bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractNo 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

AbstractNumerous 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

AbstractPhospho‐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

AbstractSuitability 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

AbstractSoil 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

AbstractMicroorganisms 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

AbstractSpatial 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractIn 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

AbstractThe 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

AbstractThe 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.
Nitrate Leaching as Influenced by Cover Cropping and Nitrogen Source
Authors: McCracken Daniel V. , Smith M. Scott , Grove John H. , MacKown Charles T. , Blevins Robert L. 
Published: July 2010

AbstractTo minimize groundwater contamination by NO−3 and to maximize efficient crop N use, it is necessary to better characterize NO−3 leaching in various cropping systems. Our objectives were to compare the contributions of hairy vetch (Vicia villosa Roth) and NH+4 N sources to NO−3 leaching in corn (Zea mays L.) production, and to compare NO−3 leaching losses in a corn production system utilizing hairy vetch as a N source and winter cover crop with leaching losses in one utilizing an NH+4 N source and a rye (Secale cereale L.) cover crop. Nitrogen, sometimes enriched with 15N, was applied to corn grown on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) in lysimeters as vetch‐ or NH+4‐N at rates between 10.5 and 14.0 g N m−2 yr−1. Treatments (N source/cover crop) were: NH+4‐N/fallow, vetch‐N/fallow, NH+4‐N/rye, and vetch‐N/vetch; mean 3‐yr cumulative NO−3 leaching losses were 6.11, 4.85, 0.35, and 2.51 g N m−2, respectively. Total recovery of added 15N in leachate was <5% for all treatments, and the percentage of leached NO−3 derived from labeled N sources was generally <15%. In the winter‐fallow lysimeters, effects of N source on the fraction of water input discharged, concentration of NO−3, and quantity of NO−3 leached varied with year and time of year; differences in N‐source availability and mulch effects were sometimes indicated. Generally, cover crop effects were larger than N‐source effects. The NH+4 N source/rye cover system leached consistently less NO−3 than the vetch N source/vetch cover system, even though the fraction of water discharged was not consistently different.