bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurement of Microbial Biomass by Fumigation‐Extraction in Soil Stored Frozen
Authors: Winter Julien P. , Zhang Zhiyuan , Tenuta Mario , Voroney R. Paul 
Published: July 2010

AbstractThis research examined the effect of freezing on soil microbial C and N measured by CHCl3 fumigation‐extraction (CFE). A soil was stored frozen (−15°C) and sampled after 1, 7, and 170 d. Compared with a nonfrozen soil, freezing had no effect on microbial C or N, except after 7 d when C increased by 24% and N increased by 34%. The soil was also subjected to freeze‐thaw cycles (18/6 h). Microbial C and N were unaffected by one cycle, increased with two, and decreased with three cycles. In a second experiment, soil was amended with 14C‐glucose and incubated for 1, 7, or 35 d (25°C), then stored frozen for either 1, 7, 21, or 35 d. Soil incubated for 1 d showed a decline in microbial 14C (measured by CFE) after freezing for 7 to 35 d. Soil incubated for 7 and 35 d contained a 14C microbial population that was unaffected by freezing. At first glance, these observations indicated that the CFE assay was not greatly affected by freezing soils; however, closer examination indicated that microbial mortality had been masked by a freezing‐induced improvement in CFE efficiency. Increased efficiency may have resulted from improved aggregate dispersal following freezing. Homogenization of soil samples improved extraction of microbial C by 40%. In conclusion, we don't recommend that soils be frozen prior to CFE. Also, the physical disruption of soil during CFE must be severe to remove any interference of aggregate stability on the results of this assay.
Parameters Affecting Residue Nitrogen Mineralization in Flooded Soils
Authors: Becker M. , Ladha J. K. , Simpson I. C. , Ottow J. C. G. 
Published: July 2010

AbstractIf N mineralization from organic residues could be matched to plant uptake, N loss will be reduced. However, it is important to understand the transformations of residues and their controlling factors. Six‐week phytotron and two‐season field experiments were conducted to determine the influence of soil properties, residue composition, and soil fauna on N mineralization in flooded soils. Seven legume species, three legume‐rice (Oryza sativa L.) straw combinations, rice straw alone, and an Azolla sp. were incorporated into two soils (an Andaqueptic Haplaquoll and a Tropofluvent) at 100 mg N kg−1 dry soil and incubated for 6 wk. Residue N release in clay was about twice that of sandy soil, but was not correlated with the residues' N, C/N, water, or polyphenol contents. Net N mineralization was correlated to lignin/N (L/N). In the field, Sesbania rostrata Brem. & Oberm. and S. emerus Taub were incorporated at 60 kg N ha−1 1 d before rice transplanting. Additionally, rice straw was applied at 30 kg N ha−1 alone or with S. rostrata. Soil exchangeable NH+4‐N in unplanted light and dark subplots was measured biweekly. As in the phytotron study, initial soil NH+4‐N accumulation rates were higher from residues with relatively low L/N (S. rostrata) than from materials with higher L/N (S. emerus and S. rostrata‐rice straw mixture). Soil invertebrates were absent from dark subplots, where residue N mineralization during the first 6 wk was 30% lower than in plots exposed to light. The L/N of an applied residue may be a suitable indicator for predicting its N mineralization rate in flooded soils. Soil invertebrates may play a role in N mineralization.
Regression Models for Estimating Soil Properties by Landscape Position
Authors: Brubaker S. C. , Jones A. J. , Frank K. , Lewis D. T. 
Published: July 2010

AbstractSlope geometry and the associated variation in soil properties influence runoff, drainage, soil temperature, the extent of soil erosion and deposition, and crop yields. With the current emphasis on prescription farming, approaches are needed to more effectively match inputs to production system needs while accounting for variation in soil and water resources within a field. The objective of the study was to develop simplified regression models to predict soil properties on different landscape positions from observed values on the nearly level upper interfluve. Soil samples were taken from the upper and lower interfluve, shoulder, upper and lower linear, and footslope at each of four sites in eastern Nebraska. Predictive equations were developed for 20 soil properties using multiple linear regression. Independent variables included were observed values of the property being modeled from the upper interfluve, sampling depth, and an irrigation code. Of the 100 models developed, only eight included significant contributions from all three independent variables. Models for pH, organic matter, electrical conductivity, exchangeable K, base saturation percentage, and available P and K consistently had R2 values greater than 0.50. The upper interfluve contributed significantly to the prediction of each of these properties except electrical conductivity. A comparison between average observed and predicted values for each soil property at each sampling depth revealed that the observed values generally fell within a 95% confidence interval about the predicted values. The confidence interval half‐width was generally <10% of the mean for the observed values. Further evaluation with independent data sets could be used to help strengthen and refine such generalized or geographically based models.
Characterization of the Least Limiting Water Range of Soils
Authors: da Silva A. P. , Kay B. D. , Perfect E. 
Published: July 2010

AbstractThe supplies of O2 and water and the mechanical impedance of soil are determined by soil structural form and soil water content. The range in soil water content in which limitations for plant growth associated with matric pressure, aeration, and mechanical resistance are minimal was defined as the least limiting water range (LLWR). This study was carried out to evaluate the LLWR as an index of the structural quality of soils. Undisturbed soil cores were taken from the 5‐ to 10‐cm depth of a silt loam and a loamy sand, cropped to corn (Zea mays L.) and red clover (Trifolium pratense L.). Soil water retention, soil resistance, air‐filled porosity, and bulk density (Db) were measured. Water contents at critical limits associated with field capacity (−0.01 MPa), wilting point (−1.5 MPa), air‐filled porosity (10%), and soil resistance (2.0 MPa) were predicted and the LLWR calculated for each measured Db. The natural variation in Db on both soils gave rise to a wide variation in LLWR. Values of LLWR varied from 0 to 0.14 cm3 cm−3 for the silt loam soil and from 0.05 to 0.13 cm3 cm−3 for the loamy sand soil. At Db above 1.36 g cm−3 for the silt loam and 1.43 g cm−3 for the loamy sand, the LLWR declined sharply with increasing bulk density. Further research relating LLWR to crop response is required before LLWR can be recommended as a soil structural quality index for crop production.
Heterogeneous Flow and Solute Transport in an Unsaturated Stony Soil Monolith
Authors: Buchter B. , Hinz C. , Flury M. , Flühler H. 
Published: July 2010

AbstractField studies of solute transport have shown that water flow velocity may vary tremendously across a field. To assess the effects of flow heterogeneity on solute transport in a stony subsoil, miscible displacement experiments were conducted in a large undisturbed gravel monolith (75‐cm length, 30‐cm diam.). The soil sample contained about 0.8 kg kg−1 of gravel. Two consecutive pulses (runs) of a Cl− solution were leached through the monolith, each at matric pressures ranging from −2.0 to −2.2 kPa. The cumulated outflows, collected with 19 separate porous plates located at the bottom, ranged from 0 to 3000 mL. The outflow rates of the individual plates were constant and highly correlated between the two runs (r = 0.95). The Cl− breakthrough curves (BTCs) of the total and individual BTCs could be well described by the classical convective‐dispersive equation. Pore water velocities, dispersion coefficients, and dispersivities of the two runs indicated a high correlation of the breakthrough behavior of the individual outlets (r = 0.995, 0.88, and 0.97, respectively). In addition, the iodine starch method revealed a heterogeneous flow pattern. Even though the column was resaturated and drained between the two runs, the results between the two consecutive runs were consistent. This suggests that the flow paths of water remained invariant and might be an intrinsic feature of a soil medium for a given water content.
Propagation Velocity Errors in Time Domain Reflectometry Measurements of Soil Water
Authors: Hook W. R. , Livingston N. J. 
Published: July 2010

AbstractThe determination of soil water content by time domain reflectometry (TDR) involves two steps: the measurement of the propagation velocity of an electromagnetic pulse along a transmission line and the conversion of this measurement to an estimate of soil water content. The objective of this study was to identify and quantify errors associated with propagation velocity measurements. We developed new TDR techniques, involving the use of remotely switched diodes and differential wave form detection, that can be used to quantify and minimize propagation velocity errors. These errors are presented in terms of time interval errors. We show that the dominant time interval error term relates to the transition time of reflected pulses and that absolute time interval errors cannot be assumed to be <200 ps. We identify the presence of dissolved ions and the use of long cables as major sources of additional transition time errors. For transition times >2 ns, the time interval error caused by transition time effects can be estimated as the root mean square sum of the basic 200‐ps error and an error equal to 10% of the transition time. We show that although instrument time base errors are the main source of precision errors, they are less important in determining the absolute accuracy of propagation velocity measurements. We show that system costs can be reduced without compromising accuracy by using 75 Ω coaxial cable, which is not only inexpensive but is superior to standard 50 Ω cable.
Using Short Soil Moisture Probes with High‐Bandwidth Time Domain Reflectometry Instruments
Authors: Kelly Shaun F. , Selker John S. , Green James L. 
Published: July 2010

AbstractTime domain reflectometry (TDR) is used to measure moisture content and salinity of soils. Most TDR systems have a bandwidth of 2.5 GHz or less, limiting the precision of measurements using short probes. The primary objective of this research was to develop and test short probes for use with a high‐bandwidth (20‐GHz) TDR instrument. The secondary objective was to determine moisture content in highly conductive media by insulating the probes with Teflon heat‐shrinkable tubing. Laboratory‐packed test cells with probe lengths of 0.025, 0.05, and 0.075 m were used for the primary research objective, and 0.075‐m probes for the secondary objective. Linear relationships between the apparent refractive index and volumetric moisture content were developed for each probe length and type. The accuracy of the probes was ±0.0125, ±0.05, ±0.025, and ±0.035 m3/m3 for the probes of lengths 0.075, 0.075 (insulated), 0.05, and 0.025 m, respectively. Moisture measurements in highly conductive media were possible using insulated probes.
Reactions of Ground Magnesium Limestone and Gypsum in Soils with Variable‐Charge Minerals
Authors: Shamshuddin J. , Ismail H. 
Published: July 2010

AbstractUltisols and Oxisols in Malaysia are characterized by low pH and high Al, with their subsoils usually deficient in Ca, Mg, or both. An experiment, using polyvinyl chloride columns, was conducted to study chemical reactions in a representative Ultisol and Oxisol from Malaysia resulting from application of ground magnesium limestone (GML), gypsum, and their combinations. An increase in soil pH due to GML application in the Ultisol and the Oxisol resulted in an increase in negative charge on the soil surfaces in the zone of incorporation. Calcium was retained in that zone. In the gypsum‐treated soils, some Ca moved into the underlying horizons. Negative charge in the Oxisol increased from 2.8 to 3.7 cmolc kg−1 by an application of 8 t gypsum ha−1 due to specific adsorption of SO4 on Fe oxides. An increase in pH of the Oxisol due to SO4 adsorption and OH desorption was also observed. There was an accumulation of NO3 in the subsoils of the Oxisol and Ultisol as a result of gypsum treatment. The NO3 was adsorbed by the positively charged oxides. Leachate pH values were high at the beginning of the experiment, but the values decreased with time and were higher in the Oxisol than the Ultisol. This was attributed to a lower Al concentration in the leachate of the Oxisol. Effective alleviation of topsoil Al toxicity and subsoil Ca or Mg deficiency would require the application of 2 t GML together with 1 to 2 t gypsum ha−1.
Zinc and Cadmium Uptake by Hyperaccumulator Thlaspi caerulescens Grown in Nutrient Solution
Authors: Brown S. L. , Chaney R. L. , Angle J. S. , Baker A. J. M. 
Published: July 2010

AbstractPhytoremediation of heavy‐metal‐contaminated soils can be an inexpensive means to remove hazardous metals from soil. Two metallophytes, Thlaspi caerulescents (J. & C. Presl, a Zn and Cd hyperaccumulator) from Prayon, Belgium, and a Zn‐tolerant ecotype of bladder campion [Silene vulgaris (Moench.) Garcke L.] from Palmerton, PA, were compared with tomato [Lycopersicon lycopersicum (L.) Karsten, metal intolerant] in nutrient solution to characterize Zn and Cd uptake and tolerance. Zinc and Cd were added to solutions at a 50:1 molar ratio to simulate concentrations often found on contaminated sites. Seven treatment concentrations were used, ranging (in half‐log increments) from 3.16 µM Zn + 0.063 µM Cd to 10000 µM Zn + 200 µM Cd. Thlaspi caerulescens showed much greater tolerance to Zn/Cd treatments than the other species, with toxicity stress only apparent at the 10000 µM Zn/200 µM Cd treatment. In this treatment, shoot concentrations of Zn and Cd were 33600 and 1140 mg kg−1, respectively. Thlaspi caerulescens was also more effective at translocating both Zn and Cd from solution to shoots. Zinc concentration in shoots of T. caerulescens was higher than the other species at all Zn/Cd treatments. Cadmium concentration in shoots of T. caerulescens were significantly higher than in bladder campion only at the 316 µM Zn/6.32 µM Cd treatment. This genotype of T. caerulescens may not hyperaccumulate Cd. However, extreme Zn and Cd uptake and tolerance is evident in T. caerulescens, with >25000 mg Zn kg−1 and 1000 mg Cd kg−1 before yield is reduced. Results suggest that T. caerulescens may be a candidate for the phytoremediation of Zncontaminated soils.
Effect of Cropping and Fertilization on Plant and Soil Phosphorus
Authors: Selles F. , Campbell C. A. , Zentner R. P. 
Published: July 2010

AbstractKnowledge regarding the effects of long‐term cropping practices and fertilization on the fate of P applied to the soil is required to aid in the prediction of how such practices influence the quality and sustainability of the environment. A 24‐yr crop rotation experiment, conducted on a Swinton silt loam (Aridic Haploboroll) in southern Saskatchewan, was used to determine uptake of P by crops, its distribution in grain and straw, and the rate of change and nature of the residual P in the soil. Phosphorus concentration in the grain relative to that in the straw was 7:1 to 12:1 for spring wheat (Triticum aestivum L.), 6:1 for flax (Linum usitatissimum L.), and 5:1 for lentil (Lens culinaris Medikus) and fall rye (Secale cereale L.). Grain P concentration was lowest in cereal crops (3.6 g kg−1) and highest in flax and lentil (4.4 g kg−1). Phosphorus removed annually with the grain increased with P fertilization and decreased with an increase in fallow frequency; it was 4.8 to 5.3 kg P ha−1 for continuous wheat, 3.5 to 3.8 kg P ha−1 for fallow‐wheat‐wheat, and 3.1 kg P ha−1 for fallow‐wheat. Trend analysis showed that fertilizer P increased the Olsen P levels in soil at rates of 1.0 to 1.7 kg ha−1 yr−1, but in the systems receiving no P, Olsen P remained constant and did not decline as suggested by a P balance sheet. Residual fertilizer P accumulated in labile forms, dominated by sorbed P and microbial P, rather than in forms dominated by Ca phosphate precipitates or other organic forms.
Deep Tillage Effects on Compacted Surface‐Mined Land
Authors: Dunker R. E. , Hooks C. L. , Vance S. L. , Darmody R. G. 
Published: July 2010

AbstractFederal law requires that surface‐mined prime farmland be reclaimed and restored to premining productivity for row crops (Surface Mining Control and Reclamation Act, Public Law 95–87). In Illinois, reclamation must include soil horizon replacement (topsoil and subsoil) to a depth of 120 cm. Poor physical condition is the most limiting factor in reclarmation in Illinois. The effects of five deep tillage implements (80–120‐cm tillage depth) and two standard agricultural chisel plows (20–35‐cm tillage depth) were evaluated for 6 yr. The seven tillage treatments were applied to a scraper‐placed minesoil that had a high soil strength (2.5–3.5 MPa) throughout the reconstructed profile. A nearby tract of undisturbed Cisne silt loam (fine, montmorillonitic, mesic Mollic Albaqualf) was used as a prime farmland comparison. Crop yields for both corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] significantly increased with tillage depth. Average soil strength decreased and net water extraction increased with increasing depth of tillage. The 1.2‐m‐deep tillage treatments significantly reduced average 23‐ to 114‐cm soil strength from 2.8 to 0.93 MPa. Significant correlation occurred between 23‐ to 114‐cm average soil strength and 6‐yr mean corn (−0.97** [significant at P = 0.01]) and 4‐yr mean soybean (−0.92**) yields. Deep tillage successfully restored productivity; however, the depth of tillage necessary was influenced by initial levels of soil strength.
Simulated Small‐Channel Bed Scour and Head Cut Erosion Rates Compared
Authors: Zhu J. C. , Gantzer C. J. , Peyton R. L. , Alberts E. E. , Anderson S. H. 
Published: July 2010

AbstractConcentrated‐flow erosion is often a major part of cropland erosion. The concentrated‐flow processes of bed scour and head cut need improved characterization to better predict and prevent erosion. This study was conducted to compare the erosion rates due to simulated small‐scale bed‐scour (Db) and head‐cut (Dh) processes. A 6.4‐m‐long by 0.15‐m‐wide hydraulic flume was used to simulate concentrated‐flow erosion on five Midwestern soils: Barnes (fine‐loamy, mixed Udic Haploboroll), Forman (fine‐loamy, mixed Udic Argiboroll), Mexico (fine, montmorillonitic, mesic Udollic Ochraqualf), Sharpsburg (fine, montmorillonitic, mesic Typic Argiudoll), and Sverdrup (sandy, mixed Udic Haploboroll). For slopes of 1.5, 3.5, and 5.0%, flow rates of 3.78, 5.67, 7.65, 11.34, and 15.12 L min−1 were used to provide a range from low (0.5 Pa) to moderate (2.5 Pa) shear stresses (τ). Soil detachment rates are functions of slope, flow rate, and shear stress. Slope, flow, their squares, and the slope × flow interaction were highly significant predictors of Db. Only flow, its square, and its interaction with slope were significant predictors of Db. Nonlinear power regressions using τ as an independent variable were better predictors of detachment than simple linear regressions. Erodibility for the soils from this study does not relate well with soil erodibility calculated using the Universal Soil Loss Equation. Differences in the slope and intercept of detachment vs. τ exist among soils. The value of Db was at least four times greater than Db for all soils at equal slope and flow rate, indicating that head cutting is the main process of detachment for the conditions tested.
Rhizosphere Phosphorus Depletion Induced by Heavy Nitrogen Fertilization in Forest Nursery Soils
Authors: Teng Y. , Timmer V. R. 
Published: July 2010

AbstractThe cause of N‐induced P deficiency in white spruce [Picea glauca (Moench) Voss] seedlings was investigated in a greenhouse pot trial testing factorial additions of ammonium nitrate (AN) and phosphoric acid (PA) to root zone and root‐free compartmentalized soils. Plant growth was significantly improved by combined N and P topdressings during the growing season. However, N‐only fertilization induced P deficiency symptoms and reduced biomass and P status in shoots, demonstrating an apparent N antagonism on P. Phosphorus availability in this treatment also was 35% lower in the rhizosphere soil than in the root‐free bulk soil, reflecting rhizosphere P depletion. Soil acidity and Al activity were increased most by AN‐only applications, probably contributing to reduced P availability. A diagnosis of induced Al toxicity by N fertilization based on plant analysis data was supported by symptoms of root injury. Phosphorus capture by ion‐exchange resin bags at the base of the pots was lower than that of N with combined N‐P applications, suggesting rapid fixation and low mobility of P in the soil compared with N. Nitrogen‐induced rhizosphere P depletion in this nursery soil was attributed to restricted root development of seedlings due to Al toxicity, reduced P availability by Al‐phosphate precipitation, and low P replenishment because of slow diffusion from the bulk soil. Topdressing with both PA and AN increased P availability in the rhizosphere (320 mg kg−1), reduced soil extractable Al by 40% compared with AN‐alone treatments, and increased plant uptake of N and P by 270%, resulting in positive N × P interactions on plant growth.
Soil Carbon Stocks of the Brazilian Amazon Basin
Authors: Moraes Jener L. , Cerri Carlos C. , Melillo Jerry M. , Kicklighter David , Neill Christopher , Skole David L. , Steudler Paul A. 
Published: July 2010

AbstractWe determined stocks of C and N for soils under undisturbed vegetation across the Brazilian Amazon Basin based on 1162 soil profiles of the RADAMBRASIL survey and a digitized Brazilian soil survey map. Mean basin soil C density was 10.3 kg C m−2. Forty‐seven petagrams C and 4.4 Pg N were contained in the top 1 m of soil. Forty‐five percent of total basin soil C (21 Pg C) and 41% of total soil N (1.8 Pg N) were contained in the top 20 cm across a ≈ 5 000 000‐km2 area. Mean C/N ratio for the basin to a depth of 1 m was 10.7. Because these data represent sites with forest vegetation in the absence of significant disturbances, they represent a valuable baseline for evaluating the effects of land‐use changes on soil C stocks in the Amazon Basin.