bluuebunny/crossref_metadata_2025 huggingface dataset:
Pedogenesis in Lutitic Cr Horizons of Gypsiferous Soils
Authors: Artieda O. , Herrero J.
Published: July 2010

The weathering of lutites in aridic or near‐aridic environments leading to soil horizons is not well known. Lutites are a common soil parent rock composed of silt and clay, that may be massive or may have their sedimentary origin marked by layers of alternating color or granulometry, or by fissility along planes. Lutites underlying soils are considered Cr horizons and show different alteration stages recognizable in the field by the degree of the layering disturbance or by the loss of coherence. In the study area, neither the dry climate nor the kind of clay minerals, mainly illite, can explain the weathering of lutites. This study was conducted to investigate the initial weathering reactions as encountered in Cr horizons, and to depict the processes responsible for pedogenesis from lutites in gypsiferous soils of the Ebro Valley (Spain). We described 12 soils in the field under two different soil moisture regimes, with further characterization through chemical analyses and micromorphology by thin section and scanning electron microscope (SEM). The microscopic study revealed two distinctive pedofeatures in the Cr horizons: (i) lenticular gypsum crystals; and (ii) “queras,” sub‐millimetric biotic features produced by calcification‐decalcification processes. Growth of gypsum crystals in these horizons resulted in an “isles fabric,” that is, isles of fine materials in a mass of gypsum crystals, with much greater porosity than the parent lutite. The growth of gypsum crystals and the development of queras result in a particle‐size distribution change and an increased porosity of the Cr horizons.
Natural Isotopic Distribution in Soil Surface Horizons Differentiated by Vegetation
Authors: Quideau S. A. , Graham R. C. , Feng X. , Chadwick O. A.
Published: July 2010

The isotopic composition of soil organic matter (SOM) is a useful tool for deciphering the different mechanisms underlying decomposition processes in soils. The objective of this study was to quantify the influence of oak (Quercus dumosa Nutt.) and pine (Pinus coulteri D. Don) vegetation on the isotopic variation occurring during decomposition by measuring δ13C and δ15N in selected litter and soil fractions. Soil samples obtained from A horizons of two lysimeter soils were separated by density and mineral size to isolate the floatable, fine silt, and clay fractions. These fractions as well as the litter samples were subjected to sequential chemical extractions to differentiate between polar and nonpolar extractives, acid‐soluble carbohydrates, and acid‐insoluble residues. The physical fractions varied by up to 3.5‰ for δ13C and 4.7‰ for δ15N, while acid‐insoluble residues were depleted by 0.9 to 2.1‰ δ13C as compared with the samples before extraction. Under oak, 13C and 15N content progressively increased from the litter to the floatable, fine silt, and clay fractions (by 4.7‰ for δ13C and 4.9‰ for δ15N). By comparison, under pine, enrichment of the clay fraction was 1.7‰ for δ13C and 1.7‰ for δ15N as compared with the initial litter. The greater enrichment in heavy isotopes under oak vegetation as compared with the pine could not be explained based on differences in litter inputs. Results suggested instead that variation in decomposition processes by vegetation type caused the differences in heavy isotope enrichment.
Quantifying Deep‐Soil and Coarse‐Soil Fractions
Authors: Harrison R. B. , Adams A. B. , Licata C. , Flaming B. , Wagoner G. L. , Carpenter P. , Vance E. D.
Published: July 2010

Forest soils are often deep and/or coarse‐textured, which does not always lend itself to easy unbiased sampling. Two important Pacific Northwest (PNW) forest soil series that are deep and coarse‐textured were studied to evaluate methods of estimating soil C: (i) a loamy sand glacial outwash soil (Indianola series, mixed, mesic Dystric Xeropsamments) and (ii) a very gravelly sandy loam glacial outwash soil (Everett series, sandy‐skeletal, isotic, mesic Vitrandic Dystroxerepts). Four methods were compared for estimating soil C, including: (i) large pit (0.5 m2) excavation, (ii) dug pit with 54‐mm hammer‐core bulk‐density sampling, (iii) 31‐mm soil push sampler, and (iv) clod method. Coarse (>2 mm) fragments were also collected, processed, and analyzed for soil C. Extending soil sampling deeper than 15 cm increased soil C estimates by as much as 120%. The pit excavation method with sand‐displacement volume measurements, which is by far the most labor‐intensive and time‐consuming, was considered the “standard” by which other methods were compared, as it didn't contain any obvious biases. Soil core methods overestimated the <2‐mm soil fraction (samples taken between large rocks). Biased methods are often accepted as the “best available” due to the high time requirement of pit excavation. The 31‐ or 54‐mm soil core methods often didn't work due to the high rock content (>50%) of the Everett soil. Including C analysis of the >2‐mm soil fraction increased soil C estimates by 170% for the Everett series soil (due to organic C contained in the rocks; there were no carbonates) but did not substantially increase the estimate in the Indianola series soil.
Interpretation of Soil Carbon and Nitrogen Dynamics in Agricultural and Afforested Soils
Authors: Paul E. A. , Morris S. J. , Six J. , Paustian K. , Gregorich E. G.
Published: July 2010

Interpretation of soil organic C (SOC) dynamics depends heavily on analytical methods and management systems studied. Comparison of data from long‐term corn (Zea mays)‐plot soils in Eastern North America showed mean residence times (MRTs) of SOC determined by14C dating were 176 times those measured with13C abundance following a 30‐yr replacement of C3by C4plants on the same soils. However, MRTs of the two methods were related (r2= 0.71). Field13C MRTs of SOC were also related (R2= 0.55 to 0.85) to those measured by13CO2evolution and curve fitting during laboratory incubation. The strong relations, but different MRTs, were interpreted to mean that the three methods sampled different parts of a SOC continuum. The SOC of all parts of this continuum must be affected by the same controls on SOC dynamics for this to occur. Methods for site selection, plant biomass, soil sampling and analysis were tested on agricultural, afforested‐agriculture, and native forest sites to determine the controls on SOC dynamics. Soil‐C changes after afforestation were −0.07 to 0.55 Mg C ha−1yr−1on deciduous sites and −0.85 to 0.58 Mg C ha−1yr−1under conifers. Soil N changes under afforestation ranged from −0.1 to 0.025 Mg N ha−1yr−1Ecosystem N accumulation was −0.09 to 0.08 Mg N ha−1yr−1Soil C and N sequestration but not plant biomass were related to soil Ca, Mg, and K contents. Comparative, independent assays of long‐term plots provides information for concept testing and the confidence necessary for decision‐makers determining C‐cycle policies.
Selectivities of Potassium‐Calcium and Potassium‐Lead Exchange in Two Tropical Soils
Authors: Appel Chip , Ma Lena Q. , Rhue R. Dean , Reve William
Published: July 2010

Measurement of cation selectivity in soils provides important information about the affinity and binding strength of a particular cation on soil surfaces. Gaines‐Thomas (KGT) selectivity coefficients were determined for a variety of K/Ca and K/Pb ratios on an Oxisol and Ultisol soil from Puerto Rico. The calculatedKGTvalues indicated a preference for K+over Ca2+or Pb2+The selectivity for Pb2+was significantly greater than that for Ca2+due to Pb2+'s larger hydrated charge density relative to that of Ca2+The patterns of selectivity were independent of metal type. The selectivity of the Oxisol for Ca2+or Pb2+exhibited no trend and changed little with changes in divalent metal surface coverage. The Ultisol displayed a decrease in selectivity for Ca2+and Pb2+with increasing surface coverage of these ions. This was attributed to the presence of smectite in the Ultisol, which was able to partially collapse when K+saturated. Some of the Pb sorption in the soils was due to chemisorption. The Oxisol chemisorbed ≈3000 mg Pb kg−1while that value for the Ultisol was ≈1900 mg kg−1The differences were due to the greater quantities of Fe/Al oxides and organic matter in the Oxisol relative to the Ultisol. Scanning electron microscopy‐energy dispersive X‐ray (SEM‐EDX) spectroscopy detected discrete Pb‐C phase in both soils. The C was from organic matter. Under experimental conditions, any Pb‐carbonate phase would not have been stable. It was possible Pb was associated with organic sulfhydral groups. The selectivity exhibited by soil systems for various nutrient and heavy metals is important in elucidating how available these metals will be for plant/animal uptake as well as their mobility and stability in the soil environment.
Soil Carbon and Nitrogen Organic Fractions in Degraded vs. Non‐Degraded Mollisols in Argentina
Authors: Fabrizzi Karina P. , Morón Alejandro , García Fernando O.
Published: July 2010

The use of no‐tillage has notably increased in the Pampas region of Argentina during the last 10 yr. Two tillage experiments with contrasting previous agricultural use, degraded and non‐degraded soils, were evaluated in the southeast of Buenos Aires province, Argentina. The objectives were to: (i) quantify the effects of tillage and N fertilization on quantity and vertical distribution of C and N in the soil organic matter (SOM) and particulate organic matter (POM) fractions as well as potentially mineralizable N (PMN), and (ii) evaluate these fractions as indicators of soil quality. Tillage systems were conventional tillage (CT), minimum tillage (MT), and no‐tillage (NT) (main plots), and N fertilization rates were 0, 120, and 150 kg ha−1 (subplots). Total organic C (TOC), total N (TN), POM‐C, POM‐N, and PMN were measured at 0‐ to 7.5‐ and 7.5‐ to 15‐cm soil depth. In Exp. I (degraded soil) TOC was greater under NT (27 g kg−1) than under CT (24 g kg−1) in the 0‐N treatments. No differences in TOC and TN were found in Exp. II at 0 to 7.5 cm (non‐degraded soil). Carbon in POM and POM‐N were greater under NT in the fractions of 212 to 2000 and 53 to 212 μm at 0 to 7.5 cm, but they were similar or greater under CT at 7.5‐ to 15‐cm depth in Exp. I. Stratification of TOC, TN, and POM were observed under NT in Exp. I. Potentially mineralizable N was greater under NT (62 mg kg−1) in Exp. I, however, no differences in PMN were observed in Exp. II. Carbon in POM 212 to 2000 μm and PMN were the more sensitive indicators of tillage effects, mainly in Exp. I.
Comparing Ordinary Kriging and Cokriging to Estimate Infiltration Rate
Authors: Ersahin Sabit
Published: July 2010

Measuring infiltration within a landscape is important because it is one of the key processes controlling water budgets for the agricultural production and transport processes in the soil profile. Estimation of this process at an acceptable level of accuracy is important, especially in the case when it exhibits high variability, since its measurement is a time‐ and labor‐consuming procedure. This study was conducted to evaluate and compare kriging and cokriging to estimate infiltration rate (IR) using limited available data on an 8.5‐ha alluvial field (loamy mixed mesic Ustifluvent). Infiltration tests were conducted using double‐ring infiltrometers until steady‐state IRs were obtained at nodes of an irregular grid consisting of 24 columns and four rows. Values of field‐measured IR ranged from 1.92 to 8.88 cm h−1, with a mean of 5.11 cm h−1Bulk density of subsoil was significantly related to IR and, therefore, helped estimation of IR values at unobserved locations. Both kriging and cokriging adequately estimated IR when 50 observed IR values were used with both estimators (mean reduced error was 4.15 × 10−3for kriging and 4.10 × 10−3for cokriging). To determine the minimum number of observed IR values needed to estimate IR without losing significant spatial information, kriging and cokriging were repeated with 45, 40, 35, and 30 observed IR values. Forty‐five measured IR values with kriging, and 40 values with cokriging were adequate to estimate IR. Therefore, cokriging was found superior to kriging in estimating IR in the case of limited available data.
Dinitrogen and Nitrous Oxide Formation in Beech Forest Floor and Mineral Soils
Authors: Wolf Inken , Brumme Rainer
Published: July 2010

A 15N tracer study was conducted to determine N2 and N2O fluxes and the processes responsible for the formation of N2O in two beech (Fagus silvatica L.) forest soils: an acid mineral soil (AM) (pH = 3.8) and the overlying acid forest floor (AFF) (pH = 3.8) from the Solling and a less acid mineral soil (LAM) (pH = 5.2) from the Göttinger Wald. Ammonium and nitrate of undisturbed soil cores were labeled by injecting 15N. The evolved gases, N2O and N2, and the ammonium and nitrate concentrations in the soils were measured together with the 15N abundances over a period of 8 d. Nitrous Oxide was produced in all soils by denitrification. Nitrate was reduced to N2 at higher soil pH (LAM) and in the AFF. The end product of denitrification at the lower soil pH (AM) was N2O. The N2O and N2 emission calculated on an areal basis decreased from LAM, AFF, to AM. The N2O/(N2O + N2) ratios decreased from AM (1.0), AFF (0.97), to LAM (0.80) during the initial period indicating that the main product of denitrification was N2O. On prolonged incubation the N2O/(N2O + N2) ratios decreased for AFF and LAM to 0.78 and 0.32, respectively, and was attributed to a gradual decrease in nitrate concentration. We estimate the in situ N2 emissions to be 0.71 and 0.51 kg N ha−1 yr−1 for the Göttinger Wald and the Solling, using published annual in situ N2O emissions and our N2/N2O ratios. The in situ N2O emissions of the Göttinger Wald and Solling are 0.17 and 3 kg ha−1 yr−1 and the N2 emissions increased the annual denitrification losses to about 0.88 and 3.51 kg ha−1 yr−1 The approach for estimating in situ N2 emissions has to be improved in future studies.
Redox Range with Minimum Nitrous Oxide and Methane Production in a Rice Soil under Different pH
Authors: Yu Kewei , Patrick William H.
Published: July 2010

A Louisiana rice soil was incubated from the most oxidizing to the most reducing conditions that could be maintained. Four different pH levels were used. Nitrous oxide production initiated shortly after the incubation started under oxidized conditions. As the soil suspension became more reducing, a large amount of CH4 was produced at a critical reducing point and increased exponentially with a further decrease of redox potential (EH). The results indicated that there was no statistically significant difference between the theoretically predicted decrease of EH with increase of pH and the observed change of EH with pH for N2O production (60 mV, P = 0.932), and for significant CH4 production (93 mV, P = 0.204), respectively. Consequently, the EH range with minimum N2O and CH4 production shifted to lower values of the EH scale when pH increased. Global warming potential (GWP) contribution from the studied soil mainly comes from N2O production at moderately reducing conditions, and from CH4 production under very reducing conditions. There was a slight production of CH4 at high EHs soon after incubation started, but this CH4 production was not a significant source of GWP from soils because of its small quantity and transient occurrence. If pH is neutral, the calculated EH range with minimum GWP is generally in the range of −150 to +180 mV. This redox window accounts for >40% of the entire EH range in this study, which makes appropriate management of irrigated rice fields possible that will minimize both N2O and CH4 production.
Pedostratigraphy and Carbonate Accumulation in the Last Interglacial Pedocomplex of the Chinese Loess Plateau
Authors: Feng Z.-D. , Wang H. B.
Published: July 2010

This paper examines the geographic variations of carbonate concentrations in last interglacial pedocomplex (S1) profiles along a northwest (NW)–southeast (SE) transect across the Chinese Loess Plateau. The average S1 carbonate concentration is the same as that of overlying loess (L1) and underlying loess (L2) at the northwesternmost site (Lanzhou), but variations in carbonate concentration within S1 pedocomplex are greater than the within‐loess (L1 and L2) variations, indicating that the carbonate translocation within the S1 pedocomplex had occurred. Carbonate was leached to greater depths to form more pronounced peaks in the three paleosols (S1S1, S1S2, S1S3) within the S1 pedocomplex at the Dingxi section. Farther SE to the Qinan section, the three paleosols (S1S1, S1S2, S1S3) have more distinguishable carbonate leaching and accumulation zones than at the Dingxi section. The S1 carbonate concentration at the Tianshui section suggests that the three paleosols were partially welded, as evidenced by the S1S3 and S1S2 paleosols sharing a major portion of the paleosol profile. Soil‐forming events occurred repeatedly in a single paleosol profile and the Ck horizon might have served as the carbonate accumulation zone for all three paleosols (S1S1, S1S2, S1S3) at the southeasternmost site (Lantian). Land surface stability complicated carbonate concentration processes in loessial paleosols and extra caution should be observed when interpreting climate implication of carbonate concentration data.
Accurate Dye Tracer Concentration Estimations Using Image Analysis
Authors: Persson Magnus
Published: July 2010

In this paper, the accuracy of dye tracer concentration estimations using image analysis is examined. The variability before and after application of different image correction methods was investigated in three experiments using a digital camera. In each of these experiments, one correction was applied and the remaining variability after correction was calculated as the SD of uniformly colored patches on a color scale. Correction for inhomogeneous illumination results in a relatively small remaining variability. The variability after correction for different color temperatures (or white point) was larger if the correction was made for image files directly from the camera. However, when using the raw data from the image sensor in the camera, the remaining variability was significantly reduced. A calibration experiment was also conducted, in which photographs of calibration samples of dye‐stained soil were taken. Between 72 and 260 samples were prepared for each of three soils. The samples had dye concentrations from 0 to 1.5 g L−1Effects of exposure settings and calibration model were investigated. The exposure settings only affected the results significantly in one soil which became dark when the dye concentration was high. Overexposure made the image lighter and the root mean square error (RMSE) of the concentration estimate decreased for this soil. By applying a neural network (NN) model, the RMSE of the dye concentration estimates could be as low as 0.0747 to 0.0944 g L−1Reasonable accuracy (0.10–0.13 g L−1) could also be achieved with a polynomial calibration relationship derived from around 20 soil samples.
Ferrihydrite–Humic Associations
Authors: Schwertmann U. , Wagner F. , Knicker H.
Published: July 2010

Humic–iron oxide associations are believed to exist in various surface environments, such as soils and surface waters, and may add substantially to the stability of organic matter under oxidizing surface conditions. However, a nondestructive, solid‐state characterization of such associations is still lacking. In this paper synthetic coprecipitates between humic material (dissolved organic matter; DOM) obtained from a Podzol and synthetic ferrihydrite are examined using X‐ray diffraction (XRD) patterns and Fe‐specific Mössbauer spectra at temperatures between 4.2 K and room temperature. Lepidocrocite formed in the absence of DOM. However, DOM induced the formation of a four (XRD)‐line ferrihydrite that contained 96 mg C/kg. In contrast to a pure four‐line ferrihydrite, which was completely magnetically ordered at 4.2 K, the synthesized DOM–ferrihydrite was not fully ordered at 4.2 K and had a magnetic hyperfine field 1 to 2 T lower than the pure ferrihydrite. Such an effect was not observed when DOM was only surface‐adsorbed. We conclude that organic components of the DOM coprecipitated with the ferrihydrite. Their interaction with the Fe atoms of the oxide prevents complete spin freezing at 4.2 K. Solid‐state 13C nuclear magnetic resonance (NMR) spectra suggested that O‐alkyl C of the DOM was mainly responsible for the interaction with the Fe in the oxide.
Nutrient Leaching in Oxisols Under Native and Managed Vegetation in Brazil
Authors: Wilcke Wolfgang , Lilienfein Juliane
Published: July 2010

Brazilian savanna Oxisols are prone to nutrient leaching because of low nutrient retention and high water conductivity. We determined downward and upward fluxes of Ca, Mg, K, NH4–N, and NO3–N at 0.3‐, 0.8‐, and 2.0‐m soil depths under native savanna vegetation (Cerrado), Pinus caribaea Morelet plantation, managed productive Brachiaria decumbens Stapf pasture, degraded B. decumbens pasture, conventional tillage, and no‐till corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] cropping using exchange resin cores, and set up a nutrient budget using previously published input data. At each of the study depths, we installed three to six PVC tubes (0.10 m in diameter, 0.11 m in length) filled with a mixture of field‐fresh soil and HBr‐washed ion exchange resin (Amberlite MB‐20, 10:1 v/v), which were removed and extracted after 2 yr. Downward fluxes at 2‐m soil depth ranged from 0.22 to 2.3 g Ca, 0.02 to 0.71 g Mg, 0.08 to 1.17 g K, not detected (n.d.) to 0.96 g NH4–N, and n.d. to 4.4 g NO3–N m−2 yr−1 Upward fluxes, because of capillary rise, frequently amounted to 30 to 50% of downward fluxes. At 0.3‐m depth, net leaching fluxes of Ca in the cropping systems and productive pasture (2.3–4.9 g m−2 yr−1) and of K and NO3–N in the cropping systems (K: 0.73–0.85, NO3–N: 2.3) were significantly higher than in all other systems except for NO3–N in Pinus (Ca: 0.02–0.18, K: 0.09–0.15; NO3–N: n.d.–0.70). In forests and pastures, all nutrients accumulated on balance while in cropping systems budgets were balanced or negative except for N. To reduce these losses, timing of fertilizer amendments should be optimized and in the no‐till system evaporation and fast water fluxes reduced for example, by stubble mulching.
Soil Dielectric Spectra from Vector Network Analyzer Data
Authors: Logsdon S. D.
Published: July 2010

For more than two decades, dielectric properties (i.e., permittivity) have been used for soil water content measurements, but unexpected results have been shown for saline soils or soils high in smectite clays. Permittivity is complex with real and imaginary components, and varies with frequency. The frequency dependence is due to dipole rotation and charge migration processes under alternating current. Dielectric relaxation refers to the reorienting of molecules after an electrical field is removed. The objective of this study was to develop a procedure for determining complex permittivity spectra for soils. Six soils with a range of mineralogies were preequilibrated at four duplicated water contents. They were packed into truncated coaxial cells, and the reflection‐scattering parameter was measured for frequencies between 300 kHz to 3 GHz, although the primary calculation procedure was valid to <100 MHz. The calculated complex permittivity was difficult to use for deriving unique parameters because of overlapping influence of electrical conductivity and multiple dielectric relaxation processes that extended beyond the measured frequency range. The complex resistivity was easier to interpret, clearly showing one major relaxation process, except for the driest soils. The relaxation frequency determined from complex resistivity increased significantly as water content and electrical conductivity increased. For each soil, the square root of apparent permittivity, εa1/2, significantly increased as frequency decreased and as water content increased. The εa1/2 showed frequency dependence ranging from 1.1‐fold per order of magnitude for Cecil soil to almost 2.5‐fold for Ida soil. Developing procedures to extend the measured and calculated frequency range would enhance data analysis options.
Characterization of Humic Acid Fractions Improves Estimates of Nitrogen Mineralization Kinetics for Lowland Rice Soils
Authors: Ve Nguyen Bao , Olk D. C. , Cassman K. G.
Published: July 2010

Nitrogen mineralization in irrigated lowland rice (Oryza sativa L.) soils is poorly predicted by total soil C and N. To improve its prediction, two humic acid fractions were extracted with NaOH from lowland rice soils of Vietnam and the Philippines to evaluate their influence on N mineralization kinetics during 84‐d anaerobic incubations. Indicative of young organic matter, the mobile humic acid (MHA) fraction had a smaller C/N ratio and optical density at 465 nm (E4) than did the calcium humate (CaHA) fraction, which was extracted after removal of polyvalent cations from the soil. Nitrogen contents of both fractions combined represented 15 to 30% of total soil N. Nitrogen mineralization followed a two‐pool first‐ and zero‐order kinetic model during the incubations. More than 80% of the variation in the size of a rapidly mineralizable N pool (N1) was explained by soil organic C. However, stepwise regressions using whole soil variables explained only 27% of the variation in the rate constant for the rapidly mineralizable N pool and 36% of the variation in the rate constant for a slower steady‐state phase. Prediction of the two rate constants was improved to 64 and 75%, respectively, and of N1 to 97% by including MHA and CaHA properties in the stepwise regressions. All three mineralization parameters were negatively correlated with the degree of humification in these humic fractions. The degree of humification was positively associated with exchangeable polyvalent cations (Ca+2 and Mg+2) and negatively associated with exchangeable K+, suggesting an influence of exchangeable cations on the turnover of young organic matter. We conclude that better understanding the contribution of these humic fractions to short‐term N cycling will improve our ability to predict N supply in lowland rice soils.
Nitrous Oxide Emissions from Agricultural Toposequences in Alberta and Saskatchewan
Authors: Izaurralde R. C. , Lemke R. L. , Goddard T. W. , McConkey B. , Zhang Z.
Published: July 2010

Nitrous oxide fluxes from soils are inherently variable in time and space. An improved understanding of this variability is needed to make accurate estimates of N2O fluxes at a regional scale. The objectives of this work were to (i) characterize the influence of soil–landscape combinations and N application rates on N2O emissions and to (ii) determine the contribution of these influences on the estimation of N2O emissions at the field scale. We used static chambers and gas chromatography methods to measure N2O fluxes and collected ancillary data (mineral N, water soluble C, soil water content, soil temperature) in Canada at Mundare (AB) in the aspen parkland ecoregion and at Swift Current (SK) in the short‐grass prairie ecoregion. At Mundare, measurements were taken in 1995 and 1996 by landscape position and land use. At Swift Current, data were collected in 1999 and 2000 by landscape position and N rate. At Mundare, landscape position affected N2O emissions but the pattern varied seasonally. During a 46‐d period in summer 1995, a flux of 430 g N2O‐N ha−1 measured in a backslope was greater than the 60 g N2O‐N ha−1 measured on average in shoulder and depressional areas. The flux pattern changed during a 43‐d spring thaw of 1996 when fluxes from depressional areas were greatest (1710 g N2O‐N ha−1). Nitrous oxide emissions from natural areas were small. The emission pattern during summer 1996 was similar to that of 1995 but the fluxes were an order of magnitude larger. At Swift Current, N2O fluxes in summer 1999 were affected by topography and N rate. Fluxes were greatest in depressional areas receiving N at 110 kg ha−1 (3140 g N2O‐N ha−1). Use of the area fraction occupied by each landscape position to calculate N2O flux increased the estimates of N2O fluxes at the field scale in five out of six cases. Further research of N2O fluxes in variable landscapes should help elucidate factors controlling N2O fluxes from pedon to field scale and thus translate into improved flux estimates at regional scales.
Appalachian Mine Soil Morphology and Properties
Authors: Haering Kathryn C. , Daniels W. Lee , Galbraith John M.
Published: July 2010

Surface coal mining and reclamation methods in the Appalachians have changed dramatically since the passage of the Surface Mining Control and Reclamation Act (SMCRA) of 1977 and subsequent improvements in mining and reclamation technology. In this study, 30 pre‐SMCRA mine soil profiles (4–20 yr old) were examined and sampled in 1980 and compared with 20 mine soil profiles (8–13 yr old) described in the same area in 2002 after it had been completely remined by modern deep cut methods. Mine soils in both sampling years had high rock fragment content (42–81%), relatively well‐developed A horizons, and generally exhibited A‐C or A‐AC‐C horizonation. Although six Bw horizons were described in 1980, only two met all requirements for cambic horizons. The 1980 mine soils developed in overburden dominated by oxidized, preweathered material due to relatively shallow mining cuts. The 1980 mine soils had lower rock fragment content, finer textures, lower pH, and tended to be more heterogeneous in horizonation, morphology, and texture than soils observed in 2002, which had formed primarily in unweathered overburden from deeper cuts. Half the pedons sampled in both years had densic materials within 70 cm of the surface. Four poorly to very poorly drained soil profiles were described in each sampling year containing distinct hydric soil indicators in surface horizons. While older pre‐SMCRA mine soils do have many properties in common with newer mine soils, their properties are highly influenced by the fact that they generally have formed in more weathered overburden from higher in the geologic column. Overall, Appalachian mine soils are much more complex in subsoil morphology than commonly assumed, and differential compaction greatly complicates their internal drainage and limits their overall productivity potential.
Corn‐Residue Transformations into Root and Soil Carbon as Related to Nitrogen, Tillage, and Stover Management
Authors: Allmaras R. R. , Linden D. R. , Clapp C. E.
Published: July 2010

Soil organic carbon (SOC) is sensitive to management of tillage, residue (stover) harvest, and N fertilization in corn (Zea mays L.), but little is known about associated root biomass including rhizodeposition. Natural C isotope abundance (δ13C) and total C content, measured in paired plots of stover harvest and return were used to estimate corn‐derived SOC (cdSOC) and the contribution of nonharvestable biomass (crown, roots, and rhizodeposits) to the SOC pool. Rhizodeposition was estimated for each treatment in a factorial of three tillage treatments (moldboard, MB; chisel, CH; and no‐till, NT), two N fertilizer rates (200 and 0 kg N ha−1), and two corn residue managements. Treatments influenced cdSOC across a wide range (6.8–17.8 Mg C ha−1). Nitrogen fertilization increased stover C by 20%, cdSOC by only 1.9 Mg C ha−1, and increased rhizodeposition by at least 110% compared with that with no N fertilizer. Stover harvest vs. stover return reduced total source carbon (SC) by 20%, cdSOC by 35%, and total SOC. The amount of stover source carbon (SSC) responded to tillage (MB > CH > NT), but tillage affected the amount of cdSOC differently (NT > CH > MB). Total SOC was maintained only by both N fertilization and stover return during the 13‐yr period. The ratio of SC in the nonharvestable biomass to SSC ranged from 1.01 to 3.49; a ratio of 0.6 conforms to a root‐to‐shoot ratio of 0.4 when the root biomass includes 50% rhizodeposits. Tillage controlled the fraction of SC retained as cdSOC (i.e., humified; 0.26 for NT and 0.11 for MB and CH), even though N fertilization, stover harvest, and tillage all significantly influenced SC. Decomposition of labile rhizodeposits was a major component of the nonhumified fraction. Rhizodeposition was as much as three times greater than suggested by laboratory and other controlled studies. To understand and manage the entire C cycle, roots and rhizodeposition must be included in the analysis at the field level.
Persistence of Soil Organic Carbon after Plowing a Long‐Term No‐Till Field in Southern Ontario, Canada
Authors: VandenBygaart A. J. , Kay B. D.
Published: July 2010

There is abundant evidence that minimizing soil disturbance reduces mineralization of organic matter and can result in larger storage of soil organic carbon (SOC) relative to conventional tillage. However, little is known about the persistence of SOC when no‐till lands are plowed periodically. This study set out to determine the change in SOC when a long‐term (22 yr) no‐till field in southern Ontario, Canada, was plowed once. Four plots were located within three textural classes [sandy loam (SL), sandy clay loam (SCL), and silty clay loam (SiCL)] within two hydrologic conditions (well‐ and poorly drained) in the field. The plots were sampled before and three times after (3 d, 7 mo, and 18 mo) the no‐till field was moldboard plowed. The single tillage event homogenized the SOC through the profile and reduced the stratification. When calculated on an equivalent mass basis beyond the plow depth, there was no significant change in SOC 18 mo after plowing the SCL, SiCL, and SL high SOC plots. However, in the SL plot with low SOC, there was a loss of about 3 Mg SOC ha−1 after 18 mo, and the loss occurred primarily between the 15‐ and 30‐cm depths in the profile. The loss may have accounted for as much as two‐thirds of the SOC gained from no‐tillage. This study also emphasized the need for additional care to account for changes in bulk density when comparing the quantity of soil constituents, such as SOC, after plowing.
Crop Cover Root Channels May Alleviate Soil Compaction Effects on Soybean Crop
Authors: Williams Stacey M. , Weil Ray R.
Published: July 2010

Deep‐rooted cover crops may help alleviate effects of soil compaction, especially in no‐till systems. We evaluate compaction‐alleviating ability of three Brassica cover crops and cereal rye (Secale cereale L.). Using a minirhizotron camera, we observed soybean [Glycine Max (L.) Merr.] roots growing through compacted plowpan soil using channels made by decomposing cover crop roots. Soybean yield response to the preceding cover crops was most pronounced at the site with most severe drought and soil compaction. At this location, with or without deep tillage, soybean yields were significantly greater following a “forage radish + rye” combination cover crop. Rye left a thick mulch, resulting in conservation of soil water early in the season. Root channels left by forage radish (Raphanus sativus L. ‘Diachon’) may have provided soybean roots with low resistance paths to subsoil water. Due to lower than normal winter precipitation, this study was a conservative test of the cover crops' ability to alleviate the effects of soil compaction.
Seasonal Fluctuations in Phosphorus Loss by Leaching from a Grassland Soil
Authors: Toor Gurpal S. , Condron Leo M. , Di Hong J. , Cameron Keith C.
Published: July 2010

Phosphorus losses from soils have been reported to impair the water quality, resulting in deaths of fish and other marine animals, and can harm human health. The objective of this study was to determine the seasonal distribution of P forms and losses in leachate collected from intact soil monoliths (70‐cm depth, 50‐cm diam.) of a Lismore stony silt loam soil (fine‐loamy, mixed, superactive, frigid Aquic Cumulic Hapludoll) during a 2‐yr period. The experiment included different combinations of mineral P fertilizer at 45 or 90 kg P ha−1 yr−1 and/or farm dairy effluent (FDE) at 200 or 400 kg N ha−1 yr−1, which contained 41 to 95 kg P ha−1 yr−1 Amounts and forms of P in leachate collected during the irrigation (IR; November–April) and nonirrigation (NIR; May–October) seasons were compared. Results showed that P losses were higher in particulate forms (mainly particulate unreactive phosphorus, PUP) during the IR seasons. This may be because of regular inputs of high intensity flood IR (92 mm per application), which increased the dislocation of particles in the soil profile, thereby resulting in higher PUP losses. On the other hand, the amount of natural rainfall was much lower (usually <20 mm per event) during the NIR seasons that resulted in less dislocation of particles compared with the IR seasons; hence, lower P losses as PUP but higher losses as dissolved unreactive phosphorus (DUP). Variation in P losses during the different seasons suggest the need to develop mitigation strategies that should focus on reducing DUP losses during the NIR and PUP losses during the IR season.
Mapping Material Distribution in a Heterogeneous Sand Tank by Image Analysis
Authors: Gimmi Thomas , Ursino Nadia
Published: July 2010

Water flow and solute transport through soils are strongly influenced by the spatial arrangement of soil materials with different hydraulic and chemical properties. Knowing the specific or statistical arrangement of these materials is considered as a key toward improved predictions of solute transport. Our aim was to obtain two‐dimensional material maps from photographs of exposed profiles. We developed a segmentation and classification procedure and applied it to the images of a very heterogeneous sand tank, which was used for a series of flow and transport experiments. The segmentation was based on thresholds of soil color, estimated from local median gray values, and of soil texture, estimated from local coefficients of variation of gray values. Important steps were the correction of inhomogeneous illumination and reflection, and the incorporation of prior knowledge in filters used to extract the image features and to smooth the results morphologically. We could check and confirm the success of our mapping by comparing the estimated with the designed sand distribution in the tank. The resulting material map was used later as input to model flow and transport through the sand tank. Similar segmentation procedures may be applied to any high‐density raster data, including photographs or spectral scans of field profiles.
Simultaneous Measurement of Soil Water Content and Salinity Using a Frequency‐Response Method
Authors: Zhang N. , Fan G. , Lee K. H. , Kluitenberg G. J. , Loughin T. M.
Published: July 2010

Laboratory tests were conducted to simultaneously measure soil water content and salinity using a four‐electrode Wenner array sensor. The sensor was modified to enhance the capacitive effect. Soil bulk density and the depth to which the electrodes penetrate into the soil were strictly controlled during the experiments. Sinusoidal current signals with a constant amplitude and frequencies ranging from 1 Hz to 15 MHz were sent to the outer electrodes of the Wenner array, whereas voltage outputs were measured from the inner electrodes. Frequency‐response data were analyzed using the partial least‐squares method to establish calibration models for simultaneously predicting water content and salinity from the frequency‐response patterns. The R2 values for predicting water content and salinity at the 30‐mm penetration depth reached 0.89 and 0.91, respectively, whereas the root‐mean‐square errors for the volumetric water content and salinity measurements were 0.019 m3 m−3 and 0.173 cmol kg−1, respectively. Test results showed that, in general, the calibration models predicted the water content more accurately than salinity. The depth to which the sensor penetrates into the soil has a strong effect on the measurement accuracy. This study has demonstrated that the modified Wenner array sensor and the frequency‐response method have a potential for simultaneously measuring soil capacitive and conductive properties. However, numerous difficulties, including contact resistance, depth control, and the effect of soil type, will need to be addressed to improve the measurement accuracy.
Anomalous Transport in “Classical” Soil and Sand Columns
Authors: Cortis Andrea , Berkowitz Brian
Published: July 2010

We re‐examine—in light of recent theoretical developments—classical experiments on dispersion of a passive tracer in fully and partially saturated porous columns. We find that the dispersion breakthrough curves (BTCs) exhibit anomalous (non‐Fickian) early arrival times and late time tailing, which can be explained by the Continuous Time Random Walk (CTRW) theory. The CTRW framework includes as a special case the classical advection‐dispersion equation (ADE) for Fickian transport. We argue that existing measurements and interpretations of dispersion should be carefully reconsidered in the framework of these advances in conceptual understanding and quantification.
Lime and Soil Moisture Effects on Nitrous Oxide Emissions from a Urine Patch
Authors: Clough Tim J. , Kelliher Francis M. , Sherlock Robert R. , Ford Colleen D.
Published: July 2010

Liming has been mooted as a mitigation option for lowering soil N2O emissions. This study investigated the effect of soil pH and soil water content on N2O and N2 emissions following the addition of synthetic urine (500 kg N ha−1) containing 15N‐labeled urea‐N. Soil pH treatments ranged from 4.7 to 7.2 with either saturated or field capacity soil. Dinitrogen and N2O fluxes were measured from soil cores kept on water tension tables for 85 d following urine‐N addition. Soil inorganic N transformations were also monitored over time by destructively sampling soil cores on five occasions over the 85 d. At field capacity, soil pH affected the N2O fluxes with the lowest cumulative N2O fluxes at soil pH ≥ 5.9. Nitrous oxide losses ranged from <0.1 to 0.4% of 15N applied in the field capacity treatment but this increased to be 0.4 to 1.7% of the 15N applied in the saturated treatment. Dinitrogen fluxes were low (<23 ng N2–N cm−2 h−1) at field capacity but exceeded 4000 ng N2–N cm−2 h−1 under saturated conditions. Cumulative N2 fluxes increased with increasing soil pH in the saturated soil. The flux ratio of N2O‐N/(N2O‐N + N2–N) remained high (0.68–0.71) under the field capacity treatment but decreased with time from 0.64 to 0.16 in the saturated treatment. This study suggests that while the use of soil liming has merit for lowering N2O emissions from urine patches where soils are at field capacity, the resulting NO3–N will be susceptible to enhanced rates of N2O and N2 loss if the soils are wetted up beyond field capacity.
A LOW‐INTENSITY, HIGH‐UNIFORMITY WATER APPLICATION SYSTEM
Authors: Hanke M. , Perry D. , Kung K.-J. S. , Bubenzer G.
Published: July 2010

Rainfall simulators with high uniformity and low intensities are required in many research areas related to environmental quality. To examine the characteristics of field‐scale macropore‐type preferential flow, we designed a portable water application system suitable to apply water with intensity < 5 mm h−1 for long‐term steady‐state infiltration experiments under different climatic conditions. Our results showed that, when water was applied at 345 kPa pressure, the system could deliver 4.36 mm h−1 of water to 19.2 by 2.7 m with 80 to 85% uniformity, while uniformity of the inner 16.2 by 2.1 m reached 94 to 97%. The performance of this system was not influenced by the ambient wind speed. Lower intensities of water application can be achieved by applying water intermittently.
Soil Organic Matter Clogs Mineral Pores
Authors: Mikutta Christian , Lang Friederike , Kaupenjohann Martin
Published: July 2010

Recent N2adsorption studies have suggested a ‘pore clogging’ effect on mineral soil phases caused by organic matter coatings. For methodological reasons, this pore clogging effect has been studied only after drying. Our hypothesis was that pore clogging is affected by drying of organic coatings. In our study, we used AlOOH, which has been equilibrated with dissolved organic matter (DOM) and polygalacturonic acid [PGA; (C6H8O6)n]. To test our hypothesis, we determined the porosity of moist and freeze‐dried AlOOH samples. Freeze‐dried samples were analyzed by N2adsorption, moist samples by1H‐nuclear magnetic resonance (NMR). In addition, the samples were characterized by environmental scanning electron microscopy—energy dispersive x‐ray spectroscopy (ESEM‐EDX). Both, DOM and PGA significantly reduced specific surface area (SSABET) of AlOOH by 34 m2g−1(15%) and 77 m2g−1(36%). The reduction in SSABETnormalized to the amount of C sorbed was 1.0 m2mg−1DOM‐C and 5.9 m2mg−1PGA‐C. Dissolved OM reduced the pore volume of micro‐ and small mesopores <3 nm whereas PGA also reduced the volume of larger pores. The1H‐NMR results of moist samples showed that PGA sorption reduced the amount of water in pores <4 nm. In addition, the pore size maximum of AlOOH increased by 150%. Polygalacturonic acid coatings created new interparticle pores of about 10‐ to 70‐nm size that are not stable upon freeze‐drying. Porosity changes upon DOM‐treatment were not commensurable by1H‐NMR. Our results indicate that clogging of micro‐ and small mesopores is not an artifact of freeze‐drying. Polygalacturonic acid seems not only to cover the mouth of AlOOH‐nanometer pores but also to fill them.
Microbial Nitrogen Transformations in Response to Treated Dairy Waste in Agricultural Soils
Authors: Shi Wei , Miller Bruce E. , Stark John M. , Norton Jeanette M.
Published: July 2010

Dairy wastes are commonly applied to croplands as N fertilizers, but the dynamics of N release and transformations during the growing season are difficult to predict. We compared N mineralization kinetics and examined microbial N transformations in soil receiving dairy‐waste compost vs. lagoon effluent. Mineralization kinetics was examined with a 70‐d laboratory incubation, and a first‐order model was used to derive mineralization parameters. Measurements of N transformations were conducted with 15N pool dilution techniques in silage corn field plots that were unfertilized or fertilized with ammonium sulfate, lagoon effluent, or compost at two rates equivalent to 100 or 200 kg available N ha−1 The N mineralization potential was higher and the first‐order rate constant was lower in soil receiving compost than lagoon effluent. Approximately 6% of compost N was mineralized within 2.5 mo; in contrast, up to 90% lagoon effluent organic N was released. However, silage yield was greatest in the compost treatment, showing that synchronization of N availability is as important as the amount mineralized. The field 15N measurements indicated that microbial NO−3 consumption was negligible despite the treatments. Microbial NH+4 immobilization in soil receiving dairy wastes was similar to that in soil unfertilized or fertilized with inorganic N. Soil treated with the high‐rate compost had the highest rates of mineralization and nitrification, which led to the highest soil NO−3 accumulation. Our observations suggest that peak plant demand is met by the compost N; however, its high N mineralization potential makes the management of dairy compost a difficult task.