bluuebunny/crossref_metadata_2025 huggingface dataset:
Analyses of Adsorption Kinetics Using a Stirred‐Flow Chamber: I. Theory and Critical Tests
Authors: Bar‐Tal Asher , Feigenbaum Sala , Sparks Donald L. , Pesek John D.
Published: July 2010

The study of ion‐exchange kinetics on soils and soil constituents has attracted much interest throughout the last decade. The introduction of a stirred‐flow method to study these reactions, as well as other adsorption‐desorption phenomena, has stimulated this interest. However, the manner in which rate data are interpreted using this technique and other flow methods has been questioned. Accordingly, a numerical solution for various instantaneous equilibrium and kinetic models is presented. It was found that rate data that could be described using an instantaneous equilibrium model could also be interpreted using a kinetic model. Therefore, the validity of kinetic rate coefficients obtained by flow methods is questionable. An analytical approach was developed to outline experimental methods that could be used to distinguish between instantaneous equilibrium and time‐dependent reactions and to differentiate between solution‐concentration‐dependent kinetic models vs. those that are independent of solution concentration. By using this approach, and employing various flow rates and influent concentrations, as well as using a stopped‐flow technique, it is easy to decide whether rates of reactions can be measured using the stirred‐flow method for specific experimental conditions.
Ion Chromatographic Determination of Total Metals in Soils
Authors: Basta N. T. , Tabatabai M. A.
Published: July 2010

An accurate and precise ion chromatographic (IC) method for determination of total Cu, Ni, and Zn in soils was developed. The sample preparation method consists of three steps: (i) digestion of the soil sample by using HNO3, HClO4, and HF; (ii) extraction of the metals of interest by using dithizone in CHCl3; and (iii) destruction of the metal‐dithizonate complex with HNO3. The system consisted of a guard (HPIC‐CG5) column and a separator (HPIC‐CS5) column followed by postcolumn reaction with 4‐(2‐pyridylazo) resorcinol (par), to form colored metal complexes. The absorbance of the metal‐par complexes was measured by an ultraviolet‐visible light (uv‐vis) detector at 520 nm. Two different eluents were required for separation of these and other metals. Simultaneous determination of Cd, Cu, Mn, and Zn was achieved by using an eluent containing 4 mM 2,6‐pyridinedicarboxylic acid (pdca) and 50 mM HOAc‐NaOAc buffer (pH 4.8). Simultaneous determination of Cu, Ni, Pb, and Zn was accomplished by using an eluent containing 40 mM oxalic acid and 50 mM HOAc‐LiOAc buffer (pH 4.8). Results by the IC method for determination of total Cu, Ni, and Zn in 14 soils were in good agreement with those obtained by atomic absorption spectrophotometry, but results also showed that the proposed IC method is inadequate for determination of total Cd, Mn, and Pb in soils.
Humic Substances Formed during the Composting of Organic Matter
Authors: Inbar Y. , Chen Y. , Hadar Y.
Published: July 2010

Humic substances (HS) were extracted from separated cattle‐manure compost (CSM) at various stages of decomposition. Carbon‐13 nuclear magnetic resonance (13C‐NMR) and Fourier‐transform infrared (FTIR) spectroscopy measurements were performed on the purified humic acids (HA) as well as crude fiber and chemical analyses. Levels of HS extracted from the CSM samples doubled during the composting (from 377 to 710 g kg−1 organic matter [OM]). The HS were divided into: (i) HA, which increased from 184 to 457 g kg−1 OM; and (ii) a fulvic fraction (FF). The FF was separated on XAD‐8 resin to: (i) fulvic acid (FA), which maintained an unchanged level during composting (80–100 g kg−1); and (ii) a nonhumic fraction (NHF), which increased from 107 to 170 g kg−1 OM during the process. The ratios between the concentrations of these fractions were tested as humification indexes. These indexes changed significantly during the process and were found to correlate exponentially with the composting time, C/N ratio, or both. Quantities of low‐molecular‐weight components (FF and NHF) rapidly increased during the first 40 d of composting and were nearly constant thereafter. The HA and HS contents reached nearly constant values after ∼90 d. Only slight compositional and structural changes in CSM HA were detected with cross‐polarization magic‐angle spinning (CPMAS) 13C‐NMR, FTIR spectra, and chemical analyses. The elemental composition and functional groups of CSM HA resembled those reported for HA of plant residues, peats, and incompletely humified materials. The CPMAS 13C‐NMR spectra of the CSM HA resembled that of lignin. The aromaticity of the HA was about 40% and the lignin content was approximately 60%. The NMR data correlated well with results obtained by FTIR spectroscopy, both indicating that the CSM HA are composed of partially degraded constituents of plant tissue, which still retain to some extent their chemical structures. The major plant components identified in the HA were lignin, carbohydrates, and long‐chain aliphatic structural groups.
Kinetics of Carbon Dioxide Evolution in Relation to Microbial Biomass and Temperature
Authors: Blet‐Charaudeau Catherine , Muller J. , Laudelout H.
Published: July 2010

Intensification of agricultural practices on calcareous soils leads to drastic changes in biogeochemical processes due to modifications of CO2 partial pressure in soil pores. For this reason, CO2 evolution was measured in vitro from Typic Rendoll soils of the Champagne Crayeuse at four temperatures. Microbial biomass was also estimated by a plate‐count technique that had been calibrated by two independent methods: chloroform fumigation and bioluminescence. Carbon dioxide evolution curves fit an equation consisting of a zero‐ and first‐order reaction. The three parameters of this equation were interpreted as: (i) the amount of easily decomposable organic matter generated by the disturbance, (ii) the time constant for the disappearance of that disturbance, and (iii) the sustained respiration of the native microflora. This model implies that the rate of CO2 evolution is maximum at the start of the incubation, while the observed maximum in bacterial biomass occurred about 5 d later. Comparison of the results presented here with data from the literature shows that there is an almost continuous spectrum of values for the amounts of easily decomposable organic matter generated by any disturbance, and that the time constant for its mineralization is of the order of a very few days. Therefore, the use of the double exponential model is superfluous unless the duration of the incubation experiments exceeds 100 d.
Soil‐Geomorphic Relations on the Blue Ridge Front: I. Regolith Types and Slope Processes
Authors: Graham R. C. , Daniels R. B. , Buol S. W.
Published: July 2010

Regolith distributions and characteristics were related to slope processes along two transects in mica gneiss and mica schist terrane on the Blue Ridge Front of North Carolina. Regolith types are saprolite, soil residuum, and colluvium. Saprolite is thickest on low slope positions, where throughflow moisture promotes weathering and overlying colluvium protects the saprolite from mass wasting. Saprolite is thinnest on shoulders and backslopes, where mass wasting and rapid runoff inhibit its formation. Rock outcrop is most common on backslopes. Soil residuum, present on most landscape positions, comprises the entire regolith above saprolite only on the broad, nearly level ridge top. The pedogenic transformation of saprolite to soil residuum resulted in higher clay contents and redder hues through in situ weathering and illuvial accumulations. On sloping terrain, saprolite or soil residuum is overlain by colluvium. Lower slopes contain thick deposits of landslide colluvium. Colluvium from slope wash and soil creep comprise the upper 10 to 20 cm of regolith on all sloping surfaces. Colluvial deposits, excluding A and E horizons, are uniform in color, the result of homogenization during transport. Mass movement has also served to physically break down chemically weathered mica grains, releasing secondary minerals into finer size fractions. Knowledge of slope processes assists interpretation of regolith weathering history, which is important for understanding soil parent materials.
Aggregate Stability in the Palouse Region of Washington: Effect of Landscape Position
Authors: Pierson F. B. , Mulla D. J.
Published: July 2010

An extensive study was conducted to measure spatial patterns in aggregate stability in the steep, hilly, and highly erodible loessial soils of the Palouse region in southeastern Washington. Soil samples were collected at 20‐m spacings along four 800‐m‐long transects within a winter wheat field and analyzed for aggregate stability at a slow and a fast rate of wetting, organic C, amorphous Fe, soil water content, and particle size distribution. Aggregate stability under slow wetting, organic C, and clay content were significantly different at summit, shoulder, toeslope, and footslope positions on the landscape. More specifically, aggregate stability and organic C content were highest in footslope and toeslope positions, and lowest at the summit. Clay content was highest at the summit and lowest in footslope positions. Aggregate stability at a fast rate of wetting had a coefficient of variation (40%) that was nearly double that for slow wetting, and was not well correlated to either landscape position or measured soil properties. The variation in aggregate stability under slow wetting could be modeled in terms of organic C content and elevation. Other properties such as amorphous Fe and water or clay content were only weakly correlated to aggregate stability. Thus, although the spatial patterns in aggregate stability exhibited moderate variability (CV = 22%), the patterns were closely related to changes in a few key properties, namely, organic C content and landscape position. A likely explanation for these findings is that soil erosion removes the topsoil and organic matter from the ridgetops, thus exposing subsoil horizons, which are higher in clay content and lower in aggregate stability.
Modeling Potassium Uptake by Slash Pine Seedlings from Low‐Potassium‐Supplying Soils
Authors: Van Rees K. C. J. , Comerford N. B. , McFee W. W.
Published: July 2010

The application of diffusion/mass‐flow theory to K uptake by slash pine (Pinus elliottii Engelm. var. elliottii) seedlings from low‐K‐supplying soils is presented. Simulations for K uptake were evaluated by the Barber‐Cushman model (BCM) and the Baldwin‐Nye‐Tinker model (BNTM) under greenhouse and field conditions. Potassium uptake was overpredicted by 31 to 50% in greenhouse studies; overestimates, however, are attributed to nonuniform distribution of roots along pot walls. Simulations underpredicted K uptake by 0.48 and 0.83 times that observed in seedlings grown in the field. Although ectomycorrhizal hyphae were abundant in the field, their contribution to K uptake was not incorporated. Predictions of K uptake were excellent for seedlings grown at a tree nursery when fertilizer amendments were included. The BNTM, based on simplifying assumptions, predicted K‐uptake values similar to the BCM. Sensitivity analysis showed that root growth and initial K concentration in soil solution were the two most important factors affecting K uptake by slash pine. Soil processes that control K concentration were the limiting factors to K uptake on these soils. Monte Carlo procedures indicated that, for two harvests in the field, simulated estimates of uptake had CVs ranging from 34 to 64%.
Nutrient Cycling in a Red Pine Plantation Thirty‐Nine Years after Potassium Fertilization
Authors: Shepard James P. , Mitchell Myron J.
Published: July 2010

Red pine (Pinus resinosa Ait.) plantations planted in the late 1920s and early 1930s at the Pack Forest near Warrensburg, NY, showed severe nutrient deficiency symptoms after a few years. Numerous investigations revealed the soil to be extremely K deficient, due to a century of agricultural use. The present study was undertaken to describe long‐term effects of K fertilization and to more completely characterize nutrient cycling in K‐fertilized plantations and thus describe mechanisms responsible for the longevity of the K‐fertilization response. In 1948, three 0.04‐ha plots were established; two were fertilized with either 59 or 118 kg ha−1 K (designated LO and HI, respectively) and the third left untreated (CTL). Fertilization increased radial increment for ∼10 yr and resulted in increased basal area and tree height. In 1987 (39 yr after fertilization), soil exchangeable K in the upper 15 cm of the mineral soil remained greater in fertilized plots. Aboveground biomass in 1987 was 129, 164, and 190 Mg ha−1, respectively in CTL, LO, and HI. In LO and HI, the N, P, Ca, Mg, and Na contents were 20 to 50% greater than in CTL. There was twice as much K in the aboveground vegetation of LO and HI than CTL, due primarily to increased foliar biomass. This was reflected in the greater litterfall as well as throughfall and stemflow fluxes of K in LO and HI relative to CTL. Fertility of the plots was maintained by the efficient cycling of nutrients, especially K, in the ecosystem.
Ammonia Volatilization from Flooded Soil Systems: A Computer Model. III. Validation of the Model
Authors: Jayaweera G. R. , Paw U. K. T. , Mikkelsen D. S.
Published: July 2010

An NH3‐volatilization model predicting NH3 loss as a function of five input variables was validated using a wind tunnel to simulate rice paddy conditions and direct field experiments. A total of five variables in a central composite statistical design were compared to study the interactive effects of NH4‐N concentration, pH, temperature, wind speed, and water depth. Experiments were also conducted in a flooded rice field with polypropylene basins placed at water level. Samples were collected every hour for determination of NH4‐N concentration. Temperature, pH, and wind speed were recorded continuously, and water depth was constant. Wind‐tunnel data showed that the model predicted observed values with excellent accuracy in the range of conditions found in flooded rice systems. The regression of predicted NH3 loss on observed losses resulted in an r2 of 0.98 and a regression slope of 0.99. Field experiments also showed very close agreement between predicted and experimental values with 6‐, 12‐, and 24‐h averages of pH, temperature, and wind speed. The model validation confirmed the theory that NH3 volatilization is a function of NH3(aq) concentration and the volatilization rate constant for NH3, which are dependent on five variables: floodwater NH4 concentration, pH, temperature, water depth, and wind speed. The model is theoretically sound and predicts NH3 loss with a high level of accuracy using a menu‐driven computer program with easily measurable variables, and can be used in comparison studies of NH3 loss at the same site.
Effect of Soil Properties on Unsaturated Hydraulic Conductivity Pore‐Interaction Factors
Authors: Schuh W. M. , Cline R. L.
Published: July 2010

The variability of the pore‐interaction factor, ρ, for a microscopic model proposed for predicting unsaturated hydraulic conductivity, K(θ), from soil water‐retention, Ψ(θ), data was examined in relation to soil particle‐size data and indices, bulk density, organic C, parameters for the van Genuchten Ψ(θ) function, an index (W) of total energy of drainage and soil‐series, toposequential, and geographic groupings. The ρ exhibited no trend relationship to any of the soil properties tested. However, a change in the distribution of ρ was observed in relation to the geometric‐mean particle diameter (Gd) and other soil textural variables. For Gd < 0.08 mm, variability was much larger than for soils with Gd ≥ 0.08 mm. The latter consisted entirely of soils in the sand and loamy sand textural groups. A similar distributional relationship also occurred for ρ vs. W. Examination of ρ on three sites of the Hecla soil series and on related toposequential soils indicated that classification of ρ on the basis of soil series or of soil‐association groupings is a feasible strategy for ρ parameter estimation on some soils. The exponential factor η for a macroscopic model was also investigated. The η was found to be related to W as an exponential function over the full data range. However, η vs. W was nearly identical to a linear function for W data extending from 0 to 400 cm‐γ (where γ is the density of water). The η was also strongly related to Gd as a power function, and to other textural variables as exponential functions. The increasing slope of the power function for Gd < 0.08 mm indicated a large potential error of prediction for K(θ) on fine‐textured soils.
Simulating Water Movement in Layered and Gradational Soils Using the Kirchhoff Transform
Authors: Ross Peter J. , Bristow Keith L.
Published: July 2010

Changes in soil hydraulic properties with depth are common in field soils and need to be accounted for in simulations of field soil‐water balances. We show that this is possible using the Kirchhoff transform (K transform) when solving Richards' equation numerically, even though the K transform is not continuous across boundaries between layers with different hydraulic properties. The solution is achieved by dividing the soil into depth elements, using the K transform to compute flow within each element, and then using matric potential (which is continuous across boundaries) to couple the elements. Combination of the K transform with iterative, implicit, mass‐conserving methods of solving the flow equations results in efficient solutions that take no more than a few seconds on a personal computer to simulate infiltration. This is achieved with errors of only a few percent in the amount and distribution of soil water. Illustrative simulations using hydraulic properties that represent different soil profiles are given. These include simulation of infiltration into a layered profile consisting of tilled soil with a crust overlying an undisturbed soil, and gradational profiles with hydraulic properties of a sand varying linearly with depth to those of a clay, and conversely. Development and dissipation of surface ponding and perched water tables during simulation runs presented no difficulties. Nor did use of the Campbell formulations for the soil hydraulic properties, despite the discontinuity at the wet end.
Initial Storm Effects on Macropore Transport of Surface‐Applied Chemicals in No‐Till Soil
Authors: Shipitalo M. J. , Edwards W. M. , Owens L. B. , Dick W. A.
Published: July 2010

Previous research has established that macropores can rapidly transmit water through soil. This observation has raised concern that macropores may also promote rapid movement of agricultural chemicals to groundwater. This is a particular concern for no‐till fields where lack of disruption by tillage can lead to the development of extensive macropore systems. In order to investigate the effect of initial rainfall on chemical transport, strontium bromide hexahydrate (SrBr2·6H2O) and atrazine (2‐chloro‐4‐ethylamino‐6‐isopro‐pylamino ‐s‐triazine) were surface‐applied to six 30 by 30 by 30 cm blocks of undisturbed soil obtained from a 25‐yr‐old, no‐till corn (Zea mays L.) field with evidence of well‐defined macropores attributable to earthworm activity. Half of the blocks then received a 1‐h 5‐mm simulated rain, which did not produce percolate. Two days later, the blocks received a 0.5‐h 30‐mm simulated rain, followed by another 0.5‐h 30‐mm rain 1 wk later. The remaining blocks received only the two 30‐mm events. An average of 12% of the applied water passed through all the blocks during and shortly after the first 30‐mm rain. Bromide, Sr, and atrazine losses in this percolate were 7, 10, and 2 times less, respectively, from blocks that received the 5‐mm rain than from blocks not receiving this initial, light rain. The second 30‐mm rain on the blocks not receiving the initial 5 mm produced 1.6× more percolate than the first 30‐mm rain. Yet, transport and flow‐weighted average concentrations of Br, Sr, and atrazine were all reduced. These results indicated that the first storm after application can move solutes into the soil matrix, thereby reducing the potential for transport in macropores during subsequent rainfall events.
Further Comparison of Spatial Methods for Predicting Soil pH
Authors: Laslett G. M. , McBratney A. B.
Published: July 2010

Spatial prediction methods have been compared using a carefully and specially designed survey of soil pH. Outliers seriously affected the performance of all prediction methods, and were removed for the comparison. Interpolators, Laplacian smoothing splines, and intrinsic random functions all behaved problematically, and universal kriging using parameter estimates obtained by the novel method called restricted maximum likelihood (reml) was consistently best. The data set contained an apparently obvious trend, but prediction by universal kriging was not improved by including this trend. The inclusion of close pairs stabilized the prediction methods, but there was no dramatic improvement with reml universal kriging, the best method for this data set.
A Field Study Using Dyes to Characterize Preferential Flow of Water
Authors: Ghodrati Masoud , Jury William A.
Published: July 2010

Characterization of preferential flow in soils through normal water tracer studies are, in most cases, inconclusive because of the inability of most solute sampling devices to detect the spatial pattern of preferential flow pathways. In this study, a number of field‐plot experiments were performed to provide direct observation of the preferential flow of water and solutes by adding soluble dye to stain the flow pathways. In addition to characterizing the spatial structure of preferential flow pathways, the dye trace patterns were used to investigate the interactive role of soil structure and irrigation methods on the preferential flow patterns of water and solutes. A narrow pulse of an anionic water‐soluble dye, Acid‐Red 1, was applied to the surface of a number of 1.5 by 1.5 m field plots, some of which had the top layer completely disturbed to the depth of 30 to 40 cm. The distribution patterns of the dye in these plots were examined after the plots received 100 mm of irrigation water, under either ponding or daily sprinkler irrigation. The observed vertical and horizontal distribution patterns of the water‐soluble dye clearly indicated the preferential flow patterns for each experimental condition. These include vertical fingering of dye traces 5 to 20 cm wide, which extended more than twice as deep as the mean displacement of the dye, as well as isolated patches of dye indicating lateral flow.
Steady‐State Aerobic Microbial Activity as a Function of Soil Water Content
Authors: Skopp J. , Jawson M. D. , Doran J. W.
Published: July 2010

Soil physical properties often regulate aeration‐dependent microbial activities important to nutrient cycling, soil fertility and environmental quality. Microbial activity depends on soil water content and is maximum at a water content where the limiting effects of substrate diffusion and O2 supply are equal. The mechanism whereby this occurs and predictions of the soil water content where aerobic microbial activity is a maximum were the objectives of this study. In particular, this study predicted the shape of the microbial activity vs. water content function from soil physical concepts. Soil physical processes are assumed to influence microbial activity by limiting the steady flux of a required substrate or O2 to sites of microbial activity. Steady‐state flux relations are used to define the activity function. The dependence of diffusion coefficient on water content or air‐filled porosity is assumed. With these assumptions, it is possible to show that a maximum in the activity function exists. The predicted shape of the activity curve is consistent with experimental observations. The relationship between aeration‐dependent microbial activity and soil water content facilitates evaluating the indirect effects of soil management practices, such as tillage, on microbial activity.
Factors Affecting Rice Growth on Acid Sulfate Soils
Authors: Moore P. A. , Attanandana T. , Patrick W. H.
Published: July 2010

Rice (Oryza sativa L.) yields on acid sulfate soils, which comprise a sizable portion of the rice‐growing area in Southeast Asia, are constrained by soil parameters. The objective of this study was to identify those parameters most strongly related to rice growth. Metal availability and uptake by rice were evaluated in the Central Plains of Thailand using 134 flooded acid sulfate soils and in a growth chamber utilizing 50 of them. Nutrient‐uptake data indicated that uptake of divalent cations was most closely correlated to the divalent activity ratio (Ametal). Although many individual parameters were correlated with rice growth, results from multiple correlation analysis indicated that AFe (the ratio of Fe2+ activity to the sum of the activities of all other divalent cations), pH, and ionic strength provided the best three‐variable model describing dry‐matter production in the growth‐chamber study. In the field, the best two‐variable model describing yields included pH and AFe. Therefore, the most important constraints to rice growth on acid sulfate soils were (i) acidity, which includes the combined effects of pH, Al toxicity, and P deficiency, and (ii) Fe stress, which is due to the combined effects of Fe toxicity and deficiencies of other divalent cations such as Ca. This study indicates the importance of divalent activity ratios such as AFe when studying metal uptake or modeling plant growth. In a micronutrient fertility trial conducted under greenhouse conditions, the only significant yield response occurred when Si was applied to a limed acid sulfate soil.
Soil Inorganic Phosphorus Fractions and Their Uptake Relationships in Calcareous Soils
Authors: Yang Jae E. , Jacobsen Jeffrey S.
Published: July 2010

Crop responses to recommended P‐fertilizer applications are erratic in high pH, calcareous soils of Montana. The objective of this research was to evaluate relationships between soil inorganic P (P1) fractions, Olsen‐P, and plant uptake. Soil‐incubation and plant‐growth experiments were conducted on samples of six calcareous soils from P‐responsive locations in Montana. Rates of P were 0, 11, 22, and 33 mg P kg−1 applied to soils in a randomized complete‐block design with four replications. Spring wheat (Triticum aestivum L. cv. Newana) was grown successively during three, 4‐wk growing periods. Fertilized soils were incubated without plants during the same period. Soils were subjected to a sequential‐fractionation procedure (resin‐P, NaHCO3‐P, NaOH‐P, and HCl‐P). Soil P1 quantities were HCl‐P > NaOH‐P > NaHCO3‐P (bic‐P) > resin‐P. Higher Olsen‐P soils had higher summation of P1 fractions than lower Olsen‐P soils. Changes in resin‐P accounted for most of P1‐fraction differences induced by P application and plant uptake. Cropped soils generally contained lower amounts of P1 in each fraction than noncropped soils. Highly significant (P > 0.01) correlations were found for Olsen‐P vs. resin‐P, P uptake vs. resin‐P, and P uptake vs. Olsen‐P, but not for Olsen‐P vs. bic‐P, resin‐P vs. bic‐P, and P uptake vs. bic‐P. Resin‐P was the best indicator of P‐uptake responses on these soils to P applications and should be considered in the prediction of crop responses.
Statistical Comparison of Soil Map‐Unit Boundaries
Authors: Nash M. H. , Daugherty L. A.
Published: July 2010

Locating the exact boundaries of soil map units is one of the primary objectives for soil surveyors. Statistical methods were used to assure the most accurate location. Soil spatial variability, autocorrelation function, and soil boundary locations were examined along a 2700‐m transect in southern New Mexico. Eighty‐nine observation points were equally spaced along the transect. Selected physical and chemical characteristics through the transect were determined. A multivariate method of principal‐component analysis was used to produce one set of data. These data were first inspected for stationary manner, i.e., that the mean and variance of each property remain fairly constant for each data set. Log‐normal transformation was used to detrend the data. The stationary manner of autocorrelations was tested with semivariograms. The range of dependence obtained from the autocorrelations and semivariograms was used in a squared‐Euclidean‐distance procedure to locate the soil boundaries. These boundaries were compared with those obtained by conventional soilsurvey methods. Some of the calculated boundaries agreed with those obtained by conventional soil survey. The latter method is more economical and more productive than the statistical method.
Soil Erosion and Deposition Evidence in a Small Watershed Using Fallout Cesium‐137
Authors: Soileau J. M. , Hajek B. F. , Touchton J. T.
Published: July 2010

Soil measurements of 137Cs, a fallout component of nuclear testing, were made within a 3.8‐ha research watershed in the Limestone Valley of northern Alabama. Objectives of the study were to: (i) compare 137Cs activity in soil profiles on eroded and depositional landscape positions, and (ii) relate soil erosion and deposition calculated by 137Cs methods to erosion estimated by the Universal Soil Loss Equation (USLE) and to sediment discharge measured at the watershed outlet. Triplicate soil profiles were analyzed for 137Cs activity to a 46‐cm depth in cultivated sites representing slightly eroded ridgetop, eroded side‐slope, and depositional downslope positions. These data were compared with baseline 137Cs measurements in undisturbed adjacent woodland. Erosion calculated by 137Cs activity losses from baseline values were compared with the USLE estimates on slope transects. Mean total 137Cs activities on baseline, eroded, slightly eroded, and depositional sites were 4860, 1804, 2807, and 5367 Bq m−2, respectively. Peak 137Cs activity and depth to zero activity were much greater in depositional than in eroded and slightly eroded sites. Estimated mean annual (1954–1987) soil‐erosion rates were similar between 137Cs and USLE methods for a slope transect with slight erosion (28 and 26 Mg ha−1 yr−1). On eroded side‐slopes, 137Cs estimates of erosion were 27 to 80% higher than the USLE estimates. This may be due to rill erosion unaccounted for by the USLE. The USLE estimated losses between 9 and 52 Mg ha−1 yr−1 for uplands during 1984 to 1988 cotton production. Sediment losses measured below the downslope depositional area of the small watershed (Gilbert Farm Research Watershed) were only 1 to 4 Mg ha−1 yr−1. This indirect evidence of extensive sediment deposition in a representative small watershed of karst terrain was supported by 137Cs activity in depositional soil profiles.
Comparison of Two Static Chamber Techniques for Determining Carbon Dioxide Efflux from Forest Soils
Authors: Raich J. W. , Bowden R. D. , Steudler P. A.
Published: July 2010

The similarity of two commonly used methods of measuring CO2 fluxes from forest soils was assessed by directly comparing the sodalime method with a static chamber technique using gas chromatographic analysis of CO2 ‐concentration changes during short‐term incubations. A paired‐chamber sampling design was applied in 11 different forest stands to examine the two methods across a range of soil‐CO2 efflux rates. Carbon dioxide efflux rates were highly variable within sites, and showed no spatial autocorrelation. No consistent differences in measured rates of CO2 efflux were observed between the two methods, indicating that either method may be applied to the range of mean daily rates encountered in this study (1.7–11.4 g m−2 d−1). A large number of chambers can be deployed with the soda‐lime method, but no information on diel variations in efflux rates is obtained. The short‐term incubation technique, on the other hand, can be utilized to simultaneously monitor several trace gases and diel trends in flux rates. Selection between the methods should be based on the hypotheses being tested or on practical constraints.
Phosphate‐Fertilizer‐Induced Salt Toxicity of Newly Planted Apple Trees
Authors: Peryea F. J.
Published: July 2010

Monoammonium phosphate (MAP) or triple superphosphate (TSP) added to planting holes often stimulates early growth of apple trees (Malus domestica Borkh.); however, high rates may stunt or kill trees. A greenhouse study was conducted on a Quincy sand (a mixed, mesic Xeric Torripsamment) and a Cowiche silt loam (a fine‐loamy, mixed, mesic Aridic Argixeroll) to examine effects of soil type, P source (MAP or TSP), and P rate (0–2.75 kg P/m3) on soil salinity, soil acidity, and apple tree growth in nonleaching soil systems during a 56‐d period after planting. Rootstock and old scion masses were not affected by soil type or P treatments. In the Quincy sand, new scion mass and root mass were inversely related to P rate in both MAP‐ and TSP‐amended soil; tree death occurred at P rates above 1.65 kg/m3. In the Cowiche soil, root mass was independent of and new scion mass was inversely related to P rate. At equivalent P rates, TSP produced lower soil salinity and greater soil acidity than MAP. For a given P source, soil salinity and acidity were positively related to P rate. Soil salinity decreased and soil pH increased over time. Relative new scion mass was inversely related to time‐integrated soil salinity; however, the relationships were soil‐specific. Total exchangeable soil acidity was positively related to P rate and was soil‐dependent. Exchangeable soil Al was detected only at the two highest TSP rates in the Quincy soil. Indirect evidence suggested that Mn, NH3, and NO2 phytotoxicities and any nutrient deficiencies were absent. The results suggest that transient soil salinization is the primary mechanism for MAP‐ and TSP‐induced apple tree phytotoxicity.
Modified‐Quadratic/Plateau Model for Describing Plant Responses to Fertilizer
Authors: Bock B. R. , Sikora F. J.
Published: July 2010

Accurate estimation of optimal fertilizer rates is becoming more critical because of growing economic and environmental concerns associated with fertilizer use. Curve‐fitting techniques are often used to estimate optimal fertilizer rates, but significant problems exist in selecting a proper model for a particular cropping situation. One solution is to develop a model sufficiently general to preclude the need for selecting a proper model for each cropping situation. We developed a modified‐quadratic/plateau (MQ/P) segmented model (four or five parameters) and demonstrated its general applicability compared with the quadratic/plateau (MQ/P) segmented model (three parameters) for describing fertilizer responses. The MQ/P model contains an efficiency index (Ex) that is a quadratic function of the applied rate of nutrient X. In the Q/P model, Ex remains constant relative to the rate of nutrient X. The MQ/P and Q/P segmented models set yield equal to the maximum yield (Ym) when the rate of nutrient X is greater than that required to achieve Ym. The general applicability of the MQ/P model in comparison with the Q/P model was evaluated by determining how well these models fit hypothetical input data calculated with linear/plateau (L/P), Mitscherlich (M), and square root/plateau (SR/P) functions. The MQ/P model gave R2 values >0.99 and predicted economically optimum fertilizer rates (i.e., rates at which the first derivative of yield response functions equaled the fertilizer/crop price ratio) close to those calculated with the input functions. The Q/P model gave R2 values ranging from 0.95 to 0.99, but gave poor predictions of economically optimum fertilizer rates. The ability of the MQ/P model to fit functions as diverse as L/P, M, and SR/P, and to predict economically optimum N rates associated with these functions, suggests that the MQ/P model has utility as a general curve‐fitting technique for responses in which the right‐hand segment is a plateau. An advantage of the MQ/P model is that the regression parameters can be interpreted as physically meaningful constants.
Acidification and Liming Influence on Surface Charge Behavior of Kentucky Subsoils
Authors: Lumbanraja J. , Evangelou V. P.
Published: July 2010

Specific adsorption of ions onto soil clay surfaces influences the magnitude and behavior of the surface charge. This study evaluated the influence of acidification and liming on surface charge magnitude and behavior of three Kentucky subsoils (Eden and Lowell, fine, mixed, mesic Typic Halpludalfs; and Nicholson, a fine‐silty, mixed, mesic Typic Fragiudalf) that have consistently shown poor crop response to added fertilizer. Soil samples were adjusted to three pH values (4.0–4.3, 5.5–5.8 and 6.8–7.3) with either HCl or Ca(OH)2 and were titrated with either NH4OH or KOH as titrants and NH4Cl or KCl as background electrolytes. The titration procedure was a rapid stop‐and‐go technique. The soil samples initially adjusted with HCl to a pH range of 4.0 to 4.3 exhibited titration behavior similar to a clay surface loaded with trivalent Al. The KOH titration plots exhibited a common cross‐over point, a titration behavior commonly associated with variable‐charge surfaces, for two of the soils (Eden and Lowell). The same titration behavior was not apparent when titrated with NH4OH. For the samples initially adjusted with Ca(OH)2 to pH ranges of 5.5 to 5.8 or 6.8 to 7.3, titration behavior was influenced by the clay permanent negative charge. With increasing background electrolyte concentration, the titration plots were displaced to the right without an apparent cross‐over point. These samples also exhibited a pH‐buffering region in the range of 6.0 to 8.5. On most soils, this is often attributed to the CaCO3‐HCO3 buffer system. This buffer system cannot be implicated in this study, since CO2 and CaCO3 were excluded. It appears that in these soils, K and NH4 do not behave as analogs of each other; rather, each reacts with adsorption sites exhibiting certain ion specificity. The findings suggest that, when soils with vermiculite‐Fe oxide mineralogy change their pH, they also change their surface chemistry with respect to adsorption of K and NH4, but not in a predictable manner.
Binary and Ternary Exchange of Potassium on Calcareous Montmorillonitic Soils
Authors: Feigenbaum Sala , Bar‐Tal Asher , Portnoy Rita , Sparks Donald L.
Published: July 2010

Simultaneous K exchange with Ca, Mg, and Na occurs in soils, but most of the published information is obtained from binary systems. The theoretical question of whether selectivity coefficients obtained in binary systems are valid for ternary systems has not yet been clarified; however, no significant difference has been found between selectivity coefficients in binary and ternary systems. Potassium exchange with Mg plus Ca was studied in two calcareous soils with variable concentrations of Na, using batch and miscible‐displacement methods. Preference for K over the divalent cations was found in both soils, regardless of Na concentration and the experimental methods. Modified Gapon (kG) and Vanselow (kV) selectivity coefficients were calculated for each cation pair in binary and ternary systems. In both soils, the kv and the kG decreased with increasing K fraction in the solution, but the kG value was less affected than the kv. A simple mathematical solution of the Gapon binary equations, K − (Mg + Ca) and Na − (Mg + Ca), in combination with an assumption of constant cation‐exchange capacity (CEC), was used to predict the amount of exchangeable K as a function of solution composition in a ternary system. The high correlation of predicted exchangeable K with the directly measured values shows that binary selectivity coefficients can be used in multicationic systems on calcareous montmorillonitic soils.
Ammonium Fixation, Release, Nitrification, and Immobilization in High‐ and Low‐Fixing Soils
Authors: Beauchamp E. G. , Drury C. F.
Published: July 2010

The objective of this study was to determine if competing sinks for added NH4 (i.e., immobilization and nitrification) affected NH4 fixation and release. Low‐ and high‐fixing soils, N rate, K preaddition, and temperature were variables chosen for studying these processes. Labeled (15NH4)2)SO4 was added to soils and they were aerobically incubated. At the end of each incubation, fixed 15NH4 and KCl‐extractable 15NH4 and 15NO3 were determined. Ammonium fixation was mainly responsible for the disappearance of extractable 15NH4 in a high‐fixing soil. The fixed 15NH4 fraction comprised 68% of the nonextractable 15N fraction in the high‐fixing soil, and 28% in the low‐fixing soil. In both soils, about half of the 15NH4 fixation occurred within 6 h after application. The maximum quantity of fixed 15NH4 occurred after 30 d. An 15NH4‐addition rate of 150 mg N kg−1 doubled the fixed 15NH4 concentration over that at 75 mg N kg−1. Low temperature did not affect the quantity of added 15NH4 fixed. Potassium preaddition reduced fixed 15NH4 concentration at 6 h, but did not appear to affect it subsequently. Immobilization of 5.7% of the added 15NH4 occurred in the high‐fixing soil, and 3.9% in the low‐fixing soil. Extractable‐ and fixed‐NH4 fractions were interrelated pools. When fertilizer NH4 was added to the soil, a proportional amount was fixed by the clay minerals. When nitrification and immobilization depleted extractable NH4, fixed NH4 was released. The fixed‐NH4 pool appeared to be a slow‐release reservoir, with fixed‐NH4 release being slower than the rate of fixation.
Reactivity of Phosphorus in Northeastern Brazilian Soils Assessed by Isotopic Dilution
Authors: Salcedo I. H. , Bertino F. , Sampaio E. V. S. B.
Published: July 2010

To diagnose fertilizer requirements in regions of high soil variability where P‐fixing capacities can vary 100‐fold, single‐extraction P tests must be complemented by an evaluation of P sorption. The isotopic‐dilution kinetics of 32P was tested for its potential to measure available P and to predict the degree of soil‐fertilizer P reactivity. Six soils from northeastern Brazil were fertilized with P, incubated (1, 42, and 84 d) and then seeded with pearl millet [Pennisetum glaucum (L.) R. Br.]. Soil samples were analyzed for water‐soluble P (Pw), resin P, 32P in solution 1 min after addition over 32 P added (R1/R0), rate of 32P disappearance from solution between 1 and 100 min (n), reversible P (Prev, determined by double isotopic dilution), mobile P (Pm = Pw + Prev), and isotopically exchangeable P (E1 and E‐value [E] for 1‐min and 24‐h equilibrium periods, respectively). Use of R1/R0 successfully differentiated soils in terms of net fertilizer effects on Pw and Pm with time. We found that Pw and Pm were better predictors of plant P uptake than resin P, E1, and E, since the latter quantities overestimated available P in a high‐P‐fixing Oxisol. Based on this and published data, we propose a critical value of R1/R0 (0.26) below which E values consistently overestimated labile P, while Pw correlated satisfactorily with available P. A modified technique overcomes limitations of measuring very low concentrations of Pw in such soils. To diagnose labile P and fertilizer responses in soils with R1/R0 > 0.26, we propose a simplified methodology that avoids the double isotopic dilution.
Some Andisols from Savai'i, Western Samoa
Authors: Morrison R. J.
Published: July 2010

Five pedons in the lowlands and foothills of Savai'i were studied in detail to determine whether or not they were Andisols. All five met the requirements proposed by the International Committee for the Classification of Andisols (ICOMAND) for the designation of Andisols, as recently accepted into the soil taxonomy. Four of the pedons were Hapludands at the great group level, with subgroup differences due to base status, depth to lithic contact, and water‐retention properties being observed. The fifth pedon was a Thaptic Fulvudand with imogolite present. The results obtained indicate that Andisols are likely to dominate the landscape of Savai'i. This is rather unexpected, as Savai'i is the oldest island of the Samoa chain. Recent volcanism associated with the approach of Savai'i to the edge of the Tonga trench has “rejuvenated” much of the island, leading to the formation of young soils. Since certain soils on Savai'i and the adjacent island of Upolu are mapped as the same series, reexamination of the soils on both islands would appear necessary to determine whether or not the soils are sufficiently different to warrant the establishment of new series.
Influence of Aggregate Size and Microrelief on Development of Surface Soil Crusts
Authors: Freebairn D. M. , Gupta S. C. , Rawls W. J.
Published: July 2010

The rate of water entry during rainfall has implications for crop agronomy, erosion, and groundwater recharge. This study investigated the influences of aggregate size, microrelief and rainfall intensity on development of surface crusts and infiltration. Infiltration rate and hydraulic resistance of developing crusts on two soils under various surface conditions and simulated rainfall were measured. The two soils were Webster clay loam (fine loamy, mixed mesic Typic Haplaquoll) and Port Byron silt loam (fine‐silty, mixed, mesic Typic Hapludoll). Aggregates with sizes of <1, <2, 1 to 2, 2 to 5, 5 to 19, 19 to 25, and 25 to 50 mm were studied. Final or steady‐state infiltration rates were similar for all aggregate sizes of both soil types, but development of a soil crust was delayed when the surface was made up of aggregates >19 mm in diameter. Large aggregates (clods) were a source of finer materials for the development of soil crusts. Microrelief effects were simulated by creating a ridge‐furrow configuration in a box. Ridge‐furrow microrelief did not influence total infiltration and was only effective in modifying the spatial distribution of water in the soil during the early phase of crust development. Infiltration rates, when measured using different rainfall intensities, could be described by a single curve when expressed as a function of cumulative rainfall rather than time. Total rainfall or rainfall energy may be better parameters for describing soil crust development than rainfall intensity.
Root Growth and Water Extraction Patterns from a Calcic Horizon
Authors: Georgen P. G. , Davis‐Carter Jessica , Taylor H. M.
Published: July 2010

There is considerable uncertainty regarding the effectiveness of calcic horizons in supplying water to plants. We conducted a field experiment on Acuff fine sandy loam (fine‐loamy, mixed, thermic Aridic Paleustoll) that contained a calcic horizon starting at 0.65‐ to 1.30‐m depth. Sunflower (Helianthus annuus L. ‘Gro‐Agri 380’), kochia (Kochia scoparia [L.] Schrader), and cotton (Gossypium hirsutum L. ‘GSA‐71’) were grown to determine if (i) plant roots can proliferate readily within a calcic horizon, (ii) plant roots are as effective in extracting water from the calcic horizon as from overlying horizons and (iii) there are differences among the three species in the ability of their root systems to extract water from calcic horizons. We concluded that (i) plant roots proliferated readily in the calcic horizons, (ii) kochia roots were more effective in extracting water from the calcic horizon than from overlying layers, (iii) sunflower root systems were substantially more effective than cotton root systems in extracting water from calcic horizons, and (iv) plant roots seemed to be less effective in extracting water when they first entered a soil layer, compared with their effectiveness a few days later.