bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Field Study of Solute Dispersion in a Shallow, Unconfined Aquifer
Authors: Leland D. F. , Hillel D. 
Published: July 2010

AbstractA natural gradient tracer test was performed to (i) characterize the patterns of variation of saturated hydraulic conductivity (Ks) and longitudinal dispersivity (αL) in a shallow, unconfined aquifer in a sandy soil on a sloping site and to (ii) examine scale effects on quantification of αL. Chloride tracer was injected into the saturated zone, and its downslope movement was monitored by means of multilevel samplers.Results show that the mean value of Ks derived from the tracer test was in close agreement with values obtained independently on undisturbed core samples and from double‐ring infiltrometer tests performed in situ. Results also indicate a nonuniform distribution of velocity on both vertical and horizontal transects at right angles to the mean direction of flow. Values of αL, calculated using a simplified solution of the two‐dimensional advective‐dispersive equation, show a nonuniform distribution of αL in the profile and reveal that increasing the scale of measurement vertically at right angle to the flow leads to larger measured values of dispersivity. The effect was observed with a change in scale from point measurements to averages taken over the 60‐ to 75‐cm thickness of the profile's saturated zone. The frequency of sampling is also shown to have a significant effect on quantification of αL.
Water Infiltration and Redistribution in a Silt Loam Subsoil with Vertical Worm Channels
Authors: Bouma J. , Belmans C. F. M. , Dekker L. W. 
Published: July 2010

AbstractInfiltration and redistribution of water in a fine silty, mixed, mesic Fluventic Eutrochrept with macropores (dominantly vertical worm channels) were studied with physical and morphological techniques. Infiltration rates in individual worm channels were measured and channel morphology was studied by excavation after adding methylene blue and gypsum. Three different steady infiltration rates corresponded with different channel morphology. One channel occurred per 200 cm2 of soil. The measured, dominant infiltration rate in a channel was used to calculate ponding time on and the associated water movement in the soil matrix after adding 2 cm of water. The latter was calculated with an existing simulation model for one‐dimensional infiltration in homogeneous soil using K‐θ and h‐θ data. Calculations of h indicated lack of soil saturation. This agreed only with in‐situ measurements when small tensiometer cups were used. Large cups intercepted water‐conducting macropores, erroneously suggesting saturation of the entire soil matrix. Addition of a 5‐cm thick layer of sand to the surface of infiltration made the macropores discontinuous and induced saturated conditions, as measured and simulated. Measurement of infiltration rates into individual macropores, rather than calculation of those rates, is recommended when macropore morphology is irregular.
Effects of Rate of Application and Time on Phosphorus Sorption by Soils
Authors: Ibrahim H. S. , Pratt P. F. 
Published: July 2010

AbstractSeveral soils from southern California were treated with different rates of phosphorus (P) and then incubated in 0.01M CaCl2 to measure the effect of incubation time up to 84 d at 25°C. There were only small effects of incubation times beyond 3 d for low rates of P applications. At higher rates of application those soils that were deficient in P as indicated by the NaHCO3 test (< 10 µg P extracted/g) gave increased P sorption with increase in incubation time beyond 3 d. Those soils well supplied with available P reached equilibrium in 3 d. In those soils deficient in P, equilibrium was attained by the 42nd d of incubation.
Changes in Inorganic and Organic Soil Phosphorus Fractions Induced by Cultivation Practices and by Laboratory Incubations
Authors: Hedley M. J. , Stewart J. W. B. , Chauhan B. S. 
Published: July 2010

AbstractChanges in inorganic and organic phosphorus (P) fractions resulting from 65 years of cropping in a wheat‐wheat‐fallow rotation were studied using a sequential extraction technique. Total P content of the cultivated soil was 29% lower than that of the adjacent permanent pasture; the major loss of P (74% of total P lost) was organic P and residual P. Of the total P lost, 22% was from the extractable organic P forms, whereas 52% originated from stable P.Incubation studies were used to study seasonal P transformations during simulated fallow with and without residue incorporation and P fertilization. Nine monthly additions of cellulose (765 µg C · g−1 soil) with and without P (9 µg · g−1 soil) significantly altered levels of total extractable organic P and inorganic P in incubated soils. Evidence is provided for microbial activity playing a major role in redistributing P into different forms in the soil.
Geostatistical Analysis of Soil Chemical Properties of Large Land Areas. I. Semi‐variograms
Authors: Yost R. S. , Uehara G. , Fox R. L. 
Published: July 2010

AbstractSoil properties are usually sampled on some grid or pattern which presumes to represent the unsampled neighborhood. Spatial dependence is a measure of the extent a soil sample represents the unsampled neighborhood. Geostatistics provides procedures to measure spatial dependence. Eighty pedons (Andepts) on the Island of Hawaii were sampled and spatial dependence was measured with semi‐variograms. Areas of soil with similar properties (zones of influence) were delineated by the “range” of the semi‐variogram. Areas of similarity were much greater for soil properties of the 0‐ to 15‐cm depth than of the 30‐ to 45‐cm depth. The ranges of the semi‐variograms for soil pH, Ca, Mg, K, Si, and P sorbed at 0.02 mg P/L were 32 to 42 km while the range of the variogram of rainfall had a similar value of 32 km. Semi‐variograms for Ca, Mg, K, and P based on 30 to 45‐cm‐depth samples demonstrated much greater variability and had smaller zones of influence (Ca, Mg, and K) or were extremely variable (P). Silicon in saturation extract, however, had the same zone of influence in the subsoil as in the topsoil. These results suggest that rainfall has imposed a degree of uniformity on the surface soil properties not apparent in the subsoil. Subsoil properties were highly variable, as might be expected, resulting from great variation over short distances in age and weathering of volcanic ash. The results suggest that soil chemical properties may be spatially dependent and that the spatial dependence in this example represents the imprint of soil‐forming processes and perhaps management. Zones of influence as delineated by semi‐variograms of soil properties may suggest groupings for soil management or soil classification.
Variations in Nitrate and Chloride Concentrations below Selected Agricultural Fields
Authors: Lund L. J. 
Published: July 2010

AbstractNitrate‐nitrogen (NO‐3‐N) and chloride (Cl‐) concentrations below four agricultural fields were determined to evaluate the validity of assuming that the nitrogen (N) cycling systems were at steady state for purposes of calculating N balances. Eight or nine sites in the fields in the Santa Maria Valley of California were sampled two or four times to determine the spatial and temporal variations in NO‐3‐N and Cl‐ concentrations in the unsaturated zone. Significant spatial variations were found within all fields with mean field concentrations of NO‐3‐N and Cl‐ ranging from 40 to 136 mg/L and 4.5 to 7.1 meq/L, respectively. Temporal variations were less dramatic. Nitrate‐nitrogen and Cl‐ concentrations did not change with time over the period of study below a field that had been cropped to artichokes (Cynara scolymus) for the previous 12 years. Differences did occur with time for the other fields. For two of the fields the changes in mean concentrations could be related to past management with decreasing NO‐3‐N concentrations reflecting periods of less N fertilization.
Theories and Tests of Electrical Conductivity in Soils
Authors: Bohn Hinrich L. , Ben‐Asher Jiftah , Tabbara Hadi S. , Marwan Mukhtar 
Published: July 2010

AbstractThe soil's specific electrical conductivity (ECa) is similar in principle to the EC of a pure solution, but the nonconducting soil air and solids cause complications. The ECa measured by four‐electrode Wenner arrays in laboratory and field experiments was linearly proportional to the product of the soluble salt concentration and the soil water content over a salinity range of 0 to 40 dS/m in the soil solution and 0.1 to 15 bar soil water suction. Theories of soil EC based on a conductivity cell and microscale conduction were compared to a macroscale theory and all explained the measured results equally well. Soil can be viewed as an intricate container for electrolyte solution, as a conductor having a tortuous path, or as many conduction paths of varying cross section and length. The macro model was extended to relate ECa to soil water potential, but ECa appears to be inherently dependent on both the soil moisture and salt contents.
Effect of pH on the Rate of Gaseous Products of Denitrification in a Silt Loam Soil
Authors: Koskinen W. C. , Keeney D. R. 
Published: July 2010

AbstractTo examine the effect of soil pH on the rate and products of denitrification, a silt loam soil (Typic Argiudoll) was used that had been collected from a field experiment maintained at various pH levels for 18 years. The soil pH ranged from 4.6 to 6.9 and was nearly uniform in organic C (1.15 ± 0.05%) and texture. Incubation was performed under He in all‐glass systems that were sealed throughout the incubation period. The soils were amended with 100 µg/g of NO‐3‐N before incubation. Denitrification products (N2O, NO, and N2) and CO2 were determined by gas chromatography using an ultrasonic detector.It appears that the rate of organic C mineralization rather than pH controls the rate of denitrification in C‐limited systems. At 100 µg NO‐3‐N added per gram of soil, the overall rates of denitrification correlated with the rates of C mineralization (CO2 evolution) but were not consistently related to pH or to total organic C.Soil pH did affect the products of denitrification. Nitrous oxide comprised 83% of the gaseous‐N products for pH 4.6 and 5.4 when 90% of the NO‐3 had been denitrified. The N2O was then rapidly reduced to N2. The highest amount of NO was observed at pH 4.6 and 5.4. At pH 6.0 the rate of production of N2O exceeded the rate of reduction only for the first 2 d of incubation. However, N2O was the dominant product until ∼83% of the NO‐3 had been denitrified. At pH 6.9, N2 was the dominant product after the 1st d of incubation.
Improved Corrective Fertilizer Recommendations Based on a Two‐Step Alternative Usage of Soil Tests: II. Recovery of Soil‐Equilibrated Potassium
Authors: McLean E. O. , Adams J. L. , Hartwig R. C. 
Published: July 2010

AbstractThe objective of these studies was to improve corrective fertilizer K recommendations using soil quicktest methodology which measures K‐fixation tendencies for individual soils. Actual amounts of fertilizer K required to reach a computed sufficiency level of NH4OAc‐exchangeable K were measured from the added K vs. exchangeable‐K relationship in 15 soils with a wide range in K‐fixation tendency. Using quicktest procedures, the new Mehlich extractant removed from the various K‐equilibrated soils the same amounts of K as did NH4OAc solution, which suggests the possibility that both K and P may be simultaneously equilibrated and extracted with one extractant. Regressions were computed between the actual and variously computed amounts of K to reach sufficiency level based on constant‐fraction recovery, quicktest‐measured recovery (one‐step), and curvilinear regression‐adjusted recovery (two‐step). The results indicate that the proposed quicktest methodology (2‐h K equilibration) combined with a second calibration step based on longer‐time K equilibration of representative soils makes possible a greatly improved recommendation for fertilizer K.
Calcic Horizon Distribution and Soil Classification in Selected Soils of the Texas Coast Prairie
Authors: Sobecki T. M. , Wilding L. P. 
Published: July 2010

AbstractIn the nearly level southeastern Texas Coast Prairie, extensive areas of Udolls with calcic horizons are intimately associated with noncalcareous Aqualfs. Transect and grid studies of 1‐ to 2‐ha plots and other field studies in the area indicate that soils with calcic horizons are confined to microtopographic highs. Aqualfs occupy irregular microdepressions only 0.5 m lower than microhighs. This soil pattern is found on coastal plain geomorphic surfaces of both the Beaumont and Montgomery Pleistocene geological formations, especially on distributary elements of deltaic origin.Variation in depth to the calcic horizon in Mollisols ranges from 18 to 115 cm and results in complex soil patterns of Aeric Calciaquolls and Aquic Haplustolls in microhighs. Multitaxa map units are necessary to accurately map the soils in these landscapes. Local relief differential of <1 m within the study area is the key landform indicator of soil differences. A new category for Soil Taxonomy, Calciaquic Hapludolls, is proposed to accommodate soils currently placed as Haplustolls that have udic moisture regimes despite calcic horizons within 1.5 m of the soil surface.
Slope Angle‐Interrill Soil Loss Relationships for Slopes up to 50%
Authors: Singer Michael J. , Blackard John 
Published: July 2010

AbstractSoil loss data were collected from 1.2‐m long by 0.6‐m wide plots under 76 mm/h simulated rainfall for two soils at slopes from 3 to 50%. Soil loss and soil loss ratio (soil loss at any slope ÷ soil loss at 9% slope) were related to the sine of slope angle in degrees. Second‐ and third‐degree polynomial equations fit the data best. An equation for the Hillgate soil showed that the soil loss ratio increased rapidly up to 35 to 40% slope and then became nearly constant. This may be partly due to the experimental conditions of short slope length but is realistic because at high slope angles there is less direct raindrop impact on the soil surface.The equation for the Contra Costa soil loss ratio yielded a curve much below the Hillgate curve at slopes between 15 and 40%. These data suggest that soil properties and slope effects are not independent. The experimental conditions are not meant to be representative of field conditions but the data represent the effect of slope steepness on interrill erosion by raindrop impact and overland flow.
Soil Phosphorus and pH Influence the Growth of Mycorrhizal Sweetgum
Authors: Yawney William J. , Schultz Richard C. , Kormanik Paul P. 
Published: July 2010

AbstractThe response of sweetgum (Liquidambar styraciflua L.) seedlings grown either without or inoculated with the vesicular‐arbuscular mycorrhizal (VAM) fungus Gigaspora margarita ‘Becker’ and ‘Hall’ to 25, 50, and 100 ppm soil phosphorus (P) and adjusted soil pHs of 4.5, 5.5, 6.5, and 7.8 was observed during the first growing season. The best seedling growth for both VAM and noninoculated seedlings occurred at soil pH 4.5 and 100 ppm of soil P where mean heights and top dry weights averaged > 28 cm and 8 g, respectively. As soil pH increased, seedling growth decreased significantly and at pH 7.8 the seedlings averaged < 4 cm in height regardless of the soil P level or mycorrhizal condition. Seedling growth at all pH levels, except pH 7.8, decreased with decreasing soil P. Inoculated seedlings were significantly larger than noninoculated seedlings at 25 ppm soil P and pHs 4.5 and 5.5. Soil P, soil pH, and mycorrhizal condition significantly influenced nutrient levels in plant parts. Soil nutrient levels varied significantly with soil pH.
Clay Mineralogy in Relation to Landscape Instability in the Coast Range of Oregon
Authors: Istok J. D. , Harward M. E. 
Published: July 2010

AbstractField and laboratory data reported in this study indicate that the kind of mass movement and the mineralogy of the materials involved vary with the parent material. The clay fraction of debris avalanches is dominated primarily by nonexpanding layer silicates that have large particle sizes and small water‐holding capacities. Dehydrated halloysite, chloritic intergrade, and mica were the common minerals in those areas underlain by sandstones and siltstones of the Tyee Formation as well as the massive basalt flowrock of the Siletz River Volcanic Series. The clay fraction of soils derived from Tertiary sandstones of the Galice and Lookingglass Formations is dominated by chloritic intergrade, chlorite, mica, and kaolinite. Serpentine, chlorite, and mica were the soil clays associated with debris avalances on serpentinite of the Otter Point Formation. Expandable layer silicates, or those with high charge or water‐holding capacity, were not major constituents of debris avalanches although smectite and vermiculite commonly occurred in a thin layer of soil above the underlying bedrock.The clay fraction of samples from sites undergoing failure by creep and slump consisted primarily of smectite. Smectite, chloritic intergrade, dehydrated and hydrated halloysite, and mica were the minerals commonly associated with soil creep and slump on slopes underlain by siltstones of the Tyee Formation. Montmorillonite was the major constituent of a large rotational slump at the contact between the Nye Mudstone and the sandstones of the Astoria Formation. Smectite, chlorite, and serpentine were identified in sites underlain by serpentinite of the Otter Point Formation.The mineralogy of soils involved in earthflow consisted predominantly of hydrated and dehydrated halloysite, amorphous material, and chloritic intergrade. No difference in mineralogy could be detected between sites underlain by siltstones of the Tyee and Nestucca Formations and tuffaceous siltstones and tuff of the Siletz River Volcanic Series. Surface samples were more poorly crystallized than samples taken at lower horizons. Electron micrographs reveal an abundance of amorphous gels and “coatings” on the surface of mineral grains. The abundance of “pores” may account for the fluid behavior of these materials during failure.
Approximate Soil Water Movement by Kinematic Characteristics
Authors: Smith Roger E. 
Published: July 2010

AbstractUsing the Richard's equation in the Fokker‐Planck nonlinear diffusion form, unsaturated soil water flow may be treated as a diffusion‐convection wave process. If ∂θ/∂z is assumed a function of θ alone, the unsaturated flow equation may be solved by the method of characteristics, and when ∂θ/∂z becomes sufficiently small, the Peclet number is assumed large enough to treat unsaturated flow kinematically. Changes in θ with depth in the soil profile are treated as waves, moving downward. Advancing and receding “waves” are treated differently in the approximate analytical technique described here, with advancing wetting fronts described by kinematic “shocks.” The method is compared to the complete solution to Richard's equation for a complex rain pattern and found to predict well the location of deeper moving fronts and also general θ patterns. The kinematic method is also shown to apply to root water extraction zones and to layered soil situations.
Chemical Denitrification of Nitrite in Frozen Soils
Authors: Christianson C. B. , Cho C. M. 
Published: July 2010

AbstractThe effect of low temperature on chemodenitrification of nitrite in several Manitoba soils was investigated using highly enriched N‐15 and a mass spectrometric technique, which distinguished between N2 formed via a chemical reaction and that formed via the biological reduction of NO‐2. When a slightly acid soil (pH 6.4) was incubated with NO‐2 concentrations ranging from 25 to 300 µg N/g, the chemical N2 production rate was approximately first order with respect to initial NO‐2 concentration. When the soil was incubated with NO‐2 under different temperatures (+20 to −20°C), the rate of chemical N2 production was found to decrease with decreasing temperature up to −1.8°C. Lowering the temperature to −3.5°C resulted in the rate of N2 production greater than the value observed at 20°C on each concentration. Further decrease in temperature resulted in a gradual decrease in the rate. Similar trends were found with two other slightly acidic soils. The enhancement in the rate of chemodenitrificatoin upon freezing of moist soil was believed to be due to freeze concentration of NO‐2 into an unfrozen layer of soil water near soil colloids. Such an increase in NO‐2 concentration in solution resulted in the rate of denitrification.
Isolation and Identification of Amino Sugars in Soil
Authors: Stevenson F. J. 
Published: July 2010

AbstractChromatographic analysis of amino sugars in soil hydrolysates revealed the occurrence of a wide variety of compounds that gave color reactions typical of amino sugars when analyzed with the classical Elson‐Morgan and indole‐HCl colorimetric methods. The presence in soil of up to 11 amino sugars in addition to glucosamine and galactosamine was indicated. Mannosamine and muramic acid were positively identified and provisional identifications were made for gulosamine and fucosamine. Considerable variation was observed in amino sugar distribution patterns for soils of diverse types. The distribution of amino sugars in a humic acid preparation was similar to that of the original soil. A soil polysaccharide contained amino sugars.
Nitrification Inhibition by Nitrapyrin and Etridiazol in Soils Amended with Sewage Sludge Compost
Authors: McClung G. , Wolf D. C. , Foss J. E. 
Published: July 2010

AbstractNitrification inhibitors, which have been used to reduce fertilizer N losses from soils, may have potential for use with organic soil amendments such as sewage sludge compost. Effects of two nitrification inhibitors, nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] and etridiazol [5‐ethoxy‐3‐(trichloromethyl)‐1,2,4‐thiadiazole] on nitrification were investigated in laboratory studies with Beltsville silt loam (Typic Fragiudult), Hagerstown silty clay loam (Typic Hapludalf), and Pocomoke loamy sand (Typic Umbraquult). The soils were amended with sewage sludge compost at rates of 0.0, 44.6, and 89.2 g/kg and incubated at 25°C, and at compost rates of 0.0 and 89.2 g/kg and incubated at 15°C. In all soil‐compost combinations at either temperature, there were no significant differences between nitrapyrin and etridiazol as measured by NH4‐N or NO3‐N concentrations in the soils. At least 83% inhibition of nitrification was observed in all soil‐compost combinations following 18 weeks of incuhation at 25°C with the highest inhibitor rate of 50 µg/g. After 9 weeks of incubation at 15°C, > 76% inhibition of nitrification was observed in all soil‐compost combinations with the highest inhibitor rate of 10 µg/g. Generally NO3‐N production decreased with increased inhibitor concentration and with decreased compost rate.