bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus Sorption as Influenced by Added Urea in Two Eastern Canadian Soils
Authors: Fan M. X. , MacKenzie A. F. , O'Halloran I. P.
Published: July 2010

The interaction of urea with P in soil‐fertilizer microsites may have an important effect on P availability to crops. A laboratory study was conducted to evaluate the effect of urea on P reactions in two eastern Canadian soils (Typic Humaquepts). Phosphorus sorption was studied by equilihrating soil samples pretreated with four levels of urea for 24 h with six rates of P in either 0.01 M CaCl2 or 0.03 M KCl solutions. Phosphorus desorption was determined by sequentially extracting the residual soil with 0.01 M CaCl2 or 0.03 M KCl, and 0.5 M NaHCO3. Urea application increased the soil pH (0.01 M CaCl2) in the fertilizer microsites from 5.2 to 7.3 in the Ste Rosalie soil and from 5.9 to 7.4 in the Ormstown soil. These pH changes had variable effects on soil P sorption characteristics, depending on soil and electrolyte. Phosphorus sorption increased with increasing urea and pH when using CaCl2 as the electrolyte. Added urea and pH had little effect when KCl was used, indicating that the urea effect on P sorption was influenced by Ca content. The effect of urea was not significant at P rates <320 mg P kg−1 soil. The observed increase in P sorption and decrease in solution P with added urea was probably related to precipitation of Ca‐P compounds and the shift from H2PO−4 to HPO2−4 at higher pH values. Urea application increased 0.5 M NaHCO3 extractable P and reduced nonextractable P in both soils. For soils with high Ca content, urea application with P fertilizer could reduce P concentration in soil solution and P mobility because of the increase in P sorption and P buffer capacity, but increase available P as expressed by NaHCO3‐extractable P.
Organic Matter Role in Illitic Soil Colloids Flocculation: II. Surface Charge
Authors: Heil Dean , Sposito Garrison
Published: July 2010

The ability to predict the effect of various factors on soil flocculation depends on a knowledge of the mechanisms by which those factors operate. The purpose of this study was to investigate the mechanisms that control the effects of organic matter content, pH, and bivalent cation type on soil flocculation. The electrophoretic mobility of an illitic soil before and after treatment with H2O2 was measured at a soluble Ca or Mg charge fraction of 0.0 to 0.9 at pH 6, and at pH 4 to 9 and a soluble Ca charge fraction of 0.0 or 0.5 The change in the net particle charge as pH was increased from 6 to 8 at a soluble Ca concentration of 0.65 and 2.26 mol m−3 was determined from proton and Ca ion titrations. Electrophoretic mobility was independent of both Ca vs. Mg and organic matter content, which suggests that the influence of these factors on flocculation was caused by steric effects. The effect of pH on soil flocculation and electrophoretic mobility in the presence or absence of organic matter, on the other hand, was consistent with an electrostatic mechanism. The change in net particle charge from pH 6 to 8 became more positive as the soluble Ca concentration was increased, and this result was modeled in terms of competitive binding of H+ and Ca2+ by soil functional groups.
Interaction of Mugineic Acid with Synthetically Produced Iron Oxides
Authors: Inoue K. , Hiradate S. , Takagi S.
Published: July 2010

Interactions between mugineic acid (MA) purified from root washings of Fe‐deficient barley (Hordeum vulgare L., cv. Minorimugi) and synthetically produced Fe oxides (goethite, hematite, lepidocrocite, and ferrihydrite) were studied in the equilibrium pH range of 3 to 11. The amount of MA adsorbed on Fe oxides was related to their specific surface area and followed the order: ferrihydrite > > goethite ≥ lepidocrocite ≥ hematite. The adsorption of MA on Fe oxides also decreased with increasing equilibrium pH and increased with increasing MA concentration. The MAFe complexes were also adsorbed on Fe oxides, especially on ferrihydrite and goethite, at pH 3 to 7. At pH > 10, however, MAFe complexes were decomposed to MA and Fe(OH)3 colloids. The amount of Fe dissolved from Fe oxides by MA was in the following order: ferrihydrite > > lepidocrocite ≥ hematite = goethite. The Fe dissolution from Fe oxides by MA was related to their crystallinity and the maximum amount of Fe dissolved by MA was in the pH range of 7 to 8. The amounts of MA adsorbed on Fe oxides and Fe dissolved by MA from Fe oxides depended on MA concentration, pH, and the type and the amount of Fe oxides added in the system. The Fe dissolution processes from Fe oxides by MA could involve two factors, namely (i) the complexation of MA with Fe exposed on the surface of Fe oxides by ligand exchange; and (ii) the release of MAFe complexes from adsorption sites on Fe oxides by nucleophilic substitution. Our data further clarify the chemistry of Fe nutrition of graminaceous plants in Fe‐deficiency‐causing soils.
Ammonia Volatilization from Liquid Hog Manure: Influence of Aeration and Trapping Systems
Authors: O'Halloran I. P.
Published: July 2010

Measurements of N loss from manures may reflect differences in the types of manures and methodologies used. This study's objective was to test the suitability of 0.32 M H3BO3 and 0.9 M H2SO4 for trapping NH3 volatilized from liquid hog manure (LHM) under various experimental conditions. Samples of LHM were incubated for 15 d in containers with aeration outlets positioned above, at the middle, or at the bottom of the LHM. Lowering the position of the aeration outlet increased both the pH of the LHM and the amount of NH3 volatilized. More NH3 was trapped in H2SO4 than H3BO3, and the difference in trapping efficiency of the two acids increased with their NH3 concentrations. Neither the amount of NH3 trapped nor the exponential relationship between the NH+4 concentrations of two H3BO3 traps in series was influenced by changing the bubble path length through the acid. Regression analysis indicated that >95% trapping efficiency was obtained only when the NH3 concentration of H3BO3 was below 0.42 mg N mL−1, much lower than the 0.9 mg N mL−1 reported to be the limit for using H3BO3 in the Kjeldahl method. Even when using two traps in series, H3BO3 appeared to trap less NH3 than H2SO4. Amending LHM with sucrose lowered the pH of H3BO3 used to trap volatilized NH3, thereby interfering with NH3 determination and rendering H3BO3 unsuitable for determining NH3 volatilization. Investigators who use H3BO3 to measure NH3 volatilization in other systems must ensure that similar interferences do not occur and that NH3 concentrations do not exceed 0.42 mg N mL−1.
Fractal Description of Soil Fragmentation for Various Tillage Methods and Crop Sequences
Authors: Eghball Bahman , Mielke Lloyd N. , Calvo Guillermo A. , Wilhelm W. W.
Published: July 2010

Soil structure has been difficult to quantify and, at best, has been studied semiquantitatively. Fractal representation of soil fragmentation can provide an indication of soil structure. The purpose of our study was to use fractal analysis to quantify soil fragmentation under various tillage and crop sequence treatments at different times during the growing season. We collected soil samples from four tillage treatments (established 10 yr earlier) of chisel, disk, no‐till, and moldboard plow in factorial arrangement with two crop sequences of corn (Zea may L.)‐soybean [Glycine max (L.) Merr.]‐corn (C‐S‐C), and soybean‐corn‐soybean, (S‐C‐S) on a Sharpsburg (fine, montmorillonitic, mesic Typic Argiudoll) soil. Aggregate‐size distribution was used to calculate fractal dimension (D) for each treatment. Higher D values indicate greater soil fragmentation and a soil dominated by smaller aggregates. The opposite is true for lower D values. Differences in soil fragmentation observed for tillage treatments after autumn tillage became even greater over winter. Soil fragmentation increased over autumn and winter, with D increasing in the order of plow > chisel > disk > no‐till. Formation of larger soil aggregates increased during the growing season for all tillage systems. The D values for C‐S‐C were smaller than S‐C‐S in the no‐till, indicating that the previous year's corn in C‐S‐C provided more large aggregates. Soybean appears to have negative effects on large‐aggregate formation in no‐till. Aggregate densities, averaged across tillage and crop sequence, increased from 1.25 to 1.77 Mg m−3 as the aggregate diameter decreased from 6.38 to 0.162 mm. Fractal analysis was found to be useful in determining soil fragmentation differences due to different tillage methods and crop sequences.
Erosion Processes on Arid Minespoil Slopes
Authors: Sidle Roy C. , Brown R. W. , Williams B. D.
Published: July 2010

Surface wash and dry ravel erosion rates from minespoil were measured for 4.7 yr after initial reclamation at a site in western Nevada. Average annual total erosion from all 15 plots ranged from 0.48 to 1.10 Mg ha−1. Neither mulching treatment nor slope gradient (3:1 vs. 2:1) significantly affected surface wash from reclaimed minespoils. About 70% of the total wash load from the entire study period occurred during two midsummer to autumn periods (1989 and 1990) in which the most intense storms occurred. Southwest‐facing slopes (windward) had significantly higher surface erosion compared with northeast‐facing slopes (leeward). The higher surface roughness encountered on 2:1 slopes appeared to more effectively control surface wash than gentler (3:1) slope gradients or early‐stage vegetative cover. Straw mulch significantly reduced ravel erosion from the relatively smooth 3:1 slopes. Mulch treatment was not effective in reducing ravel erosion from rougher, 2:1 slopes. Windward (southwest‐facing) slopes had significantly higher ravel erosion than northeast‐facing slopes. Ravel rates were not as directly affected by rainfall intensity as were surface wash rates. Regressions of surface wash with EI (rainfall energy‐intensity factor) were best with short‐term intensities (i.e., EI5, R2 = 0.94); regressions of ravel with EI were best using longer term intensities (EI30; R2 = 0.83). Except for very dry collection periods (including autumn to spring), surface wash exceeded ravel.
Agroecosystem Approach to Soil and Crop Management Research
Authors: Peterson G. A. , Westfall D. G. , Cole C. V.
Published: July 2010

Research techniques that have greatly advanced agronomic science in the 20th century, and have enhanced our knowledge of cause and effect, have been accompanied by reductionism. As a result, much valuable research has been accomplished, but less synthesis of results has occurred that provides answers to landscape‐level research questions. We propose that a systems approach to the study of soil and crop management problems is a useful technique that tests our present research knowledge in a way that answers practical agricultural problems and simultaneously identifies gaps in basic research knowledge. We have used a problem common to the Great Plains to demonstrate the systems approach: minimizing the soil‐ and environment‐degrading practice of summer fallowing and simultaneously increasing farm profitability. Although much is known about summer fallow at specific locations, less is known about extrapolating this knowledge across soil and climatic gradients. We show that intensified crop sequences under no‐till techniques can replace summer fallow in many environments, and increase the productivity per unit of water received. Simultaneous reductions in the damaging factors of summer fallowing, in particular soil erosion and organic matter losses, also have occurred. We are researching the problem at a landscape level without losing the ability to detect causae and effect, and are able to simultaneously conduct basic research on soil nutrient cycling and water budgets. The approach also is being used effectively as an adult educational tool, thereby facilitating the transfer of technology from the researcher to the producer.
Flux‐Averaged Concentrations for Transport in Soils Having Nonuniform Initial Solute Distributions
Authors: Toride Nobuo , Leij Feike J. , van Genuchten Martinus Th.
Published: July 2010

The need to distinguish between volume‐averaged or resident concentrations (cr) and flux‐averaged or flowing concentrations (cf) is now widely accepted. Flux‐averaged concentrations associated with the convection‐dispersion equation (CDE) have been mostly used for solute transport problems involving uniform initial distributions. We present flux‐averaged concentrations for nonuniform initial distributions using analytical solution methods for a semi‐infinite soil system and numerical methods for a finite system. Mathematically, cf is equivalent to cr associated with a first‐type inlet condition (rather than a third‐type condition) only for semi‐infinite soil profiles having uniform initial conditions. We show that, for a stepwise initial distribution, cf can be both negative or much greater than the initial concentration of cr, especially during the early stages of solute displacement. This physically odd situation results from the fact that cf represents a solute flux rather than a directly measurable volumetric concentration. Flux‐averaged concentrations at the exit of a finite soil column with a uniform initial distribution are nearly identical to cf for a semi‐infinite system when the column Peclet number is greater than ≈ 5. However, if the initial distribution involves a high gradient in cr near the exit, cr values for finite and semi‐infinite systems at the exit can be very different, similarly as those for cr, because of the adoption of different outlet conditions.
Error Analysis of the Heat Pulse Method for Measuring Soil Volumetric Heat Capacity
Authors: Kluitenberg G. J. , Ham J. M. , Bristow K. L.
Published: July 2010

A recently developed heat pulse method allows rapid, automated measurements of the volumetric heat capacity (ρc) of soil. Estimation of ρc is accomplished by using a model for the conduction of heat away from an instantaneously heated infinite line source (IHILS). This study was conducted to examine possible errors in the use of the IHILS theory by comparing the IHILS model with three other models that account for the following characteristics of the heat pulse apparatus: finite probe length, cylindrical heater geometry, and short‐duration (noninstantaneous) heating. For typical probe geometry and heating times, estimates of ρc obtained from the IHILS theory were within 1% of the estimates obtained by using the more rigorous models. The most significant error resulted from approximating short‐duration heating with instantaneous heating in the IHILS model. A generalized error analysis is presented that permits direct graphical estimation of errors for different probe geometries, different heating times, and different soil thermal properties. First‐order error analysis was also used to examine potential error in ρc as a result of errors in probe spacing (r), temperature maximum (Tm), and heat input (q), the measured quantities that are used in the IHILS model to estimate ρc. Relative errors of 1% in measuring q and Tm lead to relative errors of 1% in ρc, whereas a relative error of 1% in r resulted in a 2% error. Measurement error in r and Tm limits the precision achievable with this method.
Phosphorus Desorption Quantity‐Intensity Relationships in Soils
Authors: Raven K. P. , Hossner L. R.
Published: July 2010

Phosphorus desorption quantity‐intensity (Q/I) relationships reveal information about the P release properties of a soil. This research was carried out to evaluate the P desorption characteristics of a group of soils of diverse properties and to compare several empirical models to describe P desorption Q/I curves. Samples of five soils (Typic Calciustoll, Udic Pellustert, Vertic Albaqualf, and Aridic Calciustoll surface soils, and Psammentic Paleudult subsoil) were enriched with five P concentrations (0, 25, 50, 75, and 100 mg P kg−1) and incubated for 31 d. Subsamples of each treated soil sample were equilibrated with different amounts of HCO−3‐saturated anion‐exchange resin. After 72 h the amount of P sorbed on the resin (Q) as well as the solution P concentration (I) were determined. Results from each subsample gave a point on the Q/I curve. The P release capacity of the soils used in this study was relatively low. In untreated samples, the solution P concentration when no P was desorbed (Io), an intensity parameter, ranged between <0.01 and 0.19 mg P L−1, while the maximum desorbed soil P (Qmax), a quantity parameter, was in the range 4.7 to 21.1 mg P kg−1. The corresponding P buffering power index, the slope of the Q/I curve at Io, ranged between 56 and 1703 L kg−1. These Q/I parameters were not closely related to any evaluated soil property, with the possible exceptions of CaCO3 content in calcareous soils and clay content. The P buffering power of a soil apparently depended on the availability of P sorption sites and their degree of depletion, and was not always directly related to the ability of a soil to release P. The P release activity of a P‐enriched soil depended on the desorbability of the applied P as well as the native labile soil P. Plots of P buffering power against intensity for a given soil were not affected by P enrichment. The Q/I curves could be best described by a proposed desorption Q/I equation (Q = a I−0.1 + b ln(I + 1) + c) and the Barrow power function, but the proposed equation followed the theoretical expected trend. The proposed equation is therefore recommended to describe P desorption Q/I curves.
Sericites in Feldspars as Source of 2:1 Phyllosilicates in Selected Sandy Soils
Authors: Arocena J. M. , Pawluk S. , Dudas J. M.
Published: July 2010

The high content of 2:1 phyllosilicates in the eluvial horizon of many sandy forested soils in North America is attributed to extraneous deposition. In this study, we evaluated the hypothesis that sericite in feldspars is a local source of 2:1 phyllosilicate by investigation of thin sections and coarse sand fractions from three pedons in an Alfisol‐Spodosol association developed on Quaternary sandy deposits in Alberta. In situ investigation of the alteration products of feldspar weathering was conducted by using x‐ray microdiffraction techniques, light and electron microscopy, and layer charge density by alkyl ammonium saturation technique. The nature of the minerals in the bulk samples and total elemental composition of the sand fractions were also investigated. Results showed that feldspars occur as orthoclase, microcline, and albite. Some of the feldspar grains were perthitic in nature. The weathering of feldspars is characterized by linear striations (parallel and cross linear) and starts mainly from grain fractures and twin planes. Several types of 2:1 phyllosilicates were identified in the alteration products: (i) a component with a fixed basal spacing around 1.0 nm, (ii) a high‐charge component with a charge density of about 0.6 molc [(Si, Al)4O10]−1, (iii) a low‐charge component with charge density of about 0.34 molc [(Si, Al)4O10]−1, and (iv) an interstratified component comprising of both the low‐ and high‐charge components.
Electrophoretic Mobility and Particle Size of Clays Using Laser Doppler Velocimetry‐Photon Correlation Spectroscopy
Authors: Anderson M. A. , Bertsch P. M.
Published: July 2010

Laser Doppler velocimetry‐photon correlation spectroscopy (LDV‐PCS) was evaluated for the characterization of clay minerals. Electrophoretic mobility and particle size of pure and mixed suspensions of KGa‐2 kaolinite and SWy‐1 bentonite were determined as a function of pH, ionic strength, and suspension concentration ratios. Kaolinite mobility changed from significant positive values at low pH to negative values at high pH, consistent with the variable‐charge nature of kaolinite. Evidence for a contribution of positive charge originating at bentonite edges at low pH (<4) was also found. Ionic strength also affected mobility of kaolinite and, at low pH, bentonite. Mixtures of kaolinite and bentonite at low pH yielded mobility distribution spectra intermediate to those of the component clays. The two populations were not resolved, which suggests that the kaolinite and bentonite formed mixed particle associations. Particle‐size analyses supported inferences from mobility data that significant particle‐particle association occurred under neutral to low pH and moderate ionic strength conditions.
Measuring In Situ Changes in Labile Soil Phosphorus with Anion‐Exchange Membranes
Authors: Cooperband L. R. , Logan T. J.
Published: July 2010

Conventional chemical extraction methods to measure labile soil P are often inadequate for detecting fine temporal‐ and spatial‐scale soil P dynamics in situ. We refined and calibrated methodology for anion‐exchange resin‐impregnated membranes (AEM), related AEM‐P to soil solution P for a high‐P‐retaining soil, and evaluated the method's viability under humid tropical field conditions. We determined: (i) AEM recyclability, (ii) AEM P sorption kinetics, (iii) the correlation between soil solution P and AEM‐P for an Andic Humitropept, and (iv) potential interference from other anions (NO−3 and SO2−4) on AEM P extraction. We used AEMs in a field decomposition study to evaluate plant residue and manure P release characteristics and concurrent fluxes in labile soil P. The AEM P sorption capacity was not altered significantly by repeated use. Nitrate solution concentrations in an aqueous medium of 50 and 100 mg NO3‐N/L reduced AEM P sorption by 50 and 75%, respectively, regardless of P solution concentration; SO4‐S at 500 and 1000 mg/L reduced AEM P sorption by ≈98%. The relationship between AEM‐P and soil solution P was curvilinear at both nonequilibrium and equilibrium soil solution P concentrations; it was essentially linear at soil solution concentrations ranging from 0 to 2 mg P/L. The AEM behaved as a dynamic exchanger rather than an infinite sink for P, particularly in the context of a low‐pH, high‐P‐retaining soil. The AEMs detected biologically relevant soil P pulses in the field decomposition study. The technique holds promise as an easy method for measuring soil P fluxes with minimal soil disturbance.
Conveyor‐Belt Apparatus for Fine Grinding of Soil and Plant Materials
Authors: Kelley K. R.
Published: July 2010

Recent advances in instrumentation have provided the capability to determine total N and 15N concentrations in milligram quantities of soil or plant material. Analytical precision with small samples is adversely affected by sample heterogeneity, however, and fine sample grinding is necessary. A grinding apparatus using a conveyor‐belt assembly and operating as a roller mill was developed. The samples are ground and stored in the same bottle, reducing the risk of cross contamination, and up to 55 samples can be processed simultaneously. Corn (Zea mays L.) leaf, bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon], and soil were finely ground in 12 h or less, but longer grinding periods are recommended for hard‐to‐grind materials such as corn grain and corn cobs. Analytical precision for measurement of total N and 15N concentrations by direct‐combustion, continuous‐flow mass spectrometry tended to increase with decreasing particle size.
Sodic Soil Toposequence Related to Focused Water Flow
Authors: Seelig B. D. , Richardson J. L.
Published: July 2010

Present concepts of sodic soil formation do not adequately account for observed variability of sodic soil properties on many landscapes in North Dakota. A conceptual model was developed to explain sodic soil genesis related to water and salt movement on a coarse‐loamy till landscape in central North Dakota. The relationship between subsurface water flow and sodic soils was determined by monitoring soil water using neutron attenuation and water wells at three contiguous landform positions. Electrical conductivity, major ions, and water‐dispersible clay were determined on extracts from selected soil samples from each landform position. Typic Argiaquolls, characterized by low salinity (electrical conductivity [EC] < 2.0 dS/m), occurred at the wetland position and were areas of recharge to groundwater. Typic Natraquolls also occurred at the wetland position but were characterized by high salinity (EC > 5.0 dS/m) and were areas of groundwater discharge. Udic and Leptic Natriborolls were areas of groundwater discharge at the intermediate and upland positions. Udic Haploborolls were hydrologically inactive areas at the upland position. Variations in sodic soil development were attributed to the concentration of water flow (focused flow) into specific areas of groundwater discharge or recharge. The most important factors that affected the direction and intensity of focused flow were stratigraphy and landform position.
Long‐Term Effects of Forest Fertilization on Site Organic Matter and Nutrients
Authors: Harding R. B. , Jokela E. J.
Published: July 2010

The long‐term effects of time‐of‐planting fertilization on the accumulation and distribution of above‐ and belowground organic matter and nutrients are largely unknown for intensively managed southern pine (Pinus spp.) stands in the U.S. lower Coastal Plain. These effects were investigated using a 25‐yr‐old slash pine (P. elliottii Engelm. var. elliottii) plantation in north Florida. The experiment was conducted on a poorly drained, P‐deficient Rutlege soil (sandy, siliceous, thermic Typic Humaquept) using a randomized complete block design. The experimental treatments included: (i) control, (ii) NPK (112, 39, and 45 kg ha−1 using ordinary superphosphate [OSP] + N and K) and (iii) P (314 kg P ha−1 using ground rock phosphate [GRP]). Fertilization significantly increased total aboveground organic matter accumulation, with levels for the OSP + NK and GRP treatments being 2.5 and 1.8 times greater than the control, respectively. Levels of soil organic matter measured to a depth of 91 cm did not vary, however. Treatment effects were found for P, K, and Ca levels in the fertilized slash pine biomass components and surface soil. Long‐term differences in extractable soil P were most pronounced for the GRP treatment, with concentrations in the surface 15 cm being 2.6 times greater than the control; only the high P treatment sustained foliar P levels within the published critical range for slash pine. While field trials are required to confirm actual fertilizer carryover effects, results from this experiment suggest that sites previously fertilized with operational P rates (40–80 kg ha−1) will again require treatment when establishing the next pine rotation.
Nitrogen and Phosphorus Interactions in an Intensively Managed Nursery Soil‐Plant System
Authors: Teng Y. , Timmer V. R.
Published: July 2010

Nitrogen in forest tree nurseries is usually applied as topdressing during the growing season, while P is incorporated in the soil before seeding. Combined N and P topdressing as monoammonium phosphate (MAP) may improve nursery stock production. To test this practice, white spruce [Picea glauca (Moench) Voss] seedlings top‐dressed with MAP, or factorial combinations of ammonium nitrate (AN) and phosphoric acid (PA) were grown for two seasons in a loamy sand nursery soil. Seedlings receiving AN alone increased in biomass (34%) but took up less P despite relatively high available P (310 mg kg−1) in the bulk soil. Phosphorus additions stimulated growth (107%) and also N and P uptake. Equivalent N dosages, as MAP or AN + PA, increased dry matter production by 362%, demonstrating a significant positive N × P interaction. Two nutritional responses seem to be involved in this interaction: (i) a countering of N antagonism on P uptake when N only was applied, and (ii) a synergistic effect of N and P uptake when these nutrients were applied together. Lower specific absorption rates of roots and suspected depletion of rhizospheric P probably accounted for the antagonistic effect in N‐only treatments, while increased root absorption efficiency and higher P availability in addition to the N supplied in N + P treatments contributed to the synergistic interaction. The N + P treatments resulted in lower seasonal NH4‐N and NO3‐N levels in subsoil than those from N‐only treatments, suggesting less leaching of N from combined N and P topdressings.
Measurement of Solute Transport during Constant Infiltration from a Point Source
Authors: Kachanoski R. G. , Thony J. L. , Vauclin M. , Vachaud G. , Laty R.
Published: July 2010

Theory describing transport from a point source is well developed, but not tested because of the lack of experimental data. There are few field studies because sampling requires either destructive soil coring or vacuum solution samplers. The objective of this study was to develop a method of measuring quickly and nondestructively the vertical flux of solute below a drip (point) source of water. The method uses vertically installed time domain reflectometry (TDR) probes making it appropriate for field studies. Water is dripped between the vertical probes at a constant rate until the wetting front has passed the ends of the probes and the measured soil water content is not changing. At this time, the water source is switched to one with a constant concentration of electrolyte tracer, dripping at the same rate. The relative change in TDR impedance is related to the advance of the solute front. Thus, measurements of average solute velocity and cumulative travel time as a function of depth are obtained. At a low drip rate into a sandy soil, the measured advance of the solute front vs. the cubed root of time was similar to that predicted from the theory of gravity‐free infiltration. Identical measurements were obtained for the advance of solute‐free water into a soil with a high background concentration of solute. Methods of estimating solute dispersivity and the relative influence of gravity vs. capillarity from the measurements were suggested but not tested. In particular a method of estimating α, the ratio of hydraulic conductivity and matric flux potential, is suggested using existing solutions of the linearized equation for flux from a point source.
Glucose‐1‐phosphate and Myo‐inositol Hexaphosphate Adsorption Mechanisms on Goethite
Authors: Ognalaga M. , Frossard E. , Thomas F.
Published: July 2010

This research was performed to elucidate the adsorption mechanisms of two monoester phosphates, glucose‐1‐phosphate (G1P) and myo‐inositol hexaphosphate (I6P), on a synthetic goethite with reference to orthophosphate (Pi). Adsorption isotherms were built and electrophoretic and pH measurements were carried out in order to determine the nature of the adsorbent‐adsorbate bonds. The quantity of adsorbed compound reached 5.41 µmol Pi m−2, 5.06 µmol G1P m−2, and 1.37 µmol I6P m−2. The G1P and I6P were adsorbed on the surface hydroxyls of goethite through their phosphate groups. The proposed adsorption mechanism, notwithstanding the nature of the organic moiety, is a specific adsorption by a ligand exchange between the phosphate groups and the surface reactive hydroxyls. Inner‐sphere surface complexes are formed between phosphate groups and Fe. Very little dissolution of the goethite occurred during the adsorption of either of the two ligands (G1P and I6P). Tentative configurations of the formed organophosphate‐goethite complexes are proposed.
Calibration of Glass Microelectrodes for in Situ pH Measurements
Authors: Yang J. , Blanchar R. W. , Hammer R. D.
Published: July 2010

Glass pH‐sensitive microelectrode fabrication, calibration, and measurement techniques have been altered to improve the applicability of the method. Insulating pipettes with inner filaments were drawn to 20‐µm tips and welded to the pH‐sensitive glass so the inner filament was not sealed. The filament allowed air to be displaced as the filling solution flowed to the pH‐sensitive tip, eliminating the need for a vacuum filling procedure. In situ calibration allowed soil pH to be measured without moving the reference electrode and altering the junction potential. Calibration is done in the same soil sample with the electrodes placed at a distance >5 cm from the site of pH measurement. The pH‐sensitive microelectrode is positioned above the soil close enough to make electrical contact. Two 0.05‐mL drops of pH buffer are added so that the drops flow down the electrode shaft to the soil as the electrode potential is measured. Soil pH values obtained by calibrating the electrodes in pH buffer solutions were 0.2 pH unit lower than those obtained by in situ calibration.

The reference electrode contacted the soil through a saturated KCl salt bridge placed in the moist soil. At soil water potentials below saturation, better electrical contact is made when the soil‐salt bridge contact point is wetted with water, 1 mol L−1 KCl, or 0.01 mol L−1 CaCl2.
An Automated Microcosm System for Studying Soil Ecological Processes
Authors: Hantschel Ralph E. , Flessa Heiner , Beese Friedrich
Published: July 2010

Soil ecological processes are characterized by high temporal and spatial variability. To evaluate effects of soil management and environmental parameters on single processes, it is necessary to investigate several replicates of each soil type under controlled laboratory conditions. We developed a microcosm system in which 64 disturbed or undisturbed soil columns, each controlled individually, may be evaluated. The technical design of the automated microcosm system demonstrates the broad applicability of the system. For demonstration the effects of the herbicide terbuthylazin (TA) on microbial respiration in microcosms treated with and without barley (Hordeum vulgare L.) straw are shown. Even high amounts of the herbicide applied did not reduce the CO2 release by the soil organisms. The C source added with the barley residues did not change this result significantly.
Accumulation of Fertilizer Nitrogen‐15 by Rice at Different Stages of Development
Authors: Guindo D. , Wells B. R. , Norman R. J.
Published: July 2010

Results from fertilizer N recovery experiments with 15N have indicated high values of fertilizer 15N lost by rice (Oryza sativa L.). Field experiments were conducted to evaluate uptake of fertilizer 15N applied at preflood and at midseason and to determine the growth stage for maximum recovery of fertilizer 15N by rice under a dry‐seeded culture system. Aboveground plant portions were sampled throughout the season for total dry matter, total N, and fertilizer 15N. Total N accumulation when N was applied in a single preflood application was maximum at heading + 21 d and then declined at maturity. When N was applied at preflood and midseason, total N accumulation continued until maturity. Fertilizer 15N recovered in the rice plant from the preflood N application was maximum (62%) at 21 d after application, and declined 10% by maturity. Fertilizer 15N from the midseason N application had maximum recovery (75%) in the rice plant at 7 d after application, and declined by 18% by maturity. Accumulation of total N in the panicle between heading + 21 d and maturity for the midseason N application was significant; however, it was nonsignificant for the preflood N application. Recovery of fertilizer 15N in the panicle did not differ between heading + 21 d and maturity for either the preflood or midseason N application. These results confirm earlier findings that sampling plants only at maturity will underestimate maximum fertilizer 15N uptake by rice.
Edge Complexation Reactions of Cadmium on Specimen and Soil‐Derived Smectite
Authors: Zachara J. M. , Smith S. C.
Published: July 2010

The contribution of edge‐complexation reactions to metal ion sorption by smectites has not been well documented through experimentation or modeling. A model containing fixed‐charge (X−) and hydroxylated edge sites (AlOH and SiOH) was applied to sorption data for Cd on SWy‐1 smectite and a smectitic soil isolate in Na+, Ca2+, and mixed electrolytes to evaluate the potential contributions of ion exchange and surface coordination to metal cation binding. Sorption modeling was performed with FITEQL. Edge reactions were described using the triple‐layer model (TLM) and an inner sphere Cd complex on AlOH sites and outer sphere complexes on SiOH sites. The complexation reactions were parameterized using (i) Cd sorption data from silica and alumina and (ii) site concentration estimates based on cation‐exchange capacity (X−) and particle size measurements (AlOH and SiOH). Ion‐exchange reactions were described in half‐reaction format; exchange constants were fit using Cd sorption data in either Na+ or Ca2+ electrolyte. The sorption data was qualitatively described across ranges in pH and electrolyte concentration using a combination of ion exchange (CdX2) and edge (AlOCd+) complexes. Complexation of Cd to edge SiOH was calculated to be unimportant. The calculated contribution of AlOCd+ complexes increased with increases in pH and ionic strength. Good predictions of Cd sorption in mixed electrolytes were obtained using constants derived from single‐electrolyte systems. Edge sorption reactions were computed to be more important for the soil smectite than for SWy‐1 because of its smaller particle size. However, the slope and magnitude of sorption on the soil isolate was inadequately described by the model. Competitive sorption reactions on the edge sites and binding to organic material are additional factors that must be considered to adequately describe Cd sorption to smectitic soil clays.
Water‐Stable Aggregates and Organic Matter Fractions in Conventional‐ and No‐Tillage Soils
Authors: Beare M. H. , Hendrix P. F. , Coleman D. C.
Published: July 2010

No‐tillage (NT) practices can improve soil aggregation and change the distribution and retention of soil organic matter (SOM) compared with conventional tillage (CT), but the relationships between aggregates and SOM fractions are poorly known. The effects of long‐term (13‐yr) CT and NT management on water‐stable aggregates (WSA) and aggregate‐associated SOM were investigated on a Hiwassee sandy clay loam (clayey, kaolinitic, thermic Rhodic Kanhapludult). Samples were collected at two depths in replicated CT and NT plots and separated into five aggregate size classes by wet sieving. The stability of intact WSA was measured turbidimetrically. The C and N content of total, particulate (POM), and mineral‐associated organic matter was determined for each size class. Whole‐soil organic C was 18% higher in NT (30.7 Mg C ha−1) than in CT (26.1 Mg C ha−1). In CT, macroaggregates (>250 µm) were fewer and less stable than those of NT. The POM C made up ≈36% of whole soil C regardless of tillage, but the quantity of POM was nearly 20% higher in NT than in CT. The POM comprised a higher percentage of total aggregate N in surface soils of NT than in CT and values increased with increases in aggregate size. In NT, concentrations of total and mineral‐associated C and N were higher in the 106‐ to 250‐µm WSA than in the other size classes but, in CT, the concentrations were similar among size classes. An alternative view of aggregate organization is discussed in which microaggregates are formed in association with POM at the center of macroaggregates, helping to explain relationships between SOM storage and aggregate size distributions under different management practices.
Morphological Properties of Surface Seals in Georgia Soils
Authors: Chiang S. C. , West L. T. , Radcliffe D. E.
Published: July 2010

The morphology of surface seals has not been extensively described for acid, sandy and loamy soils common in the U.S. Southeast. The objectives of this study were to: (i) evaluate evolution of seal morphological properties for seven soils in Georgia during the course of a rainfall event, and (ii) relate seal morphology and development to soil properties. Columns were packed with Ap horizons from seven soils in Georgia and subjected to simulated rainfall at 50 mm h−1 for intervals from 10 to 60 min. Seal morphological properties along with thickness and porosity were evaluated from thin sections. The most common feature of seals formed in all of the soils was a disruptional layer with 30 to 50% fewer pores >0.02‐mm diam. than unaffected soil. In readily sealed soils with sandy loam textures, low Fe contents, and high amounts of water‐dispersible clay, this layer formed within the first 10 min of rainfall, and thickness and porosity were constant at longer rainfall durations. In other soils, longer rainfall durations were required to form a disruptional layer. In addition to the disruptional layer, other morphological features observed in the seals included a thin layer of micromass concentration that occurred at the soil surface (skin seal). At intermediate rainfall durations in readily sealed soils, this layer was overlain by a layer of micromass‐depleted grains, which was removed by erosion at longer rainfall durations. Grain size and initial development in microtopographic lows suggest that the micromass‐depleted layer formed by transport and redisposition rather than in‐place disjunction of micromass.
Laboratory Measurements of Solute Transport Using Time Domain Reflectometry
Authors: Ward A. L. , Elrick D. E. , Kachanoski R. G.
Published: July 2010

Measurement of solute transport at different depths in layered soil columns provides more information than traditional outflow measurements. The objective of this study was to extend the time domain reflectometry (TDR) method of measuring soil water content, θ, and bulk electrical conductivity, σT, to the nondestructive measurement of resident concentration, CR, of an added electrolytic tracer. Calibration curves of CR vs. θ and σT were obtained directly, by mixing a sandy soil with different amounts of tracer and water and taking TDR readings of impedance. Similar soil was packed into a Plexiglas box fitted with curved TDR probes at different radial distances from one corner. A constant flux of water was applied at the corner of the box and a pulse of KCl tracer added. Measurements of θ and CR as a function of time and radial distance were made during the three‐dimensional flux experiment. In a one‐dimensional flux experiment, undisturbed soil columns (1.5 m long, 0.15‐m diam.) were instrumented with straight TDR probes installed horizontally at 0.10‐m increments. Indirect calibration of CR vs. θ and σT were obtained under steady‐flow conditions by using a step increase in tracer, and by numerically convolving measurements from a pulse application of tracer. The final value of σT was equated to the input concentration of the tracer to obtain the calibration relationship. The method overcomes many of the limitations associated with soil solution samplers, allowing frequent measurements at close spacings and low cost.
Calibration of Jointed Tube Model for the Gas Diffusion Coefficient in Soils
Authors: Freijer Jan I.
Published: July 2010

Modeling of gas and vapor transport in soils requires knowledge of the relative gas diffusion coefficient. The relative diffusion coefficient was determined as a function of air‐filled porosity, using a pore model based on two tortuous tubes of different radii joined in series. This model was fitted to measured relative diffusion coefficients on undisturbed samples of nine soil types at a wide range of water contents. It was found that model parameters vary with the soil types studied. Combined measurements of the water retention curve, air‐filled porosity, and relative diffusion coefficient were made to evaluate the effects of water distribution in the soil pores on the relative diffusion coefficient. After the samples were saturated with water, the residual air‐filled porosity ranged from 0.051 to 0.167 m3 m−3 and the relative diffusion coefficient was practically zero, which is due to pore blocking by soil water. At pressure heads corresponding to the air‐entry value in the water retention function, air‐filled porosity ranged from 0.095 to 0.256 m3 m−3 and the relative diffusion coefficient ranged from 0.002 to 0.013. From this point, with increasing air‐filled porosity, the relative diffusion coefficient increased rapidly to values ranging from 0.165 to 0.383 at zero water content. It was concluded that the air‐entry value is an important parameter, which indicates a priori the water content at which pore blocking becomes relevant.
Determining Nitrogen‐15 in Nitrite or Nitrate by Producing Nitrous Oxide
Authors: Stevens R. J. , Laughlin R. J.
Published: July 2010

Determining 15N in NO−3 or NO−2 is important when studying soil N transformations directly. Analysis of 15N in NO−3 by standard methods is time consuming and subject to errors such as cross‐contamination. The 15N content of NO−2 is determined conventionally as the difference between NO−3 + NO−2 and NO−3 alone. Since NO−3 concentrations are usually much greater than NO−2 concentrations in soil, determination of 15N in NO−2 has a poor detection limit. We developed new direct methods for determining 15N in NO−3 or NO−2 in 2 M KCl soil extracts, based on the production of N2O from NO−2 + NH2OH. For NO−2, N2O was produced by adding NH2OH at pH 1.7. For NO−3, NO−2 and NH2OH were produced as intermediates during the reduction of NO−3 by Cd‐Cu at pH 4.7. The 15N content of the N2O was determined by automated continuous flow isotope‐ratio mass spectrometry. Measured values of 15N in N2O were closely related to the theoretical values for 15N in NO−2 or NO−3. Five micromoles of NO−3 or 0.5 µmol of NO−2 at 0.1 atom % excess 15N could be determined with coefficients of variation of <4%. The new methods are fast, simple, and not subject to contamination from the atmosphere or from other samples. They should facilitate studies on the simultaneous measurement of gross rates of mineralization, immobilization, nitrification, and NO−3 reduction.
Tri‐ and Tetrafluorobenzoates as Nonreactive Tracers in Soil and Groundwater
Authors: Benson Carl F. , Bowman Robert S.
Published: July 2010

Several fluorinated derivatives of benzoic acid (fluorobenzoate, FBA) have proven their usefulness as nonreactive soil and groundwater tracers. In this study, four previously untested trifluorobenzoates (TFBA) and two tetrafluorobenzoates (TEFBA) were examined for their suitability as water tracers in saturated and unsaturated environments. Negative log acid dissociation constants (pKa) determined by base titration ranged from 2.71 to 3.54 at 298 K. Some sorption of FBAs was observed in batch equilibration experiments with lower pH, high organic C fraction soils. An algorithm was developed for calculating a linear partition coefficient (KD) for each FBA isomer based on pKa, soil organic C, pH, and an average organic C‐based partition coefficient for protonated FBA (K*OC). K*OC was estimated to be 18 200 ± 6 300 L kg−1 when total FBA solution concentration is less than 5 mg L−1. Column mobility experiments in sandy media under saturated and unsaturated conditions yielded breakthrough curves for TFBA and TEFBA isomers that were indistinguishable from Br−. The results presented herein suggest that all 16 ring‐substituted FBAs can serve as nonreactive water tracers.
Predicting Increases in Extractable Phosphorus from Fertilizing Soils of Varying Clay Content
Authors: Cox F. R.
Published: July 2010

The change in extractable P due to fertilization should be quantified for reliable P recommendations, but this effect is dependent on the P buffering capacity of the soil. To determine this change, rates of fertilizer P were applied in six field experiments on Ultisols that varied in clay content. Mehlich‐3 extractable P (M3P) was measured annually, and an initial increase in M3P due to fertilization followed by an exponential decrease in M3P due to sorption were modeled. The change in extractable P after 1 yr at each site was calculated from the model. These data were combined with those from previous studies on two Ultisols in North Carolina and five Oxisols in Brazil to broaden the range in clay content observed. The increase in M3P per unit of applied P after 1 yr was 0.7 for soils with only 10% clay, and it decreased exponentially to <0.2 for soils with >50% clay. The results of this study were similar to conclusions from a P incubation study extracted with Bray‐1 in Natal, South Africa, on 54 soils from five U.S. taxonomic orders, including Ultisols and Oxisols. It appears there is a broad range of cultivated soils for which knowledge of the clay content would allow more reliable predictions of fertilizer P to keep extractable P at a level sufficient for optimum crop yields.