bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fractionation of Soil Selenium by Sequential Partial Dissolution
Authors: Chao T. T. , Sanzolone R. F. 
Published: July 2010

AbstractSequential partial dissolution technique is developed to partition soil Se into association with operationally defined solid phases. The procedure extracts soil Se into five fractions: soluble (0.25 M KCl), ligand exchangeable (0.1 M KH2PO4), acid extractable (4 M HCl), oxidative acid decomposable (KClO3 + concentrated HCl), and strong mixed‐acid digestable (HF + HNO3 + HClO4). The method for the extraction and determination of fractional Se and total Se is presented in detail. The technique has been shown to be satisfactory in terms of sensitivity, accuracy, and precision for the fractionation of soil Se. On the basis of the experimental data obtained on sample types of contrasting chemical properties, the distribution of Se in different fractions has been found to depend on the chemical and mineralogical differences as a result of chemical weathering. In soils developed through intensive leaching and weathering, Se tends to be associated with oxide minerals and a great proportion of the remaining Se is resistant to chemical dissolution. For soils with high pH and low content of oxide minerals, Se is present as mobile selenate and can be easily extracted. Selenium associated with sulfide minerals may be detected by the sequential extraction as immobile and unavailable. The overall findings are consistent with the geochemical behavior of Se in a soil environment. The five‐step sequential extraction may provide insight into the surficial geochemistry of Se and should serve as a useful tool for Se studies in soil and sediment chemistry, environmental geochemistry, and mineral exploration. The simplified two‐step version involving extractions by 0.1 M KH2PO4 and 4 M HCl should indicate the immediate and potential impact of Se on the environment, both as a nutrient and as a pollutant.
Potassium in Atlantic Coastal Plain Soils: II. Crop Responses and Changes in Soil Potassium Under Intensive Management
Authors: Parker D. R. , Hendricks G. J. , Sparks D. L. 
Published: July 2010

AbstractCorn (Zea mays L.) grown on sandy Atlantic Coastal Plain soils is often unresponsive to applications of K fertilizer. The purpose of this investigation was to examine the response of irrigated, intensively managed corn to K applications, and to monitor changes in soil K status. Field studies were conducted for 3 yr at four sites on the Delaware Coastal Plain. Treatments consisted of 0, 94, or 282 kg ha−1 applied K, both as a single application and in three split applications. Grain yields were high (6.9 to 14.0 Mg ha−1), but were not significantly (p ≤ 0.05) affected by K application for any year‐site combination. Similarly, corn ear leaves at silking contained adequate K (20 to 30 mg kg−1), although these concentrations varied with K application rate on the two sandier soils. In the zero K plots, dilute double acid‐extractable K concentrations ranged from 56 to 194 mg kg−1 at the start of the study, and had declined by 29 to 45% by the end of the third growing season. Evidence was obtained for both leaching of applied K and conversion to nonexchangeable forms. The lack of observed yield response was ascribed to (i) modest crop removal of K when corn is harvested only for grain, (ii) adequate K‐buffering capacity of these soils to meet high crop demands during the growing season, and/or (iii) availability of significant quantities of subsoil K. Our results further suggested that, despite the high grain yields obtained, current recommendations by several state soil testing laboratories in the region are, if anything, somewhat excessive in that K fertilizer is recommended even when no yield response is observed.
Incubation Studies of the Fate of Organic Nitrogen in Soils Amended with Activated Sludge
Authors: Fine P. , Mingelgrin U. , Feigin A. 
Published: July 2010

AbstractMineralization of sludge organic N and the effect of transformations in nitrogen compounds on soil solution composition were studied in incubated soil‐sludge mixtures. Four soils were incubated with sludge at four mixing ratios (1–15% sludge) for 90 d at 35 °C under continuous flow of water saturated air. Soil‐water contents were maintained at 60% of the 0.033 MPa tension. The extent of ammonification was 41 to 61% of the amount of sludge organic N added. Both soil properties and sludge content affected the extent of ammonification. The soils' effect was relatively small. Only the clayey and sandy soils differed significantly (54.5 vs. 47.9%). The effect of sludge loading was more pronounced. At 1 and 5% sludge contents the ammonification was significantly greater (53 and 56% ammonified) than at 10% (48%) or 15% (43%) sludge contents. The reduced ammonification at the higher sludge and clay content might be related to the more intense nitrification‐induced salinization observed in these treatments. Sludge content and soil properties affected the initial rates of both ammonification and ammonia volatilization. Ammonification was linearly related to sludge and clay content, whereas the volatilization rate was similarly related to sludge content but inversely related to cation exchange capacity (CEC). Estimated half‐lifes for the added organic N is 2 to 8.5 d. Up to 87% of the ammonified sludge N, was lost as gaseous species, mostly as ammonia. Sludge application to soils and subsequent transformations could greatly influence soil solution chemistry and composition of exchangeable cations, depending mainly on its content.
Iron Availability and Uptake by Rice in Acid Sulfate Soils
Authors: Moore P. A. , Patrick W. H. 
Published: July 2010

AbstractIron toxicity is one of the main constrains to rice (Oryza sativa L.) growth on acid sulfate soils. The objectives of this study were to determine the solubility of Fe under natural conditions in these soils, to determine what governs Fe solubility, and to investigate Fe uptake by rice growing on these soils. Iron availability and uptake by rice was evaluated in 134 flooded acid sulfate soils in the Central Plains region of Thailand and in a growth chamber experiment utilizing 50 of the same soils. Soil and plant metal analyses were conducted at the panicle differentiation stage of growth in both studies and in the soil prior to transplanting in the growth chamber experiment. The ‘R.D. 23’ rice cultivar was used in the growth chamber study, while 88 different cultivars (native and improved) were sampled in the field study. Metal activities in soil solutions were determined from free metal concentrations using GEOCHEM and activity coefficients using the Davies equation. Exchangeable metals were determined from sodium acetate extracts buffered to the soil pH. The results indicated that Fe2+ activities in flooded acid sulfate soils are seldom in equilibrium with pure Fe solid phases under natural conditions. This is believed to be due to (i) transient redox conditions, (ii) the presence of ill‐defined ferric oxides or hydroxides, and/or (iii) cation exchange reactions. A better relationship existed between leaf Fe and the divalent charge fraction in the soil solution attributable to Fe2+ (E′‐Fe) than to Fe2+ activity indicating that ion competition may be important in determining Fe uptake in rice. If the reported critical concentration for Fe toxicity in rice of 300 mg kg−1 is correct, then the critical E′‐Fe observed for Fe toxicity conditions in this study was approximately 0.75. These findings clarify the role of other nutrients in Fe toxicity in rice.
Nitrate Accumulation and Loss in a Mungbean/Lowland Rice Cropping System
Authors: Buresh R. J. , Flordelis E. , Woodhead T. , Cabangon R. C. , Shepherd K. D. 
Published: July 2010

AbstractRice‐growing (Oryza sativa L.) soils in tropical Asia are frequently aerobic during the dry season but become waterlogged through irrigation or rainfall in the wet season. Field studies were conducted at three locations in the Philippines to measure the accumulation of soil NO3 during a dry season mungbean [Vigna radiata (L.) Wilczek] crop and subsequent weedy fallow prior to flooding the soil for wet season rice. On a silty clay (Vertic Tropaquept), no soil NO3 was detectable following a wet season rice crop. During the subsequent dry season mungbean crop, 25 and 18 kg NO3‐N ha−1 accumulated in 1986 and 1987, respectively, in the top 0.6‐m soil layer. After a subsequent 47‐d (1986) or 42‐d (1987) fallow period with no weed control, 52 and 77 kg soil NO3‐N ha−1 were present in 1986 and 1987, respectively. Soil NO3 in the top 0.6 m correlated inversely with aboveground weed dry matter (r = −0.80**, significant at the 0.01 probability level) and aboveground weed N (r = −0.84**). Soil NO3 disappeared after flooding for the succeeding wet season rice. An incubation study with 15N‐labeled NO3 revealed 99 to 100% disappearance of 15 µg NO3‐N cm−3 in 9 d and 5% or less reduction of NO3‐N to NH4‐N and organic N. On a clay (Vertic Tropaquept) and silty clay (Lithic Mollic Tropaquept) in 1987, the accumulated soil NO3 in the top 0.6 m after dry season mungbean and weedy fallow were 91 and 39 kg N ha−1, respectively. Nitrate accumulation during the dry season and subsequent loss by denitrification or leaching following flooding for wet season rice might represent a major mechanism of N loss in tropical rainfed and partially irrigated lowland rice environments.
Ferro‐Humic Podzols of Coastal British Columbia: II. Micromorphology and Genesis
Authors: Sanborn P. , Lavkulich L. M. 
Published: July 2010

AbstractFabrics of Ferro‐humic Podzols (Cryohumods and Cryochrepts) from coastal British Columbia were compared for pedons of contrasting texture on Vancouver Island (VI) (loam, clay loam) and the adjacent mainland (sandy loam). Forest floors are strongly influenced by faunal activity, with earthworm casts comprising the larger aggregates (≤10‐mm diam.) in VI Oa horizons. Albic horizons are thin or absent. The Bhs horizon fabrics reflect textural and faunal influences, resulting in aggregated or coating‐dominated fabrics. Complexes of spongy, crumb and subangular blocky microstructures occur in loamy horizons, with many of the aggregates being of possible fecal origin. Subangular blocky microstructures dominate finer textured horizons, but clay translocation is not evident. Coarser Bhs horizons are uncemented and contain amorphous organic coatings and infillings incorporating abundant root detritus. Organic matter‐rich zones within the B horizon range from loosely packed, spongy masses of humified fine roots, with little evidence of faunal activity, to dense accumulations of organic material with few recognizable tissues. Living roots are much less abundant than in surface O horizons, suggesting that some of these features may be relict. Both in situ decomposition and illuviation contribute to these organic matter accumulations, with root residues acting as sites of metal deposition. Pedologists must consider the role of root turnover in organic matter accumulation in Podzols.
Rubidium in Surface Horizons of Illinois Soils
Authors: Jones Robert L. 
Published: July 2010

AbstractThe mean total Rb content in 223 surface horizons of upland soils was 88.8 mg kg−1 and contents were normally distributed. Rubidium tended to be highest at sites where loess is very thin or absent and illitic Wisconsinan till is present. Surface horizons of soils in areas of thick loess commonly have about 80 mg Rb kg−1. The pattern of increasing soil development associated with decreasing loess thickness characteristic of Illinois is reflected by Rb concentrations that first increase with declining loess thickness and then decrease in the most intensely weathered soils. Minerals derived from the basin of Des Moines River of Iowa, which were incorporated in loess below its confluence with Mississippi River, are especially rich in Rb and gave rise to the highest levels observed (110–115 mg kg−1).
Significance of Low‐Chroma Mottles in Drained Sandy Soils in the Netherlands
Authors: Poelman J. N. B. , Bouma J. , Wösten J. H. M. 
Published: July 2010

AbstractBulk densities were determined for 1365 soil horizons from 340 pedons in well and originally poorly drained sandy soils in the Netherlands with and without mottles with chroma's of 2 or less. Tile drainage constructed in the 1950's is common and has resulted in lower water‐table levels. Occurrence of low‐chroma mottling does, therefore, not indicate present saturation with water. However, long‐lasting effects of earlier periodic saturation are evidenced by significantly higher bulk densities of mottled A, B, and C horizons with organic matter contents < 2.5%. These higher densities restrict root development and result in different hydraulic conductivity and moisture retention characteristics as compared with unmottled horizons. Thus, low‐chroma mottling can be an indicator for soil physical behavior, other than saturation, which is highly relevant for plant growth.
Characterizing Macropores in Soil by Computed Tomography
Authors: Warner G. S. , Nieber J. L. , Moore I. D. , Geise R. A. 
Published: July 2010

AbstractCross sections of a 203‐mm diam. soil core taken from a site under Kentucky bluegrass (Poa pratensis L.) were scanned using x‐ray computed tomography (CT) to determine if macropores such as cracks, earthworm holes and root channels could be distinguished and characterized. The core was physically sectioned at the same locations as the CT scans to verify the size and location of pores seen on the CT images. Macropores 1 mm and larger could be easily and quickly distinguished by the method. By manipulation of the scanner images, air‐filled pores, roots and stones were identified within the soil matrix. A wet bulk density plus an air‐filled macroporosity were calculated for scans. Prior to sectioning, a dye solution was ponded on the surface of the core and allowed to infiltrate to assess the continuity of pores through the core.
Estimation of the Saturated Hydraulic Conductivity in Clay Soils from Soil Moisture Retention Data
Authors: Messing I. 
Published: July 2010

AbstractA generalized Kozeny‐Carman equation was employed to relate saturated hydraulic conductivity (Ks) to effective porosity (φe) in clay profiles in Sweden with clay content >15% were analyzed. The value empirical constants. The term φe was defined as porosity (φ) minus soil‐water content at −30 kPa. Around 500 horizons from 60 soil profiles in Sweden with clay content >15% were analyzed. The value of n was tested with two statistical methods. According to the first method, a regression test on the log‐log relationship between Ks and φe with least‐squares lines fitted through the data, the exponent n was found to lie around 2 for soils with high clay content (>40%), and 3 for soils with lower clay content (15–40%). The correlation coefficients were moderate, ranging from 0.51 to 0.71 for different clay soil groups. In the second method, the cumulative frequency distributions of scaling factors for Ks determined from measured values of Ks were compared with scaling factors for Ks determined from φe. Reasonable agreements were obtained with n = 4 to 5 for soils with clay content >40%, and with n = 5 to 6 for soils with clay content 15 to 40%. The second method gave n‐values that correspond well with other recent published work. The results indicate that the spatial distribution of Ks is estimated reasonably well from φe values, whereas the individual values of Ks are not estimated as well.
Sample Preparation for Determining Ions in Dark Colored Sodic Soil Extracts
Authors: Robbins Charles W. 
Published: July 2010

AbstractSaturation paste extracts of sodic soils (pH >8.5 and electrical conductivity <4.0 dS m−1) usually contain dark colored, suspended organic matter that interferes with colorimetric, turbidimetric, potentiometric, ion chromatographic (IC) and to a lesser extent, atomic absorption spectrophotometry and flame emission procedures. Bicarbonate also interferes with formate analysis by IC in those extracts. This study was conducted to develop a simple pretreatment method for removing those interferences without introducing new interferences. Fifteen mL extract samples were titrated to pH 8.4, then to 4.7 and finally to a pH range of 3.0 to 3.5 with standardized H2SO4 or HCl. The first two end points determine CO2‐3 and HCO‐3 concentrations. The third pH adjustment removed the HCO‐3 interference from the formate analysis and allowed for organic matter coagulation. The acid choice depended on whether Cl‐ or SO2‐4 was to be measured later. To remove the organic matter, the extracts were contrifuged and forced through a 0.2‐µm nylon filter following 0.08 M AlCl3 or 0.04 M Al2(SO4)3 treatments. Formate and acetate concentrations were determined by IC. The Cl‐ concentrations were determined by colorimetric, and IC procedures. The SO2‐4 concentrations were measured turbidimetrically and by IC. The extracts were analyzed for Ca2+ and Mg2+ by atomic adsorption spectrophotometry, and Na+ and K+ by flame emission. Titrating the extracts as described provided CO2‐3 and HCO‐3 data, removed the HCO‐3 interference from the formate analysis, and allowed Al3+ to coagulate the suspended organic matter, which was then removed by centrifugation and filtration. This pretreatment did not interfere with any of the analytical methods tested, except for cation determination by IC and anion determination by IC when methyl orange was used as a pH end point indicator.
Biosynthesis of Cytokinins in Soil
Authors: Nieto K. F. , Frankenberger W. T. 
Published: July 2010

AbstractCytokinin biosynthesis in soil by rhizosphere microorganisms may increase upon the addition of physiological precursors and affect plant growth. This study was conducted to establish the effects of the purine, adenine (ADE), the isoprenoid, isopentyl alcohol (IA), and a cytokinin‐producing bacterium, on cytokinin biosynthesis in an Arlington soil (coarse‐loamy, mixed thermic Haplic Durixeralf). Various concentrations of ADE were applied, separately and in combination with 8.81 × 10−2 g IA kg−1 soil, and an inoculum of Azotobacter chroococcum (ATCC 9043), as soil treatments. Cytokinin bioactivity, isolation, and quantification of soil extracts were monitored over a period of 7 d using the radish cotyledon bioassay and HPLC‐UV spectrometry. Cytokinin production was evident as early as 2 d and reached a maximum at 5 d post‐treatment. An application of 1.35 × 10−4 g ADE kg−1 soil, 8.81 × 10−2 g IA kg−1 soil, and A. chroococcum enhanced cytokinin production of zeatin riboside and t‐zeatin in this soil up to 1.50‐ and 1.39‐fold, respectively, in comparison to controls containing no precursors. The production of zeatin riboside (78.0 µg kg−1) and t‐zeatin (22.1 µg kg−1) in the presence of ADE and IA was 1.35‐ and 2.44‐fold greater with the inoculation of A. chroococcum, when compared to the indigenous microflora alone. This study provides information on extraction and analytical detection of cytokinins in soil and reveals that microbial biosynthesis of cytokinins can be enhanced by applying physiological precursors to soil.
Vacuum Apparatus to Concentrate Ammonium Solutions for Nitrogen Isotope‐Ratio Analysis
Authors: Kelley K. R. 
Published: July 2010

AbstractConcentrating NH4 solutions in preparation for 15N analysis usually is accomplished by evaporating samples to dryness with open‐air or forced‐air systems. This paper describes a newly developed drying apparatus that operates under vacuum to facilitate evaporation, prevent sample contamination, and avoid several problems associated with conventional evaporative systems. Standard (NH4)2SO4 samples containing 0.20, 0.50, 1.00, or 2.00 atom % 15N were acidulated with H2SO4 or H3BO3 plus H2SO4 and evaporated to dryness with the vacuum system, a conventional forced‐air system, or a conventional open‐air system. No significant contamination by atmospheric NH3 was found in samples acidulated with H2SO4 and dried with the vacuum apparatus. In comparison, absorption of atmospheric NH3 during evaporative processing of H2SO4‐acidulated samples with the forced‐air or open‐air system resulted in dilution of 15N concentrations in excess of 0.027 and 0.047 atom % 15N in standards containing 1.00 or 2.00 atom % 15N, respectively. The atom % 15N concentrations of evaporated samples containing H3BO3 plus H2SO4 were inconsistent. No significant N loss, isotopic fractionation, or atmospheric contamination was detected in samples acidulated with H2SO4 and heated to 130 °C under vacuum for up to 4 h past dryness. Moreover, no significant cross‐contamination was detected in 4‐mL samples of varying 15N concentration that were acidulated with H2SO4 and dried under vacuum, indicating that the vacuum apparatus can be used to simultaneously process samples differing in 15N concentration. The apparatus can accommodate up to 80 samples, depending on sample volume and container size (< 5–250 mL).
Metabolism of Labeled Organic Nitrogen in Soil: Regulation by Inorganic Nitrogen
Authors: Smith M. Scott , Rice Charles W. , Paul Eldor A. 
Published: July 2010

AbstractRegulation of organic N metabolism by inorganic N availability was investigated in short‐term laboratory incubations of soil. A 14C‐, 15N‐labeled organic N substrate was produced by growing Pseudomonas stutzeri in labeled media and isolating a cytoplasmic fraction. This was added to soils that had been preincubated with glucose or glucose plus NH+4 to induce conditions of N deficiency or sufficiency. Regulation by inorganic N was indicated by stimulated proteolytic enzyme activity and greater initial rates of cytoplasmic 14C mineralization in N deficient soils. However, effects of N deficiency on 14C mineralization persisted for no more than 24 h. Preinduced N deficiency significantly decreased the extent of 15N mineralized from cytoplasmic N. Mineralization of 14C from leucine added to soil was similarly affected by N availability, yet 14C‐glutamate mineralization was apparently unaffected. In another experiment labeled cytoplasm was added simultaneously with or without a larger quantity of glucose. The glucose caused virtually complete assimilation of 15N but had no effect on apparent assimilation of 14C. Thus, there was no relationship between 15N assimilation and 14C assimilation, suggesting that the C and N contained in organic N are processed separately by soil microbes. Inorganic N availability may have short‐term effects on metabolism of C in organic N but long‐lasting effects appear to be minimal.
Microplot Size Reguirements for Measuring Balances of Fertilizer Nitrogen‐15 Applied to Maize
Authors: Stumpe J. M. , Vlek P. L. G. , Mughogho S. K. , Ganry F. 
Published: July 2010

AbstractIn order to reduce the amount of expensive labeled‐N fertilizer needed for field studies of 15N balances in maize (Zea mays L.), four experiments were conducted to determine the minimum microplot size requirement. The minimum microplot area required was ascertained by applying urea labeled with 15N to 4.5‐ by 2.0‐m microplots inside larger plots treated with the same fertilizer and observing the dilution of 15N in maize plants by N from outside the microplot with respect to proximity to microplot borders. Under the conditions of this study, interrow spacings of 75 cm resulted in dilution of 15N in only the row located 37.5 cm from the microplot border. Intrarow plant spacings of 25 cm resulted in the dilution of 15N in the plants located 12.5 and 37.5 cm from the microplot border. Microplots with 3.0‐ by 2.0‐m border dimensions, containing four rows and eight plants/row, resulted in the desired number of plants (eight) unaffected by proximity to the border from a minimum microplot area and thus minimized the requirement for 15N. Complete recovery of 15N in the plant‐soil system occurred when climatic conditions and fertilizer management practices favored N conservation, confirming that microplots were sufficiently large for an accurate determination of 15N balance.