bluuebunny/crossref_metadata_2025 huggingface dataset:
Continuous Flow Equilibration for Mass Spectrometric Analysis of Dinitrogen Emissions
Authors: Well R. , Becker K.‐W. , Meyer B. , Langel R. , Reineking A.
Published: July 2010

The measurement of denitrification in soil by the 15N gas emission method requires determination of the N2 mole masses 28, 29, and 30. Direct determination of 30N2, which is not possible with all isotope mass spectrometers, can be omitted if gas samples are equilibrated prior to isotope analysis. Because a previously published off‐line equilibration procedure was inaccurate and laborious, a continuous‐flow procedure was developed and evaluated in this study. Analysis of 29N2 and 28N2 was performed with an isotope ratio mass spectrometer coupled to an elemental analyzer. The N2 fraction of the samples was equilibrated in an electrodeless discharge unit placed within the interface connecting both instruments. Measuring sensitivity for the fraction of 15N‐pool‐derived N2 (d) and 15N atom fraction of the 15N pool (ap) was evaluated by analyzing 15N standard gases at d = 5 × 10‐6 to 5 × 10‐4 and ap = 0.4903, corresponding to δ15N = 1.3 to 68.3‰. Measured values of d and ap satisfactorily coincided with theoretical values. Coefficients of variation of d and ap ranged from 0.13 to 19.59% and from 0.66 to 12.86%, respectively. Precision was higher than the off‐line equilibration procedure and also higher than methods including direct measurement of 30N2.
Carbon Dioxide Emissions and Transformation of Soil Carbon and Nitrogen during Wheat Straw Decomposition
Authors: Curtin D. , Selles F. , Wang H. , Biederbeck V. O. , Campbell C. A.
Published: July 2010

Carbon exchange between soil and the atmosphere plays an important role in the global C cycle, but partitioning soil CO2 emissions by source (soil organic matter mineralization, crop residue decomposition, and root respiration) is difficult. Our objective was to determine the contribution of decomposing wheat (Triticum aestivum L.) straw to CO2 emissions from a Swinton silt loam (fine‐silty, mixed, mesic Typic Haploboroll) under controlled conditions (constant 20°C). Two types of straw (i.e., fresh straw collected shortly after harvest and standing stubble that had “weathered” in the field for a year) were either incorporated into or placed on the soil surface at a rate equivalent to 2800 kg ha‐1. One set of soils was watered every 2 or 3 d to 90% of field capacity and a second set was allowed to dry (from 90% field capacity) to below the permanent wilting point before watering. Emissions of CO2 were measured every 2 or 3 d with a vented chamber connected to a portable CO2 analyzer. Within 2 d, incorporation of straw increased CO2 flux from 0.3 to ≈ 1.5 µmol CO2m‐2s‐1. Surface straw had significantly increased fluxes, but the effect was small compared with incorporated straw. Straw type had little effect on emissions. Total CO2‐C emitted in 77 d from continuously moist soil was 25 g m‐2 with no added straw, 41 g m‐2 with surface straw, and 73 g m‐2 with incorporated straw (values are averages for two straw types). In all, 38% of incorporated‐straw C and 13% of surface straw C was emitted as CO2. Soil subjected to moist‐dry cycles emitted from 36 to 62% less CO2 than continuously moist soil. The Douglas‐Rickman residue‐decomposition model simulated the amount of straw C remaining in the soil as a function of time. In the absence of straw, CO2‐C emitted was similar to the amount by which light‐fraction C decreased, suggesting that this labile fraction of organic matter was a major source of respired C.
Pedological Cooperation between Russia and the USA, Past to Present
Authors: Gennadiyev A. N. , Olson K. R.
Published: July 2010

The American and Russian soil surveys have been influenced by their starting points and by the philosophy of pedology that appeared at the turn of the 20th century. The different initial approaches were a consequence of differences in purpose, scientific “environment”, and the manner by which the soil surveys were conducted. Nevertheless, formation and progress of Russian and American schools of soil survey and pedology have advanced due to mutual exchange of ideas and concepts. Some new ideas have been rejected while others were assimilated and contributed to further progress. Past and present cooperation in the development of soil science has emphasized the concept of soil‐forming factors, soil geography, classification and soil survey. For more than 100 yr, the linkage between Russian geography and soil science contributed to both the Russian tradition and to the soil survey in the USA. In the 1920s, the Russian scientific school influenced the Americans; now the influence of the American school on Russian concepts, approaches, and even terminology is evident. The agrarian reform that started in Russia in the 1980s resulted in a realistic consideration of the experience of foreign soil science in addition to the Russian national traditions. The convergence between the American and Russian schools of soil survey and pedology started in the 1980s and continues today. It is enhanced by an open exchange of ideas, which should be mutually beneficial. We think further advances in international scientific cooperation will occur as a consequence of the current willingness to cooperate and the rapidly improving means of electronic communication.
Estimation of Weibull Brittle Fracture Parameters for Heterogeneous Materials
Authors: Perfect E. , Zhai Q. , Blevins R. L.
Published: July 2010

Brittle fracture of heterogeneous materials such as dry soil aggregates is not well understood. The flaws in such materials occur as voids across a wide range of length scales. As a result, failure is an inherently variable phenomenon that is best analyzed using weakestlink (Weibull) theory combined with fractal geometry. According to this probabilistic approach, samples to be fractured are assumed to be exactly the same size. However, sample size variation can result in biased estimates of the model parameters, log(α), β, and D. Our objective was to derive and test an equation for eliminating this bias by adjusting survival probabilities to a common value of sample length. Rupture energies were determined on 1920 air‐dry soil peds collected from three long‐term tillage treatments on a Maury silt loam (fine, mixed, mesic Typic Paleudalf). Following adjustment for sample size variation, characteristic strength, as parameterized by log(α), typically decreased with increasing ped size. Unbiased estimates of β indicated a wider spread of strengths than reported previously. Unbiased estimates of D, the fractal scaling parameter, were lower than those obtained using other methods, possibly because of renormalization with respect to the distribution of fragile elements instead of voids. Tillage treatment significantly influenced all three parameters, with the strength of no‐till peds decreasing more rapidly with increasing size than conventional‐till peds. Analysis of the relative errors associated with parameter estimates computed using the adjusted survival probabilities indicated that at least 20 samples per sieved fraction should be used as a standard in future brittle fracture studies on heterogeneous materials.
Comparison of Ground Penetrating Radar and Time‐Domain Reflectometry as Soil Water Sensors
Authors: Weiler Kirk W. , Steenhuis Tammo S. , Boll Jan , Kung K.‐J. Samuel
Published: July 2010

Robust and noninvasive techniques for in situ measurement of soil water content are essential for monitoring and research of many hydrologic processes. Although in situ measurement of soil water content by means of a soil's electric and dielectric properties has been explored extensively, the use of ground‐penetrating radar (GPR) for this purpose is not well established. We compared the soil's dielectric constant as measured by GPR and time domain reflectometry (TDR) and its relationship to water content determined independently in auger holes. We propose a calibration equation relating soil water to GPR‐measured dielectric constants. The difference in calibration equations between GPR and TDR was partially attributed to the difference in frequency ranges in which TDR and GPR operate and the zero offset of the GPR.
XANES Studies of Oxidation States of Sulfur in Aquatic and Soil Humic Substances
Authors: Xia K. , Weesner F. , Bleam W. F. , Helmke P. A. , Bloom P. R. , Skyllberg U. L.
Published: July 2010

Sulfur K‐edge x‐ray absorption near‐edge structure spectroscopy (XANES) was used to identify multiple organic S oxidation states in aquatic and soil humic substances. The XANES results suggest that S in humic substances exists in four major oxidation groups similar to sulfate ester, sulfonate, sulfoxide, and thiol‐sulfide. Thiol S cannot be separated from sulfide S and must be considered as a single thiol‐sulfide peak. The second derivative spectra suggest the existence of thiophene and sulfone S. The relative quantities of each major S form in our humic samples were estimated based on the integrated cross section of each s → p transition peak corresponding to different S oxidation states in the S K‐edge XANES spectra. The XANES results of the four humic samples used in this study appear to reflect the environmental settings where the humic substances originally formed. The percentage of the most reduced organic S (thiol‐sulfide and possibly thiophene) in humic substances follows the sequence: aquatic samples > organic soil sample > mineral soil sample. The percentage of most oxidized S (sulfate group) was the greatest in the humic substance from a mineral soil and the lowest in the aquatic humic substances.
Compaction, Aging, and Raindrop‐Impact Effects on Hydraulic Properties of Saline and Sodic Vertisols
Authors: Ben‐Hur M. , Keren R. , Agassi M. , Zhang J.
Published: July 2010

Vertisols markedly swell and disperse when wet because of the high percentage of montmorillonite in the soil. We hypothesized that soil bulk compaction, time since soil wetting (aging), and raindrop impact affect seal formation, soil permeability, and salt leaching of Vertisols. Vertisol (Typic Chromoxererts) samples with exchangeable Na percentages (ESP) of 0.4 and 11.8 were subjected to simulated rainfall of deionized (DW) and saline (SW) (electrical conductivity [EC] = 5 dSm‐1) waters with 0 and 18.1 J mm‐1 m‐2 impact energies. In a Vertisol without aging (0.5 h of prewetting) and under zero compaction, subjected to DW and SW rainfall, seal formation controls the soil permeability. Under DW rainfall, the final infiltration rates (FIR) of the sealed and unsealed Vertisol samples were 6 and >44 mm h‐1 at ESP 0.4, and 5 and 17 mm h‐1, respectively. Four days of aging without compaction, followed by DW rainfall, increased the FIR of unsealed soil to 37 and to >44 mm h‐1 at high and low ESP, respectively, and that of sealed soil to 12 and 14 mm h‐1 at high and low ESP, respectively. Subjecting wet soil to pressure up to 800 kg m‐2 decreased the unsealed Vertisol FIR under DW rainfall to 8.9 and 27 mm h‐1 at high and low ESP, respectively. Seal formation and bulk compaction had little effect on salt leaching in the low‐ESP soil. Under bulk compaction or seal formation, the high‐ESP soil leachate EC decreased from 10.7 to 9.0 dS m‐1 after 300 mm of DW rain.
Global Positioning System Sampling Intensity and Pattern Effects on Computed Topographic Attributes
Authors: Wilson John P. , Spangrud Damian J. , Nielsen Gerald A. , Jacobsen Jeffrey S. , Tyler David A.
Published: July 2010

Global positioning system (GPS) and digital elevation model (DEM) technologies can provide measurements of terrain attributes that influence soil processes, soil properties, and site‐specific management. We hypothesized that the intensity and pattern of sampling points affects the computed contour maps and topographic attributes. The intensity and pattern of sampling points, selected from 6284 GPS‐derived x, y, z values, were varied to test this hypothesis on estimated elevations and topographic attributes in a 20‐ha Montana farm field. Variations of 0.05% in mean elevation between the sample and reference grids generated ≤25% differences in slope gradients, ≤38% in specific catchment area, and ≤22% in steady‐state topographic wetness index. Errors diminished as sample size (resolution) and distribution (spread) increased. Overall, the results demonstrate how relatively small differences in elevations at individual points (locations) in a landscape may mask large variations in the resultant shapes and hydrologically important topographic attributes calculated from DEMs. The intensive sampling may be practical where vehiclemounted GPS can traverse cultivated fields, but impractical in trees and rough terrain.
Ammonium Nitrate Occlusion vs. Nitrate Ion Exchange in Natural Zeolites
Authors: Park Man , Komarneni Sridhar
Published: July 2010

Several salts, such as NH4NO3 and KNO3, can be occluded in natural zeolites through molten salt treatments, which increase the capacity of zeolites to store nutrients in addition to exchangeable cations. Zeolites occluded with NH4NO3 are potential candidates as slow‐release fertilizers. This study focuses on determining the rates of NH4NO3 uptake by natural zeolites from molten salt and on evaluating kinetics of ion release from NH4NO3‐occluded zeolites. The kinetics of ion release from NH4NO3‐occluded zeolites were compared with those of NH+4‐saturated zeolites. NH4NO3‐occluded zeolites were prepared by treatment in molten NH4NO3 at 185°C for different time periods, or at 250°C for 4 h. Uptake of molten NH4NO3 by erionite apparently reached equilibrium after 8 h of treatment at 185°C. The total N uptake by NH4NO3‐occluded zeolites was not related to cation‐exchange capacity but depended on the structural type of the zeolite. Approximately a twofold increase in total N loading capacities of zeolites was achieved through salt occlusion compared with NH+4 exchange from solution. For example, phillipsite exhibited a N loading capacity of 76 g N kg‐1 when treated with molten NH4NO3, but showed a capacity of only 46 g N kg‐1 through NH+4 exchange. A simulated soil solution was used to examine the kinetics of ion release from both NH4NO3‐occluded and NH+4‐saturated zeolites. Occluded NH+4 and NO‐3 were released slowly and steadily as in the case of exchanged NH+4 alone from zeolites during 30‐d treatment in a simulated soil solution. It is evident from this study that salt‐occluded zeolites are potential candidates as slow‐release fertilizers.
Soil Compaction and Fertilization Effects on Nitrous Oxide and Methane Fluxes in Potato Fields
Authors: Ruser R. , Schilling R. , Steindl H. , Flessa H. , Beese F.
Published: July 2010

This study was conducted to determine the effect of soil compaction and N fertilization on the fluxes of N2O and CH4 in a soil (fine‐silty Dystric Eutrochrept) planted with potato (Solanum tuberosum L.). Fluxes of N2O and CH4 were measured weekly for 1 yr on two differently fertilized (50 and 150 kg N ha‐1) fields. For the potato cropping period (May–September) these fluxes were quantified separately for the ridges (soil bulk density ρb = 1.05 Mg m‐3) covering two‐thirds of the total field area, and for the uncompacted (ρb = 1.26 Mg m‐3) and the tractor‐traffic‐compacted (ρb = 1.56 Mg m‐3) interrow soils, each of which made up one‐sixth of the field area. The annual N2O‐N emissions for the low and the high rates of N fertilization were 8 and 16 kg ha‐1, respectively. The major part (68%) of the total N2O release from the fields during the cropping period was emitted from the compacted tractor tramlines; emissions from the ridges made up only 23%. The annual CH4‐C uptake was 140 and 118 g ha‐1 for the low and high levels of fertilization, respectively. The ridge soil and the uncompacted interrow had mean CH4‐C oxidation rates of 3.8 and 0.8 µg m‐2 h‐1, respectively; however, the tractor‐compacted soil released CH4 at 2.1 µg CH4‐C m‐2 h‐1. The results indicate thas soil compaction was probably the main reason for increased N2O emission and reduced CH4 uptake of potato‐cropped fields.
Relating Preseason Soil Nitrogen to Maize Yield in Tree Legume‐Maize Rotations
Authors: Barrios E. , Kwesiga F. , Buresh R. J. , Coe R. , Sprent J. I.
Published: July 2010

Legumes can be an important source of N for cereals in tropical, subsistence farming systems that use little or no fertilizers. Our objective was to identify measures of soil N availability, following growth of diverse legumes, that correlated with yield of a subsequent unfertilized maize (Zea mays L.) crop. Unfertilized maize followed nine 3‐yr‐old systems (six monocultures of planted trees legumes, a groundnut [Arachis hypogea L.]‐maize‐soybean [Glycine max (L.) Merr.] rotation, an uncultivated fallow with natural regrowth of vegetation, and unfertilized maize monoculture) in two experiments on a Ustic Rhodustalf in eastern Zambia. Total soil C and N before maize planting were not related to grain yield of maize. Preseason soil inorganic N (NO3 + NH4), aerobic N mineralization, and light‐fraction N (N in macroorganic matter, 150–2000 µm and <1.37 Mg m‐3) at 0‐ to 15‐ cm depth correlated (P < 0.01) with maize grain yield. Preseason inorganic N combined with light‐fraction N accounted for 59% of the variance in maize grain yield. The predictability of maize yield was slightly improved (64% of the variance) by including the population of the parasitic weed striga [Striga asiatica (L.) Kuntze] with preseason inorganic N and light‐fraction N. The results suggest that yield of unfertilized, rain‐fed maize following different rotational systems on a N‐limiting soil in an area with monomodal rainfall was strongly related to the additive effects of preseason soil inorganic N and a soil N fraction related to N mineralization.
Nitrate in Groundwater and Integration of Nitrogen‐Catch Crop in Rice‐Sweet Pepper Cropping System
Authors: Shrestha R.K. , Ladha J.K.
Published: July 2010

In the intensive rice (Oryza sativa L.)‐based cropping systems of the tropics, dry season (DS) nonrice crop‐fallow (dry‐to‐wet [DTW] transition)‐wet season (WS) rice is a common practice. Excessive use of N fertilizer in high‐value crops like vegetables grown in DS is economically motivated. The risk of NO3 leaching into groundwater during DTW transition is an environmental concern. Experiments were conducted in seven rice‐sweet pepper (Capsicum annuum L. var. annuum) farmers' fields to determine (i) the extent of NO3‐N contamination in groundwater, and (ii) the effectiveness of a N‐catch crop to decrease NO3 leaching. Twelve of twenty water sources had near or above World Health Organization's (WHO) NO3‐N limit for drinking water. Soil mineral N (upper 100 cm) ranged from 111 to 694 kg ha‐1 was decreased by 10 to 68% in plots with DTW crop. In fallow plots where mineral N was either maintained or increased, there was movement to lower soil profile demonstrating NO3 leaching without a crop. On average, maize (Zea mays L.) captured 176 kg N ha‐1 and indigo (Indigofera tinctoria L.) 194 kg N ha‐1. Indigo acquired <20% N from biological N fixation (BNF); this low contribution was due to inhibition by high soil mineral N. In both fallow and planted plots, mineral N declined to low levels at 100% water‐filled pore spaces (WFPS) before rice transplanting. A suggestion for developing indigo plus maize N‐catch crop rotations is made to decrease NO3 leaching and maximize N use efficiency in rice‐sweet pepper cropping system.
Sprinkler Irrigation Runoff and Erosion Control with Polyacrylamide — Laboratory Tests
Authors: Aase J. Kristian , Bjorneberg David L. , Sojka Robert E.
Published: July 2010

Many semiarid and arid soils are prone to irrigation‐induced erosion. Polyacrylamide (PAM) greatly reduces erosion from furrow irrigation. We hypothesized that PAM applied via sprinklers will provide erosion control and benefit water infiltration and aggregate stability. Screened (6.4 mm) Rad silt loam (coarse silty, mixed, superactive mesic Durinodic Xeric Haplocambid) was placed in 1.5 by 1.2 by 0.2 m steel boxes with 2.4% slope. An oscillating nozzle, 3 m above the soil, produced a median drop size of 1.2 mm diameter. We applied 0, 1, 2, 4, and 6 kg ha‐1 PAM in 20 mm of water in the first irrigation, followed by two 20‐mm water‐only irrigations. In a second test, we applied 0, 2, and 4 kg ha‐1 PAM in 8 mm of water in the first irrigation, followed by two 20‐mm water‐only irrigations. Two kilograms per hectare PAM in the first 20‐mm irrigation reduced runoff 70% and soil loss 75% compared to control. Polyacrylamide in 8 mm of water was less effective. Polyacrylamide in the 20‐mm irrigation did not affect tension infiltration; PAM in the 8‐mm irrigation doubled tension infiltration following the third irrigation. Wet aggregate stability following the first irrigation was greater in all PAM treatments than on the check. With 2 kg ha‐1 PAM in the 20‐mm irrigation, it was 55%; in 8 mm, 77%. Polyacrylamide applied in the first irrigation at low rates effectively reduced runoff and erosion. Erosion was more effectively controlled than runoff.
A Dual Function Organoclay Sorbent for Lead and Chlorobenzene
Authors: Sheng Guangyao , Boyd Stephen A. , Xu Shihe
Published: July 2010

To demonstrate the concept of organoclays with dual sorptive properties, carboxylic group‐bearing carboxydecyltriethylammonium [(HOOC)C10H20N(C2H5)3]+ cations (CDTEA) were used to substitute exchangeable inorganic cations of montmorillonite. Sorption of Pb2+ and chlorobenzene was examined as a function of pH and over a range of equilibrium concentrations at constant pH. The dual sorptive properties of CDTEA‐montmorillonite were compared with those of its nonfunctionalized analogue, decyltrimethylammonium(DTMA)‐montmorillonite, and with Na‐montmorillonite. The infrared spectra showed bands corresponding to the carboxylic acid group and alkyl chain of CDTEA in CDTEA‐montmorillonite. Titration of CDTEA‐montmorillonite with NaOH indicated the existence of two distinct types of acidity originating from the native acid groups of the clay and the carboxylic groups of CDTEA. Sorption of Pb2+ by CDTEA‐montmorillonite was much higher than that by Na‐montmorillonite. Complete removal of 0.00724 cmol L‐1 (15 mg L‐1) of Pb2+ by CDTEA‐montmorillonite occurred at pH 5 and above, but this was not achieved by Na‐montmorillonite, regardless of pH. Pb2+ sorption by DTMA‐montmorillonite was lower than that by Na‐montmorillonite. These results indicate that Pb2+ is effectively bound to carboxylic groups of CDTEA. Sorption of chlorobenzene by CDTEA‐montmorillonite was comparable to that by DTMA‐montmorillonite. These results indicate that CDTEA‐montmorillonite possesses dual sorptive properties for both heavy metals and organic contaminants. Neither Na‐ nor DTMA‐montmorillonite were effective sorbents for both types of contaminants. The simultaneous removal of Pb2+ and chlorobenzene by CDTEA‐montmorillonite and the non‐competitive nature of the sorption processes each suggest the potential utility of such functionalized organoclays in the treatment of water contaminated by both heavy metals and organic chemicals.
Naphthalene Sorption to Organic Soil Materials Studied with Continuous Stirred Flow Experiments
Authors: de Jonge Hubert , Heimovaara Timo J. , Verstraten J. M.
Published: July 2010

Estimation of sorption‐desorption kinetics of hydrophobic contaminants in soils and sediments is a prerequisite for assessing the risk of hazardous compounds and for studying the feasibility of bioremediation treatments. Naphthalene sorption studies were carried out with four organic soil materials, using a batch sorption technique and a continuously stirred flow (CSF) cell. Reproducibility of the CSF experiments was tested (root mean squared error = 0.074), and an experiment with different inputs showed that experimental results were independent of input pulse length (RMSE = 0.090). Single‐particle and multi‐particle linear driving force models and bicontinuum models were tested. When the sorption coefficient Kom was fixed at the values obtained from the batch experiments, the RMSE modeling error increased with increasing N2 surface area, SN2, of the soil materials. The high RMSE for soil materials with a high N2 surface area was the result of strong sorption‐desorption non‐singularity, most probably due to a larger fraction of the applied naphthalene diffusing to “slow” sorption sites. A dual resistance sorption model was able to accurately describe the data (average RMSE = 0.143) with two free parameters. However, parameter uncertainty resulted from the simultaneous optimization of the rate parameter, α, and Kom. The combination of batch sorption experiments, input‐response experiments, and model exercises give supporting evidence that sorption kinetics of hydrophobic organic compounds to soil OM are controlled by (i) rapid pore diffusion toward SN2 (α ≈ 0.1 h‐1) and (ii) slow diffusion into the soil organic matter structure (α ≈ 0.01–0.001 h‐1).
Statistical Analysis of Published Carbon‐13 CPMAS NMR Spectra of Soil Organic Matter
Authors: Mahieu N. , Randall E. W. , Powlson D. S.
Published: July 2010

We have collected solid‐state 13C nuclear magnetic resonance (NMR) data from the published literature (76 papers) and from our own results on 311 whole soils, physical fractions (25 clay‐, 43 silt‐, and 52 sand‐size fractions) and chemical extracts (208 humic and 66 fulvic acids). Our purpose was to see whether a comprehensive analysis of data on >300 soils that ranged in organic C content from 0.42 to 53.9% would show any universal influence of management practice on the chemical composition of soil organic matter (SOM). The relative abundance of functional groups was calculated for the following chemical shift regions: 0–50 ppm (alkyls), 50–110 ppm (O‐alkyls), 110–160 ppm (aromatics), and 160–200 ppm (carbonyls). There was a remarkable similarity between all soils with respect to the distribution of different forms of C despite the wide range of land use (arable,grassland, uncultivated, forest), climate (from tropical rainforest to tundra), cropping practice, fertilizer or manure application, and the different spectrometer characteristics and experimental conditions used. Functional groups in whole soils were always in the same abundance order despite the generally wide proportion range: O‐alkyls (a mean of 45% of the spectrum, increasing with soil C content), followed by alkyls (mean 25%), aromatics (mean 20%), and finally carbonyls (mean 10%, decreasing with soil C content). Humic and fulvic acids contained much smaller proportions of O‐alkyls than whole soils (means of 26%). Clay‐size fractions were the most different from whole soils, being more aliphatic (+8%). Sand‐size fractions generally gave very similar results to whole soils.
Salinity and Compaction Effects on Soil Water Evaporation and Water and Solute Distributions
Authors: Nassar I. N. , Horton Robert
Published: July 2010

Water evaporation and solute transport were studied in open soil columns. The study included two different soil materials — Clarinda clay (fine, montmorillonitic, mesic, sloping Typic Argiaquoll) and Fayette silty clay loam (fine‐silty, mixed, mesic Typic Hapludalf) — and three conditions. Two conditions were noncompacted solute‐free and salinized noncompacted soil columns of both Clarinda and Fayette soils, and one condition was compacted salinized soil columns of Clarinda soil only. The initial soil water contents were 0.271 and 0.181 m3 m−3 for noncompacted Clarinda and Fayette soils, respectively. The initial soil water content of compacted Clarinda was 0.393 m3 m−3 The initial KCl concentrations were 1.11 and 0.92 mol kg−1 of soil solution for Clarinda and Fayette soils, respectively. Measured ratios of evaporation loss from the noncompacted salinized soil columns to the amount of water evaporated from noncompacted solute‐free soil columns increased with time from 0.78 to 0.89 for Clarinda and 0.90 to 0.95 for Fayette soils. Evaporation from noncompacted Clarinda soil increased with time from 0.73 to 0.77 of the evaporation from compacted Clarinda soil. A numerical model of heat, water, and solute transfer was used to predict distributions of temperature, water content, and solute concentration for a given evaporation rate. Efficiency of the model for reproducing the water content and solute concentration ranged from 94.5 to 61.1%. The predicted and observed solute concentrations increased with time in the upper 0.02 m of noncompacted soil. Also, the upper soil portion, the 0.05‐m layer, dried drastically. Both observations and predictions indicate complex interactions between heat, water, and chemicals near evaporating surfaces.
Reanalysis of Boron Adsorption on Soils and Soil Minerals Using the Constant Capacitance Model
Authors: Goldberg Sabine
Published: July 2010

Inclusion of microscopic information improved the ability of the constant capacitance model to provide a quantitative description of B adsorption on various Al and Fe oxides, clay minerals, and arid‐zone soils as a function of solution pH. The same set of B surface complexation reactions was used for all adsorbing surfaces. This study tests the ability of the model to describe B adsorption using surface configurations that had been observed experimentally. In the present model application, both trigonal, B(OH)3, and tetrahedral, BOH−4, B surface complexes are postulated, consistent with experimental spectroscopic results. Boron surface complexation constants for Al and Fe oxides and kaolinites are not statistically significantly different from each other. Boron surface complexation constants for kaolinites are statistically significantly different from those for 2:1 clays and soils. Boron surface complexation constants for 2:1 clays and soils are not statistically significantly different from each other, reflecting the dominance of 2:1 clay minerals in B adsorption reactions in arid‐zone soils. Average sets of B surface complexation constants provided adequate descriptions of B adsorption behavior on all adsorbents studied, indicating some predictive capability. The constant capacitance model was able to predict B adsorption behavior on additional arid‐zone soils using the average set of B surface complexation constants.
Appraisal of the Ethylene Glycol Monoethyl Ether Method for Measuring Hydratable Surface Area of Clays and Soils
Authors: Quirk J. P. , Murray R. S.
Published: July 2010

The development of the ethylene glycol monoethyl ether (EGME) method for measuring the “hydratable” surface area of soils and clays is reviewed. We have examined the EGME retention of 18 montmorillonites and compared the surface areas obtained in this way with those obtained using the b‐axis parameter and total chemical composition of each clay. The original hypothesis of Dyal and Hendricks (1950), that a monolayer of ethylene glycol (and presumably of EGME) forms on each of the opposing lamellae within a montmorillonite quasi‐crystal, is approximately correct. However, the existing evidence for beidellites suggests that this mineral species is intermediate in retention behavior between montmorillonites and vermiculites. For illites and kaolinites the surface areas measured with EGME are significantly greater than those measured with N. However, we have shown that there is much better agreement between the surface areas measured with N and those calculated from the amount of water adsorbed at a relative vapor pressure of about , using 0.108 nm2 as the molecular area of adsorbed water. Accordingly, we recommend that the amount of water adsorbed at (a saturated solution of CaBr2 at 20°C) be used as a single point determination for the routine examination of large numbers of soil samples as an indication of surface extent. We provide reasons why it is inappropriate to convert the water adsorption value to a surface area. We briefly discuss the significance of surface area measurements in studies of the chemical and physical aspects of soil and clay behavior.
Shallow Tillage with a Traditional West African Hoe to Conserve Soil Water
Authors: Payne W. A.
Published: July 2010

Evaporation (E) from soil constitutes a large proportion of evapotranspiration (ET) of pearl millet [Pennisetum glaucum (L.) R. Br.] fields in West Africa. Reduced E would increase crop water supply and reduce the risk of resowing. We hypothesized that tillage after rain events with the hilaire, a traditional, shallow‐cultivating hoe that pulverizes and darkens the soil surface, could conserve soil water and increase pearl millet yield. Experiments were conducted using bare and cropped plots. Tillage after rain (+ or −) was the only treatment for bare plots. Treatments for cropped plots were tillage after rain with the hilaire and fertilizer addition (12 kg ha−1 N and 12 kg P ha−1). For bare plots, tillage with the hilaire reduced soil surface reflectance by as much as ≈0.2 and increased soil temperature at 0.05 m by 12°C. Tillage increased soil water storage in the upper 2.4 m of bare plots by up to 47 mm. For cropped plots, tillage increased soil water storage in the upper 1.4 m by up to 32 mm, and it increased grain yield by 68% in 1991 and 70% in 1992. Fertilizer addition increased yield by 21% in 1991 and 116% in 1992. Tillage reduced ET in 1992 from 417 to 372 mm and increased water‐use efficiency (WUEET) from 0.99 to 1.91 kg ha−1 mm−1 Fertilizer addition increased WUEET from 0.95 to 1.94 kg ha−1 mm−1 Practical exploitation of the hilaire's effect upon evaporation is not expected because it is a hand‐operated tool. However, the study demonstrates principles upon which an animal‐drawn implement might be designed.
Bacterial and Fungal Cell‐Wall Residues in Conventional and No‐Tillage Agroecosystems
Authors: Guggenberger Georg , Frey Serita D. , Six Johan , Paustian Keith , Elliott Edward T.
Published: July 2010

Agricultural management practices have been shown to influence the decomposer community in soils, with no‐tillage (NT) systems favoring fungi as compared with conventional tillage (CT) systems. In this study, we examined six North American agroecosystems with respect to the effects of NT vs. CT management systems on the accrual of microbial cell‐wall residues in surface soil. We used total amino sugar contents to estimate living and decomposing microbial cell‐wall mass in soil and the contents of glucosamine and muramic acid to separate fungal and bacterial contributions to microbial‐derived soil organic matter (SOM). Compared with estimates of glucosamine and muramic acid present in living biomass of fungi and bacteria, total concentrations of these compounds (745–2076 mg glucosamine kg−1soil and 37–79 mg muramic acid kg−1soil) were larger by factors of 54 to 745 and 26 to 82, respectively. At three sites, the ratios of glucosamine to muramic acid in NT soils (32.0, 30.0, 42.2) significantly exceeded those in the respective CT soils (18.8, 22.1, 23.0) because of a higher enrichment of glucosamine. This coincided with higher values for fungal biomass, particulate organic matter carbon (POM‐C), mean weight diameter of water‐stable aggregates (MWD), and total organic carbon (TOC). Analysis of aggregate‐size classes showed that the additional glucosamine accumulated in >53‐mm aggregates but not in smaller particles. The enrichment of SOM in fungal‐derived glucosamine suggests that the accrual of hyphal cell‐wall residues is an important process in the three NT agroecosystems which leads to higher SOM storage in surface soil concurrent with an increase in aggregate stability. The other soils, having a lower clay plus silt content, exhibited no significant differences in POM‐C, MWD, and total amino sugars between NT and CT management systems. We suggest that at lower clay plus silt contents the beneficial potential for NT to sequester microbial‐derived SOM is lower because of limited physical stabilization.
Metal Concentrations in Aggregate Interiors, Exteriors, Whole Aggregates, and Bulk of Costa Rican Soils
Authors: Wilcke Wolfgang , Kretzschmar Sigrid , Bundt Maya , Zech Wolfgang
Published: July 2010

In many temperate soils the preferential weathering and leaching of aggregate surfaces and the nonaggregated material between aggregates depletes geogenic metals. It also shifts metals from strongly to more weakly bound metal forms. Deposited metals are sorbed preferentially on aggregate surfaces and between aggregates. We examined whether preferential desilication under tropical climate causes an enrichment in the aggregate exteriors in oxidic forms of metals. We also studied where deposited metals are bound in these soils. Aggregates (2–20 mm) were selected manually from the A horizons of eight Oxisols, six Andisols, two Mollisols, and two Inceptisols in Costa Rica. All samples were fractionated into interior and exterior portions and treated with a seven‐step sequence to extract Al, Cd, Cu, Fe, Mn, Pb, and Zn. Total concentrations of all metals except Zn were higher in the aggregate exteriors than in the interiors (average differences in % of the interior concentrations: Al, 9.0; Cd, 2.2; Cu, 8.7; Fe, 4.9; Mn, 4.2; Pb, 64.7; Zn, 0.0). The average Cd and Pb concentrations in easily extractable fractions were significantly higher in the aggregate exteriors. There were no significant differences in metal partitioning between interiors and exteriors except for Pb, which had higher proportions in extractable forms with NH2OH · HCl > NH4− acetate, pH 6.0 > EDTA in the exteriors. There were few significant differences in metal concentrations and partitioning between bulk soil and whole aggregates. The results may be explained by (i) preferential desilication of the aggregate exteriors and (ii) preferential sorption of deposited heavy metals mainly in easily extractable forms.
Long‐Term Tillage Effects on Soil Chemical Properties and Organic Matter Fractions
Authors: Hussain I. , Olson K. R. , Ebelhar S. A.
Published: July 2010

Change in frequency and intensity of tillage practices alters the soil properties, distribution of nutrients, and soil organic matter in the soil profile. We hypothesized that 8 yr of no‐till (NT), chisel plow (CP), and moldboard plow (MP) treatments would affect chemical properties and organic matter of eroded soil. The corn (Zea maysL.)–soybean [Glycine max(L.) Merr.] rotation study was established in tall fescue (Festuca arundinaceaL.) sod on a previously eroded, moderately well‐drained, Grantsburg (Fine‐silty, mixed, mesic Oxyaquic Fragiudalf) soil in southern Illinois. In the eighth year, soil pH, exchangeable Ca, and Bray P‐1 were greater in NT than in CP and MP in the 0‐ to 5‐cm soil depth. In the 0‐ to 5‐cm soil depth, exchangeable K and Mg were greater with the CP than with the NT and MP. In the 5‐ to 15‐cm soil depth, exchangeable Ca and Mg were greater in the MP and CP than in NT, due to mixing. Soil pH and P were greater for CP than MP and NT in the 5‐ to 15‐cm layer. Exchangeable K in the 5‐ to 15‐cm soil depth was greater in the MP than CP and NT. In the 0‐ to 5‐cm soil depth, NT, CP, and MP had 38, 35, and 31% of their total C as particulate organic matter (POM), respectively. After 8 yr, CP and MP had less total organic C than NT in the 0‐ to 5‐cm depth. In the 0‐ to 5‐cm depth, CP and MP had less POM C than NT. The greater reduction of organic C in the POM fraction than in whole soil showed that POM was the most tillage‐sensitive fraction of organic matter. After 8 yr of study, the water‐stable aggregates in the 0‐ to 5‐cm soil depth of MP and CP was reduced compared with NT. The effects of tillage treatment and associated soil erosion either resulted in different findings from tillage treatments on uneroded soil or affected the trend and magnitude of the soil property differences between treatments. For the 10‐yr period prior to the establishment of the tillage experiment the site was managed as hayland. At the end of 8 yr, the NT maintained or improved nutrient retention and aggregate stability in the 0‐ to 5‐cm layer compared with MP and CP.
A New Drip‐Injection Irrigation System for Crop Salt Tolerance Evaluation
Authors: Aragüés R. , Playán E. , Ortiz R. , Royo A.
Published: July 2010

An irrigation system was developed for the establishment of salinity gradients in field experiments that are aimed at obtaining salinity‐yield response functions of crops. The drip‐injection irrigation system (DIS) consists of a parallel pump system (a centrifugal pump for fresh water and an injection pump for saline water) and a conventional drip irrigation system composed of various irrigation sectors. The number of emitters installed in each irrigation sector determines the discharge of the centrifugal pump that blends with the fixed discharge of the injection pump. So, for the rest of fixed variables, the number of emitters (N) installed in a given irrigation sector determines the salinity of the irrigation water (ECiw): , with a measured coefficient of determination of ≈99%. The DIS was validated in an experiment where the salinity‐yield response functions of ten barley cultivars were obtained using nine ECiw salinity treatments, with two replications per treatment. The DIS proved to be accurate and robust in that: (i) the measured ECiw gradient was similar to the target ECiw gradient (r positively correlated at P < 0.0001); (ii) the soil salinity (ECe) horizontal and vertical (0–50 cm depth) uniformities within each salinity treatment were low (average coefficient of variation [CV] of the pooled salinity treatments equal to 16–22% for the horizontal soil salinity and equal to 10% for the vertical soil salinity) and the temporal variability of soil salinity was low to moderate (average CV of the pooled salinity treatments equal to 18% during the studied period); and (iii) ECiw and ECe were positively correlated (P < 0.001). We concluded that the DIS is an excellent, low cost irrigation system for conducting field crop salt tolerance evaluations.
Revegetation and Nitrate Leaching from Lake States Northern Hardwood Forests Following Harvest
Authors: Iseman Thomas M. , Zak Donald R. , Holmes William E. , Merrill Amy G.
Published: July 2010

The sugar maple (Acer saccharum Marshall)–red oak (Quercus rubra L.) and sugar maple–basswood (Tilia americana L.) ecosystems are Lake States forests that differ in net nitrification (5 and 15 g N m−2 yr−1, respectively), but experience equivalent rates of NO−3 leaching following clear‐cut harvest (≈5 g N m−2 yr−1). Our objectives were to determine whether high rates of N leaching are sustained following harvest and whether ecosystem‐specific patterns of biomass accumulation influence NO−3 loss. We studied two stands in each ecosystem and established four research plots in each stand; two plots were clear‐cut in 1991 and two were controls. In 1996, we measured soil solution NO−3 concentration (1‐m depth) and calculated areal losses by a water balance method. We used allometric equations to estimate woody biomass in clearcut plots; herbaceous biomass was clipped. In the sugar maple–red oak ecosystem, NO−3 leaching from 5‐yr‐old clear‐cut plots (0.56 g N m−2 yr−1) was significantly greater than leaching from control plots (0.05 g N m−2 yr−1). In contrast, NO−3 leaching did not differ between control (0.41 g N m−2 yr−1) and 5‐yr‐old clear‐cut (0.02 g N m−2 yr−1) in the sugar maple–basswood ecosystem; however, loss from these clear‐cut plots was significantly lower than that from clear‐cut sugar maple–red oak plots. Five years after harvest, 7.1 Mg ha−1 of aboveground biomass accumulated in clear‐cut sugar maple–basswood plots, almost twice that of clear‐cut sugar maple–red oak plots (3.9 Mg ha−1). Five years after harvest, the highest rates of NO−3 loss occurred in the sugar maple–red oak ecosystem, in which aboveground biomass accumulation was least.
Time Domain Reflectometry Probe for Simultaneous Measurement of Soil Matric Potential and Water Content
Authors: Noborio K. , Horton R. , Tan C. S.
Published: July 2010

Simultaneous measurement of matric potential, ψ, and water content, θ, is demanded in many disciplines. Time domain reflectometry (TDR) has been routinely used to measure water content and electrical conductivity of soil. Previous efforts to combine TDR probes with porous materials functioning as tensiometers were successful, but these probes were still constrained by characteristics of tensiometers, such as the need to supply water and measuring ranges ψ > −85kPa. A new ψ–θ TDR probe was developed to overcome shortcomings of the previous work. A portion of the TDR rod was embedded in a dental plaster (gypsum), whose matric potential equilibrated with surrounding soil. The rest of the TDR rod was inserted into the soil. The TDR technique was used to determine dielectric constants, κ, of both the gypsum and the soil. The new ψ–θ TDR probes were tested in clay loam soil using a pressure‐plate apparatus to produce κ–ψ relationships of the gypsum and the soil for −1000 ≤ ψ ≤ −10 kPa. Changes in κ of the gypsum corresponded well to applied pressures for −1000 ≤ ψ ≤ −30 kPa, but κ values did not noticeably change for ψ > −30 kPa. Values of κ of the soil corresponded well to the whole ψ range tested. The new probes accurately measure θ and ψ of soil when soil water content gradually decreases or increases. The newly developed ψ–θ TDR probe requires no more maintenance than ordinary TDR probes and requires no additional instrumentation.
Gaseous Tracer Technique for Estimating Air–Water Interfacial Areas and Interface Mobility
Authors: Kim Heonki , Rao P. Suresh C. , Annable Michael D.
Published: July 2010

A series of gaseous miscible displacement experiments were conducted to estimate specific air–water interfacial areas (ai) and water contents in an unsaturated sand column. A straight‐chain hydrocarbon (n‐decane) was used as the gaseous interfacial tracer and methylene chloride and chloroform were used as the water‐partitioning gaseous tracers. A gas chromatographic technique was employed for the tracer experiments conducted at room temperature using nitrogen as the mobile phase and water as the immobile liquid. Tracer experiments covered a water saturation (Sw) range of 1.5 to 56%. The largest ai value (∼1500 cm2 cm−3), measured at the lowest Sw (1.5%), was somewhat smaller than the solid surface area (∼2000 cm2 cm−3) determined using the nitrogen‐sorption technique. As Sw increased, ai values decreased exponentially to ∼80 cm2 cm−3 at Sw of 56%. Within a limited Sw range (0.29 < Sw < 0.55), where both aqueous and gaseous interfacial tracer data were measured, the ai values measured using a gaseous tracer (n‐decane) were 2 to 3 times larger than those measured in a previous study using an aqueous interfacial tracer (sodium dodecylbenzene sulfonate [SDBS]). The velocity of the air–water interface was estimated to be between 23 and 36% of the bulk pore‐water velocity. The water contents measured using water‐partitioning tracers were within ±5% of those based on gravimetric measurements.