bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crop Residue Effects on Nitrogen Mineralization, Microbial Biomass, and Rice Yield in Submerged Soils
Authors: Clément A. , Chalifour F.‐P. , Ladha J. K. 
Published: July 2010

AbstractUrea, crop residues, and green manure are all suitable sources of N for lowland rice (Oryza sativa L.). However, N sources undergo mineralization at different rates, affecting rice N uptake and utilization. Little is known about the effect of the chemical composition of crop residues on N mineralization and rice performance. Two greenhouse experiments were conducted to determine the dynamics of N mineralization, microbial biomass, and rice N uptake. Twelve treatments representing a wide range of crop residue chemical composition and two controls (with and without urea) were compared. The N mineralization pattern ranged from rapid (Sesbania rostata Brem. & Oberm.) to immobilization at the beginning of the season (Cassia velosa L.). Immediately after incorporation, N mineralization was positively correlated to crop residue N concentration (r2 = 0.64, significant at P < 0.01), and negatively correlated to tannin concentration. However, at tillering, the tannin/N ratio was best correlated to the rate of N release (r2 = 0.86, significant at P < 0.01). Grain yield was best predicted by the (lignin + polyphenol)/N ratio (r2 = 0.67, significant at P < 0.01). Incorporation of residue into soil generally increased microbial biomass ninhydrin‐reactive N compared with control treatments at the tillering stage, but not at maturity. Microbial biomass N was highly correlated to soil NH+4‐N at rice tillering (r2 = 0.76, significant at P < 0.01). The N derived from fertilizer in rice was 35.4% on average for residue treatments, which was comparable with that of the urea control (33.5%). This study emphasizes the importance of considering the interactions among chemical constituents of crop residues to understand the dynamics of N release and uptake by rice.
Decomposition Rate Constants of Size and Density Fractions of Soil Organic Matter
Authors: Hassink Jan 
Published: July 2010

AbstractOne of the main drawbacks of models describing soil organic matter turnover is that most pools cannot be experimentally identified. The aim of this study was to define meaningful soil organic matter fractions that can be physically isolated and to determine their decomposition rate constants so that they can be incorporated into models. This would be a major step toward verification of models. In this study, soil organic matter was separated into five fractions: the light (density <1.13 g cm−3), intermediate (density 1.13–1.37 g cm−3), and heavy (density >1.37 g cm−3) fractions of macroorganic matter (>150 µm) and the microaggregate fractions with particle sizes between 20 and 150 µm and smaller than 20 µm. The decomposition rate constants of the fractions decreased in the order light, intermediate, and heavy macroorganic matter (23.9, 9.8, and 3.9 × 10−4 d−1, respectively) and were lowest for C in the microaggregate fractions <20 and 20 to 50 µm (0.5–0.7 × 10−4 d−1). Since the rate constants of the fractions seemed not to depend on soil texture, they can probably be applied widely. We propose to use these fractions as the principal pools in future soil organic matter models.
Spectroscopy of Aqueous Extracts of Forest Litter. I: Suitability of Methods
Authors: Gressel N. , McGrath A. E. , McColl J. G. , Powers R. F. 
Published: July 2010

AbstractStructural characteristics of dissolved organic matter (DOM) have not been closely examined until recent analytical techniques became available. We examined the applicability of ultraviolet‐visible (UV‐VIS), Fourier‐transform infrared (FTIR), and electron spin resonance (ESR) spectroscopies using aqueous extracts of pine and broadleaf understory leaf litter. The ratio of UV‐VIS absorbances at 465 nm and 665 nm (E4/E6) were 7.8 to 8.5 for extracts of pine and 6.3 to 7.7 for the understory between pH 3.0 and 6.0. Using the standard method for humic substances (in 0.05 M NaHCO3 solution, pH 8.0), E4/E6 measurement produced varying results, and is not recommended for DOM. Well‐resolved FTIR spectra had features similar to those of humic substances; peak‐height ratios were used for semiquantitative analysis of DOM functional groups. Two FTIR sample‐preparation procedures were also compared: dried extracts on AgCl disks, and freeze‐dried DOM in KBr pressed pellets. The first allowed better analysis of COOH functional group deprotonation; the second preparation procedure produced spectra with identical absorbance ranges as those of AgCl disks, with similar peak‐height ratio trends as a function of pH, except for those associated with COOH/COO−. Contact between DOM and the salt in pressed pellets may have aided deprotonation of COOH, even at low pH. Interference from water occurred with KBr pressed pellets. Free radicals identified by ESR increased with pH, and shifts from 2.0036 to 2.0050 in ESR g values indicated that oxidation also increased with pH. We conclude that these spectroscopic techniques, modified from those developed for analysis of humic substances, are complementary and together provide useful information about the structure of the DOM of forest litter.
Comparison of Available Soil Nitrogen Assays in Control and Burned Forested Sites
Authors: Knoepp Jennifer Donaldson , Swank Wayne T. 
Published: July 2010

AbstractThe existence of several different methods for measuring net N mineralization and nitrification rates and indexing N availability has raised questions about the comparability of these methods. We compared in situ covered cores, in situ buried bags, aerobic laboratory incubations, and tension lysimetry on control and treated plots of a prescribed burn experiment in the southern Appalachians. Environmental influences were examined with soil moisture and temperature measurements. All methods detected significant differences in net N mineralization rates between treated and control plots; P = 0.04, 0.007, 0.001, and 0.07 for covered cores, buried bags, lab incubations, and lysimeters, respectively. Mean rates of N mineralization during the growing season were similar for the three soil incubation methods. The laboratory incubation of soil from treated plots produced significantly greater potential nitrification rates than the in situ methods. The four methods were not well correlated; this indicates the need for caution when comparing N transformation data derived from different methods. We conclude that the in situ covered core method is superior because it best incorporates site‐specific soil temperature and moisture changes into N transformation measurements.
Anion Transport through Columns of Highly Weathered Acid Soil: Adsorption and Retardation
Authors: Bellini Giampaola , Sumner Malcolm E. , Radcliffe David E. , Qafoku Nikolla P. 
Published: July 2010

AbstractSubsoils of highly weathered, acid soils usually contain appreciable quantities of anion‐exchange capacity (AEC), which retards the passage of anions through the profile. This AEC varies in magnitude with ambient soil solution parameters such as pH and ionic strength. In order to be able to predict NO‐3 movement in such soils, estimates of the effect of subsoil charge characteristics on retardation are required. The effect of subsoil liming and ionic strength on the movement of NO‐3 in repacked Kanhapludult soil columns was studied for this purpose. Columns comprising topsoil (untreated) over subsoil limed to different levels to give a range of AEC were used. The soil was first leached with a solution of 10 mmolc Ca(NO3)2 L‐1 followed by a 10 mmolc CaCl2 L‐1 solution. Convection‐dispersion equation (CDE) parameters for Cl‐ were determined using CXTFIT. Liming reduced the retardation coefficient (R) from 2.39 in the unamended subsoil to 1.12 in the treatment that received 2.08 g Ca(OH)2 kg‐1. Both subsoil pH (r2 = 0.96) and AEC (r2 = 0.98) were correlated with R for Cl‐. To test the effect of electrolyte concentration on retardation, columns of untreated subsoil were leached with solutions of Ca(NO3)2 and CaCl2 at four input concentrations: 5, 10, 20, and 30 mmolc L‐1. Retardation coefficients for Cl‐ at these concentrations were 2.81, 2.25, 1.76, and 1.51, respectively. Anion retardation needs to be taken into account in modeling NO‐3 movement through acid subsoils.
Nitrogen and Water Interactions in Subsurface Trickle‐Irrigated Leaf Lettuce: I. Plant Response
Authors: Thompson Thomas L. , Doerge Thomas A. 
Published: July 2010

AbstractRising water costs and concerns about groundwater contamination by NO‐3 are forcing growers in arid regions to adopt practices to improve water and N use efficiency. Subsurface trickle irrigation offers the ability to precisely deliver appropriate amounts of water and N to the crop root zone. The objectives of this research were to: (i) determine the optimum level (with respect to marketable yield) of soil water tension for subsurface trickle‐irrigated leaf lettuce (Lactuca sativa L. cv. Waldmann's Green), (ii) determine N by water interactions on crop yield and quality, and (iii) determine seasonal patterns of crop N uptake. Three field experiments were conducted during the 1990 to 1993 winter growing seasons on a Casa Grande soil (fine‐loamy, mixed, hyperthermic, Typic Natriargid [reclaimed]) in southern Arizona. Deficient to excessive N (35–300 kg ha‐1) and target soil water tension (SWT) treatments (12.0–4.0 kPa) were applied in factorial combinations each year. Maximum marketable leaf lettuce yields observed were 54.0 Mg ha‐1. Nitrogen rates associated with maximum yields ranged from 120 to 300 kg ha‐1, and depended on average SWT. Excessive irrigation (5.3 kPa average SWT) resulted in lower yields, head weight, and head length. Marketable yields showed a pronounced water × N interaction, but yield quality (head length and weight) did not. Maximum N flux was 4.3 kg ha‐1 d‐1, and an average of 75% of total N accumulation occurred in the 38 d prior to harvest. Results suggest that the soil water tension at 0.3‐m depth should be maintained at 6 to 7 kPa for optimum yields of trickle‐irrigated leaf lettuce.
Phosphorus in Urban Sewage Sludges as Assessed by Isotopic Exchange
Authors: Frossard E. , Sinaj S. , Dufour P. 
Published: July 2010

AbstractSewage sludges have been used for years as fertilizers but little information exists on the availability of P in these complex materials. Isotopically exchangeable P was measured in 12 urban sewage sludges using the isotopic exchange kinetics method. The results obtained with this method were then interpreted according to the multicompartmental model recently proposed. The two activated sludges and the composted sludge had the highest quantities of P isotopically exchangeable within 1 min (E1min higher than 0.77 g P kg‐1 sludge). The flocculated and heat‐treated sludges contained low quantities of rapidly exchangeable P but high quantities of slowly exchangeable P (E >12wk higher than 9 g P kg‐1 sludge). The quantity of P exchangeable within 1 d was positively correlated to the sum of water‐ and bicarbonate‐extractable P while slowly exchangeable P was positively correlated to the quantity of P present in precipitated forms deduced from a sequential extraction (i.e., HCl plus NaOH‐extractable P for FeSO4‐flocculated sludges and HCl‐extractable P for the other sludges). Results of this study demonstrate that the isotopic exchange kinetics method can give valuable information on inorganic P forms and exchangeability in urban sewage sludges.
Mineralogical Investigation of Soils Formed in Calcareous Gravelly Alluvium, Eastern Crete, Greece
Authors: Timpson M. E. , Lee S. Y. , Ammons J. T. , Foss J. E. 
Published: July 2010

AbstractThe mineralogical composition of soils along a toposequence formed on Quaternary‐aged alluvium from the northeastern portion of the island of Crete, Greece, and the examination of their mineral weathering characteristics should help provide an insight into the stage of weathering and relative age of the soils. Four soils were described and sampled from three landscape positions along the toposequence and the clay and silt fractions from all horizons of each soil were examined using a combination of x‐ray diffraction and electron microprobe techniques. Coarse and fine silt fractions from each soil contained dolomite, calcite, quartz, feldspars, mica, and chlorite. Feldspar content generally decreased with depth, whereas calcite increased with depth. Minerals identified in the silt fractions resulted from a combination of physical and chemical weathering and possible eolian additions. Clay fractions were dominated by trioctahedral ferrous chlorite and dioctahedral mica (muscovite), with minor amounts of kaolinite, quartz, dolomite, and calcite. Goethite was also identified in the clay fraction of some soil horizons. The source of the phyllosilicates was inheritance from phyllite gravels in the alluvium and chemical dissolution of the dolostone releasing entrained clay minerals. Some portion of the kaolinite in surface horizons was probably the result of eolian additions. Goethite formation resulted from release of Fe from the chlorite. The extent of clay mineral inheritance, limited expansion of the chlorites, and lack of a chlorite or mica weathering product (vermiculite), as well as the presence of carbonates in the clay fractions, all suggest that these soils are still in the initial stages of weathering.
Oxidation States and Fractionation of Plaque Iron on Roots of Common Reeds
Authors: Wang Tiangen , Peverly John H. 
Published: July 2010

AbstractCharacterization of iron plaque stability on roots of wetland plants is of value in consideration of several wetland issues. Active and dormant roots of common reed [Phragmites australis (Cav.) Trin. ex Steudel] sampled from a constructed wetland were treated sequentially with 0.5 M MgCl2 (salt extraction), HCl solution at pH 3, 2, 1.6, 0.6, 0.3, and 0 (acid extraction), and 0.385 M Na2S2O4 (reductant extraction). Iron was measured with an orthophenanthrolene method. Results indicated that dormant roots contained 6, 890, 180, and 140 µg Fe g‐1 fresh root weight in salt extractable, acid extractable, reductant extractable, and residual fractions, respectively, and active roots had a higher proportion of acid extractable Fe and lower proportions of reductant extractable and residual Fe than dormant roots. Following acid extraction, substantial Fe2+ was detected. Ferric iron reduction after extraction was also found. The models of Fe extraction dynamics at different pH levels were fit to standard equations. According to the comparison of the constants in these models, the Fe release rate and potential for extraction in the acid solutions tended to increase as the pH decreased, but the effect on Fe extraction became saturated when pH approached zero. The oxidation state of Fe in root plaque was examined with Mossbauer spectroscopy after the roots were dried at 80°C in a regular oven and were powdered. The results indicated that the Fe(II) proportion is 33% in powdered dormant roots, and 27% in active roots. Based on these results, we suggest that the previously accepted concept of plaque composed entirely of Fe3+ needs to be further examined.
An Extended Transfer Function Model of Field‐Scale Solute Transport: Model Development
Authors: Liu H. H. , Dane J. H. 
Published: July 2010

AbstractCommonly used one‐dimensional models for predicting solute transport in the field are based on either a deterministic convection‐dispersion equation or a stochastic‐convective principle. These models, however, are limited to describing solute transport characterized by either a linear or a quadratic increase in the travel time variance with depth in a steady‐state flow field. Based on an existing transfer function model, we propose a solute transport model in which the travel time variance increases proportionally with depth to the power 2a, where a is an adjustable constant representing the degree of horizontal solute mixing. The model based on the deterministic convection‐dispersion equation is well approximated by the proposed model for a = 0.5, while the model based on a stochastic‐convective principle is a special case of our model for a = 1. Effects of different a values on solute transport and relevant problems are briefly discussed.
Field Measurement of Air‐Entry and Water‐Entry Soil Water Pressure Heads
Authors: Fallow D. J. , Elrick D. E. 
Published: July 2010

AbstractAn effective field measurement of the air‐entry and water‐entry soil water pressure heads gives an improved description of the hydraulic properties of soils. One study obtained measurements of air‐entry soil water pressure heads using a modified falling head infiltrometer. This study then estimated the value of the water‐entry soils water pressure head from this value. Now direct field measurements of both the air‐entry and water‐entry soils water pressure heads can be easily obtained using an external tension bottle attached to the Guelph Pressure Infiltrometer at the conclusion of quasi‐steady state infiltration readings.
A Parametric Model for Two‐Dimensional Water Uptake Intensity by Corn Roots under Drip Irrigation
Authors: Eugenio Coelho F. , Or Dani 
Published: July 2010

AbstractModeling of water distribution for drip irrigation management under cropped conditions requires information on water uptake patterns by plant roots. Based on experimental data, we propose using Bivariate Gaussian distribution density functions (normal, semilognormal, and lognormal) as parametric models for two‐dimensional water uptake intensity patterns under drip irrigation. These models offer (i) a concise representation of large amounts of uptake information; (ii) parameters that may be useful for modeling and comparisons between crops, locations, and management scenarios; (iii) physical and statistical insight into spatial and temporal changes in uptake patterns that may be gained by applying moment analyses for the center of activity location and the spread in uptake intensity about it. Different water uptake patterns associated with four basic plant‐dripper configurations (surface and subsurface source, within and between crop rows) were identified and measured in field and greenhouse experiments. Uptake intensity pattern was influenced by the relative positions of the plant and the source and by the presence of no‐uptake boundaries (e.g., soil surface) requiring different models based on various forms of the Bivariate Gaussian model (normal, semi‐log, and log‐log). The proposed models were in good agreement with corn (Zea mays L.) uptake data measured by dense grids of time domain reflectometry probes in large containers and in the field.
Solid‐Phase Manganese Fractionation Changes in Saturated Arid‐Zone Soils: Pathways and Kinetics
Authors: Xiang Han Feng , Banin Amos 
Published: July 2010

AbstractShort‐ and intermediate‐term transformations of Mn among the solid‐phase components of two arid‐zone soils were studied under saturated paste incubation. Manganese was fractionated by a selective sequential dissolution procedure into several empirically defined fractions. Before incubation, Mn was predominantly in the easily reducible oxide (ERO) fraction, followed by the carbonate (CARB) fraction and the residual (RES) fraction, with almost negligible amounts present in the exchangeable (EXC) fraction. During saturation incubation, Mn in both soils was transformed from the ERO fraction to the EXC and CARB fractions. However, the pathways differed between the two soils. The rates of the transformations were initially very high: major changes occurred during the first 6 d in the sandy soil and the first 12 d in the loessial soil. Following the initial rapid changes, both soils showed only subtle changes for the rest of the period (1 yr). The transformation (reduction) of Mn from the main source, the ERO fraction, was controlled by, and synchronized with, changes of soil pe + pH. The initially measured rates of reduction in ERO Mn were 1.43 × 10−4 and 0.828 × 10−4 mg kg−1 s−1 in the sandy and loessial soils, respectively. A parameter, Uts, measuring the departure from the initial state of equilibrium in the soil showed that Mn initially departed rapidly from the native state of quasi‐equilibrium in the oxidized soils, but tended to return toward it during prolonged incubation. The flux of Fe to the EXC and CARB fractions during the early stages of incubation was very small compared with that of Mn, suggesting increased Mn availability.
Acetate Fate in Organic and Conventionally Managed Soils
Authors: Wander M. M. , Dudley R. B. , Traina S. J. , Kaufman D. , Stinner B. R. , Sims G. K. 
Published: July 2010

AbstractOrganic management practices and mixed‐crop rotations have beneficial impacts on biologically active soil organic matter (SOM); however, the specific impacts of these practices on SOM composition and turnover characteristics are not known. The effect of organic and conventional management on soil C cycling was assessed using soils collected from Rodale's Farming Systems Trial experiment, which included organic‐manure amended, organic‐legume cover cropped, and conventionally managed‐inorganically fertilized farming systems. Soil respiration rates, atom % 13C, and cross polarization 13C nuclear magnetic resonance (CP‐MAS 13C NMR) were used to trace the fate of 13C‐labeled acetate added to soils incubated for 2 and 13 wk. Microbial activity and C turnover rates were initially greater in the manure‐amended soil than in the other two soils. Acetate mineralization lagged in the cover‐cropped soil during the first 2 wk. Low atom % 13C in the conventional soil showed that, even though its soil respiration rates, and therefore overall microbial activity, equaled rates in the cover‐cropped soil, microorganisms present in this soil metabolized significantly more of the applied acetate. By the end of the experiment, C cycling characteristics of the cover‐cropped soil were similar to the manure‐amended soil; NMR spectra indicated 13C was incorporated into new SOM in both of these soils. Soil respiration and 13C assimilation rates in the conventional soil remained relatively low. Microorganisms in the organic soils mineralized and respired more native C and assimilated more 13C than the conventional soil. Conversely, the conventional soil mineralized more and assimilated less 13C than the organic soils. Differences observed in this laboratory experiment may or may not reflect on C cycling occurring in the field.