bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fitting Ammonia Volatilization Dynamics with a Logistic Equation
Authors: Demeyer P. , Hofman G. , Van Cleemput O. 
Published: July 2010

AbstractTo improve the interpretation of the results from NH3‐volatilization experiments, the cumulative loss rates for different treatments were fitted to a simple logistic equation. This equation is a function: Y = a(1 − e−ct)i, with Y the cumulative N loss (%). The first derivative of this function represents the daily volatilization rate and is Y′ = acie−ct(1 − e−ct)i‐1. Important parameters such as the total cumulative loss (a), and the maximum (Rm) and average (Ra) volatilization rates can easily be calculated. In the case of urea applications, an estimation can be made of the time it takes to hydrolyze all applied urea (th). This parameter also corresponds to the lag phase of the cumulative volatilization curve. Parameter i determines the position of the point of inflection of the curve. For values of i between 0 and 1, volatilization rates cannot be adequately calculated. This can be encountered if the initial volatilization rate is very high, e.g., after ammonium sulphate application upon calcareous soils. In this case, volatilization rates will be estimated by fitting the results to a modified logistic equation in which i = 1. This value of i is most common for NH4NO3 application. The best applicability of the logistic equation is with i values > 1. These values are typical for the shape of cumulative volatilization curves obtained on application of urea‐containing fertilizers. Possible applications of the logistic equation are illustrated by some experimental results.
Methane and Reduced Sulfur Gas Production by Fresh and Dried Wetland Soils
Authors: Crozier C. R. , Devai I. , DeLaune R. D. 
Published: July 2010

AbstractWetland soil microorganisms are probably influenced by fluctuating water levels and by longer‐term climatic change. This study investigated production of CH4 and reduced S gases [H2S, CH3SH, (CH3)2S, COS, and CS2] by both freshly collected and air‐dried, rewet soils from four wetlands in the Mississippi deltaic plain. Soils from three depth intervals (0–10, 10–20, and 20–30 cm) from a swamp forest (Typic Hydraquent), a freshwater marsh (Terric Medisaprist), an intermediate salinity marsh (Typic Medisaprist), and a salt marsh (Typic Medisaprist) were incubated under anaerobic conditions. At repeated time intervals, the headspace gas was analyzed and then purged with N2. Peak production rates of both CH4 and H2S occurred earlier in the fresh soils than in the dried soils in almost all cases. Presumably, this time lag associated with drying was caused by an increase in potentially reducible Mn and Fe. Nevertheless, drying increased labile C levels, thus total CH4 production was similar during the entire 69‐d incubation. Production of CH4 was positively correlated with organic matter content (fresh, R2 = 0.52; dried, R2 = 0.64) and labile C (fresh, R2 = 0.83; dried, R2 = 0.89). Due to their relatively low concentrations, inclusion of soil oxidants in a model did not significantly improve the fit of a model that already contained a term for labile C. Production of S gases was positively correlated with initial SO2−4 concentrations (fresh, R2 = 0.75; dried, R2 = 0.42). Drying significantly decreased total H2S production only for the salt marsh soils. In contrast, the drying treatment increased CH3SH production; only these soils produced (CH3)2S, COS, and CS2.
Wall Material and Capping Effects on Microlysimeter Temperatures and Evaporation
Authors: Evett S. R. , Warrick A. W. , Matthias A. D. 
Published: July 2010

AbstractThe microlysimeter (ML) is useful for measurements of evaporation from soil but questions persist regarding correct ML design. We studied the effects of length and wall material on evaporation and the effects of wall material and capping on ML temperatures. Cylindrical steel and plastic MLs of 10‐, 20‐, and 30‐cm lengths and 8.8‐cm o.d. were used in two field experiments on a bare Pima clay loam (fine‐silty, mixed, thermic Typic Torrifluvent). Steel MLs significantly underestimated 8‐d cumulative evaporation compared with plastic MLs for 20‐cm lengths. Steel MLs conducted heat more easily and their surfaces were significantly cooler during the day and warmer at night than either plastic MLs or the adjacent field soil. Capping the bottoms with 0.6‐cm‐thick plastic disks caused accumulation of heat in the MLs. For plastic MLs, only the 20‐ and 30‐cm lengths were long enough for continuous use for 9 d under our conditions. It was unclear if cumulative evaporation varied with length for steel MLs. We recommend that walls be constructed of material with low thermal conductivity and that end caps be designed to maximize thermal transfer between the soil inside and below the ML. A length of at least 30 cm is recommended if measurements are needed at the same location for several days.
Nitrogen Effects on Conservation of Carbon during Corn Residue Decomposition in Soil
Authors: Green C. J. , Blackmer A. M. , Horton R. 
Published: July 2010

AbstractNitrogen fertilization is widely recognized for its potential to help maintain soil organic matter (SOM) concentrations by increasing plant growth and amounts of plant material decomposed in soils. We studied possible mechanisms by which annual additions of more N than needed to maximize yields of corn (Zea mays L.) could cause losses of SOM. Various amounts of stover and NO−3 were added to a Galva silty clay loam (fine‐silty, mixed, mesic Typic Hapludoll), and NO−3 concentrations and CO2 evolution were monitored for periods up to 90 d at 24°C in the laboratory. The added NO−3 suppressed mineralization of C from SOM and stimulated mineralization of C from stover. Adjustment of rates of stover decomposition to temperature regimes normally encountered in Iowa fields after harvest showed that stover decomposition would not be complete within 1 yr and that increases in NO−3 availability decreased the amount of stover C remaining in the soil. This effect of NO−3 could explain how additions of unneeded N could decrease concentrations of SOM in long‐term studies in which residues and NO−3 are added in annual cycles. These observations suggest that practices that reduce unnecessary fertilization could help conserve SOM and reduce net amounts of CO2 released to the atmosphere.
Amelioration of Degraded Rain Forest Soils by Plantations of Native Trees
Authors: Fisher Richard F. 
Published: July 2010

AbstractEmpirical evidence from temperate Europe and North America indicates that old‐field succession, resulting in reforestation and a protracted period of forest fallow, can improve soil condition on lands once badly degraded. However, the ability of trees to ameliorate degraded sites in the tropics is widely debated. In 1988 eight native tree species: Hyeronima alchorneoides Allemao, Inga edulis Mart., Pentaclethra macroloba (Willd.) Ktze, Pithecellobium macradenium Pittier, Stryphnodendron microstachyum Poepp. et Endl., Virola koschnyi Warb., Vochysia guatemalensis J.D. Smith, and Vochysia ferruginea Mart. and three exotic tree species: Acacia mangium Willd., Gmelina arborea L., and Pinus tecunumanii (Schw.) Equiluz et Perry were planted on abandoned pasture land in northeastern Costa Rica cleared of rain forest 25 yr earlier. Four replicates of 0.25‐ha plots of the 11 species and a control were established in a randomized complete block design. All species survived fairly well, but some grew much better than others. The soil was thoroughly sampled before trees were planted and again 4 yr after trees were established. Although bulk density decreased significantly beneath eight of the 11 species, organic C increased significantly under only three species. Significant increases in base cations also occurred beneath the majority of species. Nitrogen did not increase as much as expected beneath the N2‐fixing legumes; however, the availability of P was significantly enhanced beneath both species of Vochysia. The changes in soil properties were dramatic, and significant amelioration of these degraded soils occurred in a short time beneath the majority of species.
Interactions of Monovalent Organic Cations with Montmorillonite: Adsorption Studies and Model Calculations
Authors: Rytwo G. , Nir S. , Margulies L. 
Published: July 2010

AbstractComplexes between organic cations and clays provide a research tool and have ecological applications. The purpose of this study was to elucidate details of interactions between monovalent organic cationic dyes and montmorillonite. Interactions were studied by x‐ray diffraction and ultraviolet and infrared (IR) spectroscopies, IR linear dichroism, and adsorption isotherm measurements with model calculations. The adsorption model combined electrostatic equations with specific binding and considered neutral and positively charged complexes between surface sites and organic cations in a closed system. The model was extended to account for dye aggregation in solution. The adsorption of the dyes to montmorillonite was described by binding coefficients that were at least six orders of magnitude larger than those of inorganic cations such as Na+ and Cd++. The maximal amounts of crystal violet (CV), methylene blue (MB), and acriflavin adsorbed were 200, 150, and 175%, respectively, of the cation‐exchange capacity (CEC) of the clay mineral. The model also simulated the competition between dyes for adsorption sites. The c‐spacing of montmorillonite increased by the adsorption of CV. With MB at loadings of up to 40% of the CEC, the spacing was reduced, indicating desorption of water from the interlayer space. We conclude that MB lies preferentially parallel to the clay mineral plates, whereas CV lies at a slight inclination relative to the plates.
In Situ Determination of Detrital Breakdown in Wetland Soil‐Floodwater Profile
Authors: Schipper Louis A. , Reddy K. R. 
Published: July 2010

AbstractThe chemical and biological environment in which detritus undergoes breakdown changes markedly with depth through the wetland soil‐floodwater profile. However, it has been difficult to quantify the change in breakdown rate with soil depth due to a lack of suitable methodology. We modified porewater equilibrators to measure breakdown of cattail leaves (Typha sp.) at centimeter depth increments through a wetland soil‐floodwater profile. During the first week, up to 30% of the plant dry‐weight loss occurred at all depths presumably due to leaching, followed by a second phase of breakdown with a further loss of 20 to 30% of initial dry weight in 16 wk. Calculated exponential breakdown constants for the second phase of breakdown were highest in the floodwater (0.0068 d−1) and decreased linearly down the soil profile, with decay constants of <0.003 d−1 at 20 cm below the soil surface. The decrease in the rate of detrital breakdown was partly thought to be driven by decreases in O2 availability. This technique will allow future studies to better quantify organic matter dynamics in wetlands.
Water and Solute Movement in an Undisturbed, Macroporous Column: Extraction Pressure Effects
Authors: Phillips R. E. , Zeleznik J. M. , Quisenberry V. L. 
Published: July 2010

AbstractUndisturbed soil columns are commonly taken to conduct water and solute flow experiments. The proper boundary condition to impose at the bottom boundary of a soil column is most difficult to define and control. The objective of this study was to evaluate the effects of the magnitude of extraction pressure at the lower boundary of the soil column and the water application rate on the amount, distribution, and percentage of leachate and solute drained through the soil column. Water and Cl− were applied to a 325 by 325 by 339 mm undisturbed soil column of a Nolin silt loam soil (fine‐silty, mixed, mesic Dystric Fluventic Eutrochrept). The soil column was placed on a collection chamber that allowed constant extraction pressures (0, − 1.3, or −2.0 kPa) to be maintained at the lower boundary of the soil column. Water containing solute was applied at rates of 5, 10, and 15 mm h−1. The leachate was partitioned into 100 cells. Flow of water and solute through macropores increased as the extraction pressure maintained at the lower boundary of the soil column increased, and as the application rate decreased. Extraction pressure had a greater effect on preferential flow than did application rate.
Predicting Field‐Scale Solute Transport Using In Situ Measurements of Soil Hydraulic Properties
Authors: van Wesenbeeck I. J. , Kachanoski R. G. 
Published: July 2010

AbstractPredicting unsaturated solute transport using measured hydraulic parameters has been difficult due to the inherent variability of soil properties, and the difficulty in obtaining accurate estimates of hydraulic properties in situ. The objective of this study was to determine if in situ measurement of soil hydraulic conductivity, the α soil parameter, and the water content (θ) vs. pressure head (h) relationship could be used to predict field‐scale solute transport. A series of steady‐state solute transport experiments were conducted on a Fox sand (fine‐loamy over sandy or sandy‐skeletal, mixed, mesic Typic Hapludalf) soil in Ontario, Canada. The transport of Cl− under steady‐state water flux was monitored in three separate experiments using solution samplers. Steady‐state water flux densities applied at the soil surface were 9.72 × 10−6, 1.53 × 10−5, and 8.68 × 10−8 m s−1, respectively, for the three sites. After completion of the transport experiments at Site II, measurements of soil hydraulic conductivity and the α parameter were made using the Guelph pressure infiltrometer (GPI) beside each location and depth where solute breakthrough curves (BTCs) were measured, as well as at the soil surface. Undisturbed soil cores were taken at each location where GPI measurements were made for estimating the parameters in the θ(h) using van Genuchten's equations. The GPI‐ and core‐measured hydraulic parameters obtained at Site II were used to predict the field‐scale solute travel time probability density function (PDF) at the same site, and at Sites I and III using a stochastic‐convective model. Observed solute travel time PDFs were predicted quite well at high surface water fluxes, which were close to the field saturated hydraulic conductivity, Kfs by both the GPI and core methods. Both methods underpredicted the variability of the observed travel time PDF.
Determination of Rate Coefficients for Potassium‐Calcium Exchange on Vermiculite using a Stirred‐Flow Chamber
Authors: Bar‐Tal Asher , Eick Matthew J. , Feigenbaum Sala , Sparks Donald L. , Fishman Svetlana 
Published: July 2010

AbstractA stirred‐flow technique has been widely used to study the rate of ion adsorption on clays and soils. However, no mathematical analysis of chemical kinetics combined with mass transport has been used to derive rate coefficients for ion exchange phenomena. Accordingly, the objectives of this study were to: (i) develop a mathematical model of the kinetics of an elementary cation‐exchange reaction combined with transport processes in a stirred‐flow chamber and (ii) determine rate coefficients based on this model for K‐Ca exchange on a vermiculite. The kinetics of exchange were described by a second‐order mechanistic rate law from which the equilibrium exchange equation was derived. The second‐order mechanistic rate law combined with an equation of mass balance describing transport were solved numerically. The equilibrium K‐Ca exchange data were described by the Gaines and Thomas approach with a thermodynamic exchange equilibrium constant Kex = 754.6 L mol−1. The values of the apparent adsorption rate coefficient (ka) ranged from 84 to 185 L2 mol−2 min−1, as influent rate increased from 0.3 to 2.0 mL min−1. The calculated K‐Ca exchange half‐life (t1/2) ranged from 0.5 to 1.5 min, in agreement with published data based on batch methods.
Earthworm (Lumbricus rubellus and Aporrectodea caliginosa) Effects on Carbon Flux in Soil
Authors: Zhang Q. L. , Hendrix P. F. 
Published: July 2010

AbstractEffects of earthworm activities on litter and soil C flux were studied in a laboratory incubation experiment using two types of isotopic tracers and two earthworms with different ecological strategies‐Lumbricus rubellus, an epigeic species, and Aporrectodea caliginosa, an endogeic species. The soil was prelabeled with 14C. Dry sorghum [Sorghum bicolor (L.) Moench] leaves labeled with 13C were applied to the soil surface. Activity of both earthworm species significantly (P < 0.001) enhanced total C efflux (479 ± 8 [standard error], 483 ± 4, and 395 ± 5 mg C jar−1 for L. rubellus, A. caliginosa, and the control, respectively) and significantly (P < 0.05) reduced total surface soil microbial biomass (251.7, 205.2, and 312.1 mg C kg−1 soil for L. rubellus, A. caliginosa, and the control, respectively) during the 30‐d incubation. Activity of A. caliginosa also reduced subsurface soil microbial biomass. The epigeic earthworms assimilated significantly more 13C from the litter and significantly less 14C from the soil than the endogeic species. In the absence of earthworms, 14C in the soil was translocated into the surface litter, as shown by a 15.5‐fold increase in 14C enrichment in the surface litter by the end of the experiment. This translocation of soil C into the litter was significantly reduced by earthworm activities (155.43, 121.11, and 240.58 kBq kg−1 litter for L. rubellus, A. caliginosa, and the control, respectively), possibly due to disruption by earthworms of fungal‐hyphal connections between litter and soil. These interactions between earthworms and soil microbial processes have important implications for soil C turnover.
Seasonal Soil Nitrate Dynamics in Corn as Affected by Tillage and Nitrogen Source
Authors: Dou Z. , Fox R. H. , Toth J. D. 
Published: July 2010

AbstractA better understanding of seasonal soil NO−3 dynamics in corn (Zea mays L.) as affected by different tillage and N sources is essential to refine N management options for more profitable production and less negative impact on water resources. We conducted an experiment in central Pennsylvania to study seasonal soil NO−3 dynamics in corn managed with conventional tillage (CT) or no‐till (NT) and supplied with commercial N fertilizer or legume green manures of red clover (Trifolium pratense L.) or hairy vetch (Vicia villosa Roth) double‐cropped with winter wheat (Triticum aestivum L.). The legume cover crops and winter fallow after the wheat harvest were followed by two corn crops. Soil samples taken biweekly during the corn growing seasons were analyzed for NO−3 concentrations in the 0‐ to 25‐ (Ap horizon) and 25‐ to 45‐cm (upper B horizon) soil layers. In the first corn crop, soil NO−3 concentrations peaked about 4 wk after planting in all treatments. Where no broadcast N fertilizer was applied, mid‐ to late‐season soil NO−3‐N concentrations in the Ap horizon averaged 6, 25, and 1.3 mg kg−1 in the clover CT, vetch CT, and fallow CT treatments, respectively, while the NO−3‐N concentrations in all NT 0 N treatments were similar (1.3–1.9 mg kg−1). After the first corn harvest, the clover and vetch CT 0 N treatments had 113 and 124 kg NO−3‐N ha−1 in the 120‐cm soil profile, slightly higher than that estimated for the fallow treatment with N fertilizer at the economic optimum rate (99 kg NO−3‐N ha−1). No‐tillage also reduced the amount of NO−3 accumulated in the 0‐ to 120‐cm soil profile to one‐half of the NO−3 levels in the corresponding CT treatments, regardless of N source. Both tillage and N source strongly affected seasonal soil NO−3 dynamics in the first corn season, with the major difference appearing in the Ap horizon.
Experimental Formation of Aquod‐like Features in Sandy Coastal Plain Soils
Authors: Harris W. G. , Crownover S. H. , Comerford N. B. 
Published: July 2010

AbstractCoastal‐plain Spodosols of the southeastern USA are inexplicably associated with fluctuating water tables. This study tested hypotheses that account for water‐table influence in Aquod genesis: (i) sand‐grain coatings are released when Fe (a binding agent) is dissolved by organic acids; (ii) coatings migrate to form an eluvial‐illuvial sequence; (iii) C and metals accumulate in the illuvial matrix; (iv) imperfectly drained sands are predisposed to podzolization due to low crystalline Fe; and (v) a minimum solution residence time near the site of acid release is required. Toeslope and summit positions on hillslopes were sampled and subjected to physical, chemical, and mineralogical characterization. Iron dissolution at increasing loading rates of oxalic acid was monitored by batch extractions. A column experiment was conducted to test predisposition and residence‐time effects on formation of Aquod‐like features and on effluent composition. Columns were eluted daily with oxalic acid (0.001, 0.05, and 0.01 M) under freely drained or 22‐h saturation conditions. Ratios of iron/aluminum in oxalic acid extracts were higher at higher loading rates. Iron abundance and crystallinity increased from toeslopes to summits. Aquod‐like features (light eluvial zones, darkened lamellae, etc.) developed most conspicuously in toeslope columns, and only for the 22‐h residence treatment. Columns most affected released less Fe, Al, and oxalic acid. Results supported our hypotheses for laboratory conditions. Further study is needed using in situ methods and indigenous solution components.
Soil Properties beneath Ceanothus and Pine Stands in the Eastern Sierra Nevada
Authors: Johnson Dale W. 
Published: July 2010

AbstractSoils and soil solutions were collected from adjacent ceanothus (Ceanothus velutinus Dougl.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf) stands in Little Valley, Nevada. It was hypothesized that excessive N fixation by ceanothus, like red alder (Alnus rubra Bong.), causes accelerated nitrification, NO−3 leaching, and soil acidification. This hypothesis was not supported. Comparisons of soils from five paired ceanothus‐pine plots showed that ceanothus soils not only had greater C and N concentrations, but also greater cation‐exchange capacity, base saturation, and exchangeable Ca2+, Mg2+, and K+ than pine soils. There were no significant differences in extractable P or SO2−4 overall, although there were differences at some sites. Extractable P levels were quite high relative to more humid forest soils, whereas extractable SO2−4 levels were very low. Soil solutions from ceanothus, pine, and a riparian mountain alder (Alnus tenuifolia Nutt.) stand were characterized by low NO−3 concentrations, circumneutral pH, and high base cation, HCO−3, SO2−4, Cl−, and Si concentrations. The chemical composition of nearby streamwaters was similar to that of soil solutions with respect to NO−3, pH, HCO−3, and base cation and Si concentrations. Streamwater SO2−4 and Cl− concentrations (≈ 3–17 µmolc L−1) were more than an order of magnitude lower than those in soil solutions (≈ 150–270 µmolc L−1), however, indicating that soils adjacent to the stream had little influence on its chemistry. Thus, the NO−3 pulse (from <1 to ≈ 30 µmolc L−1) measured in both streamwaters and ceanothus soil solutions during snowmelt most likely originated from the melting snowpack.