bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon Fractions Associated with Silt‐Size Particles in Surface and Subsurface Soil Horizons
Authors: Adisa Shade John , Nortcliff Stephen
Published: December 2010

Information on the distribution and behavior of C fractions in soil particle sizes is crucial for understanding C dynamics in soil. At present little is known about the behavior of the C associated with silt‐size particles. We quantified the concentrations, distribution, and enrichment of total C (TC), readily oxidizable C (ROC), hot‐water‐extractable C (HWC), and cold‐water‐extractable C (CWC) fractions in coarse (63–20‐μm), medium (20–6.3‐μm), and fine (6.3–2‐μm) silt‐size subfractions and in coarse (2000–250 μm) and fine (250–63 μm) sand and clay (<2‐μm) soil fractions isolated from bulk soil (<2 mm), and 2‐ to 4‐mm aggregate‐size fraction of surface (0–25 cm) and subsurface (25–55 cm) soils under different land uses. All measured C fractions varied significantly across all soil particle‐size fractions. The highest C concentrations were associated with the <20‐μm soil fractions and peaked in the medium (20–6.3‐μm) and fine (6.3–2‐μm) silt subfractions in most treatments. Carbon enrichment ratios (ERC) revealed the dual behavior of the C fractions associated with the medium silt‐size fraction, demonstrating the simultaneous enrichment of TC and ROC, and the depletion of HWC and CWC fractions. The medium silt (20–6.3‐μm) subfraction was identified in this study as a zone where the associated C fractions exhibit transitory qualities. Our results show that investigating subfractions within the silt‐size particle fraction provides better understanding of the behavior of C fractions in this soil fraction.
Nitrogen Fertilization Effects on Grassland Soil Acidification: Consequences on Diffusive Phosphorus Ions
Authors: Stroia Ciprian , Morel Christian , Jouany Claire
Published: December 2010

Soil acidification due to N supplied from fertilizer or aerial deposition in grasslands is well recognized and documented; however, little is known about its consequences on soil P availability. This question was addressed on a long‐term field experiment done on grassland in Ercé (Central Pyrenees, France), where plots were treated for 6 yr with a factorial combination of mineral N added as NH4NO3 (0 and 190 kg ha−1 yr−1) and P (0 and 50 kg ha−1 yr−1) and managed with a frequent defoliation regime (3 cuts yr−1). Diffusive PO4 ion dynamics at the soil–solution interface was determined by coupling sorption studies with 32P labeling of PO4 ions (Pi) and dilution analysis. Results showed that the soil pH did not change in zero‐N treatments (5.9 ± 0.1) in comparison with the initial soil (5.9 ± 0.1), whereas it decreased to 5.3 ± 0.1 on N‐treated soils. Meanwhile the cation exchange capacity and exchangeable Ca2+ and Mg2+ contents decreased significantly and the saturation percentage of the adsorption complex by Al3+ increased from 2 to 15; no changes were observed for untreated soils. Furthermore, the gross amount of diffusive Pi (Pr) was accurately described as a function of the concentration of PO4 ions in the solution (Cp) and time (t) by a Freundlich kinetic equation; these dynamics were significantly modified by N supply but not by P.
Soil Nitrous Oxide Emissions in Corn following Three Decades of Tillage and Rotation Treatments
Authors: Omonode Rex A. , Smith Doug R. , Gál Anita , Vyn Tony J.
Published: December 2010

Few experiments have directly compared the long‐term effects of moldboard, chisel, and no‐till tillage practices on N2O emissions from the predominant crop rotation systems in the midwestern United States. This study was conducted from 2004 to 2006 on a tillage and rotation experiment initiated in 1975 on a Chalmers silty clay loam (a Typic Endoaquoll) in west‐central Indiana. Our objectives were to assess (i) long‐term tillage (chisel [CP], moldboard plow [MP], and no‐till [NT]), rotation (continuous corn [Zea mays L.] and corn–soybean [Glycine max (L.) Merr.]), and rotation × tillage interaction effects on soil N2O emission, and (ii) how soil N2O emission is related to environmental factors during corn production under identical N fertilizer management. Seasonal N2O emissions were measured at intervals ranging from a few days to biweekly for up to 14 sampling dates in each growing season for corn. Nitrous oxide emissions during the growing season were significantly affected by tillage and rotation but not their interaction; however, 50% of total emissions occurred shortly after N application regardless of tillage or rotation practices. Seasonal cumulative emissions were significantly lower under NT but not statistically different for CP and MP. Overall, emissions under NT were about 40% lower relative to MP and 57% lower relative to CP. Rotation corn lowered N2O emissions by 20% relative to continuous corn. Higher N2O emission under MP and CP appeared to be driven by soil organic C decomposition associated with higher levels of soil–residue mixing and higher soil temperatures.
Global Prospects Rooted in Soil Science
Authors: Janzen H. H. , Fixen P.E. , Franzluebbers A. J. , Hattey J. , Izaurralde R. C. , Ketterings Q. M. , Lobb D. A. , Schlesinger W. H.
Published: December 2010

The biosphere, our fragile and exquisite home, is changing abruptly and irrevocably, largely from human interference. Most or all of the coming stresses have links to the land, so finding hopeful outcomes depend on wide and deep understanding of soils. In this review, we pose eight urgent issues confronting humanity in coming decades: demands for food, water, nutrients, and energy; and challenges of climate change, biodiversity, “waste” reuse, and global equity. We then suggest some steps soil scientists might take to address these questions: a refocusing of research, a broadening of vision, a renewed enticement of emerging scientists, and more lucid telling of past successes and future prospects. The questions posed and responses posited are incomplete and not yet fully refined. But the conversations they elicit may help direct soil science toward greater relevance in preserving our fragile home on this changing planet.
Phosphorus Budget and Soil Extractable Dynamics in Field Crop Rotations in Mollisols
Authors: Ciampitti Ignacio A. , García Fernando O. , Picone Liliana I. , Rubio Gerardo
Published: December 2010

A better understanding of the P cycle is necessary to provide insights into management strategies that could enhance P bioavailability for crops. Our objectives were to evaluate the effects of continuous P fertilization on (i) the P budget, (ii) soil‐extractable P (Pe) dynamics, and (iii) the relationship between these variables. Two crop rotations during a 6‐yr period were analyzed in seven on‐farm experiments: corn (Zea mays L.)–double cropped wheat (Triticum aestivum)/soybean [Glycine max (L.) Merr.] (C‐W/S), and corn–soybean–double cropped wheat/soybean (C‐S‐W/S). Calculations of net P input considered only P removal (output) and fertilization (input). Initial soil‐test P was 13.4 mg P kg−1 (average for the four sites) for the C‐W/S rotation and 37.9 mg P kg−1 for the C‐S‐W/S rotation (average for the three sites). Treatment combinations were two annual rates: unfertilized and grain P removal estimation +10% (average 34 kg P ha−1 yr−1). Not applying P to soils testing 45 to 68 mg kg−1 of initial Pe resulted in a steep Pe decline (slope 0.2 mg kg−1 per unit of negative P budget). Nevertheless, soils with <25 mg kg−1 of initial Pe levels resulted in a very small and gradual decline (slope 0.02 mg kg−1). Use of current P rates applied by local farmers probably results in a small soil‐test P buildup with time. The P required to increase Pe by 1 mg P kg−1 was 11 and 8 kg P ha−1 yr−1 for the C‐W/S and C‐S‐W/S rotations, respectively.
Temperature and Time of Day Influence on Double‐Ring Infiltrometer Steady‐State Infiltration Rates
Authors: Clancy Katherine , Alba Veronica M.
Published: December 2010

Steady‐state infiltration rates (IRs) correlate well with temperature. They have been observed, however, to have values 1.5 to 2.5 times higher than predicted by viscosity, known as the t‐effect Many field studies that have observed the t‐effect used continuous IR measurement systems. We measured 67 IRs using double‐ring infiltrometers (DRIs) during the 2007 and 2008 autumn seasons in sand and loamy sand soils across a temperature range of 5 to 35°C. We found above‐average to good correlation between temperature and IR. For loamy sand (n = 17), IR rate differences were accounted for by viscosity differences, but for sand (n = 30) the IR values were 2.0 to 2.9 times higher than the viscosity‐predicted rate. Additionally, we found a difference in the IR temperature regressions based on the time of day of the measurements in the sand. Morning measurements were two times the viscosity‐predicted IR, while afternoon measurements were nearly three times. This research corroborates other field studies that observed the t‐effect using DRIs.
Comparison of Average and Point Capillary Pressure–Saturation Functions Determined by Steady‐State Centrifugation
Authors: Cropper S.C. , Perfect E. , van den Berg E.H. , Mayes M.A.
Published: December 2010

The capillary pressure–saturation function can be determined from centrifuge drainage experiments. In soil physics, the data resulting from such experiments are usually analyzed by the “averaging method.” In this approach, average relative saturation, 〈S〉, is expressed as a function of average capillary pressure, 〈ψ〉, i.e., 〈S〉(〈ψ〉). In contrast, the capillary pressure–saturation function at a physical point, i.e., S(ψ), has been extracted from similar experiments in petrophysics using the “integral method.” The purpose of this study was to introduce the integral method applied to centrifuge experiments to a soil physics audience and to compare S(ψ) and 〈S〉(〈ψ〉) functions, as parameterized by the Brooks–Corey and van Genuchten equations, for 18 samples drawn from a range of porous media (i.e., Berea sandstone, glass beads, and Hanford sediments). Steady‐state centrifuge experiments were performed on preconsolidated samples with a URC‐628 Ultra‐Rock Core centrifuge. The angular velocity and outflow data sets were then analyzed using both the averaging and integral methods. The results show that the averaging method smoothes out the drainage process, yielding less steep capillary pressure–saturation functions relative to the corresponding point‐based curves. Maximum deviations in saturation between the two methods ranged from 0.08 to 0.28 and generally occurred at low suctions. These discrepancies can lead to inaccurate predictions of other hydraulic properties such as the relative permeability function. Therefore, we strongly recommend use of the integral method instead of the averaging method when determining the capillary pressure–saturation function by steady‐state centrifugation. This method can be successfully implemented using either the van Genuchten or Brooks–Corey functions, although the latter provides a more physically precise description of air entry at a physical point.
Active Solarization as a Nonchemical Alternative to Soil Fumigation for Controlling Pests
Authors: Yates S.R. , Ashworth D.J. , Yates M.D. , Luo Lifang
Published: December 2010

Deterioration of soil, water, and air resources by soil fumigants represents a serious threat to agricultural production in semiarid regions due to their high volatility and high emission rates. New pest control methods are needed that do not rely on fumigant chemicals. Soil heating via solarization has been proposed as a nonchemical alternative to soil fumigation but has not found wide acceptance due to limitations in soil temperatures and heating depth, especially in cooler environments. We have developed a new soil heating method, termed active solarization, to increase the soil temperature and heating depth in the root zone. An experiment was conducted to compare heating for bare soil, standard (i.e., passive) solarization, and active solarization methodologies. A cumulative heat stress index, CHT30, was computed and has been shown to be related to plant‐pest survival. After 15 d of heating, passive solarization increased at the 10‐ and 20‐cm depths by 263 and 65°C h, respectively, compared with leaving the soil bare. For active solarization, CHT30 increased by 387 and 105°C h, respectively, compared with bare soil. After 30 d of passive solarization, CHT30 at 10 and 20 cm was 345 and 66°C h, respectively, and for active solarization CHT30 was 755 and 252°C h. The results indicate that active solarization increases soil temperatures and heat stress on plant pests. Based on published pest survival information, observed CHT30 after active solarization would provide better control of a plant pest (nematode) than passive solarization. Active solarization may offer a suitable nonchemical alternative to soil fumigation.
Landscape Determinants of Exchangeable Calcium and Magnesium in Ozark Highland Forest Soils
Authors: Kabrick John M. , Goyne Keith W. , Fan Zhaofei , Meinert Dennis
Published: December 2010

Exchangeable base cations, particularly Ca and Mg, largely govern soil acidity and, consequently, plant species composition in temperate forests. Although studies have identified soil and terrain characteristics affecting exchangeable Ca and Mg, few studies have identified the relative importance of factors affecting Ca and Mg distribution across landscapes. Objectives of this study were to: (i) identify the relative importance of geomorphic and soil properties for exchangeable Ca and Mg concentrations and quantities, and (ii) examine relationships between these properties and tree species abundance. A classification and regression tree (CART) analysis was applied to 74 pedons sampled across a 3800‐ha forested research area in the Ozark Highlands in southeastern Missouri. This analysis identified depth to bedrock and the bedrock lithology as important factors associated with exchangeable Ca and Mg concentrations, which ranged from 0.30 to 2.88 and 0.24 to 1.35 g kg−1, respectively. The CART analysis also indicated that the underlying bedrock was associated with exchangeable base cation quantity, and values ranged from 4263 to 20,144 kg ha−1 for Ca and 1650 to 9977 kg ha−1 for Mg. Analysis of variance indicated that the most common oak (Quercus L.) and hickory (Carya Nutt.) species were significantly more abundant on soils with lower Ca concentrations. The analysis framework applied in this study provides a basis for distinguishing among soils and ecological land types by pools of exchangeable Ca and Mg, thereby aiding in the identification of locales where base cation depletion may be of concern.
Use of Physically Based Models to Evaluate USDA Soil Moisture Classes
Authors: Bonfante Antonello , Basile Angelo , Manna Piero , Terribile Fabio
Published: December 2010

Soil Taxonomy differs from other international soil classification systems because it includes the estimation of the soil moisture regime (SMR) and is primarily based on the estimation of dry days in a soil moisture control section (SMCS). Alternatively, the International Committee on Soil Moisture and Temperature Regimes (ICOMMOTR) has proposed a new approach based on biweekly soil water potential values determined at a fixed depth. Currently, SMR estimation is performed through simple models (standard approaches), such as the Newhall and Billaux models, that are not physically based. The aims of this work were to test the appropriateness of both standard Soil Taxonomy and the ICOMMOTR approaches through the use of a hydrologic model based on the Richards equation (SWAP), and to evaluate possible SMR classification alternatives. The SWAP‐derived SMR classifications were compared with those derived by standard approaches, as well as the ICOMMOTR proposals, under eight pedoclimatic conditions (southern and northern Italy) where the SWAP model was calibrated and validated. The standard approaches clearly overestimated the dry conditions in the SMCS. Being mainly climate based, however, they were able to separate different pedoclimatic settings. In contrast, the physically based approach showed realistic results in terms of SMR estimation but did not differentiate pedoclimatic settings for either Soil Taxonomy or ICOMMOTR approaches. Three possible alternatives to SMR classification were investigated: (i) applying the ICOMMOTR classification approach supported by the use of hydrologic Richards‐based models; (ii) changing the rules of Soil Taxonomy for classifying SMR and SMCS to better fit “real” soil hydrologic behavior; and (iii) continuing to apply Newhall and Billaux models but clearly clarifying their climate‐driven criteria.
Agricultural Management and Soil Carbon Storage in Surface vs. Deep Layers
Authors: Syswerda S.P. , Corbin A.T. , Mokma D.L. , Kravchenko A.N. , Robertson G.P.
Published: December 2010

Soil C sequestration research has historically focused on the top 0 to 30 cm of the soil profile, ignoring deeper portions that might also respond to management. In this study we sampled soils along a 10‐treatment management intensity gradient to a 1‐m depth to test the hypothesis that C gains in surface soils are offset by losses lower in the profile. Treatments included four annual cropping systems in a corn (Zea mays)‐soybean (Glycine max)‐ wheat (Triticum aestivum) rotation, perennial alfalfa (Medicago sativa) and poplar (Populus x euramericana), and four unmanaged successional systems. The annual grain systems included conventionally tilled, no‐tillage, reduced‐input, and organic systems. Unmanaged treatments included a 12‐yr‐old early successional community, two 50‐yr‐old mid‐successional communities, and a mature forest never cleared for agriculture. All treatments were replicated three to six times and all cropping systems were 12 yr post‐establishment when sampled. Surface soil C concentrations and total C pools were significantly greater under no‐till, organic, early successional, never‐tilled mid‐successional, and deciduous forest systems than in the conventionally managed cropping system (p ≤ 0.05, n = 3–6 replicate sites). We found no consistent differences in soil C at depth, despite intensive sampling (30–60 deep soil cores per treatment). Carbon concentrations in the B/Bt and Bt2/C horizons were lower and two and three times more variable, respectively, than in surface soils. We found no evidence for C gains in the surface soils of no‐till and other treatments to be either offset or magnified by carbon change at depth.
Rescue Nitrogen Applications for Corn
Authors: Nelson Kelly A. , Scharf Peter C. , Stevens William E. , Burdick Bruce A.
Published: December 2010

Rescue N applications to corn (Zea mays L) may be needed when wet conditions prevent N applications or when the loss of applied N is suspected due to wet conditions. Crop injury when N is broadcast applied may counteract the yield benefits of a rescue N application. The objective of this research was to determine the effect of corn height, N placement, and source on injury and yield response. Five site‐years of research evaluated the impact of broadcast and between‐row placement of NH4NO3(AN), urea–NH4NO3(UAN), urea, and urea plus N‐(n‐butyl) thiophosphoric triamide (NBPT), a urease inhibitor, at 170 kg N ha−1either preplant or when the corn was 30, 60, 90, or 120 cm tall. Visual injury for broadcast‐applied N sources was ranked urea = urea plus NBPT < AN ≤ UAN 7 d after treatment. Injury was dependent on plant height. Leaf injury resulted in reduced yield when UAN or AN was broadcast on corn that was 60, 90, or 120 cm tall. Broadcast urea or urea plus NBPT caused minimal crop injury and effectively supplied N to the corn crop. Application of NBPT‐treated urea increased yield 260 kg ha−1averaged across timings when compared with urea alone. Application when corn was 30 cm tall produced the highest yields, but excellent yield response to rescue N was obtained at all application heights. The placement and source of N should be considered when rescue N applications are made to corn >30 cm tall.
Pre‐ and Post‐Irrigation Mapping of Soil Salinity with Electromagnetic Induction Techniques and Relationships with Drainage Water Salinity
Authors: Urdanoz V. , Aragüés R.
Published: December 2010

Irrigated agriculture may impair negative “on‐site” (i.e., soil salinization) and “off‐site” (i.e., salts exported in irrigation return flows) effects. The aim of this study was to assess these effects, and the relationships between soil‐ and drainage‐water salinity in a basin before and after the development of irrigation. Soil salinity (ECe) was estimated through electromagnetic induction (EMI) techniques (ECa) and the corresponding calibration equations, and drainage water salinity (ECdw) was measured in the outlets of 22 watersheds delineated within a 505‐ha study area before (Year 2006) and after (Year 2008) irrigation development. Apparent soil EC was about 50% higher in 2008 than in 2006 due to increasing soil water contents, but estimated ECe was about 15% lower in 2008 than in 2006 due to salt leaching induced by irrigation. Drainage water EC increased by one order of magnitude from the upper (ECdw = 0.4 dS m−1) to the lower (ECdw = 4.5 dS m−1) reaches of the drainage network. The mean ECdw of the 22 watershed drainage outlets increased from pre‐irrigation 2006 (2.4 dS m−1) to post‐irrigation 2007 (3.1 dS m−1) and 2008 (2.7 dS m−1) years. Drainage water EC significantly depended (P< 0.001) on surface‐weighted EC (ECe*) of each watershed, but the linear regressions were different in 2006 and 2008. The transformation from dryland to irrigation led to the leaching of salts and its export in the irrigation return flows. A compromise needs to be attained in the study area to achieve the beneficial “on‐site” leaching of salts while minimizing the detrimental “off‐site” export of salts.
Soil Thermal Conductivity as Influenced by Aggregation at Intermediate Water Contents
Authors: Ju Zhaoqiang , Ren Tusheng , Hu Chunsheng
Published: December 2010

Soil thermal conductivity (λ) is strongly influenced by soil water content as well as the arrangement of solid particles in soil. In this study we investigated the influences of soil aggregation on soil thermal conductivity at relatively higher water contents by the thermo‐time domain reflectometry (TDR) technique. The relationship between thermal conductivity and water content (θv) was measured for both aggregated (<2 mm) and non‐aggregated (<0.1 mm) loam and clay loam soils using two different experimental approaches: continuous vs. non‐continuous measurements. The results from the continuous measurement showed that thermal conductivity was significantly higher in the non‐aggregated soils than in the aggregated soils at intermediate water contents. This is explained by the formation of intra‐aggregate pores in aggregated soils that decreases the contacts and heat flow between aggregates. Alternatively the non‐aggregated soils have a relatively uniform pore system that enhances bridging between neighboring particles through pore water, thus improves heat conduction. For the non‐aggregated soils, relatively larger bulk density increase during the drying process also contributes to the greater thermal conductivity than that of aggregated soils. The results from the non‐continuous approach, however, showed similar thermal conductivity values for the aggregated and non‐aggregated soils, which was possibly caused by aggregate reformation in non‐aggregated samples during soil mixing and packing.
Carboxylic Acids Affect Sorption and Micro‐Scale Distribution of Phosphorus in an Acidic Soil
Authors: Schefe C. R. , Kappen P. , Pigram P. J.
Published: December 2010

The availability of P fertilizer to plants is decreased in acid soils due to phosphate sorption onto solid‐phase binding sites. A combination of solution analysis, micro‐x‐ray fluorescence (μ‐XRF) and micro‐x‐ray absorption near edge structure (μ‐XANES) spectroscopy were used to investigate the degree to which sorption of fertilizer P is determined by reaction with Al compounds, the extent to which carboxylic acid addition can influence these reactions, and the relative distribution of sorbed P in an acid soil. The addition of carboxylic acids did not change total P sorption, with solid‐phase P binding to metal and organic complexes. No treatment effects on P bonding were evident, as measured by μ‐XRF and μ‐XANES. While μ‐XRF and μ‐XANES did provide information on P interactions, the high spatial heterogeneity within samples and the need to focus on areas of high P concentration diminished our ability to identify clear treatment effects at the micro scale. Nevertheless, this research did highlight the value of utilizing complementary techniques (solution analyses, XRF, μ‐XRF mapping, and XANES) to generate new knowledge about P chemistry in soils.
Whole‐Profile Soil Carbon Stocks: The Danger of Assuming Too Much from Analyses of Too Little
Authors: Kravchenko A. N. , Robertson G. P.
Published: December 2010

Whole soil profile assessments of soil C stocks are enormously important for evaluating a soil's potential for sequestering C. Carbon stock measurements are often highly variable, which makes the detection of statistically significant differences among different land uses and management systems difficult. A common mistake is to interpret a lack of statistical significance as evidence for the absence of differences. This mistake is costly: failure to identify practices and habitats that accumulate C can affect our understanding of soil C cycling and hide possible sequestration potentials. In this study, we investigated inadequate replication as a major cause of a lack of statistical significance. Power analysis is a well‐established statistical tool that allows researchers to infer whether the lack of statistical significance is due to the absence of meaningful differences or due to insufficient replication. We used data from two published studies to illustrate the value of power analysis. In particular, we showed that in these studies the chances of detecting even substantial (e.g., 50%) differences among experimental treatments can be as low as 20 to 60% due to the natural variability in soil C concentrations and stocks. Carbon variability in different soil horizons suggests that statistical analyses of soil C stocks should be conducted separately for each sampled horizon and that conclusions about the profile as a whole should be made based on the individual horizon results. Devising an optimal sampling strategy that identifies the appropriate number of replicates needed to detect significant C change by horizon is essential.
Assessing Decadal Change in Mineral Soil Cation Chemistry at the Turkey Lakes Watershed
Authors: Hazlett P. W. , Curry J. M. , Weldon T. P.
Published: December 2010

Mass balance studies and direct measurement of changes in soil chemistry have provided evidence of depletion of base cations in soils across decadal time scales. Losses of base cations have been attributed to leaching as a consequence of elevated levels of S and N deposition. Chemical properties of mineral soil horizons were determined at seven plots in a tolerant hardwood forest at the Turkey Lakes Watershed in 1986 and in 2003 and 2005. Archived soils from the original sampling were used to assess the impact of storage and changing methodology on results. Exchangeable cation concentrations were compared between the two sampling times, as were concentrations normalized for organic C. The effects of air‐dry storage were significant for some cations, but in absolute terms the changes were small when contrasted with the spatial variation in exchangeable cation concentrations for the samples collected in 2003 and 2005. There were no statistically significant declines in pH, exchangeable Ca, Mg, or K concentrations, or Ca, Mg or K concentrations normalized for organic C concentration during the 17‐ to 19‐yr sampling period across the watershed. Exchangeable Na and normalized Na concentrations decreased in deeper horizons of the soil profile. There were various patterns of cation change at the plot level, but these changes were unable to be attributed to the range of soil profile base status at the site. Mineral weathering inputs appeared to provide stability to the exchangeable base cation pool in spite of large leaching losses at the Turkey Lakes site.
Characterization of Volcanic Ash‐Influenced Forest Soils across a Geoclimatic Sequence
Authors: Kimsey Mark J. , Garrison-Johnston Mariann T. , Johnson Leonard
Published: December 2010

The pedogenic development of volcanic ash mantles within the interior U.S. Pacific Northwest is thought to be a function of the interaction between climatic regimes, plant communities, eolian reworking, and colluvial mixing with subsurface soil parent materials. Little research, however, quantitatively characterizes the extent of these interactions on soil property expression and nutrient retention. This study examined soil physical and chemical properties associated with volcanic ash mantles overlying extrusive and metasedimentary geologic parent materials across an array of precipitation zones. The results were then correlated with NO3, SO4, and BO3 sorption isotherms to assess parent material influence and degree of mineral weathering on nutrient retention. Analyses indicated that ash‐mantled extrusive soils had ∼25 to 50% more plant‐available water, two to three times greater volcanic glass, two to five times less quartz, and up to five times more short‐range‐order Fe in the Bw1 and 2Bw2 horizons than ash‐mantled metasedimentary soils. Mean annual precipitation zones showed a strong positive correlation with the development of short‐range‐order Al minerals. Anion sorption isotherms were in the order of SO4 > BO3 ≥ NO3 for surficial Bw1 horizons, and SO4 ≥ NO3 > BO3 for subsurface Bw2 and 2Bw2 horizons. Anion retention mechanisms were positively correlated with the presence of short‐range‐order Al and Al‐substituted Fe oxides. Soil property characterization indicated that surficial ash soils often reflect the physical and mineral characteristics of subsurface soils, but climatic conditions control their chemical expression through the degree of mineral weathering.
Forage Radish Cover Crops Increase Soil Test Phosphorus Surrounding Radish Taproot Holes
Authors: White Charles M. , Weil Ray R.
Published: December 2010

Cover crops can influence nutrient cycling in the agroecosystem. Forage radish (FR) (Raphanus sativus L. var. longipinnatus) is unique in terms of P cycling because of its high tissue P concentration, rapid growth in the fall, and rapid decomposition in winter and spring. In addition, FR produces a taproot that decays during the winter and leaves distinct holes in the surface soil. This study measured P uptake by FR and cereal rye (CR) (Secale cereale L.) cover crops; the Mehlich 3 P concentration (M3P) in bulk soil following FR, CR, and no cover crop (NC); and M3P in soil within 3 cm of FR taproot holes. Cover crop treatments of FR, CR, and NC were established at two sites each fall for three subsequent years in a cover crop–corn (Zea mays L.) silage rotation. Cover crop shoot P uptake ranged from 5.9 to 25 kg P ha−1 for FR measured in the fall and from 3.0 to 26 kg P ha−1 for CR measured in the spring. The greatest cover crop effect on bulk soil M3P was observed at the 0‐ to 2.5‐cm depth after 3 yr of cover crops, with M3P values of 101, 82, and 79 mg P kg−1 after FR, CR, and NC, respectively. Soil within 3 cm of FR taproot holes had greater M3P than FR and NC bulk soil. Further studies should be conducted to determine if FR could increase P removal rates in excessively high P soils or increase P availability in low P soils.
Impact of Sampling Depth on Differences in Soil Carbon Stocks in Long‐Term Agroecosystem Experiments
Authors: VandenBygaart A. J. , Bremer E. , McConkey B. G. , Ellert B. H. , Janzen H. H. , Angers D. A. , Carter M. R. , Drury C. F. , Lafond G. P. , McKenzie R. H.
Published: December 2010

The depth of sampling has recently been highlighted as critical to making accurate measurements of changes in SOC stocks. This paper aimed to determine the effects of land management changes (LMC) on soil organic carbon (SOC) by re‐sampling long‐term agoecosystem experiments (LTAEs) across Canada using identical sampling and laboratory protocols. The impact of sampling depth on the monitoring of LMC‐induced differences in SOC stock in LTAEs in Canada, and the implications on statistical power and sampling design, were assessed. In most cases, four cores would be suitable for detecting a significant difference in SOC stock of 5 Mg ha−1 at 95% confidence for LMCs in western Canada. The impact of eliminating fallow on SOC stocks was typically restricted to the surface 15 cm. The impact of perennial forages on the average cumulative SOC was sufficiently large to be detectable at all sampling depths (to 60 cm). In three of the six LTAEs sampled in western Canada comparing conventional tillage to no‐till, there was a significantly greater SOC storage in the 0‐ to 30‐depth than the 0‐ to 15‐cm depth, suggesting that sampling below 15 cm could be necessary. The same comparisons in eastern Canada suggested that sampling often must exceed the 30‐cm depth to account for any changes in SOC due to moldboard plow tillage. Nonetheless, there was little evidence to suggest that increasing sampling intensity or sampling deeper would improve the ability to detect a difference in SOC stocks for this LMC.
Controls of Volatile Ammonia Losses from Loblolly Pine Plantations Fertilized with Urea in the Southeast USA
Authors: Zerpa J. L. , Fox T. R.
Published: December 2010

Ammonia volatilization losses from surface applied urea could reduce the N‐use efficiency in loblolly pine (Pinus taeda L.) plantations. Three field studies were conducted to assess the effectiveness of two urea formulations: coated‐urea fertilizer (CUF) and the urease inhibitor N‐(n‐butyl) thiophosphoric triamide‐treated urea (NBPT) at reducing ammonia (NH3) losses in loblolly pine plantations under different forest floor moisture (dry vs. wet), substrate (forest floor vs. mineral soil), and site/soil type conditions (Piedmont vs. Coastal Plain). An additional laboratory study under controlled environmental conditions helped validate the results from the field. Ammonia volatilization losses were influenced more by the initial forest floor moisture than by the fertilizer formulations and were 43% lower when the fertilizer treatments were applied directly on the forest floor than on the exposed mineral soil. The average NH3 losses, expressed as a percentage of applied N, in the Piedmont ranged from 1 to 9%, and from 7 to 16%, 7 and 30 d after fertilization, respectively. At Day 7, both CUF and NBPT reduced NH3 losses, as compared with untreated urea, by 39 and 80%, respectively. In the Coastal Plain, NH3 losses ranged from 7 to 17%, 7 d after fertilization. Both CUF and NBPT reduced NH3 losses, as compared with untreated urea, by 35 and 25%, respectively. This difference in treatment ranking between sites suggests a fertilizer by site/soil type interaction which the laboratory study confirmed. These results highlight the importance of knowing the environmental and site conditions before fertilization and can help decide where and when these formulations might be used more effectively.
Carbon Sources and Dynamics in Afforested and Cultivated Corn Belt Soils
Authors: Hernandez-Ramirez Guillermo , Sauer Thomas J. , Cambardella Cynthia A. , Brandle James R. , James David E.
Published: December 2010

Afforestation of degraded cropland can sequester atmospheric C; however, source partitioning and turnover of soil organic C (SOC) in such ecosystems are not well documented. This study assessed SOC dynamics in two 35‐yr‐old, coniferous afforestation sites (i.e., a forest plantation situated in northwestern Iowa on a silty clay loam soil and a shelterbelt situated in eastern Nebraska on a silt loam soil) and the adjacent agricultural fields. Soil samples were collected at both sites to determine SOC and total N concentrations and stable C isotope ratios (δ13C, natural abundance) in both whole soil and the fine particulate organic matter (POM) fraction (53–500 μm size). In these fine‐textured soils, afforestation of cropland performed through either shelterbelt or forest plantation caused substantial increases in surface SOC storage compared with conventionally tilled cropping systems (≥57%; P < 0.05); this confirms the direct benefits of tree planting on SOC sequestration. Relative to cropped soils, afforested soils exhibited a more depleted δ13C signature (−17 vs. −22‰), indicating a shift in C sources. Source‐partitioning assessment revealed that tree‐derived C contributed roughly half of the SOC found directly beneath the trees. The C‐enriched afforested surface soils exhibited SOC turnover rates of 0.018 to 0.022 yr−1 and mean residence times of 55 to 45 yr. Fine POM in afforested surface soils accounted for a large proportion (21%) of the existing SOC, 79% being derived from tree inputs. This supports the role of POM as a significant sink for recently sequestered SOC in these ecosystems.
Procedures for Initializing Soil Organic Carbon Pools in the DSSAT‐CENTURY Model for Agricultural Systems
Authors: Basso Bruno , Gargiulo Osvaldo , Paustian Keith , Robertson G. Philip , Porter Cheryl , Grace Peter R. , Jones James W.
Published: December 2010

Process‐based soil organic C (SOC) models are widely used for simulating, monitoring, and verifying soil C change. In such models, determining the initial distribution of SOC across multiple pools is often not well defined, yet pool initialization can strongly influence the subsequent SOC dynamics. We developed a model‐based procedure to initialize SOC fractions that uses site‐specific soil, climatic, and land use history information, along with measured initial total SOC, to estimate SOC distribution across pools. The procedure consists of creating sets of SOC fractions for scenarios including different field histories, soil texture, and management practices for medium‐ and long‐term simulations to provide a broad spectrum of conditions, using data from an experimental site in Georgia. Tables created using this procedure can help model users select the SOC fractions needed to properly initialize the model. The model is executed for the duration of the prior land use history time period, and the simulated final total SOC is compared with the soil C measurement at the beginning of the subsequent experimental time period. If these values are equal, the final SOC fractions from the land use history simulations are used with the measured soil C to start the simulation of the cropping system being studied. If these values are not equal, then the procedure is repeated iteratively until the measured value of soil C is adequately predicted. We demonstrated the improved prediction accuracy by using the proposed procedure in simulating soil C for a long‐term field experiment in Michigan.
The Role of Soil Characteristics on Temperature Sensitivity of Soil Organic Matter
Authors: Haddix Michelle L. , Plante Alain F. , Conant Richard T. , Six Johan , Steinweg J. Megan , Magrini-Bair Kim , Drijber Rhae A. , Morris Sherri J. , Paul Eldor A.
Published: December 2010

The uncertainty associated with how projected climate change will affect global C cycling could have a large impact on predictions of soil C stocks. The purpose of our study was to determine how various soil decomposition and chemistry characteristics relate to soil organic matter (SOM) temperature sensitivity. We accomplished this objective using long‐term soil incubations at three temperatures (15, 25, and 35°C) and pyrolysis molecular beam mass spectrometry (py‐MBMS) on 12 soils from 6 sites along a mean annual temperature (MAT) gradient (2–25.6°C). The Q10 values calculated from the CO2 respired during a long‐term incubation using the Q10‐q method showed decomposition of the more resistant fraction to be more temperature sensitive with a Q10‐q of 1.95 ± 0.08 for the labile fraction and a Q10‐q of 3.33 ± 0.04 for the more resistant fraction. We compared the fit of soil respiration data using a two‐pool model (active and slow) with first‐order kinetics with a three‐pool model and found that the two and three‐pool models statistically fit the data equally well. The three‐pool model changed the size and rate constant for the more resistant pool. The size of the active pool in these soils, calculated using the two‐pool model, increased with incubation temperature and ranged from 0.1 to 14.0% of initial soil organic C. Sites with an intermediate MAT and lowest C/N ratio had the largest active pool. Pyrolysis molecular beam mass spectrometry showed declines in carbohydrates with conversion from grassland to wheat cultivation and a greater amount of protected carbohydrates in allophanic soils which may have lead to differences found between the total amount of CO2 respired, the size of the active pool, and the Q10‐q values of the soils.
Nitrogen Mineralization from Soil Organic Matter: A Sequential Model
Authors: Gilmour John T. , Mauromoustakos A.
Published: December 2010

A reliable method to predict N mineralization from soil organic matter (SOM) has proved difficult across a wide range of soils. Previous prediction models used discrete pool(s) of SOM that simultaneously decompose and mineralize organic N according to zero‐ or first‐order kinetics, with each pool characterized for size and N mineralization rate. We propose a different approach: two N pools based on total N that decompose and mineralize organic N in sequence according to first‐order kinetics. Data sets from four long‐term studies were used to evaluate the sequential model. The 108 soils represented differing soil depths, tillage practices, organic amendments, and cropping systems. The rate constant for Pool I was correlated with N mineralization during the first week (k1wk), calculated using long‐term data. The percentage of total N in Pool I was estimated using the rate constant for Pool I. The rate constant for Pool II was related to the Pool I rate constant and the percentage of total N in Pool I. Because a long‐term mineralization study to determine k1wk is impractical as a routine test, k1wk was correlated with total N, CO2 evolution at 3 d, and clay content using data from one study (38 soils). The rate constant and size of Pool I and were also correlated with total N, CO2 evolution at 3 d, and clay content. An equation describing the impact of temperature and water holding capacity on the rate constant for Pool I suggested that a single Q10 value is inappropriate for N mineralization from SOM.
Pedogenesis and Soil‐Geomorphic Relationships in an Arid Mountain Range, Mojave Desert, California
Authors: Hirmas Daniel R. , Graham Robert C.
Published: December 2010

Mountains are impressive features of many desert landscapes because of their elevation, complex topography, and sheer extent. Soil genesis and landscape processes were studied in the southern Fry Mountains, Mojave Desert, California. Our aim was to better understand the processes responsible for the distribution of soil properties in this landscape. Measured properties in 65 soil pits across the study site show that dust, soluble salt, NO3−–N, and carbonate distributions are correlated with the prevailing wind direction. This finding suggests that the mountain range effectively traps eolian sediment. Soils mantling these mountains have accumulated, on average, 41 kg m−2silicate dust, 172 g m−2soluble salts, 3.3 g m−2NO3−–N, and 79 kg m−2carbonate and reached maximum concentrations of 156 kg m−2, 1800 g m−2, 43 g m−2, and 398 kg m−2, respectively, on windward sides of the range. The basin floor encompassing Soggy Lake, an upwind playa, is the probable primary source of these materials. Soil morphology and land surface characteristics from four major mountain landforms were used to interpret the pedogenic and soil‐geomorphic processes that have led to the distribution patterns of these accumulations. Our study demonstrates that arid mountains accumulate and store appreciable quantities of dust, soluble salts, NO3−, and carbonate and are therefore important to the overall geomorphic evolution and biogeochemical cycling of the region. The previously unaccounted storage of pedogenic carbonate in similar mountain ranges could increase the global soil inorganic C pool estimate by as much as 15 to 174 Pg C.
Spatial Variability in Soil Microbial Communities in a Nitrogen‐Saturated Hardwood Forest Watershed
Authors: Gilliam Frank S. , McCulley Rebecca L. , Nelson Jim A.
Published: December 2010

The long‐term reference watershed (WS4), at Fernow Experimental Forest, West Virginia, displays symptoms of N saturation despite considerable spatial heterogeneity in soil properties, such as texture, N pools, and cycling rates. We identified a weathering gradient of three sites within WS4 by assessing differences in clay content across a common geologic substrate. Across these sites (LN, MN, and HN), NO3 production rates vary significantly (low, medium, and high nitrification, respectively) and are negatively related to clay content. It is unknown whether microbial communities vary across these sites and contribute to variability in NO3 production. This study characterized soil microbial communities along this gradient and assessed factors potentially important in explaining microbial composition. We sampled mineral soil from each of the sites, analyzing for moisture, pH, organic matter, extractable N, and microbial biomass and community composition via phospholipid fatty acid (PLFA) analysis. Analysis of variance and canonical correspondence analysis indicated that microbial community composition varied among sites, with a predominance of fungal markers (18:2n6 and 18:1n9c) at the most weathered LN site and Gram negative bacteria (18:1n7c) at the less weathered MN and HN sites. Accordingly, the fungi/bacteria ratio increased in the direction of LN plots in ordination space. Correlations between measured environmental parameters and PLFA data suggest that acidic conditions and low NO3 abundance at the LN site have selected for fungal dominance, although other important factors known to exert an influence on soil microbial communities, such as differences in plant community and clay and organic matter content, may also be playing a role in determining the observed patterns.
Formation and Transformation of Iron Oxide–Kaolinite Associations in the Presence of Iron(II)
Authors: Wei Shi-Yong , Liu Fan , Feng Xiong-Han , Tan Wen-Feng , Koopal Luuk K.
Published: December 2010

Iron oxide–kaolinite associations are important components of tropical and subtropical soils and have significant influence on the physical and chemical properties of soils. In this study, the formation and transformation of Fe oxide–kaolinite associations as a function of pH, temperature, and time were investigated at different Fe(II)/Fe(III) molar ratios (R). Results show that the formation of crystalline Fe oxides was significantly inhibited due to the presence of kaolinite, while accelerated by Fe(II). The formation of lepidocrocite– and goethite–kaolinite associations were accelerated by Fe(II) at R = 0.04 to 0.06, an initial pH (pHi) of 5 to 8, and a temperature (T) of 50 to 70°C; the formation of hematite–kaolinite association was accelerated by Fe(II) at R = 0.06, pHi 7 to 8, and T = 60 to 80°C; magnetite–kaolinite association was obtained at R = 0.06, pHi 9, and T = 60°C or at R = 0.1 to 0.5, pHi 7, and T = 60°C. The pH as a function of time (pHt) decreased sharply when crystalline Fe oxides were formed in the presence of Fe(II), Fe(III), and kaolinite. The decrease in pHt was slow, however, in the system with Fe(III) and kaolinite but without Fe(II) and in the system with Fe(II) and kaolinite but without Fe(III). The morphologies of lepidocrocite, goethite, hematite, and magnetite in associations are strip shaped, nanorod like, pseudo‐cubic shaped, and nanosphere like, respectively. In a system with Fe(II), Fe(III), and kaolinite, Fe(II) weakened the inhibition of the formation of crystalline Fe oxides by kaolinite; the presence of kaolinite decreased the acceleration by Fe(II); and the morphologies of Fe oxides were influenced by both Fe(II) and kaolinite.