bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus Forms and Extractability from Three Sources in a Recently Exposed Calcareous Subsoil
Authors: Robbins C. W. , Westermann D. T. , Freeborn L. L.
Published: July 2010

Irrigation‐induced erosion and land leveling have decreased crop yields on ≈800000 ha of south‐central Idaho silt loam soils because of topsoil removal. Phosphorus availability is a known production problem after topsoil removal. This study evaluated the effect of three P sources on soil P solubility by three standard methods for calcareous soils. A long‐term study was initiated on a Portneuf silt loam (Coarse‐silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid) by removing the surface 0.3 m of topsoil from strips between undisturbed topsoil strips. Phosphorus treatments applied across all strips were conventional fertilizer (applied according to soil test), dairy manure, and cheese whey. All treatments increased the freshly exposed subsoil bicarbonate extractable ortho‐P concentrations up to or greater than the topsoil concentrations, which were more than adequate for economical crop production. The high‐whey and manure treatments increased the subsoil saturation paste and 0.01 M CaCl2 extractable ortho‐P concentrations up to or greater than the untreated topsoil ortho‐P concentrations. The initial topsoil ortho‐P solubility was along the β‐tricalcium phosphate (β‐TCP) isotherm and the initial subsoil was well below the β‐TCP isotherm. The ortho‐P solubility of the subsoil monocalcium phosphate (MCP) treatment remained just below the β‐TCP isotherm. The cottage cheese whey treatment increased subsoil P solubility up to the β‐TCP isotherm and the manure treated subsoil ortho‐P solubilities were between the β‐TCP and octacalcium phosphate (OCP) isotherms. Most subsoil ortho‐P concentrations by all three extraction methods decreased from spring to fall and then increased over winter in the subsequent spring samples. Soil solution ortho‐P concentrations decreased with time in the subsoil treatments except immediately following treatment applications. The topsoil ortho‐P extract concentrations by all three methods varied among samplings but remained about the same during the study period.
Fate of Fertilizer Nitrogen Applied to Corn as Estimated by the Isotopic and Difference Methods
Authors: Schindler F. V. , Knighton R. E.
Published: July 2010

The percentage of applied fertilizer N taken into plants is often estimated by measuring the difference in plant N uptake between treated and check plots. This method has often overestimated plant N uptake. The objectives of this study were to (i) compare the recovery of fertilizer N in corn (Zea mays L.) as calculated by the difference and isotopic methods and (ii) track fertilizer N in the plant–soil system using isotopic enrichment of N. Sixteen N plots (3 m × 3 m) were established on a Hecla fine‐sandy loam (sandy, mixed, frigid Oxyaquic Hapludolls) and replicated four times in a completely random design. Corn received sidedressed band applications (15 cm from row and 5 cm deep) of 15N‐enriched and nonlabeled urea N at 135 kg N ha−1 in 1993 and 1994. Plant uptake of fertilizer N as estimated by the isotopic and difference methods was 45% and 39% in 1993 and 40% and 22% for 1994, respectively. Nearly 42% and 36% of the applied labeled N was accounted for in the soil at the end of 1993 and 1994, respectively. The difference method did not overestimate plant N uptake because of high soil N availability. Lower corn yield potential in 1993 was the consequence of a cooler, shorter growing season. This climatic difference had less effect on the results generated by the isotopic method. Reasons for the N deficit in this investigation are speculative since no attempts were made to measure gaseous emissions; however, denitrification and/or leaching are thought to be the primary mechanisms.
Soil Wind Erosion Hazard of Spring Wheat–Fallow as Affected by Long‐Term Climate and Tillage
Authors: Merrill Stephen D. , Black Alfred L. , Fryrear Donald W. , Saleh Ali , Zobeck Ted M. , Halvorson Ardell D. , Tanaka Donald L.
Published: July 2010

We hypothesized that drought accelerates wind erosion by increasing plant and soil factors of erodibility together, compounding the erosion hazard. Erodibility factors measured in biennial spring wheat–fallow on Pachic and Typic Haploborolls soil were (i) soil‐inherent wind erodibility (SIWE) by rotary sieving, (ii) surface roughness by pin meter and chain methods, (iii) standing residue profile, and (iv) residue coverage photographically. Four tillage treatments ranged from low residue (LR) to no‐till (NT). The erodible fraction of surface soil (a SIWE measure) changed from 53% during a dry period (1989–1990) to a less erodible 26% during a wet period (1992–1994). Median erosion protection values calculated from flat and standing residue measurements made after seeding were, respectively, 16 and 43% in 1989 to 1990, and 80 and 76% in 1992 to 1994. Soil losses estimated by RWEQ model equations were 11 to 6100 times greater during 1989 to 1990, compared with 1992 to 1994. No‐till was protective, and estimated soil losses on LR were up to 3000 times greater than those on NT. However, low residue yields in 1988 (930 vs. 3640 kg/ha avg.) resulted in inadequate protection after seeding in 1990, even in NT; and soil losses in LR and NT were 13 and 8 Mg/ha, respectively. Results indicate biennial small grain–fallow is nonsustainable in the long term from a soil‐erosion perspective.
Erosion Potential of a Torrertic Paleustoll after Converting Conservation Reserve Program Grassland to Cropland
Authors: Unger Paul W.
Published: July 2010

Extensive cropland areas were covered by the Conservation Reserve Program (CRP) in the semiarid southern Great Plains. Because soils were highly erodible, would erosion again become a problem when CRP land was converted to cropland? The erosion potential due to tillage methods used to convert CRP grassland to cropland was determined on Pullman clay loam (Torrertic Paleustoll). Tillage methods were no‐, sweep, disk, and moldboard + disk tillage with CRP grass retained or removed (mowing and baling), and grass burning followed by sweep or disk tillage. Wind erosion potential was based on percentage of >0.84‐mm diam. and mean weight diameter (MWD) of dry aggregates at 2 to 3 yr after converting to cropland. Water erosion potential was based on MWD and percentage of <0.25‐mm water‐stable aggregates, and water stability of 1‐ to 2‐mm aggregates at crop planting and harvest. Few differences due to tillage methods were significant. For dry aggregates, more than 60% were >0.84‐mm diam. and MWD was >10 mm with all tillage methods, indicating a low wind erosion potential. Wet aggregate stability and MWD values at some sampling times indicated water erosion could occur. Although erosion potential was low, continued use of residue‐incorporating tillage could lead to greater potentials. Because of initially low potentials, CRP land on Pullman and similar soils could be converted to cropland by any tillage method. Then, a conservation tillage system (e.g., no‐tillage) could be implemented before erosion by wind or water became a serious problem.
Field Water Drainage under Traditional and Improved Irrigation Schedules for Corn in Central Spain
Authors: Román R. , Caballero R. , Bustos A.
Published: July 2010

Traditional irrigation schedules used by farmers in central Spain may result in overirrigation and deep percolation. The objective of this research was to test whether an improved irrigation schedule based on restoring field capacity in the 0‐ to 0.5‐m soil layer could save irrigation water and reduce drainage (D) without impairing grain yield. A 4‐yr field experiment was conducted near Madrid, Spain. A neutron probe and tensiometers were used to measure water in storage and flux in a sandy‐loam soil (Typic Xerofluvent) with a corn (Zea mays L.)–wheat (Triticum aestivum L.)–corn–oat (Avena sativa L.) crop rotation common in the area. Crop water consumption and D were estimated with the zero flux plane–water balance equation. The improved irrigation schedule, only applied to the two corn crops, saved 170 mm of irrigation water, or 15% of the irrigation water used for traditionally irrigated plots. Drainage during the experiment was reduced from 235 mm in traditional to 119 mm in improved treatment. The cumulative grain yield for subsequent crops was unaffected by the irrigation treatments (31230 ± 3900 vs. 30770 ± 3430 kg ha−1). Grouped across the 4‐yr period, variation of evapotranspiration (ET) between individually instrumented sites (4%) was lower than the variation of D (30%). When daily ET and D estimates were grouped for cropping and intercultivation periods and compared with changes in water storage added to irrigation and rainfall, the mass balance principle was satisfied. Experienced corn farmers may apply this improved schedule by assessing soil depth of wetting.
Application of Capillary Electrophoresis to Anion Speciation in Soil Water Extracts II. Arsenic
Authors: Naidu R. , Smith J. , McLaren R. G. , Stevens D. P. , Sumner M. E. , Jackson P. E.
Published: July 2010

A method has been developed for the speciation of arsenic (AsO−2, AsO3−4, and dimethylarsinic [DMA]) in natural soil solutions from contaminated sites in Australia. The separation of these anions was achieved by capillary zone electrophoresis (CZE) using a fused silica capillary (72‐cm by 50‐μm i.d.) with a basic chromate buffer and on‐column indirect UV detection at 254 nm. Method parameters, such as electrolyte pH, run voltage, and capillary temperature were studied in order to establish suitable analytical conditions. The ideal separation for As(III) and DMA was achieved with a buffer pH of 8.0, a run voltage of 25 kV, and a capillary temperature of 30°C. Under these conditions, As(V) and orthophosphate ions comigrated. However, the use of a chromate buffer at pH 10, a run voltage of 20 kV, and capillary temperature of 20°C led to complete separation of As(V) and phosphate peaks. Results of these investigations together with recovery test data suggest that separation of the As species from soil solutions can be achieved in less than 5 min with detection limits of 0.50, 0.10, and 0.10 mg L−1 for As(III), As(V), and DMA, respectively.
Oat and Rye Root Decomposition Effects on Nitrogen Mineralization
Authors: Malpassi R. N. , Kaspar T. C. , Parkin T. B. , Cambardella C. A. , Nubel N. A.
Published: July 2010

Decomposition and mineralization of cover crop roots needs to be understood to determine if N taken up by cover crops is mineralized during main crop growth. Two experiments were conducted in a controlled environment to measure decomposition of oat (Avena sativa L. ‘Ogle’) and rye (Secale cereale L. ‘Rymin’) root residues and to examine its effect on soil N mineralization. In the first, oat and rye roots were mixed with soil and in the second, roots were grown in situ. At 7, 14, 28, 56, 84, and 112 d after the start of decomposition, denitrification, soil NO−3, and soil NH+4 were measured to determine net mineralized N. Soil respiration and C and N contained in roots and coarse soil organic matter were measured to determine decomposition. All treatments in both experiments showed an increase in net mineralized N during the first 56 d. After 56 d, net mineralized N in the control remained relatively constant, whereas mineral N continued to accumulate in the treatments with root residues. Net N mineralization of the rye and oat root treatments did not differ. Roots mixed with soil had high respiration rates during the first 3 d and there were no differences between oat and rye root treatments. In the roots in situ experiment, however, respiration peaked for oat roots at Day 12 and for rye roots at Day 33. The oat treatment also had less C and N remaining in roots and coarse organic matter throughout the experiment. Even though oat roots decomposed faster than the rye roots, we predict that <55% of the N contained in the roots of a spring‐killed oat or rye cover crop will become available to the following crop.
Soil Water Components Based on Capacitance Probes in a Sandy Soil
Authors: Fares A. , Alva A. K.
Published: July 2010

Understanding soil water movement is needed to manage irrigation to minimize water drainage, nutrient leaching below the root zone, and contamination of groundwater. We hypothesized that soil water content determined by capacitance probes can be used for irrigation scheduling and estimating soil water components. Objectives of this study were (i) to evaluate the performance of capacitance probes for optimizing irrigation management for ‘Hamlin’ orange trees [Citrus sinensis (L.) Osb.] on Swingle citrumelo [Citrus paradisi Macf. × Poncirus trifoliata (L.) Raf.] rootstock on a Candler fine sand soil (hyperthermic, uncoated, Typic Quartzipsamment) in Central Florida and (ii) to determine soil water balance components. Irrigation levels were determined based on available soil water (ASW) and tree growth stage. The soil water data measured at finite time interval by capacitance probes were used with irrigation and rainfall data to calculate daily evapotranspiration (ET) and drainage rates. Daily ET rates showed strong seasonal patterns and varied from <0.4 mm d−1 in January to 5 mm d−1 in July and August. The annual ET in 1997 was 920 mm or 53% of the total water input (irrigation and rainfall). The cumulative annual drainage in 1997 was 890 mm, or 47% of the total water input. Furthermore, 82% of the cumulative annual drainage was contributed by rainfall. Irrigation based on monitoring soil water content using capacitance probes minimized water drainage below the root zone in a system where rainfall contributed substantially to drainage.
Tracer vs. Pressure Wave Velocities through Unsaturated Saprolite
Authors: Rasmussen Todd C. , Baldwin Roger H. , Dowd John F. , Williams Andrew G.
Published: July 2010

Saprolite is a form of weathered bedrock that is commonly used as the host material at waste disposal sites in the Southeastern Piedmont. However, estimating the unsaturated hydraulic and transport properties of saprolite is difficult due to saprolite's low permeability. We demonstrate the use of short‐duration fluid irrigation pulses for maintaining unsaturated conditions in intact saprolite columns. Concomitant Cl− tracer experiments demonstrate that irrigated waters moved through an effective volumetric porosity (0.038–0.108 cm3 cm−3) substantially less than the ambient water‐filled porosity (0.44 cm3 cm−3). We observed the unexpected result that irrigation‐induced pressure wave velocities (1983–3670 cm d−1) were ≈1000 times faster than tracer velocities (2.04–6.00 cm d−1). The relationship between pressure wave velocities and fluid velocities is described using kinematic wave theory, presented for four parametric representations (Brooks–Corey, van Genuchten–Mualem, Broadbridge–White, and the Galileo Number), that predicts fluid pressure velocities to be from approximately two to fifteen times faster than saprolite tracer velocities. None of the kinematic models was able to reproduce observed rapid pressure wave velocities. A hydraulic form of the advection–diffusion equation based on Richards' equation is presented that favorably predicts the shape of pressure response curves only when the kinematic velocity is ignored and the hydraulic diffusivity of the unsaturated saprolite is considered. Based on the advection–diffusion equation, diffusion‐dominated soil water pressure wave velocities should decrease with depth, eventually conforming with kinematic wave theory. Pressure pulse velocity monitoring may be an additional tool for estimating unsaturated hydraulic properties in low permeability media.
Modeling the Gas Diffusion Coefficient in Analogy to Electrical Conductivity Using a Capillary Model
Authors: Weerts Albrecht H. , Freijer Jan I. , Bouten Willem
Published: July 2010

A conceptual model that accounts for the influence of pore geometry is presented to model gas diffusion coefficients in soils as a function of water content. To model the diffusion coefficient of the gas phase, we rewrote the Mualem and Friedman bulk electrical conductivity model. The model was calibrated using measured soil water retention curves and gas diffusion coefficients of seven mineral soil horizons. The model with only one free parameter fitted the data of five horizons. The model failed to describe the data of two clayey surface horizons. Estimated gas tortuosity parameters were tested on measured hydraulic conductivity data of three of the soils studied. The use of the gas tortuosity parameter led to overestimation of the unsaturated hydraulic conductivity at low water contents. This systematic deviation suggests that the gas (non‐wetting) tortuosity parameter is not equal to the hydraulic (wetting) tortuosity parameter, although a relationship is likely.
Inverse Estimation of Parameters in a Nitrogen Model Using Field Data
Authors: Schmied Barbara , Abbaspour Karim , Schulin Rainer
Published: July 2010

An important step in numerical modeling is the determination of model parameters. Because of practical limitations, as well as time and financial constraints, inverse algorithms have in recent years presented an attractive alternative to direct methods of parameter estimation. In this study we linked the inverse algorithm of SUFI with the simulation program LEACHM to study N turnover of an agricultural field. Addressing the inherent modeling uncertainties, we introduce the concept of conditioned parameter distributions as being a more appropriate alternative to best‐fit parameters Conditioned parameter distributions are quantified within uncertainty domains, and the task of an inverse model then is to reduce or condition this domain through minimization of an appropriate objective function. Propagating the uncertainty in the conditioned parameter distributions will result in simulations where most of the measurements are respected or fall within the 95% confidence interval of the Bayesian distribution (95PCIBD). In this study we used measured pressure heads and NO3 concentrations to estimate 12 hydraulic parameters and up to 14 N turnover–related parameters. Most of the measurements in three soil layers fell within the 95PCIBD. Exceptions were some observed pressure heads corresponding to intense rainfall events and periods of soil freezing, as well as some high NO3 concentrations in the subsoil between 40‐ and 70‐cm depth. We attributed the discrepancies to processes that were not addressed by the simulation model such as freezing and short‐circuiting due to macropore flow.
Bacterial Degradation of Atrazine in Redox Potential Gradients in Fixed‐Film Sand Columns
Authors: Crawford Jennifer J. , Traina Samuel J. , Tuovinen Olli H.
Published: July 2010

The purpose of this study was to assess the biodegradation of atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] under different redox conditions in the presence and absence of an electron donor (glucose) and electron acceptors (oxygen, NO−3). Experiments were conducted in sand‐column systems saturated with a liquid medium and characterized by the vertical separation of oxic, anoxic, and reduced zones with distinct redox regimes. The columns were inoculated with an atrazine‐mineralizing bacterium to establish a fixed film on sand particles. Aerobic and anaerobic zones were created in the column by sparging with air or N2, respectively, and Na2S was added to the deepest zone of the column to establish redox potential gradients ranging from about −400 to 400 mV. Samples were removed from the various depths of the column to determine changes in redox potential and in the concentration of atrazine, NO−3, and NO−2 with time. Atrazine biodegradation in the sand columns could be described with a first‐order rate equation. Concurrent atrazine and NO−3 consumption occurred in both de‐aerated (N2–purged) and sulfide‐poised anaerobic zones of the columns, whereas only atrazine was used under aerobic conditions. Atrazine degradation was not adversely influenced by low redox potential and was enhanced under anaerobic conditions with combined NO−3 and glucose amendment.
Phosphorus Status of Intensively Cropped Soils of the St. Lawrence Lowlands
Authors: Beauchemin Suzanne , Simard R. R.
Published: July 2010

The P saturation degree of agricultural, neutral to slightly alkaline soils in areas where P fertilization is mainly inorganic is relatively unknown. The objective of this study was to determine the P status of the whole profile of 27 intensively cropped soils from an area receiving mainly inorganic fertilizers, the St. Lawrence lowlands in the province of Quebec, Canada, and to compare their P status to soils from a very different agrosystem with high animal density in the Appalachians. The A, B, and C horizons of nine soil series (three sites per soil series) showing a gradient in clay content were collected and analyzed for their Mehlich‐III extractable P (M3P), water‐soluble P (Pw), organic P (Po) and total P (Pt) contents. The P sorption index (Psi) and the P saturation degree (Pox/(Alox+Feox)) were also determined. Nine of the 27 studied fields exceeded 112 mg M3P kg−1, the level considered as excessive for corn (Zea mays L.) and soybean [Glycine max (L.) Merrill]. The results suggest that the impact of agricultural practices on the soil P status in the lowlands was mainly limited to the A horizon as few sites had elevated labile P contents or saturation degree in their subsoils. Compared to long‐term manured, acidic soils from a high animal density watershed, neutral to slightly alkaline soils from the lowlands had much lower Pt contents and the proportion of Pt as Po was also two to three times lower. However, given their low to medium P sorption capacity, P saturation degree of the A horizons was comparable to soils from the high animal density watershed.
The Influence of Organic Carbon on Nitrogen Transformations in Five Wetland Soils
Authors: Davidsson Torbjörn Emil , Ståhl Mattias
Published: July 2010

Today we see an increased use of wetlands for N removal in agricultural catchments. Since the most important process for nitrate (NO−3) removal, denitrification, requires organic C, different soils could be expected to be differently suited for wetland construction. In this study, we evaluate the importance of soil organic C and the effects of added dissolved organic C on N transformations in existing and proposed wetlands. We used 15N‐labeled NO−3 to study N transformations in soil columns from five locations (a forest peaty soil, a field peaty soil, a silt loam, a loam, and a sandy loam). All five soils removed NO−3 at substantial rates (13–73% of the load). The field peaty soil had highest denitrification rate (11 mmol m−2 d−1), while sandy loam soil had the lowest rate (2 mmol m−2 d−1). Dissolved organic C did not seem to limit N removal in the soils, as glucose additions affected N turnover only slightly. The forest peat soil differed from the others by exhibiting low nitrification, and relatively high production of nitrite (NO−2), probably a result of low pH. Nitrate removal in the field peat soil and the sandy loam soil was counteracted by production of ammonium (NH+4) and dissolved organic N, causing net N release. Although there was a positive relationship between soil organic matter and NO−3 consumption, we conclude that all soils were suited for N removal. The lack of response to glucose additions indicate that there was no short‐term lack of electron donor in any of the soils, including the sandy loam soil.
Stratigraphy and Hydrology of the Jackson‐Frazier Wetland, Oregon
Authors: D'Amore David V. , Stewart Scott R. , Huddleston J. Herbert , Glasmann J. Reed
Published: July 2010

The relationship between wetland soils and hydrology can be better understood by linking soil geomorphological features to the measurement of groundwater depths in the soil. Soil stratigraphic analysis and long‐term measurements of soil water levels in piezometers were used at the Jackson‐Frazier wetland in western Oregon to investigate the interaction between local geomorphological history and the hydrology of the wetland. Morphological descriptions confirm the presence of a recent smectitic alluvial deposit (80–180 cm) overlying Malpass clay (≈35 cm thick), which overlies Irish Bend Silt. X‐ray diffraction and isotope analysis support the conclusion of the presence of the Holocene alluvium and Irish Bend Silt, but are inconclusive regarding the Malpass clay. Piezometer data from 1992 to 1996 show that the smectitic alluvium controls saturation and drying of the wetland surface, and that a separate water table is present below the Malpass clay in the Irish Bend silt. The recent alluvium and Malpass clay act as an aquitard that restricts the vertical infiltration of surface water and helps restrict the groundwater table in the Irish Bend silt deposit. These stratigraphic relationships and associated hydrologic responses provide a means to identify wetlands and predict hydrologic conditions on similar wetland landscapes.
Recycling of Residual Soil Nitrogen in a Lowland Rice–Sweet Pepper Cropping System
Authors: Shrestha R. K. , Ladha J. K.
Published: July 2010

Residual mineral N after the dry season (DS) crop in an intensive rainfed lowland is lost upon flooding for rice (Oryza sativa L.) planting. The conservation and recycling of this N are essential for maintaining groundwater quality and system sustainability. Experiments conducted in rice–sweet pepper (Capsicum annuum L.) cropping systems in farmers' fields aimed (i) to quantify the levels of soil mineral N after the incorporation of residues of different dry‐to‐wet (DTW) transition crops in combination with two formulations of fertilizer N, as well as their effects on rice yields and N use efficiencies, and (ii) to estimate the soil N balance. Significant amounts of NH4–N accumulated in soil at 15 d after incorporation of residues of indigo (Indigofera tinctoria L.) alone (12 kg ha−1) and indigo mixed with mungbean (Vigna radiata L.) residue (24 kg ha−1), and at 60 d after incorporation of maize (Zea mays L.) residue (8 kg ha−1). Soil NH4–N in treatments with maize residue was lower than that from indigo and mungbean, but it was improved when maize residue was mixed with fertilizer N. Nitrate N peaked in the upper soil layer before flooding occurred, followed by its leaching and disappearance later. Crop residues incorporated in the plot maintained low NO3 throughout the soil profile. The crops during DTW transition reduced N losses by 33 to 72%, and residue incorporation supplied N equivalent to 87 kg ha−1 to rice. The results suggest that a transition crop alone cannot completely reduce the N losses; therefore, strategies for reducing N fertilizer rates to better match N demand of the DS crop are needed.
Dynamics of Dissolved Organic Carbon and Methane Emissions in a Flooded Rice Soil
Authors: Lu Yahai , Wassmann Reiner , Neue Heinz-Ulrich , Huang Changyong
Published: July 2010

Limited information is available on the dynamics of dissolved organic C (DOC) and its relationship with CH4 emissions in flooded rice (Oryza sativa L.) soils as affected by rice cultivar. Greenhouse and laboratory experiments were conducted to determine root C release in culture solution, DOC and dissolved CH4 concentration in soil solution, and CH4 emission in a flooded soil planted with three rice cultivars. Soil solutions were sampled in the root zone (soil surrounding rice roots) and the non‐root zone (soil outside the root zone). The release of root exudates increased in the order: IR65598 (new plant type) < IR72 (modern cultivar) < Dular (a traditional cultivar). Correspondingly, DOC concentrations in the root zone and CH4 emission rates increased. The dynamics of DOC and dissolved CH4 differed greatly between the root zone and the non‐root zone. Dissolved organic C in the root zone increased with plant growth and reached maximum (13–24 mmol C L−1) between rice flowering and maturation (Week 11–13), whereas DOC in the non‐root zone remained low (1–5 mmol C L−1) throughout the growing season. Similarly, dissolved CH4 concentrations in the root zone increased sooner and were greater (mean 138 μmol CH4 L−1) than those in the non‐root zone (mean 97 μmol CH4 L−1). The seasonal patterns of CH4 emissions closely followed the dynamics of DOC concentrations in the root zone. The results suggest that (i) DOC pool in the root zone of rice plants is enriched by root‐derived C; (ii) the rates of CH4 emissions are positively correlated with the dynamics of DOC in the root zone; (iii) the intercultivar difference in root C releases is responsible for the intercultivar difference in DOC production, and consequently in CH4 flux.
Laboratory Compaction of Soils using a Small Mold Procedure
Authors: Díaz-Zorita M. , Grove J. H. , Perfect E.
Published: July 2010

The compactability of a soil can be determined from parameters derived from laboratory compaction curves generated using the Proctor test. However, this is a destructive, time‐consuming, and labor‐expensive procedure. Our objective was to evaluate a new more rapid test to determine the maximum dry bulk density (ρMaxb) and soil water content at ρMaxb (SWCMax) from laboratory compaction curves using a mold with smaller dimensions than established for the standard procedure. Laboratory compaction curves were developed for nine soils with clay contents ranging from 232 to 385 g kg−1 using the standard Proctor test procedure and the proposed procedure, which uses a 54‐mm diam. mold and a 24.4 N rammer dropped from a height of 305 mm to produce a compactive effort (CE) of 109 kJ m−3 drop−1 At a CE of 545 kJ m−3, which is similar to the 540 kJ m−3 produced by the standard test, the ρMaxb and SWCMax parameters derived from the proposed procedure were positively and significantly correlated with those derived from the standard Proctor test. With both procedures, ρMaxb decreased and SWCMax increased as the soil clay content increased. The small mold method did not affect the linear relationship between soil clay content and ρMaxb However, different relationships between SWCMax and clay content were observed, depending on the compaction procedure. Use of the small mold procedure requires less dry sieved soil, saves time, and labor in evaluating soil compactability. Based only on the reduction in rammer drops, use of the small mold procedure involves 15 times less labor requirements than the standard Proctor test.
Short‐Range Spatial Variability of Nitrogen Fixation by Field‐Grown Chickpea
Authors: Walley Fran , Fu Gaoming , van Groenigen Jan-Willem , van Kessel Chris
Published: July 2010

Biological N fixation (BNF) by legumes under field conditions is known to vary widely across landscapes and between agroecosystems. A poor correlation between the 15N Natural Abundance (15NA) and 15N Enriched (15NE) approaches for estimating BNF across the landscape has been observed by many. These observations led some to conclude that the two approaches are measuring different processes and can not be compared. Others argue that short‐range spatial variability of BNF is very high, thereby obscuring any relationships between experimentally measured estimates of BNF. Our study, which quantifies spatial variability of BNF using the 15NA approach, provides evidence that short‐range spatial variability of BNF is very high. In a field study, BNF of chickpea (Cicer arietinum L.) was measured at 0.3‐m intervals on a 33‐m transect, using wheat (Triticum aestivum ‘Katepwa’) as reference crop. Each crop was sampled at 110 points along the transect. Estimates of BNF in the grain varied from 36 to 70%, with a mean value of 55%. The variogram for BNF had a range of 3.2 m and a relative nugget effect of 71%. Using a simulation study, we calculated r2 of 0.12 and 0.02 for BNF at sites spaced 1 m and 2 m apart, respectively. We concluded that short‐range spatial variability of BNF across the landscape is the likely cause of reported discrepancies between the 15NA and 15NE approaches used in other studies. Moreover, if such a high spatial variability in BNF is the norm rather than the exception, comparisons between 15NA and 15NE approaches for estimating BNF under field conditions will be unreliable.
Organic carbon extraction efficiency in chloroform fumigated and non‐fumigated soils
Authors: Needelman Brian A. , Wander Michelle M. , Shi Guangqin S.
Published: July 2010

The chloroform‐fumigation extraction (CFE) method is widely used to estimate soil microbial biomass. The relationship between extraction efficiency and the extractant‐to‐soil ratio has not been fully investigated in chloroform fumigated and non‐fumigated soils. We analyzed the extraction efficiency of 0.5 M K2SO4 in five soils at six extractant‐to‐moist soil ratios (3:1, 5:1, 7.5:1, 10:1, 12.5:1, and 15:1). A positive relationship between extractant‐to‐soil ratio and the amount of extracted dissolved organic carbon (DOC) was observed for both non‐fumigated and fumigated samples. The extractant‐to‐dry soil ratio required for 90% extraction averaged 12.0 for non‐fumigated samples and 8.2 for fumigated samples. A minor, yet statistically significant, positive relationship between extractant‐to‐dry soil ratio and chloroform‐labile carbon was observed in four of five soils, with a 5.6 average extractant‐to‐dry soil ratio required for 90% extraction. For analyses where DOC extracted from non‐fumigated samples is a critical variable, an extractant‐to‐soil ratio greater than 5:1 should be considered.
Correcting Laboratory Retention Curves for Hydrostatic Fluid Distributions
Authors: Jalbert Marc , Dane Jacob H.
Published: July 2010

Many experimental methods for obtaining capillary pressure–volumetric fluid content relations in porous media are affected by the occurrence of hydrostatic pressures that create nonuniform fluid content distributions throughout the sample of interest. Such conditions exist, for example, in suction apparatuses and pressure cells, which are widely used in vadose zone hydrology, agronomy and environmental engineering, and for Hg intrusion porosimetry routinely applied in the petroleum industry. We show how to correct experimental data for nonuniform pressure and fluid content distributions, which leads to retention or pore‐size distribution curves applicable to physical points. This is necessary to make the retention information consistent with the differential equations modeling fluid flow in porous media. The advantage of the proposed method is that it does not require an a priori assumption of any given model describing the retention relation. The proposed correction formula is validated both numerically and experimentally and is compared with an existing correction procedure. By deconvoluting retention relations from the averaging taking place in the sample, the correction method presented should enhance the description of porous media–immiscible fluids systems at low capillary pressure values.
Adsorption Behavior of Cadmium, Zinc, and Lead on Hydroxyaluminum– and Hydroxyaluminosilicate–Montmorillonite Complexes
Authors: Saha U.K. , Taniguchi S. , Sakurai K.
Published: July 2010

The current imperfect understanding about the adsorption behavior of heavy metals on hydroxyaluminum (HyA)‐ and hydroxyaluminosilicate (HAS)‐interlayered phyllosilicates led us to conduct this study. We examined the adsorption behavior of Cd, Zn, and Pb on synthetically prepared HyA– and HAS–montmorillonite (Mt) complexes in comparison with that on untreated Mt. A very dilute initial metal concentration of 10−6 M in 0.01 M NaClO4 background was used in all the adsorption systems. The presence of HyA and HAS polymers on Mt greatly promoted the adsorption of all three metals. Such promoting effects of HyA and HAS polymers on the metal adsorption were, however, not very different from each other. The observed adsorption selectivity sequences of Pb > Zn > Cd on Mt as well as Pb ≫ Zn ≥ Cd on the complexes resemble the reported metal selectivity sequences on amorphous Fe and Al hydroxides. At different pHs, partitioning the adsorbed metals into strongly and weakly held fractions indicated that specific adsorption rather than nonspecific adsorption might have largely controlled the metal selectivity, particularly on the complexes. This led us to assume a predominant involvement of interlayered HyA or HAS polymers in metal adsorption from such dilute solutions. On Mt, the metals were predominantly adsorbed on the permanent charge sites in an easily replaceable state. However, a substantial involvement of the edge OH− groups of Mt in specific adsorption of the metals was also evident, especially at higher pH. Obviously, on Mt and on the complexes, the relative abundance of each type of site and their affinity to heavy metals were substantially different.
Perched Water Tables on Argixeroll and Fragixeralf Hillslopes
Authors: McDaniel P.A. , Gabehart R.W. , Falen A.L. , Hammel J.E. , Reuter R.J.
Published: July 2010

Seasonally perched water tables (PWTs) are common in loess‐derived Argixerolls and Fragixeralfs of the Palouse region of northern Idaho and eastern Washington. However, little is known about the short‐term PWT dynamics in these rolling to hilly landscapes and how they are influenced by a regional climatic gradient. In this study, PWTs on an Argixeroll hillslope receiving 700 mm of mean annual precipitation (MAP) and a Fragixeralf hillslope receiving 830 mm of MAP were monitored hourly for four seasons. Results demonstrate that timing of PWT formation may vary considerably from year to year, and may occur up to 3 wk earlier in Fragixeralfs than in Argixerolls. Once formed, the PWTs respond rapidly to precipitation and snowmelt in both soils, with PWT levels increasing as much as 60 cm within a period of <24 h. Water table levels are at or near the soil surface numerous times during the season following periods of rainfall or snowmelt. Perched water table dynamics are remarkably consistent across the region, with similar responses observed in hillslopes located 28 km apart. Relatively dense, light‐colored E horizons overlying the restrictive horizons remain continuously saturated for up to 6 to 7 mo yr−1 and develop redox potentials sufficiently low for Fe reduction to occur. Results suggest that seasonal PWTs drive the processes of ferrolysis and hydroconsolidation, and these processes are responsible for many of the E horizon properties common to Argixerolls and Fragixeralfs of the region.
Five Geostatistical Models to Predict Soil Salinity from Electromagnetic Induction Data Across Irrigated Cotton
Authors: Triantafilis J. , Odeh I.O.A. , McBratney A.B.
Published: July 2010

Various approaches have been used to estimate soil salinity (ECe) at unsampled locations. Some of these approaches are briefly discussed. Of these, geostatistical methods such as ordinary kriging (OK1 and OK2), regression kriging (RK), three‐dimensional kriging (3‐DK), and cokriging (Co‐K), provide best linear unbiased estimates (BLUE). These methods were tested with a raw electromagnetic induction instrument (Type EM38) in a soil electrical conductivity (ECa) survey, and calibrated ECe data were obtained from an irrigated cotton (Gossypium hirsutum L.)‐growing area in the Edgeroi district of the lower Namoi valley, northern New South Wales, Australia. We compared these methods, on the basis of precision and bias of estimation, and found that RK was the best performer. This is because of the incorporation of regression residuals within the kriging system. Mean and standard deviation of ranks (SDR) showed that Co‐K performed best against these criteria.
Effects of Amphiphilic Amines on Moisture Characteristics of Alluvial and Volcanic Soils
Authors: Suetsugu Atsushi , Miyazaki Tsuyoshi , Nakano Masashi
Published: July 2010

If organic matter (OM) has amphiphilicity, the properties of hydration of the OM‐coated soil particles would vary drastically in dry conditions. Therefore, soil‐moisture characteristics within the relatively low water potential should be understood in relation to the conformation of the sorbed amphiphilic OM. In the present study, the effects of amphiphilic behavior of OM on the moisture characteristics of alluvial soil (AS) and volcanic soil (VS) were investigated using three simple amphiphilic amines. The psychrometry of AS showed the decrease of sorbed water around 1.8 nm of statistical thickness because of the sorption of hexadecyltrimethyl ammonium (HDTMA). Fourier transform infrared spectroscopy (FTIR) of soils showed an increase in the wavenumber of the antisymmetric stretching of ‐OH and ‐CH2, suggesting the formation of hydrophobic outer surfaces by n–hexadecyl function. The peaks in the ‐CH2 rocking band suggest that the HDTMA sorbed at AS had the residual amorphous moieties. In the case of VS–HDTMA, the peak was hidden by a broad peak due to hydrated aluminosilicates in VS. These findings imply that the amorphous moieties of HDTMA sorbed at both soils were affected by residual water in the air dried samples. According to the clay mineralogy of the soils, the greater hydrophobicity in AS–HDTMA was attributed to intercalation of HDTMA into the expansible phyllosilicates in AS. In contrast, the relatively moderate hydrophobicity in VS–HDTMA indicated that the hydrophilic micropores (D < 2 nm) in VS restrict the sorption of HDTMA but enable it to exchange water.
Taxonomic and Geographic Distribution of Total Phosphorus in Florida Surface Soils
Authors: Chen Ming , Ma Lena Q.
Published: July 2010

Taxonomic and geographic distributions of background P concentrations are important in assessing whether a soil P level is influenced by anthropogenic activities. This study was conducted to establish an upper baseline concentration (UBC) of soil P, which is defined as 97.5% of the background concentration, using 448 geographically and pedogenically representative Florida surface soils (genetic horizon A, A1, Ap, O, O1 or Op) using total P as determined by the USEPA Method 3052 (HCl–HNO3–HF digestion). A significant difference existed in total P concentrations between disturbed (126 mg kg−1, n = 180) and undisturbed (60 mg kg−1, n = 268) soils. Geometric mean (GM) concentration of total P in the undisturbed soils decreased in the order of Histosols (350 mg kg−1) > Mollisols (171 mg kg−1), Inceptisols (140 mg kg−1) > Ultisols (88 mg kg−1) > Alfisols (54 mg kg−1), Entisols (53 mg kg−1) > Spodosols (24 mg kg−1). Aquic suborders tended to have greater P contents than the dry suborders, e.g., Aquents (92 mg kg−1) > Psamments (47 mg kg−1) and Aquods (27 mg kg−1) > Orthods (14 mg kg−1). Total P estimation based on digitized taxonomic soil maps suggested that native soil properties were primary factors in controlling total P in soils. The wide occurrence of P bearing parent materials resulted in many soils having high P concentrations. Twenty‐four P‐elevated samples from the disturbed soils were identified using the UBC of P for the undisturbed soils at suborder level as reference criterion. Anthropogenic P inputs were related to commercial PO4–fertilizer application and population growth as nonpoint sources.
Microsite Influences on Productivity and Nutrient Circulation Within Two Southeastern Floodplain Forests
Authors: Schilling Erik B. , Lockaby B. Graeme
Published: July 2010

At broad spatial scales, floodplain forests of the southeastern USA are often perceived as either nutrient poor or nutrient rich. Perceived differences in nutrient availabilities between oligotrophic blackwater and eutrophic redwater floodplain forests suggest rates of aboveground net primary production (ANPP) are lower on the former. However, for these floodplain types, microsite variation may influence relationships between nutrient circulation and ANPP to a greater extent than landscape position and geomorphology of their associated watershed. Therefore, our objectives were to compare ANPP, nutrient circulation through litterfall and decomposition, and the microbial biomass among microsites that differed in terms of soils and hydrology within two riverine floodplain forests. The two floodplains used in this study were located along the Satilla River, a Coastal Plain blackwater system, and the Altamaha River, a Piedmont redwater system, both of which are located in southeastern Georgia. Microsite influences on ANPP were not significantly different during 1999 and 2000 for the Satilla (SAT) and Altamaha (ALT) floodplains. Litterfall production and patterns of P and Ca circulation on the SAT floodplain were significantly lower for the driest microsite type during both years. Microbial biomass N and P were also lowest for the driest microsite, especially in 2000. Overall, microsites on the SAT displayed greater variation in P and Ca cycling than did those of the ALT. Litterfall production, nutrient circulation in litterfall and decomposition, and the microbial biomass were similar among microsites of the ALT floodplain during both years. These findings suggest that spatial variability in nutrient cycling may be greater for oligotrophic floodplain forests.
Origin of Silica Particles Found in the Cortex of Matteuccia Roots
Authors: Fu FengFu , Akagi Tasuku , Yabuki Sadayo
Published: July 2010

A root sample from a species of fern (Matteuccia) was observed in detail under scanning electron microscopy (SEM), and some micron‐sized particles were observed in the cortex. Energy‐dispersive x‐ray spectroscopy (EDX) analysis of the particles indicated that they were almost pure silica. The concentrations of rare earth elements (REEs) in the silica particles from the roots, and silicate mineral particles from the soil, were analyzed by inductively coupled plasma–mass spectrometry (ICP‐MS). The REE composition of the silica particles from the roots was similar to that of the silicate mineral particles in the soil. The absence of a “Ce anomaly” in the REE patterns implies that the silica particles found in the cortex of Matteuccia roots were produced not by chemical deposition, but most likely by incorporation of silicate minerals into the root cortex and subsequent leaching of nutrient elements from the particles. This process is both a novel mechanism for plants to obtain nutrients and a means whereby plants accelerate the weathering of soil minerals.
Estimating Hydraulic Properties of a Fine‐textured Soil Using a Disc Infiltrometer
Authors: Schwartz R. C. , Evett S. R.
Published: July 2010

Inverse optimization of parameters offers an economical means to infer soil hydraulic properties from in situ measurements of infiltration. We evaluated optimization strategies to inversely estimate soil hydraulic parameters using field measured tension disc infiltrometer data. We estimated the parameters n, α, and Ks of the van Genuchten‐Mualem (VGM) model, and a piecewise representation of conductivity near saturation using a numerical inversion of Richards' equation. In addition to cumulative infiltration, optimizations included in the objective function water retention data, water contents from cores extracted after termination of infiltration, or transient measurements of water contents using time domain reflectometry (TDR) probes. Three‐parameter fits to field data were nonunique because of a positive correlation between α and Ks In contrast, fits of n and Ks with α estimated from separate fits to retention data improved parameter identifiability while not compromising the fit to measured infiltration. Inverse optimizations that included in the objective function both water retention and cumulative infiltration, led to excellent fits of this data when initial volumetric water contents were >0.23 cm3 cm−3 Close fits to cumulative infiltration were also obtained at lower water contents, however, water retention data was underestimated likely because of hysteresis. Optimizations of cumulative infiltration with final soil core water content or TDR data led to estimates of final water contents that closely approximated measured water contents. However, measured TDR water contents were poorly matched by simulations at early times. A piecewise loglinear interpolation of hydraulic conductivity near saturation improved fits to measured cumulative infiltration and water retention data as compared with using the VGM model at all pressure heads.