bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parameter Estimation Analysis of the Evaporation Method for Determining Soil Hydraulic Properties
Authors: Šimůnek Jiří , van Genuchten Martinus Th. , Wendroth Ole 
Published: July 2010

AbstractSoil hydraulic properties are important parameters affecting water flow in variably saturated soils. We estimated the hydraulic properties from a laboratory evaporation experiment using both a parameter estimation method and the modified Wind method. The parameter estimation method combined a one‐dimensional numerical solution of the Richards equation with the Marquardt‐Levenberg optimization scheme. In our study we used both numerically generated data and data measured in the laboratory. Two experiments were carried out on 10‐cm‐high soil cores containing two different soils. Pressure heads inside the cores were measured with five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The objective function for the parameter estimation analysis was defined in terms of the final total water volume in the core and pressure head readings by one or several tensiometers. An analysis of numerically generated data showed that the optimization method was most sensitive to the shape factor (n) and the saturated water content (θs) and least to the residual water content (θr). Pressure heads measured close to the soil surface were found to be more valuable for the parameter estimation technique than those measured at lower locations. The optimized hydraulic parameters corresponded closely with those obtained using Wind's analysis. All optimizations gave similar results for the soil hydraulic properties within the range of measured pressure heads (0 to −700cm). Extrapolation beyond this range involved a high level of uncertainty because of high correlation between parameters θr and n.
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

AbstractThe 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

AbstractCarbon 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

AbstractThe 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

AbstractBrittle 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

AbstractRobust 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

AbstractSulfur 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

AbstractVertisols 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

AbstractGlobal 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

AbstractSeveral 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

AbstractThis 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

AbstractLegumes 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

AbstractIn 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

AbstractMany 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.