bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen Mineralization in a Pine Plantation Fifteen Years After Harvesting and Site Preparation
Authors: Piatek Kathryn B. , Allen H. Lee
Published: July 2010

Intensive site preparation for forest tree planting may result in a mid‐rotation decline in soil N availability. Such decline has not been fully documented. This study was conducted in a loblolly pine (Pinus taeda L.) plantation in the Piedmont of North Carolina to evaluate the effects of nutrient removal during harvest and site preparation on N availability at mid‐rotation. Treatments, installed in 1981, consisted of a combination of harvest (stem‐only vs. whole‐tree) and site preparation (chop and burn vs. shear, pile, and disk), with a split‐plot of vegetation control (no herbicide vs. herbicide). In 1995 net N mineralization was examined by monthly in situ soil incubations from May through November (7 mo). Net N mineralization was approximately 3 times lower at mid‐rotation than shortly after treatment. A 5°C drop in soil temperature at 10‐cm depth helped explain ≈50% of this decline. At mid‐rotation, harvest intensity, but not site preparation intensity, affected N mineralization, with stem‐only harvest plots mineralizing 11 kg N ha−1 more than whole‐tree harvest plots during the seven months. Chop–burn–no herbicide plots mineralized 34(±3) kg N ha−1, chop–burn–herbicide: 30(±3) kg N ha−1, shear–pile–disk–herbicide: 28(±3) kg N ha−1, and shear–pile–disk–no herbicide: 19(±3) kg N ha−1 in the seven months. Mid‐rotation mineralization was positively correlated with soil temperature and negatively correlated with soil P and soil C:N ratio. The effect of harvest on N mineralization was probably exerted through P nutrition, whereas the lack of site preparation effects suggested that large nutrient removals that occurred with shearing and piling did not have lasting and negative effects on N availability in this plantation.
Comparison of Phosphorus Soil Test Extractants for Plant Availability and Environmental Assessment
Authors: Magdoff F. R. , Hryshko C. , Jokela W. E. , Durieux R. P. , Bu Y.
Published: July 2010

A number of soil tests have been proposed to predict crop response to added P or to assess potential for soil P loss to runoff waters. A series of four separate experiments were conducted over a 10‐yr period to evaluate soil test methods on a total of 163 Vermont and New York field soils. The experiments included the following: (i) a pot study with alfalfa grown in the greenhouse with 31 soils either unfertilized or fertilized with 18 mg P kg−1; (ii) routine chemical analysis on 54 soils; (iii) a 360‐d incubation study with 24 soils receiving either 0, 20, or 40 mg P kg−1 as CaH2PO4, in which soils were analyzed for desorption and adsorption and the equilibrium P concentration (EPC0); and (iv) another set of 54 agricultural soils incubated with 0 or 40 mg P kg−1 and analyzed for CaCl2, distilled water, and ammonium acetate (Vermont 1)–extractable P (VT1P) and EPC0 Although P extracted by VT1 was significantly correlated with P removed by F extractants, it was better correlated with the ratio of F‐extractable P/Al extracted by either acetate or F. Phosphorus additions increased VT1P, as well as P extracted by acetate + F (Vermont 2 [VT2]), and they decreased reactive soil Al (VT1Al) and P adsorption. The amount of P needed to increase VT1P by a certain amount was directly related to the amount of Al in the VT1 extract. Phosphorus availability to plants, CaCl2‐extractable P, and the EPC0 were all more closely related to VT1P than P extracted by solutions containing F, such as Mehlich 3 (M3), Bray and Kurtz 1 (BK1), and VT2. In a number of instances the ratio VT2P/VT1Al had a better relationship with CaCl2P and EPC0 than did VT1P. Thus, the fraction of reactive Al that has reacted with P (as estimated by VT1P or the ratio of VT2P/VT1Al) appears to be a better indicator of P availability and potential P desorption to runoff water than is P extracted with F.
Use of Brooks‐Corey Parameters to Improve Estimates of Saturated Conductivity from Effective Porosity
Authors: Timlin D. J. , Ahuja L. R. , Pachepsky Ya. , Williams R. D. , Gimenez D. , Rawls W.
Published: July 2010

Effective porosity, defined here as the difference between satiated total porosity and water‐filled porosity at a matric potential of 33 kPa, has been shown to be a good predictor for saturated hydraulic conductivity (Ks) using a modified Kozeny‐Carman equation. This equation is of the form of a coefficient (B) multiplied by effective porosity raised to a power (n). The purpose of this study was to improve the predictive capability of the modified Kozeny‐Carman equation by including information from moisture release curves (soil water content vs. matric potential relation). We fitted the Brooks‐Corey (B‐C) equation parameters (pore size distribution index and air entry potential) to moisture release data from a large database (>500 samples). Values of Ks were also available from the same source. Inclusion of the pore size distribution index into the Kozeny‐Carman equation improved the Ks estimation over using only effective porosity, but only slightly. The improvement came through a better estimation of large values of Ks We also fit a relationship for the coefficient (B) of the Kozeny‐Carman equation as a function of the two B‐C parameters with a constant value of n = 2.5 for the exponent. Overall the use of Brooks‐Corey parameters from moisture retention data improved estimates of Ks over using effective porosity (ϕe) alone. There is still considerable error in predicting individual Ks values, however. The best forms of the equation was when λ was included in the term for the coefficient for the modified Kozeny‐Carman equation. The next best form was when λ was included in the exponent for ϕe The two best models appeared to better preserve the mean, standard deviation and range of the original data.
Mineralization of Amino Acids Applied to Soils Impact of Soil Sieving, Storage, and Inorganic Nitrogen Additions
Authors: Jones David L. , Shannon David
Published: July 2010

The effect of inorganic N additions on the biodegradation and microbial use of organic N pools in soil is poorly understood. To examine the effects of inorganic N on the mineralization rates of amino acids, four soils under contrasting management regimes were subjected to increasing loadings of NH4NO3, ranging from 0 to 120 kg N ha−1In addition, the effect of soil sieving and storage temperature and time on amino acid mineralization was also investigated. At times ranging from 1 to 40 d after the addition of the inorganic N, the mineralization kinetics of an equimolar mixture of fifteen14C‐labeled amino acids was followed for a subsequent 24‐h period. The rate of14CO2evolution was soil dependent, with half‐lives ranging from 2 h for topsoils to 25 h for subsoils. For all soils, at all times, and at all inorganic‐N loadings, the addition of inorganic N appeared to have little effect on the mineralization kinetics of the amino acids to14CO2In addition, the presence of inorganic N also had no major effect on the C use efficiency of the microbial biomass. It is speculated that N release from the amino acids into the soil by the microbial biomass may also be little affected by inorganic‐N additions. Sieving and storage of soil at either 4 or 18°C for up to 40 d had little impact on amino acid mineralization rate. Experiments with potential microbial disrupting agents (autoclaving, CHCl3fumigation, HgCl2, and freeze–thaw) all indicated that the observed mineralization of amino acid C was due to microbial activity. We conclude therefore that inorganic N and soil storage has little effect on the microbial use of readily assimilatable amino acids.
Lignin in Particle‐Size Fractions of Native Grassland Soils as Influenced by Climate
Authors: Amelung W. , Flach K.-W. , Zech W.
Published: July 2010

The turnover of soil organic carbon (SOC) in grasslands can be predicted as a function of climate, plant lignin content, texture, and kinetically defined C pools. Particle‐size fractionation has been used to identify soil C pools. This study was conducted to investigate influences of climate on the dynamics of lignin in particle‐size fractions. Composite samples were taken from the top 10 cm of 18 native grassland sites along temperature and precipitation transects from Central Saskatoon, Canada, to South Texas. Lignin‐derived phenols were determined in the <2 μm (clay), 2‐ to 20‐μm (silt), 20‐ to 250‐μm (fine sand) and 250‐ to 2000‐μm (coarse sand) size separates. With decreasing particle size the concentration of lignin‐derived phenols decreased significantly from 72 g kg−1 SOC in the coarse sand fractions to 12 g kg−1 SOC in the clay fractions. Increasing phenolic acids to aldehyde ratios indicated that side chain oxidation proceeded as particle size decreased. Moreover, these ratios decreased in fractions <250 μm with increasing mean annual temperature (MAT) at the sites. This suggests that the degree of lignin decomposition decreased with increasing MAT, possibly because there was a lack of additional C sources, such as saccharides of root litter, which are needed for the cometabolic decay of lignin.
On‐Farm Spatial and Temporal Variability of Soil and Water in Pearl Millet Cultivation
Authors: Rockström Johan , Barron Jennie , Brouwer Joost , Galle Sylvie , de Rouw Anneke
Published: July 2010

Crust‐prone sandy soils of low fertility, combined with unreliable and erratic rainfall, affect spatial variability of crop growth in the Sahel. We hypothesized that spatial variability in soil properties and soil water content on a hillslope scale affected pearl millet [Pennisetum glaucum(L.) Br.] yields. We focused on the effects of crust development, micro topography, rill distribution, and soil nutrients on crop yield variability within and between years (1994–1996) in a farmer's field in semi‐arid Niger. Yields in plots of 15 by 6 m varied within a year by a factor of 46 for nonfertilized millet (27–1249 kg ha−1), and by a factor of 16 (76–1213 kg ha−1) for fertilized millet. Despite this variation, a linear yield gradient was observed along the 300‐m‐long field with a gentle 1 to 3% slope. Grain yields decreased 0.5 kg ha−1for nonfertilized millet and 1 kg ha−1for fertilized millet per meter along the slope when moving from the bottom to the top of the field. Soil water availability varied greatly, with individual neutron probe access tubes (36 tubes on an 8‐ha field) presenting a percent infiltration ranging from 15 to 182% of rainfall for individual rainstorms. Upslope had significantly lower percent infiltration (75%) than both midslope (90%) and downslope (84%). Between years, soil water and nutrients alternated in limiting crop growth, depending on rainfall distribution (annual rainfall ranging from 488–596 mm). However, in all three years toposequence related factors dominated yield variability and caused similar yield gradients along the slope.
Soil Characteristics and Management Effects on Phosphorus Sorption by Highland Plateau Soils of Ethiopia
Authors: Duffera Miressa , Robarge Wayne P.
Published: July 2010

Differences in crop and fertilizer management are known to influence P retention by soils. An experiment was conducted to study the effect of soil characteristics and management practices on P sorptoin behavior of the highland plateau soils of Ethiopia. Surface samples from two Vertisols, an Andisol, and an Alfisol were collected from farmers' fields, research station farms, and from non‐cultivated‐non‐fertilized areas. Phosphorus sorption data were obtained by equilibrating 3‐g soil samples in 30 mL of 0.01MCaCl2containing various amounts of KH2PO4Inorganic P fractions were determined by the Hedley P fractionation scheme. There was little variation in P sorption among Vertisol samples of alluvial origin as a result of cultivation‐fertilization practices. For soils of volcanic origin (Vertisol2 and Andisols), and the Alfisol, samples collected from farmers' fields sorbed more P than the non‐cultivated and research station samples. Least amounts of applied P sorbed by the non‐cultivated Andisol samples reflect the relatively large amounts of resin extractable P initially present in these soils and demonstrate that labile P initially present in the soil can influence subsequent P sorption. Stepwise regression analysis of the P sorption data showed that resin P accounts for 81% of the variation in P sorption at 0.2 mg P L−1in solution. The highest amount of P was sorbed by samples collected from farmers' fields and was mainly due to the practice of continuous cropping with minimal P fertilization, which depletes labile P, and therefore requires higher levels of P fertilization for optimum crop yield.
Errors of Dual Thermal Probes Due to Soil Heterogeneity across a Plane Interface
Authors: Philip J. R. , Kluitenberg G. J.
Published: July 2010

The dual thermal probe enables estimation of the thermal diffusivity, volumetric heat capacity (C), and thermal conductivity of soils. It has been much employed for moisture estimation because of the strong dependence of C on soil water content. The present study investigates the effectiveness of dual probes near heterogeneities. Exact solutions are found for four probe/soil configurations involving heterogeneity. In one configuration the heating probe is on the plane interface between different soils. For the three other configurations it is located close to three different discontinuities: near a soil surface and outside, and behind, a wetting front. Heterogeneity errors are found to be small provided the heterogeneity is no closer to the probes than probe separation (typically 0.006 m). Estimates of C may provide good resolution of soil water content in critical regions such as near surfaces and fronts.
Comparison of calibration and direct measurement of cable and probe properties in time domain reflectometry
Authors: Huisman J. A. , Bouten W.
Published: July 2010

For the measurement of soil bulk electrical conductivity using time domain reflectometry (TDR), it is necessary to determine cable and probe properties. This can be done by direct measurement or by calibration of the TDR system in salt solutions. For a three‐wire probe system, the results showed that with least‐squares fitting, the electrical conductivity of salt solutions could be measured most accurately. Comparison of several calibration techniques suggested that directly measured cable properties deviate from their calibrated (optimal) values. The difference in accuracy between calibration and direct measurements of cable properties could not be explained with overfitting, as has been suggested. It was concluded that a reduction of calibration time by direct measurement of probe and cable properties is not advisable in case of three‐wire probes. When necessary, a reduction of calibration time can be achieved by limiting the calibration procedure to two well chosen combinations of cable length and solution concentration.
Development and Assessment of a Sequential Extraction Procedure for the Fractionation of Soil Cadmium
Authors: Ahnstrom Z. S. , Parker D. R.
Published: July 2010

Extraction efficiency, reagent specificity and selectivity, and element redistribution are potential problems with trace element fractionation by sequential extraction. As part of a larger study of Cd reactivity in soils, we optimized a sequential extraction procedure for accurate, reproducible Cd fractionation using four soil samples and two soil standard reference materials diverse in Cd source, physicochemical properties, and total extractable Cd (CdT, varying from 22 to 42 mg kg−1). Cadmium was partitioned into five operationally defined fractions: 0.1 M Sr(NO3)2 (F1, soluble–exchangeable); 1 M Na acetate, pH 5.0 (F2, sorbed–carbonate); 5% NaOCl, pH 8.5 (F3, oxidizable); 0.4 M oxalate + 0.1 M ascorbate (F4, reducible); and 3 HNO3:1 HCl (F5, residual). By repeating treatments at F1, F3, F4, and F5, we maximized the amount of Cd released for these respective steps. Supernatant pH was used to evaluate carbonate dissolution at F2. Multi‐element analyses were used to assess reagent specificity/selectivity. Cd redistribution was estimated by extraction with Pb acetate. Reagent specificity and selectivity were good, suggesting the dissolution of major components at targeted phases (e.g., high Ca in F2). In general, redistribution was minimal (≤3%), but reached 12% for F3 of the sludge‐amended soil. Quantitative, reproducible recovery of Cd (96.5 ± 2.1%) was obtained across all samples and averaged 11, 32, 40, 8, and 6% CdT in the respective five fractions. Fractionation trends reflect the Cd sources and physicochemical properties of the samples with Cd being dominant in F3 for soils high in organic matter or contaminated by metal sulfides.
Characterization of Pesticide Desorption from Soil by the Isotopic Exchange Technique
Authors: Celis Rafael , Koskinen William C.
Published: July 2010

The reversibility of pesticide sorption–desorption in soil is of fundamental importance in the understanding of the fate of these agrochemicals in the environment. We used an isotopic exchange method to characterize the irreversibility of the sorption–desorption process of the insecticide imidacloprid (1‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐Nnitro‐2‐imidazolidinimine) and its degradation product imidacloprid‐urea (1‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐2‐imidazolidinone) on a silty clay loam (SiCL) soil, and that of the metabolite imidacloprid‐guanidine (1‐[6‐chloro‐3‐pyridinyl)methyl]‐4,5‐dihydro‐1H‐imidazol‐2‐amine) on a loamy sand (LS) soil. The exchange between12C‐pesticide molecules and14C‐labeled pesticide molecules in soil suspensions preequilibrated for 24 h was monitored and indicated that a fraction of the sorbed chemicals was resistant to desorption. A two‐compartment model was applied to describe the experimental sorption data points of the sorption isotherms as the sum of a reversible component and a nondesorbable, irreversible component. The quantitative estimation of the irreversible and reversible components of sorption, experimentally derived from isotopic exchange experiments, indicated degree of irreversibility (percentage irreversibly bound) in the order: imidacloprid–SiCL soil (6–32%) < imidacloprid urea–SiCL soil (15–23%) < imidacloprid guanidine–LS soil (32–51%), with greater irreversibility at lower pesticide concentration. Increasing the preequilibration time and decreasing pH in the imidacloprid–SiCL soil system resulted in increased sorption irreversibility. The irreversible component of sorption determined by the isotopic exchange technique also allowed accurate prediction of the sorption–desorption hysteretic behavior during successive desorption cycles for all three soil–pesticide systems studied. The isotopic exchange technique appears to be a suitable method to quantitatively characterize pesticide desorption from soil, allowing prediction of hysteresis during sorption–desorption experiments.
Kinetics of Iron Complexing and Metal Exchange in Solutions by Rhizoferrin, A Fungal Siderophore
Authors: Shenker M. , Hadar Y. , Chen Y.
Published: July 2010

Rhizoferrin, a siderophore produced by Rhizopus arrhizus, has been shown in previous studies to be an outstanding Fe carrier to plants. Yet, calculations based on stability constants and thermodynamic equilibrium lead to contradicting conclusions. In this study a kinetic approach was employed to elucidate apparent contradictions and to determine the behavior of rhizoferrin under conditions representing soil and nutrient solutions. Stability of Fe3+ complexes in nutrient solution, rate of metal exchange with Ca, and rate of Fe extraction by the free ligand were monitored for rhizoferrin and other chelating agents by 55Fe labeling. Ferric complexes of rhizoferrin, desferri–ferrioxamine–B (DFOB) and ethylenediamine‐di(o‐hydroxyphenylacetic acid) (EDDHA) were found to be stable in nutrient solution at pH 7.5 for 31 d, while ferric complexes of ethylenediaminetetraacetic acid (EDTA) and mugineic acid (MA) lost 50% of the chelated Fe within 2 d. Iron–calcium exchange in Ca solutions at pH 8.7 revealed rhizoferrin to hold Fe at nonequilibrium state for 3 to 4 wk at 3.3 mM Ca and for longer periods at lower Ca concentrations. Ethylenediaminetetraacetic acid lost the ferric ion at a faster rate under the same conditions. Iron extraction from freshly prepared Fe hydroxide at pH 8.7 and with 3.2 mM Ca was slow and followed the order: DFOB > EDDHA > MA ≥ rhizoferrin > EDTA. Based on these results we suggest that a kinetic rather than equilibrium approach should be the basis for predictions of Fe chelates' efficiency. We conclude that the nonequilibrium state of rhizoferrin is of crucial importance for its behavior as an Fe carrier to plants.
Submeter Spatial Variability of Selected Soil and Bermudagrass Production Variables
Authors: Solie J. B. , Raun W. R. , Stone M. L.
Published: July 2010

The optimal resolution at which soil and plant variables should be sensed and treated is not well defined. This study was conducted to determine the semivariance range where soil test and plant variables were related, and to estimate the minimum spatial scale at which variable rate applications of nutrients should be made. Soil and plant analyses were performed in 490 0.3‐ by 0.3‐m plots from bermudagrass (Cynodon dactylon L.) sod at two locations. Eight soil cores (0–15 cm deep) were collected and composited from each 0.3‐ by 0.3‐m plot. Semivariance analysis was used to estimate the range over which samples of the five soil variables (total N, extractable P, and K, organic C, and pH) and two plant variables (forage total N and biomass) were related. Semivariance statistics including the nugget, sill, correlation range, and integral scale were calculated. Correlation ranges were between 1.9 and 11.4 m with corresponding integral scales between 0.5 and 2.1 m. At one location, P exhibited nested sills with multiple ranges. Results indicate that the fundamental field‐element dimensions (the area over which variable rate fertilizer applicators should sense and apply materials) is likely to be 1.0 by 1.0 m or smaller. To describe the variability encountered in these experiments, soil and plant measurements should be made at the meter or submeter level.
Modeling of Sulfur Sequestration in Coastal Marsh Soils
Authors: Hussein A. H. , Rabenhorst M. C.
Published: July 2010

In transgressive coastal areas, marshes form in response to sea‐level rise and they generally represent an ideal environment for the sequestration of S species. Various predictions in rates of sea‐level rise associated with global warming and concern for potential environmental problems from acid‐sulfate weathering have prompted interest in modeling rates of S sequestration during coastal marsh pedogenesis. In this study, predictive models were derived for organic and pyrite S using data from pedons along two marsh transects in Dorchester County, MD. Organic S accumulates mainly in the organic horizons, and the rate is mainly driven by sea‐level rise. Rates of organic S accumulation for the last 150 yr averaged 4.3 ± 1.19 g m−2yr−1; before this, long‐term rates ranged between 0.95 and 2.05 g m−2yr−1Pyrite S sequestration reflects accumulations both in organic horizons and in the submerged mineral soil. The rate of pyrite sequestration in organic horizons is generally driven by sea‐level rise and the availability of reactive Fe. During the last 150 yr, the rates of pyrite accumulation averaged 7.2 ± 1.6 g m−2yr−1; before this, long‐term rates ranged between 0.53 and 1.14 g m−2yr−1Modeled predictions of pyrite and organic S accumulations in newly forming marshes during the next century were 15 ± 4.3 g m−2yr−1and 19 ± 8.2 g m−2yr−1, respectively.
Modeling Arsenic(III) Adsorption and Heterogeneous Oxidation Kinetics in Soils
Authors: Manning Bruce A. , Suarez Donald L.
Published: July 2010

Arsenite [As(III)] is a soluble and toxic species of arsenic that can be introduced into soil by geothermal waters, mining activities, irrigation practices, and disposal of industrial wastes. We determined the rates of As(III) adsorption, and subsequent oxidation to arsenate [As(V)] in aerobic soil–water suspensions using four California soils. The rate of As(III) adsorption on the soils was closely dependent on soil properties that reflect the reactivity of mineral surfaces including citrate–dithionite (CD) extractable metals, soil texture, specific surface area, and pH. Heterogeneous oxidation of As(III) to As(V) was observed in all soils studied. The recovery of As(V) from As(III)‐treated soils was dependent on levels of oxalate‐extractable Mn and soil texture. After derivation of rate equations to describe the changes in soluble and recoverable As(III) and As(V) in soil suspensions, soil property measurements were used to normalize the empirically derived rate constants for three soils. The fourth soil, which had substantially different soil properties from the other three soils, was used to independently test the derived soil property–normalized model. The soil property–normalized consecutive reaction model gave a satisfactory description of the trends seen in the experimental data for all four soils. Understanding the effects of soil properties on the kinetics of chemical reactions of As(III) and As(V) in soils will be essential to development of quantitative models for predicting the mobility of As in the field.
A Simple Approach to Determine Reactive Solute Transport Using Time Domain Reflectometry
Authors: Vogeler Iris , Duwig Céline , Clothier Brent E. , Green Steven R.
Published: July 2010

Time domain reflectometry (TDR) possesses potential for determining solute‐transport parameters, such as dispersion coefficients and retardation factors for reactive solutes. We developed a simple method based on peak‐to‐peak measurements of water and solute velocities through the soil using TDR. The method was tested by carrying out unsaturated leaching experiments in the laboratory on two soil columns packed with a South Pacific soil from Maré, which is a ferrasol with variable surface charge. One column was left bare and the other was planted with mustard. Pulses of CaBr2 and Ca(NO3)2 were applied to the surface of either wet or dry soil and then leached by water from a rainfall simulator applied at a steady rate of between 30 and 45 mm h−1 Water and solute transport were monitored by collecting the effluent. Contemporaneous in situ measurements of the water content and electrical conductivity were made using TDR. Transport parameters for the convection–dispersion equation, with a linear adsorption isotherm, were obtained from the flux concentration and the solute resident concentrations measured by TDR. Anion retardations between 1.2 and 1.7, and dispersivities between 1 and 9 mm, were found. Retardations also were calculated using our simple approach based on TDR‐measured water and solute front velocities. These used TDR measurements of soil water content and bulk soil electrical conductivity with time, and were similar to those obtained from the effluent. The agreement suggests TDR could be a valuable in situ technique for obtaining the parameters relating to reactive solute transport through soil.
Phosphorus Fractions and Fate of Phosphorus‐33 in Soils under Plowing and No‐Tillage
Authors: Daroub S.H. , Pierce F.J. , Ellis B.G.
Published: July 2010

Minimum tillage may alter soil P fractions through the application of P fertilizers and the deposition of organic matter on the surface rather than being incorporated into the soil. This study was conducted to determine whether no‐tillage (NT) systems affected soil organic and inorganic P fractions and the transformation of P from residues applied to soils. Surface soils (0–2 cm) under NT and conventional tillage (CT) were sampled from three long‐term research sites. Inorganic and organic P was measured in the NaHCO3, microbial, NaOH, NaOH after sonication, HCl, and residual fractions extracted sequentially. Soybean (Glycine maxL.) residues labeled with33P were added to soils, incubated, and extracted periodically, and33P was counted in the different P fractions. Levels of31P in NT were higher in some of the fractions compared with CT; however, there was no consistency in31P fractionation across soil types due to tillage in any of the inorganic and organic fractions. At the start of incubation, 56 to 82% of the applied33P was extracted in the resin fraction in the three soils. Resin‐33P followed a three‐parameter single exponential decay model with a corresponding increase in other pools depending on soil. The increase in these pools followed a quadratic model in the three soils. By the end of the incubation period, the NaOH fraction accounted for the majority of the33P released from the labile resin pool. An increase in the calcium phosphate pool occurred in the calcareous soil. Tillage had no effect on the fate of33P released from soybean residues during the incubation period.
Use of15N‐Labeled Soil in Measuring Nitrogen Fertilizer Recovery Efficiency in Transplanted Rice
Authors: Bronson K. F. , Hussain F. , Pasuquin E. , Ladha J. K.
Published: July 2010

In transplanted flooded rice (Oryza sativaL.) culture in Asia, N fertilizer recovery efficiency (RE) estimates are usually greater with the difference method than with the15N method. These reported differences are greater and more common for transplanted irrigated rice than for upland crops and might be associated with basal N applications when plant demand is low. Added N interactions (ANI), or greater soil N accumulation in fertilized plants than in unfertilized plants, are often cited as the reason for these differences. The causes of ANI can be stimulation of mineralization of soil organic matter by fertilizer or greater root exploration in fertilized plants. The objectives of this pot study were (i) to compare the15N dilution method using enriched15N‐urea (5.0 atom %), and14N‐urea (0.366 atom %) plus15N‐labeled (0.447 atom %, Maahas clay [isohyperthermic Andaqueptic Haplaquoll]) soil, with the difference method of measuring RE of N, as affected by timing of application, and (ii) to use15N‐labeled (0.447 atom %) soil to directly measure ANI as15N accumulation in14N fertilized pots minus15N accumulation in unfertilized pots. Recovery efficiency measures at physiological maturity were higher with the difference method (54%) than with the two isotope dilution methods (44%), which were in turn similar. TherealANI measured was negligible, as the root biomass in this clay soil was not greatly affected by fertilization. Therefore, the ANI wasapparentand due to isotope substitution. The RE estimate by difference (54.4%) was therefore more accurate than the RE measure by15N methods (44.4%). The 33.2% of added15N not accounted for in the plant–soil system was a measure of N fertilizer losses (NH3volatilization from floodwater, denitrification, NH3loss through the plant during grain fill) that were not affected by isotope substitution. Recovery efficiency estimated with15N‐enriched soil plus ordinary urea was identical to the RE estimate using enriched15N‐urea, although both were underestimations because of isotope substitution.
A New Solution for Water Storage to a Fixed Depth for Constant Flux Infiltration
Authors: Si Bing Cheng , Kachanoski R. Gary
Published: July 2010

A quantitative description of water infiltration under constant flux boundary conditions is useful for predicting water flow and chemical transport processes occurring in surface soils. A new quasi‐analytical solution for water storage to a fixed depth for constant flux infiltration is presented. The solution, based on the flux–concentration relationship, allows general forms of soil hydraulic functions to be used and provides a direct interpretation of measurements from vertically installed time domain reflectometry probes. To evaluate the solution, a constant flux infiltration experiment was conducted and the hydraulic parameters for the experimental site were determined independently. The solution predictions using the approximate flux–concentration relationship for linear soils were essentially identical to an existing analytical solution using the Broadbridge and White form of hydraulic functions and to the measurements.
Nitrate Leaching in a Tile‐Drained Silt Loam Soil
Authors: de Vos J. A. , Hesterberg D. , Raats P. A. C.
Published: July 2010

Nitrate (NO3) leaching was studied for a winter leaching period in a layered calcareous silt loam with tile‐drains at about 1‐m depth and 12‐m spacing. Groundwater levels, drain discharge rates, and NO3 concentrations in the drainage water were monitored, and the soil hydraulic characteristics were measured for the different soil layers. The data were interpreted using the two‐dimensional water flow and solute transport model SWMS_2D. This model uses Darcy's law for water flow and the convection–dispersion equation for solute transport for both the saturated and unsaturated zones. A nitrogen‐production term of 39 kg N ha−1 was used to account for the net N mineralization in the topsoil during the leaching period. The model was calibrated by varying the hydraulic conductivity at saturation (Ks) for the different soil layers, using the measured groundwater level–drain discharge rate relationship as calibration target. Peaks in NO3 concentrations in the drainage water are well explained by the temporal two‐dimensional behavior of convective transport. Measured NO3 leaching was 11 kg N ha−1 yr−1 and simulated NO3 leaching was 15 kg N ha−1 yr−1 in the relatively dry winter leaching period 1991–1992. The two‐dimensional transport model SWMS_2D is a useful tool to evaluate the relative effects of management practices to reduce N leaching.
Chemical and Biochemical Properties of Humic Substances Isolated from Forest Soils and Plant Growth
Authors: Nardi S. , Pizzeghello D. , Reniero F. , Rascio N.
Published: July 2010

To investigate the relationships among litter composition and 13C–nuclear magnetic resonance spectra (13C–NMR), we studied δ13C values and biochemical activities of the humic constituents extracted from the Ah horizons of two undisturbed forest soils, located in a unique climatic area under different vegetative covers, Pinus mugo T. and Pinus sylvestris L. The two litters differed greatly in composition, while the 13C–NMR spectra of the humic substances extracted from the two Ah horizons were similar. The 13C–NMR spectra of the low molecular humic size (LMS) 1–2 revealed high aromatic and carboxylic contents and low aliphatic and carbohydratic ones. The total humic extracts (TQ) 1–2 and the high molecular humic size (HMS) 1–2 exhibited an opposite trend. The δ13C values of the humic fractions ranged from −24.96 to −25.84‰, indicating an advanced stage of humification. The biochemical activities of the humic fractions were studied by evaluating the invertase, peroxidase, and esterase activities in Pinus mugo and Pinus sylvestris seedling roots grown in the presence of their humic matter. These forest species were differently affected by their humic substances. In particular, the Pinus sylvestris humic matter, endowed with a higher indoleacetic acid (IAA) content, positively influenced all the enzymes tested in Pinus sylvestris seedlings, while the Pinus mugo humic matter only increased the peroxidase activity in its seedlings. The plant species differ in their capacity to respond to biological humus activity, which is reflected in their natural distribution.
Relationships Between Soil Test Phosphorus, Soluble Phosphorus, and Phosphorus Saturation in Delaware Soils
Authors: Pautler Maria C. , Sims J. Thomas
Published: July 2010

Methods to identify agricultural soils that contribute to nonpoint‐source pollution of surface waters by P are of increasing importance, particularly in areas with high animal densities (animal units per hectare of cropland). Our objective was to determine the relationship between agronomic soil test P (STP = Mehlich 1) and other soil P tests proposed to measure the potential for P loss by erosion, runoff, and leaching. We compared STP with soluble P, P in the “fast desorbing pool” (strip P), and soil P saturation for 127 soils (122 from Delaware and five from the Netherlands). Soil test P was significantly correlated with total , soluble , strip , and oxalate‐extractable Strip P was a better predictor of soluble P than The ratio of strip P/Pox (the percentage of reversibly sorbed P in the fast desorbing pool) increased as P sorption capacity, estimated from oxalate‐extractable Al and Fe (Alox + Feox), decreased. We also determined the degree of P saturation (DPS) using three methods: Langmuir P sorption isotherms; oxalate extractions of P, Al, and Fe; and STP plus a single‐point P sorption index (PSI). Soluble P, STP, and desorbable P increased for DPS values >30%, similar to upper DPS limits in the Netherlands and Belgium. Soils rated agronomically excessive in STP (>50 mg kg−1) had higher ratios of soluble P, strip P, and Pox to total P than those in agronomically optimum or lower categories.
Soil and Crop Response to Variable‐Rate Liming for Two Michigan Fields
Authors: Pierce F. J. , Warncke D. D.
Published: July 2010

Soil pH is known to vary spatially, making variable‐rate lime application attractive where soil acidity occurs. This study examined the efficacy of variable‐rate lime applications based on grid sampling at various scales on soil pH and the yield of corn (Zea mays L.) and soybean [Glycine max L. (Merr.)] during 3 yr. Lime was applied in two fields according to five lime management strategies: lime requirement (LR) estimated from maps interpolated from soil samples obtained from 30.5‐, 61‐, and 91.5‐m grids; LR determined for the plot; and no lime. The LR interpolations consistently underestimated and were not correlated with LR measured on each plot. Granulated lime, used to insure uniform lime application, was slow to react in the field and a lab incubation verified that it reacted much slower than agricultural lime. Changes in pH occurred in the surface 10 cm, reflecting the depth of lime incorporation by chisel plowing. Corn yield did not respond to liming in 1995 and 1996. Soybean yield in 1997 increased due to liming at the Durand field, which had a lower range of soil pH values. Normalized soybean yields at both fields followed the same linear‐plateau response to pH, with soybean yields declining below a threshold pH of about 5.9. While there is need for improvements in grid sampling design, variable lime applications under all of the grid sampling scales increased soil pH above the threshold pH for soybean in these fields, resulting in an improvement compared with whole field management.
Chemical Fluxes from Sediments in Two Adirondack Wetlands Effects of an Acid‐Neutralization Experiment
Authors: Cirmo C. P. , Driscoll C. T. , Bowes K.
Published: July 2010

As a strategy of acid deposition mitigation, the application of neutralizing agents to hydrologic source areas has received substantial attention for the past decade. To compare mass balance–determined fluxes with field measurements at the sediment–water interface, we used benthic enclosures to determine chemical fluxes from the sediments of a reference beaver pond (no chemical treatment) and a beaver pond within the watershed of an acid‐neutralization experiment (CaCO3 treatment). Baseline O2–consumption rates, the effects of reacidification, and the effects of CaCO3 and CaCl2 additions were determined. Oxygen consumption rates in pond sediments were higher in the CaCO3–treated wetland, indicating stimulation of microbial activity and the subsequent enhancement of organic‐matter decomposition. In the reference wetland, anoxia was followed by the sequential consumption of NO−3 and SO2−4, basic cation (CB) and Fe2+ release, and the production of acid‐neutralizing capacity (ANC), while the release of Ca2+ from cation‐exchange sites dominated ANC in the treated wetland. Reacidification of CaCO3–treated sediments caused an immediate increase in Al concentration in the water column, initially in the inorganic monomeric form (AlIM), followed by increasing concentrations of the organic monomeric form (AlOM). Hydrolysis of Al inputs from upland drainage, complexation of Al with dissolved organic carbon (DOC), and the formation of less toxic AlOM were all observed. Our evidence reveals that these sediments may act as sinks for inputs of strong acid anions (e.g., SO2−4 and NO−3) from atmospheric deposition, and as sinks and transformation zones for Al associated with acidic upland drainage.
Calibrating an Electromagnetic Induction Instrument to Measure Salinity in Soil under Irrigated Cotton
Authors: Triantafilis J. , Laslett G. M. , McBratney A. B.
Published: July 2010

Various calibration approaches have been proposed for determining profiles of apparent soil electrical conductivity (ECa) or soil electrical conductivity of a saturated soil paste extract (ECe) using an EM38 instrument. One of the most promising of these, the established‐coefficients approach, was selected for calibration of the EM38 to some irrigated cotton (Gossypium hirsutum L.)‐growing soil located in the Edgeroi district of the lower Namoi valley, northern NSW, Australia. However, the fitted salinity profiles were locally erratic, although global trends could be recognized. This method was compared with simple linear regression applied to the data from each depth increment separately. This was also unsatisfactory, and in fact, was not obviously different from the established‐coefficients method on the data. An alternative and statistically more rigorous approach was used in which a logistic curve is fitted to each calibration hole (the logistic profile model). This mixed random and fixed effects nonlinear model predicts ECe from measurements generated by an electromagnetic (EM) instrument (EM38) held in the horizontal mode of operation EM0,H The logistic profile model fitted the data well, with no obvious patterns in the residuals, and depended on far fewer parameters than the two alternative methods. In addition, unlike the established‐coefficients approach, the logistic model provided meaningful prediction errors.
Soil Structure and Soil Organic Matter II. A Normalized Stability Index and the Effect of Mineralogy
Authors: Six J. , Elliott E. T. , Paustian K.
Published: July 2010

Soil aggregate distribution and stability measurements have been proposed as soil quality indicators. However, pretreatment of soil, antecedent water content and differences in sand size distribution among soils can confound interpretation of these measurements. We propose a normalized stability index (NSI) which (i) compares aggregate distribution after slaking and rewetting to characterize whole soil stability and eliminate confounding effects of pretreatment and antecedent water content, (ii) corrects for the confounding effect of differences in sand size distribution among soils, aggregate size classes and pretreatments, and (iii) normalizes the level of disruption imposed by slaking by using a maximum level of disruption. The NSI was tested on three soils dominated by a 2:1 clay mineralogy and one soil characterized by a mixed (2:1 and 1:1) clay mineralogy. Each site had native vegetation (NV), no‐tillage (NT), and conventional tillage (CT) treatments. In soils dominated by 2:1 clays, NSI decreased with increasing cultivation intensity (NV > NT > CT). However, NSI was higher in the soil with mixed clays compared to the other soils and was not different along the cultivation gradient. These observations are hypothesized to be related to the presence of Fe‐ and Al‐oxides and kaolinite. In conclusion, NSI appears to be a good indicator for soil structural quality since it is sensitive to changes in agricultural practices and it minimizes confounding effects. A decrease of SOM levels results in a smaller decrease of soil stability in soils dominated by oxides and 1:1 minerals compared to soils dominated by 2:1 minerals.
Soil Erosion and Vegetation in Grasslands of the Peloncillo Mountains, New Mexico
Authors: Moir W. H. , Ludwig J. A. , Scholes R. T.
Published: July 2010

We report soil erosion and vegetation cover in montane desert grassland pastures where livestock grazing had been discontinued at least 5 yr prior to our initial measurements in 1977. Changes in soil surface elevation measured with a precision transit level during a 9‐ to 13‐yr period are compared with changes in vegetation cover and surface hydrological features. We describe changes in soil surface elevation on 10 transects situated on an active hillslope gully system, across two hillslope ravines, and on an intracanyon alluvial landform. Overall we measured a small rate (0.8 mm yr−1) of sediment accumulation across the four study locations. On most slopes, sediment additions were balanced by sediment losses (transportation slopes), or changes in surface elevation along transects were insignificant. A portion of one transect was denudational, with a net loss rate for 12 yr of 3.9 mm yr−1 Another transect accumulated sediments at 6.8 mm yr−1 during an 11‐yr interval. The dynamics of sediment transport are not explained by vegetation cover alone. Rather, cover, slope gradient, ground surface roughness, soil depth, and soil infiltration rates interact to regulate sediment transport during and after storm events. There was no evidence that past livestock grazing affected the measured erosion rates.
Kaolinite and Gibbsite Weathering of Biotite within Saprolites and Soils of Central Virginia
Authors: Jolicoeur Serge , Ildefonse Philippe , Bouchard Mireille
Published: July 2010

The mineralogical and chemical characteristics of saprolites and soils developed from granulitic, monzonitic, and charnockitic gneisses and mylonites of the Blue Ridge Mountains and western Piedmont foothills of central Virginia, were studied. Micromorphological, x‐ray diffraction (XRD), scanning electron microscopy (SEM), and microprobe analysis showed that the mineralogical and geochemical evolution of biotite in profiles developed on gneisses is consistent with pseudomorphic weathering of mica to kaolinite and halloysite, with or without a mica–vermiculite intermediate phase. On mylonitic rocks, saprolites and soils also contain multimineral pseudomorphs after biotite, in which gibbsite crystals eventually fill the whole volume. There is evidence of topotaxial formation of halloysite after biotite. Although gibbsite is present at the first stages of the weathering of biotite, it is not clear if gibbsite forms directly from the mica or if it is a weathering product of kaolinite and/or halloysite. The source of aluminium may also be located outside the original biotite crystal. These multimineral assemblages suggest that microenvironments of weathering are controlling the formation of secondary products from the parent biotite rather than the so called anti‐gibbsite effect, at least at this scale of investigation. It is suggested that the mylonitic fabric and subvertical foliation planes of these rocks are responsible for this mineralogical and geochemical evolution.