bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Water Flow from Subirrigation with Drainage
Authors: Kirkham Don , Horton Robert
Published: July 2010

The stream function for a flow domain, if properly chosen, can be used analytically to generate the boundary conditions of the domain and obtain flow velocities at all points in it. To illustrate the procedure, we developed and mathematically analyzed a physical model that describes saturated water flow from a subirrigation system with drainage. The theory takes the radius of drain and irrigation tubes into account and thus refines earlier work, which hypothesized slit irrigation tubes and slit drain tubes of thin rectangular cross section rather than circular ones. The theory additionally shows how the subirrigation water table changes when the drain tubes are switched to an irrigation mode. A series of three flow nets are included representing subirrigation alone, subirrigation with simultaneous drainage, and dual‐pipe subirrigation. The three cases show how the problem parameters influence heads and flows and thus give insight into strengths and weaknesses of the three water management systems.
Soil Solution Sampled with and without Tension in Arable and Heathland Soils
Authors: Magid Jakob , Christensen Niels
Published: July 2010

The composition of soil solution is of importance in many aspects of soil science. It is therefore of interest to reach an understanding of when to apply a certain sampling method in preference to others. For this reason we evaluated both zero‐tension and tension samplers for use in long‐term monitoring of soil solutions sampled fortnightly in a sandy arable soil plot from 1987 to 1990 and in a sandy calluna heathland plot from 1986 to 1990. Compared with tension solution, the zero‐tension solution in the arable plot was more influenced by the soil solution composition from the upper fertilized plow layer, and in the heathland plot the zero‐tension solution was more influenced by the composition of rainwater. On both plots the temporal variability in the amount of nonsorptive solutes, as well as systematic differences in the amount of sorptive solutes sampled by these techniques, give support to the notion that zero‐tension samples represented the flux concentrations, whereas the tension samples were approximations of resident concentrations. In conclusion, if the objective of sampling soil solution is to gain insight in internal processes in a specific soil layer, tension methods are most appropriate. On the other hand, if the objective is to study the loss of solutes from a given layer, zero‐tension methods should be used. Using less mobile water as a basis for the estimate of leaching processes may lead to biased results, especially when considering sorptive solutes. The estimates of nonsorptive solute leaching may also become biased, dependent on the coincidence of high drainage with biased concentration measurements.
Nitrogen Transformations in Surface‐Applied Poultry Litter: Effect of Litter Physical Characteristics
Authors: Cabrera M. L. , Chiang S. C. , Merka W. C. , Thompson S. A. , Pancorbo O. C.
Published: July 2010

Passing poultry litter through a fine sieve (<0.83 mm) generates a fine fraction that is higher in N concentration than the whole litter and cheaper to transport per unit of N. This fine fraction can be pelletized to facilitate handling, but changing the physical characteristics of the litter may change the amount of N loss or the rate at which N mineralizes. The objective of this work was to evaluate the effect of physical characteristics of the fine poultry litter fraction (pelletized or fine particles) on net N and C mineralization, NH3 volatilization, and denitrification resulting from surface applications of the fine fraction to Cecil loamy sand (clayey, kaolinitic, thermic Typic Kanhapludult) and Dothan loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudulf) soils. The soils were adjusted to 52% water‐filled porosity, treated with either pelletized or fine‐particle poultry litter at 30.7 g N m−2, and incubated at 25 °C for 35 d. Humidified air was circulated over each sample (15 chamber volumes min−1) and the NH3 evolved was trapped in 0.025 M H2SO4. Inorganic N contents and rates of denitrification and respiration were measured at 1, 3, 7, 14, 21, and 35 d after application. The physical characteristics of the litter did not affect total amounts of net N mineralized and NH3 volatilized in 35 d. However, total denitrification losses were significantly higher for pelletized (6.2% of the applied N in Dothan and 7.9% in Cecil) than for fine‐particle litter (0.2% in Dothan and 0.8% in Cecil). Thus, surface application of pelletized litter may result in increased denitrification losses compared with fine‐particle litter.
Potassium and Phosphorus Uptake by Competing Pine and Grass: Observations and Model Verification
Authors: Smethurst P. J. , Comerford N. B.
Published: July 2010

A computer model (COMP8) was recently presented that simulates nutrient uptake by competing and single root systems. However, the model needed independent verification. Our objectives here were to: (i) determine if uptake by each species was a simple function of each species' root surface area, and (ii) verify COMP8 for K and P uptake by slash pine (Pinus elliottii Engelm. var. elliottii) seedlings in competition with Panicum aciculare Desv. ex Poir. in Lam. grass plants. Pine and grass plants were grown together at low and high initial soil‐solution concentrations. Observed and predicted uptake values were compared by linear regression and by t tests using variances predicted by Monte Carlo analysis. For high initial solution conditions, we quantitatively predicted pine uptake for all cases of P and for three of four cases for K. Grass K uptake was accurately predicted in all three cases; however, none of the three cases of grass uptake of P were correct. For the low initial solution concentrations, only one case of pine and no cases of grass uptake were predicted accurately. For neither K nor P was uptake by pine (expressed as a percentage of that taken up by pine and grass combined) in a 1:1 relationship with the percentage of surface area in pine roots. We conclude that uptake by the competing root systems is not a simple function of their relative root surface areas and that COMP8 provides an adequate description of nutrient uptake by competing and contrasting root systems under certain, well‐defined conditions.
A Perspective on Diffuse Natural Recharge Mechanisms in Areas of Low Precipitation
Authors: Stephens Daniel B.
Published: July 2010

Extensive studies document that significant recharge can occur in arid and semiarid climates, even where annual potential evapotranspiration exceeds precipitation. This overview focuses on the importance of considering diffuse recharge mechanisms. The recharge mechanisms discussed include infiltration, redistribution, and evapotranspiration, particularly as they are influenced by climate, spatial heterogeneity, anisotropy, preferential flow, and multidimensional flow. Diffuse recharge, calculated for sites having substantially different geography and soil types, only varies by roughly four orders of magnitude. Temporal variability in recharge is attributed primarily to variability in precipitation patterns, evapotranspiration demands, runoff characteristics, and soil hydraulic properties. Examples of field studies of diffuse recharge emphasize sites in New Mexico.
Positional and Temporal Changes in Ponded Infiltration in a Corn Field
Authors: Prieksat M. A. , Kaspar T. C. , Ankeny M. D.
Published: July 2010

Infiltrating rainwater can move agricultural chemicals through soil and may contribute to contamination of drinking water supplies. Ponded infiltration rates were measured in corn (Zea mays L.) fields at four positions relative to plants and to crop rows: center of a trafficked interrow (TRK), center of an untrafficked interrow (UNT), between corn plants in a row (BPIR), and directly over the base of a plant in a row (OPIR). Measurements were taken in chisel‐plow plots during 1990 and 1991, and in no‐till plots during 1991. A Canisteo silty clay loam (fine‐loamy, mixed [calcareous], mesic Typic Haplaquoll) was the predominant soil type in the plots. In chisel‐plow plots, infiltration rates for TRK and UNT positions remained relatively constant during both years, with temporary increases after tillage or cultivation. At BPIR and OPIR positions, infiltration rates increased steadily over the growing season. Infiltration rates at the OPIR position increased from 43 to 211 µm s−1 in 1990 and from 63 to 257 µm s−1 in 1991. At the end of both growing seasons, the OPIR position had the greatest infiltration rate, and the TRK position the lowest. In no‐till, infiltration rates at all positions remained relatively constant throughout the 1991 growing season. Infiltration rates at BPIR and OPIR positions were not different from each other, were greater than 200 µm s−1, and were higher than rates at TRK and UNT positions. High potential infiltration rates in the row, especially around the bases of corn plants, have implications for the management of row‐banded chemicals.
Seal Formation and Interrill Soil Erosion
Authors: Levy G. J. , Levin J. , Shainberg I.
Published: July 2010

Interrill soil erosion depends primarily on soil detachment by raindrop impact (splash) and the transport capacity of thin sheet flow. Both splash and sheet flow erosion depend on soil surface properties. The purpose of this study was to investigate the effect of seal formation on interrill soil loss. Samples of three soil types — a Typic Chromoxerert, a Calcic Haploxeralf and a Typic Rhodoxeralf — with various naturally occurring exchangeable sodium percentage (ESP) levels were used. The soils were exposed to simulated rain using three different waters: distilled (DW), tap (TW), and saline (SW). The electrical conductivity (EC) of the TW and SW was 0.8 and 5.0 dS m−1, respectively. Seal formation was characterized by the final infiltration rate (FIR) and amount of runoff. Seal formation was enhanced with an increase in soil sodicity and a decrease in water salinity for each soil type. Nearly 70% of the variation in FIR (and seal formation) was explained by water salinity and soil ESP. Most of the variation in soil loss was explained by clay content, soil ESP, and water salinity. With the exception of samples with ESP <5 rained on with DW, soil loss increased linearly with an increase in soil clay content. Seal strength, as inferred from surface pitting by impacting raindrops, decreased with an increase in clay content, and was inversely related to soil erosion.
Soil Microbial Biomass Dynamics and Net Nitrogen Mineralization in Northern Hardwood Ecosystems
Authors: Holmes William E. , Zak Donald R.
Published: July 2010

Soil temperature, water potential, and substrate (C) availability are the primary constraints on microbial activity within soil and display substantial seasonal variation within northern deciduous forests. Following autumn litterfall, soil C availability is relatively high, and N should be assimilated by soil microorganisms to maintain or form new biomass. Conversely, N should be mineralized from microbial biomass during midsummer when C availability is relatively low and soil temperatures are high. Because N availability is directly controlled by microbial activity, we hypothesized that microbial biomass and net N mineralization are inversely related on a seasonal basis. To test this hypothesis, we studied the temporal relationship between microbial biomass (C and N) and rates of net N mineralization in two different northern hardwood ecosystems, one dominated by sugar maple (Acer saccharum Marsh.) and basswood (Tilia americana L.) and the other by sugar maple and red oak (Quercus rubra L.). In situ buried bags were used to estimate net N mineralization and nitrification at monthly intervals for 1 yr. Microbial C and N contents of the incubated soil were determined using the chloroform fumigation‐incubation method. Net N mineralization displayed marked seasonal variability, ranging from 35 to 115 mg N m−2 d−1 during the growing season. In contrast, microbial biomass C and N were relatively constant throughout the year, averaging 112 g C m−2 and 17 g N m−2. Neither microbial biomass (C or N) nor the change in microbial biomass between sampling dates were significantly inversely correlated with mean daily rates of net N mineralization. As such, our data do not support the idea that N availability is controlled by large seasonal fluctuations in soil microbial biomass. Rather, our results suggest that N availability is primarily controlled by changes in the turnover rate of microbial biomass such that a relatively constant pool is maintained through time. In addition, mean annual rates of net N mineralization and nitrification did not differ significantly from those previously measured by others in the same stands, suggesting that annual rates may be relatively consistent in climatically similar years.
Volatilization of a Multicomponent Liquid through Dry Soils: Testing a Model
Authors: Nye P. H. , Yaron B. , Galin Ts. , Gerstl Z.
Published: July 2010

Spilled or leaked petroleum products often contaminate groundwater and subsequently evaporate through the soil to the atmosphere by gaseous diffusion. This study developed and tested a model that can predict the rate of diffusion through a dry soil column of the individual components in a liquid mixture when they are of low or intermediate volatility. We derived equations that relate the vapor pressures of the components to their sorption from the gaseous phase by the soil. We also provided for slow sorption. Three cases of increasing complexity were treated: evaporation of a mixture directly into the atmosphere; evaporation of a mixture through a soil column without significant sorption; and finally, evaporation through a highly sorting soil column, for which a computer program was written. The model has been tested by comparing the evaporation of m‐xylene and n‐dodecane mixtures through sand, and air‐ and oven‐dry Evesham clay soil (Aquic Eutrochrept or orthic grumaquert) in the laboratory. The equilibrium sorption isotherms and sorption kinetics for these soils and compounds were determined in separate experiments, and other parameters were obtained from the literature, so that the model contained no adjustable fitting parameters. There was fair agreement between the model predictions and the experimental results. Discrepancies were attributed to errors in chemical analysis and the boundary effects that arose from rather short columns, and to the assumptions that the compounds did not compete for sorption sites on the soil, that Raoult's Law was obeyed, and that there was no hysteresis in the sorption isotherms.
Sorption and Redox Transformation of Arsenite and Arsenate in Two Flooded Soils
Authors: McGeehan S. L. , Naylor D. V.
Published: July 2010

The fate of As in soils is regulated mostly by its participation is sorption reactions and redox transformations. Few studies have examined the rate of arsenite and arsenate reduction or the extent to which these redox transformations may be affected by sorption reactions. The objective of this study was to examine changes in solution concentrations of H3AsO03 and H2AsO−4 in two soils subjected to prolonged flooding. The soils, which differed in H3AsO03 and H2AsO−4 sorption capacities, were flooded by suspending 1 g of soil in 25 mL of a solution containing 0.01 M CaCl2 and 1 g d‐glucose kg−1. The suspensions were amended with NaAsO2 or Na2HAsO4·7H2O and were incubated for 0.5 h to 20 d. Changes in solution chemistry (electrode potential [Eh], pH, and dissolved Fe, Mn, H3AsO03, and H2AsO−4) were observed with time. Sorption processes controlled the dissolved concentrations of H3AsO03 and H2AsO−4 during initial stages of flooding. When anaerobic conditions were achieved, dissolution of Fe and Mn oxyhydroxides occurred, causing desorption of H3AsO03 and H2AsO−4. In NaAsO2‐amended suspensions, desorbed H3AsO03 disappeared from solution within 10 d. In Na2HaSO−4‐amended suspensions, desorbed H2AsO−4 also disappeared within 10 d. Concurrent with the disappearance of H2AsO−4 was the appearance of H3AsO03, indicating that H2AsO−4 was rapidly reduced to H3AsO03. First‐order plots of H3AsO03 and H2AsO−4 disappearance had a linear relationship. Rates of desorption and disappearance of H3AsO03 and H2AsO−4 were slower in the soil with higher adsorption capacity, suggesting that sorption processes may influence redox transformations of As oxyanions.
Adsorption of Aniline on Layer Silicate Clays and an Organic Soil
Authors: Homenauth O. P. , McBride M. B.
Published: July 2010

Adsorption isotherms of organic pollutants such as aniline on soil colloidal materials have generally not been described for a wide range of solution concentrations. The characteristics of isotherms for aniline adsorption on Ca‐saturated kaolinite, montmorillonite, vermiculite, and an organic soil were determined for a wide range of aqueous concentrations at acid and neutral pH. Aniline adsorption was greater at acid than neutral pH for all adsorbents, an indication of preferred adsorption of anilinium. Adsorption on montmorillonite, vermiculite, and kaolinite across the aniline concentration range of 1 × 10−4 to 2 × 10−2 M was best described by a sigmoid (S‐type) isotherm, an equation for which was derived from a model of cooperative adsorption, in which aniline was assumed to adsorb in molecular “clusters”. Adsorption on the organic soil across the same wide range of aqueous concentration was not described adequately by the S‐type isotherm, but rather by the Brunauer‐Emmett‐Teller (BET) function. Within the restricted range of low aniline adsorption, the adsorption isotherms were linear for all adsorbents. At somewhat higher (intermediate) aniline adsorption, the isotherms remained linear for kaolinite and vermiculite, but curvilinear (L‐type) isotherms were obtained for montmorillonite and the organic soil. Generally, the equation best describing adsorption data was different in form for each range of adsorption being considered. Fourier‐transform infrared (FTIR) spectroscopy indicated that, at least at low pH and high adsorption levels, aniline‐anilinium complexes adsorbed on all of the adsorbents. Adsorption on clay and organic matter had characteristics of both electrostatic and weak physical bonding.
Carbon‐13 and Nitrogen‐15 Natural Abundance in Crop Residues and Soil Organic Matter
Authors: van Kessel C. , Farrell R. E. , Pennock D. J.
Published: July 2010

Spatial variability in the 13C and 15N natural abundance of plant residues (δ13Cresidue and δ15Nresidue) and soil (δ13Csoil and δ15Nsoil) at the landscape scale remains largely unexplored. This 2‐yr study assessed landscape‐scale patterns and investigated topographic and soil factors that control spatial variability. Low values of δ13Cresidue were associated primarily with the lower level and footslope elements, with significantly (P ≤ 0.001) higher (less negative) values in the upper level and shoulder elements. Strong similarities in the spatial patterns observed for δ13Cresidue and δ13Csoil indicate that the 13C content of soil organic matter is largely dependent on δ13Cresidue. Although the δ13C of the crop residues exhibited marked year‐to‐year variability, which reflected genetic differences and variations in growing season precipitation and perhaps N‐fertilization regime, landscape‐scale patterns for δ13Cresidue were similar in both years. These data support the hypothesis that δ13Cresidue varies in response to environmental conditions and also suggest that topographic or hydrologic controls are at work. The presence of a landscape‐scale pattern in δ13Cresidue and δ13Csoil may be expected to have a confounding effect on studies that employ the 13C natural abundance method to detect changes in plant species composition or to estimate the rate of soil organic matter turnover. Spatial patterns for δ15Nresidue and δ15Nsoil indicated that 15N was distributed in an essentially random pattern.
Determining Parameter Precision for Modeling Nitrate Leaching: Inorganic Fertilization in Nordic Climates
Authors: Larocque M. , Banton O.
Published: July 2010

Most NO−3 leaching models require the quantification of many parameters. Because the majority of these parameters are difficult to estimate, it is important to know the impact of parameter imprecision to make proper use of a model. A study was performed to identify the relative influence of the parameters in a deterministic NO−3 leaching model (SOILN) used with inorganic fertilization in nordic climates. A sensitivity analysis of the model was performed using parameters related to the N cycle with two reference systems for the parameters corresponding to field sites located in Quebec and in southern Sweden. Results from both sites showed that atmospheric deposits had little influence on NO−3 leaching in agricultural areas in Quebec and Sweden; the variation of parameters related to nitrification also had little impact on NO−3 leaching at the sites studied; parameters used for mineralization, plant uptake, and denitrification had a significant impact on NO−3 leaching in the simulated conditions; parameters related to abiotic factors had a variable influence, depending mostly on soil water contents.
Soil Morphology‐Peoria Loess Grain Size Relationships, Southeastern Minnesota
Authors: Mason J. A. , Nater E. A.
Published: July 2010

Soil profiles formed in Peorial Loess in southeastern Minnesota allow further examination of the widely observed morphological variation of loess‐derived soils with distance from the loess source. In these profiles, morphological variables representing depth of clay accumulation and solum thickness decrease with increasing ratios of coarse silt to total silt in the loessial parent material (R2 = 0.574–0.772). Variables representing depth of clay accumulation also decrease with increasing parent material carbonate content (R2 = 0.297–0.585), but the relationship is weaker. Clay accumulation depth increases with increasing parent material clay content, but the relationship is very weak (R2 = 0.044–0.102). The observed relationship between grain size and clay accumulation is consistent across a wide range of organic matter accumulation, although Typic and Mollic Hapludalfs tend to have shallower clay maxima than darker colored Mollisols. In this study area, unlike other regions of the midwestern USA, stronger soil development in the finer loess cannot be attributed to a shallow, perched water table. We hypothesize that abrupt downward increases in grain size at coarse loess sites inhibit downward moisture flux and, over the long term, limit both the depth of soil development and the amount of weathering and clay accumulation.
Response of Buried Mineral Soil Bags to Experimental Acidification of Forest Ecosystem
Authors: Mitchell M. J. , David M. B. , Fernandez I. J. , Fuller R. D. , Nadelhoffer K. , Rustad L. E. , Stam A. C.
Published: July 2010

At Bear Brook Watershed in Maine, H2SO4 and/or HNO3 was added to 15 by 15 m plots (three replicates per treatment) from 1988 through 1990. Total loading above ambient treatments for the 3 yr was 0 (control), 5100 (low S, low N), 10 200 (high S and N + S), and 11 950 (high N) molc ha−1 yr−1. Changes in soil chemistry were evaluated using tension lysimeters and buried mineral soil bags placed below the forest floor before treatments were initiated. Total soil S was highest in the high S treatment (355 mg S kg−1 soil), intermediate in the low S and N + S treatments (314 and 310 mg S kg−1 soil, respectively), and lowest in the low N, high N, and control treatments (278, 275, and 270 mg S kg−1 soil, respectively). Differences in total S were mostly attributed to phosphate‐extractable SO4, although smaller changes in ester sulfate and C‐bonded S were also detected. Low pH and elevated SO4 in solution resulted in increased SO4 in solution resulted in increased SO4 adsorption. There were no differences caused by treatments in N or C constituents in the soil bags, although N was strongly linked with C (r = 0.86). Nitric and sulfuric acid additions lowered soil pH (H2O) from 4.83 in the control to 4.67 and 4.70, respectively. Sulfuric acid treatments increased exchangeable Ca to 0.32 cmolc kg−1 compared with 0.24 cmolc kg−1 in the control, whereas HNO3 treatments decreased Ca to 0.18 cmolc kg−1. A strong correlation (r = 0.94) between exchangeable Ca and base saturation reflected the quantitative dominance of exchangeable Ca among base cations. Similarities in effects of the N + S and the low S treatments were due to identical additions of SO4 and the absence of a marked effect of NO3 additions on the mineral soil. Changes in the chemistry of the buried mineral soil bags can be explained by both the effects of H2SO4 and HNO3 additions as well as pedogenic processes.
Comparison of Saturated Hydraulic Conductivity Measurement Methods for a Glacial‐Till Soil
Authors: Mohanty B. P. , Kanwar R. S. , Everts C. J.
Published: July 2010

Hydraulic conductivity is the single most important hydraulic parameter for flow and transport‐related phenomena in soil, but the results from different measuring methods vary under different field conditions. To evaluate the performance of four in situ saturated hydraulic conductivity (Ks) measuring methods, Ks measurements were made at four depths (15, 30, 60, and 90 cm) and five locations on a glacial‐till soil of Nicollet (fine‐loamy, mixed, mesic Aquic Hapludoll)‐Clarion (fine‐loamy, mixed, mesic Typic Hapludoll) association. The four in situ methods were: (i) Guelph permeameter, (ii) velocity permeameter, (iii) disk permeameter, and (iv) double‐tube method. The Ks was also determined in the laboratory on undisturbed soil cores collected from all the five sites and four depths. The Guelph permeameter method gave the lowest Ks values, possibly because of small sample size, whereas the disk permeameter and double‐tube methods gave maximum values for Ks with minimum variability, possibly because of large sample size. Maximum variability in Ks values for soil cores at shallow depths may have occurred because of the presence or absence of open‐ended macropores. Estimates of Ks, however, are most comparable for the velocity permeameter and the laboratory method using a constant‐head permeameter.
Axisymmetric Transport of Water and Solute underneath a Disk Permeameter: Experiments and Numerical Model
Authors: Quadri M. B. , Angulo‐Jaramillo R. , Vauclin M. , Clothier B. E. , Green S. R.
Published: July 2010

No analytical solution exists for two‐dimensional, axisymmetric flow of both water and solute underneath a disk permeameter. We developed a finite‐difference numerical scheme for such flows. Laboratory experiments were also conducted using a box containing repacked sand. A ¼‐sector disk permeameter was located on the surface in one corner. The disk, first containing pure water, was placed on the soil for 200 s. It was then removed, refilled with a KBr solution, and replaced at 225 s. Finally after 12.5 min the disk was removed and soil samples extracted along three radial transects under the disk. In two other experiments, the disk, containing only pure water, was left on the soil surface and soil samples removed at the end i.e., 6 and 14 min. A tensiometer inserted through one face of the box and located just 20 mm under the disk recorded the changing soil water pressure head with time, h(t). Good predictions of both the water content and Br− profiles were achieved with the numerical model, and good renditions of h(t) and the transient flow rate from the disk, q(t). Our results reinforce the need for caution when determining the soil's sorptivity from observations of q vs. t½. Care is required in deciding when q has indeed become steady. Numerical models, such as this one might serve as parameter‐identification tools when using a tracer‐filled disk permeameter to infer the chemical transport properties of soil.
Cultivar and Nitrogen Rate Influence on Nitrogen Uptake and Partitioning in Rice
Authors: Guindo D. , Wells B. R. , Norman R. J.
Published: July 2010

Numerous empirical studies have shown that semidwarf rice (Oryza sativa L.) cultivars require higher N fertilizer rates for optimum yields than standard‐statured cultivars; however, these studies do not indicate the reason for this increased N requirement. Field studies were conducted with semidwarf ‘Lemont’ and standard‐stature ‘Lebonnet’ rice to evaluate N uptake and partitioning as related to fertilizer 15N rates and developmental stages. Four fertilizer N rates bracketing the recommended ranges for the two cultivars were applied as 15N‐labeled urea in split applications at preflood (PF) and panicle differentiation (PD). Aboveground plant portions were sampled at PD, heading, and heading + 21 d for dry matter, total N, and fertilizer 15N. Lebonnet produced more total dry matter at all N rates and had higher panicle weights at the lower two N rates, whereas Lemont had higher panicle weights at the highest N rate. Lemont continued to accumulate total N between heading and heading + 21 d, whereas Lebonnet showed either a decline or leveling. Fertilizer 15N uptake and accumulation decreased after heading for both cultivars, thus Lemont appears to continue accumulating soil N through grain filling. Nitrogen harvest index for total and fertilizer N with Lemont was greater than with Lebonnet, therefore, N utilization differences between the two cultivars may be associated only with total N uptake and partitioning after heading.
Optimal Conditions for Phosphorus Analysis by the Ascorbic Acid‐Molybdenum Blue Method
Authors: Rodriguez J. B. , Self J. R. , Soltanpour P. N.
Published: July 2010

Phospho‐molybdo blue color intensity, its relation to P concentration in solution, and color stability are greatly influenced by the solution acidity and matrix. Our objectives were to: find the acid‐stability plateau for the ascorbic acid‐Mo blue complex and its application to colorimetric P analysis; identify the stability of the calibration graphs for Soltanpour‐Schwab, Watanabe‐Olsen, and Bray‐Kurtz P‐1; and study the stability of the mixed and color‐developing reagents. Standards containing 0.0, 0.2, 0.4, 0.6, 0.8, 0.9, 1.0 and 1.1 mg P L−1 were prepared across a range of acidity from 0.0 to 0.6 M H2SO4. The acid‐stability plateaus were between 0.17 and 0.28 M and 0.17 and 0.46 M H2SO4 when absorbances were obtained after 10 min and 24h, respectively, after adding the color‐developing reagent. The blue color was stable with time for P concentrations up to 0.30 mg L−1 for AB‐DTPA and 0.80 mg L−1 for other extracts. The mixed reagent was stable for 16 wk and the color‐developing reagent was stable 2 and 14 d for the open and sealed‐cold conditions, respectively.
Effects of Flooding on pH of Rice‐Producing, Acid Sulfate Soils in Indonesia
Authors: Konsten Carla J. M. , van Breemen Nico , Suping Supardi , Aribawa Ida Bagus , Groenenberg J. E.
Published: July 2010

Suitability of acid sulfate soils for lowland rice cultivation in coastal swamps in Kalimantan, Indonesia, is limited by low pH and associated high levels of dissolved Al and Fe. In the dry season, oxidation of pyrite lowers the pH wherever the groundwater table drops below the depths at which the soil contains pyrite. Reduction and leaching in the wet season deacidifies the soil at some sites but not at others. This study was conducted to examine the factors that determine the rise of pH after flooding. Seasonal dynamics of soil physical and chemical parameters were monitored for 2 yr at four representative sites. Dominant redox processes varied with physiography and drainage of the soils. In acidified surface horizons of potential acid sulfate soils of coastal backswamps, pH rose quickly to 5 to 6.5 after flooding. In inland backswamps, pH rose much more slowly to 4 to 5.5. Acid sulfate soils in artificially drained backswamps retained their low dry‐season pH of 3.5 to 4 in the wet season. On levees and ridges, the pH rose to 5.5 in the peaty topsoil only, while the mineral soil remained very acidic with pH values ranging between 3 and 4. Low concentrations of Fe(III) oxides and SO4 relative to the soil acidity appear to be a major cause of the static pH following soil reduction after flooding. Horizons with an accumulation of Fe(III) oxides and Jarosite, which is characteristic of acid sulfate soils of monsoonal and dry regions, were not observed in Kalimantan. The perhumid climate, in combination with a highly organic parent material, probably prevents sufficient oxidation for the accumulation of large amounts of Fe(III) oxides and jarosite and permits the leaching of iron as Fe2+.
Humic Substances and Surfactants Effects on the Stability of Two Tropical Soils
Authors: Piccolo A. , Mbagwu J. S. C.
Published: July 2010

Soil conservation in the tropics is influenced by soil management practices that include addition of organic matter and agrochemicals, which often contain surfactants. Changes in the structural stability of a weakly aggregated Entisol and a strongly aggregated Ultisol from southern Nigeria following additions of humic acids (HA) and anionic (AS) or nonionic (NS) surfactants were evaluated in a laboratory study. Four rates of HA and four rates of either AS or NS (0, 0.1, 1.0, and 10 g kg−1) were used. At the macroaggregation level, the percentage of water‐stable aggregates (WSA) increased with increasing rates of HA and NS, whereas the AS reduced WSA at all application rates on both soils. At high application rates, the combination of HA and NS increased WSA more than either of the soil additives acting alone. Humic acids also significantly reduced the magnitude of disaggregation caused by AS additions on the soils. For example at zero HA addition, the 10 g kg−1 AS rate reduced WSA by 13.8% on the Ultisol and 23.8% on the Entisol, whereas at the highest combined rates of both additives WSA increased by 5.3 and 47.6% on the Ultisol and Entisol, respectively. At the microaggregation level the combination of HA and NS significantly decreased the amount of dispersible clay (i.e., increased stability) especially at higher application rates. On the Ultisol each HA and AS combination rate decreased stability but on the Entisol addition of HA significantly reduced the amount of water‐dispersible clay induced by AS application. At moderate to high application rates, therefore, humic acids appear to have the potential to positively counteract the negative effects of anionic surfactants on the structural stability of fragile soils.
Influence of Soil Organic Matter and Soil Surfaces on a Bacterial Consortium that Mineralizes Fenamiphos
Authors: Ou L.‐T. , Thomas J. E.
Published: July 2010

Microorganisms are often responsible for enhanced degradation of pesticides in soil. This study was conducted to isolate microorganisms capable of mineralizing fenamiphos [ethyl‐3‐methyl‐4‐(methylthio)‐phenyl(1‐methylethyl)phosphoramidate] from soil collected at a turfgrass site that showed an enhanced degradation rate of the chemical. Batch‐culture enrichment techniques were employed to isolate microor‐ganisms from the soil capable of mineralizing 14C‐fenamiphos, and the evolved 14CO2 was quantified by liquid scintillation counting. No axenic bacterial cultures capable of mineralizing fenamiphos could be isolated. A mixed bacterial consortium enriched with glucose‐basal mineral medium mineralized fenamiphos only in the presence of a small amount of the nonsterile soil, autoclaved soil, or H2O2‐treated soil. The mixed culture consisted of at least 6 gram‐negative rod‐shaped bacteria, with none of the individual isolates having any capacity to mineralize fenamiphos. The mixed culture grew well in soil extract and, at the same time, mineralized fenamiphos. This suggests that soluble organic components serve as inducers for the production of enzymes necessary for the mineralization of fenamiphos or that soil surfaces might play a role in induction of the enzymes.
Spatial Analysis of Soil Fertility for Site‐Specific Crop Management
Authors: Cahn M. D. , Hummel J. W. , Brouer B. H.
Published: July 2010

Spatial patterns of soil properties and nutrient concentrations need to be characterized to develop site‐specific farming practices that match agricultural inputs with regional crop needs. The spatial variation of soil organic C (SOC), soil water content (SWC), NO3‐N, PO4‐P, and K were evaluated in the 0‐ to 15‐cm layer of a 3.3‐ha field (Typic Haplaquoll and Argiaquic Argialboll) cropped with maize (Zea mays L.) and soybean [Glycine max (L.) Merr.]. The range of spatial correlation was determined from semivariance analyses of the data and was found to vary among and within fertility parameters. Nitrate had the shortest correlation range (<5 m) and SOC had the longest (>180 m), whereas SWC, PO4‐P, and K had intermediate spatial correlation ranges. In addition, SOC was found to have small‐scale spatial variation nested within large‐scale spatial variation. The spatial pattern of NO3‐N changed with time. Frequency distributions of SOC and SWC were close to normal, whereas the distributions of NO3‐N, K, and PO4‐P data were skewed. Median polishing detrending and trimming of outlying data were useful methods to remove the effects of nonstationarity and non‐normality from the semivariance analysis. The results suggest that reducing sampling intervals from 50 to 1 m would reduce the variance of SWC, SOC, NO3‐N, PO4‐P, and K estimates by 74, 95, 25, 64, and 58%, respectively. A useful sampling pattern for characterizing the spatial variation of several soil properties‐nutrients and scales should be random with sample spacing as close as 1 m and as far apart as the longest dimension of the field.
Characterization of Clay Minerals in White Clay Soils, People's Republic of China
Authors: Xing B. , Dudas M. J.
Published: July 2010

The widely distributed white clay soils are major agricultural soils in China. While some of the chemical, physical, and morphological properties have been documented for these soils, there is little information available on their clay mineralogy. The purpose of this study was to conduct a detailed characterization of the clay mineralogy of white clay soils. Representative pedons were sampled by horizon and used in the detailed mineralogical study of these soils. Clay separates were analyzed by x‐ray diffraction methods. Layer charge of 2:1 expandable phyllosilicates was determined by the n‐alkylammonium ion exchange technique. Elemental composition of clay separates was determined by inductively coupled plasma atomic emission spectrometry. Vermiculite and smectites, which have not been recognized before, were identified in these soils. Other phyllosilicates were mica, kaolinite, and chloritic intergrades. Vermiculite had a uniform charge distribution of 0.82 molc/O10(OH)2. Layer charge of smectites ranged from 0.36 to 0.47 molc [O10(OH)2]−1 with a mean of 0.41 molc [O10(OH)2]−1. Content of vermiculite in clay fractions ranged from 150 to 230 g kg−1, mica from 180 to 250 g kg−1, and kaolinite from 310 to 370 g kg−1. The high contents of kaolinite and mica in A and E horizons may be caused by aerosolic dust input and lessivage. Chloritic intergrades are thought to form from progressive filling of interlayer space of expanding phyllosilicates during pedogenesis. Smectites may have been derived from pedogenic weathering of vermiculite in these soils. Systematic documentation on clay mineralogy of white clay soils provides fundamental information for agricultural use and management of these soils.
Characteristics of Clay Minerals in Saline Alkaline Soils in Alberta, Canada
Authors: Kohut Connie K. , Dudas M. J.
Published: July 2010

The stability of clay minerals in extremely saline alkaline soils is not well understood, but may be expected to differ from those in other soils due to differences in the geochemical environment. A survey of the clay mineralogy of surface horizons of 39 salt‐affected soils in Alberta, Canada, showed that many samples had unusual x‐ray diffraction characteristics in that essentially no basal reflections for smectite minerals were recorded. Four sites were subsequently selected for detailed mineralogical characterization. Extremely diffuse smectite diffraction maxima were found to occur primarily in the coarse clay fraction of surface soils, and appear to be the result of interaction with organic matter. After traditional pretreatments to remove organic matter and carbonates, the clay mineralogy of salt‐affected soils was found to be similar to nonsaline soils. Slight changes were sometimes noted in the diffraction maxima of the smectite minerals, possibly indicating lower crystallinity and layer charge. Tetrahedrally substituted smectites were not identified, while variable amounts of high‐charge smectite or vermiculite were detected in most samples. Despite very high ionic strengths and pH values as high as 10, little or no degradation of clay minerals appears to be occurring in these soils. Analysis of immiscibly displaced pore water indicated that the soil solutions were supersaturated with respect to common phyllosilicates. Relatively low amounts of fine clay, however, indicate that neoformation of clay minerals is unlikely.
Ammonium‐Potassium and Ammonium‐Calcium Exchange Equilibria in Bulk and Rhizosphere Soil
Authors: Chung Jong‐Bae , Zasoski Robert J.
Published: July 2010

This study was conducted to determine whether differential soil properties in bulk and rhizosphere soil could influence cation‐exchange equilibria. The pH of rhizosphere samples collected from peach [Prunus persica (L). Batsch var. persica] seedling roots grown in Arbuckle gravelly loam (fine‐loamy, mixed, thermic Typic Haploxeralf) were 0.4 units lower than bulk soil. Organic C content, cation‐exchange capacity, clay, and amorphous oxide content were higher in the rhizosphere. Mineralogical differences apparent to x‐ray analysis were not evident. As soil pH decreased, the selectivity for NH4 over Ca increased but pH effects on NH4‐K exchange were insignificant. Organic matter addition increased the selectivity for NH4 over K, and Ca over NH4. As exchange solutions were diluted, the selectivity of the higher valent cation increased. Although the effect of individual soil properties on the exchange reactions could be fully determined, there were significant differences in the exchange equilibria between the bulk and rhizosphere soil. In the rhizosphere samples, selectivity for NH4 over K was relatively higher at an ionic strength of 0.02, but selectivity reversed at an ionic strength of 0.05. At ionic strengths of 0.02 and 0.05, the selectivity for NH4 over Ca was higher in the bulk soil. The differential exchange equilibria between bulk and rhizosphere soils are expected to affect cation distributions in the soil environment around roots, nutrient uptake, and toxicity relations of plant roots.
Aluminum‐Potassium and Aluminum‐Calcium Exchange Equilibria in Bulk and Rhizosphere Soil
Authors: Chung Jong‐Bae , Zasoski Robert J. , Burau Richard G.
Published: July 2010

In drip‐irrigated soil treated with high rates of NH4 fertilizer, acidification can be significant and the level of soluble Al may be high. Whether these changes in bulk soil are reflected in the rhizosphere is unknown. Because rhizosphere and bulk soils may have different physiochemical properties, the cation dynamics involving Al in acidic bulk and rhizosphere soil may also differ. We examined cation‐exchange equilibria between Al‐K and Al‐Ca pairs in bulk and rhizosphere soils generated by growing peach seedlings. Overall, compared with a calculated nonpreference line, K and Ca were preferred over Al in Arbuckle soil (fine‐loamy, mixed, thermic Typic Haploxeralf), but soil selectivity for each cation was highly dependent on the soil conditions. The selectivity for Al over K or Ca was greater at higher pH and at higher organic matter level. As exchange solutions were diluted, selectivity for the higher valent cation (Al) increased. Although the effect of individual soil properties on the exchange reactions could not be fully determined, there were significant differences in the exchange equilibria between the bulk and rhizosphere soil. When we compared the cation exchange of bulk and rhizosphere soil, the preference for Al over K was apparent in the bulk soil and the preference for Al over Ca was apparent in the rhizosphere soil. Because a strong Al adsorption can reduce Al level in solution and the Al toxicity in acidic conditions, the less preferred Ca ion will be less effective than K in displacing Al. This effect would be greater in the rhizosphere soil where Al selectivity was greater than that of Ca.
Kinetics of Zinc Desorption from Vertisols
Authors: Dang Y. P. , Dalal R. C. , Edwards D. G. , Tiller K. G.
Published: July 2010

The rate of Zn desorption from soil surfaces into soil solution is a dynamic factor that regulates its continuous supply to growing plants. To ascertain the pattern of Zn desorption, the soil characteristics affecting it, and whether cropping alters its rate, the kinetics of Zn desorption from the <2‐mm fraction of 14 Vertisols by diethylenetriaminepentaacetic acid (DTPA) and ethylenediaminetetraacetic acid (EDTA) were investigated using soil samples taken before and after one wheat (Triticum aestivum L.) crop. Nine kinetic models were evaluated to describe the rate of desorption of soil Zn by DTPA, which was rapid initially but gradually declined with time. The parabolic double diffusion, the two‐constant rate, and the simple Elovich equation adequately described Zn desorption from Vertisols. Rate constants for the parabolic double diffusion equation (k'σ), the two‐constant (a and b) rate equation, and the initial Zn desorption rate constant (α) from the simple Elovich equation were closely associated with clay content, soil pH, and amorphous Fe and Al contents of the soil—the soil characteristics that affect solubility, sorption and desorption, and diffusion of Zn in Vertisols. Rate constants from the latter two equations for Zn desorption by DTPA from 14 Vertisols were highly correlated with those from Zn desorption by EDTA and also with those for Zn desorption by DTPA on soil samples taken after one wheat crop. Thus, the rate constants obtained on initial samples can be used to predict Zn availability for at least two cropping seasons.
Saturated Zones and Soil Morphology in a Mollisol Catena of Central Iowa
Authors: Khan F. A. , Fenton T. E.
Published: July 2010

The zone of saturation plays significant roles in decisions regarding soil classification systems and land use both present and potential. This study was conducted to determine the status of water tables, morphological features, and groundwater hydrology and to evaluate the zone of saturation on selected soils (Aquolls and Hapludolls) of a Mollisol catena. Water table depths and the amount of precipitation were measured for a 10‐year period on five soils formed in glacial till or till‐derived sediments in central Iowa. Results show that the depth of the water table, duration of saturation, morphological features, and recharge and discharge to groundwater varied with geomorphic position in the Mollisol catena. In general, soils on summit and shoulder positions (Hapludolls) are not saturated and have high chromas without redoximorphic features in the B horizon, have deeper water tables, and have maximum fluctuation of water table levels. The soils on toeslopes and depressions (Aquolls) have the shallowest water tables, have the longest time of saturation, and have B horizons with gray matrices, bright mottles, and Fe‐Mn concretions. Nicollet soils (fine‐loamy, mixed, mesic Aquic Hapludoll) on backslope positions have intermediate characteristics. Redoximorphic features present in these soils are correlated with the fluctuating depth of the present‐day water table. The extent of recharge and discharge and artificial the drainage are contributing factors to the water table level. Data for water table level and calcite/dolomite ratio indicate that ephemeral recharge and discharge of groundwater occur in the soils on lower landscape positions. Recharge is the dominant process in the soils of higher landscape. This study was designed to contribute to the understanding of drainage class‐water table‐morphological features of soils in this region. The apparent drainage conditions and the redoximorphic features contribute to the testing and clarification of soil classification and soil taxonomy.