 6.0. The finding that soil pH influenced when nitrification occurred helps to explain why the effects of nitrification inhibitors have been variable in this region. Significant relationships between soil pH and recovery of fertilizer N as exchangeable NH4+and NO3−were observed in years with above‐average rainfall before samples were collected in April. The effects of soil pH on nitrification, therefore, influenced the amounts of NO3−lost by denitrification or leaching during spring rainfall. The observed effects of pH on nitrification rates suggest that economic and environmental benefits of delaying application of fertilizer N may be greater in higher‐pH soils than in lower‐pH soils.
Plant Competition Effects on the Nitrogen Economy of Field Pea and the Subsequent Crop
Authors: Soon Y. K. , Harker K. N. , Clayton G. W.
Published: January 2014

We evaluated weed competition effects on the N economy of field pea (Pisum sativum L.) and the subsequent crop to address the paucity of such information. Plots were seeded to pea, canola (Brassica napus L.) and barley (Hordeum vulgare L.) in 1997 and 1998. Weeds, augmented by cross‐seeding experimental plots with oat (Avena sativa L.), were removed with herbicides one and four weeks after crop emergence (WAE). The subsequent barley crop received 0 or 6 g N m−2 Mean percentage of N derived from the atmosphere (%Ndfa) for the 2 yr, estimated by 15N isotopic dilution, was 81% for the 4‐WAE treatment and 51% for the 1‐WAE treatment, indicating that a pea plant subjected to greater weed competition derived more of its N from symbiotic fixation. Total N fixed by pea was not affected by the time of weed removal, however, and total N uptake and seed yield were greater with early weed removal due to less competition for soil N. Early weed removal resulted in net N export in pea seeds (because of higher production) while later weed removal resulted in gains of 1.1 to 1.3 g N m−2 However, time of weed removal during pea cultivation had no effect on the yield or N uptake of the subsequent barley crop. Higher barley yield and N uptake following pea than following barley were mostly the result of greater N availability. Nitrogen fertilization benefited the subsequent barley regardless of preceding crop type.
Modeling Volume Change and Mechanical Properties with Hydraulic Models
Authors: Baumgartl Th. , Köck B.
Published: January 2014

Volume change of soils may be caused either by external (mechanical) or internal (hydraulic) stresses or a combination of both. A complete description of volume change must therefore include both mechanical and hydraulic stresses. By combining theories of mechanical and hydraulic stress states, a hydraulic function, which predicts the change of water volume as a function of the stress state parameter soil water suction (water retention curve), is adopted to model volume change. The utilization of such a continuous function also enables the derivation of soil mechanical parameters (e.g., preconsolidation stress, Youngs modulus) by determining mathematically the point of maximum curvature and inflection point. This information can then be used to calculate the preconsolidation stress according to the method of Casagrande. The presented calculation has considerable advantages compared with the graphic method of Casagrande or other methods. On the basis of stress–strain relationships of various textured and structured soils and soil substrates and various test procedures (oedometer test, triaxial test, shrinkage test), volume change is modeled using the described method. It is shown that modeling volume change by the van Genuchten equation using the software RETC is possible with high accuracy. Soil mechanical parameters are derived using the parameters of the van Genuchten equation. The comparison of results of this method with the Casagrande and a statistical method shows that these methods have deficiencies when the data sets have a high variability, the samples are not homogeneous, and when the stress–strain curve is flat. The accuracy of the mathematical method in contrast is very high and the calculated preconsolidation stress very reliable.
Mapping Soil pH Buffering Capacity of Selected Fields in the Coastal Plain
Authors: Weaver A. R. , Kissel D. E. , Chen F. , West L. T. , Adkins W. , Rickman D. , Luvall J. C.
Published: January 2014

Soil pH buffering capacity, since it varies spatially within crop production fields, may be used to define sampling zones to assess lime requirement, or for modeling changes in soil pH when acid‐forming fertilizers or manures are added to a field. Our objective was to develop a procedure to map this soil property. One‐hundred‐thirty‐six soil samples (0‐ to 15‐cm depth) from three Georgia Coastal Plain fields were titrated with calcium hydroxide to characterize differences in pH buffering capacity of the soils. Since the relationship between soil pH and added calcium hydroxide was approximately linear for all samples up to pH 6.5, the slope values of these linear relationships for all soils were regressed on the organic C and clay contents of the 136 soil samples using multiple linear regression. The equation that fit the data best was b = 0.00029 − 0.00003 × percentage clay + 0.00135 × percentage OC−1, r2 = 0.68, where b is the slope of pH vs. lime added, and OC is organic carbon. This equation was applied within geographic information system (GIS) software to create maps of soil pH buffering capacity for the three fields. When the mapped values of the pH buffering capacity were compared with measured values for a total of 18 locations in the three fields, there was good general agreement. A regression of directly measured pH buffering capacities on mapped pH buffering capacities at the field locations for these samples gave an r2 of 0.88 with a slope of 1.04 for a group of soils that varied approximately tenfold in their pH buffering capacities.
Persulfate Digestion and Simultaneous Colorimetric Analysis of Carbon and Nitrogen in Soil Extracts
Authors: Doyle Allen , Weintraub Michael N. , Schimel Joshua P.
Published: January 2014

Persulfate digestions have been used for analyzing dissolved organic carbon (DOC) and nitrogen (DON), but most existing methods do not simultaneously analyze the same digest. Persulfate oxidizes DON to NO−3, and DOC to CO2, which was trapped in the alkaline digest solution. We optimized the persulfate digestion for simultaneous analysis of dissolved CO2 and NO−3 with flow injection analysis (FIA). Dissolved CO2 was diffused across a Gore‐Tex (W.L. Gore & Associates, Inc., Sunnyvale, CA) membrane and analyzed with a pH indicator, while NO−3 was analyzed with a standard Griess‐Ilosvay reaction after Cd reduction. Digestions of glycine, urea, and yeast extract solutions recovered 97 to 99% of C and 92 to 96% of N, while digestions of lysine and nicotinimide recovered slightly less (93 to 94% C, 87 to 93% N). Glycine N, used as a digested standard to which sample recoveries were scaled, improved calculated recovery 94 to 103%. Dissolved organic C concentrations were not significantly different for persulfate oxidation (PO) and high temperature catalytic oxidation (HTCO) for 13 organic and mineral soil extracts with and without prior chloroform fumigation. Nitrogen recovery was higher for PO than HTCO. The DOC blanks were 0.5 to 1.0 mg C L−1 and detection limit was 0.5 mg C L−1, and both could be lowered if needed. The upper limit of analysis was at least 2000 mg C L−1 with dilution. The digest was performed at temperatures as low as 80°C or as high as 125°C with equivalent results. We recommend the low temperature to reduce leakage. This analytical system is particularly convenient for the simultaneous analysis of microbial biomass C and N with the fumigation‐extraction procedure.
Stability of Ion Exchange Resin Under Freeze–Thaw or Dry–Wet Environment
Authors: Mamo Martha , Ginting Daniel , Renken Roger , Eghball Bahman
Published: January 2014

Ion exchange resins have widely been used in mineralization studies of organic materials. However, the stability of resin (anionic and cationic) under changing physical environmental conditions is not well known. Our objective was to evaluate N and P adsorption or desorption characteristics of resins exposed to freeze–thaw or dry–wet cycles. Mixed bed resins (1:1 oven‐dry mass strong base anion A464‐D and strong acid cation C‐249) were subjected to 0, 1, and 30 freeze–thaw or dry–wet cycles. To accomplish the dry–wet cycles, fresh resin was kept in a forced‐air oven at 25 (±2)°C for 28 h and rewetted to initial moisture condition for 20 h. To accomplish the freeze–thaw cycle, fresh resin was frozen for 16 h and thawed to room temperature for 8 h daily. At the end of the freeze–thaw or dry–wet cycles, resin was equilibrated with 3.2 mM L−1 NH4–N, 3.2 mM L−1 NO3–N, or 0.97 mM L−1 PO4–P for a period of 1 h. Dry–wet cycles induced desorption of N and P associated with shrinkage of resins and expulsion of interstitial liquid. At the highest dry–wet cycle, 3.3, 0.35, and 0.15% of the total adsorbed PO4–P, NH4–N, and NO3–N was desorbed, respectively. Scanning electron microscopy (SEM) revealed that the dry–wet or freeze–thaw cycles did not alter the physical integrity of these resins. Freeze–thaw cycles had no effects on N and P adsorption or desorption characteristics of resins of the specific resins used in this study. Ion exchange resins used for in situ nutrient monitoring should be screened using similar techniques to assess its adsorption and desorption stability and physical integrity to fluctuating environmental conditions. Resin types and stability should be mentioned when comparisons are made to other studies.
Carbon Accumulation and Storage in Mineral Subsoil beneath Peat
Authors: Moore Tim R. , Turunen Jukka
Published: January 2014

We showed that sandy subsoils beneath peat near Ramsey Lake, MI, contained 7.5 to 8.0 kg organic C (OC) m−2 to a depth of 70 cm, compared with 1.6 to 3.6 kg m−2 in adjacent forest soils, from which the peatland had evolved through paludification. Compared with the soils beneath the forest, those beneath the peat contained similar amounts of oxalate‐extractable Al (Alo) and less Fe, owing to loss of Fe under reduced leached conditions beneath the peat. Most of the extractable Al in the mineral horizons beneath peat was organically bound. Atomic pyrophosphate‐extractable (Fep + Alp) Fe + Al/C ratios were smaller (<0.2:1) in the mineral horizons beneath peat than in the forest mineral subsoils (generally >0.2:1), indicating larger inputs and retention in the mineral subsoils beneath peat. Concentration of OC in subsoil samples was strongly (r2 = 0.58, p < 0.001) related to the subsoil Al, null‐point dissolved organic C (DOC) and clay concentrations. A DOC sorption study using peat pore water ranging from 0 to 117 mg DOC L−1 revealed null‐point DOC (DOCnp) concentrations (at which there is neither gain nor loss of OC by the soil) varied from <1 to 417 mg DOC L−1 and was primarily related to Feo (negatively), Alo (negatively), and C (positively). We suggest that the increase in mineral subsoil OC beneath peat is related to the sorption of DOC carried by pore water percolating through the mineral subsoil, combined with slow rates of mineralization of sorbed DOC under anoxic conditions.
Effects of Compaction on the Acoustic Velocity in Soils
Authors: Lu Zhiqu , Hickey Craig J. , Sabatier James M.
Published: January 2014

Soil compaction induced by the use of agricultural machinery changes the mechanical and structural properties of soils. Assessment of its effects may be made by acoustic techniques. In this study, a triaxial cell modified to measure the acoustic velocity was used to simulate the compaction process. Unconsolidated‐undrained triaxial tests were performed on two air‐dry remolded soils and one undisturbed field soil taken from sites in Sharkey, Neshoba, and Marshall Counties, Mississippi. Both the deformation and the acoustic behaviors of the soils were studied during a compaction process. It was found that the acoustic velocity and the deviator stress behaved similarly. Both the acoustic velocity and the deviator stress increased linearly at the early stage of compaction and they changed nonlinearly with intermediate compaction. At the extreme case where the soil was compacted to failure, the acoustic velocity and the deviator stress changed only slightly with further compaction. During the unload‐reload cycle, the acoustic velocity and the deviator stress varied steeply and presented hysteretic and load‐history‐dependent properties. Significant influence of water content on both acoustic and deformation behaviors was found. The similarity between the acoustic behavior and the deformation characteristics make the acoustic velocity a promising parameter for monitoring the ongoing compaction process in situ and for long‐term soil survey.
A NEW IDEA IN MARSH CORING
Authors: Inglett Patrick W. , Viollier Eric , Roychoudhury Alakendra N. , Van Cappellen Philippe
Published: January 2014

Standard coring techniques are often ineffective in the unconsolidated and vegetated soils and sediments of marsh environments. In this paper, a novel coring device is presented that minimizes the problems of compaction, core plugging, and root disturbance to allow the collection of intact 35+ cm cores from densely vegetated marsh areas. The simple concept uses a sharpened main body and cover plate that are inserted sequentially to obtain a wedge‐shaped soil or sediment slice. In a typical application, the corer is transferred to the field laboratory where sectioning can occur. Removal of the cover plate exposes a large surface area of soil or sediment for visual inspection and sampling. The advantages of the wedge corer design are described in relation to its use in a Spartina alterniflora salt marsh.
Observations and Modeling of Profile Soil Water Storage above a Shallow Water Table
Authors: Nachabe Mahmood , Masek Caroline , Obeysekera Jayantha
Published: January 2014

The storage capacity of a soil profile (soil water storage capacity [SWSC]) is the depth of water required to raise a shallow water table to the land surface. The concept of SWSC is fundamental to many hydrological processes, including surface runoff by saturation excess, expansion, and contraction of wetlands, and estimation of the length of an overland flow plane. A model is introduced and tested to estimate SWSC using simultaneous observations of shallow water table fluctuations and soil moisture in a shallow, sandy soil (hyperthermic Aeric Alaquods). The water table at the selected site fluctuated between a shallow depth and the land surface during the summer, allowing frequent observation of surface inundation and profile storage. An equation of the form SWSC = AdB + Cd + D adequately described the variability of SWSC with d, depth to the water table. It is shown that parameters A, B, C, and D are easily derived from basic physical properties of the soil horizons, including porosity and water retention. The SWSC can be significantly limited by the capillary fringe above the water table, encapsulated air (the volume of air trapped under positive pressure beneath the water table), or the presence of a clay pan at shallow soil depths. The capillary fringe had some influence on SWSC in this sandy soil, but encapsulated air as high as 11.0% of the soil volume was observed at the site. Encapsulated air reduced the available soil storage and resulted in a rapid rise in water table. Ignoring encapsulated air significantly overestimated profile storage. Storage results including and excluding air encapsulation were compared as a function of water table depth.
Hydrolysis of Cyclotri‐ and Cyclotetraphosphate in Soil
Authors: Hossner L. R. , Trostle C. L. , Shahandeh H.
Published: January 2014

Cyclotriphosphate (Na3P3O9, C3P) and cyclotetraphosphate (Na4P4O12, C4P) are not appreciably sorbed by soil constituents. This property combined with a reduced rate of hydrolysis of C4P and its hydrolysis products may maintain P availability for plant uptake. The primary objective of this study was to determine the residence times of C3P and C4P and their hydrolysis products in four soils. Hydrolysis of C3P and C4P was dependent on soil moisture, temperature, biological activity, and time. Cyclic P hydrolysis followed apparent first‐order reaction. Recovery of hydrolysis products of C3P and C4P was higher in soils, such as Falba sandy loam (sl), which demonstrated limited sorption for mono‐, di‐, and triphosphate. The presence of hydrolysis products may explain the decreasing rate constants observed in soils incubated for longer than 48 h. Cyclotetraphosphate was more stable than C3P in all comparable treatments, often by three to six times. The energy of activation (EA) for C3P and C4P was 45.8 and 61.1 kJ mol−1, respectively, in a Falba sl, and 38.6 and 51.2 kJ mol−1, respectively, in a Branyon clay (c). Cyclotriphosphate was more readily hydrolyzed in soils compared with C4P. These results indicate a potential advantage of C4P over C3P because of its slower hydrolysis in soils, and over all linear phosphates, which are strongly sorbed by soil constituents.