bluuebunny/crossref_metadata_2025 huggingface dataset:
A SIMPLE METHOD FOR MEASURING THE CARBONATE CONTENT OF SOILS
Authors: Horváth Balázs , Opara-Nadi Oliver , Beese Friedrich
Published: July 2010

The traditional measurement of the carbonate content of soils with the Scheibler apparatus is slow and labor intensive. Our objective was to develop a relatively simple and accurate method. The pressure calcimeter principle was used; the pressure change caused by the reaction between HCl and a weighed soil sample was measured with a digital plunge‐in manometer through a silicone‐rubber septum placed on a screw‐capped tube. The method was calibrated with pure CaCO3 The correlation between the measured and weighed amounts was excellent (r2 = 0.999). The carbonate content of a natural soil sample was measured 10 times; the coefficient of variation was 1.9%. Ten ISE (International Soil‐Analytical Exchange) samples were analyzed with this method which contained a carbonate content of 3 to 170 g kg−1 Satisfactory results were obtained, indicating the suitability of the proposed method for practical purposes.
Emission of Nitrogen Gas, Nitrous Oxide, and Carbon Dioxide on Rehydration of Dry Feathermosses
Authors: Startsev N. A. , Lieffers V. J.
Published: July 2010

Two experiments were conducted to examine the fate of N in feathermosses when mosses were dehydrated and then rewetted. In the first experiment, dry feathermoss shoots were sealed in containers where the N2 was replaced by He. After rewetting and incubating for 20 h, gas in the containers had significant amounts of N2 and N2O and had elevated levels of CO2 compared with mosses maintained in a moist condition or dried mosses that had not been rewetted. In the second experiment, samples of feathermoss were subjected to five dry–wet cycles. By the fifth cycle, there was a 9% reduction in mass of the moss and a similar decline in quantity of N. The results of this study suggest that in forests undergoing dry–wet cycles, there is a potential for N volatilization directly from the moss layer. After drying and rewetting, the moss releases sugars and soluble forms of N into the substrate, creating a suitable environment for aerobic denitrification. Thus, more N is lost from an already N‐deficient ecosystem.
Time Dependence of Soil Mechanical Properties and Pore Functions for Arable Soils
Authors: Horn Rainer
Published: July 2010

Progressive soil degradation due to tillage operations affects crop production and its yield uncertainty, soil erosion by wind and water, and gas emission. The possibility of soil regeneration due to natural or anthropogenic processes is of major concern to sustain soil functions. Material properties like precompression stress, shear strength, and hydraulic conductivity are time dependent, while bulk density is less sensitive to time effects. The hypothesis that the change from conventional to conservation tillage affects mechanical soil strength and pore functions was tested for a stagnic Luvisol derived from glacial till in northern Germany. For more than 7 yr precompression stress, shear strength, and hydraulic conductivity were determined at three depths down to 60 cm. Approximately 3 yr after starting with the Horsch system (annual shallow chiseling in autumn down to an 8‐cm depth) as a kind of conservation tillage, soil strength, and the hydraulic conductivity increased in the topsoil by more than 50 kPa and 500 cm d−1, respectively, even at a higher bulk density as compared with the corresponding values for the conventionally tilled plots. Within the following 2 to 3 yr, these changes were also detected at the 30‐ to 35‐cm soil depth. At the depth of 55 to 60 cm the same trend started after around 7 yr. These changes can be only detected, if the tillage systems were applied continuously and if all tillage and soil operations were performed with light machines, which enable the preservation of newly formed pores and the rearrangement of soil particles creating a more stable soil structure. Thus, the susceptibility to soil deformation will be reduced due to an increased shear strength, which in turn improves pore functioning.
A Conceptual Model to Predict the Deflation Threshold Shear Velocity as Affected by Near‐Surface Soil Water
Authors: Cornelis Wim M. , Gabriels Donald , Hartmann Roger
Published: July 2010

A crucial parameter in predicting wind erosion is the deflation threshold shear velocity, which is highly dependent on near‐surface soil water. The empirical and theoretical models to predict the deflation threshold as affected by near‐surface water that have been reported in literature all suffer from a weak physical background and very large differences between the predicted results can be observed. The present study was conducted to develop a new conceptual model to predict the deflation threshold as affected by near‐surface wetness and to contribute to a better understanding of the role of the latter on deflation of sediment. The model was developed by solving the moment balance equation for entrainment of soil particles by wind, including the moments associated with drag forces, lift forces, aerodynamic moment forces, gravitational forces, and interparticle forces due to dry and wet bonding. The wet bonding force, which represents the effect of near‐surface soil water, is due to liquid bridge bonding or capillary forces, and adsorbed layer bonding or adhesive forces. It was related to the particle diameter squared, surface tension squared and the inverse of matric potential. The latter was then converted to water content by assuming a logarithmic relationship, which was shown to be valid between oven dryness and a matric potential of −1.5 MPa, a range that is of interest in the light of deflation of soil particles by wind. The conceptual model presented in this paper is relatively simple and predicts, for a given particle diameter and surface tension, the deflation threshold shear velocity as a function of the ratio between water content and the water content at a matric potential of −1.5 MPa.
Influence of Exchangeable Cations on Water Adsorption by Soil Clays
Authors: Dontsova Katerina M. , Norton L. Darrell , Johnston Cliff T. , Bigham Jerry M.
Published: July 2010

The interaction of water with the clay fractions (<2 μm) from two midwestern soils was studied using Fourier transform infrared (FTIR) spectroscopy and gravimetric methods. The soil clay fractions were obtained from a Blount loam (fine, illitic, mesic Aeric Epiaqualfs) and a Fayette silty clay loam (fine‐silty, mixed, mesic, superactive Typic Hapludalfs). These clay fractions were exchanged with Mg2+, 50:50 Ca2+/Mg2+, Ca2+, Na+, and K+ to determine the influence of the exchangeable cation on their water sorption behavior. Water sorption isotherms and FTIR spectra of the clays were collected simultaneously using a gravimetric‐spectroscopic cell. Overall, the amount of water sorbed by the samples increased as the ionic potential of the exchangeable cation increased and was strongly correlated to the hydration energy of the cations (P > F < 0.0001). The position of the H–O–H bending band (ν2 mode) also increased with increasing ionic potential of the exchangeable cation indicating strengthening of water H bonds. In addition, it was observed that the position of this band decreased with increasing water content for the Mg‐exchanged clays compared with an overall increase for the Ca‐exchanged samples. X‐ray diffraction patterns indicated an expansion of the phyllosilicate clay minerals as the water activity increased; however, no differences were observed between the Ca‐ and Mg‐exchanged samples. This study shows that the molecular properties of water on Ca‐ and Mg‐exchanged soil clays are similar to that on specimen clays and provides new insight about the role of exchangeable cations in soils.
Runoff, Soil Erosion, and Erodibility of Conservation Reserve Program Land under Crop and Hay Production
Authors: Zheng Fen-li , Merrill Stephen D. , Huang Chi-hua , Tanaka Donald L. , Darboux Frédéric , Liebig Mark A. , Halvorson Ardell D.
Published: July 2010

There are concerns that restored grasslands currently under the Conservation Reserve Program (CRP) will experience increased soil erosion when they are returned to crop production. Our objective was to compare runoff, erosion, and erodibility on CRP land converted to annual hay production (permanent hayed, PH) and crop production under conventional‐till (preplant disk tillage, CT) and no‐till (NT) management. Erosion study was conducted in central North Dakota on Typic Argiustoll soil 6 yr after the CRP land had been converted to hay production and crop production with a spring wheat (Triticum aestivum L.) –winter wheat–dry pea (Pisum sativum L.) rotation. Runoff volumes and soil loss (by alum precipitation of sediment) were measured on 1.5 by 5 m bordered plots on 4% slope under a rainfall simulator delivering 1‐ to 3‐h rains at 50 or 75 mm h−1, followed by three rains of 20 min or less at rates from 25 to 125 mm h−1 Erodibility was calculated from ratios and regressions of soil loss rates versus runoff rates measured at relative steady state. Runoff rates from 50 and 75 mm h−1 rains for CT, NT, and PH averaged 9, 12, and 21 mm h−1, respectively, and supported soil loss rates of 20, 7, and 8 g m−2 h−1 Erodibility of undisturbed CT, NT, and PH was 1.65, 0.29, and 0.28 g m−2 mm−1, respectively, showing NT did not differ from PH and that CT management increased erodibility six‐fold above PH. Thorough disk tillage increased erodibility three‐fold over CT, 15‐fold over NT, and nine‐fold over PH. Complete, nondisturbing residue removal increased erodibility less than tillage, from 1.2 times for CT to 2.5 times for NT. Chemically weeded NT exhibited the same low erodibility as the grassland PH treatment under the conditions of study—4% land slope, above average precipitation, and a residue‐productive crop rotation. However, erodibility of tilled NT was significantly higher than that of tilled PH, showing the higher inherent stability of grassland surface soil with its perennial plant root structures.
Carbon Dioxide and Nitrous Oxide Emissions following Fall and Spring Applications of Pig Slurry to an Agricultural Soil
Authors: Rochette Philippe , Angers Denis A. , Chantigny Martin H. , Bertrand Normand , Côté Denis
Published: July 2010

In Québec, most pig slurry is applied to agricultural soils in the spring and fall. A study was initiated to compare the impact of the contrasting spring and fall weather conditions on CO2 and N2O emissions, and on the transformation of pig slurry C and N in a loamy soil cropped to maize (Zea mays L.). Treatments were approximately 200 kg total N ha−1 either as a spring (SPRING) or fall (FALL) application of pig slurry, and 150 kg N ha−1 as NH4NO3 (control). Fluxes of CO2 and N2O, and soil O2, CO2, N2O, NH4+, NO3−, extractable C and microbial biomass C (MBC) contents were measured 50 times over a 1‐yr period. Fluxes of N2O were generally low during the experiment but were greatly increased in recently manured soils when soil O2 concentration fell below 0.20 mol mol−1 Soil was warm and well‐aerated following spring slurry application. Under these conditions, slurry NH4–N was rapidly nitrified and high N2O emissions attributed to denitrification occurred when soil was rewetted by abundant rainfall. For the fall applied slurry, wet and cool conditions limited net nitrification and resulted in little accumulation of NO3–N, thus limiting potential for subsequent denitrification and N2O emissions. Cumulated N2O emissions during the experiment represented 1.74, 2.73, and 1.14% of added N in the FALL, SPRING, and NH4NO3 plots, respectively. Fluxes of CO2 and cumulated CO2–C losses were also greater for SPRING than for FALL application. Our results clearly show that the impacts of the timing of animal manure application on N2O emissions cannot be generalized, but will vary between years in response to interactions between crop, climatic, and soil factors.
Two‐dimensional Markov Chain Simulation of Soil Type Spatial Distribution
Authors: Li Weidong , Zhang Chuanrong , Burt James E. , Zhu A.-Xing , Feyen Jan
Published: July 2010

Soils typically exhibit complex spatial variation of multi‐categorical variables such as soil types and soil textural classes. Quantifying and assessing soil spatial variation is necessary for land management and environmental research, especially for accurately assessing the water and solute transport processes in watershed scales. This study describes an efficient Markov chain model for two‐dimensional modeling and simulation of spatial distribution of soil types (or classes). The model is tested through simulations of a simplified soil map. The application of the model for predictive soil mapping with parameters estimated from survey lines is explored. Analyses of both simulated maps and associated semi‐variograms show that the model can effectively reproduce observed spatial patterns of soil types and their spatial autocorrelation given an adequate number of survey lines. This indicates that the model is a feasible method for modeling spatial distributions of soil types (or classes) and the transition probability matrices of soil types in different directions can adequately capture the spatial interdependency relationship of soil types. The model is highly efficient in terms of computer time and storage. The model also provides an approach for assessing the uncertainty of soil type spatial distribution in areas where detailed survey data are lacking. The major constraint on applications of the model at this stage is that the minor soil types are relatively underestimated when survey lines are too sparse.
Soil Respiratory Quotient Determined via Barometric Process Separation Combined with Nitrogen‐15 Labeling
Authors: Müller Christoph , Abbasi M. Kaleem , Kammann Claudia , Clough Tim J. , Sherlock Robert R. , Stevens R. James , Jäger Hans-Jürgen
Published: July 2010

The barometric process separation (BaPS) and 15N dilution techniques were used to determine gross nitrification rates on the same soil cores from an old grassland soil. The BaPS‐technique separates the O2 consumption into that from nitrification and that from soil organic matter (SOM) respiration. The most sensitive parameter for the calculations via the BaPS technique is the respiratory quotient (RQ = ΔCO2/ΔO2) for SOM turnover (RQSOM). Combining both methods (BaPS–15N) allowed the determination of the RQSOM The RQ value determined in such a way is adjusted for the influence of nitrification and denitrification, which are both characterized by totally different RQ values. The results for the grassland soil showed that 6 to 10% of O2 was consumed by nitrification when incubated at 20°C and 0.49 g H2O g−1 soil. A set of BaPS measurements with the same soil at various temperature and moisture contents showed that up to 49% of the total O2 consumption was due to nitrification. The calculated RQSOM values via the BaPS–15N technique presented here are more closely associated with the overall SOM turnover than the usual net RQ reported in the literature. Furthermore, the RQSOM value provides an overall indication of the decomposability and chemical characteristics of the respired organic material. Hence, it has the potential to serve as a single state index for SOM quality and therefore be a useful index for SOM turnover models based on substrate quality.
Biodegradability of Humic Substances and Other Fractions of Decomposing Leaf Litter
Authors: Qualls Robert G.
Published: July 2010

Formation of chemically resistant humic substances might be an important process controlling recycling of soil C to the atmosphere. Humic substances are believed to be resistant to microbial decomposition because they accumulate in soil, but there is little direct experimental evidence for their inherent recalcitrance. My objective was to compare the microbial mineralization rates of the humic and fulvic acid fraction to other fractions of decayed plant matter in soil. Uniformly 14C labeled Populus fremontii leaf litter that had decomposed for 180 d was fractionated into the NaOH‐insoluble residue, phenolic, humic acid, fulvic acid, hydrophilic acid, and hydrophilic neutral fractions. Humic acid comprised 22.7% of the C in the decomposed litter. These fractions were added to intact cores of soil or sand. Respired 14CO2 was collected in NaOH and the radioactivity counted. The substrate C mineralized in soil at the end of 1 yr was, in order from least to greatest percentage of added radioactivity mineralized: humic acid (12.7%), fulvic acid (29.2%), phenolic (35.4%), ground litter (38.8%), hydrophilic acid (44.6%), hydrophilic neutral (51.3%), and the NaOH‐insoluble residue (57.6%). In acid‐washed, nutrient‐amended sand, inoculated with soil microbes, the relative order of mineralization rates of the fractions was the same as in soil, but approximately 10% less C was mineralized. Results supported the hypothesis that humic substances are inherently difficult for microbes to mineralize, and this property can contribute to the sequestration of C in soil. Results also supported the hypothesis that the fulvic acid fraction is more rapidly mineralized than humic acid.
Post‐fire Soil Water Repellency
Authors: MacDonald Lee H. , Huffman Edward L.
Published: July 2010

Fire‐induced soil water repellency is a key control on post‐fire runoff and erosion rates, but there are few data on the persistence of soil water repellency and the soil moisture threshold at which water repellent soils become hydrophilic. This study used repeated sampling to quantify changes in soil water repellency over time and identify soil moisture thresholds for the loss of soil water repellency. The study area was a wildfire in the northern Colorado Front Range that burned 43 km2 of ponderosa and lodgepole pine forests in June 2000. Soil water repellency and soil moisture were measured periodically from June 2000 through June 2001 at 36 sites stratified by burn severity and nine unburned sites. Water repellency was assessed in the field at depths of 0 to 18 cm using the critical surface tension (CST) test. Soil water repellency was strongest in sites burned at high and moderate severity, decreased with increasing depth, and was spatially highly variable. The fire‐induced soil water repellency progressively weakened and became statistically nondetectable by 1 yr after burning. The effect of time since burning on soil water repellency was increasingly significant with increasing burn severity and progressively less important with increasing soil depth. The soil moisture thresholds at which water repellent soils become hydrophilic apparently increase with increasing burn severity. The data suggest soil moisture thresholds of approximately 10% for unburned sites, 13% for sites burned at low severity, and no less than 26% for sites burned at moderate and high severity.
Forest Floor Composition in Aspen‐ and Spruce‐Dominated Stands of the Boreal Mixedwood Forest
Authors: Hannam K. D. , Quideau S. A. , Oh S.-W. , Kishchuk B. E. , Wasylishen R. E.
Published: July 2010

The ability of high‐resolution cross‐polarization magic‐angle spinning 13C nuclear magnetic resonance spectroscopy (CPMAS 13C NMR) to characterize soil organic matter (SOM) has been previously demonstrated, but rarely has this information been directly related to local environmental conditions that affect SOM formation. In this study, CPMAS 13C NMR was used to characterize the forest floor (Oe + Oa horizon) of stands dominated by trembling aspen (Populus tremuloides Michx.) or white spruce [Picea glauca (Moench) Voss] in the boreal mixedwood forest of Alberta, Canada. Aromatic C content was higher and carbonyl C content was lower in the forest floor of spruce stands than in aspen stands. Within stand types, correlation analyses indicated significant relationships between the composition of the forest floor and soil temperature, mass of the Oi horizon, and mass of the moss layer. However, these relationships could not explain observed differences in the chemical composition of the forest floor between stand types. Although forest floor from spruce stands was largely composed of moss, which is low in aromatic C, it had a greater aromatic C content than forest floor from aspen stands, where moss was rare. Furthermore, a lack of significant correlations across stand types suggests that there are different relationships between the chemical and environmental characteristics of forest floor from spruce and aspen stands.
Rainfall Timing and Ammonia Loss from Urea in a Loblolly Pine Plantation
Authors: Kissel D. E. , Cabrera M. L. , Vaio N. , Craig J. R. , Rema J. A. , Morris L. A.
Published: July 2010

Surface application of urea to pine forests may lead to ammonia (NH3) loss. It is generally believed that rainfall received soon after urea application will wash the urea and its hydrolysis products into the soil and stop NH3 loss, but quantitative data are lacking, especially for the forest environment. The objective of this study was to quantify the effect of rainfall on loss of NH3 when received at different times following urea application. Four field studies were performed in a midrotation loblolly pine (Pinus taeda L.) plantation, where NH3 volatilization chambers were fertilized with 200 kg ha−1 N and NH3 losses were measured for either 29 or 58 d. In a complementary lab study, both NH3 loss and movement of fertilizer N into the soil were measured following simulated rain. Loss of NH3 from urea was either increased or not affected by simulated rainfall applied after the urea granules were dissolved by dew. Increased NH3 loss due to simulated rainfall was attributed to inefficient downward leaching of urea and increased water content, which is known to increase the rate of urea hydrolysis. In contrast, simulated rainfall applied immediately after urea application reduced NH3 losses to <1% of the applied urea. Our results show that unless rain occurs before urea is dissolved by morning dew, it may not be effective at leaching urea into the soil and reducing NH3 losses. Further research should be conducted to elucidate the mechanism of urea retention by the O horizon in pine forests.
Properties of Water‐Dispersible Colloids from Macropore Deposits and Bulk Horizons of an Agrudalf
Authors: Kjaergaard Charlotte , Hansen Hans Christian B. , Koch Christian B. , Villholth Karen G.
Published: July 2010

Mobility of colloids depends in part on the release from aggregates and the stability in suspension. This study determined the soil dispersibility of the different horizons in a Typic Agrudalf. Water‐dispersible colloids (WDC) from bulk horizons and macropore deposits were characterized for mineralogy and physical chemical properties. The effect of solution pH and ionic strength on ζ‐potential and flocculation behavior was evaluated using dynamic light scattering, and the role of colloid associated organic C (OC) and sesquioxides were elucidated. The soil dispersibility did not reflect the contrasting physicochemical conditions, but was directly correlated with total clay content. Generally, WDC were enriched in OC and sesquioxides. Water‐dispersible colloids from the Ap‐horizon and from macropore deposits differed markedly from the remaining WDC‐fractions due to a significantly higher content of OC (14–35 g kg−1), AlCBD (9.3–10.6 g kg−1) and a much smaller N2–adsorption surface area (14–25 m2 g−1). Treatment with Na2S2O8 for removal of OC increased the surface area by 171–225%, indicating surface coatings of OC. The contribution of OC to the colloidal stability was inferred from: (i) a more negative ζ‐potential and larger suspension stability of WDC with larger content of OC, and (ii) reduced negative ζ‐potential as well as suspension stability after OC removal. Large variations were observed in the flocculation behavior for WDC with rather similar mineralogical composition. A two‐fold increase of the initial particle diameter occurred at an electric conductivity of 91 μS cm−1 for the least stable colloids and at 1023 μS cm−1 for the most stable and OC‐rich colloids. The effect of solution pH on flocculation was significant only at pH below 4.5.
Salinity and Zinc Application Effects on Phytoavailability of Cadmium and Zinc
Authors: Khoshgoftar A. H. , Shariatmadari H. , Karimian N. , Kalbasi M. , van der Zee S. E. A. T. M. , Parker D. R.
Published: July 2010

Salinity and Zn deficiency in soils are two factors that may change the phytoavailability of Zn and Cd. The aim of this study was to determine the effects of salinity and Zn application on soil Cd and Zn solubility and their concentration in wheat shoots. A greenhouse experiment with wheat (Triticum aestivum L. cv. Rushan) consisting of two levels of Zn (0 and 15 mg Zn kg−1, in the form of ZnSO4), and five salinity levels of irrigation water (0, 60, 120, and 180 mM NaCl, and 120 mM NaNO3) in triplicate was conducted. Wheat was seeded in pots. After 45 d of growth, the shoots were harvested, and Zn and Cd concentrations were determined. After harvesting, electrical conductivity (EC), pH, and concentrations of anions and cations were determined in soil saturation extracts. Concentrations of Cd and Zn species in soil solution were predicted using the speciation program MINTEQA2. Increasing salinity increased total Cd (CdT), Cd2+, CdCl+, CdHCO3+, and CdCl20 concentrations in the soil solution, whereas no such effect was found for the NaNO3 treatment. Higher salinity decreased the total Zn (ZnT) and free Zn2+ concentrations in the soil solution and decreased Zn concentrations in the wheat shoots. With application of Zn fertilizer, shoot Cd concentrations decreased by 11 to 90%, whereas Zn concentration increased by 75 to 103%. Increasing salinity of irrigation water decreased shoot dry matter, especially if no ZnSO4 was applied. Application of Zn had a positive effect on salt tolerance of plant and increased dry matter of shoot.
Nitrogen Fertilization on Uptake of Soil Inorganic Phosphorus Fractions in the Wheat Root Zone
Authors: Zhang Fucang , Kang Shaozhong , Zhang Jianhua , Zhang Renduo , Li Fusheng
Published: July 2010

Plant nutrient uptake from the soil is dependent on fertilizers applied, soil chemicals, and other factors. The purpose of this study is to quantify the effects of applied N fertilizers on P uptake by winter wheat (Triticum aestivumL.) and on the change of soil pH in the root zone related to reductions of inorganic P fractions in the rhizosphere soil. An experiment was conducted using different forms of N fertilizers (i.e., NH4+–N and NO3−–N) with three N concentrations (0, 100, and 300 mg kg−1) applied in a calcareous soil. Biomass and total N uptake of the plant increased with the N concentrations and NH4+–N fertilizer resulted in a greater biomass than NO3−–N nutrition. Total P uptake in the plant was also higher with NH4+–N fertilizer than with the NO3−–N nutrition. Compared with the zero N treatment, the soil pH around the roots decreased by 0.30 and 0.65 units, respectively, with N treatments of 100 and 300 mg kg−1of NH4+–N fertilizer. The amount of soil inorganic P fractions in the root zone decreased with increasing NH4+–N applied. The NO3−–N treatments reduced rhizosphere acidification and had a less impact on the soil inorganic P fractions. The results suggest that enhancing rhizosphere acidification attributable to applications of NH4+–N fertilizer can increase P availability in calcareous soils for plant uptake.
Spectral Reflectance Properties of Crusted Soils under Solar Illumination
Authors: Eshel G. , Levy G. J. , Singer M. J.
Published: July 2010

Reflectance of soil crusts has been studied under artificial light but not under solar illumination. Our objectives were to (i) compare reflectance from crusted and noncrusted soil surfaces under solar illumination, and (ii) explore the relationship between crust permeability and spectral signature. Two California soils were studied, Capay (fine, smectitic, thermic Typic Haploxererts) and Reiff (coarse‐loamy, mixed, superactive, nonacid, thermic Mollic Xerofluvents), with samples for the latter taken from plots under organic (ReiffOM) and conventional (ReiffCM) management. A laboratory rainfall simulator was used to form crusts which were sampled at different stages of development and permeability. A portable spectroradiometer was used to collect spectral data in direct sunlight for wet and dry crusted samples. Baseline spectra (albedo) of the dry samples were, in most cases, higher than spectra from the corresponding moist samples. Crusted samples exhibited higher baseline spectra compared with the noncrusted samples. The absorption feature at ≈1400 nm (related to lattice OH of montmorillonite) suggested accumulation of clay in the crust of the ReiffCM, and clay depletion from the crusts of the Capay and ReiffOM An inverse linear relationship existed between reflectance at many wavelengths and crust permeability at different stages of crust development. The reflectance at 1700 nm provided highly significant correlations with infiltration rate (IR) for all three soils, and reflectance at 2130 nm also had a highly significant correlation for the Capay. Our data suggest that spectral measurements of soil surfaces under solar illumination can differentiate between crusted and noncrusted surfaces and assist in evaluating the degree of crust development.
Soil Wetting and Texture Effects on Aggregate Stability, Seal Formation, and Erosion
Authors: Lado M. , Ben-Hur M. , Shainberg I.
Published: July 2010

Previous studies about the effect of antecedent moisture content (AMC) on seal formation have shown contradictory results. We hypothesize that this controversy is related to differences in slaking during wetting. The objectives were to analyze the effects of: (i) clay content on aggregate stability and slaking; (ii) clay content and slaking on seal formation and interrill erosion under various wetting rates (WR) and AMC under simulated rain. Aggregate stability was determined on six smectitic soils from Israel with clay content from 80 to 630 g kg−1 In the rain simulator, soils with 230, 410 and 620 g kg−1 clay were prewetted with WR = 1 and 5 mm h−1 to AMC = 0.25 and 0.5 of field capacity (FC), prior to the application of 80 mm of rain. Aggregate stability and slaking by fast WR increased with increase in clay content. In soils with 230 and 410 g kg−1 clay, raindrop impact was enough to disintegrate the aggregates and sealing was not affected by WR and AMC. Conversely, in the soil with 620 g kg−1 clay, seal formation increased with slaking caused by fast wetting. Thus, final infiltration rate of the clay soil with AMC = 0.5 FC and WR = 1 mm h−1 was 11.1 mm h−1 compared with 6.0 mm h−1 in the air‐dry soil (fast wetting by rain). The effects of WR and AMC on soil loss were similar to their effect on runoff but more pronounced. The relation between wetting process and clay content should be considered when predicting soil erosion in smectitic soils.
Map Quality for Ordinary Kriging and Inverse Distance Weighted Interpolation
Authors: Mueller T. G. , Pusuluri N. B. , Mathias K. K. , Cornelius P. L. , Barnhisel R. I. , Shearer S. A.
Published: July 2010

The selection of a spatial interpolation methods will impact the quality of site‐specific soil fertility maps. The objective of this study was to describe and predict the relative performance of inverse distance weighted (IDW) and ordinary kriging. Soil samples were collected on 30.5‐m grids for fields in five Kentucky counties and analyzed for pH, buffer pH, P, K, Ca, and Mg. From these data sets, 61‐m grid subsets were extracted. Data were interpolated with IDW and kriging procedures. Prediction efficiency (PE) was determined using an independent dataset (PEvalidation) and with cross‐validation (PEcross‐validation). Multiple stepwise regression was used to develop models that described the relative performance of ordinary kriging and IDW with statistical properties of the data. At the 30.5‐m grid scale, the performance of ordinary kriging relative to IDW improved as the range of spatial correlation increased and fit of the semivariogram model improved. However, at the 61.0‐m grid scale, the performance of ordinary kriging relative to IDW diminished as the degree of spatial structure increased and the fit of the semivariogram model improved. Alone, PEcross‐validationpoorly describes the performance of PEvalidationacross locations, soil properties, and sampling intervals (r2= 0.18). However, in combination with the range of spatial correlation, substantial variability at the 30.5‐m grid scale was described for variables with sample semivariograms that reached plateaus (R2= 0.61). In some situations, better decisions will be made regarding the use of these methods by considering the range of spatial correlation and cross‐validation statistics.
Corn‐Soybean Sequence and Tillage Effects on Soil Carbon Dynamics and Storage
Authors: Huggins D. R. , Allmaras R. R. , Clapp C. E. , Lamb J. A. , Randall G. W.
Published: July 2010

Soil organic carbon (SOC) in agroecosystems is regulated by crop rotation and soil disturbance. We assessed crop sequence and tillage effects on SOC dynamics and storage using natural 13C abundance of corn (Zea mays L.) and soybean [Glycine max (L.), Merr.]. Treatments consisted of tillage: moldboard plow (MP), chisel plow (CP), and no‐tillage (NT); and crop sequence: continuous corn (CC), continuous soybean (SS), and alternating corn–soybean (CS). Soil samples were collected after 14 yr in each treatment and in fallow alley‐ways and were analyzed for SOC, δ13C, bulk density, and pH. Tillage by crop sequence interactions occurred as treatments with MP and SS as well as fallow averaged 135 Mg SOC ha−1 (0‐ to 45‐cm depth), while CP treatments with corn (CC and CS) and NT with CC averaged 164 Mg SOC ha−1 Crop sequence effects on SOC (0‐ to 45‐cm depth) occurred when tillage was reduced with CP and NT averaging 15% greater SOC in CC than SS. In addition to less C inputs than CC, SS accelerated rates of SOC decomposition. Tillage effects on SOC were greatest in CC where CP had 26% and NT 20% more SOC than MP, whereas SOC in SS was similar across tillage treatments. Up to 33% of the greater SOC under CC for CP and NT, compared with MP, occurred below tillage operating depths. Substantial losses of SOC were estimated (1.6 Mg SOC ha−1 yr−1) despite lowering SOC decay rates with reduced tillage and high levels of C inputs with CC.
Estimating Root Biomass in Rocky Soils using Pits, Cores, and Allometric Equations
Authors: Park Byung Bae , Yanai Ruth D. , Vadeboncoeur Matthew A. , Hamburg Steven P.
Published: July 2010

Measuring root biomass is time consuming and prone to sampling error. We compared three different methods of measuring root biomass in six northern hardwood stands at the Bartlett Experimental Forest. We found that root coring, the most common method of root sampling, yields estimates of fine root biomass about 27% greater than the estimates based on roots sampled in soil pits. Soil compaction contributes about 10% to this difference; the other contributing factor is that cores cannot be taken through obstructions such as rocks and coarse roots. Pits are the only method allowing characterization of root distribution by depth in rocky soil. If the depth and diameter distribution of roots are not required, allometric equations, if available, provide the easiest method of estimating total root biomass. Equations developed at the nearby Hubbard Brook Experimental Forest predicted root mass measured in soil pits with a mean absolute error of 32%. Allometric equations systematically underpredicted observed soil pit root mass in the young stands, presumably because of mature root systems remaining from the previous cohort, and systematically overpredicted observed root mass in the oldest stands. Soil pits can accurately characterize roots up to about 2 cm; coarser roots are encountered too rarely to be estimated by this method. Soil cores sample only fine roots (up to 1–2‐mm diameter) but are much less work than excavating soil pits. Root mass estimates made using cores are more accurate if larger diameter corers are used (5 cm rather than 2.5 cm); subsampling before picking roots can help to control labor costs in the face of larger sample sizes.
TEMPORAL PERSISTENCE IN VERTICAL DISTRIBUTIONS OF SOIL MOISTURE CONTENTS
Authors: Pachepsky Ya. A. , Guber A. K. , Jacques D.
Published: July 2010

When a field or a small watershed is repeatedly surveyed for soil water content, sites often can be spotted where soil is consistently wetter or consistently dryer than average across the study area. The phenomenon has been called time stability, temporal stability, or temporal persistence in spatial patterns of soil water contents. Relatively less is known about temporal persistence of water content at various depths. The objectives of this work are to demonstrate the temporal persistence in soil water contents measured on a vertical two‐dimensional grid, and to propose a technique to use this persistence to remedy the effect of probe malfunctioning on the estimates of the average water content in the layer. Sixty time domain reflectometry (TDR) probes (two rods) were installed along the trench in loamy soil at 12 locations with 50‐cm horizontal spacing at five depths (15, 35, 55, 75, and 95 cm). The water content data were incomplete due to malfunctioning of connections in the automated measurement system. When all probes worked, some probes at a given depth consistently showed water contents below average whereas others showed water contents above the average. To quantify the persistence, we computed relative water contents as ratios of individual‐probe water contents to average water contents from the same depth. Average relative water contents were used in a technique we proposed to correct estimates of depth‐average water contents by accounting for missing data. A numerical experiment showed the efficiency of the proposed technique. Corrections for temporal persistence can be useful in estimating layer‐averaged water contents and their uncertainty.
Soil Surface Fluxes of Greenhouse Gases in an Irrigated Maize‐Based Agroecosystem
Authors: Amos Brigid , Arkebauer Timothy J. , Doran John W.
Published: July 2010

An understanding of the effect of fertility management on soil surface fluxes of CO2, N2O, and CH4 is essential in evaluating C sequestration measures that attempt to increase the amount of crop residue returned to the soil through increased fertilizer inputs. In this study, soil surface CO2 flux was measured over a 27‐mo sampling period in continuous maize (Zea mays L.) plots managed under either an intensive fertility regime (M2) or recommended best management (M1). Flux was significantly higher in the M2 treatment on only 2 d during the first growing season. Annual estimates of soil surface CO2 flux, based on a modified exponential equation that incorporates leaf area index (LAI) to predict temporal changes in soil respiration, averaged 11550 kg C ha−1 yr−1 for both treatments (approximately 31.64 kg C ha−1 d−1 on average). Within row soil surface CO2 flux was, on average, 64% higher than between row flux. Plant population did not significantly affect measured soil surface CO2 flux. While fertility management had no significant effect on CH4 flux, N2O flux as measured on 3 d during the 2000 growing season was significantly higher in the M2 treatment. In 2001, no significant differences in N2O flux were observed, possibly due to changes in N management and irrigation method. Electrical conductivity measured during the 2000 and 2001 growing seasons was significantly higher in the M2 treatment while pH measured during the 2001 season was significantly lower for M2.
An Inverse Method to Estimate the Source‐Sink Term in the Nitrate Transport Equation
Authors: Shi Jianchu , Zuo Qiang , Zhang Renduo
Published: July 2010

The source‐sink term (SST) in the convection‐dispersion equation (CDE) to simulate nitrate (NO3−–N) transport integrates several NO3−–N transformation processes in soils. The term is affected by considerably complicated micro‐environmental conditions and is difficult to be measured directly. In this study, the average SST distribution was estimated by solving the CDE with an unknown SST iteratively using an inverse method. The required input information for the SST estimation was easily obtained, including soil hydraulic properties, two successively measured NO3−–N concentration distributions, and the boundary and initial conditions. Numerical experiments were designed to examine the accuracy and stability of the inverse approach, considering spatial intervals of measurement data along the soil profile, time intervals between the successive measurements of soil NO3−–N concentration, boundary conditions, layered soils, and measurement errors of NO3−–N concentration. Comparisons with theoretical results showed that the inverse method was reliable for estimating the SST in the CDE. Data from a column experiment with winter wheat (Triticum aestivum L. ) growth were used to demonstrate applications of the inverse method. The root‐nitrate‐uptake (RNU) rate distributions were estimated according to the proposed inverse procedure and the soil NO3−–N transport with RNU in the columns was simulated. The simulated soil NO3−–N concentration distributions were comparable with the measured values. The relative errors between the simulated and measured values of the total N mass extracted by winter wheat were <10%.
Soil Carbon, Nitrogen, and Ergot Alkaloids with Short‐ and Long‐Term Exposure to Endophyte‐Infected and Endophyte‐Free Tall Fescue
Authors: Franzluebbers A. J. , Hill N. S.
Published: July 2010

Tall fescue (Festuca arundinaceaSchreb.) is an important cool‐season perennial forage naturally infected with an endophyte,Neotyphodium coenophialumGlenn, Bacon, & Hanlin, which produces ergot alkaloids. We conducted a controlled incubation study to determine the fate of C, N, and ergot alkaloids in tall fescue leaf tissue added to soil. The experimental setup was a factorial combination of endophyte‐free (E−) and endophyte‐infected (E+) leaf tissue (short term) incubated in soil exposed to 10 yr of E− and E+ tall fescue pasture (long term). Soil history of E+ compared with E− reduced C mineralization per unit of soil organic carbon (52 vs. 55 mg g−1SOC) and the fraction of inorganic N as nitrate (0.68 vs. 0.72 g g−1), but increased ergot alkaloid concentrations in soil sediment (<1 mm; 28 vs. 12 ng g−1), coarse fraction (>1 mm + remaining leaves; 5.8 vs. 2.2 ng g−1), and water extract (0.27 vs. 0.22 ng g−1soil). Short‐term exposure of soil to E+ leaves compared with E− leaves reduced C mineralization (660 vs. 688 μg g−1soil) and soil microbial biomass C (487 vs. 583 μg g−1soil), but increased net N mineralization (70 vs. 59 μg g−1soil), soil microbial biomass N (56 vs. 19 μg g−1soil), and ergot alkaloid concentration in the coarse fraction (0.36 vs. 0.27 μg g−1original leaf). Both short‐ and long‐term exposure of soil to E+ tall fescue were affecting soil organic matter dynamics by altering biochemical transformations of C and N. Our results suggest that wild‐type E+ tall fescue can alter soil organic C storage through a reduction in soil microbial activity. This research has also demonstrated the presence of ergot alkaloids in soil under E+ tall fescue.
Mapping and Classification of Southwest Virginia Mine Soils
Authors: Haering Kathryn C. , Daniels W. Lee , Galbraith John M.
Published: July 2010

Mine soils on central Appalachian coal‐mined lands are currently classified by the Soil Taxonomy as Typic Udorthents, which does not distinguish these unique anthropogenic soils from other weakly developed natural soils. Our overall objectives were (i) to critically evaluate currently available USDA‐NRCS mine soil series for classifying a range of mine soil pedons in southwest Virginia, and (ii) to compare two different approaches for detailed Order 1 soil mapping of these highly altered landscapes. Using established series concepts, we mapped and classified 450 ha of mine soils in an area that had been recently reclaimed, and we used these same series concepts to reclassify mine soils in an older adjacent and overlapping 250‐ha mine area that had been mapped using nontaxonomic mine soil classification criteria in 1980. Established mine soil series provided adequate information on particle‐size and reaction class, but did not adequately describe drainage class, rock type, or parent materials. Classification differences occurred on well‐drained soils primarily at the family level and below. There are no established series that describe mine soils with impeded drainage, densic layers, and shallow or moderately deep depth classes, all of which commonly occurred in this study area, and are important criteria for separating soil series. Cambic horizons were also described, and generate classification issues at the order level. Because reaction class, drainage class, densic contacts, and soil depth directly affect soil management, we feel that it is important to recognize these features by establishing new mine soil series or phases of established series. Detailed Order 1 map scales (≤1:12000) are required to adequately resolve and delineate strongly contrasting mine soil landscapes, particularly on older (pre‐1977) mined lands.
Evapotranspiration of Two Vegetation Covers in a Shallow Water Table Environment
Authors: Nachabe Mahmood , Shah Nirjhar , Ross Mark , Vomacka Jeff
Published: July 2010

A method is introduced to estimate evapotranspiration (ET) in shallow water table environments. The method involves measuring the diurnal fluctuations in total soil moisture above the water table to estimate (i) the net lateral and vertical subsurface flux in the aquifer and (ii) evapotranspiration from the vegetation cover. In a hillslope discharge zone, the net lateral subsurface flux was calculated from the recovery rate of soil moisture between midnight and 0400 h. Evapotranspiration was then estimated from a daily water balance in a soil column that included the water table. The method was tested on two vegetation covers, a pasture in a groundwater recharge area, and a riparian zone with woody vegetation in a groundwater discharge area. A moisture probe carrying eight sensors was used in each area to estimate the total soil moisture in a sandy soil environment. The observed water table fluctuated between land surface and a depth of 1.2 m during the study period, allowing observation and estimation of the total soil moisture in a soil column that included the water table. The results of this investigation support another hypothesis that, in humid, shallow water table environments, ET demand may be supported by adjacent ecosystems. This method provided reasonable results for the two landscapes investigated and was able to capture the variability of evapotranspiration in heterogeneous vegetation covers. It provided a relatively inexpensive alternative to characterize ET within regionally heterogeneous but microhomogenous landscapes. Though tested for coarse‐textured soil, the method involving soil moisture monitoring can be easily adapted to other soil types with shallow water table. Another advantage of using this method is that ET can be successfully estimated without detailed knowledge of soil hydraulic properties, subsurface flow patterns, or vegetation characteristics.