bluuebunny/crossref_metadata_2025_split huggingface dataset:
Precipitation of Dicalcium Phosphate Dihydrate in the Presence of Organic Acids
Authors: Grossl Paul R. , Inskeep William P. 
Published: July 2010

AbstractInhibition of dicalcium phosphate dihydrate (DCPD) precipitation rate by organic acids may play an important role in controlling phosphate activity and availability in P‐fertilized soils. The precipitation rate of DCPD was measured at pH 5.7 and 25 °C in the absence and presence of organic acids common to soil solutions using a seeded crystal growth method. Forward rate constants (kf) were determined from an integrated form of the second‐order rate law expression: rate = kfS[Ca2+][HPO2‐4]γ22, where brackets represent concentrations, S is the surface area (m2 L−1), and γ2 is the divalent ion activity coefficient calculated from the Davies equation. The average kf (L2 mol−1 m−2 s−1) for DCPD precipitation without organic acids was 9.7 ± 0.5. Additions of 0.26 to 2.06 mM C as humic acid and 1.1 to 3.3 mM C as fulvic acid resulted in induction periods lasting 2.0 to 632 and 1.5 to 10 min, respectively, prior to subsequent precipitation of DCPD. This indicates that DCPD precipitation was able to overgrow adsorbed humic and fulvic acids. Rates of DCPD precipitation were determined in the presence of humic, fulvic, citric, and tannic acids at concentrations ranging from 0.26 to 9.0 mM total soluble C (CTS). The highest levels of humic, fulvic, citric, and tannic acids added were 2.05, 7.8, 8.0, and 9.0 mM CTS, which resulted in decreased kf values of 1.1, 0.1, 0.6, and 2.1 L2 mol−1 m−2 s−1, respectively. Precipitation was inhibited by adsorption of these organic acids onto DCPD surfaces blocking sites acting as nuclei for new crystal growth. Adsorption characteristics of these organic acids were related to their functional‐group content and size. The ability of DCPD to precipitate on seed crystals with adsorbed C may explain the kinetically favored formation of DCPD vs. more thermodynamically stable octacalcium phosphate (OCP) and hydroxyapatite (HAP), where precipitation rates are more strongly inhibited by soluble C.
Rhizobacteria Suppressive to the Weed Downy Brome
Authors: Kennedy A. C. , Young F. L. , Elliott L. F. , Douglas C. L. 
Published: July 2010

AbstractRhizobacteria have the potential to suppress plant growth. We evaluated the effect of native pseudomonads on downy brome (Bromus tectorum L.), a troublesome weed in small‐grain‐producing lands. Pseudomonas spp. were isolated from winter wheat (Triticum aestivum L.) and downy brome roots and tested to determine their potential as biological control agents for this weed. Pseudomonads were screened in agar and soil for inhibition of downy brome root growth and lack of inhibition of winter wheat root growth. Of more than 1000 isolates tested, 81 inhibited downy brome and not winter wheat in the agar seedling bioassay. Six isolates consistently inhibited downy brome growth and not winter wheat in soil contained in pots in the growth chamber. In nursery field trials in which downy brome was planted in rows and adequately fertilized, some of the bacterial isolates reduced downy brome populations up to 30% and shoot dry weight up to 42%. Field studies were also conducted at three sites in eastern Washington in which brome‐inhibitory bacteria were applied to wheat fields infested with natural populations of downy brome. Of the three isolates studied in the field, two reduced plant populations and aboveground growth of downy brome up to 31 and 53%, respectively, compared with noninoculated controls. At two of the three locations, winter wheat yields were increased 18 to 35% because of the suppression of downy brome growth. Brome‐suppressive bacteria isolated from the rhizoplane of winter wheat and downy brome can be used as biological control agents for downy brome.
Theoretical Analysis of Carbon and Nutrient Interactions in Soils under Energy‐Limited Conditions
Authors: Bosatta Ernesto , Ågren Göran I. 
Published: July 2010

AbstractThe cycles of S and P in soil have received only limited attention from a theoretical or modeling point of view, relative to those of C and N. In this study, the interactions between the cycles of C, N, P, and S in decomposing litters and soils have been analyzed using a theory based on changes in substrate quality during decomposition. The C cycle requires information about microbial efficiency and growth rate as functions of substrate quality, with initial litter quality as a parameter distinguishing different materials. Nitrogen, P, and S are given similar descriptions and the parameter differentiating them are the concentrations of the elements in microbial populations and fresh litter. The theoretical predictions are compared with empirical data on C, N, P, and S behavior in a number of different conditions covering both steady states of soils and dynamics in incubation experiments in laboratories. The agreement between theoretical and empirical results indicate that the cycles of N, P, and S basically follow similar rules.
Aggregate Stability of an Eroded and Desurfaced Typic Argiustoll
Authors: Gollany H. T. , Schumacher T. E. , Evenson P. D. , Lindstrom M. J. , Lemme G. D. 
Published: July 2010

AbstractAggregate stability is a measure of the ability of soil to withstand the disrupting forces of rain and nonsymmetrical wetting. Erosion may influence aggregate stability by exposing soil with properties different than the original soil surface. This study was conducted to determine: (i) the influence of antecedent soil water content on wet aggregate stability using aggregates prehumidified to near saturation; (ii) the effects of organic C and clay content on the soil water content‐aggregate stability relationship; and (iii) the effect of topsoil removal on aggregate stability. Seventy‐eight soil samples were taken from six profiles of Beadle clay loam (fine, montmorillonitic, mesic, Typic Argiustoll). These samples were analyzed for pH, organic C, texture, CaCO3, antecedent soil water content, cation‐exchange capacity (CEC), and aggregate stability. Isolated test plots were also saturated with an overhead sprinkling infiltrometer. Samples were taken periodically throughout a 4‐d period for aggregate‐stability determination. A modified wet sieving technique, which included pre‐humidifying of the sample to near saturation, was used to determine aggregate stability. A negative linear relationship was found between aggregate stability of prehumidified aggregates and antecedent soil water content. Prediction equations were developed that explain up to 77% of variability for the aggregate stability. Organic C was the most important of the independent variables, followed by antecedent soil water content in the multiple regression analysis. Topsoil removal by desurfacing and erosion reduced aggregate stability. Aggregate stabilities for soils with high organic C and clay content were less affected by antecedent soil water content.
Macroporosity of a Well‐Drained Soil under No‐Till and Conventional Tillage
Authors: Dunn G. H. , Phillips R. E. 
Published: July 2010

AbstractConventional tillage and no‐tillage have been shown to affect the hydraulic properties of soil. For this reason, a field experiment was conducted in 1987 and 1988 to determine the effect of tillage practice and cover crop on the macroporosity of a Maury silt loam (fine, mixed, mesic Typic Paleudalf). The field used for this study has been in continuous no‐till and conventional‐till corn (Zea mays L.) since 1970. Ponded steady‐state infiltration measurements were made using double‐ring infiltrometers; afterwards, a tension infiltrometer was used to measure water flux at −0.4, −0.9, and −1.4 kPa water pressure. These negative water pressures were used to calculate equivalent cylindrical pore diameters from the capillaryrise equation. Flux at a pressure of −0.06 kPa was determined from regression equations for each plot. Equivalent pore diameters of 5.0, 0.75, 0.33, and 0.21 mm correspond to −0.06, −0.4, −0.9, and −1.4 kPa, respectively. In June 1987, conventional tillage had significantly higher water flux than no‐till for the 5.0‐ to 0.75‐mm equivalent‐diameter pore size range. In 1987, rye (Secale cereale L.) cover crop plots had significantly higher water‐flux values than hairy vetch (Vicia villosa Roth.) plots for the same range of equivalent pore sizes. In June 1988, no‐till plots had significantly higher water‐flux values for all equivalent pore size ranges. In 1987, 73 and 80% of the total water flux at −0.06 kPa water pressure was transmitted through pores >0.21‐mm equivalent diameter in no‐till and conventional tillage plots, respectively. The corresponding values in 1988 were 83 and 73%.
Biomass and Soil Nitrogen Relationships of a One‐Year‐Old Sycamore Plantation
Authors: Tschaplinski T. J. , Norby R. J. , Todd D. E. , Johnson D. W. 
Published: July 2010

AbstractMaximum efficiency in biomass production in short‐rotation woody crops requires a level of N fertilization that achieves a balance between maximum growth and minimum NO‐3 leaching into groundwater. The effects of urea‐N fertilizer applied under various timing regimes were investigated in a plantation of American sycamore (Platanus occidentalis L.), and different aspects of optimum fertilization were explored. A plantation of sycamore was established at Oak Ridge, TN, typically a N‐poor area. Nitrogen treatments consisted of differing schedules of urea application, including trees fertilized at the beginning of the growing season with 0, 50, 150, and 450 kg N/ha, and trees fertilized periodically (three times during the growing season) at 37.5 kg N/ha. Fertilization effects on stem and leaf biomass, leaf nutrient concentration, soil N characteristics, including available N, mineralizable N, nitrification potential, and NO‐3 leaching loss were determined. The greatest aboveground biomass accumulation (three times greater than that of unfertilized controls) was obtained with 450 kg N/ha, but with greater NO‐3 leaching. Nearly as much biomass was obtained with almost no NO‐3 leaching when much less N was added either early in the season (150 kg N/ha) or in periodic applications (37.5 kg N/ha three times). The rapid decline to control levels of soil available N in all treatments, and the results of the aerobic incubations, indicate high nitrification potential at the site. The results suggest that periodic, low N fertilization may be optimal on sites with a high nitrification potential, and that the lower rates tested minimize NO‐3 contamination of groundwater.
Steel Rod Oxidation as a Hydrologic Indicator in Wetland Soils
Authors: Bridgham Scott D. , Faulkner Stephen P. , Richardson Curtis J. 
Published: July 2010

AbstractDepth of rusting on steel rods has been proposed as an inexpensive means of determining depth to the water table and the reducing zone in wetland soils. The suitability of steel‐rod oxidation as a hydrologic indicator in wetland soils was tested in a series of laboratory and field experiments in both Histosols and a mineral soil (Typic Fluvaquent). In laboratory microcosms, the steel‐rod rusting depth exactly matched water‐table levels under both permanently flooded and drained conditions. But under a rapidly fluctuating hydrology, once heavy rust formed on the rods it did not dissolve upon partial reflooding. Field experiments showed a good correspondence between steel‐rod rusting depth and water‐table depth under both relatively constant and seasonally changing hydrology in Histosols (r2 = 0.80, slope = 0.81). In the Typic Fluvaquent, a close correspondence between steel‐rod rusting depth and water‐table depth occurred under relatively constant hydrological conditions but, with a rapidly dropping water table, rod oxidation showed a lag period in response. We conclude that the steel‐rod technique is valuable as a hydrologic indicator of the reducing zone in basic science studies. We recommend frequent sampling (monthly) and the use of other hydrological measures to ensure unambiguous results. The technique is unsuitable for jurisdictional delineation in areas with a fluctuating hydrology due to prolonged lag periods in rod oxidation under some conditions and the inability of previously formed rust to dissolve upon reflooding.
Simultaneous Measurement of the Spatial Distribution of Soil Water Content and Bulk Density
Authors: Phogat V. K. , Aylmore L. A. G. , Schuller R. D. 
Published: July 2010

AbstractContinuous nondestructive measurements of the spatial distributions of soil water content and bulk density are essential prerequisites to the resolution of many problems in the study of soil‐plant‐water systems. Computerized axial tomography (CAT) was applied to dualsource (137Cs and 169Yb) gamma‐ray attenuation in soil columns to determine nondestructively the spatial distributions of volumetric water content (θv) and bulk density (ρs) for two soils that exhibit swelling to different degrees. Beam slice thickness was 2 mm and pixel dimensions 2 by 2 mm. The CAT scanning technique for average ρs and θv provided excellent agreement with the corresponding values obtained gravimetrically. Average standard deviations (σ) for ρs of pixels for the dry soils, although large, were highly reproducible and provide a measure of the structural status of the soils. Changes in the mean and σ of pixel ρs following wetting were related to the texture, structure, mineralogy, and Ca or Na exchange status of the soil. Systematic errors arising from the random nature of radioactive emissions, for count times of 2 s, resulted in large σ in estimated θv of pixels even for dry soils. Very large counting times (some 169 s for an individual ray‐sum and, hence, 112 h to complete a dual‐source scan) were required to achieve σ values of pixel θv, on the order of 0.025 cm3/cm3 for a uniform field of water. Such large count times limit this approach to steady‐state or only slowly changing systems. Thus, while the application of CAT to dual‐energy‐level scanning has the potential to become a major tool for nondestructive studies of soil water content, structural status, and stability, realization of this potential awaits substantial improvements in scanning geometry and counting electronics.
Liquid Ion Exchanger Microelectrodes Used to Study Soil Solute Concentrations near Plant Roots
Authors: Hamza M. , Aylmore L. A. G. 
Published: July 2010

AbstractA technique for using Na+ liquid ion exchanger (Na+‐LIX) microelectrodes to accurately measure, repetitively, and in a nondestructive fashion, Na+ concentrations in the soil solution at single points is described. The method has been used to examine solute (NaCl) accumulation in proximity to single roots of lupine (Lupinus angustifolius L.) and radish (Raphanus sativus L.) plants subjected to two levels of transpirational demand and five soil solute concentrations. The results obtained indicate that, at soil water contents corresponding to matric water potentials >−140 kPa, back diffusion of solute significantly counteracts the tendency for solute accumulation at root surfaces during transpiration.
Effect of Sodium‐Humate on the Rheological Characteristics of Montmorillonite Suspensions
Authors: Zhang Yiping , Gan Huamin , Low Philip F. 
Published: July 2010

AbstractHumic compounds are supposed to have an aggregating effect on soil particles. This study was conducted to determine whether Na‐humate aggregates montmorillonite, a common clay mineral. A rotational viscometer was used to investigate the rheological behavior of suspensions of Na‐montmorillonite containing different concentrations of Na‐humate. Thereafter, the pan of an electrobalance was submerged at a given depth in each suspension and the particle‐size distribution of the montmorillonite was determined by continually weighing the sediment that accumulated on the pan. The effect of Na‐humate on swelling of the clay was also investigated by means of a miniature pressure membrane apparatus and by an x‐ray diffractometer. It was found that θ, the extrapolated shear stress, and ηpl, the plastic viscosity of the suspensions, decreased rapidly with Na‐humate concentration up to 0.1% (w/w) and then remained nearly constant. However, there was essentially no change in the particlesize distribution and swelling of the clay. These results were interpreted to mean that, in a suspension of montmorillonite and Na‐humate, the humic polyanions absorb on the edges of the particles and, as a result, reduce the attractive force between them. This implies that the aggregating effect of organic matter on soils cannot be attributed to the Na‐humate present in the organic matter.
Enzymatic and Microbial Interactions in Response to Pitch Pine Root Growth
Authors: Tate Robert L. , O'Reilly Laurie , Parmelee Robert W. , Ehrenfeld Joan G. 
Published: July 2010

AbstractRoot growth stimulates many soil metabolic and enzymatic activities through, in part, loss of photosynthate as root exudates. Because of the abundance and structural simplicity of the carbonaceous compounds comprising root exudates, compared with native soil organic matter, it can be hypothesized that not only the magnitude but also the relationship between various soil microbial and enzymological processes vary with proximity to the growing root. To test this hypothesis, metabolism of amino acids and glucose, microbial growth, microbial biomass C, and potential acid phosphatase, protease, and invertase activities were examined in pitch pine (Pinus rigida Miller) rhizosphere and near rhizosphere soils. The trees were grown in microcosms (total volume ≈145 cm3) in the greenhouse in O or A horizon soils (Lakehurst sand, a mesic, coated Haplaquodic Quartzipsamment) from the New Jersey Pinelands. The microbial and enzymological activities in the organic‐matter‐rich O horizon soil were 2‐ to 25‐fold greater than those detected in the organic‐matter‐poor A horizon soils throughout the study. Phosphatase activity and glucose and amino acid metabolic rates did not correlate with tree root mass, whereas protease activity, microbial growth rate, and microbial biomass C varied with root mass. No effect of proximity to the root on these relationships was detected. In the A horizon soil after 22 wk of growth, amino acids and glucose metabolic rates declined with increasing root mass, whereas the microbial growth rate increased. Phosphatase activity was not detected in the A horizon soil. The interrelationship of these activities was evaluated in O horizon soil. Significant (P <0.05) correlations were detected between microbial biomass C and the various indices of microbial activity, but glucose metabolism and phosphatase and proteolytic activities varied independently of microbial biomass C. In conclusion, significant effects of tree root growth on enzymatic and metabolic activities were detected, but, with a few minor exceptions, relationships between these enzymological and metabolic activities were not altered by proximity to the growing tree root.
Crop Residue Type and Placement Effects on Denitrification and Mineralization
Authors: Aulakh M. S. , Walters D. T. , Doran J. W. , Francis D. D. , Mosier A. R. 
Published: July 2010

AbstractNutrient release from legume and cereal crop residue is important to N crycling and the success of conservation and sustainable farming systems. Residue type, placement, and degree of incorporation, and soil water regimes largely control availability and loss of soil N and were evaluated in the laboratory. Four residues, i.e., vetch (Vicia villosa Roth.), soybean (Glycine max [L.] Merr.), corn (Zea mays L.), and wheat (Triticum aestivum L.) having C/N ratios ranging from 8 to 82 were applied on the soil surface or incorporated in repacked cores of a Nicollet loam (fine‐loamy, mixed, mesic Aquic Hapludoll) and incubated for 17 or 35 d at 60 and 90% water‐filled pore space (WFPS) with enriched 15N‐NO3 (76.7%). Denitrification losses from all treatments were negligible at 60% WFPS. At 90% WFPS, total denitrification losses from residue‐incorporated soils represented 87 to 127% of the initial soil NO3 level (80.5 mg N kg−1); losses increased with decreasing residue C/N ratio. Denitrification was greatest during the first 8 d, as was CO2 evolution. Initial denitrification with surface‐placed residues was less than with incorporated residues, but cumulative losses over 35 d did not differ significantly. Substantial N immobilization occurred with incorporated or surface‐placed wheat, corn, and soybean residue with wide C/N ratios at 60% WFPS, whereas, with low‐C/N‐ratio vetch, significant mineralization occurred. After 35 d, 51 and 36% of N in incorporated and surface‐placed vetch residue, respectively, was mineralized. Residue C/N ratio was inversely related to initial rates of residue decomposition, and effects of residue type and placement and soil water on denitrification and mineralization were most important during early (8‐10 d) decomposition.
Urea Transformations in Flooded Soil Columns: I. Experimental Results
Authors: Hongprayoon C. , Lindau C. W. , Patrick W. H. , Bouldin D. R. , Reddy K. R. 
Published: July 2010

AbstractThe main form of fertilizer applied to lowland rice (Oryza sativa L.) is urea, but very little is known about its movement and transformations under flooded soil conditions. Laboratory incubation studies were conducted to measure adsorption, movement, and transformations of urea and hydrolyzed ammoniacal N in flooded soil columns. Urea was added to the floodwater (750 mg N L−1, equivalent to 150 kg N ha−1) of sterilized and nonsterilized Crowley silt loam soil (fine, montmorillonitic, thermic Typic Albaqualf) columns and urea diffusion, urea hydrolysis, and subsequent NH+4‐N diffusion were measured during a period of 30 d. Urea adsorption by the soil increased with increasing concentration of added urea‐N and adsorption coefficients ranged from 0.037 to 0.064 but modeling found adsorption to be too small to be an important factor in urea movement and hydrolysis. Urea hydrolysis rates in the flooded soil columns increased with time and followed first‐order reaction kinetics. Rate constants measured in the soil varied from 0.036 to 0.288 h−1. The diffusion coefficient for both N forms (urea and NH+4) was estimated to be 3.5 × 10−10 m2 s−1 in the flooded soil columns. The basic urea data generated in this study should help provide a data base to model urea‐N behavior in submerged soils.
Nontronite Catalysis in Polycondensation of Pyrogallol and Glycine and the Associated Reactions
Authors: Wang M. C. , Huang P. M. 
Published: July 2010

AbstractThe objective of this study was to investigate the catalytic power of nontronite (0.2‐2 µm) in the polycondensation of pyrogallol (1,2,3‐trihydroxybenzene) and glycine and the associated reactions involving the ring cleavage of pyrogallol and the decarboxylation and deamination of glycine in systems free of microbial activities. At the end of a 90‐h reaction period, nontronite catalyzed the ring cleavage of pyrogallol, as shown by the release of CO2. The release of CO2 in the nontronite‐pyrogallol system was six times higher than that for pyrogallol alone. Nontronite also catalyzed decarboxylation and deamination of glycine, as shown by the release of CO2 and NH3. The ability of nontronite to catalyze deamination of glycine was substantially enhanced by the presence of pyrogallol. Polycondensation of glycine and pyrogallol was greatly catalyzed by nontronite. This is indicated by the absorbances of the molecular visible absorption spectroscopy of the supernatants, yields of total N‐containing humic acids (HA) and fulvic acids (FA) and the fraction of glycine converted to nitrogenous polymer. The infrared (IR) and electron spin resonance (ESR) spectra of HA and FA formed in the supernatants of the reaction systems were similar to those of soil HA and FA. The sequence for the amounts of the total humic polymers formed in the system was: nontronite‐glycine‐pyrogallol > nontronite‐pyrogallol > glycine‐pyrogallol > pyrogallol. The catalytic effects of nontronite on the C turnover, N transformations, and humic substance formation in soils thus merit attention.