bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizing Macropores in Soil by Computed Tomography
Authors: Warner G. S. , Nieber J. L. , Moore I. D. , Geise R. A.
Published: July 2010

Cross sections of a 203‐mm diam. soil core taken from a site under Kentucky bluegrass (Poa pratensis L.) were scanned using x‐ray computed tomography (CT) to determine if macropores such as cracks, earthworm holes and root channels could be distinguished and characterized. The core was physically sectioned at the same locations as the CT scans to verify the size and location of pores seen on the CT images. Macropores 1 mm and larger could be easily and quickly distinguished by the method. By manipulation of the scanner images, air‐filled pores, roots and stones were identified within the soil matrix. A wet bulk density plus an air‐filled macroporosity were calculated for scans. Prior to sectioning, a dye solution was ponded on the surface of the core and allowed to infiltrate to assess the continuity of pores through the core.
Estimation of the Saturated Hydraulic Conductivity in Clay Soils from Soil Moisture Retention Data
Authors: Messing I.
Published: July 2010

A generalized Kozeny‐Carman equation was employed to relate saturated hydraulic conductivity (Ks) to effective porosity (φe) in clay profiles in Sweden with clay content >15% were analyzed. The value empirical constants. The term φe was defined as porosity (φ) minus soil‐water content at −30 kPa. Around 500 horizons from 60 soil profiles in Sweden with clay content >15% were analyzed. The value of n was tested with two statistical methods. According to the first method, a regression test on the log‐log relationship between Ks and φe with least‐squares lines fitted through the data, the exponent n was found to lie around 2 for soils with high clay content (>40%), and 3 for soils with lower clay content (15–40%). The correlation coefficients were moderate, ranging from 0.51 to 0.71 for different clay soil groups. In the second method, the cumulative frequency distributions of scaling factors for Ks determined from measured values of Ks were compared with scaling factors for Ks determined from φe. Reasonable agreements were obtained with n = 4 to 5 for soils with clay content >40%, and with n = 5 to 6 for soils with clay content 15 to 40%. The second method gave n‐values that correspond well with other recent published work. The results indicate that the spatial distribution of Ks is estimated reasonably well from φe values, whereas the individual values of Ks are not estimated as well.
Sample Preparation for Determining Ions in Dark Colored Sodic Soil Extracts
Authors: Robbins Charles W.
Published: July 2010

Saturation paste extracts of sodic soils (pH >8.5 and electrical conductivity <4.0 dS m−1) usually contain dark colored, suspended organic matter that interferes with colorimetric, turbidimetric, potentiometric, ion chromatographic (IC) and to a lesser extent, atomic absorption spectrophotometry and flame emission procedures. Bicarbonate also interferes with formate analysis by IC in those extracts. This study was conducted to develop a simple pretreatment method for removing those interferences without introducing new interferences. Fifteen mL extract samples were titrated to pH 8.4, then to 4.7 and finally to a pH range of 3.0 to 3.5 with standardized H2SO4 or HCl. The first two end points determine CO2‐3 and HCO‐3 concentrations. The third pH adjustment removed the HCO‐3 interference from the formate analysis and allowed for organic matter coagulation. The acid choice depended on whether Cl‐ or SO2‐4 was to be measured later. To remove the organic matter, the extracts were contrifuged and forced through a 0.2‐µm nylon filter following 0.08 M AlCl3 or 0.04 M Al2(SO4)3 treatments. Formate and acetate concentrations were determined by IC. The Cl‐ concentrations were determined by colorimetric, and IC procedures. The SO2‐4 concentrations were measured turbidimetrically and by IC. The extracts were analyzed for Ca2+ and Mg2+ by atomic adsorption spectrophotometry, and Na+ and K+ by flame emission. Titrating the extracts as described provided CO2‐3 and HCO‐3 data, removed the HCO‐3 interference from the formate analysis, and allowed Al3+ to coagulate the suspended organic matter, which was then removed by centrifugation and filtration. This pretreatment did not interfere with any of the analytical methods tested, except for cation determination by IC and anion determination by IC when methyl orange was used as a pH end point indicator.
Biosynthesis of Cytokinins in Soil
Authors: Nieto K. F. , Frankenberger W. T.
Published: July 2010

Cytokinin biosynthesis in soil by rhizosphere microorganisms may increase upon the addition of physiological precursors and affect plant growth. This study was conducted to establish the effects of the purine, adenine (ADE), the isoprenoid, isopentyl alcohol (IA), and a cytokinin‐producing bacterium, on cytokinin biosynthesis in an Arlington soil (coarse‐loamy, mixed thermic Haplic Durixeralf). Various concentrations of ADE were applied, separately and in combination with 8.81 × 10−2 g IA kg−1 soil, and an inoculum of Azotobacter chroococcum (ATCC 9043), as soil treatments. Cytokinin bioactivity, isolation, and quantification of soil extracts were monitored over a period of 7 d using the radish cotyledon bioassay and HPLC‐UV spectrometry. Cytokinin production was evident as early as 2 d and reached a maximum at 5 d post‐treatment. An application of 1.35 × 10−4 g ADE kg−1 soil, 8.81 × 10−2 g IA kg−1 soil, and A. chroococcum enhanced cytokinin production of zeatin riboside and t‐zeatin in this soil up to 1.50‐ and 1.39‐fold, respectively, in comparison to controls containing no precursors. The production of zeatin riboside (78.0 µg kg−1) and t‐zeatin (22.1 µg kg−1) in the presence of ADE and IA was 1.35‐ and 2.44‐fold greater with the inoculation of A. chroococcum, when compared to the indigenous microflora alone. This study provides information on extraction and analytical detection of cytokinins in soil and reveals that microbial biosynthesis of cytokinins can be enhanced by applying physiological precursors to soil.
Vacuum Apparatus to Concentrate Ammonium Solutions for Nitrogen Isotope‐Ratio Analysis
Authors: Kelley K. R.
Published: July 2010

Concentrating NH4 solutions in preparation for 15N analysis usually is accomplished by evaporating samples to dryness with open‐air or forced‐air systems. This paper describes a newly developed drying apparatus that operates under vacuum to facilitate evaporation, prevent sample contamination, and avoid several problems associated with conventional evaporative systems. Standard (NH4)2SO4 samples containing 0.20, 0.50, 1.00, or 2.00 atom % 15N were acidulated with H2SO4 or H3BO3 plus H2SO4 and evaporated to dryness with the vacuum system, a conventional forced‐air system, or a conventional open‐air system. No significant contamination by atmospheric NH3 was found in samples acidulated with H2SO4 and dried with the vacuum apparatus. In comparison, absorption of atmospheric NH3 during evaporative processing of H2SO4‐acidulated samples with the forced‐air or open‐air system resulted in dilution of 15N concentrations in excess of 0.027 and 0.047 atom % 15N in standards containing 1.00 or 2.00 atom % 15N, respectively. The atom % 15N concentrations of evaporated samples containing H3BO3 plus H2SO4 were inconsistent. No significant N loss, isotopic fractionation, or atmospheric contamination was detected in samples acidulated with H2SO4 and heated to 130 °C under vacuum for up to 4 h past dryness. Moreover, no significant cross‐contamination was detected in 4‐mL samples of varying 15N concentration that were acidulated with H2SO4 and dried under vacuum, indicating that the vacuum apparatus can be used to simultaneously process samples differing in 15N concentration. The apparatus can accommodate up to 80 samples, depending on sample volume and container size (< 5–250 mL).
Metabolism of Labeled Organic Nitrogen in Soil: Regulation by Inorganic Nitrogen
Authors: Smith M. Scott , Rice Charles W. , Paul Eldor A.
Published: July 2010

Regulation of organic N metabolism by inorganic N availability was investigated in short‐term laboratory incubations of soil. A 14C‐, 15N‐labeled organic N substrate was produced by growing Pseudomonas stutzeri in labeled media and isolating a cytoplasmic fraction. This was added to soils that had been preincubated with glucose or glucose plus NH+4 to induce conditions of N deficiency or sufficiency. Regulation by inorganic N was indicated by stimulated proteolytic enzyme activity and greater initial rates of cytoplasmic 14C mineralization in N deficient soils. However, effects of N deficiency on 14C mineralization persisted for no more than 24 h. Preinduced N deficiency significantly decreased the extent of 15N mineralized from cytoplasmic N. Mineralization of 14C from leucine added to soil was similarly affected by N availability, yet 14C‐glutamate mineralization was apparently unaffected. In another experiment labeled cytoplasm was added simultaneously with or without a larger quantity of glucose. The glucose caused virtually complete assimilation of 15N but had no effect on apparent assimilation of 14C. Thus, there was no relationship between 15N assimilation and 14C assimilation, suggesting that the C and N contained in organic N are processed separately by soil microbes. Inorganic N availability may have short‐term effects on metabolism of C in organic N but long‐lasting effects appear to be minimal.
Microplot Size Reguirements for Measuring Balances of Fertilizer Nitrogen‐15 Applied to Maize
Authors: Stumpe J. M. , Vlek P. L. G. , Mughogho S. K. , Ganry F.
Published: July 2010

In order to reduce the amount of expensive labeled‐N fertilizer needed for field studies of 15N balances in maize (Zea mays L.), four experiments were conducted to determine the minimum microplot size requirement. The minimum microplot area required was ascertained by applying urea labeled with 15N to 4.5‐ by 2.0‐m microplots inside larger plots treated with the same fertilizer and observing the dilution of 15N in maize plants by N from outside the microplot with respect to proximity to microplot borders. Under the conditions of this study, interrow spacings of 75 cm resulted in dilution of 15N in only the row located 37.5 cm from the microplot border. Intrarow plant spacings of 25 cm resulted in the dilution of 15N in the plants located 12.5 and 37.5 cm from the microplot border. Microplots with 3.0‐ by 2.0‐m border dimensions, containing four rows and eight plants/row, resulted in the desired number of plants (eight) unaffected by proximity to the border from a minimum microplot area and thus minimized the requirement for 15N. Complete recovery of 15N in the plant‐soil system occurred when climatic conditions and fertilizer management practices favored N conservation, confirming that microplots were sufficiently large for an accurate determination of 15N balance.
Texture, Climate, and Cultivation Effects on Soil Organic Matter Content in U.S. Grassland Soils
Authors: Burke I. C. , Yonker C. M. , Parton W. J. , Cole C. V. , Flach K. , Schimel D. S.
Published: July 2010

Soil organic C content, a major source of system stability in agroecosystems, is controlled by many factors that have complex interactions. The purpose of this study was to evaluate the major controls over soil organic carbon content, and to predict regional patterns of carbon in range and cultivated soils. We obtained pedon and climate data for 500 rangeland and 300 cultivated soils in the U.S. Central Plains Grasslands, and statistically analyzed relationships between C and soil texture and climate. Regression models of the regional soils database indicated that organic C increased with precipitation and clay content, and decreased with temperature. Analysis of cultivated and rangeland soils indicated that C losses due to cultivation increased with precipitation, and that relative organic C losses are lowest in clay soils. Application of the regression models to a regional climate database showed potential soil organic matter losses to be highest in the northeastern section of the Central Plains Grasslands, decreasing generally from east to west. These statistical data analyses can be combined with more mechanistic models to evaluate controls of soil organic matter formation and turnover, and the implications for regional management.
Birdsfoot Trefoil Seedling Response to Soil Phosphorus and Potassium Availability Indexes
Authors: Russelle M. P. , Meyers L. L. , McGraw R. L.
Published: July 2010

Birdsfoot trefoil (Lotus corniculatus L.) is a promising forage legume, yet little is known about its nutrient requirements during early growth. Several soil P and K indexes were evaluated for their ability to predict dry mass (DM) and P and K concentration and uptake by ‘Fergus’ and ‘Maitland’ birdsfoot trefoil seedlings grown for 6 wk in the greenhouse in four diverse soils amended to attain a broad range of plant‐available P and K. Soils were extracted with 0.01 M CaCl2, neutral 1 M ammonium acetate, or H2SO4 to estimate plant‐available K, and 1 mM SrCl2, Bray and Kurtz no. 1 (Bray‐P), or anion exchange resin (AER) to estimate available P. Shoot DM was not influenced by soil K and increased with increasing soil P, being best predicted across soils by AER‐P. Maitland DM exceeded that of Fergus at all fertility levels. Tissue concentration of P and K were best related to soil solution concentration (extracted with weak salt solutions), but only one‐half the variation in tissue P concentration was explained by soil solution‐P concentration. Across soils, P and K uptake were best related to Bray‐P and to solution‐K concentration, respectively, but exchangeable‐K exhibited less sensitivity to cultivar differences than solution‐K. Anion exchange resin appeared to extract a constant fraction of nonoccluded Fe‐ and Al‐bound P (47%), regardless of the oxide content of the soil, whereas the Bray‐1 reagent appeared to extract a constant proportion of P per unit mass Fe oxide present. These differences may account for the relatively poor performance of AER in predicting P uptake across soils differing in parent material.
Tillage and Surface Residue Effects on Evaporation from Soils
Authors: Steiner J. L.
Published: July 2010

Many crop growth models require modification for dryland farming systems because they do not predict an effect of residues on the soil water balance. Daily evaporation (E) from a Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) was measured in three experiments using laboratory cores or field microlysimeters to determine effects of tillage and residues on cumulative E and on E rate. The first experiment showed that the disk treatment had the highest rate of Stage 1 E and a lower slope of the Stage 2 E curve than sweep and no‐tillage treatments. Effects of tillage on surface wheat (Triticum aestivum L.) residues and on soil physical properties both seemed related to E. In a subsequent experiment, no effect of tillage‐induced differences in soil properties on daily E was measured when wheat residues were removed before tillage. In the third experiment the effect of cotton (Gossypium hirsutum L.), sorghum [Sorghum bicolor (L.) Moench], or wheat residue (x, m3 m−2) on the initial, energy‐limited rate of E (y, the potential E at the surface relative to bare soil E) was described by a logarithmic relationship [y = −0.99 − 0.236 (ln x), n = 36, r2 = 0.87]. With residues described on a mass/unit area basis, crop‐specific curves were obtained; but with residues described on a thickness or volume/unit area basis, the curves obtained with the different crop residues were very similar to the pooled relationship given above. This simple relationship between residue level and daily E can be incorporated into water balances of commonly used crop growth models to increase the accuracy of water balance prediction for different cropping systems.
Effect of Whole‐Tree Harvesting on the Sulfur Dynamics of a Forest Soil
Authors: Mitchell M. J. , Driscoll C. T. , Fuller R. D. , David M. B. , Likens G. E.
Published: July 2010

Sulfur constituents in the soil at the Hubbard Brook Experimental Forest are dominated by C‐bonded S and ester‐sulfate with smaller concentrations of adsorbed sulfate and ZnHCl‐reducible S forms. The relative proportions of these constituents are similar to those found in other Spodosols. Two years after a whole‐tree harvest of Watershed 5 there was a significant increase in adsorbed sulfate in the E and Bh horizons from 0.70 to 3.16 and from 2.73 to 4.96 kg ha−1, respectively, while organic S pools remained relatively constant except for some change in ester‐sulfate pools. This increase in sulfate in these horizons is consistent with patterns of soil solution and stream chemistry, which indicate increased sulfate adsorption due to acidification following mineralization of N, nitrification, and nitric acid leaching. Mass balance calculations comparing SO4 flux in stream water from watershed 5 with Watershed 6 (reference) accounted for 88% of the sulfate adsorbed in the E and Bh horizons of the former watershed. Organic S ranged 0.7 to 9.5 µmol S L−1 in stream and soil solutions. When this organic S is transported through the soil and deposited in the B horizon, it may serve as a large, stable pool of soil S, less subject to change than that of adsorbed sulfate.
Some Factors Limiting the Dissolution Rate of Phosphogypsum in an Acid Soil
Authors: Frenkel H. , Fey M. V. , Noble A. D.
Published: July 2010

Granules up to 6 mm in diameter were collected in the field from an acid Natal soil (Palehumult) under cultivation, following reports of unexpected persistence of the material 2 yr after incorporation. The granules were subjected to a dissolution procedure employing electrical conductivity measurements of a stirred solution in which the granules were suspended in a perforated container. The rate of dissolution of the soiled granules which had first been washed in water to remove adhering soil was slower than that of the fresh granules pretreated in the same way. Scanning electron microscopy showed that a coating approximately 5‐µm thick enveloped the soiled granule. The coating was found by energy dispersive x‐ray analysis to contain a co‐concentration of Al and P. X‐ray diffractometric study of the water‐insoluble residue of scrapings from granule exteriors showed the presence of an unidentified, crystalline, lazulite‐like phase which could not be detected in the surrounding soil matrix or in the interior of the granules. The slow dissolution of the granules in the field soil is only partly due to the coating, however, with particle size being the dominant influence.
Wettable Porous Plastic for Use as a Porous Barrier in Soil Hydraulic Studies
Authors: McCoy Edward L.
Published: July 2010

Two grades of wettable porous plastic were examined for their applicability in water characteristic measurements and other soil hydraulic studies. The porous plastic is available in sheets (0.46 m wide, arbitrary lengths) and the two grades are composed of different amounts of polyvinyl chloride (PVC) and silica. Grade A‐20 exhibited a range of bubbling pressures between 62 and 69 kPa and a mean conductance of 0.20 h−1. Grade A‐40 exhibited a range of bubbling pressures between 21 and 35 kPa and a mean conductance of 1.60 h−1. These conductances generally exceed that of commonly employed porous barriers with comparable bubbling pressures. Comparison of the water retention curves of grades A‐20 and A‐40 indicate that grade A‐20 is more uniform, has lower porosity, and has smaller effective pore diameters with a narrower range of pore sizes. The porous plastic is easily cut to size by scissors and bonded to itself, PVC, or acrylic. The material is also durable and inexpensive.
Application of Fractal Mathematics to Soil Water Retention Estimation
Authors: Tyler Scott W. , Wheatcraft Stephen W.
Published: July 2010

In this paper, we present an analysis correlating the fitting parameter α in the Arya and Paris (1981) soil water retention model to physical properties of the soil. Fractal mathematics are used to show that α is equal to the fractal dimension of the pore trace and expresses a measure of the tortuosity of the pore trace. The fractal dimension of the particle‐size distribution can be easily measured and related to the α parameter of the Arya and Paris model. By suggesting a physical significance of the coefficient, the universality of the model is greatly improved. Soil water retention data, estimated strictly from particle‐size distributions, are proven to match measured data quite well. The fractal dimension of pore traces range from 1.011 to 1.485 for all but one soil tested.
Sand Detachment by Single Raindrops of Varying Kinetic Energy and Momentum
Authors: Sharma P. P. , Gupta S. C.
Published: July 2010

Soil detachment by raindrops is a precursor to the start of interrill erosion and surface seal formation. Soil detachment occurs when erosive forces of raindrops are greater than the inherent strength of soil. Experiments were conducted to study the importance of inherent soil strength on detachment of soil by raindrops. Sand strength was controlled by varying matric potentials before raindrop impact. A range of raindrop kinetic energies and momentum was created by changing drop diameter (3.6–5.0 mm) and fall height (1–8 m). The experimental setup consisted of a varying height water drop former, an electronic drop discriminator, and a single‐drop soil splash collector. Splash collected by varying drop height of a 4.6‐mm‐diam. drop on sand equilibrated at a matric potential (ψm) of −1.5 kPa (higher strength) showed that a larger threshold energy is needed to initiate soil detachment than when equilibrated at ψm = −0.1 kPa (lower strength). Also, the threshold erosivity was larger in magnitude and more significant when using momentum as an index of erosivity instead of kinetic energy. The relationships between sand splash and erosivity were linear (P < 0.001) for raindrops with diameters of 3.6 to 5 mm falling from heights of 0.76 to 7.6 m on sand equilibrated at ψm = −1.0 kPa. Sand splash was represented by a model of the form D = Kd[E − Eo]b, where D is detachment, E is raindrop erosivity, Eo is threshold erosivity, Kd is sand detachability, and b is an exponent equal to 1. This equation of describing soil detachment as a function of erosivity is an improvement over the currently used nonlinear relationship of the form D = Kd Eb.
Relationship Between Soil Potassium Forms and Mineralogy
Authors: Sharpley Andrew N.
Published: July 2010

The relationship between soil K forms (water soluble, exchangeable, HNO3‐extractable, and mineral) as a function of clay mineralogy and taxonomy, was determined using 102 soils from the continental USA and Puerto Rico, representing 10 soil orders. These relationships may have use in evaluating potential soil K fertility and prediction of K cycling and plant uptake. The soils were divided into three groups (kaolinitic, mixed, and smectitic) based on dominant mineralogy of the clay fraction. For each group of soils, water soluble K was related to exchangeable K content (r2 of 0.86 to 0.96), with exchangeable K solubility increasing from smectitic, mixed, to kaolinitic soils. For each group, exchangeable K was also related to HNO3‐extractable K (r2 of 0.81 to 0.83), thus, the capacity to supply K under continuous cropping, is greater for smectitic than kaolinitic soils of similar exchangeable K contents. Mineral K was a function of clay content for each soil group (r2 of 0.66 to 0.90). Using these relationships, water soluble (2–37 mg kg−1), HNO3‐extractable (21–2691 mg kg−1), and mineral K contents (1.59–16.93 mg kg−1) of 60 independent soils, were closely predicted (r2 of 0.78 to 0.96) from exchangeable K, clay content, and clay mineralogy. These results indicate that determination of both exchangeable and HNO3‐extractable K could give a better indication of the potential K supplying power of a soil. Further, the relationships obtained will allow determination of initial soil K pool sizes from readily available soil taxonomic, clay mineralogy, and chemical properties, for use in modeling the cycling and plant uptake of soil K.
Ammonium Fixation by High‐Charge Smectite in Selected Texas Gulf Coast Soils
Authors: Chen Cy‐Chain , Turner Fred T. , Dixon Joe B.
Published: July 2010

The Beaumont (fine, montmorillonitic, thermic Entic Pelludert) and Lake Charles (fine, montmorillonitic, thermic Typic Pelludert) soils along the Texas Gulf Coast produce only about 2 Mg rice (Oryza sativa L.) ha−1 without N fertilizer, while the Nada soil (fine, montmorillonitic, thermic Typic Albaqualf) frequently produces 5 Mg ha−1. In studying differences between these soils, data showed that NaCl applied to the Beaumont soil did not reduce rice yield, but equivalent amounts of KCl did. The KCl‐induced yield reduction may have been the result of NH+4 entrapment in clay minerals caused by added K. Clay mineral characterization showed that the Beaumont soil fixed more NH+4 than the Nada soil because the Beaumont soil was higher in soil K, high‐charge smectite [i.e., 0.76 equivalents per (Si,Al)4O10(OH)2] and charges in the tetrahedral sites. The 8‐wk incubation of Beaumont soil in the rice root zone resulted in partial release of added Nh+4 and no release of native NH+4 when the Beaumont soil had been Ca saturated. The K‐saturated Beaumont soil did not release fixed Nh+4 during incubation as the Ca‐saturated soil did. The Lake Charles soil showed clay and fixation characteristics similar to the Beaumont soil, while the Nada soil did not fix beyond its native level or release any upon incubation. The presence of 2:1 layer silicates in Beaumont and Lake Charles soils with x‐ray diffraction characteristics similar to smectite, and NH+4 fixation characteristics similar to vermiculite, was recognized.
Comparison of the Titration and Ion Adsorption Methods for Surface Charge Measurement in Oxisols
Authors: Marcano‐Martinez E. , McBride M. B.
Published: July 2010

The pH‐dependent charge properties of the A and B horizons of two representative oxisols from the Cerrado Region, Brazil, were studied by a comparison of the potentiometric titration method of net charge measurement and direct measurement of anion and cation exchange capacity from K+ and Cl‐ adsorption. Most soil samples bore net negative charge at their native pH, but variability in the magnitude of this charge was attributed to the effect of Al‐blocked exchange sites or contributions from strongly acidic organic functional groups, since these soils had similar mineralogies. The soils also bore significant pH‐dependent positive charge at their natural acidic pH values, which was more evident in the B horizons than the surface horizons. Estimates of net surface charge by potentiometric titration and ion adsorption did not agree, especially as the soil pH was adjusted away from the point of zero charge. This lack of agreement is attributed to dissolution reactions of minerals and organic matter at high and low pH, which consume acid or base and overestimate surface charge.
Phosphorus‐31 Magic Angle Spinning Nuclear Magnetic Resonance of Wastewater Sludges and Sludge‐Amended Soil
Authors: Hinedi Zeina R. , Chang Andrew C. , Yesinowski James P.
Published: July 2010

Phosphorus‐31 magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was used to examine the forms of P in two municipal sludges and a sludge‐amended soil. The signal‐to‐noise ratio and the resolution of the spectra improved considerably when paramagnetics in the sludge and sludge‐treated soil samples were removed by a reducing treatment involving citrate‐bicarbonate‐dithionite (CBD). The spectra suggested that the P solid phases in the anaerobically digested sludge from Los Angeles County, California were calcium phosphates. The strong paramagnetic effects, however, precluded more precise identification of the calcium phosphate phase. In the anaerobically digested alum‐treated sludge from Riverside, three P solid phases are detected, carbonated apatite, a pyrophosphate, and aluminium phosphate. In the Domino soil (fine‐loamy, mixed, thermic Xerollic Calciorthid), amended with sludge from Los Angeles County, 31P MAS NMR indicated the presence of carbonated apatite and pyrophosphate solid phases.
Pedogenic Factors Affecting Magnetic Susceptibility of Northern California Soils
Authors: Singer Michael J. , Fine Pinchas
Published: July 2010

Mass magnetic susceptibility (χ) was measured on samples taken from horizons from 27 northern California soils to determine the amount and vertical distribution of χ, and if the observed χ distribution could be related to parent material, climate, topography and time. In most of the soils with vertical morphological distinctions, eluvial horizon χ was greater than illuvial, R or CR χ. This susceptibility enhancement was interpreted as being due to pedogenic processes. Soils formed on parent material rich in Fe‐bearing minerals (e.g. basalt) had higher absolute χ and greater χ enhancement than did soils formed on Fe‐poor parent material (e.g. siltstone). Enhancement was greater in soils from areas of high (>1000 mm) mean annual precipitation compared with areas of low (<500 mm) mean annual precipitation, and soils formed under mean annual temperature ≤6 °C had less distinct enhancement than soils formed in warmer temperature regimes provided the precipitation was the same. Two soils with poor and somewhat‐poor drainage classes had distinctly lower absolute χ than associated well‐drained soils. Both absolute χ in eluvial horizons and susceptibility enhancement of eluvial over illuvial, and eluvial over C horizons increased as soils became older. Older soils were enhanced to a greater depth than younger soils. Eluvial and illuvial χ was greater than parent material χ in most profiles because non‐ or weakly magnetic minerals were converted to maghemite, which accumulated in eluvial horizons. In young soils with little morphological differentiation formed on transported parent material, χ measurements help to locate lithologic discontinuities.
Relationship of Soil Crust Morphology to Inter‐rill Erosion Parameters
Authors: Remley P. A. , Bradford J. M.
Published: July 2010

Research on soil surface sealing and crust formation has taken two approaches: (i) measurement of common soil erosion parameters such as infiltration, permeability, detachment, and strength and (ii) observation of seal or crust morphology using both microscopic and submicroscopic techniques. The purpose of this research was to combine the two approaches to extend our knowledge of surface sealing and crusting and its role in the erosion process. Eight soils with exchangeable sodium percentages (ESP) <1 and with textures ranging from sandy loam to clay were exposed in the laboratory to simulated rainfall with an intensity of 63 mm h−1 for 1 h. Seal and crust formation were investigated by measuring splash and wash erosion, single waterdrop splash, and fall‐cone strength and by observing scanning electron microscope (SEM) and thin‐section photographs. Medium‐textured soils (five silt loams and a silty clay loam) developed homogeneous, silty surface seals of high strength ranging from 14 to 43 kPa and low splash detachment. Splash amounts for single drop impact ranged from 0.8 to 1.8 mg soil per drop, and for multiple raindrops in erosion pans, from 9 to 26 g soil during the final 5 min of a 60 min rain. For a clay soil, no morphological evidence of crusting was observed; strength of the seal was low (6.4 kPa) and splash amount was high (40.0 g in 5 min). For a sandy loam soil, splash was high (41.8 g) and strength, low (10.8 kPa). Crust morphology indicated slight crusting. The subjective nature of interpreting SEM and thin section photographs makes it difficult to draw conclusions about erosion processes or rates.
Nitrogen Isotope Fractionation in Burned and Unburned Chaparral Soils
Authors: Herman D. J. , Rundel P. W.
Published: July 2010

Plant and soil processes involving N‐transformations have been monitored by techniques measuring the 15N/14N ratio in a sample relative to the atmosphere (δ15N). Unusually low δ15N values have been reported in the tissues of chaparral shrubs. The primary objective of this study was to investigate soil N‐cycling processes which may yield the low plant tissue δ15N levels. Since the chaparral is subject to periodic brush fires, which in turn result in high levels of inorganic N‐forms in the soil during the first year following the burn, possible effects of burning on soil δ15N were also investigated. Incubations were conducted on soils from an area which had been subjected to a brush fire, and an adjacent unburned area; both soils are fine, thermic, schistose, very steep Ultic Haploxeralfs. Concentrations and δ15N of soil NH+4 and NO‐3 were periodically measured. A C‐ and N‐rich ash resulted in rapid mineralization of N in the burned soil; a substrate more resistant to biological degradation resulted in an initial loss, then subsequent slow accumulation of inorganic‐N in the unburned soil. Nitrate was the dominant mineral species in each soil after a few weeks. As nitrification progressed, δ15N of NH+4 increased and δ15N of NO‐3 decreased. Since the mineral pool in each soil became dominated by NO‐3, δ15N of the mineral pool became strongly negative. A mathematical model of isotope dynamics fits empirical data well.
Simulation of Soil Water Above a Water Table in a Forested Spodosol
Authors: Phillips L. P. , Comerford N. B. , Mansell R. S. , Neary D. G.
Published: July 2010

The relationships between soil water potential and water table depth in the upper five horizons of an Ultic Haplaquod of the lower Coastal Plain flatwoods are described. Soil water pressure head in the E, Bh, Bs, and E′ horizons was in hydrostatic equilibrium with the underlying water table during all conditions when water was perched above an argillic horizon. The A horizon was in equilibrium with the water tables only when water tables were <65 to 70 cm from the soil surface. Water pressure heads and contents in the soil profile were simulated using a finite‐difference, one‐dimensional, unsaturated water‐flow model. Simulations of water pressure head were excellent for the lower horizons (E through E′) under all conditions, and poor for the A horizon. During high water tables, water pressure head simulations for the A horizon were improved. Fewer discrepancies between measured and simulated conditions occur when water pressure head values are converted to volumetric water contents. Unfortunately, the water‐flow model described here did not adequately handle high infiltration rate rainfall events experienced at the site. It is concluded that in these sandy soils: (i) water content is the preferred prediction variable; and (ii) further advances in mechanistically modeling water uptake from each soil horizon in forest ecosystems will be limited by adequate information on plant root biology.
Acidic Zones from Ammonia Application in Conservation Tillage Systems
Authors: Robbins S. G. , Voss R. D.
Published: July 2010

Subsurface soil acidity resulting from repeated NH3 applications in long‐term conservation tillage systems that do not disturb the NH3 injection zone was studied in six different crop‐fertilizer‐tillage systems by: (i) observation of the size, shape, and distribution of acidic zones in the field by using a pH color indicator method and (ii) intensive quantitative sampling of the upper 25‐ to 30‐cm soil layer with subsequent laboratory analysis for soil pH. Acidic soil zones created by the nitrification of the injected NH3 were roughly circular with 12‐ to 18‐cm diam. Soil pH of the acidic zones was generally 0.9 to 1.8 pH units lower than that of the surrounding bulk soil. In the ridge till‐plant and ridge slot‐plant systems studied, a distinct highly localized persistent acidic soil zone was detected in each interrow. On the basis of the extent and degree of acidity observed, it is concluded that yield‐limiting problems due to acidification by continuous NH3 applications are not likely in the ridge management systems studied. In the flat no‐till systems studied, numerous persistent acidic soil zones were observed scattered throughout each interrow. It is concluded that soil acidity problems due to long‐term NH3 usage potentially could develop in the no‐till systems studied where NH3 is not injected in the same vicinity each year. Efforts toward localized placement of N by the farm operator could effectively minimize potential problems due to the acidifying effects of NH3 in conservation tillage systems.
Measuring Nitrogen Losses from Lowland Rice Using Bulk Aerodynamic and Nitrogen‐15 Balance Methods
Authors: De Datta S.K. , Trevitt A.C.F. , Freney J.R. , Obcemea W.N. , Real J.G. , Simpson J.R.
Published: July 2010

Management practices, designed to reduce ammonia (NH3) volatilization and total N loss from flooded rice fields, after application of urea, were assessed in the dry season at Mabitac, Philippines. The assessment was made in replicated 4.8‐m × 5.2‐m plots by determining NH3 and total fertilizer N losses with bulk aerodynamic and 15N balance methods, respectively. The bulk aerodynamic method was first evaluated by comparison of ammoniacal‐N concentrations, pH values, and equilibrium NH3 concentrations for a 50‐m diam, circular area and small plots receiving the same fertilizer treatment. Good agreement was obtained so the bulk aerodynamic method was used to determine NH3 loss from the small plots receiving the different management treatments. Ammonia loss was high when urea was broadcast into floodwater 10 d after transplanting—48 and 56% of the applied N was volatilized as NH3 during the first 8 d after application of 53 and 80 kg N ha−1, respectively. Total N losses were 60 and 59%, respectively. Ammonia loss was reduced slightly (to a mean of 43% of the applied N for the two application rates) by broadcasting the fertilizer into 0.05‐m‐deep floodwater and incorporating it into the soil by harrowing before transplanting. Removal of the floodwater before applying urea onto saturated soil and incorporation by harrowing reduced NH3 loss to a mean of 9% and total fertilizer N loss to a mean of 33%. Fertilizer N recovery by rice plants was significantly increased by incorporation without surface water.
Two‐Site/Two‐Region Models for Pesticide Transport and Degradation: Theoretical Development and Analytical Solutions
Authors: van Genuchten M. Th. , Wagenet R. J.
Published: July 2010

Analytical solutions are presented for two convection‐dispersion type transport models useful for studying simultaneous pesticide sorption and degradation. One solution is for the familiar two‐site sorption model in which adsorption‐desorption proceeds kinetically on one fraction of the sorption sites, and at equilibrium on the remaining sites. Another solution holds for two‐region (or mobile‐immobile liquid phase) transport appropriate for aggregated or fractured media. The transport models account for degradation in both the solution and sorbed phases. The dimensionless analytical solutions for the two‐site and two‐region models are shown to be identical; they contain up to six independent dimensionless parameters: a column Peclet number, a retardation factor, a coefficient partitioning the soil/chemical system in equilibrium and nonequilibrium parts, a rate coefficient, and two dimensionless degradation coefficients. One of the two independent degradation coefficients may be eliminated when the solution and sorbed phase degradation rate coefficients are assumed to be identical, or when, with additional but reasonable assumptions, adsorbed phase degradation is assumed to be negligible.
Analysis of Water Flow under Trickle Irrigation: I. Theory and Numerical Solution
Authors: Lafolie F. , Guennelon R. , van Genuchten M.Th.
Published: July 2010

Estimating the size of the ponded surface area is a major source of error in modeling water movement under trickle irrigation. After reviewing available approaches and models for simulating water flow under trickle irrigation, we present a new numerical solution of the governing partial differential equations that improves the prediction of the size of the ponded area at the soil surface. A common formulation could be used for both Cartesian and axicylindrical flow geometries. The spatial operator was approximated using finite differences, and time integration was performed with an implicit method. Nonlinearity was treated by means of a fixed point iterative algorithm. The proposed model is applicable to saturated‐unsaturated flow in layered soils having anisotropic hydraulic properties. Accuracy and stability of the solution are checked and comparisons made with previous numerical solutions for several trickle irrigation and other unsaturated flow problems.
Factors Influencing Early Performance of Leguminous Plants in Forest Soils
Authors: Schoeneberger M. M. , Volk R. J. , Davey C. B.
Published: July 2010

Subterranean clover (Trifolium subterraneum L.), a winter annual, and big trefoil(Lotus pedunculatus Cav.), a summer perennial, are being studied for use in forestry operations. Establishment and performance of these plants with their associated rhizobia (+RHIZ) are adversely affected by the infertile, acid conditions generally encountered in forest soils. Using the 15N isotope dilution technique, we investigated the effects of N fertilization and inoculation with the vesicular‐arbuscular mycorrhizal fungus, Gigaspora margarita Becker and Hall (+VAMF) on early growth and N2‐fixing capabilities of these plants in a pasteurized acid forest soil containing low levels of both P and N. In clover, dual inoculation with + RHIZ, + VAMF at 10 kg N ha−1 enhanced N derived from the atmosphere (Ndfa), both on a per‐plant (350%) and a per‐gram total N (151%) basis, as well as plant biomass (68%) and flower production (100%) over the corresponding values for + RHIZ plants. Increasing N to 100 kg N ha−1 resulted in greater biomass (24%) in dual‐inoculated clover, but concurrently decreased the amount of Ndfa while increasing the amount of N derived from the soil (Ndfs). Compared to + RHIZ trefoil, dual inoculation of trefoil (+ RHIZ, + VAMF) resulted in greater biomass production at 100 kg N ha−1, but had no significant effect on Ndfa or Ndfs. Increasing soil N increased biomass production, but did not reduce Ndfa in dual‐inoculated trefoil. The difference in response to G. margarita inoculation may be a reflection of the annual vs. perennial nature of subterranean clover and big trefoil, respectively. The shift in biomass production and Ndfa in nodulated plants at the higher N level demonstrates the need to modify site management practices in order to maximize tree growth and leguminous plant‐biological N fixation benefit to the site.
Soybean Response to Phosphorus and Potassium Fertilizers as Affected by Soil Drying
Authors: Kaspar T. C. , Timmons D. R. , Zahler J. B.
Published: July 2010

Soybean, Glycine max (L.) Merr., response to P and K fertilzers can vary with the amount of rainfall received during a growing season, but it is often difficult to determine whether growth is limited by unavailability of nutrients and/or water. A 2‐yr study was conducted in a rhizotron at Ames, IA, to determine whether drying of the fertilized, surface soil layer reduces plant growth and utilization of P and K fertilizers when subirrigation replenishes water below the fertilized surface layer. Low, medium, and high fertility levels were established on soil obtained from the upper 0.15 m of a Sparta loamy, fine sand (sandy, mixed, mesic Entic Hapludoll). Two surface‐drying treatments, one beginning during late flowering (dR2) and the other after the start of seed fill (dR5), and a control were imposed. Shoot tissue concentrations and dry weights at the fullseed stage (R6) and mature seed yield were measured. Surface drying reduced total shoot accumulation of P and K. Leaf and pod P concentrations were lower for the dR5 treatment than for the dR2 treatment. Shoot K concentrations of the dR2 treatment increased less than those of the other treatments as soil K levels increased. Shoot dry weights at R6 and mature seed yield were reduced at the low fertility level. Surface‐drying treatments reduced total shoot dry weight (42.8 and 40.9 g plant −1) compared with the control (49.5 g plant−1) in both years, but yield was reduced only in 1984. This study shows that drying of the fertilized soil layer reduced shoot growth and utilization of applied P and K fertilizers even though water was available at greater depths.
Water Table Fluctuation in Representative Immokalee and Zolfo Soils of Florida
Authors: Hyde Adam G. , Ford Richard D.
Published: July 2010

Depth and duration of the seasonal high water table in soils are important factors affecting land use. Most water‐table statements are based on soil properties and field observations; very few long‐term measurements have been recorded. This study was conducted to determine how well current water‐table statements agree with the actual data on the representative Immokalee (sandy, siliceous, hyperthermic Arenic Haplaquod) and Zolfo (sandy, siliceous, hyperthermic Grossarenic Entic Haplohumod) soils. The water table depths were measured approximately every 2 wk from 1977 to 1986. Rainfall was also measured. Water‐table statements can be improved with long‐term data on key soils. Long periods of more than two consecutive years have high‐water tables below that given in the water‐table statements used in this study. Short‐term measurements taken during these long periods of low water tables could be misleading.
Detecting Soil Information on a Native Prairie Using Landsat TM and SPOT Satellite Data
Authors: Su Haiping , Ransom M. D. , Kanemasu E. T.
Published: July 2010

Computer pattern recognition techniques were used to discriminate soil information from the Landsat Thematic Mapper (TM) and the French Systeme Probatoire d'Observation de le Terre (SPOT) satellite data on a native prairie near Manhattan, KS. Digital Elevation Model (DEM) data were merged to Landsat TM and SPOT data to delineate soil mapping units within the study area. Soil mapping units from a conventional soil survey were compared with a classified soil spectral map obtained from Landsat TM or SPOT, and DEM derived elevation, slope, and aspect data, using an overall accuracy assessment. The overall accuracy of soil spectral classes from TM and SPOT data was improved after DEM data were merged. A higher average accuracy for soil mapping units was obtained with a low frequency filtering transformation of the data. For Landsat TM data, Band 5 (middle infrared, 1.55–1.75 µm) was most useful for soil information extraction, and a higher overall accuracy was obtained in the dormant season compared with the accuracy in the growing season. The overall accuracy (about 57%) from SPOT data was slightly higher than the accuracy (about 53%) from Landsat TM at a similar wavelength range. Our results indicate that high resolution Landsat TM and SPOT satellite data can be used to aid second‐order soil surveys in areas where the dominant land use is rangeland.