bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Measurements of Soil Physical Properties by Acoustical Techniques
Authors: Sabatier J. M. , Hess H. , Arnott W. P. , Attenborough K. , Römkens M. J. M. , Grissinger E. H.
Published: July 2010

Knowledge of porosity, air permeability, pore structure, and surface layering of soils is desirable in agricultural research. The conventional techniques are invasive, typically requiring sample extraction. When monitoring seasonal changes, the conventional methods disrupt considerable proportions of the test plot surface. The sample area used in conventional measurements may be too small to represent the variations in the test plot. Here, the feasibility of acoustical techniques for monitoring surface air porosity (total porosity minus volumetric water content), air permeability, and pore structure and the variation of these properties to depths of several centimeters below the surface is demonstrated. Test soil plots prepared using three soil materials, masonry sand, a Grenada silt loam (fine‐silty, mixed, thermic Glossic Fragiudalf) and a Catalpa silty clay (fine, montmorillonitic, thermic Fluvaquentic Hapludoll), were considered. Variation in water content and compaction of each soil material were considered. Both acoustic reflection and transmission measurements were made in the audio‐frequency range. The soils are modeled as air‐filled, rigid‐framed porous media. The acoustic‐reflection measurements involve analysis of propagation data from a small loudspeaker and two vertically separated microphones. The acoustic‐transmission measurement requires a specially designed probe microphone. Analysis of the acoustic‐reflection data yields qualitative indications of the relative air permeability of the soils. The transmission measurement yields information about the changes in air permeability with depth. Quantitative information on surface porosity, air permeability, tortuosity, and layering is presented by fitting theoretical predictions based on the soil model to the measured sound reflection and transmission data. The acoustically determined air porosity for the soils considered is within 10% of the values determined by gravimetric techniques.
X‐ray Photoelectron Spectroscopy as a Tool to Differentiate Silicon‐Bonding State in Amorphous Iron Oxides
Authors: Vempati R. K. , Loeppert R. H. , Dufner D. C. , Cocke D. L.
Published: July 2010

An x‐ray photoelectron spectroscopy (XPS) study was conducted to: (i) compare the Si (2p) and O (1s) peaks of selected Si‐containing minerals, and (ii) evaluate the application of XPS in identifying probable Si‐bonding environments in Si‐containing ferrihydrites. For silica gel, the Si (2p) and O (1s) XPS peaks occurred at 104.0 and 534.2 eV, respectively; with biotite, these peaks occurred at 102.8 and 532.4 eV. The difference in the Si (2p) binding energies between silica gel and biotite was attributed to differences in the Si‐bonding environment and the number of ‐Si‐O‐Si‐ linkages at corners of the SiO4 tetrahedron, and the charge deficit in the tetrahedral layer of biotite. The Si (2p) XPS peak for silicate adsorbed on ferrihydrite occurred at 100.9 eV, which indicated the probable presence of ligand‐bound silicate or small units of polymerized silica at the ferrihydrite surface. For ferrihydrite samples treated with an excess of Si (≥75 g kg−1), peaks attributable to a separate Si‐rich phase were identified on decomposition of the Si (2p) and O (1s) XPS peaks. In the case of ferrihydrite coprecipitated with silicate at Si/Fe molar ratios ≥0.10, the Si (2p) peak occurred at approximately 102.8 eV, which is a position similar to that observed for layer silicates, indicating the possible presence of Si, i.e., the presence of ‐Fe‐O‐Sl‐ bonds, within the ferrihydrite structure.
Mineralization of Amino Acids and Evidence of Direct Assimilation of Organic Nitrogen
Authors: Barak Phillip , Molina J. A. E. , Hadas Aviva , Clapp C. E.
Published: July 2010

Rival hypotheses, the mineralization‐immobilization‐turnover (MIT) hypothesis and the direct hypothesis, contend that deamination of soluble, low‐molecular‐weight nitrogenous compounds in soil is mediated by either extracellular or intracellular enzymes, respectively. To test these hypotheses, two amino acids, glycine (C/N = 1.7) and leucine (C/N = 5.2), were added to an acid Hubbard loamy sand (sandy, mixed Udorthentic Haploboroll) and incubated for 7 d. Net mineralization of both C and N were S‐shaped functions of time, indicating that simple first‐order substrate‐dependent kinetics were not applicable. The net mineralization of C and N were strongly correlated with each other and reflect the C/N ratio of the substrate and the C/N ratio and microbial efficiency of the microbial biomass. Labeled 15N data, when analyzed using kinetic models reflecting either the direct or MIT hypotheses, reject the MIT hypothesis (α = 0.01) and show evidence of direct incorporation of amino acids into the microbial biomass.
Soil Property Relationships with SPOT Satellite Digital Data in East Central Illinois
Authors: Agbu Patrick A. , Fehrenbacher Donald J. , Jansen Ivan J.
Published: July 2010

The second‐generation remote sensing satellites with improved spatial and spectral resolution offer additional possibilities for conducting soil surveys. This study was undertaken to determine the relationships that exist among high‐resolution satellite digital data and soil properties useful in map‐unit delineation and classification. A second objective was to develop models (linear equations) based on soil properties to predict satellite spectral response. Site, morphological, physical, and chemical soil properties were determined to a depth of 1.2 m for 442 observation sites in two rectangular grids, at two contrasting areas of 3108 ha each. Multiple‐regression analyses between SPOT spectral data and soil properties showed that many surface and some subsurface soil properties were significantly correlated to spectral data. Landscape position and percent slope were not important as site characteristics that predict satellite spectral variables. Color of dominant mottles and depth to loess did not significantly affect satellite data. Measured soil properties were tested in terms of their usefulness in predicting SPOT spectral response. The results showed that most surface soil properties and some subsurface properties pertinent to soil classification and map‐unit separation can be used to predict satellite data and vice versa. Brightness index proved to be a more useful spectral parameter if surface soil properties are to be extracted from spectral data, but ratioing of the original data resulted in more association of spectral data with subsurface soil properties.
Characterization of Tillage and Traffic Effects on Unconfined Infiltration Measurements
Authors: Ankeny Mark D. , Kaspar T. C. , Horton R.
Published: July 2010

Tillage and wheel‐traffic compaction alter pore structure and hydraulic properties of agricultural soils. These alterations will affect root growth and movement of water and solutes. This study was conducted to develop new methods needed to characterize the effects of wheel traffic and tillage on pore structure as measured by water flow through macropores. Unconfined (three‐dimensional) saturated and unsaturated infiltration measurements (0‐, 30‐, 60‐, and 150‐mm water tension) at the soil surface were taken sequentially at field sites to determine the steady‐state rate of water flow through different pore‐size classes on a Tama silty clay loam (fine‐silty, mixed, mesic Typic Argiudoll). A tension infiltrometer was used to obtain the unsaturated infiltration rates. Sites were selected on trafficked and untrafficked interrow positions in two tillage systems (chisel plow and no‐till). Steady‐state infiltration rates from 2 to 300 µm s−1 were measured. Increasing the tension of applied water resulted in decreasing infiltration rates for both tillages and traffic treatments because, as tensions increased, larger pores emptied. Wheel traffic reduced infiltration rates in both tillages, but caused a greater decrease in infiltration rates in the chisel‐plow system than in no‐till. Increasing tension caused proportionately smaller decreases in infiltration rates for wheel‐trafficked positions. This suggests that larger macropores were transporting a greater proportion of the total water flow in untrafficked soil than in trafficked soil and reinforces the concept that larger, as opposed to smaller, pores are more easily destroyed by wheel traffic. Unconfined infiltration measurements were shown to be useful in quantifying the effects of tillage and compaction on soil macropores.
Corn Root Distribution and Yield Response to Subsoiling for Paleudults Having Different Aggregate Sizes
Authors: Vepraskas M. J. , Wagger M. G.
Published: July 2010

Chisel plowing loosens dense root‐restricting layers within 0.25 m of the soil surface, while subsoiling can be used to routinely loosen dense layers down to a depth of approximately 0.45 m. Selecting one tillage method over the other to maximize yield is problematic because the lower depth of a root‐restricting layer is often difficult to determine precisely if the layer contains structural aggregates. We hypothesized that the ability of roots to penetrate dense soil layers is related to the size of aggregates in the dense layers. Therefore, this study compared root distributions for chisel plowed and subsoiled tillage treatments and related them to soil properties and corn (Zea mays L.) grain yield for soils having dense layers that varied in their aggregate size. Yields and root distributions were determined for the two tillage treatments on eight Typic and Arenic Paleudults. Each site had a dense, high‐strength soil layer below the depth of chiseling. Subsoiling significantly (P = 0.10) increased yields over chisel plowing at five sites. At four of these sites, the proportion of roots between depths of 0.3 and 1.0 m in the chiseled treatment was low (≤0.20) due to the root‐restricting layer extending below the depth of chiseling. Although all sites had pan‐like layers, which were characterized on the basis of bulk‐density and cone‐index measurements, only layers whose ped meanweight diameter was ≤1.2 mm resulted in root proportions being ≤0.20 in the chiseled treatment. These virtually nonaggregated layers also tended to have low amounts of plant‐available water (<0.12 m3 m−3). To adequately characterize root‐restricting layers that reduced yield in these soils, some measure of subsurface aggregation or a correlated property such as plant‐available water or texture had to be evaluated along with bulk density or cone index.
Nitrogen Mineralization Potentials of Shrub‐Steppe Soils with Different Disturbance Histories
Authors: Bolton H. , Wildung R. E. , Smith J. L.
Published: July 2010

Disturbance of shrub‐steppe soils and changes in the dominant plant cover may alter soil N‐cycling processes. The mineralization of organic N to plant‐available forms is an important component of the N cycle in shrub‐steppe soils. Therefore, the soil N‐mineralization potential (No) was determined for two arid ecosystems, an undisturbed perennial shrub‐steppe and an annual grassland, which was initially shrub‐steppe and has been an annual grassland since farming disturbance in the 1940s. The soils at both study sites are similar and are classified as coarse‐silty, mixed, mesic Xerollic Camborthids. Soils were sampled at 0‐ to 5‐, 5‐ to 10‐, and 10‐ to 15‐cm depths, before plant growth in the spring, underneath big sagebrush (Artemisia tridentata Nutt.) bluebunch wheatgrass [Elytrigia spicata (Pursh) D.R. Dewey], Sandberg bluegrass (Poa secunda J.S. Presl), and soil crust at the perennial site and underneath downy brome (Bromus tectorum L.) at the annual grassland site. The 0‐ to 5‐cm soil depth from underneath all plants had the highest No. The No at the 0‐ to 5‐cm soil depth was influenced by plant type and decreased in the order P. secunda, B. tectorum, A. tridentata, E. spicata, and soil crust. The No decreased with soil depth until the 10‐ to 15‐cm soil depth, when all soils had the same value. The production of plant‐available N will, therefore, be largely limited to the soil surface, and losses from the first 5 cm of soil will be detrimental to both ecosystems. Spatial distribution of these plant species in the arid ecosystem result in “islands” where enhanced N mineralization occurs. When plant cover was used to compute a site‐specific No for the perennial shrub‐steppe and the annual grassland, a similar value was obtained indicating similar dynamics of soil N processes at these two sites.
Coupled Water and Heat Transport in Ridged Soils
Authors: Benjamin J. G. , Ghaffarzadeh M. R. , Cruse R. M.
Published: July 2010

Study of ridge‐tillage effects on the soil environment has been impeded by the lack of models to adequately describe water and heat movement in the ridge system. The ridge system introduces many nonuniform characteristics into the field problem, such as variable solar radiation across the soil surface, unevenly distributed surface mulches, and variable water and heat transport properties caused by ridge construction or wheel traffic. A finite‐element model was developed to simulate coupled water and heat flow in ridge systems. The finite‐element solution scheme was chosen because of the ease by which nonuniform soil transport properties and nonuniform boundary conditions can be included in the problem specifications. Model predictions of soil water and temperature were compared with field measurements for two ridge configurations. Predicted and measured average daily temperatures over a 10‐d period were within 1 °C and water contents were within 0.02 m3 m−3 for 80% of the measurements.
Organic Selenium Distribution in Selected California Soils
Authors: Abrams M. M. , Burau R. G. , Zasoski R. J.
Published: July 2010

The distribution of organic Se was determined in seven soils from central California. Six of these soils (one Typic Pelloxerert, three Typic Torriorthents, one Vertic Torriorthent, and one Entic Chromoxerert) were in a toposequence from an area thought to be relatively high (>1000 µg total Se kg−1) in native Se. The seventh soil, Yolo (a Typic Xerorthent), thought to be low in native Se, was included for comparison. Three of the soils in the toposequence had total Se levels less than 1000 µg kg−1; the basin soil (Tachi; Typic Pelloxerert) had less than the Yolo soil. A solution of 0.1 M NaOH/0.1 M Na4P2O7 (alkaline pyrophosphate) extracted an average of 12% of the total Se, but this ranged from 5 to 32%. Organic Se accounted for 50% or more of the NaOH‐Na4P2O7 extractable Se in all but the poorly drained Ciervo clay (Typic Torriorthent), which had about 40% in an organic form. Extracted organic Se compounds were fractionated into humates and hydrophobic and hydrophilic fulvates. Selenium associated with hydrophobic fulvates was high in the soils of intermediate toposequence elevation. Selenomethionine was identified by gas chromatography/mass spectrometry in the hydrophilic fulvate fraction of the Yolo soil and in three soils from the toposequence. The high percentage of extractable Se associated with organic matter in these soils represents a pool of potentially plant‐available Se.
Procedure for Determining Sodium‐Calcium Selectivity in Calcareous and Gypsiferous Soils
Authors: Amrhein C. , Suarez D. L.
Published: July 2010

A procedure to determine the exchanger‐phase composition (and thus the Na/Ca selectivity) of calcareous and gypsiferous soils was developed and tested on three soils and three phyllosilicate minerals. The procedure corrects for anion exclusion and mineral weathering by measuring the Cl, SO4, and HCO3 in the soil solution and in the extracting solution. Anion exclusion was found to be significant in the montmorillonite system, but generally less than 10% of the cation‐exchange capacity in the soil, illite, and vermiculite systems. Mineral weathering contributed significantly to the total extracted Ca. Thus, exchangeable‐Ca values were overestimated by 30 to 500% in the gypsiferous soils and 3 to 20% in the calcareous soils when weathering was neglected. The proposed method allows the determination of cation‐exchange capacity, exchangeable‐cation composition, and anion exclusion at any solution composition, concentration, and pH.
Ethylene Accumulation in Soil in Response to Organic Amendments
Authors: Arshad Muhammad , Frankenberger W. T.
Published: July 2010

One of the major factors affecting ethylene (C2H4) accumulation in soil is the availability of organic substrates. Various organic compounds were screened for their stimulatory effect on C2H4 accumulation in soil. Since L‐methionine (L‐met), a sole precursor of C2H4 synthesis in plants, is also an excellent precursor for microbial biosynthesis of C2H4, all the compounds tested were added on a C‐equivalent basis with respect to 1 g L‐met kg−1 soil. Incubation was carried out under ambient conditions (24 ± 3 °C) for 14 d and the soil was maintained at field capacity (−33 kPa). Among the 63 compounds tested, the majority of amino acids, organic acids, carbohydrates, proteins, alcohols, and met analogs promoted C2H4 generation to a greater degree than did the unamended soil. Use of 1‐aminocyclopropane‐1‐carboxylic acid (acc) enhanced C2H4 synthesis much more than any other treatment (2400‐fold over the unamended nonsterile control). Of the five vitamins tested, inositol was the most effective in promoting C2H4 production. L‐Ethionine (L‐eth) was an excellent precursor among the five met analogs. Nonbiological production of C2H4 was observed only upon treatment with L‐met, L‐cysteine, acc, ethanol, and L‐eth, which were 7.9, 19.0, 3.0, and 4.2% and 2.1‐fold, respectively, of the total C2H4 detected under nonsterile amended conditions. Since the majority of these compounds are excreted by plant roots, the rhizosphere may be an active site for C2H4 generation.
Unbuffered and Buffered Salt Methods for Exchangeable Cations and Effective Cation‐Exchange Capacity
Authors: Amacher M. C. , Henderson R. E. , Breithaupt M. D. , Seale C. L. , LaBauve J. M.
Published: July 2010

This study was conducted to determine if a single unbuffered salt extractant for exchangeable bases and Al could be used in place of a buffered salt extractant for exchangeable bases and an unbuffered salt extractant for exchangeable Al. Barium chloride and a mixed NH4Cl‐BaCl2 extractant were compared with NH4OAc for determining exchangeable bases and with KCl for determining exchangeable Al in soils. In general, BaCl2 extracted less exchangeable K than either NH4OAc or NH4CL‐BaCl2. The NH4CL‐BaCl2 extractant was equivalent overall to NH4OAc for extracting exchangeable bases and to KCl for extracting exchangeable Al, although less K was extracted by NH4Cl‐BaCl2 at low levels of K for some Coastal Plain soils. The NH4Cl‐BaCl2 extractant can be used by soil‐test or soil‐characterization labs as a simple one‐step extractant in place of NH4OAc and KCl for the determination of exchangeable cations and effective cation‐exchange capacity of soils.
Soybean Yield Response to Various Depths of Erosion on a Fragipan Soil
Authors: Rhoton F. E.
Published: July 2010

Erosion of soils with limited profile thickness can reduce soil productivity to the point that crop yields are no longer profitable. The intention of this study was to determine the effects of progressive erosion on the productivity of a fragipan soil. Soybean [Glycine max (L.) Merr.] was the indicator crop. Twelve experimental plots were installed at each of the three differentially eroded sites on a Grenada silt loam (fine silty, mixed, thermic Glossic Fragiudalf). Average depth to fragipan ranged from 16 to 63 cm. Soil P and K levels were adjusted to 140 and 280 kg ha−1, respectively, on one‐half of the plots, and pH was adjusted up to 6.5. The remaining plots received no lime or fertilizer. No significant differences were found for yield between the two fertility treatments. Average grain yields for the 3‐yr study were 2417, 1953, and 1877 kg ha−1 at the slight, moderate, and severely eroded sites, respectively. The lowest yields, for these same plots were 2286, 1773, and 1549 kg ha−1 recorded in 1986, when soil water content during pod‐fill stage was least. Depth to fragipan accounted for 56, 60, and 67% of the variability in grain yields for 1984, 1985, and 1986, respectively. A yield‐depth‐to‐fragipan curve derived from these data showed that the greatest grain‐yield reduction per increment of soil loss occurred as soil depth decreased from 60‐ to 50‐cm. This indicates that, to maintain productivity on these soils, management systems should be designed to preserve a minimum soil thickness above the fragipan of ∼60 cm.
Bare Fallowing on Sandy Fields of Niger, West Africa
Authors: Payne W. A. , Wendt C. W. , Lascano R. J.
Published: July 2010

An experiment was conducted in three rainfall zones of Niger, West Africa, to evaluate the potential of mulched and nonmulched bare fallow to conserve water in deep, sandy soils. Water content of adjacent bare and cropped experimental plots was monitored with a neutron probe at three sites during the 1985 growing season and the subsequent dry season. Experimental sites, with soil type and 1985 rainfall, were near the villages of Chikal (Ustic Torripsamment; 233 mm) N'Dounga (Psammentic Paleustalf; 344 mm), and Kala Paté (Alfic Ustipsamment; 428 mm). Cropped plots were managed using traditional low‐input practices. Bare plots were weeded using a traditional, shallow cultivating hoe. At the end of the growing season, portions of the bare and cropped plots were mulched with millet stalks at a rate of 25 Mg ha−1. At the end of the dry season, no significant increases in profile water storage were detected in mulched treatments. Increased soil water storage in the upper 1.65 m of bare fallowed plots toward the end of the dry season was 16.5 ± 10.5 mm at Chikal, and 40.6 ± 17.9 mm at N'Dounga. No increase in storage was observed in bare fallowed plots at Kala Paté. Mean increases in storage efficiency at Chikal and N'Dounga were 7.1% and 11.8%, respectively. Position of the zero‐flux boundary during the dry season and profile water distribution toward the end of the dry season indicate that drainage was substantial at all sites. However, large losses due to evaporation are also possible, due to high evaporative demand during the dry season. Data obtained in this study suggest that bare fallowing, with and without dry‐season mulching, is an inefficient means of water conservation for these soil systems. A possible application of bare fallow is in sandy soils underlaid by laterite in high‐risk, low‐rainfall zones of the Sahel if accompanied by adequate erosion prevention.
Low‐Molecular‐Weight Organic Acids in Selected Forest Soils of the Southeastern USA
Authors: Fox T. R. , Comerford N. B.
Published: July 2010

Organic acids can form stable complexes with metals and therefore can affect metal solubility and speciation. The low‐molecular‐weight aliphatic organic acids extracted in water and present in soil solution from O, A, Bh and Bt horizons from a group of forested Utlisols, Entisols and Spodosols were identified by high performance liquid chromatography (hplc). Oxalic acid was found in all samples and was present generally in the highest concentrations. Oxalate concentrations in soil solution ranged from 25 to 1000 µM and were greater in the Bh and Bt horizon soils than in the A horizon soil. High concentrations of formic acid were also identified in most soils, ranging from 5 to 174 µM in soil solution. Trace amounts of citric, acetic, malic, lactic, aconitic, and succinic acids were detected in some samples. In a greenhouse pot study, the concentrations of low‐molecular‐weight organic acids in the rhizosphere of slash pine (Pinus elliottii Engelm.) seedlings growing in A, Bh, and Bt horizons from an Ultic Haplaquod were compared with the concentrations in the nonrhizosphere soil. The observed concentrations were approximately an order of magnitude greater than in native soils. Oxalate was the only low‐molecular‐weight organic acid identified in the non‐rhizosphere soil. The suite of organic acids identified in the rhizosphere was more complex than in the bulk soil. In the rhizosphere, high concentrations of both oxalate and formate were detected, along with trace amounts of citric, acetic, and aconitic acids. Since oxalate forms stable complexes with Al, the presence of large concentrations of oxalate may affect P availability in these soils.
Dicyandiamide Influence on Uptake of Preplant‐Applied Fertilizer Nitrogen by Rice
Authors: Wilson C. E. , Wells B. R. , Norman R. J.
Published: July 2010

A field study was conducted to determine the influence of dicyandiamide (dcd) on fertilizer N recovery from soil and rice (Oryza sativa L.) when 15N‐labeled urea was applied preplant (20 g N m−2). Microplots consisted of polyvinyl chloride pipes, 20.3 cm in diameter, driven into the soil. ‘Newbonnet’ rice was seeded, thinned to five plants per microplot, and flooded when the plants were at the four‐ to five‐leaf stage of development. Soil and plant samples were analyzed for N every 7 d for 49 d following application (plant samples beginning at 35 d) and then every 14 d. Prior to flooding, urea with dcd reduced nitrification. With dcd, 51 and 8% of the applied N was recovered at flooding as NH4 and NO3, respectively, compared with 8 and 23%, respectively, without dcd. Dicyandiamide, by maintaining more fertilizer N in the NH4 form, appeared to cause greater immobilization of the fertilizer N than when dcd was not applied (19 and 15% of applied N, respectively). More fertilizer N was recovered in the shoots and roots (17.2 and 2.9% of applied N, respectively) when urea was applied with dcd than when used alone (9.7 and 1.9%, respectively). However, fertilizer N recovered in the panicles and grain yield were not significantly different between treatments. Fertilizer N recovered in the total plant increased significantly from 35 to 42 d, after which no further changes occurred. However, total plant N and native soil N uptake increased significantly throughout the growing season.
Phosphorus Release in Sodium Ion Dominated Soils
Authors: Gupta Raj K. , Singh R. R. , Tanji K. K.
Published: July 2010

Calcareous sodic soils having high sodicity and high pH often maintain high solution P concentration. The effect of high exchangeable Na, high pH, and alkali anions and carbonates on the release of inorganic P was investigated in soils representing the three major benchmark sodic soil series found in the Indo‐Gangetic plains of India. Sodium saturation of the exchange complex, high pH, carbonate ions, and low electrolyte level shifted the solid P‐solution P equilibrium in favor of maintenance of high P concentrations in aqueous solutions. In the sodic soil environment, release of P can be accounted for by the dissolution of various forms of Ca‐P compounds at high alkalinity and pH. Cultivation of alkali soils improves the organically bound P forms. Together or in combination, high sodicity, high pH, and the presence of carbonate ions at low salinity markedly increased P desorption and P availability in sodic soils.
Mineralization of Nitrogen from Nitrogen‐15 Labeled Crop Residues and Utilization by Rice
Authors: Norman R. J. , Gilmour J. T. , Wells B. R.
Published: July 2010

The availability of N from the residues of the previous crop to the subsequent rice (Oryza sativa L.) crop is largely unknown. The objectives of this study were to (i) measure the mineralization of N from 15N‐labeled rice, soybean (Glycine max L.), and wheat (Triticum aestivum L.) residues and the uptake by a subsequent rice crop; and (ii) compare the 15N tracer method with the standard fertilizer‐N response method used in field studies to quantify the N contribution from the crop residue to the next crop. Nitrogen mineralization from decomposing crop residues was measured by soil sampling prior to seeding the rice crop and after seeding by plant sampling the rice at maturity. The minimum estimate of the amount of residue N mineralized from the time of residue incorporation until rice harvest was 9, 52, and 38% of the rice, soybean, and wheat residue N, respectively. The amount of residue N recovered in the rice crop was 3, 11, and 37% of the rice, soybean, and wheat residue N, respectively. The lower the C/N ratio and the higher the amount of N in the residue, the lower was the amount of residue N recovered in the soil organic fraction at harvest and the higher was the amount of residue N mineralized. The 15N tracer method compared favorably with the fertilizer N response method when the uptake efficiency of the fertilizer N was taken into account.
Soil‐Geomorphic Relations on the Blue Ridge Front: II. Soil Characteristics and Pedogenesis
Authors: Graham R. C. , Buol S. W.
Published: July 2010

Soils along two mountain slope transects in mica gneiss and schist terrane were studied to better understand soil distribution and genesis on the Blue Ridge Front landscape in North Carolina. Soils may form entirely in residuum or colluvium, but on most slope positions they have developed in both materials. The colluvial/residual nature of soils is related to geomorphic position and has a strong influence on soil properties and the evolution of the soils. Soils on upper slopes have a significant residual component as a result of weathering into the parent rock. Low slope positions are sites of accumulation, resulting in deep soils formed in colluvium. Dystrochrepts, or very weakly expressed Hapludults, have developed entirely in colluvium, whereas soils with at least a partial component of residuum are Hapludults. Soils on landscape positions down wearing into fresh mica gneiss or schist are in the micaceous mineralogy class, whereas those in highly weathered colluvium and in very stable residuum (i.e., nearly level summit positions) have been depleted of mica and are in the oxidic class. A conceptual model relating slope processes to pedogenesis is proposed in which colluvial transport interrupts the orderly in situ progression of residual soil development. The genesis and distribution of soils are best understood when studied in landscape contexts, rather than at the level of individual pedons or classification units.
Water Balance Estimation Model: Field Test and Sensitivity Analysis
Authors: Chopart J. L. , Vauclin M.
Published: July 2010

A simplified, capacity‐based simulation model has been developed to predict components of the field water balance. This requires only daily information such as the atmosphere evaporative demand and soil‐wetting events, maximum available soil water storage, and root growth characteristics, as well as crop and soil parameters. Actual evapotranspiration was modeled using Eagleman's parameterization. The model was tested for upland rice grown on a 3500‐m2 field plot, and on an undisturbed lysimeter. The predicted actual evapotranspiration (AET) and drainage (D) at the bottom of the soil profile matched the lysimeter data. Also, the model predicted reasonably well the field soil water content data, which were obtained at 15 sites. In the latter case, the root mean square error was about 16% for the seasonal AET, and 19% for D. Errors were within the limits of experimental uncertainties expected when such measurements are analyzed by Darcy's law. The results of a sensitivity analysis with respect to changes in parameter inputs show that the model is physically realistic. However, the sensitivity depends strongly on the supply of water in the soil. This clearly justifies the need to simulate the root‐zone water balance as a time‐dependent process, especially if there is a practical interest in accurate prediction during drought periods.
Kinetics of Phosphorus Release from Spodosols: Effects of Oxalate and Formate
Authors: Fox T. R. , Comerford N. B. , McFee W. W.
Published: July 2010

Organic anions have been implicated in the release of P to soil solution and may thus increase the availability of P to plants. Oxalate and formate have been identified as the most prevalent low‐molecular‐weight organic anions in the soil solutions in Spodosols under forest vegetation in northern Florida. The purpose of this study was to investigate the effect that these two organic anions have on the kinetics of inorganic‐ and organic‐P release from the A, Bh, and Bt horizons of a representative forested Spodosol. Soil samples were equilibrated for various periods of time with solutions of either oxalate, formate, or water. The extracts were analyzed for pH, inorganic P, organic P, Al, and organic acids. Results showed that oxalate had little effect on P release in the A horizon. This was due to the lack of Al oxides to hold P. Conversely, oxalate greatly increased solution P in the Bh and Bt horizons. In the subsoil horizons, the release of P was rapid, followed the disappearance of oxalate from solution, and was coincident with an increase in pH. These facts suggested that P was released via a ligand‐exchange reaction. A longer term reaction was consistent with the reprecipitation of the P as an amorphous Al phosphate when oxalate was either totally sorbed or degraded. The presence of formate did not increase P release.
Ammonia Volatilization from Flooded Soil Systems: A Computer Model. I. Theoretical Aspects
Authors: Jayaweera G. R. , Mikkelsen D. S.
Published: July 2010

Ammonia volatilization from flooded rice (Oryza sativa L.) is a major mechanism for N loss and poor fertilizer use efficiency. Ammonia volatilization is influenced by five primary factors: NH4‐N concentration, pH, temperature, depth of floodwater, and wind speed. This NH3‐volatilization model is based on chemical and volatilization aspects. The chemical aspects of the model deal with the NH4/NH3(aq) equilibrium in floodwater. Ammonium ions undergo dissociation with a first‐order rate constant, while NH3(aq) and H undergo a diffusion‐controlled association reaction with a second‐order rate constant. The transfer of NH3 across the water‐air interface of flooded soil systems is characterized by a first‐order volatilization rate constant. By utilizing the chemical dynamics of the NH4/NH3(aq) system in association with transfer of gaseous NH3 across the interface, an equation was derived to determine the rate of NH3 volatilization from flooded systems as a function of the five primary factors. The chemical aspects of the model include the derivation of association and dissociation rate constants. The volatilization aspects of the model, which is based on the two‐film theory, allows it to compute the volatilization rate constant for NH3. Expressions are derived to compute the Henry's law constant, gas‐phase and liquidphase exchange constant, and the overall mass‐transfer coefficient for NH3.
Defining Soil Buffer Power: Implications for Ion Diffusion and Nutrient Uptake Modeling
Authors: Van Rees K. C. J. , Comerford N. B. , Rao P. S. C.
Published: July 2010

Various definitions of the nutrient buffer power of soils, based on ion‐exchange isotherms, have been proposed in the literature. However, incorrect definitions can result in erroneous estimations of solute diffusion coefficients and nutrient replenishment of soil solution, hence, rates of nutrient supply for plant nutrient uptake. This note presents conditions under which each definition of buffer power is valid, and situations where inherent assumptions may not be valid.
Statistical Parameters Characterizing the Spatial Variability of Selected Soil Hydraulic Properties
Authors: Ünlü K. , Nielsen D. R. , Biggar J. W. , Morkoc F.
Published: July 2010

The knowledge of the statistical parameters of the variance, σ2, and the correlation scale, λ, characterizing the spatial structures of the log of the saturated hydraulic conductivity, lnKs, pore size distribution parameter α, and the specific water capacity, C, is required in stochastic modeling in order to understand the overall response of large‐scale heterogeneous unsaturated flow systems. These parameters are estimated assuming second‐order stationarity and an exponential semivariogram model with nugget effect. Methods of ordinary least squares (OLS), maximum likelihood (ML), and restricted maximum likelihood (RML) are used for estimating σ2 and λ, while methods of cross‐validation (kriging) and uncorrelated residuals are used to validate the semivariogram model with estimated σ2 and λ. The objectives of this study were to evaluate the sensitivity of σ2 and λ to the estimation methods and to discuss the implications of the analysis in view of the stochastic modeling. The significance of the results of parameter estimation and model validation in relation to the stochastic modeling of large‐scale transient unsaturated flow is demonstrated with two examples involving the variance of soil‐water pressure head, σ2h, and the vertical component of effective hydraulic conductivity, K*11. Results show that the estimated values of σ2 and λ are highly dependent on the estimation method. Although the majority of the estimated parameters pass the validation tests, the RML estimates of σ2 and λ used in estimating σ2h and K*11 significantly reduce the prediction uncertainties.
Microwave Radiation and Incubation Effects on Resin‐Extractable Nutrients: II. Potassium, Calcium, Magnesium, and Phosphorus
Authors: Yang Jae E. , Skogley Earl O. , Schaff Bernard E.
Published: July 2010

The phytoavailability soil test (PST) is a resin‐extraction methodology being developed for use on fresh soil samples. Mineralization or other nutrient conversions during shipment of samples to a soil‐testing laboratory are of concern with this soil‐test approach. The objective of this research was to investigate microwave‐radiation (MWR) treatment of soil samples to arrest microbial conversions of nutrients during incubation of fresh samples. Fresh samples from three Ap horizons of Montana soils (Haploborolls) were subjected to MWR for 0 to 4 min and then incubated at 20 °C for 0 to 12 d. Subsamples were also dried before being subjected to the same treatments. Nutrients were extracted with mixed‐bed ion‐exchange resin extractors placed in saturated pastes of each sample. Standard soil tests were also conducted on dried soil samples. Results for K, Ca, and Mg indicate increased resin extractability with increasing MWR, and incubation without MWR caused both increases and decreases in extractability, depending on length of incubation. Neither MWR nor incubation resulted in consistent changes in resin‐extractable P. Results from dried soil were generally similar, except one soil did not produce significant changes in resin‐extractable cations due to MWR or incubation. Extractable cations by standard soil tests were not influenced by MWR, but P levels increased with length of MWR. These results support those for N and S, providing additional evidence that MWR should not be recommended for soil samples intended for soil testing by either standard or PST methods.
Characteristics and Taxonomy of Sodic Soils as a Function of Landform Position
Authors: Seelig B. D. , Richardson J. L. , Barker W. T.
Published: July 2010

Sodic soils in central North Dakota are related to landform position in relation to the water table and plant communities. Classification problems are commonly encountered when field observations are compared with established taxa. This study focused on relating soil and plant characteristics to differences in soil water regime. Soils at three landform positions, designated as upland, intermediate, and wetland, were sampled at regular intervals. The sampling pattern at each position formed a grid (49 pedons/grid). Each pedon was described and classified. Selected pedons were analyzed for major cations, electrical conductivity (EC), and dispersible clay. Water‐table observations were made from wells with perforated casings at each area sampled. Plant composition was determined by the point‐frame and quadrat methods. Landform position and plant communities reflected variations in sodic soil properties and soil water regime. The highest amounts of dispersible clay and lowest Ca/Mg ratios were in the sodic soils at the two lowest positions. The highest sodium adsorption ratios (SAR) were in soils at the intermediate position. These soils were associated with a plant community dominated by inland saltgrass [Distichlis spicata ssp. stricta (Torrey) Thorne] in the intermediate position. Sodic soils from the upland position were drier than the sodic soils at the two lower positions and were not so severely affected by Na.
Modeling Water Balance and Grass Production
Authors: de Jong R. , Kabat P.
Published: July 2010

The previously developed soil water‐crop production model SWA‐CROP was adapted and tested for grassland production under the weather conditions and management practices encountered on sandy soils in the Netherlands. The model, which required soil physical and crop properties as input, was driven by meteorological data. The main output of the soil water balance module (SWATRE) included actual transpiration and the distribution of soil water contents and pressure heads over depth and time. The crop production module (CROPR) calculated dry‐matter yields of roots, stubble, and harvestable sward. The CROPR module was also used to calculate leaf‐area index and soil cover, which formed feedback loops with the soil water balance. After initial calibration, 85% of the predicted soil water contents in the root zone fell within 10% of the measured data. Seasonal accumulated grass yield, predicted by the model under non‐stressed conditions, was within 10% of the measured yield, but yields during dry periods were overestimated. Discrepancies between measured and predicted yields under irrigated and nonirrigated conditions were attributed to the model's inability to simulate growth and death rates of individual plant organs.
Fertilizer Effects on Dinitrogen, Nitrous Oxide, and Methane Emissions from Lowland Rice
Authors: Lindau C. W. , DeLaune R. D. , Patrick W. H. , Bollich P. K.
Published: July 2010

Dinitrogen, N2O, and CH4 emissions were measured from a Louisiana flooded rice (Oryza sativa L.) field. Field experiments were conducted on a Crowley silt loam soil (a fine, montmorillonitic, thermic Typic Albaqualf) to determine the effect of fertilizer types and rice plants on evolution of N2, N2O, and CH4 to the atmosphere. Highly labeled (60–74 atom% 15N) urea, (NH4)2SO4, and KNO3 fertilizers were applied into the floodwater at the four‐ to five‐leaf stage to maximize N loss. The direct emissions of N2, N2O, and CH4 were measured at 1, 3, 5, 7, 9, 11, 13, 15, 17, and 21 d after N application. Maximum N2 fluxes from the planted rice plots were 254, 516, and 3 330 g ha−1 d−1 for the urea, (NH4)2SO4, and KNO3 treatments, respectively. Dinitrogen fluxes from the urea, (NH4)2SO4, and KNO3 unplanted plots were 264, 484, and 1 720 g N2 ha−1 d−1, respectively. Nitrous oxide emissions due to fertilizer addition to the soil were low. No increases in N2O emission above control values were recorded for any of the sampling intervals after urea addition. Maximum N2O flux from the (NH4)2SO4 treatments was 4 g ha−1 d−1 on Day 17 and 122 g ha−1 d−1 for the KNO3‐treated plots measured on Day 1. Peak CH4 emissions from the planted and unplanted urea‐treated plots were 75 and 22 g ha−1 d−1, respectively. Fluxes of CH4 from the (NH4)2SO4 and KNO3 plots were much lower and did not exceed 9 and 18 g ha−1 d−1, respectively, over the 21‐d sampling period. This study shows that the type of fertilizer N and presence of rice plants affects the evolution of N2, N2O, and CH4 from a flooded‐rice soil to the atmosphere.
Hydroxy‐Aluminum's Effect on Permeability of Clay‐Sand Mixtures
Authors: Keren R. , Singer M. J.
Published: July 2010

The effect of the hydroxyl‐Al synthesis method on the hydraulic conductivity (HC) of a clay‐sand mixture in the presence of hydroxy‐Al was studied. Hydroxy‐Al precipitates were formed by adding Al(NO3)3 and NaOH solutions to continuously stirred smectite suspension. Aluminum nitrate was added either before or after NaOH. When the mixtures were leached with deionized water, HC reduction was much less when Al(NO3)3 was added prior to rather than after NaOH. Dispersion and transport of clay from the clay‐sand mixture occurred only when the NaOH was added prior to Al(NO3)3. The differences in behavior between the two systems is due to the location of hydroxy‐Al. When Al(NO3)3 is added to the clay followed by NaOH, hydroxy‐Al polymers interact with the clay particles to reduce swelling and dispersion. When clay and NaOH are mixed, followed by Al(NO3)3, precipitates form as a separate phase from the clay platelets.
Cropping and Sulfur Fertilization Influence on Sulfur Transformations in Soil
Authors: Castellano S. D. , Dick R. P.
Published: July 2010

The dynamics of S cycling in soils are not well understood. A 2‐yr field study was conducted to determine the effects of two S fertilizers (CaSO4·2H2O [CS] or elemental S [ES]) at two fertilization rates (0 or 50 kg S ha−1 yr−1) on the temporal distribution of soil S fractions (inorganic SO4, ester sulfate, and C‐bonded and residual S), arylsulfatase activity, and microbial‐biomass C and S in soil. The soil studied (a fine‐silty, mixed, mesic Aquultic Argixeroll) was cropped with winter rape, Brassica napus L. var. napus or left uncropped. Sulfate levels (0–15 cm depth) were significantly (P < 0.01) affected by S‐fertilizer treatment. During the rainy winter season, SO4 levels ranged from 7 to 13 mg kg−1 in CS plots, compared with 2 to 7 mg kg−1 in control plots. In the months from March to May, biomass S increased and SO4 levels decreased (<6 mg SO4‐S kg−1 soil), indicating S immobilization was occurring in the spring. Ester sulfate and residual S varied seasonally, whereas C‐bonded S showed minimal seasonal fluctuations. Cropping significantly increased biological activity (arylsulfatase activities and biomass C) over uncropped treatments. Subsoil SO4 appeared to be both a source (upward movement during high evapotranspiration) and a sink for S in surface soil, with extractable SO4 in the 60‐ to 90‐cm depth being significantly affected by cropping and S fertilization. The limitations of using extractable SO4 as a soil test were shown by wide variations in SO4 over time (2–14 mg SO4 kg−1 soil) in control plots, even though there was a seed yield response to S.
Water Quality Effects on Soils and Alfalfa: II. Soil Physical and Chemical Properties
Authors: Costa J. L. , Prunty Lyle , Montgomery B. R. , Richardson J. L. , Alessi R. S.
Published: July 2010

Salt accumulation can occur in northern Great Plains soils during irrigation with saline water. The objective of this study was to quantify effects of salinization produced in Barnes loam (fine‐loamy, mixed Udic Haploboroll), Parshall loam (coarse‐loamy, mixed Pachic Haploboroll), Svea loam (fine‐loamy, mixed Pachic Haploboroll), and Williams loam (fine‐loamy, mixed Typic Argiboroll) soils by irrigation with seven water qualities during 21 mo of greenhouse alfalfa production in undisturbed columns. Eight physical and chemical soil properties were evaluated and related to soil, water quality, and depth in the soil. Saturation percentage (SP) of the soil increased 0.2% for each unit increase in soil‐extract sodium adsorption ratio (SARe). Saturation‐extract electrical conductivity (ECe) increased with depth, at rates dependent on water quality, to maximums of 1 to 17 ds m−1. Parshall was the soil most susceptible to dispersion as SARe increased. From the surface to 15‐cm depth, bulk density was reduced 0.04 to 0.06 Mg m−3 by the water that resulted in the highest soluble‐Ca concentration. Significant regression models were developed for SP, ECe, SARe, and salt precipitation. Parshall, the most irrigable soil, was the most detrimentally affected, as judged by dispersion, ECe, and SARe, indicating a need for further investigation. Barnes, Svea, and Williams soils proved more suited to irrigation than previously believed.