bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Aluminum Complexation in Multiple Ligand Systems
Authors: Anderson Michael A. , Bertsch Paul M.
Published: July 2010

The role of complexing ligands in attenuating aluminum (Al) toxicity and in influencing Al transport in soils and waters has been recognized for some time though the kinetics of such complexation reactions within complicated multi‐ligand aqueous solutions have not been previously evaluated. As a result, this study was undertaken to examine the dynamics of Al complexation in the presence of multiple ligands, specifically fluoride (F), oxalate (Ox), and citrate (Cit), utilizing an ion chromatographic speciation method. The rate constant for formation (kf) of AlF2+ under the experimental conditions used in this investigation was found to be 12.3 ± 1.1 M−1s−1 in the absence of competing ligands, but was observed to increase to 23.4 ± 0.6 and 52.0 ± 5.7 M−1s−1 in the presence of Ox and Cit, respectively. The rate of formation of the AlOx+ complex was more rapid than that of AlF2+ (kf ≃ 100 M−1s−1) and was unaffected by the presence of F. Citrate complexed with Al sufficiently rapid that kf could not be determined. That kf for AlF2+ increased in the presence of competing ligands contradicts the accepted dogma on the kinetics of concurrent reactions, where reactions are envisioned to proceed independently and in relative isolation. This aberrance can be explained by one of two possible mechanisms: (i) the rapidly complexing Ox and Cit form reduced charge Al‐species with resultant increased rates of water exchange (k); the increased kH2O exceeds the reduction in the extent of outer sphere Al‐F association, thus creating a condition favorable for inner sphere penetration of F through displacement of a coordinated water molecule with ejection of inner sphere Ox or Cit; or (ii) F may exchange directly with inner sphere Ox or Cit, perhaps through HF. Additionally, AlCit formation in the presence of F was found to exceed the thermodynamically imposed equilibrium level and necessarily reequilibrated to a lower solution concentration as the slower Al‐F complexation reaction proceeded, though no such behavior was witnessed for AlOx+ formation in the presence of F.
Effects of Terpenoids on Nitrification in Soil
Authors: Bremner J. M. , McCarty G. W.
Published: July 2010

It has recently been hypothesized that vegetation in ponderosa pine (Pinus ponderosa Dougl.) ecosystems inhibits nitrification in these systems by releasing volatile terpenoids that retard oxidation of NH+4 by nitrifying microorganisms. This hypothesis is based largely on observations that exposure of a ponderosa pine ecosystem to fire decreased the amount of volatile organic compounds and stimulated production of NH+4 and NO−3 in the forest floor and that exposure of soil samples to vapors from a terpenoid mixture decreased production of NH+4 and NO−3 by mineralization of organic N in these samples. To test the validity of this hypothesis, we studied the effects of different amounts of six terpenoids (α‐terpinene, limonene, myrcene, α‐pinene, β‐pinene, and α‐phellandrene) on nitrification in soils incubated at 25 °C after treatment with (NH4)2SO4. The results showed that the terpenoids studied did not significantly affect nitrification in soil even when the amounts applied greatly exceeded the amounts that have been reported to occur in soil. They also indicated that the apparent inhibition of nitrification observed when soils were exposed to terpenoid vapors was due to immobilization of ammonium N by microbial activity stimulated by the organic C in these vapors.
Controls on Natural Nitrogen‐15 and Carbon‐13 Abundances in Forest Soil Organic Matter
Authors: Natelhoffer K. J. , Fry B.
Published: July 2010

We used δ15N and δ13C measurements to study formation and decay of soil organic matter in surface soils of two oak (Quercus spp.) forests in Wisconsin. There were two controls of soil isotopic compositions: new litter inputs and overall isotopic fractionation during decomposition. Litter inputs lowered soil δ15N and δ13C values while decomposition increased δ15N and δ13C values. Leaf and root litter inputs averaged −3.8 and −1.6‰ δ15N and −27.3 and −28.2‰ δ13C, respectively. Field experiments showed that low surface soil δ15N and δ13C values resulted when litter inputs were high. Laboratory experiments showed that overall isotopic fractionation during decomposition left residual soil N and C enriched in 15N and 13C, and could explain the high δ15N and δ13C values observed in deeper forest soils (+5.9‰ δ15N and −23.6‰ δ13C for 10 to 20 cm soils). Our results suggest two pools of naturally labeled N in forest soils: surface N with low δ15N values and subsoil N with high δ15N values. Natural abundance measurements of soil N may be useful for following the importance of these two N pools in forest N cycles. We found no evidence for selective preservation of 13C depleted litter components, such as lignin, during long‐term decomposition in forest soils.
Comparison of Percolation Test Results and Estimated Hydraulic Conductivities for Mollisols and Alfisols
Authors: Bicki Thomas J. , Fenton Thomas E. , Luce Harvey D. , Dewitt Thomas A.
Published: July 2010

Percolation tests were performed on an array of biosequences, topo‐drainage sequences, and stage of profile development sequences of soils in Iowa and results were compared to estimated subsoil hydraulic conductivities from Soil Interpretation Records. Within a biosequence, Mollisols had higher percolation rates and lower coefficients of variation than Alfisols. The difference in permeability was attributed to higher subsoil clay content, higher subsoil bulk density, more continuous argillans, and stronger subsoil consistence in Alfisols. High coefficients of variation for percolation rates in Alfisols were attributed to large diameter root channels, lateral flow of water on sloping sites, and increased distinctness of subsoil horizon boundaries. Percolation rates of Mollisols commonly exceed Soil Interpretation Records' estimates of hydraulic conductivity by a factor of two or three while percolation rates of Alfisols approximate estimated subsoil hydraulic conductivity. In soils without argillic horizons, percolation test results of topo‐drainage sequences are similar and reflect similar morphological characteristics. Soil Interpretation Records assign slower estimated hydraulic conductivity to some topo‐drainage sequences as drainage becomes more restrictive. Percolation rates decreased in topo‐drainage sequences of soils with argillic horizons as drainage became more restrictive, even though morphological characteristics were quite similar. Differences in percolation rates within topo‐drainage sequences may reflect errors inherent in the procedure. Additional permeability data is needed to quantify and more accurately estimate subsoil hydraulic conductivity. Criteria used to establish estimated hydraulic conductivity in Soil Interpretation Records should be applied consistently among biosequences and topo‐drainage sequences.
Estimating Confidence Bands for Soil‐Crop Simulation Models
Authors: Shaffer M. J.
Published: July 2010

A general method is described that provides confidence bands for the ouput from soil‐crop simulation models. Stochastic data are generated for model inputs and model coefficients. These data reproduce the statistical characteristics of the climate, soil properties, and internal model coefficients including distributions, temporal, spacial and variable cross correlations, means, and standard deviations. Model output based on these inputs is then analyzed to produce means, standard deviations, and confidence bands. A typical application of the method is illustrated using a stochastic model for soils input data together with the nitrogen‐tillage‐residue management (NTRM) simulation model to generate confidence bands for soil NO3‐N profiles in Houston County, MN. Results indicate that 380 to 1800+ computer runs may be required to provide confidence bands for soil NO3‐N concentrations that are within 10% of the means, and that use of singular mean input data sets in a nonlinear model such as NTRM can produce deviations in the simulated results ranging from 0.7 to 101% of the mean output obtained from many runs.
Nature of Cementing Materials in Ortstein Horizons of Selected Florida Spodosols: II. Soil Properties and Chemical Form(s) of Aluminum
Authors: Lee F. Y. , Yuan T. L. , Carlisle V. W.
Published: July 2010

Possible differences in soil characteristics between ortstein and nonortstein Spodosols were studied. Organic C, fine particles (silt plus clay), and extractable Al by dithionite‐citrate, pyrophosphate, acid NH4 oxalate, and NaOH were all higher in Bh than other horizons, except silt plus clay contents in Btg horizons of the St. Lucie County soils. While dithionite‐citrate‐extractable Si was higher at the surface, larger amounts of Fe seemed to occur in lower horizons. Both contents were much lower than extractable Al with the exception of Si in the A and E horizons. Quartz, gibbsite, kaolinite, and hydroxy‐Al interlayered vermiculite were dominant clay‐size minerals. In general, no consistent differences were found in soil properties between the paired ortstein and nonortstein Spodosols except that the ortstein horizons contained more clay and more extractable Al. The cementing materials were shown to dissolve in reagents commonly used for Al and Fe extractions. The dithionite‐citrate reagent was the most effective extractant. The amounts of extractable Al and Fe by dithionite‐citrate, acidic oxalate, and NaOH were small after the ortstein samples were treated with pyrophosphate. These findings suggested that Al in the cementing materials was likely in organic complex form. Ratios of pyrophosphate‐extractable Al to oxalate‐extractable Al and the percentage of maximum Al‐organic complexes supported this assumption. Higher fulvic‐C contents and higher fulvic‐C to humic‐C ratios in ortstein than in nonortstein spodic horizons indicated the complex probably was an Al‐fulvate form.
Effect of Clay Charge Density and Adsorbed Ions on the Rheology of Montmorillonite Suspension
Authors: Keren R.
Published: July 2010

The rheological characteristics of montmorillonite suspension as a function of exchangeable sodium percentage (ESP), (when the complementary cation is either Ca2+ or Mg2+) and specific electrostatic charge density were studied in aqueous media at a clay concentration of 25 g kg−1, at pH 7 and temperature of 25 °C. The suspension showed a Newtonian rheology when the clay was saturated by either Ca2+ or Mg2+, but the differential viscosity (the derivative of shear stress with respect to shear rate at a given shear rate) of Mg‐clay (2.3 mPa s) was higher than that of Ca‐clay (1.5 mPa s). The higher value for the Mg‐clay suspension is due to the smaller average number of platelets in a tactoid of Mg‐montmorillonite than in the Ca‐montmorillonite suspensions. Introducing Na+ at a low percentage (10%) into the exchange complex of Mg tactoid was enough to break down some of the tactoids to smaller ones, whereas the Ca tactoids remained stable. The differential viscosity at high shear stresses increases with increases in ESP, showing higher values for Na/Mg systems at a low ESP range. At higher ESPs, no difference in differential viscosity between Ca and Mg systems was observed. The higher extrapolated shear stress values for Na/Mg‐montmorillonite suspensions suggest that the number of linkages between clay particles per unit weight of clay is higher than that found in Na/Ca‐montmorillonite for the same ESP and clay concentrations. The differential viscosity and the extrapolated shear stress values for the various smectites (the electric charge density varied between 0.91 and 1.22 molc kg−1) suggest that the extent of particle‐particle interaction in clay suspension decreases with increases in electrostatic charge density of smectites.
A Computer Simulation of Fe(III) and Fe(II) Complexation in Limited Nutrient Solution: I. Program Development and Testing
Authors: Schwab A. P. , Lindsay W. L.
Published: July 2010

The mechanism by which Fe‐stressed roots increase Fe availability was determined with the assistance of a computer model (written in PASCAL) that predicted the effects of redox and pH on the stability of Fe chelates. The program solves a series of simultaneous equilibrium equations to calculate the concentrations of all species in a nutrient solution containing Fe, Ca, and two competing chelating agents as a function of pH and redox potential. Experimental data were used to test the model. Model calculations based on results published by other investigators supported the theory that Fe‐deficient soybean [Glycine max (L.) Merr.] plants have the ability to lower the redox potential near their roots. It also showed that this phenomenon is the primary means by which iron‐stressed plants are able to increase the availability of Fe. The redox potential of a nutrient solution at pH 5 must be below pe + pH 7 to account for observed trends in the stability of ferric chelates and the availability of Fe to soybean.
Calcium‐Magnesium Exchange Selectivity of Wyoming Montmorillonite in Chloride, Sulfate and Perchlorate Solutions
Authors: Suarez D. L. , Zahow M. F.
Published: July 2010

The need to consider CaCl+ and MgCl+ complexes in Ca‐Mg exchange reactions on montmorillonite was evaluated by examining cation selectivity in various anion backgrounds. The Ca‐Mg exchange isotherms on SWy‐1 Wyoming bentonite were determined in 0.0125 M SO4, 0.025, 0.050, and 0.100 M Cl and 0.03 M perchlorate background. Calculated selectivity values for the reaction Ca2+ + MgX ⇌ Mg2+ + CaX were Kv = 1.15, 1.11 and 1.10 for the SO4, Cl and perchlorate media, respectively. There was no trend in Kv, with exchangeable Ca with any anion or with ionic strength in Cl media. The Ca preference in SO4 and perchlorate media indicates that montmorillonite preference for Ca is not an artifact of complexation in Cl media. These Kv values are also consistent with earlier published Ca‐Mg selectivity of the same clay in perchlorate media. The CaCl+ and MgCl+ complexes comprised an insignificant amount of the exchangeable cations.
Calcium and Sulfate Retention by Two Oxisols of the Brazilian Cerrado
Authors: Marcano‐Martinez E. , McBride M. B.
Published: July 2010

The ability of two representative oxisols from the Cerrado region of Brazil to adsorb Ca2+ and SO2‐4, when in their natural acidic state, was determined by using dissolved CaCl2, K2SO4 and CaSO4 salts as adsorbates. Calcium adsorption from CaCl2 and CaSO4 was nearly linearly dependent on the equilibrium Ca2+ concentration, and was most successfully fitted to a Freundlich equation. Conversely, sulfate adsorption from K2SO4 and CaSO4 was curvilinearly dependent on equilibrium SO2‐4 concentration, conforming more closely to Langmuir adsorption behavior. Calcium adsorption was explained by nonspecific electrostatic attraction to soil clays, and did not appear to be adsorbed to any significant degree by the native organic matter. Sulfate adsorption was attributed at least in part to a ligand exchange mechanism, resulting in a measured increase in the negative charge of the soil surfaces. Simultaneous adsorption of Ca2+ and SO2‐4 from CaSO4 solutions caused an enhancement in retention of both ions at higher concentrations, despite undersaturation with respect to gypsum precipitation. A mechanism of CaSO04 ion pair adsorption on mineral surfaces is proposed in which the presence of one ion facilitates adsorption of the other.
Predicting Rates of Wheat Residue Decomposition
Authors: Stroo H. F. , Bristow K. L. , Elliott L. F. , Papendick R. I. , Campbell G. S.
Published: July 2010

Predicting the rate and extent of decomposition of residues at the soil surface is necessary to evaluate the impacts of minimum‐tillage practices on erosion control and thus ensure the most effective use of residues. A mechanistic model simulating the decomposition of surface‐managed winter wheat residues was developed and model predictions were compared to results from field studies of decomposition rates. The model consists of two submodels. The first simulates decomposition of the various components of wheat residues (straw, leaves, and chaff) under constant conditions. This submodel requires input on the N content of the residue, and is based on results of laboratory experiments in which respiration was measured. The second submodel uses meteorological data to simulate environmental conditions in the residue layer. This information is combined with laboratory derived estimates of the effects of temperature and moisture to calculate the cumulative decomposition days. To apply the model to field situations, the relationships between respiration and mass loss were estimated experimentally. The effects of added microarthropods and nematodes were also measured, but no effects on respiration were observed in either case. Model predictions agreed well with data from field experiments in which bundled straw was used, but decomposition of straw in litter bags was slower than predicted. When grab samples were used to measure the loss of residues containing leaves, chaff, and straw, the model performed well even across climatic regions until early summer (32–36 wk after residue placement in the field), when residues began to disappear more rapidly than predicted.
Geomorphic Age and Genesis of Some San Luis Valley, Colorado, Soils
Authors: Nettleton W. D. , Brasher B. R. , Yenter J. M. , Priest T. W.
Published: July 2010

San Luis Valley is a semibolson in south central Colorado that has varying geomorphic and soil properties. Three sets of geomorphic surfaces were identified corresponding to young, intermediate, and old surfaces. A 14C date of 11 170 YBP on a peat deposit on the valley floor was used to separate Holocene geomorphic surfaces (Set 1) from late‐Pleistocene ones (Set 2). The oldest‐Pleistocene surfaces (Set 3) studied are believed to be Illinoian in age. They are above the late‐Pleistocene age valley floor and are more dissected than the other Pleistocene surfaces. Entisols have formed on the Holocene surfaces (Set 1). These Entisols have some accumulation of organic C and movement of carbonate, but none have calcic horizons. Their sand grains lack clay cutans or other evidence of soil formation. Most of the soils on late‐Pleistocene geomorphic surfaces (Set 2) have argillic and calcic horizons, and some have mollic epipedons. Grain argillans on sands are the most common form of illuvial clay and there are calcans in the calcic horizons. Some of the soils have natric horizons. The soils on mid‐Pleistocene geomorphic surfaces (Set 3) have a greater clay accumulation than any of the other soils and have calcic horizons. Clay accumulation is largely masked by the carbonate accumulation. The distribution of salt for the most part is in balance with today's arid climate in the valley. The occurrence of carbonate in horizons with illuvial clay, especially in the soils on the oldest surfaces, suggests an arid climate following one or more Pleistocene pluvials. Some of the salt and carbonate may have been added as dust from playas on the valley floor.
A Re‐Examination of Alternative Test Procedures for Soil Consistency Limit Determination: I. A Compression‐Based Procedure
Authors: McBride R. A. , Bober M. L.
Published: July 2010

A static uniaxial (drained) compression test procedure using effectively saturated, remoulded soil samples is proposed which unifies soil consistency limit determination procedurally under similar experimental conditions. It yields numerically comparative (r2 = 0.786–0.931), rather than only correlative, indices of the upper and lower limits of soil plasticity while providing ancillary information on the effective stress regime when in these states of consistency. For the 44 soil horizon samples used in this study, apparent equivalent stresses at the Atterberg consistency limits ranged from 0.26 to 1.84 MPa for the lower plastic limit and 3.9 to 268 kPa for the upper plastic limit. Clay and organic matter contents had a significant influence on defining these equivalent static loadings. Organic matter was further shown to expand the range of moisture contents representative of the semisolid consistency state while constricting the plastic range. Potential areas for improvement in the procedures are discussed.
A Re‐Examination of Alternative Test Procedures for Soil Consistency Limit Determination: II. A Simulated Desorption Procedure
Authors: McBride R. A.
Published: July 2010

A soil water retention model was used to simulate a desorption procedure for Atterberg consistency limit determination (i) to test the validity for Ontario soils of this procedural alternative to the A.S.T.M. standard methods in light of past research efforts, and (ii) to allow for the assessment of soil plasticity and related soil qualities for soil inventory interpretive purposes with only a minimum of soil physical data. From a remoulded and effectively saturated initial condition, the upper and lower plastic limits of the 290 soil horizons investigated were generally found to occur at the upper and lower flex points, respectively, of the estimated moisture retention curve. The presumed absolute equivalence of the effective normal stress required to bring soils to their respective Atterberg consistency limit moisture contents in a compression‐based test procedure with the negative pore water pressure potential at the estimated moisture characteristic flex points was corroborated. The observed tendency to underestimate the A.S.T.M. lower plastic limit of low clay content (marginally plastic) soils was attributed to procedural limitations in the A.S.T.M. standard methods which set the lower moisture content limit of plasticity of such soils unrealistically high. Clay and organic matter contents influenced both the effectively saturated gravimetric moisture content attained by free swelling soils in a remoulded condition and the pore water pressure potential at the lower plastic limit. Only clay content was a significant factor in explaining variations in pressure potential at the upper plastic limit with soil texture.
Modeling of Wheat Imbibition and Germination as Influenced by Soil Physical Properties
Authors: Bouaziz A. , Bruckler L.
Published: July 2010

A theoretical model that was used previously for predicting maize (Zea mays L.) seed imbibition, and subsequently, germination, is applied to wheat (Triticum aestivum L.) seeds. The proposed model takes into account the seed‐soil water movements in both liquid and vapor phases under nonlimiting aeration conditions. The main variables that govern the imbibition process are (i) the seed‐soil water potential difference, (ii) the seed contact area as affected by vapor or liquid transfers, and (iii) conductive properties of the seed for both liquid and vapor phases. Laboratory experiments show that (i) the imbibition process occurs both in liquid and vapor phases, (ii) wheat seed must reach a critical moisture content before germination (0.27 kg kg−1 approximately), and (iii) the rate of the imbibition depends upon the seed surface area affected by liquid or vapor transfers and on the water potential of the external medium that governs the ability of the seed to reach its critical moisture content. The proposed model is regarded as satisfactory after calibration of the seed conductive properties in liquid and vapor phases. Field experiments involved irrigated and nonirrigated treatments (31.7% clay, 42.5% loam, 25.8% sand) and manual or mechanical sowing. Moisture content, bulk density profiles, and soil porosity analyses were used to estimate the seed‐soil contact area. The previous imbibition model was applied to field experiments, combining field data with the laboratory results. This model accurately predicted wheat imbibition and germination. Finally, simulated results compared the effects of climatic conditions and sowing techniques on wheat germination for three climatic sequences. Climate was the major limiting factor illustrating the importance of selecting the suitable sowing techniques to optimize the seed imbibition and germination processes.
Influence of Topsoil Removal and Fertilizer Application on Spring Wheat Yields
Authors: Tanaka D. L. , Aase J. K.
Published: July 2010

Topsoil loss by wind and water erosion has reduced crop productivity and created soil management problems. Crop yield‐soil loss relationships vary, depending on soil, climate, crop, and management practices. The purpose of this study was to determine the relationships among surface soil removal and additions of nitrogen (N) and phosphorus (P) fertilizer on spring wheat yields and yield components. Soil was mechanically removed from the surface of a Williams loam (fine‐loamy mixed, Typic Argiboroll) to 0.00‐, 0.06‐, 0.12‐, and 0.18‐m depths in a spring wheat (Triticum aestivum L.)‐fallow rotation. Three levels of N (0, 35, and 70 kg ha−1) and three levels of P (0, 20, and 40 kg ha−1) were applied in all combinations to each soil removal treatment prior to seeding a spring wheat crop. In 3 of 5 years, soil removal treatments reduced spring wheat yields an average of 9, 28, and 45% for 0.06‐, 0.12‐ and 0.18‐m soil removal treatments, respectively, when averaged over all fertilizer treatments compared to 0.00‐m soil removal treatment. The other 2 years were water limiting and soil removal treatments were not a factor. Application of 20 and 40 kg ha−1 of P fertilizer increased grain yields 75 to 400 kg ha−1 with yield increase associated with an increase in heads m−2 and kernels head−1. Phosphorus application tended to decrease grain N concentration because grain yields were increased which caused a dilution in grain N concentrations. Application of 35 and 70 kg ha−1 of N, in combination with either 20 or 40 kg ha−1 of P, resulted in greater grain yield increases when compared to N application without P. Generally 70 kg ha−1 of N and 20 kg ha−1 of P increased grain yields on 0.06‐, 0.12‐, and 0.18‐m soil removal treatments to at least the same yield as 0.00‐m soil removal treatment without N or P fertilizer. These data suggest P was the most limiting nutrient and additions of N fertilizer without P resulted in small yield increases.
Effect of Polysaccharides, Clay Dispersion, and Impact Energy on Water Infiltration
Authors: Ben‐Hur M. , Letey J.
Published: July 2010

Effects of clay dispersion, impact energy of water drops, and chemical amendments on crust formation and infiltration rate (IR) of Haplic Durixeralf soil were studied using a sprinkler infiltrometer. The soil was subjected to two impact energies, high energy = 240 J m−2 h−1 and low energy = 0, and to three waters: (i) distilled water [DW, electrical conductivity (EC) < 0.05 dS m−1], (ii) saline water (SW, EC = 5.0 dS m−1), and (iii) regular water (RW, EC = 1.0 dS m−1). The chemical amendments, polysaccharides, guar derivatives were supplied with the DW and RW and with high impact energy. Crust formation by the impact energy was found as a dominant factor in the IR reduction. This factor reduced the total soil infiltration capacity by more than 40%. Conversely, clay dispersion in the soil surface reduced the total soil infiltration capacity by 24%. Likewise, it was found that clay dispersion in the soil surface decreased the hydraulic conductivity of the crust and sharply increased its hydraulic resistance. The polymers had an amendatory effect on the IR. The polymers apparently adsorbed on the particle surfaces and acted as a cementing material holding primary particles together against the destructive forces of the water drops. The order of the maximum effect of the chemical amendments (0.01 kg m−3), that were supplied in DW, on the maintenance of IR was: high charge cationic polymer (HCCP) > low charge cationic polymer (LCCP) ≫ nonionic polymer > anionic polymer (had no effect). A concentration of 0.01 kg m−3 of HCCP and LCCP in RW prevented crust formation and preserved the high initial IR of the soil throughout the water application period. The HCCP and LCCP under sprinkled DW and RW conditions apparently adsorbed at the soil surface and did not move with the water into the soil layer.
Effect of Subsoiling on Yield and Quality of Corn and Potato at Two Irrigation Frequencies
Authors: Ibrahim B. A. , Miller D. E.
Published: July 2010

High strength soil layers within a rooting zone restrict rooting and reduce the supply of water and nutrients to plants. Frequent irrigation may be required to prevent plant water stress. Studies were conducted in 1983, 1984, and 1985 to evaluate the yield responses of potato (Solanum tuberosum L.) and field corn (Zea mays L.) to subsoiling and sprinkler irrigation frequency on Warden loam (coarse‐silty, mixed, mesic Xerollic Camborthids) and Quincy sand (mixed, mesic Xeric Torripsamments) soils. Leaf water potential, stomatal resistance, and canopy temperature were measured. On the loam soil, yield and % U.S. no. 1 potato tubers responded positively to subsoiling with biweekly irrigation but not with weekly irrigation. Corn silage yields were increased by subsoiling with both irrigation regimes but grain yields were not. Plants growing on subsoiled sand and irrigated every 4 d were stressed less than plants grown without subsoiling. With this irrigation regime total tuber yield, % U.S. no. 1 tubers, and corn grain yields were increased by subsoiling. Benefits from subsoiling were relatively unimportant for either crop or soil if irrigation was adequate.
Nitrogen Placement Evaluation for Winter Wheat in Three Fallow Tillage Systems
Authors: Varvel G. E. , Havlin J. L. , Peterson T. A.
Published: July 2010

Increased soil water storage with increasing amounts of surface residue in winter wheat (Triticum aestivum. L.)—fallow cropping systems has not consistently resulted in higher grain yields in the Great Plains. Earlier results had suggested increased amounts of surface residue may increase N immobilization and limit N availability, thereby reducing potential for use of the additional stored soil water. This study was conducted to determine if N placement below the zone of organic matter or surface residue accumulation would reduce N immobilization and increase yields. The effects of N placement were evaluated by surface broadcasting and injecting below the soil surface 15N depleted NH4NO3 at 45 kg ha−1 in no‐till, stubble mulch, and plow fallow method systems on an Alliance silt loam (fine‐silty, mixed mesic Aridic Argiustolls) in a long‐term study in western Nebraska. Dry matter and grain yield, N concentration, N uptake, 15N concentration, 15N uptake, and fertilizer recovery in plant tissue were determined for fallow method and N placement during the 1985, 1986, and 1987 growing seasons. Dry matter and grain yield, N concentration, N uptake, 15N uptake, and fertilizer recovery were all significantly affected by fallow method during all 3 yr of the study, being highest in plow and lowest in no‐till with stubble mulch values intermediate. Nitrogen placement, however, had no effect on any of the variables in any of the tillage systems. In this environment, N immobilization does not appear to be a factor limiting use of additional stored soil water in reduced tillage systems because fertilizer recovery was equal for both placement methods in all three tillage systems.
Soil NO3‐N Analysis in CA(OH)2 Extracts by the Chromotropic Acid Method
Authors: Haby V. A.
Published: July 2010

Methodology and instrumentation improvements have contributed to the increased use of nitrate‐nitrogen (NO3‐N) analysis of soil extracts for predicting crop N requirements. This research was conducted to determine the accuracy of the modified chromotropic acid (CTA) procedure for NO3‐N in saturated Ca(OH)2 extracts of soils. Sixty‐two soil sample extracts were analyzed for NO3‐N by the CTA method modified to eliminate oxidizing agents, NO‐2, and possible interferences from CI‐ and Fe. Results were compared with the same samples extracted and analyzed by use of the phenoldisulfonic acid method (PDSA). Comparison indicated the two methods were in close agreement (slope = 0.92 and r2 = 0.94). The graph of CTA NO3‐N concentration vs. absorbance at 410 nm followed Beer's Law. The modified CTA method, combined with Ca(OH)2 extraction of soil NO3‐N, is described in detail and presented as a standard.
Predicting Oil Infiltration and Redistribution in Unsaturated Soils
Authors: Cary J. W. , Simmons C. S. , McBride J. F.
Published: July 2010

The infiltration and redistribution of two viscous hydrocarbon oils, with viscosities 4.7 and 77 times greater than water, were observed in columns of moist silt loam and loamy sand soils. The time required for water and oil to infiltrate the two soils and the final volumetric liquid contents after 8 h were measured. These observations are compared to the results predicted by a simple multiphase flow code based on scaling oil flow to unsaturated soil‐water flow by using classical capillary theory and relative viscosities. A new function for describing the oil permeability was derived and, when used in the code, produced oil content distributions with depth that agreed reasonably well with those observed. The actual oil infiltration time was generally less than predicted, however. The flow of the two organic liquids into moist soils was found to be predictable, based only on classical soil‐water relations and the organic liquids' physical properties, under the imposed experimental conditions.
Effect of Low Electrolyte Concentration on Hydraulic Conductivity of Clay‐Sand‐Hydroxy Polymers Systems
Authors: Keren R. , Singer M. J.
Published: July 2010

Iron and Al oxides are ubiquitous in soils and have profound affects on soil structure. The objectives of this study were to (i) determine the effect of Fe‐ or Al‐polymers on saturated hydraulic conductivity (HC) of smectite‐sand mixtures at different percentages of the clay cation exchange capacity (CEC) at different sodium adsorption ratios (SAR) and solution electrical conductance (EC), and (ii) determine the reason for the observed effect. The HC of 5% smectite, 95% acid washed quartz sand (0.1 to 0.5‐mm diam.) with and without polymer additions was determined by leaching with SAR 5, 10, or 20 and EC 500, 100, 50, 10, 5, 3, 2, 1 solutions, and distilled water (DW) at pH 7.5. The HC of clay leached with SAR 5 solution decreased with a reduction in solution concentration from 500 to 1 molcm−3, after which clay was leached from the system and HC increased. No clay was leached from the column in the presence of hydroxy‐Al polymers in excess of 25% of clay CEC. Little HC reduction occurred at SAR 10 in the presence of hydroxy‐Al polymers. At SAR 20, HC of the clay‐sand mixtures decreased greatly, but no clay was observed in the leachate. Hydroxy‐Fe polymers produced similar effects, but to a lesser extent. The presence of hydroxy‐Fe polymers equivalent to 50% of CEC was insufficient to prevent clay dispersion and removal from the column when SAR 5 solution of 1 molcm−3 was replaced by DW. At 100% of CEC, Fe prevented clay dispersion when leached with SAR 5, 10, and 20 solutions. Iron was not as effective as Al‐polymers in preventing reduction of HC at SAR 10. The Al‐polymers appeared to be more effective than the Fe‐polymers because they bound clay particles into larger stable microaggregates than did the Fe‐polymers. A smaller percent of particles <2 µm was measured in the Al‐treated clay than the Fetreated clay. Both treatments increased the size of stable microaggregates compared to the untreated clay.
Fractionation of Soil Selenium by Sequential Partial Dissolution
Authors: Chao T. T. , Sanzolone R. F.
Published: July 2010

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

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

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

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

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

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

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

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