bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Calibration Methods for Interpreting Soil Salinity from Electromagnetic Induction Measurements
Authors: Johnston M. A. , Savage M. J. , Moolman J. H. , du Plessis H. M.
Published: July 2010

The EM‐38 electromagnetic induction sensor of Geonics Ltd. (Canada) is a most useful instrument for rapid field identification and mapping of soil salinity. Interpretation of instrument measurements in terms of meaningful parameters of soil salinity is difficult, however, due largely to the non‐uniform response distribution with depth. Various models have been proposed that allow the conversion of measurements made on this instrument to the electrical conductivity of the bulk soil (ECa, as measured with the four‐electrode probe) or EC of the saturation extract (ECe). Seven of these models were evaluated in this study by comparing predicted with measured values. Four allow the estimation of ECa at 0.30‐m depth intervals down to 0.90 m, two allow the estimation of a single valued ECe, weighted for instrument response with depth, and one estimates ECe for 0.30‐m intervals down to 0.90 m. The performance of the models varied greatly, and likely reasons for poor prediction are discussed. For the model that produced the most accurate estimate of ECa, the estimated values were, based on 95% confidence limits, within 0.8 dS m‐1 of the values predicted using the regression equations. For the models that predict weighted ECe, the corresponding value was typically about 2.2 dS m‐1. While salinity measurements made with the EM‐38 are not highly accurate, the strength of the technique is that measurements of reasonable accuracy can be made very rapidly. Categories of soil salinity for large areas can be readily established, which represents useful information for salinity management and certain research applications.
Citrate‐Ascorbate as a Highly Selective Extractant for Poorly Crystalline Iron Oxides
Authors: Reyes I. , Torrent J.
Published: July 2010

Existing methods for dissolving poorly crytalline Fe oxides (primarily ferrihydrite) in soils and mineral mixtures are simple and rapid but often lack selectivity. In this work, we tested a more selective, alternative ascorbate‐based extractant. Ascorbate combined with citrate was found to be highly effective in dissolving poorly crystalline Fe oxides while dissolving little goethite and hematite. Citrate‐ascorbate and oxalate extracted similar amounts of Fe from most of the soils and Fe‐rich materials studied. However, citrate‐ascorbate was more selective than oxalate, since it dissolved only negligible amounts of allophane or imogolite and magnetite. The recommended citrate‐ascorbate extraction procedure (0.2 M sodium citrate‐0.05 M sodium ascorbate, pH 6, 16 h) is simple to implement and relatively inexpensive, and uses nontoxic chemicals. Thus, it can be used on a routine basis for estimating poorly crystalline Fe oxides in soils. By subtracting citrate‐extractable Fe and Al from citrate‐ascorbate‐extractable Fe and Al values, respectively, one can estimate Fe and Al contained in poorly crystalline Fe oxides. The citrate‐ascorbate extraction, combined with others (oxalate, Tiron, hydroxylamine) can help detect and quantify other soil components such as allophane and magnetite.
Moist‐ and Dry‐Season Nitrogen Transport in Sierra Nevada Soils
Authors: Burcar S. , Miller W. W. , Tyler S. W. , Blank R. R.
Published: July 2010

Characterization of ion mobility is a first step in the understanding of nutrient flux relationships in alpine forested watersheds. Our purpose was to: (i) investigate the transport dynamics of inorganic N in Sierra Nevada soils by applying unspiked source water as a control, and a 1 mmolc L‐1 NH4NO3 spiked solution to two soil types (granitic and andesitic) under forest and meadow conditions via artificial rainfall during moist (spring) and dry (late summer‐early fall) seasons; and (ii) evaluate the presence of macropore or preferential matrix flow from characteristic profile distributions of the two N forms. Peak concentrations in surface flow discharge (runoff) of both N forms from control treatments occurred early for both soil types and were highest from the meadow areas (1.6–0.4 mg NO‐3‐N L‐1 meadow to forest for granitic soil and 0.3–0.1 mg L‐1 meadow to forest for andesitic soil; 0.75–0.37 mg NH+4‐N L‐1 meadow to forest for granitic soil and 0.25–0.18 mg L‐1 meadow to forest for andesitic soil). Both soils exhibited NH+4‐N adsorption, but only the soil of andesitic origin appeared to sorb NO‐3‐N. Andesitic soils of the Sierra Nevada may thus serve as a temporary sink for NO‐3‐N deposition, whereas meadow areas of both soil types appear to serve as a source. Higher initial soil moisture for the spiked treatments generally resulted in the transport of NH+4‐N to greater depths in both soils of forested cover (≈ 40 compared with 20 cm from spring to late summer‐early fall), and for NO‐3‐N (≈ 50 compared with 40 cm) as well. Wet‐season (spring) mobility must therefore be considered an important groundwater nutrient transport mechanism in Sierra Nevada watershed soils.
Nitrate Leaching from Cattle Urine and Feces in Northeast USA
Authors: Stout W. L. , Schnabel R. R. , Priddy W. E. , Elwinger G. F. , Fales S. A. , Muller L. D.
Published: July 2010

Management intensive grazing (MIG) is a grazing system in which animals at a high stocking density are rotated frequently through a series of paddocks in a manner that maximizes both forage yield and quality. Although MIG has the potential to increase dairy farm profitability in the U.S. Northeast, the uneven recycling of N through feces and urine can increase NO3‐N leaching. The extent to which NO3‐N can leach from beneath urine and fecal spots under soil and climatic conditions of the Northeast is not known. We conducted a field study to measure NO3‐N leaching loss from spring‐, summer‐, and fall‐applied urine and summer‐applied fecal beneath N‐fertilized orchardgrass (Dactylis glomerata L., cv. Pennlate) using 60‐cm‐diameter by 90‐cm‐deep drainage lysimeters. The study site was located in central Pennsylvania on a Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf). Averaged across the 3 yr of the study, NO3‐N losses were 1.17, 1.68, 22.0, 24.0, and 31.5 g m‐2 for the control, feces, and spring‐, summer‐, and fall‐applied urine, respectively. These losses represent about 2% of the N applied in the feces and about 18, 28, and 31% of the spring‐, summer‐, and fall‐applied urine N. If dairy farmers in the Northeast continue to increase the utilization of MIG, the amount of N leached to the groundwater from beneath pastures could become substantial if not mitigated by improved grazing management.
Measuring Instantaneous Solute Flux and Loading with Time Domain Reflectometry
Authors: Hart G. L. , Lowery B.
Published: July 2010

Time domain reflectometry (TDR) can be used to measure water content and conservative tracer concentration in soils. An important contribution of TDR for assessing or monitoring water‐soluble contaminant loading in real time under transient flow may be possible because of the ability to acquire rapid, multiplexed measurements of variables necessary for calculating loading — the water flux and resident contaminant concentration. An empirically derived equation relating resident soil Br− concentration (CBr, mg L−1) to apparent soil bulk electrical conductivity (σa, dS m−1) and soil water content (θ, m3 m−3) was established for Sparta sand (mesic, uncoated Typic Quartzipsamment). This equation has the form CBr = ασaγθδ, where α, γ, and δ are empirical constants. Using TDR, we conducted real‐time monitoring of a Br− tracer transported through a repacked Sparta sand soil column at four depths. Under steady‐state and transient‐flow experiemntal conditions and assuming a unit gradient and uniform vertical flow, instantaneous water flux at each monitored depth was estimated from TDR‐acquired θ data and soil hydraulic conductivity. For steady‐state conditions, recovery of Br− ranged from 72% at 15 cm to 133% at 45 cm, while water recovery averaged 92% for all depths. Under transient conditions, Br− recovery ranged from 65% at 15 cm to 121% at 60 cm. Percentages of Br− recovery were congruent across depths between steady‐ and transient‐flow experiments, leading us to conjecture that nonhomogeneous flow patterns and pockets of immobile water had developed within the column.
Clay Particle Differentiation in Alluvial Soils of Southwestern Niger (West Africa)
Authors: Ducloux Jacques , Guero Yadji , Fallavier Paul
Published: July 2010

In arid lands, textural and structural differentiation between the surface soil and deeper horizons is commonly attributed to mechanical transfer of finer material by wind and runoff, but other processes may be influential as well. This study was conducted to determine whether physico‐chemical and mineralogical processes could participate in differentiation. The study area is in Sona (Niger Republic) on alluvial deposits of the Niger River. After a soil survey, soil samples were collected from eight profiles. The particle‐size distribution was determined by the sedimentation and centrifugation methods. The clay fractions were studied by x‐ray diffractometry, chemical analyses, transmission electron microscopy, and energy dispersive x‐ray analysis. The particle images were computed and displayed by an image analysis program. The surface horizons contained fewer particles <0.1 µm than the deeper horizons. However, they were relatively richer in <83‐nm particles and these were corroded on the edges and (001) faces. From a mineralogical viewpoint, detrital kaolinite and smectite clays presented wides x‐ray diffraction lines, indicating smaller, thinner particles with fewer silicate layers than in deeper horizons. Textural differentiation of the surface horizons was enhanced by weathering and dissolution of the smectite and kaolinite particles under acidolitic conditions caused by soil ultradesiccation.
Monitoring for Temporal Changes in Soil Salinity using Electromagnetic Induction Techniques
Authors: Lesch S. M. , Rhoades J. D. , Herrero J.
Published: July 2010

Electromagnetic induction surveys are often used in practice to estimate field‐scale soil salinity patterns, and to infer changing salinity conditions with time. We developed a statistical monitoring strategy that uses electromagnetic induction data and repetitive soil sampling to measure changing soil salinity conditions. This monitoring approach requires (i) the estimation of a conditional regression model that is capable of predicting soil salinity from electromagnetic (EM) survey data, and (ii) the acquisition of new soil samples at two or more previously established survey sites, so that formal tests can be made on the differences between the predicted and observed salinity levels. We examined two test statistics in detail: a test for detecting dynamic spatial variation in the new salinity pattern and a test for detecting a change in the field median salinity level with time. We applied this monitoring and testing strategy to two EM survey‐soil salinity data sets collected at multiple points in time from the saline irrigation district of Flumen, Spain, Our results demonstrate that this monitoring approach was successfully able to quantify the temporal changes in the soil salinity patterns occurring within these two fields.
Screening a Selective Chelator Pair for Simultaneous Determination of Iron(II) and Iron(III)
Authors: Wang Tiangen , Peverly John H.
Published: July 2010

Direct determination of Fe(II) and Fe(III) is a fundamental technology for environmental Fe chemistry research. The key to accurate determination of Fe(II) and Fe(III) in soil, water, and plant samples is to stabilize Fe oxidation states during Fe extraction and analysis, but the goal has only been partially achieved in previous research. In this research, an approach to stabilizing the original oxidation states of Fe during extraction and analysis was studied. The following sequential procedures were conducted: computer simulation → colorimetric tests → Fe(III) reduction resistance tests → metal interference tests → sensitivity tests → determination of optimal pH for Fe extraction. Results indicated that EDTA (ethylenediamine‐N,N,N′,N′‐tetraacetate, disodium salt) and BPDS (bathophenanthroline disulfonate, disodium salt) were the most effective chelator pair with which to stabilize Fe oxidation states and that they may allow accurate, simultaneous determination of Fe(II) and Fe(III).
Model for Nonreactive Solute Transport in Structured Soils with Continuous Preferential Flow Paths
Authors: Wallach R. , Steenhuis T. S.
Published: July 2010

A mathematical model for solute movement in a structured soil with well‐defined and continuous preferential paths was developed. The model divides the soil profile into one mobile and one “stagnant” pore group. For well‐structured soils, the mobile pore group consists of a few well‐connected pores that conduct the nonreactive solute downward very rapidly. Only a narrow matrix layer of stagnant solute along the interface between the two pore groups takes part in solute exchange with the preferential paths. Due to differences in time scales between convection and chemical transfer, the rate of chemical exchange between the preferential path and the active matrix layer for short and moderate times after chemical application is controlled mainly by the preferential flow concentration and, to a lesser extent, by the concentration in the matrix active layer. This is expressed mathematically by multiplying the concentration in the active matrix layer in the mass balance equation by a small dimensionless parameter, ɛ ≪ 1. A regular small perturbations problem is then obtained whose solution is expressed as the sum of the zeroth‐ and first‐order approximations. The simulated breakthrough curve (BTC) is made up of piecewise linear lines and shows a good fit to the measured solute concentration in the outflow of undisturbed columns that have significant preferential flow. Due to the model's simplicity, the transport parameters are estimated directly by fitting the model output to the measured BTCs.
Hydric Conditions and Hydromorphic Properties within a Mollisol Catena in Southeastern Minnesota
Authors: Thompson James A. , Bell Jay C.
Published: July 2010

Wetlands are characterized by wetland hydrology, hydrophytic vegetation, and hydric soils. The multiparameter approach to wetland identification and delineation requires independent evaluation of all three diagnostic characteristics. Hydric soils can be determined from data collected under saturated and anaerobic soil conditions or by using accepted field indicators. The objectives of this research were to: (i) evaluate the presence of wetland hydrology and hydric soil conditions, (ii) examine associations between observed soil hydrology and soil morphologic properties, and (iii) evaluate current field indicators of hydric soils for their applicability to presumed hydric Mollisols. We used wells, piezometers, and tensiometers to measure saturated conditions, and Pt electrodes to measure anaerobic and reducing conditions for five soils along a hillslope transect from summit to drainageway in southeastern Minnesota. Saturated conditions were observed within 25 cm of the soil surface for all five soils for at least a few days each year between 1992 and 1995, mainly in the early spring and the late fall when soil temperatures at 50 cm were not always >5°C. Only the soil in the drainageway was saturated and anaerobic during the microbial activity season in more than one year. Soil morphology reflects the presence of saturated and anaerobic conditions in the form of thick, black surface horizons. Absence of Fe concentrations and depletions in the upper 30 cm of presumed hydric soils may reflect the absence of Fe‐reducing conditions as a result of saturated conditions when soil temperatures do not facilitate abundant microbial activity.
Improved Transient‐Flow Air Permeameter Design: Dampening the Temperature Effects
Authors: Smith James E. , Robin Michel J. L. , Elrick David E.
Published: July 2010

Air permeability of soil is an important parameter for soil aeration and contaminant remediation techniques such as soil vacuum extraction. Transient‐flow air permeameters are inexpensive and portable, but have been shown to be sensitive to small changes in temperature in the air tank induced by the changing air pressure. We have developed a simple and inexpensive modification to the design of transient‐flow air permeameters that improves both the accuracy and precision of the method. The apparatus was modified by the addition into the air tank of a heat capacitor, i.e., fiberglass insulation. The fiberglass insulation filling the tank acts as a uniformly distributed heat source‐sink (capacitor) and thereby dampens the temperature changes. Data from the near‐isothermal air tank design were compared with data from the standard air tank design and data from a method that uses the standard air tank design but measures both pressure and temperature simultaneously. An air permeability value determined with a steadystate flow method was used as a reference. The results show that nonisothermal air tank data can produce large inaccuracies relative to the steady‐state permeability. Applying a temperature correction to the nonisothermal air tank data improved the results considerably, but this method requires additional temperature and pressure measurements of extreme precision. The permeabilities produced with the “nearly isothermal” air tank closely matched the steady‐state values without having to apply any correction to the data. It is therefore recommended that the air tank of transient air permeameters be filled with a heat capacitor, such as fiberglass insulation.
Thermodynamics of Bromide Exchange on Ferrihydrite: Implications for Bromide Transport
Authors: Brooks S. C. , Jardine P. M. , Taylor D. L.
Published: July 2010

Because Br‐ is often assumed to be nonreactive with mineral surfaces, it is frequently employed as a tracer in transport experiments. We investigated the thermodynamics of Br‐‐Cl‐ exchange on the synthetic ferric oxide ferrihydrite [Fe5O7(OH)·4H2O]. Even with 475 times more Cl‐ than Br‐ in solution, sites on the ferrihydrite surface selectively adsorbed Br‐. The implications of these results for Br‐ transport were examined in a series of column flow experiments. During flow through columns packed with ferrihydrite‐coated silica, Br‐ retardation increased from 0.912 to 2.42 as the pH of column experiments decreased from 7.8 to 5. This behavior is consistent with the variable‐charge nature of ferrihydrite, which exhibits increasing positive surface charge below the pH of its zero point of charge (pHzpc ≈ 7.5). These results show that Br‐ can behave as a reactive tracer under certain circumstances, thus leading to erroneous estimates of transport parameters that rely solely on the use of Br‐ as a nonreactive solute.
Retention and Turnover of Corn Residue Carbon in Some Eastern Canadian Soils
Authors: Liang B. C. , Gregorich E. G. , Schnitzer M. , Monreal C. M. , MacKenzie A. F. , Voroney R. P. , Beyaert R. P.
Published: July 2010

Agricultural practices determine the level of soil organic C by influencing the amount of residue returned to, and retained by, soil. We conducted field experiments on four soils in Ontario and Quebec to test the hypothesis that short‐term changes in soil organic C and the proportion of corn (Zea mays L.)‐residue C retained in soils are affected by soil texture, fertility, and tillage management. We measured the amount of stover to estimate C input into the soils, and total soil C and 13C natural abundance to determine the soil C derived from corn residues. Only the sandy clay loam exhibited changes in total soil C, related to levels of fertilizer N and quantity of residues returned to the soil. The proportion of soil C derived from corn residues varied from 4 to 19%, depending on the time under continuous corn. Our data indicate a rapid increase in the proportion of cornderived C in the early stage of cropping to corn, but a markedly reduced rate of increase beyond 12 yr. Measured δ13C of archived samples of two soils with different clay contents (71 and 28% clay) but similar residue inputs (11 Mg stover ha‐1 yr‐1) indicated that the rate of increase in the proportion of corn‐derived C was higher in the soil with higher clay content (2.4 vs. 1.9% yr‐1). The results of this study are consistent with the hypothesis that the quantity of crop residue inputs and soil texture greatly influence the retention and turnover of crop residue C.
Parameter Uncertainty Analysis of Common Infiltration Models
Authors: Clausnitzer V. , Hopmans J. W. , Starr J. L.
Published: July 2010

Water infiltration is a driving force influencing crop growth, soil erosion, and chemical leaching processes. Knowledge of the relative precision and accuracy of infiltration models is needed for best characterization of the infiltration parameters. The two‐parameter Green‐Ampt and Philip, three‐parameter Horton, Mezencev, Swartzendruber, and Parlange et al., and four‐parameter Barry et al. infiltration models were compared for their precision and accuracy of estimated parameter confidence intervals using simulated infiltration reference data. To account for potential levels of uncertainty, three levels of measurement error were included using a Monte Carlo analysis. Reference data were generated for a clay and a sandy loam soil using an adaptive‐grid finite‐element code. Results show that extending the measurement period provided parameter estimates with higher confidence, a more precise estimate of that confidence, and better defined minima in the objective function. The empirical Horton model resulted in the worst fits due to model bias, which also prevented estimation of parameter uncertainty for this model. The semianalytical Swartzendruber and the physically based Parlange et al. and Barry et al. models provided the best fits. Considering all selected criteria, the Swartzendruber model was a reasonable compromise under the conditions imposed in this study.
Copper(II) Activity in Aged Suspensions of Goethite and Organic Matter
Authors: McBride M. , Martínez C. E. , Sauvé S.
Published: July 2010

Suspensions of natural organic matter and iron oxide (FeOOH) were equilibrated with a wide range of concentrations of added Cu2+ (50–5000 mg kg‐1) for as long as 400 d, in order to observe the time‐dependent solubility of the free Cu2+ ion. Adsorption was conducted at two pH ranges (5.0–5.5 and 6.5–7.0) and in the presence and absence of phosphate. The Cu2+ activity, measured by ion‐selective electrode, was one to two orders of magnitude lower for the organic systems at all Cu loadings investigated when the pH was near 5.5, indicating that the organic matter was a more effective adsorbent for Cu2+ than goethite. Longer reaction times generally caused the Cu2+ activities to decrease due to drifting pH and slow reactions. At higher pH, organic matter again resulted in lower Cu2+ activity than the oxide at all Cu loading levels, but the difference was generally less than at low pH. A downward pH trend in the organic system initially at pH 6.5 caused the Cu2+ activity to increase with longer reaction times. Most of the long‐term changes in Cu2+ activity could be attributed to shifting pH, although an aging effect on activity could be discerned. Phosphate added to the oxide or organic matter had little effect on the activity of Cu2+. The EDTA extracted a larger fraction of Cu2+ adsorbed on organic matter than on the oxide, suggesting that strong chelating agents selectively extract metals in quantities not directly related to activity or potential toxicity.
Bacterial Composition in the Rhizosphere of Nodulating and Non‐Nodulating Soybean
Authors: Cattelan A. J. , Hartel P. G. , Fuhrmann J. J.
Published: July 2010

Little is known about the particular species of bacteria that are favored for growth in the rhizosphere. Obtaining this information will facilitate a better understanding of root colonization and competitiveness of rhizosphere organisms. We used fatty acid methyl ester (FAME) analysis to identify bacteria in two different soils and in the rhizosphere of nodulating and non‐nodulating ‘Lee’ soybean [Glycine max (L.) Merr.]. In a light‐room experiment, bacterial isolates from each soil and soybean rhizosphere were selected at 3 (emergence), 6 (V1 stage) and 15 (V2–V3 stage) d after planting (DAP). Of 1131 bacterial isolates examined, 572 (50.6%) were identified. The majority of the identified isolates were Bacillus (324 isolates), Pseudomonas (121 isolates), and Arthrobacter (48 isolates). Of the 49 total bacterial species identified, 29 were detected in only one soil or the other. Numbers of Bacillus spp. were lower in the rhizosphere of nodulating and non‐nodulating soybean than in root‐free soil, and these lower numbers were usually offset by higher numbers of Gram‐negative bacteria, especially Pseudomonas spp. Principal components analysis showed a distinct clustering in each of the two soils. The percentages of isolates identified from each habitat, and the clusters derived from the FAME analysis, showed differences between soybean rhizosphere and root‐free soil and, to a lesser extent, between nodulating and non‐nodulating soybean rhizosphere. These results suggest that each soil offered specific populations of bacteria and from these populations, soybean roots favored growth of certain bacteria. To a lesser extent, this specificity was also apparent between nodulating and non‐nodulating soybean.
Climatic Effects on Soil Organic Phosphorus in the North American Great Plains Identified by Phosphorus‐31 Nuclear Magnetic Resonance
Authors: Sumann M. , Amelung W. , Haumaier L. , Zech W.
Published: July 2010

Considering the influence of the climate is important in studying the dynamics of P in soils. In this study, we investigated the effect of climate on the composition of organic P in uncultivated soils of the North American prairie. We present 31P nuclear magnetic resonance (NMR) spectra of alkaline extracts of bulk samples and clay fractions along gradients of mean annual temperature (MAT) and mean annual precipitation (MAP) across the Great Plains. Orthophosphate monoesters (monoester‐P) accounted for 32 to 71% and orthophosphate diesters (diester‐P) for 7 to 40% of the total signal intensity. Compared with bulk soils, diester‐P structures were enriched in the clay fractions (P < 0.01). In contrast, monoester‐P structures were enriched in particle‐size classes coarser than clay (P < 0.05). As MAT increased, the proportion of diester‐P increased, whereas that of monoester‐P decreased. These statistically significant correlations were more pronounced for both diester‐P (r = 0.91) and monoester‐P (r = −0.87) in the clay fractions than in the bulk soils. As MAP increased, the proportions of diester‐P also increased at the expense of monoester‐P. This correlation was more significant for bulk soils (r = 0.70 for diester‐P and r = −0.47 for monoester‐P) than for the clay fractions. We believe that temperature and precipitation strongly influence the organic P in North American grassland soils through their influence on microbial activity and plant production.
Cadmium Fixation in Soils Measured by Isotopic Dilution
Authors: Smolders E. , Brans K. , Földi A. , Merckx R.
Published: July 2010

There is conflicting evidence on the effect of time of contact between soil and Cd on Cd availability to plants. If Cd can be fixed in soil by aging, higher soil contamination may be tolerated. Fixation of Cd by soil can be studied by adding small quantities of 109Cd to the indigenous soil Cd. The ratio of 109Cd to indigenous Cd in soil extracts or in plants gives information on the lability of Cd in soil. This isotope exchange technique was used to measure the labile and fixed Cd fractions in 10 Belgian agricultural soils (Soils A‐I) with both background and elevated Cd content (0.33–6.5 mg Cd kg‐1). The isotopically exchangeable Cd pool (E value) was measured after equilibrating 109Cd spiked soil suspensions in CaCl2 0.01 M for 7 d. The %E values (the E value relative to aqua regia soluble Cd) ranged from 62 to 90% in the eight soils where %E values could be detected. The plant labile Cd pool, relative to aqua regia soluble Cd (%L value) was measured from the specific activities in wheat (Triticum aestivum L.) seedlings grown for 16 to 21 d on soils spiked with 109Cd. The Cd %L value varied from 55 to 109% (mean: 82%) with five soils having a significant (P < 0.05) fixed Cd fraction. Varying the soil incubation procedure after soil spiking and before plant growth marginally affected the specific activity of Cd in plants. The %L values always exceeded the respective %E value between 1.05‐ and 1.4‐fold. It is concluded that Cd fixation, where found, is not very pronounced.
Influence of Available Nitrogen and Rice Genotype on Associative Dinitrogen Fixation
Authors: Malarvizhi P. , Ladha J. K.
Published: July 2010

Rice (Oryza sativa L.) genotypes with a high ability to support biological N2 fixation are of interest because they would enhance N gains in the rice‐soil system without changing existing cultural practices. Pot experiments were conducted in a greenhouse during the 1994 wet season to determine the amount of N2 derived from the atmosphere (Ndfa) by 10 rice genotypes grown in three soils with varying levels of initial soil‐NH+4‐N. Enriched 15N and natural abundance δ15N dilution methods were employed. Flooded soils were puddled with and without 99.5 atom 15N%‐labeled urea to minimize spatial variation of the isotope. The integrated 15N enrichment of plant available N, calculated using a model that accounts for temporal changes in the isotopic composition, was used as a reference to estimate genotypic differences in Ndfa. The 15N enrichment of soil available N declined exponentially and was half the original level at 122 d. The δ15N values correlated with atom 15N% excess of enriched 15N for the rice genotypes grown in two out of three soils. Percentage Ndfa for the genotypes across three soils ranged from 4.2 to 32.2 when calculated using as a reference plant, and from 10.8 to 35.9 when calculated using 15N enrichment of soil available N as a reference. Genotypic differences were significant and more pronounced at low soil‐NH+4‐N (11 mg kg‐1) than at higher soil‐NH+4‐N (79 and 92 mg kg‐1); they ranged from 14.9 to 35.9% at low N and from 10.8 to 23.6% at high N. Some genotypes consistently gave either high or low Ndfa. Because of the low levels and narrow range of genetic differences in associative N2 fixation, the potential for its improvement through breeding appears to be limited.
Nitrogen Mineralization Responses to Cropping, Tillage, and Nitrogen Rate in the Northern Great Plains
Authors: Wienhold Brian J. , Halvorson Ardell D.
Published: July 2010

Nitrogen‐mineralization rates are needed to accurately determine N fertilization requirements to meet plant needs while minimizing environmental contamination. A spring wheat (Triticum aestivum L.)‐fallow (SW‐F) system was compared with a spring wheat‐winter wheat‐sunflower (Helianthus annuus L.) (SW‐WW‐SF) system on a Temvik‐Wilton silt loam (fine‐silty, mixed Typic and Pachic Haploborolls) at three N rates (0, 22, and 45 kg ha‐1 for SW‐F and 34, 67, and 101 kg ha‐1 for SW‐WW‐SF) under conventional, minimum, and no‐tillage. After 10 yr, soil samples were incubated to determine N‐mineralization rates. Cropping intensity, N rate, and tillage intensity interacted to affect N‐mineralization rates. Within the SW‐F system N‐mineralization rates in 0‐ to 0.05‐m depth were 8.2 ± 0.8 kg ha‐1 wk‐1 in the fallow phase vs. 5.0 ± 0.7 kg ha‐1 wk‐1 in the crop phase under conventional tillage and were 6.2 ± 0.3 kg ha‐1 wk‐1 under minimum and no‐tillage in both phases. The N‐mineralization rates were 2.3 ± 0.4 kg ha‐1 wk‐1 in 0.05‐ to 0.15‐m depth soils of the SW‐F system. In spring wheat, N‐mineralization rates in 0‐ to 0.05‐m depth soil were 9.9 ± 0.8 kg ha‐1 wk‐1 in the SW‐WW‐SF system vs. 5.6 ± 0.4 kg ha‐1 wk‐1 in the SW‐F system and in the 0.05‐ to 0.15‐m depth were 3.6 ± 0.1 kg ha‐1 wk‐1 in the SW‐WW‐SF system vs. 2.4 ± 0.2 kg ha‐1 wk‐1 in the SW‐F system Within the SW‐WW‐SF system, N‐mineralization rates in the 0‐ to 0.05‐m soil layer were 6.8 ± 0.5 kg ha‐1 wk‐1 under winter wheat vs. 9.9 ± 0.8 kg ha‐1 wk‐1 under spring wheat and 9.2 ± 0.6 kg ha‐1 wk‐1 under sunflower. In the 0.05‐ to 0.15‐m soil layer, N‐mineralization rates were 3.3 ± 1.0 kg ha‐1 wk‐1. More intensive cropping and conservation tillage increased N‐mineralization rates in this soil and may ameliorate the decline in N fertility associated with crop‐fallow systems.
Nutrient Supply Changes within a Growing Season in Two Deciduous Forest Soils
Authors: Kelly J. M. , Mays P. A.
Published: July 2010

Little information is available on how the indices of nutrient availability used in mechanistic nutrient uptake models might be influenced by the temperature at which the equilibrium soil solution (Cl) is extracted or how this parameter, and the solid‐phase nutrient concentration (Cs) might be altered by the progression of the growing season. Objectives of this study were to determine: (i) if the laboratory extraction temperature would influence Cl estimates, and (ii) the degree of change in Cl and Cs during the growing season. Soil samples were collected from two forest sites in eastern Tennessee in April, July, and October. Samples were returned to the laboratory and equilibrium soil solution concentrations of NO3‐N, NH4‐N, P, K, Ca, and Mg determined at the average soil temperature (11–18°C) or at laboratory temperature (24°C). Solid‐phase (Cs) concentrations were also determined and both values used to calculate the buffer power (b) and the effective diffusion coefficient (De). Extraction temperature did not alter Cl values. All solution nutrient concentrations except P declined by 16 to 99% after the July sample. Increases in P in the A horizon at one site were as high as 100%. Solid‐phase nutrient concentrations exhibited declines ranging from 6 to 91% while solid‐phase P concentrations increased by up to 40%. Disproportionate changes in the Cl and Cs values lead to changes in the calculated b and De estimates. Results indicate that efforts directed at establishing soil supply parameters needed for mechanistic nutrient uptake models should take into consideration changes that occur in solution and solid‐phase nutrient concentrations during the growing season.
Soil Carbon and Nutrients in a Coastal Oregon Douglas‐Fir Plantation with Red Alder
Authors: Cromack Kermit , Miller Richard E. , Anderson Harry W. , Helgerson Ole T. , Smith Robert B.
Published: July 2010

Carbon and nutrients in the forest floor and mineral soil were measured to determine amounts and variation among eighteen 0.081‐ha plots in a Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] plantation growing with volunteer red alder (Alnus rubra Bong.). Ten years earlier, the preceding mature conifer stand was clearcut and nearly all logging slash and forest floor were consumed by slash fire. Forest floor mass in the 9‐yr‐old plantation averaged 9.86 Mg ha‐1, with 3.71 Mg C, 98.0 kg N, 10.6 kg P, and 8.4 kg S ha‐1. Mineral soil to 1‐m depth averaged 176 Mg C, 8330 kg N, 3340 kg P, and 605 kg S ha‐1 in the <2‐mm fraction. The 2‐ to <6‐mm soil fraction averaged an additional 100 Mg C, 4480 kg N, and 1700 kg P ha‐1. Net mineralizable N as NH4 (anaerobic N mineralization index) totaled 99 kg N ha‐1 in the top 45 cm of the mineral soil and 62 kg N ha‐1 in the 45‐ to 100‐cm depth. Density fractionation showed that the light fraction (<1.65 Mg m‐3) was only 13.4% of the fine soil mass of the 0‐ to 15‐cm depth, yet contained about 40% of the total C and N capital in the <2‐mm size fraction. The substantial amounts of C and nutrients in this low‐bulk density soil (<2‐mm fraction, 0.30 Mg m‐3) indicate a fertile soil despite large previous losses of organic matter and N from the site.
Development of a Resonant Length Technique for Soil Water Content Measurement
Authors: Starr G. C. , Lowery B. , Cooley E. T. , Hart G. L.
Published: July 2010

Oven drying a soil sample of known volume is one of the few inexpensive methods for measuring volumetric water content (θv). Repetitive application of this technique to field soil sampling is a laborious, time‐consuming, and destructive process. Faster and less destructive low‐cost methods are needed in all branches of soil science. A technique has been developed that quickly determines θv by monitoring the reflected power amplitude with a parallel‐rod waveguide probe inserted into soil. Reflected power reaches a distinct minimum when a resonant condition is reached; at this point, the depth of insertion or resonant length (Lres) is measured and calibrated against θv. An inverse relationship is derived showing that Lres increases with decreasing water content. This measurement does not require a microprocessor, as do most time domain reflectometry (TDR) systems. Second‐order polynomials adequately describe the calibration curves between Lres and θv in three soils with coefficients of determination >0.99. Zone of influence varies with θv, but the range of Lres and θv may be tailored to experimental needs by varying the operational frequency or probe length. For a 30‐cm probe and 141‐MHz operating frequency, Lres varies from 1 to 6 cm with a θv range from 0.20 to 0.0 m3 m‐3. The need for calibration, water content range, and variable zone of influence could be disadvantages; thus, this technique is not a replacement for more complex and expensive methods, such as TDR.
In Situ Efficiency of Ion Exchange Resins in Studies of Nitrogen Transformation
Authors: Kjønaas O. Janne
Published: July 2010

Mixed‐bed ion‐exchange resin bags have previously been used in studies of soil N transformation rates with NH4‐N and NO3‐N being adsorbed from the solution percolating through the incubated soil core. An evaluation of the in situ adsorption efficiency of mixed‐bed resin bags was performed by comparing dissolved inorganic nitrogen (DIN, sum of NH4‐N + NO3‐N) accumulated in resins with DIN fluxes in throughfall (TF) and with DIN concentrations in soil water. A significant correlation was found between DIN fluxes in TF and accumulated DIN in resins placed at the soil surface (r2 = 0.92 for NO3‐N, r2 = 0.86 for NH4‐N, P < 0.001). The ratio of accumulated DIN in resins to DIN flux in TF was significantly affected by season. A low but significant correlation was found between NO3‐N concentrations in soil water and NO3‐N contents in resins deployed in the bottom of soil cylinders (r2 = 0.34, P < 0.01), however, when only the winter periods were taken into account, the correlation improved (r2 = 0.72, P < 0.001). As little water and few nutrients are removed from the soil water by the vegetation during the dormant season, the conditions inside and outside the core were more comparable. For NH4‐N there was no correlation between accumulated amounts in the resins and concentrations in soil water sampled at depths of 13 cm and 20 cm, respectively, probably due to the strong depth gradient in the NH4‐N concentrations of the soil. Although the resin bags were unable to adsorb all the incoming DIN, they gave valuable information on small‐scale inpnt of N and on small‐scale differences in NO3‐N leaching.
Arsenic Sorption in Phosphate‐Amended Soils during Flooding and Subsequent Aeration
Authors: Reynolds J. G. , Naylor D. V. , Fendorf S. E.
Published: July 2010

Phosphate enhances the mobility of As in well‐aerated soils by competing for adsorption sites. Phosphate and As may also coexist in large concentrations in hydric soils, and the influence of P on As in anaerobic systems is largely unknown. To determine the effects of P on As dynamics during a soil flooding and aeration cycle, samples of two soils were amended with Na2HAsO4 and Na2HPO4 and incubated under a N2 atmosphere for 41 d, and then reaerated for 7 d. Subsamples were collected intermittently and dissolved As, Fe, Mn, Ca, S, P, and H3AsO3 concentrations were determined. Arsenic speciation in the soil solids was determined after 14 and 41 d of flooding and then after 13 h of aeration by X‐ray absorption near edge structure (XANES) spectroscopy. Arsenic sorption was small under anaerobic conditions, and H2PO−4 additions enhanced As(V) reduction rate in both soils and slightly suppressed As sorption in one soil. Arsenopyrite (FeAsS) was identified in the soil solids. Rapid and simultaneous As sorption and Fe precipitation occurred during the first 0.25 d of aeration, suggesting that As was retained on freshly precipitated Fe (hydr)oxides. Manganese precipitation and concomitant As sorption occurred after 1 d of aeration. Arsenopyrite was largely destroyed upon aeration but As(III) persisted. Thus, As is partitioned into the solid phase under both aerobic and anaerobic conditions, although more appreciably under the aerobic conditions of this study, and P has little influence on dissolved As during soil flooding–aeration cycles.
Alfalfa Yield Response to Nitrogen Applied After Each Cutting
Authors: Raun W. R. , Johnson G. V. , Phillips S. B. , Thomason W. E. , Dennis J. L. , Cossey D. A.
Published: July 2010

Although alfalfa (Medicago sativa L.) usually obtains a high percentage of its required N via symbiotic N fixation, additional fertilizer N applied once in the spring can increase forage yields. However, little is known about alfalfa yield response to low N rates (<50 kg N ha−1) immediately following each cutting. Low N rates (immediately following each cutting) were evaluated for total alfalfa dry matter production on a Grant silt loam (fine‐silty, mixed, thermic, Udic Argiustoll). This nonirrigated experiment was initiated on a 2‐yr‐old alfalfa stand where sufficient P and K had been applied. Nitrogen rates of 11, 22, and 44 kg N ha−1 were applied immediately following each cutting for 5 yr (4–5 cuttings yr−1). After 5 yr of continuous N application, no differences in soil NH4–N or NO3–N were found at depths >15 cm (0‐ to 240‐cm sampling depth). In 1994, total alfalfa dry matter yield (sum of five harvests) increased 1.29 Mg ha−1 from a total annual N application of 110 kg N ha−1 (22 kg N ha−1 following each cutting). Total forage N decreased from the second to the fifth harvest in most years. By‐harvest dry matter yield increases due to applied N were only found in late‐season harvests, consistent with late‐season decreased N2‐fixing capacity in alfalfa documented by others.
Nitrate Concentrations in the Root Zone Estimated Using Time Domain Reflectometry
Authors: Das Bhabani S. , Wraith Jon M. , Inskeep William P.
Published: July 2010

Improved ability to monitor soil water and ionic chemical distributions in field soils will contribute to better land management opportunities. We evaluated the potential to use time domain reflectometry (TDR) to simultaneously estimate volumetric soil water content (θ), soil solution electrical conductivity (σw), and soil nitrate concentrations in an irrigated peppermint (Mintha piperita L.) field using simple models and calibration methods. Two models and three calibration approaches for estimating σw from TDR were compared to σw obtained from soil cores and soil solution samplers at three depths, and over a wide range in applied KNO3 The applied N rates were well within those commonly used in peppermint production. Soil nitrate concentrations were estimated based on TDR σw predictions and a simple linear calibration of σw vs. nitrate concentration and then compared to independent soil core measurements. Estimates of σw and nitrate concentrations using TDR exhibited similar pattern, magnitude, and variance to those based on direct soil measurements. The Mualem and Friedman (1991) model (MF), which is based on soil water retention measurements, provided σw and nitrate estimates in better agreement with soil cores than did the Rhoades et al. (1976) model. Our results suggest that simple physical–conceptual models combined with laboratory or field parameter estimation methods may be suitable for automated real‐time field monitoring.
Response of the Osmotic Tensiometer to Varying Temperatures Modeling and Experimental Validation
Authors: Biesheuvel P. Maarten , Raangs Ron , Verweij Henk
Published: July 2010

In an osmotic tensiometer, the hydrostatic pressure of a confined polymer solution is measured to infer the soil water potential. Essential in the operation is the osmotic potential of the polymer solution. Because the osmotic potential depends on the temperature, a significant and undesired pressure lag may develop when the osmotic tensiometer is used under conditions of varying temperature. To understand and eliminate the pressure lag, a dynamic transport model was derived that describes the time response of the osmotic tensiometer while assuming complete temperature equilibration and a resistance to water transfer that is fully located within the filter. Essential elements of the model are the filter conductance and the sensitivity of the pressure transducer, for which submodels are set up. The transport model is validated with measurements on an osmotic tensiometer that uses an inorganic membrane as filter. The experiments were done for instrument‐limited conditions by placing the osmotic tensiometer in free water. For these conditions, the model describes measurements with reasonable accuracy. The new transport model clarifies the behavior of the osmotic tensiometer for changing temperatures and can be used to design an osmotic tensiometer with a lower pressure lag.
Estimation of Soil Evaporation Using the Differential Temperature Method
Authors: Qiu Guo Yu , Ben-Asher J. , Yano T. , Momii K.
Published: July 2010

Evaporation of soil water is a major water balance component during early growth stages of irrigated field crops, row crops with incomplete cover, and in soils with high water table. Quantification of soil evaporation can help in environmental and irrigation management. The objective is to develop a new method to estimate daily soil evaporation using differential measurements of temperature. A major advantage of this approach is that measurements of sensible heat flux can be replaced by those of surface temperature. An empirical coefficient was determined from integrated energy fluxes over daytime hours and mean daytime temperatures. It leads to a new soil evaporation transfer coefficient that can replace the aerodynamic resistance to calculate sensible heat flux. Experiments were conducted in a field with sandy soil that was irrigated with sprinklers and included a weighing lysimeter to measure actual evaporation. Measurements were of net radiation, soil heat flux over a wet and a reference air‐dried soil, and air and surface temperatures of both soils. Regression between modeled and actual evaporation on a daily basis produced a slope of 1.05 and r2 = 0.9. Thirty days of cumulative model evaporation exceeded the measurements by 5%. The proposed coefficient can theoretically vary from 0 for wet soil to 1 for dry soil and can thus provide limits between 0 and potential evaporation. Actually, the coefficient increased from 0.2 to 0.8 in wet soil and from 0.8 to 1.0 in dry soil. The soil evaporation transfer coefficient was easy to measure, and it was sufficiently stable to adequately estimate soil evaporation.