bluuebunny/crossref_metadata_2025_split huggingface dataset:
Persistence of Loosened Horizons and Soybean Yield Increases in Bolivia
Authors: Barber R. G. 
Published: July 2010

AbstractSoil compaction is a major factor limiting soybean [Glycine max (L.) Merr.] production in tropical eastern Bolivia. An experiment was conducted from 1985 through 1989 on a fine‐loamy, siliceous, isohyperthermic Aquic Ustropept with a compacted horizon (0.12–0.33 m) to determine the persistence of subsoil loosening by deep tillage and its effect on soybean yield responses. Four tillage treatments were investigated: conventional tillage consisting of disk harrowing to 0.12‐m depth (CN), subsoiling in 1985 only to 0.40‐m depth (SS/85), disk plowing in 1985 only to 0.30‐m depth (DP/85), and annual subsoiling (SS/YR). All three deep tillage treatments completely loosened the compacted horizon, reducing penetrometer resistance (PR) from a maximum of 3.05 to 2.01 MPa. From December 1987 onward, which coincided with an exceptionally wet period, subsoil reconsolidation occurred, and by June 1989 the PR of CN, DP/85, and SS/85 exceeded 3 MPa. Reconsolidation was attributed to a close‐packing rearrangement of soil particles under wet conditions. Coupled with increasing subsoil strength, a relatively greater reconsolidation occurred in SS/85 and DP/85, resulting in reduced “loosened” zones of 0.07‐m and 0.04‐m thickness, respectively. The pattern of relative reconsolidation suggests it occurred from above downward and from below upward, the latter perhaps being related to a high water table. In contrast SS/YR maintained a much thicker “loosened” horizon. overall subsoil reconsolidation, soybean yield responses continued for 3 yr with SS/85, and for 4 yr with DP/85 and SS/YR. Although substantial differences in relative reconsolidation existed between DP/85, SS/85, and SS/YR, few significant differences in yield were found when soil water was limiting.
New Mexican Locust and Parent Material: Influence on Forest Floor and Soil Macronutrients
Authors: Klemmedson James O. 
Published: July 2010

AbstractThe effect of the New Mexican locust (Robinia neomexicana Gray) on N, P, S, and Ca, Mg, K and organic C in the soil‐litter system of a ponderosa pine (Pinus ponderosa Douglas, ex P. Lawson & Lawson) forest in central Arizona was studied on sites with either basalt or limestone parent material. Samples of the Oi and Oe + Oa horizons (forest floor) and 0‐ to 5‐ and 5‐ to 15‐cm soil layers from 10 pairs (with and without locust) of randomly located pine stands were sampled and analyzed for total N, P, and S, total (forest floor) and exchangeable (mineral soil) Ca, Mg, and K, and organic C (Corg). The 10 stand pairs represented five sites with basalt and five with limestone parent material. There were no significant parent material × locust interactions for the nutrients considered. Locust presence increased nutrient concentrations of N and Ca most strongly (in both Oe + Oa and soil layers) and Corg, P, S, and K concentrations to a lesser extent. Concentrations of N, P, and K were significantly higher in mineral soils derived from basalt. Increased amounts of N in forest floor and mineral soil, and increased amount of P, Ca, Mg, and K in the forest floor were associated with locust presence. Amounts of Corg, N, P, and exchangeable K were greater in soil components of stands with basalt parent material. Forest floor mass was greatest for basalt sites with locust; this and nutrient composition differences between locust leaves and pine needles suggest greater nutrient differences between parent materials may accrue with age of locust stands.
Simplified Model of Integrated Water and Solute Uptake by Salts‐ and Selenium‐Accumulating Plants
Authors: Ben‐Asher J. 
Published: July 2010

AbstractThe rate of soil salinization and the accumulation of toxic ions in soils are affected by evapotranspiration and the uptake of ions by plant roots. These are two counteracting processes and the interrelationship between them can be quantified by a mathematical model. The objectives of this study were to: (i) formulate an analytical model describing soil salinization and accumulation of toxic ions and (ii) suggest a criterion for irrigation water quality (C*0) and demonstrate its behavior under varying transpiration rates. The processes by which the soil becomes saline were simulated with an analytical solution to the convection‐diffusion equation. The model was based on ion and water uptake by plant roots. The calculations indicated that crops classified as salinity tolerant remove more salt from the soil than salinity‐sensitive crops. The rates of ion removal are 5, 15, and 40 × 10−3 dS m−1 d−1 for salinity‐sensitive, semisensitive, and tolerant crops, respectively. Therefore the ratio between the uptake rates of ions and water per unit soil volume is presented here as a criterion for the upper limit of allowable salinity in irrigation water. This ratio is inversely related to transpiration rate (evaporation neglected). Theoretically, the maximum allowable salinity of salt‐tolerant crops, C*0, decreases from 20 to 4 dS m−1 when the transpiration rate increases from 2 to 10 × 10−3 m d−1. For the same transpiration rate increase, C*0 of sensitive crops decreases from 3 to 0.5 dS m−1; thus, a lower quality of water can be permitted for irrigation in a moderate or cool climate than in an arid climate. The model applies also for Se‐accumulating crops. Theoretically, at a transpiration rate of 5 × 10−3 m d−1, Se can be removed from a soil solution containing a high concentration (C*0 = 1 mg kg−1) when the uptake rate of the growing crop is 25.8 × 10−3 mg kg−1 d−1.
Simulation of Cation Exchange Involving Hydrogen Ion in Soil
Authors: Houng Kun‐Huang 
Published: July 2010

AbstractA computer program for simulating cation‐exchange reactions in soil was developed and used for simulating the determination of exchangeable acidity with 1 M KCl and of hydrolytic acidity with 1 M NaOAc. The acidification process resulting from extraction of an initially base‐saturated soil with a dilute solution of an acid having various dissociation constant may also be simulated. From the calculated pH‐base saturation relationships for assumed K‐H exchange coefficent (KK‐H) varying from 1 × 101 to 1 × 10−6, it is noted that for KK‐H values of 1 × 10−n, the inflection point of the pH‐base saturation curve is at the pH value of n. Thus, the permanent charge sites of mineral soils appeared to have a KK‐H value of 1 × 10−1 and greater, while for the pH‐dependent charge sites the KK‐H values are smaller than 1 × 10−2. The acidity extracted by 1 M KCl solution corresponded to the H+ on the permanent charge sites, with KK‐H values of 1 × 10−2 and greater, but it may also include some portions of H+ bound on exchange sites with KK‐H values smaller than 1 × 10−2. Exchangeable H+ from sites with KK‐H smaller than 1 × 10−5 were practically not displaced by 1 M KCl solution. The use of 1 M NaOAc instead of Kcl could quantitatively displace the H+ held on the sites with KNa‐H values >1 × 10−3 by a single extraction, while those of 1 × 10−6 and greater may be displaced by repeated extractions. Calculations with KNa‐H values of 1 × 10−7 did not converge, but available soil data indicate that the pH‐dependent sites of soils have KNa‐H values in the order of 1 × 10−7. Use of a dilute acid solution in place of KCl or NaOAc solution simulates the acidification process of acid precipitations.
Purge‐and‐Trap Extraction of Geosmin and 2‐Methylisoborneol from Soil
Authors: Stahl Peter D. , Parkin Timothy B. 
Published: July 2010

AbstractAlthough a number of techniques are available for estimating the biomass of filamentous microorganisms in soil, determination of their activity is much more difficult. We report on preliminary studies evaluating the potential use of the volatile microbial secondary metabolites geosmin and methylisoborneol as indicators of activity of filamentous microorganisms. The purge‐and‐trap technique for analysis of low concentrations of volatile organic compounds in air and water was tested for extracting the earthy‐musty odor compounds geosmin and 2‐methylisoborneol from soil. Two variations of this method were tried, one in which soil samples were placed in water for purging and another in which samples were purged with no added water. Volatile organic compounds purged from soil were collected on a porous polymer sorbent, Tenax TA. Naturally occurring geosmin and 2‐methylisoborneol and added standards were successfully extracted from soil by both methods. Recovery efficiencies, however, were low. Results indicated that wet purging was the most efficacious extraction method yielding maximum recovery rates of added geosmin and 2‐methylisoborneol standards of 15 and 24%, respectively.
Phosphorus Relationships in Flooded Rice Soils with Low Extractable Phosphorus
Authors: Shahandeh H. , Hossner L. R. , Turner F. T. 
Published: July 2010

AbstractRice (Oryza sativa L.) grain yields on some flooded soils are not increased by P fertilizer despite their low soil test P status determined on air‐dry soils by soil test methods such as Bray, Olsen, or Texas A&M. Conventional soil test methods apparently do not accurately assess the capacity of these soils to supply P to rice grown under flooded conditions. To test the possibility of an Fe‐P association, oxalate extractant (which would extract noncrystalline Fe and its associated P) was used to provide a more accurate measure of available P in flooded soil. Phosphorus response experiments were conducted on 10 rice soils under greenhouse and field conditions and related to the oxalate‐extractable Fe and P, P uptake, P adsorption, and P desorption under aerobic and anaerobic conditions. Oxalate‐extractable Fe significantly increased under anaerobic conditions in all soils including the soils that were nonresponsive to P and had low levels of extractable P using conventional extractants. Phosphorus adsorption and desorption data confirmed the importance of oxalate extractant in predicting P availability following anaerobiosis. The inability of Bray 1, Olsen, and Texas A&M soil test methods to accurately predict P availability in flooded rice soil appears to be due to their failure to extract the active reductant‐soluble P fraction. The measurement of P associated with poorly crystalline Fe by oxalate extractant is a useful soil test method for predicting the availability of P in flooded rice soils.
Sodium‐Affected Soil Identification in South‐Central Illinois by Electromagnetic Induction
Authors: Nettleton W. D. , Bushue L. , Doolittle J. A. , Endres T. J. , Indorante S. J. 
Published: July 2010

AbstractThe irregular shape, small size, and spotty occurrence of sodium‐affected soils (NaAS) in moderately thick to thin loess over Illinoian till have continued to slow mapping in south‐central Illinois. Use of a Geonics EM‐38 ground conductivity meter to recognize soils with natric horizons in Tennessee suggested that this device would be useful in Illinois. We selected eight areas of NaAS in five counties of south‐central Illinois to find if the EM‐38 would be useful for predicting exchangeable sodium percentage (ESP). Approximately 225 observation points, spaced at 10‐m intervals, were established in each area and 107 sample cores were collected for laboratory analyses. Weighted averages of the ESP, electrical conductivity of the saturation extract from a saturated soil paste (ECe), and field pH data for 0 to 75‐ and 75 to 150‐cm depths were compared with the horizontal (EMh) and vertical (EMv) responses and the mean ESP data increases with depth, i.e., 7.0 at 35 cm, 9.7 at 75 cm, and 12.5 at 135 cm. The EMh readings correlate almost as well with ESP (r = 0.73) as with ECe (r = 0.76) for the 0‐ to 75‐cm depths. The EMv readings correlate slightly better with ESP (r = 0.76) than with ECe (r = 0.68) for the 75‐ to 150‐cm depth. These results show that EM readings may by used to predict ESP. The correlations of the depth‐weighted average ESP at the maximum depth for meeting natric horizon criteria in these soils (75 cm), and the EMv readings show that the EM‐38 provides a rapid and accurate method to describe the composition of the map units of NaAS on moderately thick to thin loess over Illinoian till in south‐central Illinois.
Soil Structural Form and Stability, and Organic Matter under Cool‐Season Perennial Grasses
Authors: Carter M. R. , Kunelius H. T. , Angers D. A. 
Published: July 2010

AbstractTemperate grasses conserve soil by providing vegetative cover and by favoring soil aggregation. A field study was conducted on a Charlottetown fine sandy loam (a coarse‐loamy, mixed, frigid Typic Haplorthod) to determine the effect of cultivars of orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.), in comparison to timothy (Phleum pratense L.), on soil structure and organic matter fractions after 4 yr of growth. Timothy is one of the main grasses grown in the cool humid climate of eastern Canada. Bulk density (1.27–1.32 Mg m−3), pore‐size distribution, and shear strength (12.5–15.6 kPa), as a measure of soil structural form, were within the optimum range for this soil type under each grass species. Dry‐aggregate mean weight diameter (MWD) was similar (3.66–4.30 mm) among grass species. Wet‐aggregate MWD was greater under tall fescue cultivars and ‘Farol’ timothy (2.81–3.22 mm) compared with the orchardgrass and ‘Champ’ timothy (2.08–2.36 mm). These differences were also reflected by the difference or ratio of MWD between dry and wet sieving. Aggregate‐size distribution indicated that wet‐aggregate MWD differences were associated with greater levels of macroaggregates (>2 mm). Differences in water‐stable aggregate stability were not related to differences in plant parameters, organic matter, or organic matter fractions (i.e., microbial biomass C, carbohydrates, and particulate organic matter). These data suggest that organic matter parameters, commonly used to characterize soil stability in cropping systems, are less useful for soils under perennial grass with stable microaggregate structures.
Measuring and Predicting Ridge‐Orientation Effect on Soil Surface Roughness
Authors: Saleh Ali 
Published: July 2010

AbstractSurface roughness significantly reduces soil erosion by wind. Methods commonly used to measure soil roughness function only in parallel and perpendicular directions to the oriented (ridge) roughness. This study was conducted to develop a simple procedure to estimate soil roughness at any given angle with respect to ridge orientation, for aggregated or nonaggregated ridged surfaces. Surface roughness was determined by the chain method. Surface roughness measured at different angles on simulated and field plots matched very closely (R2 ≥ 0.985, P ≤ 0.001) with those predicted from equations developed in this study. This simple method enables one to estimate a surface roughness parameter for any wind direction with respect to ridge orientation. This should result in a better evaluation of roughness influence on wind erosion.
Methane Production and Emissions from Four Reclaimed and Pristine Wetlands of Southeastern United States
Authors: Schipper Louis A. , Reddy K. R. 
Published: July 2010

AbstractWetlands are significant contributors to global CH4 emission. We measured CH4 emissions at two pristine wetlands [Okefenokee swamp and the Everglades (Water Conservation Area 2A)] and two reclaimed wetlands (Sunny Hill Farm and Apopka Marsh) in Southeastern USA, and we attempted to relate emissions to CH4 production rates of the soil and the soil's biological and chemical properties. Methane emissions through cattail [Typha sp.] and waterlily [Nymphaea ordorata (L.)] ranged from 0.09 to 1.7 g CH4 m−2 d−1 and exhibited high spatial and temporal variability. Diffusive flux of CH4 was calculated using dissolved CH4 profiles in the soil pore water and accounted for <5% of the plant‐mediated emissions. Potential CH4 production rates were measured as a function of depth using soil samples obtained at 2‐cm increments. Methane production rates were the same order of magnitude at all sites (<1–70 ng CH4‐C g−1 soil C d−1) and were highest in the surface soils (0–6 cm) at three of the wetland sites, indicating that the predominant source of C available to methanogens was in the surface soils. Methane production rates in the top 24 cm ranged from 0.3 to 1.1 g CH4 m−2 d−1 and annual C losses due to anaerobic decomposition accounted for between 0.68 and 3.7% of the total C in the surface 24‐cm soil depth. Methane production was observed at sites with porewater SO4 concentrations of up to 20 mg SO4‐S L−1, suggesting that methanogenesis occurred in the same soil layer as SO4 reduction, possibly in microsites where SO4 concentration was depleted.
Measurement of Soil Thermal Properties with a Dual‐Probe Heat‐Pulse Technique
Authors: Bristow Keith L. , Kluitenberg Gerard J. , Horton Robert 
Published: July 2010

AbstractAlthough soil thermal properties are required in many areas of engineering, micrometeorology, agronomy, and soil science, they are seldom measured on a routine basis. Reasons for this are unclear, but may be related to a lack of suitable instrumentation and appropriate theory. We developed a theory for the radial conduction of a short‐duration heat pulse away from an infinite line source, and compared it with the theory for an instantaneously heated line source. By measuring the temperature response at a short distance from the line source, and applying short‐duration heat‐pulse theory, we can extract all the soil thermal properties, the thermal diffusivity, heat capacity, and conductivity, from a single heat‐pulse measurement. Results of initial experiments carried out on air‐dry sand and clay materials indicate that this heat‐pulse method yields soil thermal properties that compare well with thermal properties measured by independent methods.
Network Modeling of Diffusion Coefficients for Porous Media: I. Theory and Model Development
Authors: Steele D. D. , Nieber J. L. 
Published: July 2010

AbstractGas diffusion often dominates constituent transport in porous media and is dependent on pore geometry, water content, and water distribution in a porous medium. Network models of porous media offer the ability to investigate the influence and interaction of pore‐scale porous media properties and fluid properties on macroscopic properties of the medium. This study was conducted to investigate the macroscopic relative gas diffusion coefficient vs. air‐filled porosity relationship (diffusion characteristic) of porous media using a network modeling approach. A cubic sphere‐and‐tube network model of porous media was adapted from petroleum engineering using Fick's law and the principle of conservation of mass to simulate one‐dimensional, steady‐state, isothermal, isobaric, molecular diffusion of a dilute binary gas in a nonadsorbing porous medium containing a single nonwetting fluid (air) and a single wetting fluid (water). The network model simulates hysteresis in air and water distributions in porous media for boundary drying and wetting curves of the soil water characteristic and demonstrates the effect of air‐filled porosity, Henry's law liquid‐gas partitioning coefficient, the ratio between gas‐ and liquid‐phase diffusion rates, and pore geometry on the diffusion characteristic.
Factors Affecting Field‐Saturated Hydraulic Conductivity Measured by the Borehole Permeameter Technique
Authors: Campbell C. M. , Fritton D. D. 
Published: July 2010

AbstractThe borehole permeameter method for measuring field‐saturated hydraulic conductivity, Kfs, is prone to variability due to soil smearing during borehole excavation, and swelling that results from differences in initial soil‐water content. The effects of borehole preparation techniques and initial soil‐water pressure on Kfs were analyzed in this study. Eighty boreholes were studied in a strongly structured clayey soil (a fine, mixed, mesic Typic Hapludalf). A version of the borehole permeameter method was used to measure Kfs in soil that was initially at soil‐water pressures of 0, −0.016, −0.050 and −0.080 MPa. Three different borehole excavation techniques were also studied to determine the effect on Kfs of soil smearing during borehole preparation. The treatments consisted of removing a uniform thickness of soil from the sides of the borehole with an ice pick, scarifying the sides of the borehole with a wire brush, and no treatment. Field‐saturated hydraulic conductivity for the brushed treatments was similar to Kfs values obtained when no treatment was used. The ice pick method resulted in significantly higher Kfs. When Kfs values measured using the ice pick method were analyzed, no significant effect of initial soil‐water pressure was evident. This could possibly be due to soil variability.
Steady‐State Temperature Distribution in Nonisothermal, Unsaturated Closed Soil Cells
Authors: Prunty Lyle , Horton Robert 
Published: July 2010

AbstractAmbient temperature interference (ATI) is a concern that has not been adequately addressed in studies of coupled water and heat transport in unsaturated soil. Our objectives were to detect ATI, minimize it, and obtain nonisothermal, steady‐state temperature and moisture profiles with minimum ATI. Two soils, a sand and a silty clay loam (sicl), were packed into cylindrical cells with uniform moisture. Temperature gradients were imposed by making one end warmer (40, 23, or 19°C) than the other end (1 or 9°C). Steady‐state temperature profile data were obtained for various cell configurations and ambient temperatures. The configuration showing least ATI was a 2.5‐cm‐diam., 5‐cm‐long cell, with 8 cm radial insulation. Longer cells of the same basic design or with less insulation had greater ATI, as did a larger diameter cell (4 cm diam. and 14 cm long). All tests (sand at 0.049 m3 m−3 moisture; sicl at 0.049 and 0.146 m3 m−3) using lowest ATI cells produced concave upward temperature profiles. In contrast, the larger diameter cell (sicl, high ATI) had concave downward profiles. Water redistribution into the cooler half of cells was more pronounced with sand (>90%) than sicl. Cells exhibiting low ATI appear to provide more consistent and meaningful soil temperature and moisture profiles than had previously been obtainable.
Cation Exchange Chemistry of Hexadecyltrimethylammonium in a Subsoil Containing Vermiculite
Authors: Xu Shihe , Boyd Stephen A. 
Published: July 2010

AbstractSubstituting native inorganic exchangeable cations of soil clays with cationic surfactants like hexadecyltrimethylammonium (HDTMA) greatly increases the sorption of organic contaminants, and hence reduces their transport potential. Both static and kinetic studies were conducted to probe the inorganic‐HDTMA exchange processes in a subsoil containing vermiculite and to determine the chemical stability of the resultant HDTMA‐soil complexes. The HDTMA generally had much higher affinity for the clay surface than inorganic cations native to soil and thus HDTMA saturation of soil resulted in a low residual HDTMA concentration in solution (≈ 10−6 to 10−5 M). Conditions leading to flocculation of soil clays (e.g., high ionic strength or divalent exchangeable cations) resulted in inorganic cation entrapment in the interlayers of clays and decreased cation selectivity coefficients of inorganic‐HDTMA exchange. Under these conditions, a portion of HDTMA was adsorbed via nonpolar interactions (hydrophobic bonding) resulting in a higher residual concentration of HDTMA in solution (≈ 10−4 M) and a greater tendency for HDTMA desorption. The change in electrophoretic mobility of soil clays and turbidity of soil suspensions as HDTMA loading increased suggested that HDTMA, if adsorbed via cation exchange mechanism, caused clay aggregation and tended to distribute on the internal sites of the aggregates, leaving inorganic cations on external surfaces. The kinetic study revealed that inorganic‐HDTMA exchange was fast on external surfaces but slow on internal sites of Al‐hydroxy‐interlayered vermiculites or flocculated vermiculites where the inorganic cation entrapment had been found. We concluded that the most stable HDTMA‐soil complexes form at HDTMA loading of 0.6 to 0.7 cation‐exchange capacity for nonsodic soils.