bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessing the Impact of Land Conversion to Urban Use on Soils with Different Productivity Levels in the USA
Authors: Nizeyimana Egide L. , Petersen G.W. , Imhoff M.L. , Sinclair H.R. , Waltman S.W. , Reed-Margetan D.S. , Levine E.R. , Russo J.M.
Published: July 2010

There has been increased public concern in the USA over the long‐term impact of urbanization on the available land used to produce food, feed, and fiber. Concern that urban use of highly productive soils may threaten our food security and sustainability has been debated for nearly three decades. This study was primarily initiated to compare different soil productivity classes in terms of areas and proportion of land converted to urban uses in the USA. The methodology consisted of analyzing data resulting from a geographic information system (GIS) overlay of urban land use maps derived from the Defense Meteorological Satellite Program's Operational Linescan System (DMSP/OLS) nighttime imagery and layers of potential soil productivity. Soil productivity distributions were obtained using the Soil Rating for Plant Growth (SRPG) model based primarily on soil and landscape parameters contained in the State Soil Geographic (STATSGO) database. Currently, the urban land use covers ≈3% of the conterminous USA and is primarily on areas that were originally of low and moderate soil productivity. Only 6% of the total land under urbanization had consisted of highly productive soils. However, land with highly productive soils, roughly 3% of the total U.S. area, has a higher level of urbanization (5%) than that of any other soil productivity category. States differ in the areas and proportion of land converted to urban uses in each soil productivity class. These results are a first step in determining the current status of soil resources in relation to urbanization and should be interpreted according to the scale and resolution of data sources and assumptions made in the soil productivity modeling.
Overwinter Changes in Wind Erodibility of Clay Loam Soils in Southern Alberta
Authors: Bullock Murray S. , Larney Francis J. , Izaurralde R.César , Feng Yongsheng
Published: July 2010

Soil dry aggregate size distribution (DASD) and surface roughness are important factors affecting wind erodibility. This study monitored overwinter changes in DASD and surface roughness and identified relationships with climatic variables in the chinook‐dominated region of southern Alberta. A different site was monitored in each of three winters (18 Sept. 1992 to 12 May 1993; 26 Oct. 1993 to 29 Apr. 1994; 30 Aug. 1994 to 24 May 1995) on Dark Brown Chernozemic clay loams (fine‐loamy, mixed, Typic Haploborolls). The DASD was expressed as geometric mean diameter (GMD) and wind erodible fraction (EF). The GMD ranged from 1.88 to 0.08 mm in 1992‐1993, from 9.05 to 1.17 mm in 1993‐1994, and from 4.71 to 0.80 mm in 1994‐1995. The EF ranged from 38.9 to 74.0% in 1992‐1993, from 12.6 to 43.7% in 1993‐1994, and 31.3 to 55.0% in 1994‐1995. Surface roughness was measured parallel (Cpar) to tillage direction on two of the sites. Using the chain method, Cpar ranged from 15.1 to 3.7% in 1993‐1994 and from 14.4 to 3.3% in 1994‐1995. Regression analysis with time revealed significant exponential decay for GMD (R2 = 0.57 in 1992‐1993, 0.97 in 1993‐1994, and 0.78 in 1994‐1995) and Cpar (R2 = 0.98 in 1993‐1994, 0.91 in 1994‐1995) and a positive linear fit for EF (R2 = 0.57 in 1992‐1993, 0.91 in 1993‐1994, and 0.62 in 1994‐1995). Three overwinter periods, differentiated by the timing and form of precipitation and designated as “fall rain/snow”, “winter snow”, and “spring snow/rain”, were used to assess the changes in EF using cumulative freeze–thaw cycles, precipitation, and snow cover variables. Results indicated that precipitation, which directly influences soil water content, is necessary for freeze–thaw cycles to be effective in disrupting soil aggregates. Snowmelt and spring rainfall appear capable of reducing wind erodibility on these clay loam soils by promoting soil crusting. Our study showed that overwinter soil properties affecting wind erodibility are highly transitory and that the timing and form of precipitation played a major role in determining wind erosion risk in southern Alberta.
Near‐Infrared Reflectance Spectroscopy–Principal Components Regression Analyses of Soil Properties
Authors: Chang Cheng-Wen , Laird David A. , Mausbach Maurice J. , Hurburgh Charles R.
Published: July 2010

A fast and convenient soil analytical technique is needed for soil quality assessment and precision soil management. The main objective of this study was to evaluate the ability of near‐infrared reflectance spectroscopy (NIRS) to predict diverse soil properties. Near‐infrared reflectance spectra, obtained from a Perstrop NIR Systems 6500 scanning monochromator (Foss NIRSystems, Silver Spring, MD), and 33 chemical, physical, and biochemical properties were studied for 802 soil samples collected from four Major Land Resource Areas (MLRAs). Calibrations were based on principal component regression (PCR) using the first derivatives of optical density [log(1/R)] for the 1300‐ to 2500‐nm spectral range. Total C, total N, moisture, cation‐exchange capacity (CEC), 1.5 MPa water, basal respiration rate, sand, silt, and Mehlich III extractable Ca were successfully predicted by NIRS (r2 > 0.80). Some Mehlich III extractable metals (Fe, K, Mg, Mn) and exchangeable cations (Ca, Mg, and K), sum of exchangeable bases, exchangeable acidity, clay, potentially mineralizable N, total respiration rate, biomass C, and pH were also estimated by NIRS but with less accuracy (r2 = 0.80∼0.50). The predicted results for aggregation (wt% > 2, 1, 0.5, 0.25 mm, and macroaggregation) were not reliable (r2 = 0.46∼0.60). Mehlich III extractable Cu, P, and Zn, and exchangeable Na could not be predicted using the NIRS–PCR technique (r2 < 0.50). The results indicate that NIRS can be used as a rapid analytical technique to simultaneously estimate several soil properties with acceptable accuracy in a very short time.
Tortuosity, Diffusivity, and Permeability in the Soil Liquid and Gaseous Phases
Authors: Moldrup P. , Olesen T. , Komatsu T. , Schjønning P. , Rolston D.E.
Published: July 2010

Tortuosity phenomena of pore space influence the transport of water, solutes, and gases in soil. This study presents three analyses linking tortuosity and transport in unsaturated soil. The first is a diffusion‐based analysis of tortuosity in the soil water and soil air phases, related to soil surface area (SA) and pore‐size distribution (PSD) (characterized by Campbell b and content of pores >30 μm). The analysis is based on recent models to predict the diffusion coefficients, Dp, of (i) a solute in soil, (ii) a gas in repacked soil, and (iii) a gas in undisturbed soil, each as a function of fluid‐phase (soil water or soil air) content, α. For use in the analysis, the relation between SA and the threshold water content where solute diffusion ceases due to disconnected water films was measured for eight soils (5–46% clay). The tortuosity analysis supported by measured Dp(α) data shows that SA governs and has a larger impact on liquid‐phase tortuosity than PSD has on gaseous‐phase tortuosity. At the same value of α, the tortuosity is typically larger in the soil water than in the soil air phase, and the difference becomes more pronounced with increasing SA and at low α. In the second analysis air permeability, ka, and gas diffusivity, DP,g, are linked in the Millington and Quirk fluid flow model to describe soil structure‐forming potential and to establish a model platform to describe ka as a function of DP,g and α. Measurements on repacked, nonaggregated soil support the ka(DP,g;α) model platform, while measurements on repacked, aggregated soils and on undisturbed soils show that ka is greatly affected by soil aggregation and structure and DP,g is not. In the third analysis, a constitutive parameter model is applied to gas and solute diffusivities and air and water permeabilities in six soils along a soil texture gradient. This illustrates the different behavior of the four transport parameters with PSD and α. The liquid‐phase transport parameters show a steeper decrease with α compared with the gaseous‐phase parameters, in part due to the higher tortuosity in the liquid phase. Also, ka in undisturbed soil exhibited a less steep decrease with α compared with DP,g, probably due to preferential air flow in larger pores during convective transport. Any attempt to develop a unifying and PSD‐dependent model for transport parameters in the soil liquid and gaseous phases will require careful distinction between repacked and undisturbed soils.
An Improved Empirical Equation for Uniaxial Soil Compression for a Wide Range of Applied Stresses
Authors: Fritton D.D.
Published: July 2010

The response of soil to compaction forces is nonlinear and not completely described by existing statistical equations. The objective of this study was to find a better empirical equation for uniaxial soil compression. Disturbed and undisturbed samples from three to five horizons of four soils, and from soil mixed with four different amounts of sand, were subjected to applied stresses ranging from 0 to 2971 kPa at one to four initial water contents. Data from individual samples representing the three resulting curve shapes were used to evaluate existing and new empirical equations. A new equation was found that fit all three curve shapes better than any of the existing equations. The new equation fit data points of representative data sets with an average difference of 0.002 to 0.009 Mg m−3, compared with an average difference for two existing equations of 0.011 to 0.033 and 0.014 to 0.060 Mg m−3 The new equation was then fit to all 120 sets of experimental data, using nonlinear regression procedures. Regression relationships were established between three parameters that have traditionally been used to characterize soil compression (preconsolidation stress, compression index, and elastic rebound/recompression parameter) and the parameters of the new equation.
Sensitivity of Soil Manganese Oxides
Authors: Ross Donald S. , Hales Heidi C. , Shea-McCarthy Grace C. , Lanzirotti Antonio
Published: July 2010

Effects of sample treatment must be well understood to avoid artifacts during analysis. The effect of drying and storage was examined on nine medium‐ to high‐Mn aerobic soils using extractable Mn(II), the Cr Oxidation Test, estimated soluble C, and XANES spectroscopy. Long‐term storage (430 d) at 3°C had little effect on the Cr test. Air drying at room temperature (25°C ± 3°C) caused a drop in the Cr test within 24 h, with a further decline to as low as 45% of the original after 72 h, and less than 2% after 264 d. Extractability of Mn with pH 4.8 NH4OAc increased nearly linearly over the same time period from 0.2 mmol kg−1 to as high as 2.3 mmol kg−1 Increases in the absorbance of the extract at 360 nm, an estimate of soluble C, were well correlated within each soil with the increase in Mn(II). Pre‐treatments to remove soluble organics did not cause any increases in the Cr test of dried samples. Therefore, the loss of Cr oxidizing ability appears to be due to reduction of the oxides, not because of increased reduction of the Cr(VI) formed. No changes in XANES spectra were found after short‐term air drying at room temperature, but in the three samples examined after 428 d of drying, the main‐edge position had a downward shift of about 1.5 eV, indicating reduction. These results confirm previous findings that studies on the reactivity of soil Mn oxides need to avoid sample drying.
Short‐Term Dynamics of Root‐ and Shoot‐Derived Carbon from a Leguminous Green Manure
Authors: Puget P. , Drinkwater L.E.
Published: July 2010

Although roots are an important source of soil organic matter (SOM) and are thought to be the major constituent of the particulate organic matter (POM) fraction, few studies have documented the fate of belowground C inputs in situ. The main purpose of this experiment was to determine the fate of root‐derived C vs. shoot‐derived C and to identify factors contributing to any differences in the retention of aboveground vs. belowground C inputs. We labeled hairy vetch (Vicia villosa Roth subsp. villosa) in situ with 13CO2 and followed both root‐ and shoot‐derived C in total soil organic C (SOC) and labile C pools for the first growing season following hairy vetch incorporation. At the end of the growing season, nearly one‐half of the root‐derived C was still present in the soil, whereas only 13% of shoot‐derived C remained. A greater proportion of root‐derived C was found as occluded POM and associated with the clay and silt fraction. Greater root‐derived C also was retained as chloroform‐extractable microbial biomass. We suggest that three different mechanisms contributed to the increased retention of root‐derived C: (i) the greater biochemical recalcitrance of root litter, (ii) increased physical protection of root‐derived POM within aggregates, and (iii) the continuous nature of root C inputs from exudates and fine root turnover. We conclude that shoot residues are broken down rapidly and serve as the source of N for the following cash crop, whereas the root litter is probably largely responsible for the short‐term soil structural improvements associated with the use of green manures. Furthermore, on the basis of these findings, we hypothesize that the greater retention of root‐derived C in the first 6 mo of decomposition will increase the persistence of this C in SOM in the long term.
Dynamics of Sulfur Fractions in Brazilian Soils Submitted to Consecutive Harvests of Sorghum
Authors: Ribeiro E.S. , Dias L.E. , Alvarez. V. V.H. , Mello J.W.V. , Daniels W.L.
Published: July 2010

Different extractants have been used to determine sulfur availability in tropical soils. Due to variability in their composition, different soil S fractions are solubilized and taken up differentially by plants. We studied the dynamics of S fractions in tropical Oxisols, in the presence and absence of liming, over five consecutive harvests of sorghum [Sorghum bicolor (L.) Moench]. Fourteen soil samples (0–20 cm) with differing levels of S adsorption capacity (SAC) were characterized for the following S fractions: S‐s = ignition of a soil–sodium bicarbonate mixture; S‐a = S available in NH4OAc (0.5 M) and HOAc (0.25 M); S‐c = S available in CaCl2 (0.01 M); S‐p = S available in Ca(H2PO4)2 (500 mg P L−1 in 2.0 M HOAc); and S‐r = S‐s − S‐a. Combined soil–root–shoot results indicate the existence of a short‐term labile organic fraction and a second more recalcitrant organic fraction. In soils with low and medium SAC, the labile organic fraction drives short‐term S availability. In high‐SAC soils, the mineral fractions became the main drivers of S availability. Soil SAC strongly affected the extractant predictive potential for long‐term S availability. In low‐SAC soils, S availability was best correlated with the S‐c fraction. In medium‐SAC soils, the best predictive capacity was also associated with the S‐c fraction, followed by the S‐a fraction. Conversely, in high‐SAC soils, S availability was best correlated with the S‐a fraction, followed by the S‐p fraction. No single S‐extraction procedure appears well suited to predicting long‐term S availability across the range of soils studied.
Predicting bulk density of Ohio Soils from Morphology, Genetic Principles, and Laboratory Characterization Data
Authors: Calhoun F.G. , Smeck N.E. , Slater B.L. , Bigham J.M. , Hall G.F.
Published: July 2010

A 937‐horizon data set composed of site characteristics, morphology, and laboratory characterization data for soils of Ohio was used to develop soil bulk density (Db) prediction models. We tested the hypothesis that using a combination of continuous variables (laboratory data) and nominal variables (site/state factor and morphological class descriptors) would enable the development of improved Pedo‐Transfer Functions (PTFs) for Db Three primary models were developed. The Lab Model, composed entirely of continuous variables, accounted for 56% of the variability in Db Using only state factors and morphology as nominal variables, the Field Model explained 69%. A combined Field + Lab Model accounted for 72%. Restricting the data set to samples derived from loess and glacial till generated a Field + Lab Model that explained nearly 80% of the variability in Db for a subset of 402 horizons.
Seasonal Nutrient Dynamics of Forested Floodplain Soil Influenced by Microtopography and Depth
Authors: Stoeckel Donald M. , Miller-Goodman Mary S.
Published: July 2010

Edaphic and hydrologic influences on floodplain soil nutrient dynamics must be characterized in order to more fully understand ecosystem functions of forested floodplains. The objective of this study was to characterize the impacts of microtopography and depth on soil microbial processes related to nutrient dynamics in a forested floodplain soil. Nutritional and biological parameters were measured seasonally for 2 yr at paired plots representing two microtopographic classes (swales and slopes) and three soil profile locations—surface organic material, root zone (RZ, 0–0.1 m), and sub‐root zone (SR, 0.2–0.3 m)—on the Coosawhatchie River floodplain, South Carolina. Litter decomposition dynamics followed trends previously described in the literature: N and P concentrations increased relative to C following litterfall, and the relative increase was greater in swales than on slopes. Mineral soil on the Coosawhatchie floodplain was rich in total P compared with other sites. Soil N pools fluctuated together with C, while P was redistributed by floodwater independently of major C and N pools. As a result, P accumulated more in swale soil. Carbon/N ratios in RZ soil were seasonally constant, averaging 14 in swales and 19 on slopes. Carbon/total P ratios were more variable, ranging from 77 to 118 in swales and 151 to 246 on slopes. Microtopographic differences (<1 m) profoundly influenced nutrient dynamics, particularly P, of surface organic material and soil on this floodplain.
Modeling the Impact of Tidal Inundation on Submerging Coastal Landscapes of the Chesapeake Bay
Authors: Hussein A.H. , Rabenhorst M.C.
Published: July 2010

Chronofunctions describing changes in electrical conductivity (EC) and exchangeable sodium percentage (ESP) were derived for upland and submerged pedons along two coastal soil transects in Dorchester County, Maryland. The weighted mean EC and ESP were regressed against time in order to derive models that describe changes in salinization and alkalinization. This was best approximated using exponential and linear models. During the early and intermediate stages of pedogenesis, the exponential model estimated the average rate of salinization for the whole profile to increase from 0.02 to 0.06 dS m−1 yr−1, while the average rate of alkalinization increased from 0.02 to 0.05% yr−1 The linear model estimated the average rate of salinization to be 0.04 dS m−1 yr−1, while it estimated the average rate of alkalinization to be 0.03% yr−1 Because only data from early and intermediate stages of the idealized chronofunctions of salinization and alkalinization were available, the use of the models to predict late‐stage impact on EC and ESP is limited. To address the limitation, the measured data were joined with theoretical limits to derive sigmoidal chronofunctions. The future changes in soil salinity and alkalinity were projected using the sigmoidal models and various sea level rise scenarios.
State Space Analysis of Soil Water and Salinity Regimes in a Loam Soil Underlain by Shallow Groundwater
Authors: Wu L. , Skaggs T. H. , Shouse P. J. , Ayars J. E.
Published: July 2010

Improved methods of irrigation scheduling are needed to reduce irrigation and drainage water volumes while not affecting yield. State space models based on mass balance principles and empirical flux laws can be used to estimate and forecast soil water and salinity regimes in the field. In this research, a state space model was developed that describes soil water and salinity dynamics and includes the effects of shallow, saline groundwater. The model was evaluated using daily time domain reflectometry (TDR) measurements of the soil water content (θ) and bulk soil electrical conductivity (ECb). Data were collected throughout the 1997 growing season in a field where cotton (Gossypium hirsutum L.) was being grown using an experimental shallow groundwater management technique that was designed to reduce both irrigation and drainage volumes. The model was tested by supposing that either weekly or biweekly profile‐averaged measurements of θ and ECb were available, and then comparing the resulting filtered model forecasts with the full data set. The results show that the measured water content was within the predicted confidence intervals of 1‐ or 2‐wk forecasts of the profile‐averaged water content, soil water EC (ECw), and EC of saturated extract (ECe), even though the performance of the model in predicting the resident salt concentration (mass of salt per volume of soil) was less satisfactory.
Predicting Temperature and Heat Flow in a Sandy Soil by Electrical Modeling
Authors: Guaraglia Dardo O. , Pousa Jorge L. , Pilan Leonardo
Published: July 2010

A model based on an electrical analogy between a soil column and an electrical transmission line was developed to predict temperature and heat flow as functions of depth and time in a sandy soil, taking into account changes in soil thermal conductivity and volumetric heat capacity due to variations in water content. The model was excited alternatively by both measured soil temperature at the 1‐cm depth and solar radiation [Sr(t)], and solved with available electrical analysis software. The results were compared with field data collected during a 35‐d field experiment carried out in the Lido beach, Venice, Italy. A very simple transfer function was identified for using measured Sr(t) as the input signal. This transfer function turned out to vary inversely with Sr(t). When the model is excited by temperature, and soil water content corrected every 5 d, the root mean square error (RMSE) for the calculated temperature at the 5‐cm depth is less than 1°C. When it is excited by Sr(t), the RMSE at the 1‐cm depth is less than 2°C. Hourly temperatures at different depths were found to depend strongly on surface phenomena, and to a lesser extent on other factors like soil water content below the top layers.
Predicting Aluminum and Soil Organic Matter Solubility Using the Mechanistic Equilibrium Model WHAM
Authors: de Wit Helene A. , Groseth Tore , Mulder Jan
Published: July 2010

The mechanistic equilibrium model WHAM is used to describe solution–solid phase interactions in the forest floor with regard to Al and soil organic matter (SOM) solubility. WHAM takes into account specific and nonspecific ion‐binding to humic compounds. Experimental data from a forest soil that was manipulated with respect to its Al content were obtained from batch studies and a field manipulation experiment. WHAM was parameterized using observations of pH, concentrations of inorganic Al, and DOC obtained in batch. Model fits of pH, concentrations of inorganic Al (>5 × 10−6 mol L−1), and DOC were good to tolerable (1, 9, and 15% deviation, respectively). Values of optimized model parameters agreed reasonably with analytically determined quantities. Using the optimized parameters, WHAM simulated addition of AlCl3 to the same soil. Comparison between model predictions and batch observations showed a deviation for pH, Al (>5 × 10−6 mol L−1), and DOC of 3, 60, and 15%, respectively. We regard this as a reasonable model performance and support for the assumption of an organic complexation control of Al solubility in organic soils. Application of WHAM to predict effects of AlCl3 addition in the field resulted in qualitative agreement between simulations and observations from tension lysimeters in the forest floor, but in a failure regarding the observed ranges of H, Al, and DOC. The discrepancy between model simulations and field observations may be explained qualitatively by a lack of equilibrium due to the diffusion‐limited exchange of solutes between immobile water in micropores and mobile water in macropores.
A Procedure for Isolating Soil Organic Matter Fractions Suitable for Modeling
Authors: Sohi Saran P. , Mahieu Nathalie , Arah Jonathan R. M. , Powlson David S. , Madari Beáta , Gaunt John L.
Published: July 2010

Fractions of soil organic matter (SOM) were obtained from three soils using alternative physical fractionation procedures, and evaluated against the requirements of model pools. We compared two‐stage density fractionation (isolating free and intra‐aggregate fractions, before and after dispersion, respectively) with particle‐size separation of dispersed soil. For full comparison, the organomineral fraction residual from density fractionation was also size separated. In standardizing the density‐based method, we found recovery of intra‐aggregate organic matter highly sensitive to separation density as compared with the free. Recovery of the intra‐aggregate was also influenced by dispersion energy. The greatest amount was obtained using a combination of the highest density (1.80 g cm−3) and dispersion energy (1500 J g−1). Analysis by 13C nuclear magnetic resonance (NMR) showed O‐alkyl/alkyl‐C ratios 1.38 to 2.30 times greater in intra‐aggregate organic matter than in the free. Diffuse reflectance Fourier transform infrared spectroscopy (DRIFT) also indicated a greater proportion of aliphatic hydrocarbon, carboxylic anions, and aromatic C in intra‐aggregate organic matter. The findings suggest this fraction comprises more decomposed and transformed organic matter relative to the free. Higher signal/noise ratios in NMR spectra of particle‐size fractions (compared with their organomineral equivalents) were attributed to C in particulate SOM, not removed by prior density separation. Whilst particle‐size fractions confuse particulate SOM with that attached to mineral surfaces, fractions isolated by two‐stage density separation are small in number and display distinct chemical properties. We suggest they provide a sound basis for a model of SOM turnover based on measurable pools.
Soil aggregate stability and organic matter in clay and fine silt fractions in urban refuse‐amended semiarid soils
Authors: Caravaca F. , Lax A. , Albaladejo J.
Published: July 2010

Organic refuse application to soil may improve soil structure and thus soil quality and productivity. Two semiarid, structureless soils with <10 g kg−1 organic C (OC), differing in clay mineralogy, were amended annually at rates of 30 g kg−1 fresh or composted refuse to a total of 60 g kg−1 in a greenhouse experiment lasting 2 yr. Fresh refuse additions significantly increased the soil aggregate stability in water by 17%. Composted refuse application only increased aggregate stability in the beidellitic clay‐dominated soil (13%). In both soils, the greatest increase in OC and humin following refuse additions occurred in the fine silt fraction, which contained less decomposed organic matter than the clay fraction. In the beidellitic clay soil, this increase in OC was larger than in the illitic clay soil. The aggregate stability of the beidellitic clay soil was significantly correlated with OC and humin of fine silt fraction.
Long‐term patterns in forest‐floor NITROGEN‐15 natural abundance at hubbard brook, nh
Authors: Pardo L. H. , Hemond H. F. , Montoya J. P. , Siccama T. G.
Published: July 2010

To test the hypothesis that δ15N in the forest floor remains constant over time, we measured δ15N in forest‐floor samples from 1969, 1978, 1987, and 1992 at the reference watershed, W6, at the Hubbard Brook Experimental Forest (HBEF), New Hampshire. The δ15N of the Oa horizon increased significantly (P < 0.05) from 3.00‰ in 1969 to 4.89‰ in 1978, then decreased significantly to 3.81‰ in 1987 and remained near that level in 1992. In the Oie horizon, δ15N increased significantly from 0.17‰ in 1969 to 0.91‰ in 1978 and remained at the higher level for the later years. Thus δ15N was not at steady state in either the Oie or Oa horizon for the period 1969 to 1992 in the reference watershed. These data suggest that even relatively short‐term disruptions of the N cycle (either by anthropogenic or natural disturbance) can alter the δ15N in the forest floor, and should be considered in evaluating natural abundance data.
Leaf Litter Decomposition and Nutrient Dynamics in Four Southern Forested Floodplain Communities
Authors: Baker Terrell T. , Lockaby B. Graeme , Conner William H. , Meier Calvin E. , Stanturf John A. , Burke Marianne K.
Published: July 2010

Decomposition of site‐specific litter mixtures was monitored for 100 wk in four floodplain communities: (i) a mixed oak community along the Cache River in central Arkansas, (ii) a sweetgum (Liquidambar styraciflua L.)–cherrybark oak (Quercus falcata var. pagodaefolia Ell.) community along Iatt Creek in central Louisiana, (iii) a sweetgum‐swamp tupelo [Nyssa sylvatica var. biflora (Walt.) Sarg.] community, and (iv) a laurel oak (Quercus laurifolia Michx.) community along the Coosawhatchie River in southeastern South Carolina. Soil temperature, hydroperiod, and litter quality (C:N, C:P, N:P, lignin:N) were used to interpret differences in the rates of mass loss and nutrient dynamics. After 100 wk, litter mixtures retained 33, 18, 8, and 5% of original mass on the Cache, Coosawhatchie (laurel oak community), Coosawhatchie (sweetgum–swamp tupelo community), and Iatt floodplains, respectively, and these differences appeared related to hydroperiod. Decay rates were comparable to rates reported in similar floodplain environments. Net mineralization of both N and P was observed after 100 wk, but both elements accumulated in litter mixtures periodically. Differences in hydroperiod were observed among the four floodplain communities and decomposition of and nutrient mineralization from litter among them appeared to be inversely related to the number and duration of flood events. Litterbags containing leaf litter of a single‐species (i.e., cherrybark oak) were also monitored on three of the four sites to compare decay rates and nutrient dynamics with the litter mixtures. On the Cache River floodplain, slower decay of poorer quality cherrybark oak litter suggested that litter quality drove decomposition under similar edaphic conditions.
Influence of a Nonionic Surfactant on the Water Retention Properties of Unsaturated Soils
Authors: Karagunduz Ahmet , Pennell Kurt D. , Young Michael H.
Published: July 2010

Surfactants are widely used in household products, industrial processes and as adjuvants to improve the delivery and effectiveness of agrochemicals. Due to their amphiphilic nature, surfactants tend to accumulate at gas‐liquid and solid‐liquid interfaces, and thus, have the potential to influence water flow and retention in unsaturated soils. The objective of this study was to investigate the effects of a nonionic surfactant, Triton X‐100, on the interfacial properties and capillary pressure‐water content relationships of F‐70 Ottawa sand and Appling soil. In the presence of surfactant, soil water contents decreased incrementally as the surfactant concentration was increased from 0 g L−1 up to the critical micelle concentration (CMC) of Triton X‐100 (0.15 g L−1). Over the same surfactant concentration range, the surface tension of water decreased from 7.2 × 10−2 J m−2 to 3.2 × 10−2 J m−2 while solid‐liquid contact angle decreased from 40° to 10°. No further changes in interfacial properties or soil water characteristics were observed at surfactant concentrations above the CMC. The experimental results were used to develop and evaluate alternative scaling approaches to describe concentration dependent changes in soil water characteristics based on the van Genuchten model. A scaling factor that incorporated both surface tension and content angle relationships provided accurate predictions of soil water retention curves over a range of surfactant concentrations. A simplified form of the scaling factor also was developed, on the basis of a single fitting parameter without the need for surface tension and contact angle data. Although further validation of the simplified scaling factor will be required, this approach offers an efficient means to describe the effects of concentration dependent changes in interfacial properties on soil water characteristics.
Phosphorus‐Sorption Characteristics of Calcareous Soils and Limestone from the Southern Everglades and Adjacent Farmlands
Authors: Zhou Meifang , Li Yuncong
Published: July 2010

The understanding of P sorption and desorption by soils is important for safeguarding water quality and for fertilizer management. Little is known about the P‐sorption characteristics of the calcareous soils and limestone bedrocks in southern Florida. In this study, 19 samples of calcareous soil and subsurface limestone bedrock were collected from the southern Everglades wetland, pineland, and nearby farmland. At very low P concentrations, P sorption in these soils fit the linear isotherm. The equilibrium P concentration at zero‐net P sorption (EPCo) of soils correlated positively with P saturation. Phosphorus‐sorption data of soils at medium P concentrations fit the Freundlich and Langmuir equations up to a point at high P concentrations where the slope of the isotherm changed abruptly. In bedrock samples the sorption‐isotherm‐inflection point, which is caused by P precipitation, occurred at much lower solution P concentrations than in the case of soils (4–18 vs. 400–600 mg mL−1). Also bedrock samples had significantly lower Freundlich values, Kf, than soils. The sorption of P in soils occurred at relatively low solution P concentrations (as indicated by Freundlich value, Kf), and appears to be caused by strong affinity of the noncarbonate clay, while the P sorption at relatively high solution concentrations (as indicted by Langmuir maximum sorption, Smax) appears to be caused by the affinities of both the noncarbonate clay and carbonate clay. Phosphorus‐sorption values (Psorption) estimated from the one‐point isotherm were comparable with the Smax values calculated from the Langmuir isotherm. Phosphorus saturation and the P‐retention capacities (Smax or Psorption) were correlated strongly to the percentage of P desorption.
Effect of Composted Organic Matter on Boron Uptake by Plants
Authors: Yermiyahu U. , Keren R. , Chen Y.
Published: July 2010

Boron uptake by plants is controlled by the B level in soil solution rather than the total B content in soil. The affinity of organic matter for B can affect B uptake by plants because of changing B concentration in soil solution. The role of soil organic matter content on B soil solution concentration and uptake by bell pepper (Capsicum frutescensL.) were studied. The organic matter used was mature compost (COM), produced from the solid fraction of separated straw‐containing cattle manure. Plants were grown in five soil–sand–COM mixtures containing 0, 1, 3, 6, or 10% COM by weight. Four levels of B were applied. The soil was analyzed for B content at the beginning of the experiment and at harvest. Boron concentration in the leaves was determined 45 d from planting. Boron concentration in the soil solution at the beginning of the experiment decreased with increasing levels of COM. This decrease was most prominent at high levels of B application. The effect of the COM level on leaf B concentration was also prominent at high B application rates, with increasing levels of COM resulting in less B in the leaf tissues. Boron concentration in the leaves was highly significantly correlated (r2= 0.88) with the B concentration adjusted in the soil solution. This correlation coefficient was further improved (r2= 0.98) when B concentration in the soil solution was calculated using a B adsorption model. The results presented herein indicate that organic matter plays an important role in controlling B concentration in the soil solution, and that it has a prominent effect on reducing B uptake by plants.
Altered Podzolization Resulting from Replacing Heather with Sitka Spruce
Authors: Mossin Lone , Jensen Birgit Tejg , Nørnberg Per
Published: July 2010

Podzolization processes were studied under heather (Calluna vulgaris L. Hull) and Crowberry (Empetrum nigrum L.) and sitka spruce [Picea sitchensis (Bong.) Carr] planted on former heathland at Hjelm Hede, Jutland, Denmark. The aim was to compare changes in soil‐water chemistry with changes in the solid‐state chemistry after vegetation change. Fourteen profiles under heather and five profiles under spruce were examined and soil water was collected in lysimeter wells from the bottom of individual soil horizons A, E, Bh, and Bs from four representative profiles. The investigated area has been heathland for more than 2000 yr and part of it was planted with sitka spruce in 1933. The sitka spruce litter provided a more acidic soil environment, and the taller canopy increased the deposition of seasalts. The acidifying effects were increased by increased evapotranspiration from the plantation compared with the heathland. The investigation indicates disturbance of the podzolization process under spruce. Soil‐water chemistry showed a lack of Al immobilization in the B horizon under spruce, contrary to the heather system. Analyses of the spruce soil reveal a depletion of pyrophosphate (PYR) extractable Al and Fe. The charge balance in soil water showed a high deficit of anions under spruce compared with the dissolved organic C (DOC) concentration. Therefore, the deficit cannot be exclusively ascribed to negative charge on DOC. Sources of anion deficit might include (i) dissociated organic acids (R‐COO−), (ii) reduction in positive charge because of the existence of organo‐metal complexes [R‐(COO)2Al+], and (iii) reduction in positive charge because of an inorganic pH‐dependent species distribution of Al [Al(OH)2+, Al(OH)+2
Changes in Soil Organic Matter Fractions under Subtropical No‐Till Cropping Systems
Authors: Bayer C. , Martin-Neto L. , Mielniczuk J. , Pillon C. N. , Sangoi L.
Published: July 2010

Conservation management systems increase soil C and N pools. However, their effects on particulate (>53 μm) and mineral‐associated (<53 μm) soil organic matter (SOM) fractions are less understood under subtropical climatic conditions. This study evaluated the long‐term (12‐yr) effects of three no‐till cropping systems {bare soil, BS; oat (Avena strigosaSchreb.) + vetch (Vicia sativaL.)/maize (Zea maysL.) + cowpea (Vigna unguiculataL. Walp.), O + V/M + C; and maize +Cajanus[Cajanus cajan(L.) Millsp.], M + C} on C and N pools in particulate and mineral‐associated SOM. The study was performed in southern Brazil, on a sandy clay loam Acrisol. Cropping systems that included cover crops increased C and N pools in both particulate and mineral‐associated SOM when compared with BS. Mineral‐associated SOM had five to nine times more C and 13 to 26 times more N than particulate organic matter and was responsible for 69 to 80% of total atmospheric CO2sequestred by soil in O + V/M + C (38 Mg ha−1) and M + C (51 Mg ha−1). The higher C and N pools were associated with greater recalcitrance of mineral‐associated SOM to biological decomposition, resulting from its interaction with variable charge minerals. The negative relationship between decay rates of SOM and the concentrations of Fe oxides and kaolinite demonstrated the physical stability of SOM caused by interaction with variable charge minerals. Power saturation curves of electron spin resonance (ESR) spectroscopy in the 20‐ to 53‐, 2‐ to 20‐, and <2‐μm granulometric fractions also reinforced this hypothesis. The SOM interaction with variable charge minerals plays an important role in preserving SOM storage, enhancing the potential of tropical and subtropical soils to act as an atmospheric CO2sink.
Evaluating Soil Quality–Soil Redistribution Relationship on Terraces and Steep Hillslope
Authors: Li Y. , Lindstrom M. J.
Published: July 2010

Soil redistribution from tillage and water erosion have the potential to modify the spatial patterns of soil quality on terraced and steep cultivated hillslopes. However, few studies have investigated this relationship. Our objectives were to quantify soil quality parameters along terraced and steep hillslopes and determine the relationship between soil redistribution from tillage erosion and water erosion on soil quality parameters in the Chinese Loess Plateau. Soil quality indicators, i.e., soil organic matter (OM), available P, N, bulk density (Db), and clay and silt contents were measured at 5‐m intervals on a terraced field and at 10‐m intervals on a steep cultivated hillslope in a down slope transect. Soil redistribution rates from tillage and overland flow were obtained by137Cs technique integrated with a tillage erosion prediction model (TEP). Water erosion was the primary cause for the overall decline in soil quality on the steep cultivated hillslope while tillage erosion had a comparable contribution to overall level in soil quality on the terraced hillslope. Soil movement by tillage controlled the spatial patterns in OM, N, and P on both terraced and steep cultivated hillslopes. Selective removal of finer particles by water erosion caused a linear decrease in clay content of 0.02% m−1and corresponding increase in silt content of 0.04% m−1downslope on the steep cultivated hillslope. The impact of tillage erosion on OM, N, and P on the steep cultivated hillslope can be assessed using the change in adjacent slope gradients (X) through a soil quality‐topography regression model,Y=aX+b
Analytical Models for Soil Pore‐Size Distribution After Tillage
Authors: Leij Feike J. , Ghezzehei Teamrat A. , Or Dani
Published: July 2010

Tillage causes soil fragmentation thereby increasing the proportion of interaggregate (structural) pore space. The resulting tilled layer tends to be structurally unstable as manifested by a gradual decrease in interaggregate porosity until a new equilibrium has been reached between external loads and internal capillary forces at a rate governed by the soil rheological properties. The soil pore‐size distribution (PSD) will change accordingly with time. We have previously applied the Fokker‐Planck equation (FPE) to describe the evolution of the PSD as the result of drift, dispersion, and degradation processes that affect the pore space in unstable soils. In this study, we provide closed‐form solutions for PSD evolution, which can be used to predict temporal behavior of unsaturated soil hydraulic properties. Solutions and moments of the PSD were obtained in case: (i) drift and degradation coefficients depend on time and the dispersivity is constant and (ii) drift and dispersivity are also linearly related to pore size. Both solutions can model the reduction in pore size during the growing season while the second solution can account for a reduction in the dispersion of the PSD. The solutions for PSD were plotted for a mathematically convenient expression for the drift and degradation coefficients and for an expression derived from a model for soil aggregate coalescence. Experimental data on the settlement of a Millville (coarse‐silty, carbonatic, mesic Typic Haploxeroll) silt loam during wetting and drying cycles were used to determine time‐dependent drift and degradation coefficients according to this coalescence model. The solution for the PSD was used to independently predict the water retention curve, which exhibited a satisfactory agreement with experimental retention data at the end of two drying cycles.
VERTICAL DISTRIBUTIONS OF CARBON DIOXIDE DIFFUSION COEFFICIENTS AND PRODUCTION RATES IN FOREST SOILS
Authors: Hashimoto Shoji , Suzuki Masakazu
Published: July 2010

In this study, we developed a new method for evaluating vertical profiles of CO2 gas diffusivity and CO2 gas production in soil samples. The CO2 flux at the boundary and the steady‐state CO2 gas profile are measured under two boundary gas conditions. The differential form of Fick's second law can then be used to calculate the gas diffusion coefficients and CO2 production rate. This method was applied to an undisturbed forest soil sample in the laboratory. Both gas diffusion coefficients and CO2 production rates decreased with increasing depth. The relative gas diffusion coefficients ranged between 0.03 and 0.15, and the CO2 production rates ranged between 2.1 × 10−8 and 4.7 × 10−8 kg CO2 m3 s−1 at 20°C. Unsteady changes in the CO2 concentration profile in the soil column, and flux from the soil surface were successfully simulated with these values.
Adsorption and Desorption of Indifferent Ions in Variable Charge Subsoils
Authors: Qafoku Nikolla P. , Sumner Malcolm E.
Published: July 2010

The relationship between soil solution ionic strength (IS) and the surface or counter‐ion charge density (CICD) is well described by the double layer theory. However, the magnitude of the counter‐ion charge may be affected by phenomena that are likely to occur in variable charge subsoils, and research to investigate the extent of indifferent ion sorption as a function of IS is certainly needed. The objective was to study adsorption and desorption of ions in batch and column experiments, and to propose a mechanism that describes best the experimental observations in subsoils from the southeastern USA. Results showed that the cation and anion of an electrolyte were simultaneously adsorbed in approximately equivalent amounts with no net release of other ions into the soil solution. Ions were adsorbed in the Stern and diffuse layers of oppositely charged colloids since the subsoil was treated with dilute solutions. They were immediately displaced when the subsoil was washed with distilled water (dH2O), confirming the reversible nature of this phenomenon. Three different magnitudes of the CICD were observed at similar IS values. The surface charge density on negatively and positively charged soil particles may not be equal to the CICD in dilute soil solutions, and other mechanisms may operate to balance the surface particle charges. It is possible that a portion of the surface charge may be balanced as a result of the interactions among oppositely charged soil particles when their diffuse layers extend and overlap, or compress and separate in response to IS changes.
A dynamic cone penetrometer for measuring soil penetration resistance
Authors: Herrick Jeffrey E. , Jones Tim L.
Published: July 2010

Recognition of the importance of soil compaction is increasing, but instrument cost, measurement repeatability, and data interpretation limit its measurement on agricultural and rangelands. The dynamic penetrometer described here follows American Society of Agricutlural Engineers standards, but replaces the proving ring with a strike plate, a shaft extension, and a sliding hammer. The penetrometer cone is pushed into the soil by successive hammer blows. Penetration resistance is calculated as the work by the soil needed to stop cone movement divided by the penetration distance. The work by the soil is defined as the kinetic energy of the hammer when it impacts the strike plate. Construction cost is approximately $100 to $150. The standard drop height and hammer mass ensure measurements are consistent between operators.