bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen Mineralization in Semiarid Soils of Morocco: Rate Constant Variation with Depth
Authors: Soudi Brahim , Sbai Abderrahmane , Chiang Claude N. 
Published: July 2010

AbstractDevelopment of drought‐resistant crops through breeding for extensive root systems emphasizes the importance of subsoil N mineralization for crop production in arid regions. This study was conducted to determine the influence of soil depth on N‐mineralization rate, total N, and amino acid N contents for eight representative soils of the subarid zone of Morocco. Nitrogen‐mineralization ability within the profiles was evaluated through long‐term soil incubation/leaching experiments. Total N and amino acid N were measured by the Kjeldahl method and acid hydrolysis, respectively. A hydrolysable‐N‐production rate was also evaluated, through successive acid hydrolysis of samples from two soil profiles. The changes with depth for the three variables studied were described by two equations. One is a power law of the type Y = AD−B, where Y is one of the variables, A and B are two positive constants, and D is depth. The second is an exponential equation, Y = A exp(−BD). Parameter B had values of 1.3 and 0.04 for N‐mineralization rate, 0.7 and 0.021 for amino acid N, and 0.40 and 0.012 for total N for the power‐law and exponential models, respectively. Significant differences were found between the rates of change with depth (B value) of the three quantities studied using the second equation. The hydrolysable‐N‐production rate decreased with depth in the profiles, indicating a reduction of the chemical degradability of N compounds in deeper horizons. These results suggest that the decrease of N mineralization with depth may be attributed to a recondensation of amino acids in complex biochemical compounds more resistant to biodegradation.
Sweetgum Half‐Sib Seed Source Response to Nitrogen and Phosphorus Fertilization in Mississippi
Authors: Nelson Lyle E. , Switzer George L. 
Published: July 2010

AbstractThis field experiment was undertaken to determine the response to N and P of sweetgum (Liquidambar styraciflua L.) under plantation culture, and the variation in response among seedlings derived from four half‐sib seed sources from alluvial and upland sites. Two‐year‐old seedlings were planted in a Mathiston silt loam (fine‐silty, siliceous, acid, thermic Aeric Fluvaquent) in 1972. In 1973, 0‐0‐0, 100‐0‐0, 100‐100‐0, and 200‐100‐0 kg/ha of N‐P‐K were broadcast. In 1975, the N treatments were repeated. Height, diameter at breast height (DBH), and foliar N were monitored through nine field growing seasons. There was no response to P. At 9 yr, the mean total height of the unfertilized half‐sibs was 7.1m, mean DBH was 7.8 cm, basal area was 5.0 m2/ha, stem volume outside bark was 15 m3/ha, and woody biomass was 8.1 Mg/ha. Increases from fertilization were 9, 14, 28, 39, and 40%, respectively. There was a half‐sib × fertility interaction with maximum response of three half‐sibs to 200 kg N/ha and one to 400 kg N/ha. The response of the two half‐sibs from alluvial seed sources was about double that of the two from upland seed sources. Foliar N concentrations of all treatments decreased during the 9 yr; however, foliar concentrations in fertilized trees were only slightly higher than in the unfertilized throughout. Although increases in annual increments due to fertilization were measurable for only 1 or 2 yr following fertilization, the resulting differences in volume and biomass were maintained in subsequent years.
Microplot Design for Determining Corn Recovery of Nitrogen Fertilizer Applied in the Row
Authors: Blaylock A. D. , Benjamin J. G. , Cruse R. M. 
Published: July 2010

AbstractOne‐ and three‐row corn (Zea mays L.) microplots were compared for determining 15N‐depleted fertilizer recovery from in‐row N applications. Studies were conducted with Iowa ridge‐tillage systems on Monona silt loam (fine‐silty, mixed, mesic Typic Hapludoll), Webster silty clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll), and Marna silty clay loam (fine, montmorillonitic, mesic Typic Haplaquoll). Corn rows were injected with 15N‐depleted NH4NO3 (99.99% 14N) at 56 and 112 kg N ha−1 on Monona silt loam and at 67 and 157 kg N ha−1 on Webster and Marna silty clay loams. Percentage N from fertilizer in the mature‐plant samples ranged from 19.8 for grain fertilized at 56 kg N ha−1 to 50.0 for stover at 157 kg N ha−1. One‐ and three‐row microplots were not significantly different for determining corn N recovery in the application year from in‐row N placements.
Application of Two‐Site/Two‐Region Models for Studying Simultaneous Nonequilibrium Transport and Degradation of Pesticides
Authors: Gamerdinger A. P. , Wagenet R. J. , van Genuchten M. Th. 
Published: July 2010

AbstractQuantitative laboratory study of pesticide sorption and degradation during transport can provide insight into the basic processes affecting pesticide fate in field soils. Accordingly, we demonstrate the application of analytical solutions of two‐site/two‐region transport models useful in studying simultaneous pesticide sorption and degradation. Soil‐column displacement experiments involving 3H2O, Cl, and atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) were conducted during steady‐state water flow at two pore‐water velocities and two pesticide concentrations. The soil used is a Valois silty loam (coarse‐loamy, mixed, mesic Typic Dystrochrept). Effluent data from these experiments were used to demonstrate the application of these analytical solutions, as well as a parameter‐estimation computer program based on these solutions. The ability to use laboratory‐derived estimates of equilibrium sorption parameters to describe sorption under flowing conditions was evaluated at each flow velocity. Significant correlation between soil sorption partitioning and degradation prevents the simultaneous determination of both processes using these solutions. However, estimates of degradation obtained from mass balances of the column data were useful in identifying the equilibrium sorption parameters. Data collected elsewhere for 2,4,5‐T (2,4,5‐trichlorophenoxyacetic acid) herbicide transport were used as an additional example of the application of the model with degradation. Strengths and weaknesses of the models, and suggestions for further study, are presented.
Measurement of Soil Macropore Air Permeability
Authors: Roseberg R. J. , McCoy E. L. 
Published: July 2010

AbstractSoil air‐permeability measurement is a promising tool for determining pore geometric influences on transport processes. The inability of previous systems to allow air‐flow measurement on undisturbed soil samples at and near saturation, where only macropores will conduct air, has prevented routine use of this technique for investigation of macropore geometry. The device described here allows simultaneous measurement of air permeability (Ka) and the soil water‐retention curve in the 0‐ to −6.0‐kPa matric‐potential range. This is accomplished by counteracting the effect of the gravitational‐potential gradient within the sample using controlled air pressure. Use of a wettable porous plastic of high conductance as the tension‐control medium allows equilibration times of <4 h during desaturation for each step change in matric potential (ψm). Operation of the device is illustrated with results from two undisturbed soil samples having contrasting macroporosity. The soil core with visible macropores (> 1‐mm diameter) had a higher Ka and a greater change in water content at each ψm step throughout the 0‐ to −3.0‐kPa range, compared with the core without visible macropores. The positive linear slope of the log air‐filled porosity vs. log Ka relationship was greater for the sample containing visible macropores, indicating greater pore continuity. Air permeability of the macroporous sample remained >0 at ψm = 0, but the opposite was true for the soil sample without visible macropores.
Estimating Divalent Cadmium Activities Measured in Arid‐Zone Soils using Competitive Chelation
Authors: Workman S. M. , Lindsay W. L. 
Published: July 2010

AbstractCompetitive chelation was explored as a method of measuring divalent Cd activity in neutral to alkaline soils. The most successful combination of chelating agents and competing metals comprised dtpa (diethylenetriaminepentaacetic acid) and Pb2+ in equilibrium with added PbCO3(c). A series of 10−5 M dtpa solutions containing varying initial mole fractions of Cd and Pb were reacted with soils for 140 h. Some solutions lost Cd and gained Pb, while others gained Cd and lost Pb. From these results it was possible to estimate the composition of a unique solution that does not change upon reaction with a given soil. The composition of this unique solution reflects equilibrium conditions and was used to calculate Cd2+ activity. Eight soils ranging in pH from 7.15 to 8.25 showed Cd2+ activities ranging from 10−6.6 to 10−9.4 M. The Cd2+ activities measured in these soils could be predicted using the following expression:(Cd2+) = 107.61 (H+)2This solubility of Cd2+ in soils is approximately two orders of magnitude lower than the activity of Cd2+ in equilibrium with CdCO3(c) and atmospheric CO2. No known Cd mineral has yet been identified whose solubility reflects this low activity of Cd2+. The competitive chelation method used here avoids many of the pitfalls encountered in measuring extremely low levels of Cd in neutral and alkaline soils where Cd‐organic complexes may be present.
Evaluation of 2‐Ethynylpyridine as a Soil Nitrification Inhibitor
Authors: McCarty G. W. , Bremner J. M. 
Published: July 2010

AbstractRecent work in our laboratory showed that 2‐ethynylpyridine is a potent inhibitor of nitrification in soil. To further evaluate this compound as a soil nitrification inhibitor, we compared the effects of 2‐ethynylpyridine and 16 compounds patented or proposed as fertilizer amendments for inhibition of nitrification in soil. We measured production of NO2 and NO3 in soils incubated under aerobic conditions at 20, 25, or 30 °C after treatment with (NH4)2SO4 or urea. The data obtained showed that 2‐ethynylpyridine compared favorably with nitrapyrin [N‐Serve; 2‐chloro‐6‐(trichloromethyl)pyridine] and etridiazole [Dwell; 5‐ethoxy‐3‐trichloromethyl‐1,2,4‐thiadiazole] for inhibition of nitrification in soil and was considerably more effective than the other nitrification inhibitors tested (dicyandiamide [DCD], thiourea [Tu], guanylthiourea [ASU], potassium azide, 4‐amino‐1,2,4‐triazole [ATC], 2‐amino‐4‐chloro‐6‐methylpyridine [AM], 2‐mercaptobenzothiazole [MBT], 2,4‐diamino‐6‐trichloromethyltriazine, sulfathiazole [ST], sodium thiocarbonate [Na2CS3], N‐2,5‐dichlorophenylsuccinamide [DCS], 4‐nitrobenzotrichloride, 4‐mesylbenzotrichloride, and ammonium thiosulfate [(NH4)2S2O3]). Other studies showed that 2‐ethynylpyridine is more effective for inhibiting nitrification of NH4‐N than of urea‐N, that it has very little, if any, effect on hydrolysis of urea or denitrification of NO3 in soil, and that its effectiveness as a soil nitrification inhibitor is markedly affected by soil type and temperature. These findings and other work reported indicate that 2‐ethynylpyridine deserves consideration as a fertilizer amendment for retarding nitrification of fertilizer N in soil.
Growth of Genetically Altered Pseudomonas solanacearum in Soil and Rhizosphere
Authors: Hartel Peter G. , Williamson Joseph W. , Schell Mark A. 
Published: July 2010

AbstractThe extent to which a bacterium can grow in soil and in the rhizosphere is influenced by the presence or absence of various genes. The effect of genetic alteration of the egl gene, encoding a β‐1,4‐endoglucanase, on the growth of Pseudomonas solanacearum E.F. Smith (the causal agent of bacterial wilt) in soil and in the rhizosphere of tomato (Lycopersicon esculentum Mill.), common purslane (Portulaca oleracea L.), and pearl millet (Pennisetum glaucum (L.) R. Br.) was determined. Endoglucanase production by P. solanacearum was either inactivated by transposon (Tn5) insertion mutagenesis or enhanced twofold by increasing the egl copy number with a recombinant plasmid (pHE3). In a test of the stability of the genetic alterations in two different soils, the transposon in the chromosome was detectable for >120 d, but the recombinant plasmid was apparently lost after 14 d in one soil and after 120 d in the other. In comparison to the wild‐type strain, the generation times of the strains with the transposon and the recombinant plasmid increased 16 and 25%, respectively, in one soil solution and 35 and 53% in the other soil solution; this correlated well with the ability of the strains to grow in the same freshly moistened soils. Under conditions of soil inoculation, the genetically altered strains did not wilt tomato seedings significantly faster or slower than the wild‐type strain. Although all of the P. solanacearum strains, including the wild type, grew in the rhizosphere of gnotobiotically grown tomato plants, none of the strains grew in the rhizosphere of tomato, common purslane, or pearl millet under nonsterile conditions. The data suggest that genetic alterations slow the growth of P. solanacearum in freshly moistened soil, and that endoglucanase is of minor importance to the growth of P. solanacearum under these conditions.
Aliphatic Acids: Influence on Sulfate Mobility in a Forested Cecil Soil
Authors: Evans A. , Anderson T. J. 
Published: July 2010

AbstractDissolved organic substances derived from forest litter are believed to influence the retention and movement of SO2−4 in forest soils. A column study was conducted in which 35SO4 was surface applied to a soil and leached with either low‐molecular‐weight aliphatic acids (AA) or a forest‐litter extract. Oxalic, malonic, and succinic acids were used in the concentration range 8.0 × 10−3 to 1.0 × 10−5 mol L−1. Movement of 35SO4 was determined with column depth, as was the 35SO4 activity in the collected leachates. Labeled SO4 soil movement was found to increase with increasing AA concentration. Leachate 35SO4 activity was observed to increase in the order malonic > succinic > oxalic for acid treatments > 1.0 × 10−4 mol L−1. The 1.0 × 10−5 mol L−1 acid treatments did not result in 35SO4 break‐through in the soil columns. Reduced exchangeable 35SO4 for organic acid ≥ 1.0 × 10−3 mol L−1 suggests that at high concentrations, aliphatic acids may activate sulfate retention sites in soil, while at lower concentrations these acids may accelerate the movement of 35SO4 in forest soils due to selective organic‐acid adsorption by soil components.
Intrinsic Failure and Cracking of Clay
Authors: Murray R. S. , Quirk J. P. 
Published: July 2010

AbstractCracks play a major role in determining the strength and fluid transmission properties of clay soil. This report, which bears on the origin of cracks in a clay matrix, arose from observations made while investigating the pore‐size distribution (<100 nm) of clay using low‐temperature (77 K) N2 sorption isotherms. The two surface areas derived, by independent means, from the adsorption and desorption branches of such isotherms are in surprisingly good agreement for a range of clays. The apparent absence of network effects, implied by this surface‐area accord, can only occur if virtually all voids have access to the outside of the sample via at least one path that contains no narrower voids or constrictions. This points to the existence of a very extensive system of cracks that may form the boundaries of domains or regions of common particle orientation in clay. The formation of this system of cracks has been named intrinsic failure and is believed to result from the shrinking and swelling of the individual, randomly oriented clay domains. The possible significance of intrinsic failure is that it may be the precursor of clay cracking in general and that it may impose an upper limit on the strength of the clay matrix.
Spatial Dependence of Soil Sodicity and Tree Growth in a Natric Haplustalf
Authors: Samra J. S. , Gill H. S. , Richter J. , Anlauf R. 
Published: July 2010

AbstractA precise knowledge of the spatial variability of salt‐affected soils is a prerequisite to optimizing their land use and maximizing biomass production. This study was conducted to investigate inherent variation in pH, sodium adsorption ratio, P, and K of a Typic Natric Haplustalf, growth of Shisham (Dalbergia sissoo Roxb. ex DC.), and their interdependencies. Root‐zone soil was sampled on a 6 by 6 m grid at 162 locations (18 rows by 9 columns) of a field at 0.3‐m depth increments up to 1.2 m, and analyzed. Depending on the depth and soil properties, trend variation ranged from 14 to 47% (overall average of 27%) of the total variance. Corresponding component of the tree‐height heterogeneity varied from 16 to 20% during the four observation years. Ten to 74% of the remaining soil variability, depending on soil layer and properties, was isotropically spatially structured. Thus, on an average, about 30% of the total soil variability was structured. Similarly, the structural component of tree‐height variation ranged from 35 to 46% of the sill during 4 yr. Therefore, 33% (average of 4 yr) of the tree‐height variance was structured. Spatial correlations of soil properties with tree growth were elaborated through cross semivariograms. Spatially sensitive statistical procedures for the assessment of land qualities, technologies, and soil‐plant relationships are recommended.
Fulvic Acid Ultraviolet‐Visible Spectra: Influence of Solvent and pH
Authors: Baes A.U. , Bloom P. R. 
Published: July 2010

AbstractThe ultraviolet‐visible spectra of three fulvic acids from a Mollisol (FA1), a Histosol (FA2), and a Spodosol (FA3) were determined using four solvents: 0.05 M NaHCO3, distilled water, 95% (v/v) ethanol, and absolute ethanol. Light scattering was evaluated by varying the distance of the sample cell from the detector. This test, which gave positive results for a dilute milk sample, showed no light scattering effects for the fulvic acids. The ratios of 465 to 665 nm absorbances (E4/E6 ratios) determined in 0.05 M NaHCO3 were 16.7 for FA1, 16.8 for FA2, and 18.5 for FA3. The ultraviolet spectra in water showed only slight inflections for FA1 and FA3, but the FA2 spectrum had a pronounced shoulder centered at about 280 nm. In ethanol, the shoulder was shifted towards the red and absorbance decreased. Similar red shifts were shown to occur in 2,3‐; 2,4‐; and 2,6‐dihydroxybenzoic acids (DHB). The absorbance of bands in the range of 26 to 290 nm obeyed the Beer‐Lambert law. Estimates of molar absorptivities ranged from 2300 to 4500 L mol−1 cm−1, which is within the range of molar absorptivities of the electron transfer (ET) bands of carboxyphenols. Shifts in the position of the shoulders with pH, in both water and 95% ethanol, resembled that of carboxyphenols. Absorbance at visible wavelengths was not consistent with the behavior of simple quinones but might be due to chromophores with extended conjugation, possibly polyaromatic structures. Another possibility considered was intramolecular electron donor‐acceptor complexes.
Fluorescence Spectroscopy of Aqueous Leaf Litter Extracts and Their Complexes with Aluminum
Authors: Shotyk William , Sposito Garrison 
Published: July 2010

AbstractFluorescence spectroscopy is a sensitive method for discriminating among humic substances both in structure and in provenance. This study was conducted to determine whether the same is true for an important nonhumic organic material, the water‐soluble fraction of forest leaf litter. Aqueous extracts of leaf litter from three tree species [chestnut (Castanea sativa L. Miller), western white pine (Pinus monticola Douglas ex. D. Don), and willow (Salix spp.)] were examined by conventional excitation and synchronous‐scan excitation fluorescence spectroscopy. The spectra obtained varied with the plant source of the leaf litter extract (LLE) as well as with the LLE concentration. This sensitivity to organic‐matter origin indicates that fluorescence spectroscopy will be useful to distinguish among LLE of differing provenance. The synchronous‐scan spectra of the LLE showed some peaks that decreased in relative intensity with increasing LLE dilution, and some that increased with increasing dilution. This behavior was attributed to the presence of both Type I fluorophores, which are not quenched because they do not form charge‐transfer complexes with nonfluorescent constituents of the LLE, and Type II fluorophores, which are quenched by the formation of charge‐transfer complexes and self‐quenching processes, leading to intensity increases at high dilution. Synchronous‐scan excitation spectra also were obtained for Al/LLE mixtures at pH 4.5, with the total Al concentration varying from 0 to 60 mmol m−3. The spectra showed that Al‐complex formation may result either in increases of relative fluorescence intensity or in fluorescence quenching, depending both on the source of LLE and on its concentration. This result may reflect a concentration dependence of charge‐transfer complex formation and the possibility that excited‐state complexes of Al are less fluorescent than ground‐state Al complexes.
Residual Effects of Various Phosphorus Application Methods on Winter Wheat and Grain Sorghum
Authors: Sander D. H. , Penas E. J. , Eghball Bahman 
Published: July 2010

AbstractThe amount of residual P from previous applications and the performance of fertilizer P can be affected by application method. This study was conducted to determine the effects of different methods of P application on grain yield, yield components, fertilizer‐P efficiency, P‐utilization efficiency (kg grain per kg P uptake), and residual P in two cropping systems — a wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] system on Pawnee soil (fine, montmorillonitic, mesic Aquic Argiudoll) and a wheat‐fallow‐wheat system on Keith soil (fine‐silty, mixed, mesic Typic Argiustoll). Methods of P application to wheat included broadcasting and knifing in the fall and spring, and seed placement. Phosphorus applied to wheat and its residual effects were determined on sorghum following wheat and wheat following fallow. On sorghum, spring row and knife‐applied P methods were compared with residual treatments. For wheat production, P knifed in the fall and seed application were equally effective. Both were more effective than other application methods for grain yield, P uptake, and fertilizer efficiency. Fertilizer efficiency was increased from 5.5% for broadcast to 36% for knifed and 40% for seed application. Spring knifed and row applications of P were equally effective for sorghum. Knifed P, placed below tillage depth with little disturbance of the band area, resulted in greater residual value for grain sorghum following wheat than either seed or broadcast P. In the wheat‐fallow‐wheat system, the knifed spring P, which had the shortest time of soil contact, had significantly greater residual value than other methods. Wheat had much higher fertilizer‐uptake efficiencies, but was only about half as effective as sorghum in P‐utilization efficiency. This study indicated that undisturbed fertilizer P bands have more residual value than either seed‐placed or broadcast P, which can differentially influence the P‐fertilizer requirement for succeeding crops.