bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Situ Decomposition of Grass Roots as Affected by Elevated Atmospheric Carbon Dioxide
Authors: van Ginkel J. H. , Gorissen A. 
Published: July 2010

AbstractThe effects of elevated CO2 on belowground C input, on decomposition of roots in situ vs. decomposition of disturbed roots, and on soil microbial biomass were investigated in a perennial grass species. Forty ryegrass (Lolium perenne L.) plants were homogeneously 14C‐labeled in two controlled environments for 115 d in a continuous 14CO2 atmosphere at 350 and 700 µL CO2 L‐1 and two soil N levels (low, LN, and high, HN). Thereafter, some of the plants were destructively harvested. Undisturbed root systems of the remaining plants were incubated in situ (IRS) for comparison with a disturbed incubation of the dried and ground roots (DRS) in their original soils. At the start of the incubation, elevated CO2 had increased total 14C‐labeled soil C input by 44 and 27% at LN and HN, respectively, compared with input at ambient CO2. After incubation for 230 d, 40% of 14C soil content was mineralized to 14CO2 in the disturbed system and 52% in the intact system. Native soil organic matter (SOM) decomposition of the DRS was lower than the SOM decomposition of the IRS. The formation of 14C‐labeled soil microbial biomass (14C‐SMB) in the soil with DRS was 130% higher than in the soil with the IRS. Elevated CO2 decreased the decomposition of roots and root‐derived products by 10% and increased the size of the 14C‐SMB by 28% for both IRS and DRS, whereas the decomposition of SOM was not affected by CO2 at either LN or HN. After plant growth and in situ incubation, the 14C‐labeled C in the soil solution showed a highly positive correlation with the amount of 14C‐SMB. The ratio between 14C‐labeled microorganisms and total 14CO2 evolved was not affected by elevated CO2. It seems that microorganisms adapt to changing soil C input under elevated CO2 and there is no effect on their turnover and behavior.
Water and Nitrogen Management of Sugarcane Grown on Sandy, High‐Water‐Table Soil
Authors: Obreza T. A. , Pitts D. J. , Anderson D. L. 
Published: July 2010

AbstractLittle information exists regarding water and N fertilizer management for sugarcane (Saccharum spp.) production on Florida's high‐water‐table sandy soils. We hypothesized that sugar yield and N‐use efficiency would be affected by water table depth and N fertilizer application timing. Sugarcane (cv. CP 72‐1210) was grown in >1‐ha plots for three seasons on Basinger sand (siliceous, hyperthermic Spodic Psammaquent) to determine the effects of water table depth (0.46 vs. 0.57 m), N fertilization frequency (13 vs. 7 split applications for 3 yr, at 224 kg N ha‐1 yr‐1), and Mg fertilizer rate (0 vs. 60 kg Mg ha‐1 yr‐1) on cane and sugar yields. Annual mean high‐ and low‐water‐table differences were 0.13, 0.11, and 0.10 m, resulting in a 0.2 to 1.4 J kg‐1 difference in soil water matric potential at middle of the root zone, and a 0.02 to 0.11 m3 m‐3 difference in soil water concentration in the top 0.30 m. Three‐year mean yields for low vs. high water table were 73.7 vs. 67.9 t sugarcane ha‐1 and 9.23 vs. 8.51 t sugar ha‐1. High vs. low N fertilization frequency yielded 75.0 vs. 66.5 t sugarcane ha‐1 and 9.41 vs. 8.33 t sugar ha‐1. There were no water level × N fertilization frequency interactions. Where mean Mehlich 1 extractable Mg was 25 mg kg‐1, Mg fertilization did not affect yield, suggesting that this Mg level should be classified in the unresponsive (“high”) range. Although increasing N fertilization frequency increases the fertilization program cost, its use is justified by increased sugar yield.
Predicting Long‐Term Soil Carbon Storage from Short‐Term Information
Authors: Hyvönen Riitta , Ågren Göran I. , Bosatta Ernesto 
Published: July 2010

AbstractChanges in land use and in climate may induce changes in soil organic matter storage in different ecosystems. Predictions of future soil organic matter storage are based on extrapolations from short‐term observations. Certain errors in the extrapolation procedure will have larger consequences than others. We analyzed this error propagation using the continuous‐quality theory. We show that parameter values that predict litter‐decomposition rates within 5% for 2 yr can give rise to errors in steady‐state soil organic matter stores of a factor of three or more, whereas comparable errors in parameter estimates derived from decomposition studies of whole soil organic matter keep the deviations in soil organic matter within 10%. The processes that have to be quantified most accurately are those regulating the interaction between soil organic matter and soil texture and those regulating the rate of change in the quality of the soil organic matter during decomposition. The error propagation from errors in decomposer growth rate, and hence climatic factors, and litter quality is limited, but that from decomposer efficiency is somewhat higher. We also compared the continuous‐quality approach with some other models.
Preferential Flow in Water‐Repellent Sands
Authors: Bauters Tim W. J. , Steenhuis Tammo S. , Parlange Jean‐Yves , DiCarlo David A. 
Published: July 2010

AbstractWater‐repellent soils occur all over the world and affect both groundwater pollution and crop yield. The finger‐like wetting patterns in these soils have many similarities with unstable wetting fronts in coarse‐grained sandy soils. Our objectives were to study the water movement in water‐repellent sand and to examine how the theory for unstable wetting fronts applies to water‐repellent sands. Infiltration experiments, in which moisture content and matric potentials were measured, were carried out in slab chambers with identical sands but with different levels of water repellence. Soil water characteristics were determined in separate experiments. Infiltration in the hydrophilic soil resulted in a uniform and horizontal front. All water‐repellent sands showed a fingered flow pattern. For negative water‐entry values, water infiltrated without delay. For positive values, water entered the soil only after the depth of the ponded water equaled or exceeded the water‐entry pressure, which increased with increasing repellency. The finger widths predicted with the unstable flow theory agreed rather well with the observed values. In general, the research showed that the wetting patterns of water‐repellent sands depended directly on the soil water characteristic curve. This implies that the type of wetting front and risk to groundwater pollution can be predicted based on laboratory‐measured soil hydraulic properties.
A Field Apparatus for Measuring Unconfined Compressive Strength
Authors: Cook B. J. , Nimlos T. J. 
Published: July 2010

AbstractLaboratory techniques for measuring unconfined compressive strength are standardized by testing groups (e.g., American Association of State Highway and Transportation Officials), often requiring technologically complex and expensive equipment. However, much of this technology is not available in developing countries. We describe the construction, operation, calibration, and application of a modified hydraulic jack for determining unconfined compressive strength. Three calibration curves are presented to provide options for laboratories with varying technological capabilities. Application shows that variation in measurements comes from natural variation within materials rather than from the modified jack. Our modified jack is simple, inexpensive, and precise. Testing shows it to have a high correlation to standard laboratory techniques (R2 = 0.89) and establishes it as a reliable measure of unconfined compressive strength.
Reaction Sequence of Nickel(II) with Kaolinite: Mineral Dissolution and Surface Complexation and Precipitation
Authors: Eick Matthew J. , Fendorf Scott E. 
Published: July 2010

AbstractThe dissolution kinetics of Ni(II) sorbed to kaolinite at pH 7 were examined as a function of initial aqueous Ni(II) concentrations; the local molecular structure of the Ni surface complexes were determined using extended x‐ray absorption fine structure (EXAFS) spectroscopy. The dissolution of kaolinite was nonstoichiometric with a preferential release of Si over Al. The dissolution rate, RSi, increased with an increase in the aqueous concentration of Ni. A rate law was developed representing a fractional‐order dissolution reaction with respect to the surface concentration of Ni. Absorption spectra were obtained from kaolinite samples washed with 0.10 M NaNO3 adjusted to pH 3.4 to remove amorphous Al‐hydroxide surface deposits or adsorbed Al and from kaolinite that was untreated. For all samples, EXAFS results revealed the presence of multinuclear Ni surface complexes with a similar, but not identical, local structural environment to pure crystalline Ni(OH)2. The Ni‐Ni bond distances were shorter (3.06–3.11 Å) than in Ni(OH)2(s) (3.13 Å) and increased with an increase in surface coverage. Additionally, Al was present in all but the highest surface coverage as a second neighbor backscatterer. At the lower surface coverages (Γ ≤ 0.406 µmol m‐2), Al is present at 2.69 Å, indicating the formation of a bidentate Ni surface complex. With increased surface coverage, the d(Ni‐Al) increases to 2.96 Å, which is believed to result from a Ni,Al‐hydroxide precipitate. No significant structural differences were found between kaolinite pretreatments. Based on these results, a hypothesized mechanism for Ni sorption on kaolinite is proposed.
Flow and Reactivity Effects on Dissolved Organic Matter Transport in Soil Columns
Authors: Weigand Harald , Totsche Kai U. 
Published: July 2010

AbstractDissolved organic matter (DOM) plays a prominent role in the transport of contaminants in porous media. As DOM has to be considered as a reactive component, flow regime and sorbent reactivity should affect overall DOM transport in an important way. We focused on DOM transport in unsaturated column experiments using quartz sand (QS) and goethite‐coated quartz sand (GS). Rate constrictions to DOM sorption were investigated by varying the volumetric flow rate, while extent and reversibility of sorption were studied in consecutive adsorption and desorption steps. In the QS, DOM retention was low and unaffected by changes in flow rate. Desorption‐step breakthrough curves (BTCs) and mass balances show full reversibility of the sorption process. However, DOM retention in GS was significant and sensitive to flow variation, indicative of nonequilibrium sorption. At lower flow rates, DOM breakthrough exhibited a change in curvature (shoulder) due to the superimposition of two BTCs representing reactive and nonreactive DOM fractions. Transport was successfully modeled assuming these two fractions governed overall DOM mobility. At higher flow rates, the BTC shoulder vanished due to reduced contact time between the DOM and the solid phase (rate‐limited sorption). Sorption of DOM on GS is accompanied by a marked rise in effluent pH, indicative of a ligand‐exchange mechanism. Recovery of DOM during desorption was incomplete due to either partially irreversible sorption or strongly rate‐limited desorption. Increased DOM mobility in the consecutive adsorption step resulted from partial blocking of sorption sites by the initial pulse of DOM.
Estimating Calcium‐Magnesium Selectivity in Smectitic Soils from Organic Matter and Texture
Authors: Curtin D. , Selles F. , Steppuhn H. 
Published: July 2010

AbstractSelectivity coefficients are essential to describe the distribution of cations between the exchange and solution phases of soil. Because the factors influencing Ca‐Mg exchange have not been adequately defined, models commonly incorporate the dubious assumption that soils do not discriminate between these two cations (i.e., the selectivity coefficient is 1). The purpose of this study was to identify key variables influencing Ca‐Mg selectivity in smectite‐dominated soils of the Canadian prairies. Selectivity coefficients (K) were measured by reacting soils that differed in texture (50–500 g clay kg‐1), organic matter (4–96 g C kg‐1), and pH (4.1–7.3) with solutions containing mixtures of CaCl2 and MgCl2. The value of K for the reaction Ca + Mg‐soil ⇌ Mg + Ca‐soil ranged from 1.1 to 3.4, depending on soil type and the composition of the reacting solution. Preference for Ca increased as the equivalent fraction of Ca in solution decreased from 0.8 (average K = 1.7) to 0.05 (average K = 2.9). We identified organic matter as the major source of Ca‐preferring sites. The ratio of organic matter to clay was the best single indicator of Ca‐Mg selectivity. Measurements on soils whose pH had been altered by laboratory addition of Ca(OH)2 or field application of anhydrous NH3 indicated that selectivity was independent of pH, even though the proportion of organic sites increased as pH increased. A simple two‐site model with K of 3.9 for organic matter and K of 1.3 for clay described our data reasonably well, although selectivity for Ca tended to be underpredicted at low Ca loading.
Increased Soil Enzyme Activities under Two Row Crops
Authors: Bergstrom D. W. , Monreal C. M. 
Published: July 2010

AbstractThis study examined the influence of crop on the spatial pattern of soil enzyme activities in a Rego Humic Gleysol (Aquoll) strip‐cropped to corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. Soil samples (0–23‐cm depth) were collected at 20‐cm spacings along transects across adjacent plant rows. Activities of dehydrogenase, urease, glutaminase, phosphatase, arylsulfatase, and β‐glucosidase were compared for soil samples collected from within vs. between crop rows. Spectral analysis was used to test for a cyclical pattern of soil enzyme activities along transects. The spatial pattern of all six soil enzyme activities was sometimes influenced by the crop. Greater enzyme activity in the row than in the furrow was observed in approximately one‐third of the cases examined. In approximately two‐thirds of the cases where the class comparison indicated greater enzyme activity in the row than in the furrow, enzyme activity appeared to cycle at a period equal to the row spacing. Periodograms also indicated cycling at other periods, and there was considerable random variation in enzyme activities along the transects. Dehydrogenase and β‐glucosidase activities differed between strips of corn and soybean on some sampling dates. The spatial pattern of soil enzyme activities indicated that they behaved similarly as general indices of microbial activity at the scale of measurement. Comparisons of soil enzyme activities between sites within the growing season should account for influence of the crop.
Arbuscular Mycorrhizae and Water Stress Tolerance of Wyoming Big Sagebrush Seedlings
Authors: Stahl Peter D. , Frost Sandra M. , Williams Stephen E. , Schuman Gerald E. 
Published: July 2010

AbstractAlthough Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) is widespread in the western USA, reestablishment of this native shrub on disturbed lands by direct seeding is problematic. A number of theories have been proposed to explain this difficulty. Included are the hypotheses that seedlings are unable to obtain adequate moisture and are handicapped by reduced levels of mycorrhizae in perturbed soils. We conducted a greenhouse study to examine the influence of vesicular arbuscular mycorrhizae (VAM) and seedling age on soil moisture stress tolerance of Wyoming big sagebrush seedlings. Results demonstrated greater survival of mycorrhizal seedlings than nonmycorrhizal seedlings as soil dried down past soil water potential values of ‐2.5 MPa to as dry as −3.8 MPa. For all different aged seedlings tested (30, 45, 60, 90, 120, 150 d), the degree of soil dryness resulting in death of mycorrhizal seedlings was significantly greater (P < 0.01) than that causing death of nonmycorrhizal seedlings. Analysis of variance indicated a significant interaction of seedling age and mycorrhizae on moisture stress tolerance. Experimental data suggest that as sagebrush seedlings age, the beneficial influence of arbuscular mycorrhizae on soil water stress tolerance increases.
Ammonia Volatilization from Urea Amended with Triple Superphosphate and Potassium Chloride
Authors: Ouyang D. S. , Mackenzie A. F. , Fan M. X. 
Published: July 2010

AbstractAmmonia volatilization from urea reduces N fertilizer efficiency of crops. Addition of acidic materials to urea may reduce NH3 volatilization and improve N use efficiency. The objectives of this study were to compare the effects of compacted or blended mixtures of urea and triple superphosphate (TSP), urea and KCl, or urea, TSP, and KCl on NH3 volatilization and N use efficiency by corn (Zea mays L.) under a no‐till system. A Ste. Rosalie clay (Typic Humaquept) and an Ormstown silty clay loam (Typic Humaquept) were used with three rates of TSP (0, 26, and 52 kg P ha‐1) and two rates of KCl (0 and 100 kg K ha‐1). Total NH3 volatilization for 9 d following fertilization ranged from 27 to 31 g kg‐1 of added urea‐N on the Ste. Rosalie soil and from 50 to 82 g kg‐1 on the Ormstown soil with urea alone. Ammonia volatilization decreased when TSP, KCl, or both were applied with urea. Nitrogen recovery of added urea, N use efficiency, and corn yields increased with added TSP and KCl. Compacted mixtures of urea with TSP, KCl, or both had an advantage over blended fertilizers in reducing NH3 volatilization and improving N use efficiency and corn yields.
Impact of Saturated Hydraulic Conductivity on the Prediction of Tile Flow
Authors: Mohanty B. P. , Skaggs T. H. , van Genuchten M. Th. 
Published: July 2010

AbstractPreferential flow through macropores and other structural voids in field soils most often occurs at or near saturation. Our earlier research revealed significant differences in the value of the saturated hydraulic conductivity (Ks) of a glacial till soil in central Iowa when obtained with five different measurement techniques. The five techniques included one laboratory constant‐head permeameter method and four in situ methods: disc permeameter, Guelph permeameter, velocity permeameter, and double‐tube permeameter. Differences in measured Ks values were attributed to differences in sample size, the existence or absence of open‐ended macropores, and measurement principles. In this study, we used the different Ks estimates in a two‐dimensional numerical model, CHAIN_2D, to predict water flow into a subsurface tile drain in the same field. Comparisons between predicted and observed tile flows were made during four crop growing seasons. Preferential flow observed in the tile drain during large storm events was predicted best by the model when using Ks values measured with the disc permeameter method, which least disturbed the boundary conditions of the flow field and better accounted for the macropore structures of the field soil. Quantitative and qualitative findings suggest that the disc permeameter was best suited for the field site.
Determination of Soluble Phosphorus in the Presence of Organic Ligands or Fluoride
Authors: He Z. L. , Baligar V. C. , Ritchey K. D. , Martens D. C. 
Published: July 2010

AbstractIn the ascorbic acid‐molybdenum blue method for measurement of soluble P, the relationship between color intensity and P concentration in solution and color stability is greatly affected by organic and inorganic ligands such as oxalate, citrate, tartrate, or F. The objective of this study was to evaluate the effect of these ligands and to optimize the conditions for determination of inorganic P in the presence of the interfering ligand. The critical concentrations of the ligand at which P recovery was significantly decreased were 1.5 mM for oxalate, 3.0 mM for citrate or tartrate, and 10 mM for fluoride. The interference of the ligand with P determination was overcome by excess amounts of ammonium molybdate (AM) added before the color developing reagent (CDR). The critical molybdate/ligand molar ratios (excluding the amount of molybdate added in the CDR) required to completely eliminate the interference of the ligand were 1.12 for oxalate, 0.84 for citrate, 0.56 for fluoride, and 0.34 for tartrate. The presence of ligand and excess amount of AM did not affect the linearity of color intensity against P concentration but did alter the slope, suggesting that the modified method is reliable for P determination in the presence of an interfering ligand provided that the standard curve is prepared in the same matrix as the sample.
Quantification of Biodegradable Dissolved Organic Carbon in Soil Solution with Flow‐Through Bioreactors
Authors: Yano Yuriko , McDowell William H. , Kinner Nancy E. 
Published: July 2010

AbstractA flow‐through bioreactor method for drinking water or stream water was modified for the rapid determination of biodegradable dissolved organic C (BDOC) in small, discrete samples such as soil solutions collected in lysimeters. Biodegradable dissolved organic C was measured as the difference in dissolved organic C (DOC) concentration between the inlet and outlet when a sample was pumped through a column colonized by indigenous soil microbes. Both feed water and sample solutions were adjusted to ≈ 10 mg C L‐1 to maintain a consistent environment in the column, and inorganic nutrients (N, P, S, and K) were added to avoid a nutrient limitation on C degradation. Biodegradable dissolved organic C values obtained by this method were consistent for a year and were insensitive to changes in ambient temperature (13–24°C) and flow rate (0.36–0.42 mL min‐1). Dextrose, humic acid, and dextrose‐humic acid solutions were used to test the bioreactors. Only 5% or less of the humic acid C was lost in the bioreactor, suggesting limited abiotic sorption of C. Nearly 100% loss of dextrose, coupled with large increases in dissolved inorganic C (DIC), suggested biotic degradation of BDOC within the bioreactors.
Long‐Term Effects of Fertilization and Rotation on Denitrification and Soil Carbon
Authors: Drury C. F. , Oloya T. O. , Tan C. S. , van Luyk C. L. , McKenney D. J. , Gregorich E. G. 
Published: July 2010

AbstractVarious long‐term crop management strategies are known to have differing effects on soil organic C. This laboratory study explored the effect of long‐term (35 yr) fertilization and crop rotation on soil organic C and denitrification capacity at different depths of a Brookston clay loam soil (fine‐loamy, mixed, mesic Typic Argiaquoll). We related denitrification capacity to soil biochemical (CO2 production, organic C, microbial biomass C, soluble organic C) and soil structural properties. Denitrification capacity was determined as the increase in N2O that occurred when NO‐3‐amended soils were incubated anaerobically in the presence of acetylene. Treatments included fertilized and nonfertilized plots of continuous corn (Zea mays L.), continuous bluegrass (Poa pratensis L.), and rotation corn (corn‐oat [Avena sativa L.]‐alfalfa [Medicago sativa L.]‐alfalfa). Soils from an adjacent mixed deciduous woodlot were also sampled. Soils from the woodlot had higher denitrification capacities than the continuous or rotation corn treatments. Among the agricultural treatments, the soil under bluegrass had the greatest denitrification capacity followed by the soil under corn rotation, with the continuous corn having the lowest capacity. Long‐term fertilization resulted in 35% higher denitrification capacity and 65% higher CO2 production than nonfertilized soils. Denitrification capacity across all depths in the agricultural soils was correlated with CO2 production (r2 = 0.76), microbial biomass C (r2 = 0.60), and organic C (r2 = 0.54); however, the relationship between denitrification capacity and soil structure was not as strong (r2 = 0.28).