bluuebunny/crossref_metadata_2025 huggingface dataset:
Field‐Measured Limits of Soil Water Availability as Related to Laboratory‐Measured Properties
Authors: Ratliff L. F. , Ritchie J. T. , Cassel D. K.
Published: July 2010

Accurate evaluation of the soil water reserves available for plant use is vital in developing optimum water management for crop production in marginally dry regions. Laboratory estimates of the upper and lower limits of soil water availability used to calculate the soil water reservoir often deviate significantly from the limits measured in the field. To make a unified and broad assessment of the accuracy of laboratory measurements for estimating field soil water, we obtained and evaluated a comprehensive data base of field‐measured upper and lower limits of the soil water reservoir. The field‐measured upper limit was taken as the water content at which drainage from a prewetted soil had practically ceased. The lower limit was taken as the water content of the soil at which plants were practically dead or dormant as a result of the soil water deficit. These field‐measured limits were compared to laboratory measurements at −0.33 and −15 bar made on samples removed from each field site. A total of 401 observations were available for the comparisons of −15 bar measurements to the field‐measured lower limits and 282 observations of −0.33 bar measurements were available for comparison with the field‐measured upper limit. Variation often existed within a soil series at a particular site for the field‐measured upper and lower limits. However, the differences between the field‐measured limits, the total available water reservoir, were relatively constant. Crop species caused only minor differences in the lower limit water content for the upper part of the soil profile where root length density was apparently above some critical limit. However, some annuals extracted water to greater depths than others. The laboratory estimates of the upper limit obtained by −0.33 bar water contents were significantly less than the field‐measured drained upper limit for sands, sandy loams, and sandy clay loams and were significantly more than field measurements for silt loams, silty clay loams, and silty clays. The laboratory estimates of the lower limit obtained by −15 bar water content measurements were significantly less than field lower limit measurements for sands, silt loams, and sandy clay loams and significantly more than field observations for loams, silty clays, and clays. Because our study included relatively few measurements of loamy sands, silts, sandy clays, and clays, it was difficult to generalize about differences in field‐measured and laboratory‐estimated water limits for those textures. The results suggest that if absolute accuracy is necessary in water balance calculations, laboratory‐estimated soil water limits should be used with caution and field‐measured limits, if available, would be preferred.
Relationships Among Iron, Aluminum, Carbon, and Sulfate in a Variety of Forest Soils
Authors: Johnson Dale W. , Todd D. E.
Published: July 2010

Among several soil properties tested, percent Fec (i.e., Fe by citrate‐dithionite minus oxalate extraction) was the single parameter most closely related to SO2‐4 adsorption properties in a variety of forest soils. There were exceptions to this general relationship, however, and a combination of percent C, citrate‐dithionite, and oxalate extractions for both Fe and Al appear most promising in predicting sulfate adsorption. Percent clay, pH, and pyrophosphate‐extractable Fe + Al were either insignificantly or inconsistently related to SO2‐4 adsorption. Because organic matter had a decidedly negative influence upon SO2‐4 adsorption, surface soils and B horizons of Spodosols (and highly podzolized soils) had relatively poor SO2‐4 adsorption properties, even when their dithionite‐extractable Fe values were high. Organic matter also reduced Fe crystallinity (i.e., increased Feo/Fed, or the ratio of oxalate to dithionite Fe), and the results of this study suggest that crystalline rather than amorphous, inorganic Fe (i.e., oxalate minus pyrophosphate Fe) is most highly correlated with adsorbed, water‐insoluble SO2‐4.
Direct Colorimetric Measurement of Ammonium in Potassium Chloride Extracts of Soils
Authors: Dorich R. A. , Nelson D. W.
Published: July 2010

Although 2M KCL is widely used as an extractant for inorganic N in soils, there is no manual colorimetric methods for direct measurement of ammonium‐N (NH+4‐N) in KCl extracts. The indophenol blue method previously used for measurement of NH+4‐N in aqueous solutions has been modified to permit estimation of NH+4‐N in extracts of soils. The method entails the addition of 1 mL of 6% (wt/v) disodium ethylene‐diamine‐tetraacetic acid (EDTA) solution to an aliquot of a 2M KCl extract of soil followed by addition of phenol‐nitroprusside and buffered hypochlorite reagents. Maxiumum color development occurs in 60 min at room temperature (23°C), but color development time is reduced to 30 min and molar absorptivity of the chromophore is enhanced (60%) by incubation of the sample at 40°C. Although previous studies have shown that precipitates form when indophenol blue color developing reagents were added to KCl extracts of soils, the addition of EDTA eliminated precipitate formation in samples containing as much as 6 mg of Ca2+ or 4 mg of Mg2+ per 25 mL of final analytical volume. The proposed procedure quantitatively measures the NH+4‐N present in KCl extracts of soils and is sensitive to concentrations of NH+4‐N as low as 0.2 µg per 25 mL of final analytical volume. The proposed procedure was the most precise of the three NH+4‐N methods (steam distillation and acidimetric titration, steam distillation into phenol‐nitroprusside and NH+4‐N determination by the indophenol blue colorimetric method, and the proposed procedure) studied. The proposed method provides a sensitive, precise, and accurate colorimetric method for direct measurement of NH+4‐N in KCl extracts of soils.
Kinetics of Nonexchangeable Potassium Release from Two Coastal Plain Soils
Authors: Martin H. W. , Sparks D. L.
Published: July 2010

The kinetics of nonexchangeable‐K release using H‐saturated resin were investigated on Kalmia (fine‐loamy, siliceous, thermic Typic Hapludults) and Kennansville (loamy, siliceous, thermic Arenic Hapludults) soil profiles from the Coastal Plain of Delaware. Calciumsaturated soil samples were equilibrated with H‐saturated resin from 0.5 to 960 h. Equilibrium in K release in both soil profiles was attained in about 960 h. The kinetics of K release were evaluated using the Elovich, parabolic diffusion law, first‐order diffusion, and zero‐order equations. The first‐order diffusion equation described the K‐release kinetics best as evidenced by the highest correlation coefficient (r) and the lowest value of the standard error of the estimate (SE). The parabolic diffusion law also described the data satisfactorily indicating diffusion‐controlled exchange. The zero‐order and Elovich equations did not describe the data well as shown by higher SE values than those found with the first‐order diffusion and parabolic diffusion law equations. Nonexchangeable‐K release rate coefficients (k2) ranged from 1.20 to 2.2 × 10−3 h−1 in the Kalmia soil and from 1.5 to 2.9 × 10−3 h−1 in the Kennansville soil. The magnitude of the k2 values suggested low rates of nonexchangeable‐K release from the two soils.
Effect of Precipitation of Alkaline Earth Carbonates and Magnesium Hydroxide on Na‐Ca‐Mg Exchange in Wyoming Bentonite
Authors: Levy Rachel , Tanji K. K. , Whittig L. D.
Published: July 2010

Wyoming bentonite saturated with Ca and Mg at five different ratios was equilibrated with NaCl solution. It was found that the preference of the bentonite for Ca over Mg was not affected by the presence of exchangeable Na. The separation factor, αNaCa+Mg, of the bentonite equilibrated with NaCl was compared to that of bentonite in which alkaline earth carbonates and magnesium hydroxide precipitated. It was found that in the presence of alkaline earth precipitation only, αNaCa+Mg was a function of ionic strength and equivalent fraction of soluble Na. However, precipitation of the carbonates caused a different distribution of the exchangeable ions in the bentonite crystallite compared to the distribution in the absence of precipitation. Where carbonates precipitated, Na was found between the interlayers and Ca and Mg occupied the outside surfaces of the clay. As the pH of the equilibrium solution increased and additional precipitation of alkaline earth carbonates and magnesium hydroxide occurred, αNaCa+Mg increased with decrease in ionic strength. Apparently this increase in the preference for Na was due to the restriction on Na, occupying the internal surface of the bentonite, to diffuse into the equilibrium solution because of hydroxide coating of the crystallites.
Cation Selectivity in Sodium‐Calcium, Sodium‐Magnesium, and Calcium‐Magnesium Exchange on Wyoming Bentonite at 298 K
Authors: Sposito Garrison , Holtzclaw Kenneth M. , Jouany Claire , Charlet Laurent
Published: July 2010

Exchange isotherms were prepared for Na+ in Na+→Ca2+ and Na+→Mg2+ exchange reactions, and for Mg2+ in Na+→Mg2+ exchange reactions, at 298 K on Wyoming bentonite suspended in a 0.05M perchlorate background. These isotherms were essentially congruent with the appropriate thermodynamic nonpreference exchange isotherms. It was concluded from this fact that there is essentially no difference in the affinity of montmorillonite clay for Ca2+ vs. Mg2+. However, exchange isotherms prepared for Na+ in Na(I) → Ca(II) and Na(I) → Mg(II) exchange, as well as published ones for Mg(II) in Ca(II) → Mg(II) exchange on montmorillonite suspended in a 0.05M chloride background consistently indicate a slight preference on the clay for Ca(II) over Mg(II). This preference for Ca(II) is concluded to be the result of the formation of CaCl+ complexes, which are more stable thermodynamically and have a greater affinity for the clay than MgCl+ complexes.
Soil Temperature Regimes in Nevada
Authors: Schmidlin T. W. , Peterson F. F. , Gifford R. O.
Published: July 2010

Estimates of the 12‐month mean annual soil temperature (MAST) for well‐drained soils in Nevada can be made from two—or better—three, four, or six equally spaced monthly readings. A regression of MAST (°C) against elevation (ELEV), in meters, and latitude (LAT), in decimal degrees, using 84 well‐drained sites with < 15% slope, allows estimation of MAST for similar soils in Nevada by the equation: MAST = 50.1 − 0.0064(ELEV) − 0.66(LAT). This equation was used to construct a soil temperature regime map for Nevada that shows mesic soils are by far most extensive, thermic soils next most extensive, and that inextensive hyperthermic soils occur only in southern Nevada. Frigid and cryic soils are inextensive and occur only high on major mountain ranges or isolated peaks. Comparison of minimum elevations of frigid and cryic soils suggests that the latter are much more common in the steep mountains where they both occur. These elevations were estimated from the MAST regression and a second regression for mean summer soil temperature (MSST) using the same sites: MSST = 72.4 − 0.0077(ELEV) − 0.95(LAT). Steep slope and aspect affect both MAST and MSST in the high mountains, hence affect the location of mesic/frigid/cryic boundaries. Pergelic soils probably do not occur in Nevada.
Soil Carbon Dynamics in a Mixed Deciduous Forest Following Clear‐Cutting with and without Residue Removal
Authors: Edwards N. T. , Ross‐Todd B. M.
Published: July 2010

The effect of two harvest intensities on soil carbon dynamics was determined for the first year following harvest of a mixed deciduous forest in Tennessee. Harvest procedures were clear‐cutting (all trees of all diameters cut) with only sawlogs removed (RL) and clear‐cutting with removal of all woody material except stumps (RR). There were no detectable differences in soil carbon pools between treated and control watersheds before harvest or 5 months after harvest. During the winter months immediately following harvest, CO2 efflux rates from the soil surface were greater in the intensively harvested watersheds than in the other watersheds. However, CO2 efflux rates were greater in the control watershed than in the harvested watersheds during the first growing season following harvest. This was apparently due to greater live root respiration in the control watershed because mineral soil respiration only (as determined by laboratory incubations) was greater in harvested watersheds than the control reflecting the higher soil temperature and moisture in the harvested watersheds. Annual soil respiration rates, predicted from laboratory measurements and field temperatures, were 92, 121, and 154 g CO2/m2 in the control watershed, RL watersheds, and RR watersheds, respectively. When extrapolated to a land area equal to that represented by the annual harvest of U.S. deciduous forests these rate increases amount to only ca. 0.006% of the annual carbon released from fossil fuel burning.
The Effects of Magnetite on Oxalate‐ and Dithionite‐Extractable Iron
Authors: Walker Ann L.
Published: July 2010

Six soils from a chronosequence were chosen to test the effects of magnetite on using free Fe to estimate relative ages of soils. The acid‐ammonium oxalate and dithionite‐citrate‐bicarbonate methods were used to extract the free Fe from the samples. Iron values from these two extractions were compared for samples from which the magnetite was removed, from which the magnetite was not removed, and from the magnetite fraction itself. Visual examinations were also made of the untreated and treated magnetite grains. The oxalate solution releases Fe from magnetite in proportion to the amount of magnetite in the soil. The dithionite solution does not release Fe from magnetite, but releases Fe from hematite coatings and replacements on the magnetite grains. Large or varying magnetite concentrations can influence the amount of Fe released by either of these methods, and cause errors in estimations of relative age. Magnetite should be removed from the samples prior to treatment by oxalate extraction. Magnetite should be left in the samples to be treated by the dithionite extraction, but the concentration of magnetite in the soils should be noted. In order to get the best possible estimation of relative age using free Fe concentrations, the ratio of magnetite‐free oxalate to dithionite‐extractable Fe should be used.
Correlation of Clay Minerals and Properties of Soils in the Western United States
Authors: Nettleton W. D. , Brasher B. R.
Published: July 2010

X‐ray diffraction (XRD) studies of about 2000 soil clays show that 1500 kPa water retention, in addition to Atterberg limits, cation exchange capacity, 33 kPa water retention, volume of water retained between 33 and 1500 kPa, and linear extensibility varies with kind of soil clay and the intensity of the XRD peak of the dominant clay mineral. Hence, knowledge of soil clay mineralogy is particularly useful for predicting the behavior of soils. In standard characterization work, however, determining the property of interest is usually more efficient than determining mineralogy and then estimating the property. Determining both is not necessary if their relationship is understood. In predicting the behavior of soils, identification of the dominant clay mineral is sufficient if that mineral is smectite. If the mineral is kaolinite or clay mica, somewhat greater accuracy of prediction of properties is possible if measurements of the relative intensities of the other clay minerals in the suite are also known.
Measuring Nitrogen Leaching with Ion Exchange Resin: A Laboratory Assessment
Authors: Schnabel R. R.
Published: July 2010

A procedure using ion exchange resin to measure leaching losses of inorganic N in soils was tested in the laboratory. A 2‐cm thick bed of anion or cation exchange resin reduced the concentration of the percolating solutions to 1% of their initial concentrations until the resins were one‐third to one‐half N saturated. Greater than 90% of the nitrate adsorbed by anion exchange resin was recovered after 12 weeks of incubation indicating that N transformations were minimal.
Ion Exchange Resin Bag Method for Assessing Forest Soil Nitrogen Availability
Authors: Binkley Dan , Matson Pamela
Published: July 2010

An ion exchange resin bag technique was compared to six other methods for estimating N availability. Under a controlled greenhouse environment and with well‐mixed soils, the resin technique correlated well with more traditional N‐availability indices. However, resin bags on site in three forest stands yielded different N‐availability estimates than those in the greenhouse. This suggests that the resin bag method may be sensitive to on‐site conditions not discerned by more widely accepted laboratory techniques.
A Transient Method for Measuring Soil Water Diffusivity and Unsaturated Hydraulic Conductivity
Authors: Scotter D. R. , Clothier B. E.
Published: July 2010

A method for measuring the unsaturated diffusivity of soil is described. It involves measurement of the matric potential transient at one end of a soil sample following a step change in the potential at the other end. Small potential steps can be used in contrast with the analogous outflow methods, because the difficult task of accurately measuring small flow rates is obviated. The analysis used to obtain the diffusivity from the potential data relies mainly on the delay in the transient and does not depend critically on its shape, thus avoiding the other major problem associated with outflow methods. With the use of the graphs provided, data analysis is simple. Measurement of the total outflow induced by each potential step allows the hydraulic conductivity to be calculated from the diffusivity. Measurements made on repacked soil during desorption and sorption showed no hysteresis in the hydraulic conductivity vs. water content relationship and agreed with independent measurements using a steady‐state method. Data for field soil cores are also presented. Differences in shape between the predicted and observed matric potential transients are discussed in terms of entrapped air.
Copper Adsorption by Soils Exposed to Desiccation Stress
Authors: Lehmann R. G. , Harter R. D.
Published: July 2010

Soils undergo substantial physical, chemical, and biological changes during the process of drying. Because soils are usually dried before their use in the laboratory, it is important to understand these changes if laboratory results are to be related to field conditions. The effects of air‐drying (25°C) and over‐drying (105°C) moist soils and the effects of remoistening air‐dried and stored soils on copper adsorption are presented. Results indicate that oven‐dried soils adsorbed 3 to 10% less copper than air‐dried soils, which adsorbed 10% less than moist field soils. Remoistened samples, which were incubated for 1 month under aerated conditions, adsorbed an average of 12% more copper than air‐dried and stored soils. Remoistened soils, which were incubated without aeration under a layer of water, showed no significant deviation from adsorption onto air‐dried soils.
Infrared Dehydration Method for Determining Gypsum Content of Soils
Authors: Elprince A. M. , Turjoman A. M.
Published: July 2010

A Mettler drying unit (Model LP12) and a top‐loading balance (Model PL60) were used for determining gypsum in soils. Plotting the rate of weight loss against time upon heating by infrared (IR) radiation (at 123 or 156°C) gave a dehydration curve made of two peaks. The first peak was due to soil moisture and the second to the crystal water of gypsum. Percent gypsum was determined by extrapolation the dehydration curve (vida infra) to rate = 0. The use of computer graphics in developing the curves made this method very rapid (about 15 min per determination). The reproducibility of the IR method (σ = 0.48) was better than the barium sulfate method (σ = 0.61) over the 2 to 58% gypsum range studies. The accuracies of the two methods were comparable and estimated to be ± 0.3% gypsum when the average of triplicate determinations was used and ± 0.5% gypsum with single determinations.
Nitrification and Denitrification of Nitrogen Fertilizers in a Soil Column
Authors: Khdyer I. I. , Cho C. M.
Published: July 2010

Nitrogen transformations occuring within reconstituted Wellwood soil profile samples packed in plastic columns (4.4 cm i.d.) and amended with urea or NO‐3‐N were investigated under isothermal (20°C) laboratory conditions. The surface of the soil column was open to the atmosphere and the bottom was closed. Samples of soil atmosphere were taken regularly through sampling ports located at several different depths and analyzed for N2, O2, and N2O with a mass spectrometer. A steady‐state O2 distribution within the column was established soon after packing, making the surface layer aerobic and the lower layer anaerobic. The depth of the aerobic layer was governed by the gas‐filled pore space of the column. Urea applied uniformly throughout the column was oxidized to NO‐3 within the aerobic layer. The concentration of NO‐3 was highest at the surface and decreased to almost zero near the aerobic‐anaerobic interface. Nitrate transported downward from the aerobic layer was denitrified near the interface. Ammonium in the anaerobic zone was stable in a column at 10.5% gas‐filled pore but gradually declined as incubation at 16.5% gas‐filled pore space progressed. Nitrate N applied to the aerobic layer was transported downward to the anaerobic layer and denitrified. The magnitude of denitrification was greater than that observed with urea possibly due to a higher flux of NO‐3 into the anaerobic layer. Nitrous oxide was observed near the aerobicanaerobic interface with both the NO‐3 treatment and urea (10.5% air porosity treatments). Dinitrogen was the only gaseous dinitrification product ohserved in the column at 16.5% air porosity amended with urea.
Soil Modification by Colonies of Black Meadow Ants in a New York Old Field
Authors: Levan Mary Ann , Stone Earl L.
Published: July 2010

The above‐ground mounds of the black meadow ant Formica fusca L. had an average weight of 8.7 kg and occurred at a density of 109/ha on a small study site in central New York. Both mound and a larger diameter soil column beneath are extensively channelled and result in a coarse fragment concentration or stone line at the 10‐ to 15‐cm depth. Channels extend to at least the 1.5‐m depth, and up‐ward transport of calcareous subsoil increases Ca and Mg concentrations and pH of the upper profile. In contrast, extensive replacement of the 0‐ to 10‐cm horizon with subsoil reduces its organic matter content by about 50%. Increased concentrations of extractable P and K in the mound and upper mound profile are attributed to exogenous sources. After abandonment the mound columns remain as near‐neutral nutritionally enriched microsites that may influence the course of old field succession.
Effect of Soil Texture on Critical Bulk Densities for Root Growth
Authors: Jones C. Allan
Published: July 2010

Published and unpublished data from 10 studies were analyzed to determine the effects of soil texture on critical bulk densities for rooting at near‐optimum soil water contents. Highly significant negative relationships were found between percentage clay or silt + clay and the bulk density at which rooting was at a maximum or the bulk density at which rooting was 0.2 of that maximum. Similar relationships were also found between percentage clay or silt + clay and (i) the bulk densities of soil layers classified as fragipans and (ii) the maximum bulk densities at which “many” roots are reported in U.S. Soil Conservation Service pedon descriptions. Thus, soil texture can be used to estimate bulk densities of fragipans and critical bulk densities at which root growth is severely affected at near‐optimal soil water contents.
Noncrystalline Clay Distribution in the Major Land Resource Areas of Mississippi
Authors: Nash V. E. , Pettry D. E. , Aide M. T.
Published: July 2010

Selected horizons from 45 Mississippi soils have been examined for noncrystalline clay content as determined by 0.5M NaOH and 0.2M ammonium oxalate (pH 3). The soils represent the major soil resource areas of the state. Parent material varied in age from Cretaceous to Holocene. Only small amounts of amorphous clay were extracted from the weakly developed Inceptisols and Entisols, from calcareous soils of the Blacklands and from the alkaline Natraqualfs of the Coastal Plains. Under these nonacid conditions crystalline clay minerals are the more stable phase. The strongly developed Ultisols released large amounts of noncrystalline material with a low silica/alumina molar ratio. The low molar ratio is indicative of gibbsite; however, the large quantity of silica extracted suggests that silica may be adsorbed on the crystalline minerals.

When only soils high in smectite are considered, the following trends in noncrystalline clay formation were observed. The silica/alumina ratio increases with smectite content. The quantity of noncrystalline clay increases with increased soil acidity. The poorly drained soils contain less amorphous clay indicating that smectite is the more stable mineral in this environment.

Extraction of the clays with acid ammonium oxalate resulted in an average increase in cation exchange capacity of 14 cmol (½ Ca2+) kg−1 due to the removal of surface coatings blocking exchange sites.
Effect of Sesquioxide Coatings on Surface Charge of Standard Mineral and Soil Samples
Authors: Hendershot W. H. , Lavkulich L. M.
Published: July 2010

In nature, Fe and Al hydrous oxides often form the interface between crystalline soil minerals and the soil solution. To understand better the effect of these coatings on surface charge properties, standard minerals and cleaned C horizon samples were coated with either Fe or Al hydrous oxide and the point(s) of zero salt effect (PZSE) were measured by potentiometric titration. Five standard mineral samples (including illite, muscovite, kaolinite, microcline, and quartz) and three C horizon samples of mixed mineralogy were artificially coated with Fe and Al hydrous oxide material by precipitation of FeCl3 or AlCl3 solutions with the mineral and soil samples. The samples were then washed free of Cl‐ and aged. Uncoated samples and samples of pure sesquioxide material were prepared using similar procedures. Depending on the nature of the underlying surface, the addition of sesquioxide coatings to the samples changed the surface charge properties in different ways. In every case the buffering capacity of the samples was increased by the addition of the sesquioxide coatings. The uncoated samples that had relatively high buffering capacities had their surface charge properties changed more by the Al‐ than the Fe‐coating material. For example, the illite, muscovite, Memekay C horizon, and Marblehill C horizon all responded to the Al‐coating with a distinct shift of the PZSE to higher pH. The less reactive samples (kaolinite, microcline, quartz, and the Cox Bay C horizon) responded little to the Al coatings but showed a strong response to the Fe coatings. The results indicate that in a system containing both pH‐dependent and permanent exchange sites there is no effective means of separating the two components. Below the point of zero net charge (PZNC) of the coating material, the measured cation exchange capacity (CEC) will be decreased to a point below the permanent CEC by the coatings, whereas at pH values above this point the measured CEC will be increased. The PZSE of the pH‐dependent charge material cannot be measured separately by potentiometric titration; this method measures the PZSE of the samples as a whole. At any pH the CEC measured will be the result of a complex interaction between the two types of exchange sites.
Shape Factors for Seepage into Pits
Authors: Boast C. W. , Langebartel R. G.
Published: July 2010

In the field “pit‐bailing” method, saturated hydraulic conductivity below a water table is determined from the rate of rise of water in a pit. The relationship between the rate of rise and the soil hydraulic conductivity is expressed as a shape factor. Shape factors are presented here for pits with length/radius ratio ranging from 0 to 2, for pits ranging from empty to 0.9 full, and for impermeable‐barrier and very permeable source lower boundary conditions at various distances below the pit. The calculated shape factors are extrapolated to the situation of a pit in an effectively infinitely deep uniform soil. Shape factors for pits of a given fullness with a source or a semi‐infinite lower boundary condition are found to decrease and then increase as the length/radius ratio of the pit increases, reaching a minimum typically when this ratio is between 0.2 and 0.5 for the semi‐infinite case. This trend is investigated to determine whether it is due to calculation errors for extreme geometries or is due to real phenomena. That the trend exists is found by examining analytical solutions to two situations—a pit fully penetrating to an impermeable barrier and a disk in semi‐infinite space.
Statistical Analysis of Salinity and Texture Effects on Spatial Variability of Soil Hydraulic Conductivity
Authors: Bresler Eshel , Dagan G. , Wagenet R. J. , Laufer A.
Published: July 2010

A statistical analysis that identifies the dominant factors responsible for the spatial variability of the saturated conductivity (Ks) in a selected field is presented. The variables are considered random functions of the space coordinates. Two types of stationarity are investigated: constant mean and stationary variogram (stationarity of order 2) and trend of the means (nonstationarity of the mathematical expectation) with stationary covariances. Linear models of statistical dependence were used. Elimination of factors of minor importance was based on correlation analysis. Electrical conductivity (EC) and percent sand were the most important independent variables, whereas Ks was the dependent variable. The analysis showed that soil salinity (EC) accounted for only 10 to 15% of the variability of Ks texture (percent sand) explained 25 to 45% of the Ks variability, and 10 to 15% of the variability was explained by the interaction between salinity and texture. Various soil factors other than salinity and texture accounted for 30 to 50% of the variability in Ks. Semivariograms and covariograms of Ks, EC, and percent sand did not have a sill because of a significant horizontal linear trend. Calculations showed that the trend accounted for about a half of the variability of the original data. Semivariograms and covariograms of a new population of residuals after extracting the trend gave values of the sills equal to the variances. The integral scale of the residuals of Ks and percent sand was estimated to be about 15 to 20 m, whereas salinity (EC) did not display a spatial structure. The results can be generalized for other studies with different values of variances and covariances of soil salinity and soil texture.
Redistribution of Exchangeable Calcium, Magnesium, and Aluminum Following Lime or Gypsum Applications to a Brazilian Oxisol
Authors: Pavan Marcos A. , Bingham F. T. , Pratt P. F.
Published: July 2010

A greenhouse experiment was carried out with 16 columns of an undisturbed Oxisol that had sufficient subsoil acidity to restrict root growth of a wide variety of crop plants. The objective was to determine the effects of surface applied CaCO3, CaSO4·2H2O, and water on subsoil pH and exchangeable Al, Ca, and Mg. Eight soil columns were treated with CaCO3 or CaSO4·2H2O at rates equal to 0.25 and 1.50 × the lime equivalent (KCl‐extractable Al). The irrigation treatments consisted of trickle irrigation applied at 8.94 and 17.88 mm day−1 for 6 months. These treatments were superimposed on the amendment treatments. Observations included volume and composition of drainage water during the course of the experiment and chemical composition of the soil column by depth increments once the irrigation treatments were completed. Soil analysis included pH, cation exchange capacity (CEC), exchangeable cations, and composition of saturation extracts of soil. Effects of CaCO3 treatments were observed only in the upper 20 cm of the profiles irrespective of irrigation and fertilizer treatments. The CaCO3 treatments increased soil pH, CEC, and exchangeable Ca while decreasing exchangeable Mg and exchangeable Al; and CaSO4·2H2O treatments reduced the level of exchangeable Al and Mg throughout the 100‐cm depth profiles while increasing the level of exchangeable Ca. Soil pH and CEC were unaffected by the latter treatment. Based on the effectiveness of CaSO4·2H2O in reducing exchangeable Al and Mg while increasing exchangeable Ca, the combination of dolomitic lime and gypsum appears to be an appropriate amendment treatment for Oxisols with toxic concentrations of available Al.
Studies of Aged OH‐Al Solutions using Kinetics of Al‐Ferron Reactions and Sulfate Precipitation
Authors: Tsai Ping Ping , Hsu Pa Ho
Published: July 2010

A series of OH‐Al solutions (0.02M in Al, NaOH/Al molar ratio = 1, slow neutralization) aged from 10 d to 55 months were all clear and had similar pH values and monomeric Al concentrations but reacted differently with sodium sulfate and with ferron. The addition of sodium sulfate yielded three kinds of basic aluminum sulfates: tetrahedral crystals of composition Na0.08 Al(OH)2.46 (SO4)0.31 · xH2O, x‐ray amorphous spherical particles of composition Al(OH)2.34 (SO4)0.33 · xH2O, and irregular‐shaped crystals of composition Al(OH)2.38 (SO4)0.31 · xH2O. The distribution of these sulfates is related to the aging of the parent OH‐Al solutions. The kinetics of Al‐ferron color development indicated that the OH‐Al polymers in the fresh solutions reacted with ferron rapidly, following a pseudo first‐order reaction (rate constant = 0.096 min−1). With increased aging, the rapidly reacting polymers slowly decreased, whereas another polymeric species that reacted with ferron slowly (rate constant = 0.00038 min−1) gradually developed. The results suggest that the polymers that reacted rapidly with ferron accounted for the formation of tetrahedral crystals and spherical particles, whereas those polymers that reacted slowly accounted for the formation of irregular‐shaped crystals.
Strength Characteristics of Three Indurated Horizons in Massachusetts
Authors: Pickering E. W. , Veneman P. L. M.
Published: July 2010

Identification of fragipans is often difficult due to the lack of quantitative differentiating criteria. The unconfined compression (UC) test was used to characterize strength properties of three indurated horizons. Tests were performed in the laboratory on undisturbed core samples equilibrated to one of four moisture conditions: wet, 0.1 MPa, 0.5 MPa, or air‐dried. Fragipans developed in basal till exhibited maximum UC strength values of about 100 kPa at moisture contents < 0.10 kg kg−1 and minimum UC strength of < 25 kPa at wetnesses of 0.14 kg kg−1 or more. Between these two critical moisture contents, strength varied inversely with wetness. A pan formed in post‐glacial colluvial deposits showed similar maximum UC strength values but still retained about 70% of its UC strength at the wet moisture condition. The UC testing data enabled separation of the fragipans developed in the glacial till from indurated horizons formed in the colluvial material. Pocket and Proctor penetrometers were investigated to determine their suitability for routine recognition of fragipan horizons in the field, especially during wet soil conditions. Their application did not improve upon current field techniques.
Variation in Alluvial‐Derived Soils as Measured by Landsat Thematic Mapper
Authors: Thompson David R. , Henderson Keith E. , Houston A. Glen , Pitts David E.
Published: July 2010

Landsat thematic mapper (TM) data acquired over Mississippi County, Ark. were evaluated in order to determine the sensitivity of TM to soil properties under growing soybeans [Glycine max (L.) Merr.], and to determine whether or not established soil survey soil association boundaries were apparent on TM imagery of cropped fields. Ten fields of soybeans at the same growth stage were selected such that five fields had complex soil patterns and five fields had uniform soil patterns for the sensitivity evaluation. A detailed soil survey was available for the area. Landsat TM has six narrow spectral bands with 30 m ground resolution and a broad thermal band with 120 m ground resolution. While all bands provided useful information, the 0.76 to 0.90 µm (band 4), the 1.55 to 1.75 µm (band 5), and the 10.4 to 12.5 µm (band 6) were most useful in identifying soil association boundaries located by the USDA‐SCS general soil maps. Examination of the digital values of the individual TM bands indicated that the coefficients of variations increased as the within‐field variability of the soils increased for all TM bands; TM appears to provide information of within‐field variability related to soil differences and as reflected by the vegetation growing on the soil.
Long‐Term Effects of Tillage Method on Soil Tilth Independent of Wheel Traffic Compaction
Authors: Voorhees W. B. , Lindstrom M. J.
Published: July 2010

Field experiments were conducted on a Nicollet silty clay loam (fine‐loamy, mixed, mesic Aquic Hapludoll) in southwestern Minnesota to measure and evaluate the direct effects of tillage method on soil tilth independent of wheel‐induced soil compaction. The controlled wheel traffic concept was used on plots that had two forms of primary autumn tillage—either moldboard plow or conservation tillage (chisel plow or tandem disk). The degree of soil tilth was evaluated by measuring bulk density, clod density, and aggregate size distribution over a period of 9 y. Wheel‐induced compaction increased the density of the soil and the mean diameter of aggregates < 9 mm in diam. More importantly, wheel traffic essentially eliminated differences in tilth due to tillage method. When tilth parameters were measured in the nonwheel‐tracked soil, tillage method did have an effect on tilth, and this effect changed with time. Initially, moldboard plowing produced a more porous soil in the 0‐ to 15‐cm depth than did conservation tillage. This difference gradually changed with time, and after 3 to 4 y, conservation tillage produced a higher porosity than did plowing. A similar effect was measured in the 15‐ to 30‐cm layer, but about 7 y of conservation tillage were needed to produce a soil with porosity equal to that of plowing. Continuous conservation tillage produced larger diameter aggregates and more porous clods than did continuous moldboard plowing. These changes in soil tilth with time illustrate the need for long‐term experiments. More importantly, these studies show that wheel traffic of normal farming operations can negate or mask the true effects of specific tillage methods.
Effect of Placement Methods on Floodwater Properties and Recovery of Applied Nitrogen (15N‐Labeled Urea) in Wetland Rice
Authors: Cao Zhi‐hong , De Datta S. K. , Fillery I. R. P.
Published: July 2010

Studies at the International Rice Research Institute (IRRI) during the 1981 dry and wet seasons evaluated the effects of placement methods on recovery of fertilizer N by rice (Oryza sativa L.) using 15N‐labeled urea in field microplots. Uniform placement and point placement of urea supergranules (USG) gave the highest yield (6.4 Mg/ha) with efficiency of 51 kg rough rice/kg N in the dry season. In the wet season, point placement by USG produced the highest yield (4.4 Mg/ha) with efficiency of 40 kg rough rice/kg N. Higher floodwater pH and total N (urea + NH4‐N) concentration in floodwater were recorded after fertilization with split application and band placement of urea indicating the greater potential for NH3 volatilization and denitrification losses from these methods. Lower floodwater pH and low total N concentration in floodwater (5 mg/kg) were detected with uniform placement of prilled urea and point placement of USG, demonstrating that these methods can reduce N losses in lowland rice. Most fertilizer N (15N‐labeled urea) uptake occurred during the early crop growth stages. However, fertilizer N uptake was sustained with point placement of USG and uniform placement of prilled urea. Native soil N was taken up by the rice crop during the entire growing season, and was the major N source at the later part of crop growth in the wet season. Fertilizer 15N as high as 75% in the dry season and 65% in the wet season were recovered by the rice plant at harvest (grain and straw) with point placement of USG.
Profiles of Bromide and Increased Soil Moisture after Infiltration into Soils with Macropores
Authors: Germann P. F. , Edwards W. M. , Owens L. B.
Published: July 2010

The purpose of this study was to investigate bromide and water distributions in soils as the result of macropore structure and sprinkling rate. Water was found to have moved laterally from the macropores into the soil matrix. It also has moved deeper into the soil with higher macroporosity and when applied at higher rates, as was indicated by bromide tracer profiles. Evidence is presented that the soil volume measured with a double tube gamma‐ray probe was too small to follow the wetting process completely when macropores contributed to flow. A parameter, derived from the bromide profiles, can be used to characterize the hydraulic importance of macroporosity, based upon a simple approach to water flow along macropores.
Flux‐Concentration Relation‐Based Solution of Constant‐Flux Infiltration Equation: I. Infiltration into Nonuniform Initial Moisture Profiles
Authors: Boulier J. F. , Touma J. , Vauclin M.
Published: July 2010

The quasi‐analytical solution of the infiltration equation based on the flux‐concentration relation for constant flux condition and initially uniform water content profile is extended here to nonuniform moisture profiles for fluxes either smaller or greater than the saturated hydraulic conductivity. In the latter case, the solution is developed for the postponding stage. It is shown that the measured flux‐concentration relation is well‐approximated by F(θ*) = θ* and that no significant time dependence can be observed. The quasi‐analytical solution is then successfully compared with both laboratory experiments performed on a sandy soil column and numerical solution of the Richards equation for the nonponding, preponding, and postponding stages of infiltration.
Steady Infiltration from Circular Cylindrical Cavities
Authors: Philip J. R.
Published: July 2010

The problem of quasilinearized steady infiltration from circular cylindrical cavities, with the moisture potential fixed at the cavity surface, is solved exactly. Solutions are presented numerically and graphically for values of the dimensionless cavity radius, R0, ranging from 0.01 to 10. The dependence on R0 of the average infiltration rate around the cavity surface, and of the distributions of moisture content and potential, are examined. As R0 increases, the effects of gravity on the phenomenon increasingly dominate those of capillarity. Gravity very strongly distorts the moisture distribution from the symmetry produced by capillarity alone: for R0 as small as 0.01, the depth of the effectively wetted region exceeds 250 times its horizontal width on the cavity center line; and the ratio increases rapidly with R0, exceeding 50 000 for R0 = 5. An earlier small R0 approximation proves useful only for R0 ≤ 0.2. The cavity flow, evaluated by the present analysis, may be combined with the line source solution to give approximate results useful for the region deeper than 50 radii below the cavity.
Effects of Chemical Modifications and Extractants on the Carbon‐13 NMR Spectra of Humic Materials
Authors: Preston C. M. , Schnitzer M.
Published: July 2010

Carbon‐13 NMR was used to study the effects of methylation, 6M HCl hydrolysis and 6M HCl hydrolysis followed by methylation on two humic acids (HA's) and one fulvic acid (FA), as well as the effect of extraction by 0.5M NaOH vs. 0.1M HCl on an FA. Spectra of methylated HA's and FA's indicate that almost all CO2H groups are attached to aromatic structures, and that phenolic OH's are significant functional groups. These spectra also exhibit fine structure in the 127‐ to 131‐ppm region, possibly due to benzenecarboxylic acid‐type structures, which have been proposed as major building blocks of humic materials. Other sharp signals are observed in the 133‐ to 146‐ppm region, due to C‐substituted carbons in aromatic or heterocyclic rings. Carbon‐13 NMR spectra of hydrolyzed HA's and FA indicate, in agreement with chemical analyses, that 6M HCl hydrolysis removes all amino acids, most carbohydrates and increases the aromatic C content (aromaticity) of the residues. Carbon‐13 NMR spectra of FA extracted by 0.5M NaOH and 0.1M HCl are similar.
Natural Nitrogen‐15 Abundance as an Indicator of Soil Organic Matter Transformations in Native and Cultivated Soils
Authors: Tiessen H. , Karamanos R. E. , Stewart J. W. B. , Selles F.
Published: July 2010

The natural N isotope composition of soil organic matter associated with organo‐mineral particle size fractions of two cultivated and two native grassland soils was studied. In the native soils, N associated with the coarsest (sand size) fraction showed a low enrichment (+7 per mil 15N enrichment) typical for recent plant materials. A similarly low enrichment was observed in the silt‐sized fractions (+9 δa 15N) whereas clays had a higher 15N abundance (>12 δa 15N), characteristic of residual material from microbially‐mediated N mineralization. Cultivation initially resulted in the incorporation of a large pulse of low‐enrichment plant material that could be detected in the sand and coarse silt fractions, as well as in the fine clays that contain a large portion of the soil's microbial products. The 15N abundance of fine‐silt and coarse‐clay‐associated N appeared relatively unchanged even after prolonged cultivation of 60 yr. Increases in the 15N abundance of the sand and silt fractions were attributed to reduced inputs of plant residues under cultivation. A large drop in the 15N abundance of the fine‐clay‐sized materials indicated a major change in the nature of microbial N transformations.
The Stratigraphy and Composition of a Lakeside Wetland
Authors: Johnston C. A. , Lee G. B. , Madison F. W.
Published: July 2010

Soils were examined at 35 locations and described in detail at 22 locations to determine the stratigraphy and distribution of materials in a lakeside wetland in Wisconsin. Histic and mineral soil samples were analyzed for organic P, inorganic P, ammonium, nitrate, and organic N. Particle size distributions were determined for the mineral soils. It was found that soils formed in the wetland are young, not well developed, and derived from a variety of parent materials: glacial till, glacio‐fluvial deposits, lacustrine deposits, histic materials, colluvium, and alluvium. Major soils in the wetland include Borosaprists, Haplaquents and Fluvaquents. Phosphorus concentrations are highest in silt loam alluvium and histic deposits, and lowest in glacio‐fluvial deposits, marl, and sandy alluvium. Total P in the alluvium and glacio‐fluvial deposits is very highly correlated (P <0.01) with percent silt plus clay. Nitrate concentrations were highest in silt loam alluvial levees and lowest in a saturated Histosol, indicating that the build‐up of levees in the wetland has created aerobic soil conditions locally conducive to nitrification. The accumulation of histic materials and marl in the wetland has been an ongoing process since deglaciation, but deposition of alluvium appears to have occured primarily since logging and cultivation of the watershed began in the mid‐1800's. The rate of Histosol accumulation in the wetland was estimated by 14C dating as 0.17 cm/year, no more than one third of the rate of alluvial deposition. Since P concentrations are slightly higher in the silt loam alluvium than in the histic materials, alluvial deposition is more effective than Histosol formation for retaining phosphorus in the White Clay Lake wetland.