bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Management Influences on Zinc Desorption for Rice and Maize Nutrition
Authors: Mandal Biswapati , Hazra G. C. , Mandal L. N.
Published: July 2010

In a rice‐based cropping system soils are often subjected to different moisture regimes, which may influence desorption of adsorbed Zn and thus limit Zn availability to crops. Laboratory and greenhouse experiments were conducted to study the effect of moisture regimes with or without organic matter addition on changes in desorption of adsorbed Zn in soils and its utilization by rice and maize plants. Three different moisture regimes, flooded–dried, alternate wetting and drying and preflooding, with (50 g kg−1) and without (0 g kg−1) added organic matter were imposed in two Alfisols and two Inceptisols of West Bengal, India. Percent desorption of adsorbed Zn was significantly higher in Alfisols (64.5%) than in Inceptisols (45.5%). Desorption was also significantly higher under flooded–dried (61.4%), alternate wetting and drying (67.1%), and preflooding (47.3%) moisture treatments than in the control (43.4%). Organic matter application enhanced desorption under flooded–dried and alternate wetting and drying but decreased it under preflooding. The variation in Zn desorption among soils and moisture treatments is the result of changes in soil pH, Fe‐oxides, bonding energy constants, and free energies for Zn adsorption. Greenhouse experiments showed that dry matter yield and uptake and utilization of Zn for maize were higher under flooded–dried. For rice, yield and Zn accumulation were higher under preflooding treatments compared to the control in which the soils were not subjected to these pre‐plant moisture treatments. Soil‐zinc data and plant response were in close agreement, except in Inceptisols for rice under preflooding with added organic matter treatment. Results indicated a more efficient use of Zn fertilizer where maize followed rice, and where rice was grown after preflooding the soils.
A Functional Approach to Soil Characterization in Support of Precision Agriculture
Authors: Van Alphen B. J. , Stoorvogel J. J.
Published: July 2010

Managing soil variability is an integral aspect of precision agriculture (PA). Existing soil databases, however, are found to match few of the requirements for PA. The nature of these requirements and their implications for soil information need to be further explored. Ongoing developments towards a decision support system (DSS) for PA in the Netherlands have shed some light on this issue. Two soil related DSS‐components are presented: (i) the construction of a soil database at the farm level and (ii) the delineation of soil functional units at the field level. Developed methods were tested in a case study for two arable fields located on Dutch marine clay soils. Basic soil data were collected in a 1:5000 soil survey and supplemented with secondary data derived through pedotransfer functions. Soil characterization focused on functional properties describing soil‐specific characteristics in terms of water regimes and nutrient dynamics. Four properties were considered: (i) water stress, (ii) N‐stress, (iii) N‐leaching and (iv) residual N‐content at harvest. These were quantified for individual soil profiles using a mechanistic–deterministic simulation model. Sensitivity to water stress was evaluated for a dry year (1989), other properties were quantified for a wet year (1987). Based on functional similarity, the soil profiles were grouped into functional classes using a fuzzy c‐means classifier. Standard interpolation techniques and a boundary detection algorithm subsequently identified soil functional units in each field. Analysis of variance revealed that >65% of the spatial variation could thus be accounted for. This confirmed that (i) the proposed classification procedure was efficient and (ii) soil functional units are suitable entities to be used as management units for PA.
Slope Length Effects on Soil Loss for Steep Slopes
Authors: Liu B. Y. , Nearing M. A. , Shi P. J. , Jia Z. W.
Published: July 2010

Empirical soil erosion models continue to play an important role in soil conservation planning and environmental evaluations around the world. The effect of hillslope length on soil loss, often termed the slope length factor, is one of the main and most variable components of any empirical model. In the most widely used model, the Universal Soil Loss Equation (USLE), normalized soil loss, L, is expressed as a power function of slope length, λ, as , in which the slope exponent, m, is 0.2, 0.3, 0.4, and 0.5 for different, increasing slope gradients. In the Revised Universal Soil Loss Equation (RUSLE), the exponent, m, is defined as a continuous function of slope gradient and the expected ratio of rill to interrill erosion. When the slope gradient is 60% and the ratio of rill to interrill erosion is classified as moderate, the exponent m has the value of 0.71 in RUSLE, as compared with 0.5 for the USLE. The purpose of this study was to evaluate the relationship between soil loss and slope length for slopes up to 60% in steepness. Soil loss data from natural runoff plots at three locations on the Loess Plateau in China and data from a previous study were used. The results indicated that the exponent, m, for the relationship between soil loss and the slope length for the combined data from the three stations in the Loess Plateau was For the data as a whole, the exponent did not increase as slope steepness increased from 20 to 60%. We also found that the value of m was greater for intense storms than for less intense storms. These experimental data indicate that the USLE exponent, , is more appropriate for steep slopes than is the RUSLE exponent, and that the slope length exponent varies as a function of rainfall intensity.
Characteristics and Modeling of Runoff Hydrographs for Different Tillage Treatments
Authors: Yu B. , Sombatpanit S. , Rose C. W. , Ciesiolka C. A. A. , Coughlan K. J.
Published: July 2010

Surface runoff rate is a critical variable in determining the rate of soil erosion and sediment transport. Rainfall and runoff data at 1‐min intervals from an experiment site at Khon Kaen, Thailand, were used to test a three‐parameter runoff model originally developed for bare plots in relation to soil erosion studies. The site has a sandy soil with a slope of 3.6%. Plot length and width were 30 and 5 m, respectively. Four tillage treatments with three replicates each were considered: up‐ and down‐slope cultivation, two contour cultivation treatments with tillage depth of 25 and 50 cm, respectively, and no tillage. Runoff data for 200 individual runoff hydrographs showed that runoff amount and peak runoff rate for the no tillage treatment were significantly less than those for other treatments at the site. On average, runoff amount and peak runoff rate for the no tillage treatment were 37 and 44%, respectively, of those for the up‐ and down‐slope cultivation. Results for contour cultivation practices are between the two extremes, although the water retention was not greater with greater tillage depth as we originally thought would be the case at the site. For these 200 runoff events for the four treatments, the model for runoff hydrographs worked well, with an average coefficient of efficiency of 0.90 and an average standard error of 0.88 mm h−1 The model performance is particularly good for large storm events with high volumetric runoff coefficient. The three model parameters vary considerably from event to event and from treatment to treatment. The initial infiltration amount was found to be inversely related to prior 10‐d rainfall at the site; the spatially averaged maximum rate of infiltration can be related to the maximum retention or the Soil Conservation Service (SCS) Curve Number, and the hydrologic lag time is least variable among different storm events and tillage treatments, but tends to decrease with peak runoff rate.
On‐Farm Evaluation of Ridging and Residue Management Practices to Reduce Wind Erosion in Niger
Authors: Bielders Charles L. , Michels Karlheinz , Rajot Jean-Louis
Published: July 2010

Wind erosion is regarded as a major contributor to the desertification process in the Sahel, yet little quantitative information is available for that region on soil losses by wind erosion under different land management practices. A 3‐yr, on‐farm experiment was, therefore, set up to assess the effect of ridging and either banded or broadcast millet stover mulches (2000 kg ha−1) on soil loss in a millet‐cowpea intercrop. For wind directions approximately perpendicular to the orientation of ridges and residue bands, sediment mass balances were calculated from the change in horizontal sediment mass fluxes measured across the experimental plots with Big Spring Number Eight sand traps. Mass balance calculations for 16 events over 3 yr indicated an average soil loss of 17.5, 15.4, and 18.0 Mg ha−1 on control plots, and deposition of 15.5, 15.3, and 7.4 Mg ha−1 on banded residue plots in 1995, 1996, and 1997, respectively. Broadcast and banded residue mulches were not significantly different (P = 0.05) in terms of their sediment trapping efficiency. During the same time period, ridges reduced soil losses by an average of 57% compared with the control plots, but their efficiency was reduced to less than 15% after 100 mm of cumulative rainfall as ridges collapsed. Linear regression analysis using the incoming sand fluxes as the independent variable was used to estimate potential soil losses for all events with sediment fluxes <25 kg m−1 irrespective of wind direction. The calculations indicated potential soil losses of up to 79 Mg ha−1 on control plots and deposition of 41 Mg ha−1 on broadcast residue plots in a single year. For wind erosion control, broadcast millet stover mulching constituted the most effective control technique because it effectively protected the soil against erosion and its trapping efficiency is expected to be independent of wind direction.
Soil Phosphorus Transformations Following Forest Clearing for Pasture in the Brazilian Amazon
Authors: Garcia-Montiel Diana C. , Neill Christopher , Melillo Jerry , Thomas Suzanne , Steudler Paul A. , Cerri Carlos C.
Published: July 2010

Phosphorus limits grass production in pastures planted on most cleared moist tropical forest, but little is known about soil P dynamics in these ecosystems. We describe changes to total P and different soil P fractions that occurred after the conversion of forest to pasture in the Brazilian Amazon State of Rond o ˆ nia. We used chronosequences of forest and pasture of different ages to document patterns of labile, occluded, and organic P pools using a sequential P fractionation technique. Phosphorus released from the aboveground forest biomass substantially increased soil available P during the first 3 to 5 yr after forest clearing and burning. During this period, nonoccluded forms of inorganic P increased by 2.0‐ to 2.7‐fold in the resin‐extractable fraction and by 4‐ to 25‐fold in the dilute HCl‐extractable fraction. The introduction of grasses influenced the redistribution of soil P forms in older pastures. Occluded P comprised a lower proportion of total P (40–55%) in 20‐yr‐old pastures compared with forests (63–65%), but the proportion of organic P in these pastures increased (29–35%) compared with forests (20–21%). From the patterns in P transformations we developed a conceptual model in which we contrasted P transformations during slash and burn for pasture with changes to soil P that occur during soil formation. On cleared lands, the one‐way process by which P in primary minerals is converted to occluded and organic forms is reset by the cutting and burning of plant biomass, but instead of being released from primary minerals, P is released from the burned and decomposing biomass. Because this occurs in an already weathered soil, P transformation from nonoccluded to occluded and organic forms occurs in <50 yr instead of the thousands of years required for these same transformations to occur during primary succession.
Using Growing Degree Days to Predict Nitrogen Availability from Livestock Manures
Authors: Griffin T. S. , Honeycutt C. W.
Published: July 2010

Predictive tools are needed to better match N release from manure with crop demand. Growing degree days (GDD) have been successfully used to predict N release from crop residues and other amendments. A 112‐d incubation experiment was conducted at 10, 17, and 24°C to evaluate GDD (0°C base temperature) predictions of N transformations from beef (Bos taurus), dairy, poultry (Gallus gallus), and swine (Sus scrofa) manure. Manure was incorporated at rates estimated to provide 150 kg N ha−1 (or 75 mg N kg−1 soil). Soil NO3 and NH4 concentrations were determined at weekly or biweekly intervals. The rate of NO3 accumulation increased with increasing temperature, and could be predicted across temperature regimes using GDD. This predictive ability could be generalized across dairy, poultry, and swine manures using an exponential equation, , while N was immobilized by incorporation of beef manure. The disappearance of NH4 was a linear function of time and of GDD. A single predictive equation was sufficient for dairy, poultry, and swine manures, in the form , with soil NH4 reaching zero at ≈350 GDD. These laboratory data indicate that GDD can be used for predicting NO3 accumulation and NH4 disappearance from a range of livestock manures. If successfully extended to the field, this predictive capability may allow for improved management of N from animal manures.
Changes in Partitioning of Cadmium‐109 and Zinc‐65 in Soil as Affected by Organic Matter Addition and Temperature
Authors: Almås Å. R. , Salbu B. , Singh B. R.
Published: July 2010

Soil collected from the A horizon of a soil developed from alum shale was added organic matter at the rate of 0 and 4% (w/w) and placed in temperature‐controlled climate chambers at 9 and 21°C. After spiking the soil with 109Cd and 65Zn, sequential extraction of the tracers was performed on soil subsamples collected at time intervals ranging from 0.5 to 8760 h (1 yr). The activity concentrations of 109Cd and 65Zn determined in the seven extracts were used in a three‐component model to calculate the kinetics of 109Cd and 65Zn transfer between the water‐soluble, reversibly sorbed and irreversibly sorbed model components. The rates and the time‐dependent distribution coefficient constants for 109Cd and 65Zn distribution among the three components were determined, and the impacts of organic matter addition and increasing temperature on these constants were assessed. The reversible sorption of the tracers occurred rapidly, within 0.5 h, while the transfer of reversibly sorbed 109Cd and 65Zn into the irreversibly sorbed fractions was a significantly slower process. The addition of organic matter reduced the rate of 109Cd and 65Zn transfer into the irreversibly sorbed fractions, whereas the transfer rate increased with increasing temperature. The interaction between organic matter and temperature affected both the rates and the pseudoequilibrium constants, and the temperature regimes and rate of organic matter addition may thus influence the potential mobility of the investigated metals.
Solubility and Dissolution Kinetics of Dolomite in Ca–Mg–HCO3/CO3 Solutions at 25°C and 0.1 MPa Carbon Dioxide
Authors: Sherman Leslie A. , Barak Phillip
Published: July 2010

Dolomite solubility in water has been measured by a number of different methods during the past several decades, yielding inconsistent and unreliable results that vary more than three orders of magnitude. The most commonly used best value for dolomite solubility in water is based on HCl solution calorimetry at 300.15 K, which is not confirmed by earlier determinations based on heat capacity of dolomite nor by more recent acid solution and metal oxide melt calorimetric measurements. In this study, the solubility of a high purity dolomite was measured directly by monitoring dissolution in Ca−Mg−HCO3/CO3 solutions designed to bracket the presumed solubility product of dolomite, pKs dolomite [= −log (Ca2+)(Mg2+)(CO2−3)2, where the values in parentheses are activities at equilibrium], between 16.0 and 19.0, at 0.101 MPa (1 atm) CO2 and 25°C. The use of gas‐permeable, water‐impermeable membranes over the dissolution vessels allowed for maintenance of an open system for CO2, with minimal water loss during the course of the 672‐d experimental period. The dolomite dissolved congruently in Ca−Mg−HCO3/CO3 solutions with initial ion activity products [pIAPdolomite = −log (Ca2+)(Mg2+)(CO2−3)2, where the values in parentheses are measured activities] greater than 17.5. Both calcite and magnesian calcites can be ruled out as controlling solubility in these measurements. Based on statistical inference by comparison of alkalinity in unseeded (control) and dolomite‐seeded solutions, the pKs dolomite is between 17.4 and 17.0, expressed as 17.2 ± 0.2. A previously proposed kinetic model of successive reactions for dolomite dissolution near equilibrium—a fairly rapid dissolution of the CaCO3 component in equilibrium and a rate‐limiting protonation reaction dependent on the activity of the MgCO3 component—appears to fit the experimental data.
Use of Carbon‐13 and Carbon‐14 to Measure the Effects of Carbon Dioxide and Nitrogen Fertilization on Carbon Dynamics in Ponderosa Pine
Authors: Haile-Mariam Shawel , Cheng W. , Johnson D. W. , Ball J. T. , Paul E. A.
Published: July 2010

Soil C sequestration in predicted, future elevated CO2 environments will be important to atmospheric CO2 levels, soil tilth, and fertility. An elevated CO2 study with ponderosa pines (Pinus ponderosa Laws) grown in chambers produced above ground vegetation with a δ13C of −44‰ and roots with −42‰. This together with carbon dating made it possible to follow soil C dynamics. Fifty percent of the California upland soil C, resistant to acid hydrolysis, was designated as the resistant fraction. Carbon dating showed the mean residence times of this fraction to be 400 to 1500 yr greater than the total soil C for the horizons sampled. Young ponderosa pines grown in CO2 chambers produced negligible leaf litter. There were 32% more roots in the presence of either added N or double CO2 but 77% more in the presence of both. Root‐derived soil C was equivalent to 10% of the root C after the 6‐yr growth period. Analysis of laboratory CO2 evolution during extended incubation showed the active soil C pool represented 1 to 2% of the soil C with a field‐equivalent mean residence time (MRT) of 24 to 53 d. The slow pool represented 46 to 52% of the C with MRT of 24 to 67 yr depending on treatment and soil depth. Analysis of the 13CO2 label during incubation from the elevated CO2 treatments, showed the root‐derived 13C of the active fraction to have residence times similar to those of the total soil non labeled C at ≈35 d. Root‐derived C of the slow pool at 10 yr MRT turned over three to four time as fast as the general soil C. The 13C of the light fraction (LF), showed it to be most closely associated with the active pool. The particulate organic matter (POM) was part of the slow pool as determined with incubation.
Phosphorus Fractionation in Biosolids‐Amended Soils Relationship to Soluble and Desorbable Phosphorus
Authors: Maguire R. O. , Sims J. T. , Coale F. J.
Published: July 2010

Phosphorus has been identified as a major factor involved in decreasing water quality through its role in eutrophication, and there is now a focus on controlling nonpoint agricultural P sources. This work was conducted to identify how biosolids applications under current regulations have affected the forms and release potential of P in agricultural soils. We collected samples from eight farms with a history of biosolids amendments, selecting fields that had setback areas (where biosolids applications were not permitted) to allow comparison of amended and unamended soils. We analyzed these soils for P fractions (soluble P, Al‐P, Fe‐P, reductant soluble P, and Ca‐P; their sum equals total P), sequentially desorbable P (Fe‐strip), oxalate P, Al and Fe, Mehlich‐1 P, and the degree of P saturation. Our results show that following a N‐based biosolids nutrient management plan can significantly increase total P (from 403 to 738 mg kg−1) and initially desorbable P (from 32 to 61 mg kg−1). The main soil components associated with P retention (Aloxand Feox) also tended to be increased by biosolids amendment and this may help mitigate P release. Biosolids amendment significantly increased Fe‐P (from 137 to 311 mg kg−1), probably due to Fe added to biosolids during production, and there was also a strong trend for higher Al‐P where biosolids had been applied. Desorbable P was initially greatest from biosolids sites, but with increasing extractions, the release converged towards that from the setback areas. Mehlich‐1 P and Poxwere good predictors of desorbable P release, as measured by one and five sequential extractions with Fe‐strips. Desorbable P, by both one and five Fe‐strip extractions, was more closely correlated with Al‐P than Fe‐P, especially in setback areas, indicating that Al‐P is probably the most important source of desorbable P independent of biosolids amendment. This work indicates the importance of considering P availability at agricultural biosolids application sites and of maintaining setback areas near water bodies, where no biosolids may be applied, to reduce the risk of P losses.
Tillage and Saline Irrigation Effects on Water and Salt Distribution in a Sloping Field
Authors: Huang Z. B. , Assouline S. , Zilberman J. , Ben-Hur M.
Published: July 2010

Application of saline water using moving irrigation systems (MIS) can affect the water and salt distribution in the field and the crop yield because of runoff formation. The objective of this study was to determine the effects of tillage and water application methods on the distributions of water content, salt concentration in soil, and corn (Zea mays L.) yield under irrigation with saline water by MIS. The experimental site was located in a forage corn field in the Negev, Israel. Three tillage treatments were studied: (i) conventional tillage (control); (ii) microbasin; and (iii) diked furrows (dike). The control and the microbasin plots were irrigated with sprinkler MIS, and the dike plots with flooding MIS. The studied parameters were measured in five sampling sites located 25 m apart along the slope. The average dry canopy yields of the whole slope in the control, dike, and microbasin treatments were 21.7, 25.3, and 30.6 Mg ha−1, respectively, and their coefficient of variance (CV) values along the slope were 7.9, 5.7, and 3.5%, respectively. In the control treatment, soil water content increased from 0.12 kg kg−1 upslope to 0.19.0 kg kg−1 downslope. In contrast, no slope effect on soil water content was found in the microbasin and dike treatments. The electrical conductivity (EC) of the 0‐ to 0.3‐m soil layer in the control treatment increased in the downslope direction from 2.0 to 4.0 dS m−1 Conversely, in the microbasin and dike treatments, no consistent trend of the EC was observed with slope, and their average values were 3.4 and 7.0 dS m−1, respectively. It was suggested that these yield differences were related to the differences in the distribution of the soil water content and the salt concentration in soil within the field.
Diffusion of Sorbing Organic Chemicals in the Liquid and Gaseous Phases of Repacked Soil
Authors: Olesen T. , Gamst J. , Moldrup P. , Komatsu T. , Rolston D. E.
Published: July 2010

Transport models for sorbing organic chemicals in soil require accurate predictions of the diffusion and sorption processes in both the liquid and gaseous phases. In this study, the ability of recently‐presented diffusivity models in combination with equilibrium sorption models to predict the effective (i.e., including sorption effects) diffusion coefficient, Deff, as a function of soil‐water content, θ, is tested for different sorbing organic chemicals in different soils. The water‐induced linear reduction (WLR) gas diffusivity model, combined with a two‐component (hydrophobic and vapor) equilibrium sorption model, well described short‐term (<24 h) Deff(θ) of two volatile organic compounds, toluene and trichloroethylene (TCE), in Yolo loam (fine‐silty, thermic Typic Xerorthent). Further extended with the constant slope impedance factor (CSIF) solute diffusivity model, the resulting two‐phase diffusion and two‐component equilibrium sorption (DATES) model accurately predicted short‐term (48 h) Deff(θ) of a semivolatile pesticide, lindane (C6H6Cl6), in Gila silt loam (coarse‐loamy, thermic Typic Torrifluvents). To test the DATES model for longer‐term data, Deff(θ) of naphthalene (C10H8) in Lerbjerg sandy clay (L5) was measured at different soil‐water contents and incubation times in air‐tight diffusion cells. Because of sorption kinetics, both the apparent hydrophobic sorption coefficient, KD, derived from the column diffusion experiments and KD derived from batch desorption experiments increased with naphthalene‐soil contact time for t > 700 h. Consequently, an increasing KD value with time was required in the DATES model to obtain successful Deff(θ) predictions. Since chemical‐soil contact time and adsorption‐desorption history typically vary in each compartment of a soil profile, transport models, including sorption kinetics, will become very complex and DATES with a time‐dependent KD relation may represent a useful model alternative.
Adsorption of Arsenate (V) and Arsenite (III) on Goethite in the Presence and Absence of Dissolved Organic Carbon
Authors: Grafe M. , Eick M. J. , Grossl P. R.
Published: July 2010

The environmental fate of arsenic (As) is of utmost importance as the public and political debate continues with the USEPA's recent proposal to tighten the As drinking water standard from 50 to 10 μg L−1 In natural systems, the presence of dissolved organic C (DOC) may compete with As for adsorption sites on mineral surfaces, hence increasing its potential bioavailability. Accordingly, the adsorption of arsenate [As (V)] and arsenite [As (III)] on goethite (α‐FeOOH) was investigated in the presence of either a peat humic acid (Hap), a Suwannee River Fulvic Acid (FA) (International Humic Substances Society, St. Paul, MN), or citric acid (CA). Adsorption edges and kinetic experiments were used to examine the effects of equimolar concentrations of organic adsorbates on As adsorption. Adsorption edges were conducted across a pH range of 3 to 11, while the kinetic studies were conducted at pH 6.5 for As (V) and pH 5.0 for As (III). Both Hap and FA decreased As (V) adsorption, while CA had no effect. Humic acid reduced As (V) between pH 6 and 9 by ≈27%. Fulvic acid inhibited As (V) adsorption between pH 3 and 8 by a maximum of 17%. Arsenite adsorption was decreased by all three organic acids between pH 3 and 8 in the order of CA > FA ≈ Hap. The different pH regions in which Hap and FA decreased As (V) adsorption suggest that more than one functional group on these complex organic polymers may be responsible for binding to the α‐FeOOH surface. Similarly, the relative surface affinity of the As(III or V) species and that of the competing organic ligand as a function of pH may play a major role in the outcome of As adsorption on α‐FeOOH. The results of these experiments suggest that DOC substances are capable of increasing the bioavailability of As in soil and water systems in which the dominant solid phase is a crystalline iron oxide.
Spatial Modeling of Nitrifier Microhabitats in Soil
Authors: Grundmann G. L. , Dechesne A. , Bartoli F. , Flandrois J. P. , Chassé J. L. , Kizungu R.
Published: July 2010

Soil bacteria function in the three‐dimensional space in heterogeneous soil complex and their activities depend in part on encountering substrates at the microbial scale. The bacterial density per gram of soil, which is generally measured, does not indicate if bacteria are all in the same location or spread throughout the soil complex. We characterized spatial distribution for how dispersed or aggregated nitrifiers (NH+4and NO−2oxidizers) were at a submillimeter scale. The spatial approach was based on the relationship, obtained experimentally, between the percentage of microsamples (50–500 μm diam.) harboring nitrifiers and the volume of the microsamples. The smallest sample size (50‐μm diam.) was considered as an approximation of microhabitat. The simulated spatial pattern of NO−2oxidizer microhabitats in soil were compared with experimental data. The simulated pattern of NO−2oxidizer distribution suggested that microhabitats averaged seven NO−2oxidizers and occurred in preferentially colonized patches that had about a 250‐μm diam. These were randomly distributed and occupied 5.5% of the soil volume. They were functionally connected through microporosity and hence diffusion processes probably controlled the spatial distribution of nirifiers. The nitrifier spatial pattern enabled efficient nitrification because NH+4and NO−2oxidizers were near one another. The results showed the potential of our method to study spatial distribution of bacteria at the microhabitat scale.
Andisols of Deserts in Iceland
Authors: Arnalds O. , Kimble J.
Published: July 2010

Desert areas cover 35 to 45000 km2 of Iceland or about 35 to 45% of the country. These surfaces have very low vegetation cover as a result of several environmental factors and anthropogenic impacts. A good understanding of the soils of the deserts is a key factor for successful restoration of these ecosystems. Very limited data has previously been published about the soils of Icelandic deserts and limited research has been reported on soils that form in basaltic tephra materials under similar conditions elsewhere in the world. The purpose of the research reported here was to gain a basic understanding of properties, variability, and classification of the soils of Icelandic deserts. Eight soil pedons, representing a variety of desert surfaces, were described, sampled, and analyzed for key physical and chemical properties. The morphology was generally characterized by a frost‐heaved gravel layer at the surface, with finer subsurface horizons with abundance of volcanic glass. The soils had low organic content (<10 g kg−1), and very low levels of N. Water holding capacity was generally <50 g kg−1 at 1.5 MPa. Phosphorus retention is 24 to 93% in A and B horizons. The soils were near neutral in reaction but the pH in NaF solution was commonly around 10. Mineralogy was dominated by volcanic glass, but allophane and ferrihydrite are also present. The results of this study show that most Icelandic deserts soils are Typic Virtricryands according to soil taxonomy. Icelandic Andisols combined are 5 to 7% of the world's Andisols.
Soil Surface Structure Stabilization by Municipal Waste Compost Application
Authors: Bresson L. M. , Koch C. , Le Bissonnais Y. , Barriuso E. , Lecomte V.
Published: July 2010

Loess‐derived soils of the northern Paris basin are prone to surface structure degradation leading to erosion, flooding, and pollution. Concomitantly, recycling of municipal solid waste (MSW) has been recognized as an important environmental issue. The aim of this study was to test the impact of compost application on soil surface structure degradation and on the resulting runoff and erosion processes. Aggregates (0–30 mm) from a silty loam Typic Hapludalf were mixed with a MSW compost at a rate of 15 g kg−1 (dry matter). Repacked seedbeds were exposed to a 19 mm h−1 simulated rainfall for 60 min. Morphological evolution of the soil surface was monitored using sequential photographs. Crust and seedbed microstructures were studied after 4, 15, and 60 min of rainfall, using thin sections from resin‐impregnated replicates. Runoff was measured every five minutes, and aliquots were sampled for sediment concentration. In control seedbeds, surface crusts quickly developed and the whole seedbed slumped because of aggregate coalescence through deformation in a viscous state. Compost application delayed crust formation and prevented seedbed slumping. This, in turn, delayed runoff from 2.5 to 9.2 mm of cumulative rainfall. Sediment concentration in the incipient runoff was decreased from 36.4 to 11 g L−1 This could be ascribed to the stabilization of the aggregate framework, which allowed the particles detached from the top of surface aggregates to illuviate a few millimeters deeper. In a highly unstable soil, MSW compost application was efficient in combating soil surface structure degradation and its consequences on runoff and erosion.
Microdiffusion of Strongly Fixed Ammonium in Soil‐Acid Digests Prior to Automated Nitrogen‐15 Analysis
Authors: Eudoxie Gaius D. , Gouveia Gregory A.
Published: July 2010

The concentration of strongly fixed‐ammonium (NH4f) in soil is not high enough to allow direct injection of soil digests into automated15N analyzers. Investigations were therefore conducted to develop microdiffusion protocols primarily as a preconcentration step in NH4f‐15N analysis of soils using continuous flow–isotope ratio mass spectrometry (CF–IRMS). The 5MHF:1MHCl soil digest containing NH4fwas treated with 10MKOH in a 140‐mL polypropylene specimen container, modified to collect NH3‐N in a petri dish containing H3BO3indicator solution which was then quantified by acidimetric titration. For15N analysis, however, acidified Whatman GF‐D filter paper discs substituted for the H3BO3indicator solution trap, which were subsequently processed for direct analysis via CF–IRMS. With the modifications described, analyses (quantitative and15N) were performed on 5‐ to 20‐mL samples of 5MHF:1MHCl soil digests. Recovery was quantitative in 48 to 96 h with up to ∼525 μg NH4‐N and was more dependent on digest volume than on its N content. Fractionation of15N was effectively nonexistent within the diffusion periods used except only for immediately (a few hours) into the diffusion; suggesting that the need to optimize diffusion is not that critical to the accuracy of the15N results provided a sufficient quantity of N is obtained for the CF‐IRMS. Additionally, diffusion times were slightly affected by soil type, indicating a mild matrix effect probably because of mineralogical variation among soils. These diffusion methods therefore proved to be very accurate and reliable for practical use as a preconcentration step prior to15N analysis of the NH4ffraction in soils.
Acid fumigation of soils to remove carbonates prior to total organic carbon or CARBON‐13 isotopic analysis
Authors: Harris David , Horwáth William R. , van Kessel Chris
Published: July 2010

The use of 13C natural abundance (δ13C) to follow C input to soil has gained widespread acceptance. However, inorganic C present in the soil as carbonates will interfere with the measurement of soil organic 13C unless removed or excluded from measurement. We report a simple and convenient HCl‐fumigation method to remove inorganic C from soil. Soil samples are weighed in Ag‐foil capsules, arranged on a microtiter plate, wetted with water to approximately field capacity, and placed in a desiccator containing a beaker with concentrated (12 M) HCl. The carbonates are released as CO2 by the acid treatment in 6 to 8 h. The soil samples are then dried at 60°C prior to isotope determination. The advantages of the HCl‐fumigation method to remove inorganic C from the soil are that: (i) no water soluble C will be lost from the soil; (ii) a large number of samples can be processed simultaneously; (iii) the removal of inorganic C is rapid and complete; and (iv) the method could also be used to determine both organic and inorganic C content in the soil. A potential disadvantage, however, is that the HCl fumigation changed the 15N natural abundance of soil N.
Description of Soil Water Characteristics Using Cubic Spline Interpolation
Authors: Kastanek Ferdinand J. , Nielsen Donald R.
Published: July 2010

Solutions of differential equations describing soil water behavior frequently require a mathematical function for the soil water characteristics. Although spline interpolation provides a method to connect the data points, in many cases its use yields poor results. The mathematical representation of the soil water characteristic may also be shaped according to the imagination and judgment of the investigator. In such cases, some additional virtual data points are chosen through which the spline function passes exactly to yield a mathematical description of the entire curve consistent with the initially measured points. A computer program SWC‐SPLINE written in Delphi 2 allows the investigator to easily mark and change the position of the assumed virtual data points interactively according to visual inspection.
Analysis of Infiltration and Runoff in an Olive Orchard under No‐Till
Authors: Gómez J.A. , Giráldez J.V. , Fereres E.
Published: July 2010

Four infiltration techniques (falling head, ring, rainfall, and tension infiltrometer) were used to determine the saturated hydraulic conductivity, Ks, and the wetting potential front, hf, of the Green–Ampt model. Water release curves from soil cores were also used for estimating hf The objective was to compare the performance of the different techniques for the assessment of infiltration in a no‐tillage olive (Olea europaea L. subsp. europaea) orchard. Measurements were performed in two areas of the orchard, below canopy (C) and interrow among trees (IR). With the exception of the tension infiltrometer, all techniques showed significant differences in Ks and hf between C and IR areas, attributed to different compaction. Differences in Ks among techniques were within the range observed previously. The hf estimated from the falling‐head technique was significantly higher than that measured with the other techniques. The discrepancies in the results obtained with the tension infiltrometer were attributed to insufficient time of measurement, leading to recommendations for a different field procedure and analysis of this technique. To assess the use of the techniques described above for the characterization of plot infiltration, rainfall and runoff were measured in a 128‐m2 plot. A numerical model was then used to predict runoff using the infiltration measurements. The results showed that runoff prediction is improved when different values of Ks and hf are considered for the C and IR areas instead of a single average value. The numerical analysis of the effects of tree arrangement on runoff prediction from infiltration measurements indicated that if the trees were placed along the contour lines, runoff would decrease relative to the standard tree arrangement.
Improved evaluation procedure for heat‐pulse soil water flux density method
Authors: Kluitenberg G.J. , Warrick A.W.
Published: July 2010

Analytical solutions of the heat equation must be evaluated in order to implement the heat‐pulse method for measuring soil water flux density. We developed an improved procedure for evaluating the integrals in these solutions by recognizing that they can be reduced to a single function, W, known as the well function for leaky aquifers The evaluation procedure was improved further by developing an efficient method to approximate W This method, which involves summing the first few terms of an infinite series, also provides a simple means of determining the approximation error. For a wide range of input parameters, at most two terms of the series are needed to approximate W with error less than 10−4 in absolute value. Thus, numerical integration is not required in order to implement the heat‐pulse method for measuring soil water flux density. Our results regarding the evaluation of W are relevant to other problems in soil science and groundwater hydrology in which the function W appears.
Nitrogen Competition in a Tallgrass Prairie Ecosystem Exposed to Elevated Carbon Dioxide
Authors: Williams Mark A. , Rice Charles W. , Owensby Clenton E.
Published: July 2010

Because N is a limiting nutrient in tallgrass prairie and most ecosystems, changes in N availability or N cycling could control the long‐term response of ecosystems to elevated atmospheric CO2If more C is sequestered into the soil, then greater microbial demand for N could decrease plant‐available soil N. Alterations in N dynamics such as plant uptake, N fixation, nutrient cycling, microbial utilization, and partitioning of N into plant and soil fractions ultimately could affect the capability of ecosystems to sequester C. Our objective was to determine if competition for N between plants and microorganisms changes after 8 yr of elevated CO2relative to ambient conditions. Treatments (three replications, randomized complete block design) were ambient CO2–no chamber (NC), ambient CO2–chamber (AC), and 2 × ambient CO2–chamber (EC). Several short laboratory incubations assessed whether turnover rates of N in soil would be altered under elevated CO2Gross transformations of N were not altered significantly under elevated CO2compared with ambient conditions. To examine plant–microbial competition and altered allocation patterns of N under elevated CO2,15NH4–N was added to 25‐cm‐diam. polyvinyl chloride (PVC) cores (15‐cm depth) in the field, which were destructively sampled after ≈5 mo. Microbial biomass contained ≈75% of the total15N that occurred in the soil organic matter (SOM) and, thus, appeared to be a significant regulator of plant‐available N. The SOM under elevated CO2contained significantly more (>27%)15N compared with ambient CO2conditions. Though a chamber effect was apparent, greater15N in the SOM pool and greater percentage15N SOM/percentage15N plant suggest greater microbial demand for N under elevated CO2
Soil Organic Matter Pools and Carbon‐13 Natural Abundances in Particle‐Size Fractions of a Long‐Term Agricultural Field Experiment Receiving Organic Amendments
Authors: Gerzabek Martin H. , Haberhauer Georg , Kirchmann Holger
Published: July 2010

The present study combined a physical fractionation procedure with the natural abundance of 13C (δ13C) to evaluate the effect of organic fertilizer applications, mineral fertilization, and fallow on changes in the organic C (Corg) associated with different particle‐size fractions. The long‐term agricultural field experiment was conducted since 1956 in Ultuna, Sweden, on a Eutric Cambisol. Organic C both in bulk soil samples and size fractions changed significantly since 1956. Fallow plots lost approximately one‐third of their Corg from the topsoil layer (0–20 cm), whereas organic amendments based on an equivalent of 2000 kg C ha−1 yr−1 increased Corg up to twofold depending on the quality of the material applied (green manure < animal manure < sewage sludge < peat). Silt‐sized particles increased in plots receiving sewage sludge or peat. Organic C in particle‐size fractions responded significantly to treatments. Most Corg was found in the silt fraction. The relative contribution of the silt‐sized particles to total Corg increased by 18% as Corg in bulk soil increased from 10.8 (fallow) to 32.0 (peat) g Corg kg−1 soil; the contribution of clay‐sized particles decreased by a similar proportion. Mass balance calculations showed that the proportion of Corg originating from organic amendments decreased with particle size and that sand fractions were the most sensitive to the treatments. The natural abundance of 13C in bulk soil and size fractions increased significantly in the continuous fallow and was affected by organic amendments. The δ13C variations among size fractions were larger than among treatments and can be used as a fingerprint for differentiation. Our results suggest that silt‐sized particles acted as medium‐term sink for added Corg and that sand‐sized fractions can be useful as sensitive indicators of changes in soil C status in response to land management.
Landscape‐Level Patterns of Microbial Community Composition and Substrate Use in Upland Forest Ecosystems
Authors: Myers Rachel T. , Zak Donald R. , White David C. , Peacock Aaron
Published: July 2010

The composition and diversity of biotic communities are controlled by the availability of growth‐limiting resources. Resource availability for microbial populations in soil is controlled by the amount and types of organic compounds entering soil from plant litter. Because plant communities differ in the amount and type of substrates entering soil, we reasoned that the composition and function of soil microbial communities should differ with the dominant vegetation. We tested this idea by studying two sugar maple (Acer saccharum Marsh.)‐dominated and one oak (Quercus spp.)‐dominated forest ecosystems in northern Lower Michigan that differ in rates of soil N cycling. We used phospholipid fatty acid (PLFA) analysis to gain insight into microbial community composition, and we used a subset of Biolog GN substrates found in root exudate to assess the metabolic capabilities soil microbial communities. Although microbial biomass did not differ among ecosystems, principal components analysis of bacterial, actinomycetal, and fungal PLFAs clearly separated the microbial communities of the three ecosystems. Similarly, principal components analysis separated microbial communities by differences in growth on carbohydrates, organic acids, and amino acids. Discrimination among microbial communities in the three ecosystems by PLFAs and substrate use occurred in spring, summer, and fall, but the individual PLFAs and substrates contributing to discrimination changed during the growing season. Our results indicate that floristically and edaphically distinct forest ecosystems also differ in microbial community composition and substrate use. This pattern was consistent across the growing season and repeatedly occurred across relatively large land areas.
Carbon Balance of the Breton Classical Plots over Half a Century
Authors: Izaurralde R.C. , McGill W.B. , Robertson J.A. , Juma N.G. , Thurston J.J.
Published: July 2010

We related C input and management to soil organic C (SOC) dynamics over 51 yr (1939–1990). We used two rotations from the Breton Classical Plots at Breton, Canada, on a Typic Cryoboralf: (i) wheat (Triticum aestivum L.)–fallow (WF) and (ii) wheat–oat (Avena sativa L.)–barley (Hordeum vulgare L.)–hay (primarily alfalfa, Medicago sativa L.)–hay (WOBHH), in factorial combination with three fertility levels: no added fertilizer [Nil], N‐P‐K‐S fertilizers [F], and farmyard manure [M]. Net aboveground C productivity (NAGCP, kg ha−1 yr−1) averaged 576 in WF–Nil and 1078 in WF–F and SOC decreased in both, but NAGCP averaged 1208 in WF–M, where SOC increased. A NAGCP of 853 in WOBHH–Nil maintained SOC, while both 1831 in WOBHH–F and 1714 in WOBHH–M increased SOC. After 51 yr, WOBHH–M had 25 Mg ha−1 more SOC than did WF–Nil. Because of contrasting decay rates and root/shoot ratios, C input needed to maintain the original SOC was twofold greater in WF than in WOBHH, which required a fourfold increase in NAGCP to attain these inputs. A three‐compartment model fitted to the data suggested loss of C from the active compartments and gain of C by the passive compartments. Inputs of C that maintained SOC over 51 yr would lead to a steady state of 2.9 times more C than in 1939, and 26% higher than the native SOC content. Return of 30% of the crop C as manure would sustain SOC sequestration in all WOBHH rotations with NAGCP > 400 kg ha−1 yr−1 and in those WF rotations with NAGCP > 1000 kg ha−1 yr−1