bluuebunny/crossref_metadata_2025 huggingface dataset:
A Low Abrasion Crusher for Preparation of Air‐Dried Soils for Element Extraction
Authors: Kowalenko C. G. , Scobie B. S.
Published: July 2010

A crusher was developed for mechanizing the preparation of air‐dried soil samples for nutrient extraction including metals. The crusher simulated manual crushing of samples with a rolling pin. All surfaces contacting the soil were plastic and the crusher could be thoroughly cleaned, minimizing the risk of sample contamination. Readily available materials were used to achieve low fabrication costs. The crusher used two rollers, rotating in opposite directions and the crushed sample was further processed by a vibrating plastic sieve. The pressure between the rollers was adjustable. The prototype crushed and sieved samples from a variety of soil types faster and with less effort than manually with a rolling pin. The conceptual approach offers a consistent and reproducible mechanized process of soil sample preparation for multiple element extraction purposes.
A Dilute Medium to Determine Population Size of Ammonium Oxidizers in Forest Soils
Authors: Donaldson Jennifer M. , Henderson Gray S.
Published: July 2010

Incubation experiments using soils from mixed oak (Quercus sp.) stands showed accumulation of nitrate but standard most probable number (MPN) assays showed no NH4‐oxidizing bacteria were present. This led to a preliminary conclusion that nitrification in these soils must be heterotrophic. However, further incubation studies indicated that NH4‐N concentrations in standard MPN medium were too high for autotrophic NH4 oxidizers that are adapted to soils with low NH4‐N levels and exhibit low activities. Therefore, media with lower NH4‐N concentrations were tested against the standard MPN medium. Each medium was tested using both 1 mM phosphate buffer and deionized water as diluent to examine responses to small changes in buffer capacity. A 0.1 × medium used with deionized water diluent was found to best estimate populations of low‐activity NH4‐oxidizing bacteria present in soils with low NH4‐N concentrations.
Generalized Results from Crop Yield Model with Saline Waters
Authors: Warrick A. W.
Published: July 2010

Crop yields as influenced by water quality and quantity are of immense interest in arid areas throughout the world. In this paper, earlier results are generalized for modeling crop yield under deficit irrigation with saline water. Linear yield response functions were used for both the amount of water utilized and response to salts. Results are presented in a compact table for a wide range of conditions for salinity, water and yield response parameters. Included in the analysis is the effect of variability of available water. Results are similar to those obtained when salinity is not a factor, in that more variability of available water generally leads to lower average yields. This relatively simple approach is believed applicable to many practical scenarios for which a lack of input parameters or need for expediency rules out more comprehensive modeling.
Phosphorus Behavior in Flooded‐Drained Soils. II. Iron Transformation and Phosphorus Sorption
Authors: Sah R. N. , Mikkelsen D. S. , Hafez A. A.
Published: July 2010

Effects of flooding periods (FP), organic matter (OM) and temperature treatments during flooding on Fe transformation in flooded‐drained (FD) soils were studied on four soils representing wide variations in the effect of FD conditions on P sorptivity. The soils were extracted in sequence with ammonium oxalate at pH 6 (amorphous FeA) and at pH 3 (amorphous FeB), and with dithionite‐citratebicarbonate reagent (free Fe oxides). The amorphous FeA fraction increased with FP, OM treatment, and elevated temperature. In soils with low amorphous‐Fe to free‐Fe‐oxide ratio, both amorphous FeA and free Fe oxides increased at the expense of amorphous FeB as the FP increased. In soils with low amorphous‐Fe to free‐Fe‐oxide ratio, both amorphous Fe fractions (A and B) increased at the expense of free Fe oxides as FP increased. For all soils, the Fe transformation during soil flooding was accelerated by OM and high‐temperature treatments, both of which contributed to a decreased redox potential in the soil. Amorphous FeA fraction correlated well with P sorption under all combinations of OM and temperature in each soil, while other Fe fractions correlated well only under certain conditions. Results suggest that the nature and the magnitude of Fe transformations in these FD soils depend on interacting effects of FP, OM, and temperature.
Spectral Band Selection for Classification of Soil Organic Matter Content
Authors: Henderson Tracey L. , Szilagyi Andrea , Baumgardner Marion F. , Chen Chih‐chien Thomas , Landgrebe David A.
Published: July 2010

New instruments currently in design for Earth observational remote sensing from space offer promising advancements in the use of remote sensing for soil studies. Due to the enormous quantities of data generated by these high spectral resolution sensors, efficient use will only be feasible if new algorithms are developed to compress the data while maintaining information content. A spectral band selection algorithm is proposed to identify the important spectral bands for compression and classification of soil reflectance data. This algorithm was developed from the shape dominancy concept of Karhunen‐Loeve based optimal features. The high dimensional raw data were first transformed into much lower dimensionality by the derived spectral features. Canonical analysis was then used to transform the data under the maximal separability criterion into their final signal space where the data classification was performed. Soil data sets with and without stratification by soil order and climatic moisture zone were used to test the algorithm. The probabilities of correct classification of soil organic matter content using Landsat Multispectral Scanner (MSS) bands, Thematic Mapper (TM) bands, and the bands identified using the new band selection algorithm, were calculated and compared. The algorithm was successful in finding important spectral bands for soil organic matter content classification. The probabilities of correct classification obtained by using these bands were 0.850 and 0.883 for unstratified data sets, as compared to 0.600 to 0.640 for MSS bands and 0.640 to 0.653 for TM bands. Probabilities of correct classification for climate‐stratified data ranged from 0.910 to 0.980 using the calculated bands. The overall data compression ratio achieved using the algorithm was greater than 10 with no loss in classification accuracy.
Modeling Wheat Seedling Growth and Emergence: II. Comparison with Field Experiments
Authors: Bouaziz A. , Bruckler L.
Published: July 2010

To improve the understanding and prediction of wheat (Triticum aestivum L.) emergence under dry conditions, a model describing wheat emergence in field conditions is presented. The proposed approach separates three basic processes from sowing to seedling emergence: (i) seed imbibition and germination, (ii) root and seedling growth as influenced by soil water potential and temperature, and (iii) seedling emergence as affected by forces exerted by plant coleoptiles and soil surface structure. Previously developed models of each process were combined to predict seedling emergence. Field experiments consisting of irrigated and nonirrigated treatments and hand and mechanical seeding were used to validate the model. Model inputs included soil water content vs. time, mean air temperature (daily basis), dry bulk density, the soil water content/water potential relationship, and soil surface structure. Sensitivity analysis showed a high sensitivity of the model to geometrical characteristics (root and coleoptile tortuosities and root angle) of seedlings under field conditions. Model prediction of germination and emergence were generally satisfactory, although errors occurred after irrigation or rainfall. Discrepancies were explained by changes in the mechanical properties and increasing impedance of the soil surface after wetting and subsequent drying, or by changes in soil temperature after wetting. Finally, simulations of germination and emergence for three climatic conditions (wet, intermediate, and dry), two sowing techniques (hand and mechanical), and two soil surface structures (fine and coarse) demonstrated the effects of those factors on emergence. In the most favorable case, 95% emergence occurred 15 d after sowing. In the most unfavorable treatment, 41% emergence occurred after 29 d.
Optimum Application Parameters for Point Injection of Nitrogen in Winter Wheat
Authors: Janzen H. H. , Lindwall C. W.
Published: July 2010

Point injection may enhance N fertilizer use efficiency in winter wheat but optimum application parameters have not been identified. Three field experiments, employing 15N tracer techniques and manual injections on small plots, were established at two sites in southern Alberta, Canada, to identify optimum injection intervals and injection depth for spring point‐injection of urea‐ammonium nitrate solution (UAN). The optimum lateral (across‐row) injection interval was found to be the equivalent of two row spacings (40 cm). Higher intervals resulted in unacceptable variability in N availability because wheat in rows not directly adjacent to injections assimilated comparatively little fertilizer‐derived N. The optimum longitudinal injection interval was also approximately 40 cm. Analysis of fertilizer N distribution from the injection point demonstrated unacceptable variability when this interval was exceeded. Crop uptake of fertilizer N was reduced when the injection interval was increased from 40 to 60 cm. Adoption of smaller injection intervals in both dimensions, while not jeopardizing fertilizer use efficiency, would increase the cost of fertilizer application. The optimum injection depth was observed to be approximately 10 cm. Grain yield response and fertilizer N recovery in the crop increased four‐ and three‐fold, respectively, when injection depth was increased from 2.5 to 10 cm. This effect was attributed to the inaccessibility of fertilizer N residing in dry surface soil. Injection of fertilizer at 15 cm rather than 10 cm demonstrated no additional advantage.
Pedon Distribution of Minerals in Coastal Plain Paleudults
Authors: Harris W. G. , Hollien K. A. , Carlisle V. W.
Published: July 2010

Mineral distributions in three Florida Paleudults were investigated with respect to particle size, horizon, depth, and location within the soil matrix. Mineralogy of sand, silt, and clay was determined using optical microscopy, x‐ray diffraction, and thermal analysis. Also, mineralogy of sand‐grain coatings was compared with intergrain matrix material. Elemental‐oxide composition of siltsized phyllosilicate grains was determined by electron microprobe analysis. Sand fractions consisted mainly of quartz, with lesser amounts of feldspar and mica, which were more prevalent in lower horizons. Coarse‐ and medium‐silt fractions were also dominated by quartz, but contained appreciable feldspar and mica in B horizons. Kaolinite and hydroxy‐interlayered vermiculite (HIV) were most prevalent in fine‐silt and clay fractions. Abrupt changes in silt and clay mineralogy across the E‐ and B‐horizon boundary (E‐B) included a decrease in quartz and HIV and an increase in kaolinite. Relative amounts of HIV did not markedly change with depth in arenic epipedons, but decreased steadily below the E‐B boundary for all pedons. Sand‐grain coatings from Bt horizons contained more mica than did the intergrain matrix, whereas coatings in A and E horizons contained appreciably more HIV. Distribution of phyllosilicates in these pedons could be explained by a hypothetical sequence of processes which includes (i) illuviation of kaolinite formed from weathering or dispersed from clay lenses in the sediments, (ii) comminution of sand‐ and silt‐sized mica, (iii) incorporation of finegrained mica in sand‐grain coatings, and (iv) transformation of finegrained mica to HIV in highly permeable eluvial horizons.
Use of Civil Engineering Fabrics in Pedological Field Research
Authors: Darmody R. G. , Bicki T.J.
Published: July 2010

Soil pits are the pedologist's preferred means of examining and sampling soils. On occasion, pedologists, whether for pedagogic or research reasons, many need to re‐examine a pedon from a backfilled pit. This may be difficult especially if a backhoe is used. The backfilled materials and the in‐place soil materials comprising the pit walls can be difficult to separate, and consequently the backhoe could damage the pedon. A simple method of lining a soil pit with a civil engineering fabric prior to backfilling solves this problem. The fabric is nonbiodegradable, permeable to water but not to soil material, and strong. It has also proven to be quite useful for keeping buried equipment clean and allowing for its easy exhumation.
Penetration Model Parameter Estimation from Dynamic Permeability Measurements
Authors: Ravi Varadhan , Jennings Aaron A.
Published: July 2010

Several discrete interface‐penetration models have been proposed to quantify the permeability impacts of strong soil/solute interactions. Although it has been demonstrated that these models are capable of reproducing many of the response patterns observed in laboratory studies, their nonlinear, piecewise differentiable, implicit time boundary structure compounds efforts at formal parameter estimation. A modified Levenberg‐Marquardt algorithm is presented to resolve the constrained optimization problem of penetration‐model calibration. Examples are also presented to demonstrate that optimum parameter sets may be extracted from typical laboratory data, and to illustrate how results may be used to infer proper modeling strategies.
Laboratory Tests of a Theory of Fingering during Infiltration into Layered Soils
Authors: Baker Ralph S. , Hillel Daniel
Published: July 2010

A theory has recently been presented by Hillel and Baker to explain and predict the occurrence of fingering and the fractional wetted volume during infiltration into layered soils in terms of measurable hydraulic properties. When the conductivity of a coarse‐textured sublayer at its effective water‐entry suction is greater than the rate of transmission through a finer‐textured top layer, the flow velocity increases across the interlayer plane. Thereupon, a spatially‐distributed flow field in the top layer will tend to constrict, forming spatially separated streams (fingers) in the sublayer. To test the hypothesis, ponded infiltration experiments were conducted in transparent laboratory chambers packed with air‐dry sands. The hydraulic properties of the media were determined by equilibrium capillary rise, parameter estimation, and horizontal absorption experiments. Dynamic measurements of flux and suction at the interlayer plane during infiltration revealed that the effective water‐entry suction is characteristic of the predominant pore size in the sublayer and can be predicted from its median particle size (r2 = 0.99). Predictions regarding the onset of fingering and the wetted fractional volume of fingers were both validated for the monodisperse and polydisperse sublayers studied.
Aluminum Complexation by Protocatechuic and Caffeic Acids as Determined by Ultraviolet Spectrophotometry
Authors: Sikora F. J. , McBride M. B.
Published: July 2010

Ultraviolet (UV) spectrophotometry was used to study the complexation of Al by protocatechuic and caffeic acids at pH 3.8 to 4.5. The stoichiometry of the Al‐organic acid complex was found to be 1:1 through Job's method of continuous variation in the pH range studied. Increased pH and Al concentrations resulted in bathochromic shifts in the UV spectra of the organic acids due to the formation of an Al‐organic complex absorbing UV radiation differently than the free organic. Aluminum was concluded to be chelated by the ortho‐hydroxy group of the organic acids, as opposed to carboxyl‐group binding. The deprotonation of the carboxyl group in the free organic and Al‐organic complex had to be considered in the calculation of association constants. Association constants of 1015.33 and 1015.06 for protocatechuic and caffeic acids, respectively, were determined by Al titrations. Calculated absorbance as a function of pH agreed well with experimental titrations. Application of the determined association constants to a simplified model of a forest soil solution is presented.
Phosphate Sorption Implications on Phosphate Soil Tests and Uptake by Corn
Authors: Kuo S.
Published: July 2010

Phosphate sorption greatly affects P availability in soils. This greenhouse study was conducted to determine the influence of the quantity of P added and P sorption capacity on P soil tests and P accumulation by corn (Zea mays L.). Seven soils with varying contents of amorphous Al oxide were treated with 0 to 4 mmol P kg−1, incubated for 9 wk, and planted with corn in pot culture after uniform fertilization with N and K. Corn plants were harvested 4 wk after sowing. The dry‐matter yields, P concentration in the plants, as well as sodium bicarbonate extractable P (NaHCO3‐P) and sodium acetate extractable P (NaOAc‐P) were determined. The P‐sorption capacities of the soils were closely related to their amorphous Al oxide contents, and the average affinity coefficient was close to the intrinsic equilibrium constant for the formation of neutral surface species. While increasing in proportion to the amounts of P added, the concentration of NaHCO3‐P and NaOAc‐P decreased as the P‐sorption capacities of the soils increased. Both soil tests were a function of the fraction of P coverage on soil surfaces (Θ), defined as the ratio of the amount of P sorbed to the P‐sorption capacity. As with the soil tests, the plant P concentration and P uptake were all highly correlated with Θ. The quantity of P added and P‐sorption capacities of the soils affected the plant P concentration, dry‐matter yield, and P uptake in the same manner as they did the soil tests. As a single measurement, Θ was more successful than the two soil tests in predicting P accumulation and P uptake by the plants.
Salt Distribution and Hardpans at Dryland Saline Seeps in Southern Alberta
Authors: Sommerfeldt T. G. , Chang C. , Lamond B. J.
Published: July 2010

Hardpans at 30‐ to 60‐cm depth were found at three dryland saline‐seep sites in southern Alberta. The soils were sampled for analyses at 0.3‐m depth intervals to 1.2 m along two parallel transects across the sites. Of the acid‐extractable salts, CaCO3 was the most abundant. Shallow hardpans were found only in the saline, waterlogged, CO3‐rich soil in the discharge areas, generally at the depth where the 1:25 acid‐extractable Ca and CO3 contents exceeded 0.6 mol kg−1 of soil. Similar contents were also found in the recharge areas, where there was no detectable hardpan. Conditions in the discharge areas apparently were suitable for the precipitation and cementation necessary to form the hardpans. Further research is needed to characterize the hardpans and to study conditions, mechanisms, and causes for their formation and their relationships with saline seeps.
Rates of Change in Soil Structural Stability under Forages and Corn
Authors: Perfect E. , Kay B. D. , van Loon W. K. P. , Sheard R. W. , Pojasok T.
Published: July 2010

Data on rates of change in soil structural stability under different cropping systems are scarce. Field measurements of changes in dispersible clay (DC) and wet aggregate stability (WAS) were made during 3 yr in six forage treatments and conventional and zero‐till corn (Zea mays L.). The study was conducted on a silt loam soil (fine‐silty, mixed, mesic Typic Haplaquept intergrading to fine‐silty, mixed, mesic Typic Eutrochrept) near Elora, ON, Canada. The DC and WAS changed exponentially with soil water content at time of sampling and were adjusted for this parameter before calculating changes with time. No increases in structural stability occurred during the 3‐yr time period within the corn treatments. In contrast, all of the forage treatments resulted in highly significant rates of structural improvement. A half‐life parameter was used to quantify these changes. Calculated half lives for the different forages were similar in magnitude, being approximately 2.7 and 5.4 yr for DC and WAS, respectively. Across the treatments, highly significant correlations were found between rates of structural stabilization and mean root length (r = −0.57 for WAS, significant at P = 0.01), mean root weight (r = −0.56 for DC and −0.65 for WAS, significant at P = 0.01) and the coefficient of variation for soil water content (r = −0.64 for DC and −0.56 for WAS, significant at P = 0.01). Forages may promote structural improvement through their influence on the amplitude of wetting and drying cycles. In addition, large increases in stability were observed over the intervening winter months, suggesting a freeze‐thaw effect.
Cropping Frequencies to Sustain Long‐Term Conservation Tillage Systems
Authors: Langdale G. W. , Bruce R. R. , Wilson R. L.
Published: July 2010

Conservation tillage technologies are essential to develop long‐term alternative agriculture approaches to protect the nation's resources. This study was conducted to develop long‐term multiple cropping systems to sustain conservation crop production. Soybean [Glycine max (L.) Merrill] and grain sorghum [Sorghum bicolor (L.) Moench] cropping sequences following wheat (Triticum aestivum (L.) grain harvest were studied at three tillage‐intensity levels on a Cecil sandy loam (clayey, kaolinitic, thermic Typic Hapludult) soil. During the first 4‐yr crop rotation cycle, coulter in‐row chisel (MT) planted grain sorghum produced significantly more grain than either coulter (NT) or disk harrow (CT) planted (4.89 vs. 4.58 and 4.39 Mg ha−1), without a crop‐rotation response. In the second 4‐yr cycle, the sorghum grain yields declined NT > MT > CT (5.14 > 4.74 > 4.40 Mg ha−1) significantly with each increase in tillage‐intensity level. Soybean responded consistently and significantly to high‐frequency (1:1) rotation with grain sorghum. These responses to rotation with grain sorghum become less important to conservation tillage systems when favorable rainfall distributions permit grain yields that range between 2.00 and 3.50 Mg ha−1. Wheat yields increased significantly following soybean (first rotation cycle) until take‐all (Graeumannomyces graminis) became epidemic. Elucidation of significant grain sorghum responses to in‐row chisel and coulter conservation tillage during the first and second crop‐rotation cycles, respectively, requires additional research that focuses on characterization of temporal changes in the soil environment. Rotation of both cool‐ and warm‐season crops is necessary to sustain long‐term conservation tillage.
Nitrogen‐Fertilization Rate and Soil Nitrate Distribution for Microirrigated Sugarcane
Authors: Stanley C. D. , Green R. E. , Khan M. A. , Santo L. T.
Published: July 2010

Concern continues to grow over the fate of chemicals used in agricultural production and the associated potential for groundwater contamination. Management practices can directly influence the efficiency of inorganic fertilizer use by crops, and can affect the amount that moves away from the root zone. A field study was conducted to investigate the effect of three N‐fertilization rates (17.8, 9.1, and 6.0 kg ha−1 wk−1) on NO3 distribution and movement for the first 24 wk of growth of microirrigated sugarcane (Saccharum officinarum L.) grown on a Wahiawa silty clay (clayey, kaolinitic, isohyperthermic Tropeptic Eutrustox). One uncropped treatment receiving 9.1 kg ha−1 wk−1 was included for evaluation without crop uptake. The plots received irrigation daily, with N being applied once weekly. Clusters of soil‐solution extraction tubes were installed at depths of 15, 45, and 75 cm from the soil surface and 0, 30.5, 61, 91.5, and 122 cm away from microirrigation emitters to determine NO3 distribution patterns on a weekly basis. Soil water potential was monitored with tensiometers placed at similar locations. Results showed that all N levels were applied excessively early in the season and exhibited NO3 leaching beyond the root zone. Data collected at 22 wk after planting showed that the 6.0 kg ha−1 wk−1 rate had low NO3 concentrations through the soil profile, indicating a N‐rate closer to crop requirements. Daily irrigation applications were probably excessive and may have contributed to loss of NO3 from the root zone for all treatments. This study demonstrated that a dynamic approach to fertilization and irrigation needs to be developed to minimize water and nutrient losses from the crop root zone.
Douglas Fir Growth and Foliar Nutrient Responses to Nitrogen and Sulfur Fertilization
Authors: Blake John I. , Chappell H. N. , Bennett W. S. , Gessel S. P. , Webster S. R.
Published: July 2010

Nitrogen‐fertilizer response in conifer stands of the Pacific Northwest has been related to soil and foliar S, and growth has occasionally been enhanced by the addition of S. In order to test the effect of soil SO4‐S concentrations on N response, five stands of Douglas fir, Pseudotsuga menziesii (Mirb.) Franco, with low to moderate quantities of SO4‐S in the mineral soil horizon were treated with N and with N plus S. Sulfate‐S concentrations varied among soils from 6.0 to 19.2 mg S kg−1 in the surface soil and from 6.0 to 78.7 mg S kg−1 in the subsoil. Three treatments were applied: control, 224 kg N ha−1 as urea, and 224 kg N ha−1 plus 112 kg S ha−1 as a mixture of urea and (NH4)2SO4. Adjusted gross volume growth responses to N alone averaged −1.63 to 6.26 m3 ha−1 yr−1 after 3 to 4 yr; average volume growth gains from application of N with S over application of N alone varied from 0.73 to 4.5 m3 ha−1 yr−1 at four locations. At one location, the N‐alone effect was greater than that from N with S. Foliar N concentrations in the N‐with‐S treatments were generally higher than in the N‐alone treatments. Little change in foliar‐S content occurred in the N‐with‐S plots. Mean treatment effects were unrelated to foliar N/S, total S, or foliar SO4‐S on the controls, and the relationship between soil SO4‐S and the differential growth response between N and N with S was highly variable. Treatments were reapplied at a rate of 448 kg N ha−1, 224 kg S ha−1, and 9 kg B ha−1. Four‐year growth effects were similar to the first period except at one location where N responses appeared greatly improved by B. Periodic annual growth response to N over the entire study period was inversely related to site index and directly related to foliar N content. Prescriptions involving S will require more efficient S sources and a better assessment of S uptake and S reactions in these soils.
Adsorption of Heavy Metals by Silicon and Aluminum Oxide Surfaces on Clay Minerals
Authors: Schulthess C. P. , Huang C. P.
Published: July 2010

The pH value of an adsorption edge (i.e., the pH value where a change occurs in the amount of aqueous ions adsorbed by a solid phase) is dependent on the surface‐metal bonding strength and, consequently, on the type of adsorption site involved. The metal‐adsorption sites of natural (untreated) kaolinite, montmorillonite, and synthetic mordenite were elucidated by comparing the pH values of their adsorption edges with those of Si and Al oxides. Cation adsorption by these clays is strongly influenced by the Si/Al surfacesite ratio, steric effects of interlayers or channels, Lewis acid strength of the metal, and pH of the medium. Using Ni, kaolinite showed additive adsorption behavior by the Si and Al oxide surfaces with well‐defined boundaries. The adsorption edge of Ni by mordenite occurred at low pH values and was attributed to the increased Ni‐binding stability inside the channels of the zeolite structure. Several heavy metals (Ni, Zn, Cd, and Pb) were used to properly identify the various adsorption edges on montmorillonite. The adsorption of Ni by montmorillonite was similar to the Si and Al oxide surfaces but with an additional adsorption edge observed at low pH values, which was attributed to the interlayer structure of the clay. The presumed pH‐independent cation‐adsorption behavior below pH 6 by 2:1 clay minerals is probably due to pH‐dependent adsorption on amorphous Si oxide sites that can induce ion‐exchange reactions at much lower pH values than previously assumed.
Determination of Boron in Soils Containing Inorganic and Organic Boron Sources
Authors: Kaplan D. I. , Adriano D. C. , Mills G. L. , Sajwan K. S. , Burkman W. G.
Published: July 2010

Laboratory experiments were conducted to evaluate the potential interference of organoborates with the commonly used azomethine‐H method of determining B in soils. In addition, an alternative method, the cold‐water‐extractable B (CWE‐B) method, was developed and compared with the commonly used hot‐water‐extractable B (HWE‐B) method on soils containing organoborates. In a solution study, the organoborate sodium tetraphenyl‐boron (NaTPB) interfered more than its hydrolysis by‐product diphenylboric acid (DPBA) with the colorimetric detection of B by the azomethine‐H method. The interference was enhanced by boiling these compounds under conditions similar to those required by the HWE‐B method. However, passing these organoborate solutions through C18 cartridges (an octadecyl‐silane bond phase packing that adsorbs many organic compounds) prior to boiling alleviated the interference. Furthermore, the C18 cartridges had little effect on inorganic B levels. A study measuring indigenous B levels of 31 diverse soils collected from throughout the USA revealed that the CWE‐B method extracted less B, though its values were highly correlated (r = 0.84; P ≤ 0.01) to the HWE‐B values. In addition, these HWE‐B and CWE‐B values were almost identically correlated to the same soil properties: pH and exchangeable Ca. The use of C18 cartridges in conjunction with the CWE‐B method was satisfactory for determining inorganic B levels in soils containing organoborates.
Nitrogen Mineralization in Semiarid Soils of Morocco: Rate Constant Variation with Depth
Authors: Soudi Brahim , Sbai Abderrahmane , Chiang Claude N.
Published: July 2010

Development of drought‐resistant crops through breeding for extensive root systems emphasizes the importance of subsoil N mineralization for crop production in arid regions. This study was conducted to determine the influence of soil depth on N‐mineralization rate, total N, and amino acid N contents for eight representative soils of the subarid zone of Morocco. Nitrogen‐mineralization ability within the profiles was evaluated through long‐term soil incubation/leaching experiments. Total N and amino acid N were measured by the Kjeldahl method and acid hydrolysis, respectively. A hydrolysable‐N‐production rate was also evaluated, through successive acid hydrolysis of samples from two soil profiles. The changes with depth for the three variables studied were described by two equations. One is a power law of the type Y = AD−B, where Y is one of the variables, A and B are two positive constants, and D is depth. The second is an exponential equation, Y = A exp(−BD). Parameter B had values of 1.3 and 0.04 for N‐mineralization rate, 0.7 and 0.021 for amino acid N, and 0.40 and 0.012 for total N for the power‐law and exponential models, respectively. Significant differences were found between the rates of change with depth (B value) of the three quantities studied using the second equation. The hydrolysable‐N‐production rate decreased with depth in the profiles, indicating a reduction of the chemical degradability of N compounds in deeper horizons. These results suggest that the decrease of N mineralization with depth may be attributed to a recondensation of amino acids in complex biochemical compounds more resistant to biodegradation.
Sweetgum Half‐Sib Seed Source Response to Nitrogen and Phosphorus Fertilization in Mississippi
Authors: Nelson Lyle E. , Switzer George L.
Published: July 2010

This field experiment was undertaken to determine the response to N and P of sweetgum (Liquidambar styraciflua L.) under plantation culture, and the variation in response among seedlings derived from four half‐sib seed sources from alluvial and upland sites. Two‐year‐old seedlings were planted in a Mathiston silt loam (fine‐silty, siliceous, acid, thermic Aeric Fluvaquent) in 1972. In 1973, 0‐0‐0, 100‐0‐0, 100‐100‐0, and 200‐100‐0 kg/ha of N‐P‐K were broadcast. In 1975, the N treatments were repeated. Height, diameter at breast height (DBH), and foliar N were monitored through nine field growing seasons. There was no response to P. At 9 yr, the mean total height of the unfertilized half‐sibs was 7.1m, mean DBH was 7.8 cm, basal area was 5.0 m2/ha, stem volume outside bark was 15 m3/ha, and woody biomass was 8.1 Mg/ha. Increases from fertilization were 9, 14, 28, 39, and 40%, respectively. There was a half‐sib × fertility interaction with maximum response of three half‐sibs to 200 kg N/ha and one to 400 kg N/ha. The response of the two half‐sibs from alluvial seed sources was about double that of the two from upland seed sources. Foliar N concentrations of all treatments decreased during the 9 yr; however, foliar concentrations in fertilized trees were only slightly higher than in the unfertilized throughout. Although increases in annual increments due to fertilization were measurable for only 1 or 2 yr following fertilization, the resulting differences in volume and biomass were maintained in subsequent years.
Microplot Design for Determining Corn Recovery of Nitrogen Fertilizer Applied in the Row
Authors: Blaylock A. D. , Benjamin J. G. , Cruse R. M.
Published: July 2010

One‐ and three‐row corn (Zea mays L.) microplots were compared for determining 15N‐depleted fertilizer recovery from in‐row N applications. Studies were conducted with Iowa ridge‐tillage systems on Monona silt loam (fine‐silty, mixed, mesic Typic Hapludoll), Webster silty clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll), and Marna silty clay loam (fine, montmorillonitic, mesic Typic Haplaquoll). Corn rows were injected with 15N‐depleted NH4NO3 (99.99% 14N) at 56 and 112 kg N ha−1 on Monona silt loam and at 67 and 157 kg N ha−1 on Webster and Marna silty clay loams. Percentage N from fertilizer in the mature‐plant samples ranged from 19.8 for grain fertilized at 56 kg N ha−1 to 50.0 for stover at 157 kg N ha−1. One‐ and three‐row microplots were not significantly different for determining corn N recovery in the application year from in‐row N placements.
Application of Two‐Site/Two‐Region Models for Studying Simultaneous Nonequilibrium Transport and Degradation of Pesticides
Authors: Gamerdinger A. P. , Wagenet R. J. , van Genuchten M. Th.
Published: July 2010

Quantitative laboratory study of pesticide sorption and degradation during transport can provide insight into the basic processes affecting pesticide fate in field soils. Accordingly, we demonstrate the application of analytical solutions of two‐site/two‐region transport models useful in studying simultaneous pesticide sorption and degradation. Soil‐column displacement experiments involving 3H2O, Cl, and atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) were conducted during steady‐state water flow at two pore‐water velocities and two pesticide concentrations. The soil used is a Valois silty loam (coarse‐loamy, mixed, mesic Typic Dystrochrept). Effluent data from these experiments were used to demonstrate the application of these analytical solutions, as well as a parameter‐estimation computer program based on these solutions. The ability to use laboratory‐derived estimates of equilibrium sorption parameters to describe sorption under flowing conditions was evaluated at each flow velocity. Significant correlation between soil sorption partitioning and degradation prevents the simultaneous determination of both processes using these solutions. However, estimates of degradation obtained from mass balances of the column data were useful in identifying the equilibrium sorption parameters. Data collected elsewhere for 2,4,5‐T (2,4,5‐trichlorophenoxyacetic acid) herbicide transport were used as an additional example of the application of the model with degradation. Strengths and weaknesses of the models, and suggestions for further study, are presented.
Measurement of Soil Macropore Air Permeability
Authors: Roseberg R. J. , McCoy E. L.
Published: July 2010

Soil air‐permeability measurement is a promising tool for determining pore geometric influences on transport processes. The inability of previous systems to allow air‐flow measurement on undisturbed soil samples at and near saturation, where only macropores will conduct air, has prevented routine use of this technique for investigation of macropore geometry. The device described here allows simultaneous measurement of air permeability (Ka) and the soil water‐retention curve in the 0‐ to −6.0‐kPa matric‐potential range. This is accomplished by counteracting the effect of the gravitational‐potential gradient within the sample using controlled air pressure. Use of a wettable porous plastic of high conductance as the tension‐control medium allows equilibration times of <4 h during desaturation for each step change in matric potential (ψm). Operation of the device is illustrated with results from two undisturbed soil samples having contrasting macroporosity. The soil core with visible macropores (> 1‐mm diameter) had a higher Ka and a greater change in water content at each ψm step throughout the 0‐ to −3.0‐kPa range, compared with the core without visible macropores. The positive linear slope of the log air‐filled porosity vs. log Ka relationship was greater for the sample containing visible macropores, indicating greater pore continuity. Air permeability of the macroporous sample remained >0 at ψm = 0, but the opposite was true for the soil sample without visible macropores.
Estimating Divalent Cadmium Activities Measured in Arid‐Zone Soils using Competitive Chelation
Authors: Workman S. M. , Lindsay W. L.
Published: July 2010

Competitive chelation was explored as a method of measuring divalent Cd activity in neutral to alkaline soils. The most successful combination of chelating agents and competing metals comprised dtpa (diethylenetriaminepentaacetic acid) and Pb2+ in equilibrium with added PbCO3(c). A series of 10−5 M dtpa solutions containing varying initial mole fractions of Cd and Pb were reacted with soils for 140 h. Some solutions lost Cd and gained Pb, while others gained Cd and lost Pb. From these results it was possible to estimate the composition of a unique solution that does not change upon reaction with a given soil. The composition of this unique solution reflects equilibrium conditions and was used to calculate Cd2+ activity. Eight soils ranging in pH from 7.15 to 8.25 showed Cd2+ activities ranging from 10−6.6 to 10−9.4 M. The Cd2+ activities measured in these soils could be predicted using the following expression:

(Cd2+) = 107.61 (H+)2

This solubility of Cd2+ in soils is approximately two orders of magnitude lower than the activity of Cd2+ in equilibrium with CdCO3(c) and atmospheric CO2. No known Cd mineral has yet been identified whose solubility reflects this low activity of Cd2+. The competitive chelation method used here avoids many of the pitfalls encountered in measuring extremely low levels of Cd in neutral and alkaline soils where Cd‐organic complexes may be present.
Evaluation of 2‐Ethynylpyridine as a Soil Nitrification Inhibitor
Authors: McCarty G. W. , Bremner J. M.
Published: July 2010

Recent work in our laboratory showed that 2‐ethynylpyridine is a potent inhibitor of nitrification in soil. To further evaluate this compound as a soil nitrification inhibitor, we compared the effects of 2‐ethynylpyridine and 16 compounds patented or proposed as fertilizer amendments for inhibition of nitrification in soil. We measured production of NO2 and NO3 in soils incubated under aerobic conditions at 20, 25, or 30 °C after treatment with (NH4)2SO4 or urea. The data obtained showed that 2‐ethynylpyridine compared favorably with nitrapyrin [N‐Serve; 2‐chloro‐6‐(trichloromethyl)pyridine] and etridiazole [Dwell; 5‐ethoxy‐3‐trichloromethyl‐1,2,4‐thiadiazole] for inhibition of nitrification in soil and was considerably more effective than the other nitrification inhibitors tested (dicyandiamide [DCD], thiourea [Tu], guanylthiourea [ASU], potassium azide, 4‐amino‐1,2,4‐triazole [ATC], 2‐amino‐4‐chloro‐6‐methylpyridine [AM], 2‐mercaptobenzothiazole [MBT], 2,4‐diamino‐6‐trichloromethyltriazine, sulfathiazole [ST], sodium thiocarbonate [Na2CS3], N‐2,5‐dichlorophenylsuccinamide [DCS], 4‐nitrobenzotrichloride, 4‐mesylbenzotrichloride, and ammonium thiosulfate [(NH4)2S2O3]). Other studies showed that 2‐ethynylpyridine is more effective for inhibiting nitrification of NH4‐N than of urea‐N, that it has very little, if any, effect on hydrolysis of urea or denitrification of NO3 in soil, and that its effectiveness as a soil nitrification inhibitor is markedly affected by soil type and temperature. These findings and other work reported indicate that 2‐ethynylpyridine deserves consideration as a fertilizer amendment for retarding nitrification of fertilizer N in soil.
Growth of Genetically Altered Pseudomonas solanacearum in Soil and Rhizosphere
Authors: Hartel Peter G. , Williamson Joseph W. , Schell Mark A.
Published: July 2010

The extent to which a bacterium can grow in soil and in the rhizosphere is influenced by the presence or absence of various genes. The effect of genetic alteration of the egl gene, encoding a β‐1,4‐endoglucanase, on the growth of Pseudomonas solanacearum E.F. Smith (the causal agent of bacterial wilt) in soil and in the rhizosphere of tomato (Lycopersicon esculentum Mill.), common purslane (Portulaca oleracea L.), and pearl millet (Pennisetum glaucum (L.) R. Br.) was determined. Endoglucanase production by P. solanacearum was either inactivated by transposon (Tn5) insertion mutagenesis or enhanced twofold by increasing the egl copy number with a recombinant plasmid (pHE3). In a test of the stability of the genetic alterations in two different soils, the transposon in the chromosome was detectable for >120 d, but the recombinant plasmid was apparently lost after 14 d in one soil and after 120 d in the other. In comparison to the wild‐type strain, the generation times of the strains with the transposon and the recombinant plasmid increased 16 and 25%, respectively, in one soil solution and 35 and 53% in the other soil solution; this correlated well with the ability of the strains to grow in the same freshly moistened soils. Under conditions of soil inoculation, the genetically altered strains did not wilt tomato seedings significantly faster or slower than the wild‐type strain. Although all of the P. solanacearum strains, including the wild type, grew in the rhizosphere of gnotobiotically grown tomato plants, none of the strains grew in the rhizosphere of tomato, common purslane, or pearl millet under nonsterile conditions. The data suggest that genetic alterations slow the growth of P. solanacearum in freshly moistened soil, and that endoglucanase is of minor importance to the growth of P. solanacearum under these conditions.
Aliphatic Acids: Influence on Sulfate Mobility in a Forested Cecil Soil
Authors: Evans A. , Anderson T. J.
Published: July 2010

Dissolved organic substances derived from forest litter are believed to influence the retention and movement of SO2−4 in forest soils. A column study was conducted in which 35SO4 was surface applied to a soil and leached with either low‐molecular‐weight aliphatic acids (AA) or a forest‐litter extract. Oxalic, malonic, and succinic acids were used in the concentration range 8.0 × 10−3 to 1.0 × 10−5 mol L−1. Movement of 35SO4 was determined with column depth, as was the 35SO4 activity in the collected leachates. Labeled SO4 soil movement was found to increase with increasing AA concentration. Leachate 35SO4 activity was observed to increase in the order malonic > succinic > oxalic for acid treatments > 1.0 × 10−4 mol L−1. The 1.0 × 10−5 mol L−1 acid treatments did not result in 35SO4 break‐through in the soil columns. Reduced exchangeable 35SO4 for organic acid ≥ 1.0 × 10−3 mol L−1 suggests that at high concentrations, aliphatic acids may activate sulfate retention sites in soil, while at lower concentrations these acids may accelerate the movement of 35SO4 in forest soils due to selective organic‐acid adsorption by soil components.
Intrinsic Failure and Cracking of Clay
Authors: Murray R. S. , Quirk J. P.
Published: July 2010

Cracks play a major role in determining the strength and fluid transmission properties of clay soil. This report, which bears on the origin of cracks in a clay matrix, arose from observations made while investigating the pore‐size distribution (<100 nm) of clay using low‐temperature (77 K) N2 sorption isotherms. The two surface areas derived, by independent means, from the adsorption and desorption branches of such isotherms are in surprisingly good agreement for a range of clays. The apparent absence of network effects, implied by this surface‐area accord, can only occur if virtually all voids have access to the outside of the sample via at least one path that contains no narrower voids or constrictions. This points to the existence of a very extensive system of cracks that may form the boundaries of domains or regions of common particle orientation in clay. The formation of this system of cracks has been named intrinsic failure and is believed to result from the shrinking and swelling of the individual, randomly oriented clay domains. The possible significance of intrinsic failure is that it may be the precursor of clay cracking in general and that it may impose an upper limit on the strength of the clay matrix.
Spatial Dependence of Soil Sodicity and Tree Growth in a Natric Haplustalf
Authors: Samra J. S. , Gill H. S. , Richter J. , Anlauf R.
Published: July 2010

A precise knowledge of the spatial variability of salt‐affected soils is a prerequisite to optimizing their land use and maximizing biomass production. This study was conducted to investigate inherent variation in pH, sodium adsorption ratio, P, and K of a Typic Natric Haplustalf, growth of Shisham (Dalbergia sissoo Roxb. ex DC.), and their interdependencies. Root‐zone soil was sampled on a 6 by 6 m grid at 162 locations (18 rows by 9 columns) of a field at 0.3‐m depth increments up to 1.2 m, and analyzed. Depending on the depth and soil properties, trend variation ranged from 14 to 47% (overall average of 27%) of the total variance. Corresponding component of the tree‐height heterogeneity varied from 16 to 20% during the four observation years. Ten to 74% of the remaining soil variability, depending on soil layer and properties, was isotropically spatially structured. Thus, on an average, about 30% of the total soil variability was structured. Similarly, the structural component of tree‐height variation ranged from 35 to 46% of the sill during 4 yr. Therefore, 33% (average of 4 yr) of the tree‐height variance was structured. Spatial correlations of soil properties with tree growth were elaborated through cross semivariograms. Spatially sensitive statistical procedures for the assessment of land qualities, technologies, and soil‐plant relationships are recommended.