bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulfur Availability on Lodgepole Pine Sites in British Columbia
Authors: Kishchuk Barbara E. , Brockley Robert P.
Published: July 2010

Growth response of lodgepole pine (Pinus contortaDougl.ex. Loud var.latifoliaEngelm.ex S. wats.) to N fertilization is limited by insufficient S on certain sites in British Columbia. This study was conducted to document differences in soil and foliar S fractions between sites with either adequate or insufficient S as determined by foliar nutrient data and growth response information obtained from previously established fertilization research trials with N and N + S application, and to examine relationships among soil S fractions, foliar S status, and growth response to N fertilization. Mineral soil total S concentrations were very low (∼65 mg kg−1) at both S‐sufficient and S‐deficient sites, and were not different between the sites. Soluble inorganic SO4concentration was significantly greater in B horizon soil at the S‐sufficient sites than at the S‐deficient sites. Soluble inorganic SO4was significantly and positively correlated with organic SO4(r2= 0.24;P= 0.03) and organic C (r2= 0.76;P< 0.001). Foliar SO4‐S was significantly greater at the S‐sufficient sites, and was significantly and positively correlated with B‐horizon soluble inorganic SO4(r2= 0.84;P< 0.001), organic SO4(r2= 0.46;P= 0.032), and organic C (r2= 0.72;P= 0.002). The highestR2for a regression model between soil or foliar properties and response to N fertilization was for a model containing foliar N, foliar SO4‐S, and B horizon organic C (R2= 0.81;P= 0.004). Cycling of soluble inorganic SO4through organic SO4in mineral soil appears to be the process limiting S availability on S‐deficient sites. Organic SO4and soluble inorganic SO4concentrations at the S‐sufficient sites are maintaining foliar SO4‐S at levels required for response to N fertilization.
Forest Harvesting Influence on Water Table Dynamics in a Florida Flatwoods Landscape
Authors: Bliss C. M. , Comerford N. B.
Published: July 2010

Flatwoods are an important ecological plant community in the southeastern Coastal Plain with approximately one‐third of Florida's flatwoods in timberland. This study was conducted to investigate hydroperiod changes in the water table of both hydric and nonhydric soils following harvest in a Florida cypress [Taxodium distichum (L.)]–pine (Pinus elliottii var. elliottii Engelm.) flatwoods landscape. Shallow water‐table wells were established on a 42‐ha area and divided into three harvesting treatments containing mature slash pine plantations and pine–cypress swamps: control, clearcut (both hydric and nonhydric soils harvested), and cypress swamps only harvested (hydric soils only harvested). Water‐table measurements were obtained at 2‐wk intervals for 6 yr. Harvesting treatments occurred 2 yr into the study. Regression equations created from preharvest water‐table data between the control block and harvested blocks allowed us to predict uncut water‐table responses in the cut areas. These predicted values were compared with the actual postharvest observations. The water‐table level increased 48 and 49 cm and 19 and 21 cm in the hydric and nonhydric soils in the clearcut and cypress swamps only cut, respectively, during the first 126 d after harvesting. Significant differences (P < 0.10) in water‐table depth because of harvesting occurred throughout the four postharvest years, but the differences were less than seen initially, and the pattern was seasonal. Compared with the predicted uncut condition, water tables tended to be lower (drier) during the growing season and higher (wetter) during the nongrowing season. These seasonal fluctuations were presumably driven by changes in evapotranspiration rates resulting from differences in leaf area of the pine canopy and understory.
Estimating Soil Properties from Thematic Soil Maps
Authors: Bogaert Patrick , D'Or Dimitri
Published: July 2010

Current soil process models require the most accurate values for each of their input parameters at the finest spatial scale. Traditionally, soil property values are obtained either from soil maps or from geostatistical methods using exact laboratory measurements. Both data types convey substantial information: soil maps provide exhaustive but soft (vague) information, whereas laboratory analyses provide hard (accurate) but scarce measurements. Ideally, they should be combined. This objective can be reached using a recently developed method, namely the Bayesian maximum entropy (BME) approach, that allows the user to incorporate hard and soft data in a spatial estimation context. In this work, both the regular BME algorithm and a new variant of it using a Monte Carlo procedure (BME/MC) are proposed for obtaining an estimated map for the textural (sand, silt, and clay) fractions from a limited number of accurate measurements and a spatially exhaustive soil map. Compared with popular geostatistical methods like ordinary kriging (OK), this approach has the advantage of using soft information on a sound theoretical basis. The entire probability distribution function can be estimated at each estimation location, allowing the computation of confidence intervals, probability of exceeding a threshold, etc. Using expectation properties in a Monte Carlo procedure, the BME/MC algorithm takes additionally into account the fundamental constraints on the textural fractions (they are summing to one and belong to the [0, 1] interval). As illustrated with a real data set from Belgium, using BME results in much more accurate textural fractions estimates and more realistic maps than those obtained with regular geostatistical algorithm.
Cicada burrows as indicators of paleosols in the inland pacific northwest
Authors: O'Geen A. T. , McDaniel P. A. , Busacca A. J.
Published: July 2010

Cicada nymphs (Homoptera: Cicadidae) are soil‐dwelling insects that form cylindrical back‐filled burrows. These unique burrow features persist in soils for thousands of years and are common in soil descriptions in arid and semiarid regions of the inland Pacific Northwest (PNW). We examined the burrowing depth of live cicada nymphs and found that burrowing is concentrated in the upper 50 cm of soil. This depth may be used to distinguish between contemporary and relict burrows in soil profiles developed in transported parent materials, and can serve as a means of identifying paleosols from observations of burrows at greater depths. We then searched all official soil series descriptions within the USDA‐NRCS State Soil Geographic (STATSGO) data base for cicada‐burrowed horizons below the active burrowing depth to identify buried paleosols. We suggest that evidence of cicada nymph activity can be used to assess soil–stratigraphic relationships at broad scales in the inland PNW.
Spectral Analysis of Tillage‐Induced Differences in Soil Spatial Variability
Authors: Perfect E. , Caron J.
Published: July 2010

Tillage research has traditionally focused on mean effects; few studies have compared treatments in terms of their spatial variability. We applied several methods of time‐space series analysis to investigate the spatial variability of gravimetric water content (w), volumetric water content (θ), bulk density (ρb) and total C (TC) in the upper 10 cm of long‐term conventional‐till (CT) and no‐till (NT) soil management practices at Lexington, KY. The soil was a Maury silt loam (fine, mixed, semiactive, mesic Typic Paleudalf). Replicate transects were established in untracked interrows parallel to the direction of tillage in the CT practice. Each transect was 48.5 m long with 107 equally spaced sampling points. Soil spatial variability was higher under NT than under CT. Spectral analyses of variance identified significant differences between tillage treatments at frequencies <0.02 cycles m−1for all soil properties, and at 0.18 cycles m−1for w, 0.13, 0.31 and 0.48 cycles m−1for θ, and 0.22, 0.70 and 0.90 cycles m−1for ρbSpatial variations in water content and ρbappeared to be related to the distribution of TC. Coherency analysis indicated relationships were strongest at frequencies <0.09 cycles m−1For NT the relationship between w and TC was also significant at higher frequencies (1.01–1.05 cycles m−1). Gravimetric water content increased as TC increased, while θ and ρbdecreased. Lagged relations for w versus TC were more frequent in CT than NT, possibly due to soil translocation during tillage operations. The opposite was true for θ versus TC and ρbversus TC, suggesting that soil aggregates form at some distance from sites of carbon deposition under NT.
Saturated Hydraulic Conductivity and Its Impact on Simulated Runoff for Claypan Soils
Authors: Blanco-Canqui Humberto , Gantzer Clark J. , Anderson Stephen H. , Alberts E. E. , Ghidey F.
Published: July 2010

Saturated hydraulic conductivity (Ksat) is an essential parameter for understanding soil hydrology. This study evaluated the Ksat of in situ monoliths and intact cores and compared the results with other studies for Missouri claypan soils. These Ksat values were used as runoff‐model inputs to assess the impact of Ksat variation on simulated runoff. Lateral in situ Ksat of the topsoil was determined on 250 by 500 by 230 mm deep monoliths. These values were compared with the Ksat of 76 by 76 mm diam. intact cores with and without bentonite to seal macropores. Mean (± SD) lateral in situ Ksat was 72 ± 0.7 mm h−1 and mean intact core Ksat without bentonite was 312 ± 58 mm h−1 The mean intact core Ksat without bentonite was significantly larger than the lateral in situ Ksat (P = 0.03). The lateral in situ Ksat was not different from core Ksat with bentonite (71 ± 1.1 mm h−1). The intact core Ksat with bentonite differed from previous studies by 10 times. This was attributed to the variations in soil depth to claypan, macropore presence, and methodology. The impact of using an effective hydraulic conductivity (Keff) computed from measured Ksat on intact cores without bentonite underestimated the Water Erosion Prediction Project (WEPP) simulated runoff by 28% for a measured runoff event of 40 mm. The core Ksat with bentonite was correlated with measured runoff from long‐term erosion‐runoff plots. A quadratic regression explained 95% of the variability between measured and simulated runoff.
High‐Energy‐Moisture‐Characteristic Aggregate Stability as a Predictor for Seal Formation
Authors: Levy G. J. , Mamedov A. I.
Published: July 2010

Past attempts to use aggregate stability to predict soil susceptibility to seal formation indices (final infiltration rate and runoff) have yielded inconsistent results. We hypothesized that determining aggregate stability in a method in which a controlled wetting process was used to break aggregates will correlate well with seal formation indices, as the latter strongly depend on rate of aggregate wetting. We studied aggregate stability from soils varying in clay content, and exchangeable Na percentage (ESP), using the high‐energy‐moisture‐characteristics (HEMC) method. Aggregate stability indices were correlated with previously published seal formation data for the same soils. Aggregates were placed in a funnel equipped with a fritted disk, and wetted either fast (100 mm h−1) or slow (2 mm h−1), using a peristaltic pump. Thereafter, the aggregates were subjected to a stepwise increase in matric potential up to 5.0 J kg−1, to obtain a moisture retention curve, which served as the base for calculations of stability parameters. Aggregate stability correlated with clay content, but not with soil organic matter. Aggregate stability and sodicity correlated only in clay soils. Generally, poor correlation (R < 0.5) was obtained between aggregate stability and seal formation and runoff data, irrespective of soil ESP, when infiltration and runoff measurements were carried out on fast‐wetted soils. Conversely, aggregate stability significantly correlated (R > 0.70) with seal formation and runoff data from slow wetted soils for samples having ESP of <6.6. Our results suggest that aggregate stability determined with the HEMC method could serve as a predictor for soil susceptibility for seal formation only under the aforementioned specific conditions.
Evaluating Use of Ground‐Penetrating Radar for Identifying Subsurface Flow Pathways
Authors: Gish T. J. , Dulaney W. P. , Kung K.-J. S. , Daughtry C. S. T. , Doolittle J. A. , Miller P. T.
Published: July 2010

Complex interactions between soil heterogeneity and soil water movement have inhibited the development of a methodology to accurately monitor subsurface water or chemical fluxes at the field‐scale. A protocol is presented that identifies subsurface convergent flow pathways resulting from funnel flow which are critical for determining field‐scale water and chemical fluxes. Georeferenced ground‐penetrating radar (GPR) data were collected on a coarse resolution grid (25‐m spacings) across 7.5 ha and a fine resolution grid (2‐m spacings) across 22 0.06‐ha plots. Although spherical models generally provided the best fit to experimental semivariograms of the restricting layer depth at a variety of spatial scales, the distance over which these data showed spatial dependency, that is, as reflected by semivariogram ranges, was highly dependent upon the scale of observation. Georeferenced ground‐penetrating radar images of soil stratigraphy were used to create three‐dimensional maps of the depth to the layer or horizon which restricts vertical water movement. Hydrologic models were used in conjunction with a geographic information system to determine potential flow pathways from topographic maps of subsurface restricting layers. A network of soil moisture probes allowed GPR‐identified subsurface flow pathways to be verified. This suggests that a methodology incorporating GPR data and real‐time soil moisture sensors may be used to identify subsurface flow pathways and to monitor subsurface water flow.
Quantifying Harvesting Impacts using Soil Compaction and Disturbance Regimes at a Landscape Scale
Authors: Block R. , Van Rees K. C. J. , Pennock D. J.
Published: July 2010

Several indicators have been identified for the conservation and maintenance of soil criterion in the Montreal Protocol. The objective of this study was to use soil compaction and disturbance measures to determine harvesting impacts at a landscape scale in the boreal forest of Saskatchewan. Forest harvesting impacts were studied pre and postharvest for five harvested sites by (i) sampling soil bulk density (Db) at prescribed grid‐points, and (ii) measuring soil disturbance regimes on two 30‐m transects at each grid‐point. Mean soil Db in the harvested area increased significantly (8–11%) from pre to postharvest conditions for the two winter‐harvested sites at both the 10‐ and 20‐cm depths, while two of the three summer harvested sites also showed significant Db increases (7–15%) at the 10‐cm depth. Combining all five sites, showed that after harvest 32% of all the grid‐points had an increased Db of >15%. Mean soil Db at a 10‐cm depth for roadways and landings was significantly higher (8–14%) than postharvest Db for postharvest levels at four of the five harvested sites. Surface soil disturbance regimes were higher for the summer‐harvested sites than that for the winter‐harvested sites. Landscape position showed no significant differences in Db between the shoulder, backslope, and footslope positions; however, within each landscape position, significant differences in Db were found between pre and postharvest conditions. Soil Db and soil disturbance regimes measured on a grid basis provided a simple, but reliable method for monitoring soil compaction and disturbance effects from harvesting at a landscape scale.
Soil Water Retention Measurements Using a Combined Tensiometer‐Coiled Time Domain Reflectometry Probe
Authors: Vaz Carlos M. P. , Hopmans Jan W. , Macedo Alvaro , Bassoi Luis H. , Wildenschild Dorthe
Published: July 2010

The objective of the presented study was to develop a single probe that can be used to determine soil water retention curves in both laboratory and field conditions, by including a coiled time domain reflectometry (TDR) probe around the porous cup of a standard tensiometer. The combined tensiometer‐coiled TDR probe was constructed by wrapping two copper wires (0.8 mm diam. and 35.5 cm long) along a 5‐cm long porous cup of a standard tensiometer. The dielectric constant of five different soils (Oso Flaco [coarse‐loamy, mixed Typic Cryorthod‐fine‐loamy, mixed, mesic Ustollic Haplargid], Ottawa sand [F‐50‐silica sand], Columbia [Coarse‐loamy, mixed, superactive, nonacid, thermic Oxyaquic Xerofluvents], Lincoln sandy loam (sandy, mixed, thermic Typic Ustifluvents), and a washed sand ‐ SRI30) was measured with the combined tensiometer‐coiled TDR probe (coil) as a function of the soil water content (θ) and soil water matric potential (h). The measured dielectric constant (εcoil) as a function of water content was empirically fitted with a third‐order polynomial equation, allowing estimation of θ(h)‐curves from the combined tensiometer‐coiled TDR probe measurements, with R2 values larger than 0.98. In addition, the mixing model approach, adapted for the tensiometer‐coiled TDR probe, was successful in explaining the functional form of the coiled TDR data with about 30% of the coiled‐TDR probe measurement explained by the bulk soil dielectric constant. This new TDR development provides in situ soil water retention data from simultaneous soil water matric potential and water content measurements within approximately the same small soil volume around the combined probe, but requires soil specific calibration because of slight desaturation of the porous cup of the tensiometer.
Modeling soil compaction under uniaxial compression
Authors: Assouline S.
Published: July 2010

Knowledge about soil compaction is increasingly important within agriculture and for environmental protection. The objective of this study is to modify a previous two‐parameter model to generalize it to account for preconsolidation effect. A three‐parameter model for the relationship between soil bulk density and applied stresses during compaction is presented. It relies on the physical approach of the previous two‐parameter model and satisfies the same boundary conditions. The proposed model is applied to compaction data of four silt loam and loam soils. A good fit to data is obtained for a wide range of applied stresses, including stresses less than the preconsolidation stress. The proposed model is compared with the three‐parameter version of a recent model. The performances of the two models are similar. The root mean square errors for the four soils ranged between 0.004 to 0.011 for the recent equation and 0.005 to 0.018 for the proposed model. The advantage of the proposed model is that it releases the physically unrealistic constraint in the recent model that the maximal bulk density of a compacted soil is equal to its particle density.
Redistribution of Metals in a New Caledonia Ferralsol After Microbial Weathering
Authors: Quantin C. , Becquer T. , Rouiller J. H. , Berthelin J.
Published: July 2010

Ferralsols from southern New Caledonia developed on ultramafic rocks are very rich in Fe, Mn, and in other transition metals like Cr, Ni, and Co. Bacterial weathering of Fe and Mn oxides performed in batch experiments increases metal solubilization particularly under reducing waterlogged conditions and when organic compounds are available as nutrients. Moreover, bacterial weathering can modify the metal distribution through the geochemical compartments of the soil. Bacterial reduction of oxides led to the solubilization of Fe, Mn, Ni, and Co and brought about a significant metal redistribution into the different geochemical compartments of the soil. Selective sequential extractions showed an increase in the metal (Fe, Mn, Co, Ni, and Cr) content of the most labile compartments (water‐soluble and exchangeable) after microbial weathering. Metal concentrations of amorphous and poorly crystallized Fe oxides also increased significantly. This mineral phase acted as a strong sorbent promoting the coprecipitation of metals with Fe. The Mn oxide compartment decreased significantly, especially under high microbial activity. The metal contents of the well‐crystallized Fe oxide and residual fraction were stable showing that microbial weathering have a limited effect on these compartments. Although the soluble Cr was always nil, Cr was also significantly redistributed into the various geochemical compartments (highlighting the rapid sorption of this element versus its solubilization). Such redistribution processes are important to be known and to be quantified to define metal behavior and improve risk assessment.
A Rapid Method to Estimate Potentially Mineralizable Nitrogen in Soil
Authors: Picone L. I. , Cabrera M. L. , Franzluebbers A. J.
Published: July 2010

Rapid estimates of mineralizable N in soil are important for management decisions and soil quality assessments. We adapted and evaluated a rapid method based on measuring the gas pressure generated when soil is treated with Ca(ClO)2in a closed vessel. An experiment was conducted to determine the effects of reaction time, soil/reagent, and soil/water ratios on the gas pressure generated by the method. Based on this experiment, 5 g of soil, 5 mL of deionized water, 0.3 g Ca(ClO)2, and a reaction time of 25 min were selected as optimum conditions. The method was evaluated with 60 Cecil (fine, kaolinitic, thermic Typic Kanhapludults) sandy loam samples ranging in organic C from 4 to 16 g C kg−1Nitrogen mineralized in 24 d and soil microbial biomass C (SMBC) were measured and related to the Ca(ClO)2method and to two other rapid methods, the flush of CO2during 3 d following rewetting of a dry soil, and the NH4–N extractable with hot 2MKCl. The Ca(ClO)2method (mmol kg−1) was strongly correlated with net N mineralized in 24 d (r= 0.77) and with microbial biomass C (r= 0.90). The method was also correlated with the flush of CO2during 3 d following rewetting of dried soil (r= 0.85) and with the NH4–N extractable with hot 2MKCl (r = 0.86). These results indicate that the Ca(ClO)2method may be useful to make rapid estimates of mineralizable N and microbial biomass C in soil. Additional work is needed to investigate the nature of the compounds oxidized by the method.
Identification and Characterization of Pedogeomorphological Processes on a Hillslope
Authors: Park S. J. , Burt T. P.
Published: July 2010

This study aims to identify process‐response relationships between pedogeomorphological processes and the spatial distribution of soil properties on a hillslope. Thirty‐two physical and chemical attributes of 502 soil samples collected from 64 soil profiles on a hillslope in Somerset, UK, were analyzed using an ordination technique. Five factors explaining 80% of the total variation were first identified. Each factor was then regressed with terrain attributes to examine the influence of hillslope geomorphometry on soil distributions. Two‐way ANOVA was used to separate the total variance of individual soil properties into vertical and lateral components, and the results were compared with the results of the ordination. The five factors were interpreted as demonstrating the effects of podzolization, nutrient dynamics, Mn leaching, erosion weathering, and soil acidification. The ability to predict soil properties over the landscape using terrain information varies widely among soil properties measured. In general, topsoil properties are better correlated with terrain attributes than subsoil properties. Contemporary pedological and geomorphological processes are most active in the surface horizon, which results in clear lateral differentiation of soil properties. For subsurface soils, only those few soil properties that showed a clear spatial pattern could be successfully modeled using terrain attributes. This research demonstrates that clear differences in the spatial distribution of individual soil properties are mainly determined by differential involvement in in situ pedogenesis and lateral slope processes. Future soil‐landscape modeling attempts should pay more attention to the selection of soil properties and the interpretation of statistical results in relation to process‐response dynamics.
Soil Carbon and Nitrogen Changes Under Douglas‐fir With and Without Red Alder
Authors: Rothe Andreas , Cromack Kermit , Resh Sigrid C. , Makineci Ender , Son Yowhan
Published: July 2010

We sampled pure Douglas‐fir (DF) [Pseudotsuga menziesii (Mirb.) Franco] and mixed red alder (Alnus rubra Bong.)(RA) and DF (RA/DF) stands in 1980 and in 1999 to investigate the influence of RA on soil C and N pools. In RA/DF plots with 25% RA, the soil N pool to a 45‐cm depth increased significantly (P < 0.05) by 190 g N m−2, corresponding to 10 g N m−2 yr−1 accretion. The average between treatment soil N difference in 1999 was 166 g m−2, representing N accretion of 8.7 g m−2 yr−1 In pure DF plots, the soil N pool remained nearly constant. Resin N mineralization in RA/DF plots was about ten fold greater than on pure DF plots, but the enhanced resin N availability did not affect DF foliar N concentration. Temporal plot pairing was necessary within this landscape with high spatial variability to detect significant changes in soil N pools, and only large effects, such as N addition by RA, could be identified with statistical significance. Minimum detectable difference (MDD) estimates for mean total soil C differences in RA/DF plots showed that it would require about 30 more years of C accretion to detect differences at P < 0.05. Conversely, total soil N accretion in RA/DF plots was 28% greater than the MDD after 19 yr.
Color Attributes and Mineralogical Characteristics, Evaluated by Radiometry, of Highly Weathered Tropical Soils
Authors: Fontes Mauricio P. F. , Carvalho Ildeu A.
Published: July 2010

Highly weathered soils are important around the world. Determination of their observed colors and acquisition of spectral curves were used to study their mineralogy. Color was determined through visual comparison with Munsell Soil Color Charts, and soils spectral characterization was made with an infrared intelligent spectroradiometer (IRIS) covering a spectral window from 300 to 3000 nm. The variables of color behaved differently among soils. The Munsell hue was related to hematite content and the hematite/goethite ratio (Hm/Gt), and the Munsell value to organic content of goethitic soils. The Munsell chroma was related to the presence of Fe oxides, giving an idea of relative amounts of either hematite or goethite. Regression equations relating color indices showed that the redness factor (RF) gave the highest determination coefficients to estimate hematite content and Hm/Gt, and reconfirmed that redness saturation occurs with increasing hematite amounts. The typical minerals of these soils showed characteristic absorption bands in their spectral curves. Absorption bands of 450 and 900 nm for Fe oxides, 2200 nm for kaolinite and 2280 for gibbsite, were distinctive features of the main minerals present. Organic matter decreased the intensity of reflectance for most soils and, under its influence, the characteristic bands of goethite practically disappeared while the ones for hematite, kaolinite, and gibbsite were attenuated. High amounts of hematite decreased the reflectance factor strongly as compared with the soil organic matter (SOM). Qualitative mineralogy of highly weathered soils was assessed by radiometry using measurements in the visible and near infrared regions of the electromagnetic spectrum.
Electrical Resistivity Imaging for Detecting Soil Cracking at the Centimetric Scale
Authors: Samouëlian Anatja , Cousin Isabelle , Richard Guy , Tabbagh Alain , Bruand Ary
Published: July 2010

Electrical resistivity measurements at high resolution (1.5‐cm electrode spacing) were performed to detect, from the soil surface, small cracks developing within the soil. We recorded a vertical electrical pseudo‐section in a decimetric undisturbed homogenous soil block (silt loam) for different artificial cracking stages. Because of the unusually reduced electrode spacing associated with an air‐dried soil surface, a specific Cu/CuSO4 electrode was designed for precision wet contact at given points. The apparent resistivity measurements of the pseudo‐section and the interpreted data inverted by using the Res2Dinv software are discussed. The range of interpreted electrical resistivity associated with cracking is considerable, (from 168 to 2185 Ω m) because the cracks are filled with air that is an infinitely resistant medium. Results showed that even small structures cause perceptible changes in resistivity that can be detected by the electrical resistivity method. Results also showed that specific software is required to predict real crack depth.
Estimating Temperature Effects on Water Flow in Variably Saturated Soils using Activation Energy
Authors: Zhang Fucang , Zhang Renduo , Kang Shaozhong
Published: July 2010

Temperature effects on soil water flow are attributable to various factors in the soil water system, such as fluid viscosity, soil water content, and other soil physical and chemical properties. To account for the factors as a whole and quantify the temperature effects, the first objective was to apply the concept of activation energy and to estimate apparent activation energies of steady‐state saturated flow and horizontal as well as vertical infiltration. The second objective was to predict the water flow processes under different temperatures. Soil column experiments were conducted to measure discharge of steady‐state saturated flow and processes of cumulative infiltration using four soils at four temperatures. The parameters of the flow equations were related to temperature and apparent activation energies. Based on the relationships, apparent activation energies of the water flow processes were estimated using the experimental data. The sensitivities of temperature effects on the steady‐state saturated flow and infiltration parameters were linearly related to the activation energy and inversely proportional to the absolute temperature. In general, temperature effects on the water flow processes were larger in the fine‐textured soils and/or with higher soil water saturation. Using the parameters estimated from measured water flow processes at two temperatures, we predicted the processes at other temperatures and compared the predicted results with the measured data. The predicted results were highly correlated with the measured data with coefficients of determination (r2) larger than 0.990 and the relative errors of the predicted processes were within 12%.
In‐Season Nitrogen Status Sensing in Irrigated Cotton
Authors: Bronson Kevin F. , Chua Teresita T. , Booker J. D. , Keeling J. Wayne , Lascano Robert J.
Published: July 2010

Pre‐plant soil NO−3–N tests and petiole NO−3–N analysis are bases for Upland cotton (Gossypium hirsutum L.) N management in the western USA. Alternative approaches include proximal multispectral reflectance sensing and chlorophyll meter readings. Our objective was to determine if spectral reflectance and chlorophyll meter measurements correlate with cotton leaf N and biomass. Urea ammonium nitrate was applied after emergence and with low energy precision (LEPA) center‐pivot, surface or subsurface drip irrigation water up to peak bloom. Multispectral reflectance readings 0.5 m above the canopy, chlorophyll meter readings, and biomass samplings were taken at early squaring, early bloom, and peak bloom for 3 site‐years in Lubbock, TX and Ropesville, TX. Green vegetative indices (GVI) and green normalized difference vegetative indices (GNDVI) calculated from reflectance data generally correlated better with leaf N and leaf N accumulation than did red vegetative indices (RVI) and red normalized difference vegetative indices (RNDVI). Biomass and lint yield correlated more often with red‐based indices than green‐based indices. Chlorophyll meter readings correlated with leaf N as often as GVI and GNDVI did. Biomass, however was poorly related to chlorophyll meter readings. These results demonstrate the effectiveness of GVI, GNDVI, and chlorophyll meter readings in assessing leaf N, and RVI and RNDVI in assessing cotton biomass. However, we recommend converting vegetative indices or chlorophyll meter readings to sufficiency indices, which are calculated from indices or readings relative to well‐fertilized plots. Sufficiency indices were able to successfully predict little or no need for in‐season N fertilizer in the low‐yielding 2000 crops (sufficiency index > 0.95), and predicted greater need of N fertilizer in the high‐yielding 2001 crop (sufficiency index < 0.95).
Cropping Intensity Enhances Soil Organic Carbon and Nitrogen in a No‐Till Agroecosystem
Authors: Sherrod L. A. , Peterson G. A. , Westfall D. G. , Ahuja L. R.
Published: July 2010

Soil organic C (SOC) has decreased under cultivated wheat (Triticum aestivum)‐fallow (WF) in the central Great Plains. We evaluated the effect of no‐till systems of WF, wheat–corn (Zea Mays)‐fallow (WCF), wheat–corn–millet (Panicum miliaceum)‐fallow, continuous cropping (CC) without monoculture, and perennial grass (G) on SOC and total N (TN) levels after 12 yr at three eastern Colorado locations. Locations have long‐term precipitation averages of 420 mm but increase in potential evapotranspiration (PET) going from north to south. Within each PET location, cropping systems were imposed across a topographic sequence of summit, sideslope, and toeslope. Cropping intensity, slope position, and PET gradient (location) independently impacted SOC and TN to a 5‐cm soil depth. Continuous cropping had 35 and 17% more SOC and TN, respectively, than the WF system. Cropping intensity still impacted SOC and TN when summed to 10 cm with CC > than WF. Soil organic C and TN increased 20% in the CC system compared with WF in the 0‐ to 10‐cm depth. The greatest impact was found in the 0‐ to 2.5‐cm layer, and decreased with depth. Soil organic C and TN levels at the high PET site were 50% less than at the low and medium PET sites, and toeslope soils were 30% greater than summit and sideslopes. Annualized stover biomass explained 80% of the variation in SOC and TN in the 0‐ to 10‐cm soil profile. Cropping systems that eliminate summer fallowing are maximizing the amount of SOC and TN sequestered.
Changes in Ecosystem Carbon and Nitrogen in a Loblolly Pine Plantation over the First 18 Years
Authors: Johnson D. W. , Todd D. E. , Tolbert V. R.
Published: July 2010

Eighteen years after the establishment of a loblolly pine (Pinus taeda L.) plantation, ecosystem C content had approximately tripled (from 54 to 161 Mg C ha−1) primarily because of increases in tree biomass. Ninety‐three percent of the net ecosystem C accumulated in biomass (100 Mg C ha−1) and 6% of net ecosystem C accumulated in the forest floor (13 Mg C ha−1). No statistically significant changes in soil C were found. Growth responses to fertilization noted in Year 4 were no longer statistically significant in Year 18. Nitrogen accumulation in aboveground biomass and forest floor were approximately equal (averaging approximately 270 kg N ha−1 each) and could have come from a combination of atmospheric deposition, soil N mineralization, and, in the treated plots, fertilizer input. No statistically significant changes in soil N content were found. The results of this study are similar to those from a previous study in a loblolly pine plantation in South Carolina but contrast with those in nearby deciduous forests where substantial changes in soil C and N over similar time periods have been noted.
Heat‐Pulse Method for Soil Water Content Measurement
Authors: Ren T. , Ochsner T. E. , Horton R. , Ju Z.
Published: July 2010

The heat‐pulse method measures soil volumetric water content (θ) based on the linear relationship between soil volumetric heat capacity (C) and θ. Previous work suggested that this method was more appropriate for determining change of θ rather than its absolute value. In this study, we demonstrate that the heat‐pulse method can give accurate θ estimation when values for the specific heat of the soil solids (cs) are determined using the heat‐pulse method. Heat‐pulse measurements were performed on packed columns of three soils with a wide range of bulk density (ρb)and θ. When the commonly usedcsvalue (0.725 kJ kg−3K−1) was used, the heat‐pulse method overestimated θ by 0.052 m3m−3on average. However, whencsvalues determined from heat‐pulse measurements on oven‐dried soil were used, the heat‐pulse method provided accurate θ results (−0.006 m3m−3average error). Using soil‐specific, heat‐pulse determinedcsvalues also reduced the average root mean square error (RMSE) in θ for the three soils from 0.061 to 0.039 m3m−3
Sulfur K‐edge XANES Spectroscopy as a Tool for Understanding Sulfur Dynamics in Soil Organic Matter
Authors: Solomon Dawit , Lehmann Johannes , Martínez Carmen Enid
Published: July 2010

Sulfur K‐edge X‐ray absorption spectroscopy (XANES) was used to identify S oxidation states and assess the impact of land use changes on the amount, form, and distribution of organic S in particle‐size separates and their humic substance extracts. Soil samples (0–10 cm) were collected from natural forest, tea plantations, and cultivated fields at Wushwush and from natural forest,Cupressusplantations and cultivated fields at Munesa sites in Ethiopia. Sulfur XANES spectra measured directly from the size separates could not be quantitatively analyzed due to high background noise. However, qualitative comparison of spectra from size separates and their humic extracts were very similar and thus provides a characteristic fingerprint of S in mineral soils. X‐ray absorption near‐edge spectroscopy showed the presence of most reduced (sulfides, disulfides, thiols, and thiophenes), intermediate (sulfoxides and sulfonates) and highly oxidized S (ester‐SO4–S) forms. Sulfur in intermediate oxidation states was dominant (39–50%; where 66–96% of it being sulfonate S) in humic extracts from clay, while highly oxidized S dominated (40–56%) the silt spectra. Concentrations of C‐bonded and ester‐SO4–S extracted by the HI fractionation did not correlate with those from XANES (ester‐SO4–S revealed by XANES vs. HI‐fractionation,r= 0.23;P< 0.001). A major shift following land use changes occurred in the most reduced and intermediate S species. Their proportion decreased in the order: natural forests > plantations > cultivated fields. In contrast, highly oxidized S increased in the order: natural forests < plantations < cultivated fields at both sites. Our results indicated that C‐bonded S (most reduced and intermediate S) may represent the more labile forms of organic S compounds compared with ester‐SO4–S. Therefore, S K‐edge XANES has a significant potential to evaluate the influence of anthropogenic changes on the nature and distribution of S and to follow its dynamics in terrestrial ecosystems.
Temperature Controls on Diurnal Carbon Dioxide Flux
Authors: Parkin Timothy B. , Kaspar Thomas C.
Published: July 2010

Carbon dioxide flux from the soil to the atmosphere is an important component of terrestrial C cycling, and accurate estimates of CO2–C fluxes are critical in estimating C budgets. Accurate estimation of daily C loss from infrequent measurements of CO2 flux requires characterization of the temporal variability associated with this processes. We investigated the relationships between diurnal CO2 flux and temperature at two locations, corresponding to two soil types (a sandy loam and a clay loam) in a residue covered no‐till corn (Zea mays L.)/soybean field (Glycine Max L. Merr.). Automated chambers provided hourly measurements of CO2 flux from 4 Mar. through 6 June 2000. Hourly soil temperature measurements were made at the surface and at the 0.05‐m depth, along with air temperature and soil water content measurements. Time series analysis showed that the temporal dynamics of CO2 flux were more closely related to air temperature than to soil temperature, perhaps because a substantial portion of the CO2 originated from surface residues. Exponential temperature correction algorithms (Q10) were evaluated using a range of Q10 factors applied to both air and soil temperatures. We found that a Q10 = 2 relationship when applied to a 0.05‐m soil temperature performed poorly in this regard, however, air temperature based Q10 relationships (Q10 = 1.5 or 1.25) performed better in that they reduced time‐of‐day estimation biases from 28 to <4%. Knowledge of the efficacy of temperature correction algorithms and application of the appropriate temperature measurements should improve the accuracy of cumulative C flux estimates from short‐term measurements.
Salinity and Nitrogen Rate Effects on the Growth and Yield of Chile Pepper Plants
Authors: Villa-Castorena Magdalena , Ulery April L. , Catalán-Valencia Ernesto A. , Remmenga Marta D.
Published: July 2010

Salinity and low soil N availability are important growth limiting factors for most plants. Our objective was to determine the influence of different N fertilization rates and soil salinity levels on the growth and yield of chile pepper plants (Capsicum annuum L.) grown in a greenhouse in sandy loam soil for 2 yr. The targeted soil salinity levels were 1.3, 3.5, and 5.5 dS m−1 in 1999, and 1.3, 3.0, 4.5, and 6.0 dS m−1 in 2000 as electrical conductivity of the saturated paste extract (ECe). Total N application rates were 80, 140, and 200 kg ha−1 in 1999, and 30, 90, and 150 kg ha−1 in 2000. Nitrogen rates of 140 kg ha−1 or more increased soil salinities, in some cases by as much as 4 dS m−1 Soil salinity decreased plant relative growth rate (RGR) up to first mature pod stage. After this growth stage however, salinity increased the RGR. Low and medium N rates produced the maximum RGR up to the first mature pod stage. After this growth stage, the maximum RGR was achieved with the medium and the high N rates tested in 1999 and 2000, respectively. Increasing N rates and salinity levels interacted to reduce chile pod yield in 1999, and acted independently in 2000. This study indicates that over‐fertilization during early plant development may contribute to salinity and decreased pod yield. While salt‐stressed chile performs well when adequately fertilized, N should be applied in amounts that increase with plant need over the growing season.
Pedogenesis of Volcanic Ash Soils in Andean Ecuador
Authors: Zehetner F. , Miller W. P. , West L. T.
Published: July 2010

Weathering and development of volcanic ash soils show similar patterns in different regions of the world; however, the specific environmental conditions at a given location result in a unique combination of factors and processes governing soil formation. This research was conducted to study pedogenesis on volcanic slopes in the inter‐Andean valley of northern Ecuador. Twelve pedons representing different pedogenic environments were sampled at elevations between 2410 and 4050 m above sea level (asl). In pedons above 3200 m asl, allophane and Al–humus complexes dominate the colloidal fraction, the topsoils are high in organic matter, and the soils classify as Andisols with melanic epipedons. In pedons below 2700 m asl, halloysite is the predominant colloidal constituent, the topsoils contain <1% organic C, and the soils are Inceptisols and Entisols. The pedons at intermediate elevations mark a transition zone, in which allophane and halloysite coexist and the soils generally classify as Andisols with umbric epipedons. This general altitudinal pattern was found to be altered in unstable landscape positions, where andic soil properties have been removed along with the erosion of topsoil material. Virtually the same altitudinal weathering sequence was observed in the 3000‐yr‐old soils and in buried paleosols, which are considered to be older than 40 000 years. Thus, different time of pedogenesis has not caused marked differences in the composition of the colloidal fraction. Climate is considered the overriding factor responsible for the observed altitudinal differences in soil development by affecting leaching regime and organic matter decomposition.
Organic Carbon, Texture, and Quantitative Color Measurement Relationships for Cultivated Soils in North Central Iowa
Authors: Konen M. E. , Burras C. L. , Sandor J. A.
Published: July 2010

The quantification of soil organic C (SOC) concentrations is becoming increasingly more desirable because of environmental and economic concerns regarding the reactivity of SOC with pesticides, fertilizers, and waste materials. The objectives of this study were to quantify soil color organic C relationships and to quantify soil particle‐size organic C relationships for Ap horizons in north central Iowa. All of the 130 soils examined developed in glacigenic diamicton or local hillslope sediment derived from glacigenic diamicton. A Minolta CR‐310 chroma meter was used to quantify the percentage of reflectance, and Munsell value and chroma for both air‐dry and moist soils. Organic C concentration of the sample set ranged from 4.4 to 70.8 g kg−1 Significant relationships were observed between organic C concentration and percentage of reflectance (r2 = 0.77 moist, r2 = 0.74 air‐dry), Munsell value (r2 = 0.77 moist, r2 = 0.74 air‐dry), Munsell chroma (r2 = 0.68 moist, r2 = 0.77 air‐dry), the percentage of sand (r2 = 0.74), the percentage of clay (r2 = 0.71), and geometric mean particle diameter (GMPD) (r2 = 0.74). Logarithmic relationships existed for reflectance, Munsell value and chroma, and GMPD while linear relationships were observed for sand and clay contents. Chroma meter soil color measurements and particle‐size data are useful predictors of organic C concentrations for Ap horizons in north central Iowa. Evidence from this study and the literature suggest that unique relationships exist for different soil landscapes.
Nitrogen Distribution in Soils of Constructed Wetlands Treating Lagoon Wastewater
Authors: Szögi Ariel A. , Hunt Patrick G. , Humenik Frank J.
Published: July 2010

Constructed wetlands have the potential to be used for treatment of N‐rich livestock wastewater. Our objectives were to evaluate both the time effect and increasing N loading rates on soil N distribution and NH+4–N concentration in surface‐pore water of constructed wetlands. A 5‐yr study in North Carolina investigated two wetland systems that treated swine lagoon wastewater. Wetland System 1 was planted to aSchoenoplectus americanus(Pers.) Volkart ex Schinz & R. Keller,S. tabernaemontani(K.C. Gmel.) Palla,Scirpus cyperinus(L.) Kunth, andJuncus effususL. plant community, and Wetland System 2 was planted to aTypha angustifoliaL.,T. latifoliaL., andSparganium americanumNutt. plant community. Nitrogen loading rates were increased annually from 0.6 to 2.7 g m−2d−1Soils were analyzed for total N annually. Surface‐pore water was sampled with equilibrators and analyzed for NH+4–N. Although the total N accumulation significantly increased with time in both systems, total soil N accumulation by depth did not differ significantly between systems. Distribution profiles in the surface‐pore water column showed that NH+4–N was transported upward into surface water at N loading rates from 1.2 to 2.7 g m−2d−1As total N loading rates increased annually in both wetland systems, soil pore water had higher levels of NH+4–N but N removal efficiency of the wetlands sharply decreased. Accumulation of high levels of NH+4–N (>200 mg L−1) in soil pore water could negatively affect long‐term ability of wetland systems to treat wastewater with high N levels.