bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Soil Morphology on Hydraulic Properties II. Hydraulic Pedotransfer Functions
Authors: Lin H. S. , McInnes K. J. , Wilding L. P. , Hallmark C. T.
Published: July 2010

Pedotransfer functions (PTFs) have gained recognition in recent years as an approach to translate simple soil characteristics found in soil surveys into more complicated model input parameters. However, existing pedotransfer functions have not yet incorporated critical soil structural information. This study showed that soil hydraulic properties could be estimated from morphological features determined in situ (including texture, initial moisture state, pedality, macroporosity, and root density) through a morphology quantification system. Comparison between the class and continuous PTFs developed in this study indicated that the use of quantified morphological properties yielded predictive power similar to that of physical properties in estimating hydraulic conductivity at zero potential; water flow rates in macro‐, meso‐, and micropores; and a soil structure and texture parameter αmacro The results confirmed that soil structure was crucial in characterizing hydraulic behavior in macropore flow region; whereas texture had major impact on those hydraulic properties controlled by micropores. Depending on the flow domain to be included, estimation of hydraulic properties required the use of different combinations of morphometric indices or physical properties. The PTFs established may be used as starting points for estimating model input parameters.
Automated Microstandpipe System for Soil Erosion Research
Authors: Bryan Rorke B. , Hawke Richard M. , Rockwell David L.
Published: July 2010

The influence of soil water on erosion is well known, but the full effect of variations in water conditions on erosional processes has only recently been recognized. Micro time domain reflectometer (TDR) probes and microtensiometers have provided some precise temporal and spatial data necessary for soil erosion models, but data on local water table dynamics are also needed to explain rill incision and network development processes. An automated multiprobe microstandpipe system we developed provides continuous water table data at spatial and temporal scales comparable to those from microtensiometers and TDR microprobes (temporal precision: 1–3 min). The new system uses small probes etched with open‐ended conductors to provide incremental information on water table height with ±0.25 cm resolution. It has been used in a range of soil erosion experiments, one of which is used to demonstrate the system by examining drainage of interrill slopes in response to rill incision. This experiment was carried out in a 10 m by 0.8 m by 0.3 m laboratory flume under simulated rainfall at 43.4 mm h−1 on a 5° slope, using a composite mixture of Arenic Hapludalf sandy mixed mesic and Aquic Hapludalf clayey mixed mesic soils at 4:1 ratio. The microstandpipe system showed sensitive response to a saturated wedge that progressively extended upflume after initiation at the terminal weir. Despite separation between instruments, agreement between the microstandpipe system, microtensiometers and micro TDR probes was good. Rigorous statistical analysis was not possible, but data suggest that temporal agreement of ±5% is realistic. Despite instrumental precision, the expected interrill drainage response to rill incision was not apparent.
On the Origin of the Theory of Mineral Nutrition of Plants and the Law of the Minimum
Authors: van der Ploeg R.R. , Böhm W. , Kirkham M.B.
Published: July 2010

Modern treatises on the origin of the theory of mineral nutrition of plants and the Law of the Minimum usually refer to books published by Justus von Liebig in 1840 and 1855. These works are believed to be original reports of Liebig's own research. Occasionally, however, scholars of early agronomic literature have stated that these books by Liebig contain doctrines on mineral plant nutrition and nutrient deficiencies that had been published earlier by Liebig's countryman and colleague Carl Sprengel (1787–1859). To examine such statements, we studied the relevant literature. This study showed that the agronomist and chemist Carl Sprengel conducted pioneering research in agricultural chemistry during the first half of the 19th century. His early articles and books mark the beginning of a new epoch in agronomy. He published in 1826 an article in which the humus theory was refuted, and in 1828 another, extended journal article on soil chemistry and mineral nutrition of plants that contained in essence the Law of the Minimum. Sprengel's doctrines are presented again in the books published by Liebig in 1840 and 1855. To avoid a dispute on priorities and impacts and to recognize and commemorate the achievements of both pioneering scientists, the Association of German Agricultural Experimental and Research Stations has created the Sprengel‐Liebig Medal. We propose that the international community of agronomists acts similarly by recognizing Sprengel as a cofounder of agricultural chemistry and that the Law of the Minimum henceforth be called the Sprengel‐Liebig Law of the Minimum.
Transport of Triticonazole in Homogeneous Soil Columns Influence of Nonequilibrium Sorption
Authors: Beigel C. , Di Pietro L.
Published: July 2010

Nonequilibrium sorption of pesticides is frequently reported to greatly affect their transport and dissipation in soil. This study was aimed at evaluating the performances of equilibrium and two site–two region nonequilibrium convective–dispersive models for describing the sorption and decay characteristics during transport of triticonazole systemic fungicide in water‐saturated homogeneous soil. Chloride and 14C‐triticonazole column displacement experiments were carried out in a loamy clay soil under steady‐state water flow at high pore water velocities. The symmetrical breakthrough curves (BTC) obtained with the conservative tracer showed no significant physical nonequilibrium and were used to estimate a dispersivity of 0.06 cm. Compared with chloride, the 14C‐triticonazole BTC was strongly asymmetrical and shifted to the right, with a broad, extended tailing characteristic of sorption nonequilibrium. Chemical analysis of the soil after elution showed that bound residues were rapidly formed during transport. These bound residues were accounted for as decayed in the models. The two‐site model correctly described the first part of the tailing, with an estimated partition coefficient Kd of 1.5 L kg−1 for instantaneous sorption, and it predicted high values in the range of 58 d−1, and 7 d−1 for the sorption and decay first‐order rates, respectively. However, the model failed to describe the slower, extended release of 14C‐triticonazole. Nonequilibrium sorption and formation of bound residues of triticonazole were attributed to the rate‐limiting diffusive process. It was thus concluded that use of a single first‐order rate constant for description and prediction of both nonequilibrium sorption and dissipation of triticonazole in soil is not appropriate.
Aluminum Solubility Control in Different Horizons of a Podzol
Authors: Zysset M. , Blaser P. , Luster J. , Gehring A. U.
Published: July 2010

Aluminum extractability and solubility were investigated in detail in six horizons of a Typic Haplohumod (FAO: Haplic Podzol) from southern Switzerland. Pyrophosphate and oxalate extractions as well as successive acid leaching indicated that in the Ah, (AE), and Bh horizons reactive Al is mainly bound to soil organic matter, whereas in the Bs, BC1, and BC2 horizons it is of inorganic nature. In the latter three horizons, infrared (IR) spectroscopy and transmission electron microscopy (TEM) revealed the presence of imogolite. Batch equilibrium experiments at 20°C in the pH range of approximately 3.5 to 5.5 showed that the podzol profile can be divided into two parts of different Al solubility control. In the Ah and (AE) horizons, Al solubility was found to be controlled by complexation reactions to soil organic matter. Kinetic studies with samples of the Bh, Bs, BC1, and BC2 horizons showed that ion activity products with respect to both Al(OH)3 and imogolite, (HO)3Al2O3SiOH, reached a constant value after reaction times of 16 d. For pH >4.1, the compilation of all data revealed and These data could be shown to be consistent with either Al solubility control by imogolite‐type material (ITM) with a log , which dissolves incongruently, or a simultaneous equilibrium with ITM and hydroxy‐Al interlayers of clay minerals. For pH <4.1, data indicated solubility control by a 1:1 aluminosilicate, e.g., poorly crystalline kaolinite.
Solubility of Aluminum and Silica in Spodic Horizons as Affected by Drying and Freezing
Authors: Simonsson M. , Berggren D. , Gustafsson J.P.
Published: July 2010

For convenience, soil samples are often dried before storage and experimental use. However, the literature offers examples of drying that results in changes in pH, solubility of organic matter, and dissolution rates of Al. In this study we examined the solubility of Al and Si in fresh soil and in soil that had been dried or deep‐frozen. Five Spodosol B horizon soils were subjected to batch titrations, where portions of each soil were equilibrated with solutions with varying concentrations of acid or base added. Extractions with acid oxalate and Na pyrophosphate indicated the presence of imogolite‐type materials (ITM) in three of the soils. In the other two soils most secondary solid‐phase Al was associated with humic substances. Deep‐freezing did not significantly change pH nor the concentration of Al or Si as compared with fresh soil. Drying, on the other hand, yielded pH increases of up to 0.3 units at a given addition of acid or base, whereas Al3+ changed only slightly, implying a higher Al solubility in all of the soils. Furthermore, dissolved silica increased by up to 200% after drying, except in a soil that almost completely lacked oxalate‐extractable Si. We suggest that drying enhanced the dissolution of ITM by disrupting soil organic matter, thus exposing formerly coated mineral surfaces. In the soil where dissolved Si did not change with drying, it had been demonstrated that Al–humus complexes controlled Al solubility. We suggest that fissures in the organic material caused by drying may have exposed formerly occluded binding sites that had a higher Al saturation than had sites at the surface of humus particles.
Organic Phosphorus in Soil Size Separates Characterized by Phosphorus‐31 Nuclear Magnetic Resonance and Resin Extraction
Authors: Rubæk G. H. , Guggenberger G. , Zech W. , Christensen B. T.
Published: July 2010

Land use and soil management affect soil organic C in whole soil and size separates, but knowledge of the accompanying soil organic P (Po) is limited. The objectives of this study were (i) to identify the structure of Po in soil size separates by solution 31P‐nuclear magnetic resonance (NMR) spectroscopy, (ii) to determine the labile Po pool in the size separates by anion‐exchange resin extraction, and (iii) to characterize the labile Po pool. We used soils from two long‐term experimental sites, one in Bavaria (under spruce and deciduous forests, permanent grassland, and arable farming) and one in Denmark (with arable rotation and different fertilization strategies — unfertilized, mineral fertilizer, and animal manure). Total Po content increased with decreasing particle size. The dialyzed NaOH extracts of clay were enriched in microbial‐derived teichoic acid‐P and other diester‐P forms compared with silt and sand. Clay from permanently vegetated soil had larger proportions of teichoic acid‐P and other diester‐P forms and was richer in resin extractable Po than clay from arable soil. There was a linear relationship between the proportion of the 31P‐NMR spectra allocated to diester‐P (including teichoic acid‐P) and resin‐Po Our results suggest that the highly active and easily mineralized soil Po was mainly associated with clay. The larger part of the clay‐associated Po was tightly bound and not extractable. Although the composition of this Po remained unknown, it was probably inaccessible to rapid microbial utilization. The composition of NaOH‐extractable Po in the clay fraction was influenced to a greater extent by land use than by fertilizer inputs.
The Effect of Oxyanions on the Oxalate‐Promoted Dissolution of Goethite
Authors: Eick Matthew J. , Peak John D. , Brady Warren D.
Published: July 2010

Organic ligand–promoted dissolution of oxide minerals can be enhanced or inhibited in the presence of specifically adsorbed oxyanions. It has been proposed that an oxyanion inhibits or enhances dissolution depending on the type of surface complex formed and the strength of the bond. Mononuclear complexes (especially if they are bidentate) accelerate dissolution, while binuclear complexes inhibit dissolution. Recent spectroscopic evidence indicates that chromate and arsenate form different surface complexes depending on surface coverages. This study examined the influence of chromate and arsenate on the oxalate promoted dissolution of goethite. Based on a previous spectroscopic study, oxyanion surface coverages were varied to generate both mononuclear and binuclear surface complexes. Chromate and arsenate inhibited the oxalate promoted dissolution of goethite at all surface coverages investigated except at pH 6 It is proposed that chromate and arsenate inhibit goethite dissolution by decreasing oxalate adsorption. This is accomplished because arsenate and chromate are more effective competitors for goethite surface sites than oxalate and upon adsorption increase the negative charge of the goethite surface. At pH 6 the adsorption of chromate and arsenate increases the negative charge of the goethite surface which in turn increases proton adsorption. Since proton adsorption is a necessary step for oxalate‐promoted dissolution of goethite, and since proton activity at pH 6 is low, an increase in the negative charge of goethite upon adsorption of the oxyanions accelerates dissolution.
Soil Development and Fertility Characteristics of a Volcanic Slope in Mindanao, the Philippines
Authors: Poudel D. D. , West L. T.
Published: July 2010

Thirteen pedons representing the mountains, the upper footslopes, the lower footslopes, and the alluvial terraces of a volcanic slope in Mindanao, the Philippines were studied to understand relationships between the degree of soil development and fertility characteristics. Soils in the upper and the lower footslopes were Oxisols as were soils in the alluvial terraces, while those in the mountains were Ultisols and Inceptisols. Presence of “amorphous components”, such as allophane and imogolite, in all the pedons studied was indicated by a >9.4 soil pH in NaF. Halloysite, gibbsite, goethite, hematite, and cristoballite were more common minerals in the clay fraction. Surface layers of all the pedons were slightly acidic and pH increased by depth. Phosphate sorption maxima ranged from 6944 to 14208 μg P g−1, and it was closely associated with oxalate‐extractable Al (Alo) and clay content. Inceptisols had higher phosphate sorption maxima than Oxisols. Soil samples representing the mountains showed the lowest level of both the available K and the potential buffering capacity for K (PBCK), while the upper footslopes had the highest level of available K. The PBCKvalues were lower for Inceptisols than for Oxisols, and they were found to be positively correlated with soil pH. There was a large difference between the cation‐exchange capacity (CEC) and the effective cation‐exchange capacity (ECEC), an indication of a large pH‐dependent charge. Mountain soils showed lower base saturation than soils representing the upper footslopes, the lower footslopes, and the alluvial terraces.
Importance of Microscopy in Durability Studies of Solidified and Stabilized Contaminated Soils
Authors: Klich I. , Wilding L. P. , Drees L. R. , Landa E. R.
Published: July 2010

Solidification/stabilization (S/S) is recognized by the U.S. EPA as a best demonstrated available technology for the containment of contaminated soils and other hazardous wastes that cannot be destroyed by chemical, thermal, or biological means. Despite the increased use of S/S technologies, little research has been conducted on the weathering and degradation of solidified and stabilized wastes once the treated materials have been buried. Published data to verify the performance and durability of landfilled treated wastes over time are rare. In this preliminary study, optical and electron microscopy (scanning electron microscopy [SEM], transmission electron microscopy [TEM] and electron probe microanalyses [EPMA]) were used to evaluate weathering features associated with metal‐bearing contaminated soil that had been solidified and stabilized with Portland cement and subsequently buried on site, stored outdoors aboveground, or archived in a laboratory warehouse for up to 6 yr. Physical and chemical alteration processes identified include: freeze–thaw cracking, cracking caused by the formation of expansive minerals such as ettringite, carbonation, and the movement of metals from waste aggregates into the cement micromass. Although the extent of degradation after 6 yr is considered slight to moderate, results of this study show that the same environmental concerns that affect the durability of concrete must be considered when evaluating the durability and permanence of the solidification and stabilization of contaminated soils with cement. In addition, such evaluations cannot be based on leaching and chemical analyses alone. The use of all levels of microscopic analyses must be incorporated into studies of the long‐term performance of S/S technologies.
A Tracer Sphere Detectable by Neutron Activation for Soil Aggregation and Translocation Studies
Authors: Plante A. F. , Duke M. J. M. , McGill W. B.
Published: July 2010

Current radiological and particle tracer methods used in soil translocation studies have several limitations. Studies of soil aggregate dynamics also require an improved particle tracer approach. Our objective was to develop an inert tracer sphere applicable in soil aggregation and translocation studies. We selected ceramic prills in varying size fractions, labeled with 10 to 15% (w/w) Dy during manufacture, as inert tracers to simulate soil aggregates because of their similar surface properties. Prills added to soil (Typic Cryoboroll) were detected and quantified via the Dy content of a mixed tracer–soil sample using instrumental neutron activation analysis (INAA). Detection limit measurements demonstrated that the tracers were easily detected; approximately one 300‐μm sphere is detectable in 5 g of soil containing a background level of 3.1 μg g−1 Dy. Coefficients of variation for tracer sphere properties within size fractions were determined: 5.3 to 16.6% for mass in composite samples, 12.2 to 22.6% for diameter, and 6.5 to 10.8% for Dy concentration. However, no difference between actual and calculated numbers of spheres was detected (P = 0.05), indicating that the variability is insufficient to affect tracer sphere detection. Tracer integrity tests showed no leaching losses of the Dy label, and tracer sphere abrasion resulted in losses of <1% of sphere Dy content. The tracers have proven sufficiently homogeneous and robust for practical use and are currently being used to study soil aggregate dynamics.
Bare‐Soil Evaporation Under Semiarid Field Conditions
Authors: Wythers K. R. , Lauenroth W. K. , Paruelo J. M.
Published: July 2010

Bare‐soil evaporation is an important component of the water balance in semiarid systems. However, little is known quantitatively about the influence of soil texture on bare‐soil evaporation. We hypothesized that soil texture would have a great influence on both the temporal dynamics of bare‐soil evaporation as well as on the depth to which evaporation‐influenced soil water content throughout a 51‐d simulated drought period. We measured soil water in lysimeters filled with three different soils. We measured daily evaporation gravimetrically and estimated evaporation rates using the energy balance method of Ben‐Asher et al. We estimated soil water content at depths of 3.8 cm, 11.4 cm, 19.0 cm, 26.6 cm, and 34.2 cm (Layers 1–5, respectively) with time domain reflectometry rods and with soil cores. Bare‐soil evaporation during the first 15 d of the experiment was ≈25% higher in the silt loam than the sand loam, and ≈42% higher than the clay loam. By Day 30, bare‐soil evaporation in all soils was ≈0.5 mm d−1 Soil water content decreased in all five lysimeters layers, and it was related to time and depth (r2 values ranged from 0.60 to 0.95). The slope describing change in soil water content was greatest in the top 3.8‐cm layer in all soil types (−0.52 in the clay loam, −0.32 in the silt loam, and −0.21 in the sand loam). At 14 d, bare‐soil evaporation had the greatest influence on the upper 4.62 cm in the sand loam and the upper 7.18 cm in the clay and silt loams. At 51 d bare‐soil evaporation had the greatest influence on the upper 7.36 cm in the sand loam, the upper 9.79 cm in the silt loam and the upper 14.1 cm in the clay loam.
Aggregate and Soil Organic Matter Dynamics under Conventional and No‐Tillage Systems
Authors: Six J. , Elliott E. T. , Paustian K.
Published: July 2010

Tillage generally reduces aggregation and particulate organic matter (POM) content. We hypothesized that reduced C sequestration in conventional tillage (CT) compared with no‐tillage (NT) is related to differences in aggregate turnover. Four soils (Haplustoll, Fragiudalf, Hapludalf, and Paleudalf), each with NT, CT, and native vegetation (NV) treatments, were separated into aggregates. Free light fraction (LF) and intraaggregate POM (iPOM) were isolated. At one site we used 13C natural abundance to differentiate crop‐ and grassland‐derived C. Concentrations of coarse iPOM C (250–2000 μm iPOM in macroaggregates), expressed on a per unit aggregate weight (g iPOM C kg−1 aggregate), did not differ between tillage treatments. In contrast, concentrations of fine iPOM C (53–250 μm iPOM in macroaggregates) were less in CT compared to NT macroaggregates. On a whole soil basis, fine iPOM C was on average 51% less in CT than in NT, and accounted for 21% of the total C difference between NT and CT. The concentration of free LF C was not affected by tillage, but was on average 45% less in the cultivated systems than NV. Proportions of crop‐derived C in macroaggregates were similar in NT and CT, but were three times greater in microaggregates from NT than microaggregates from CT. We suggest that a faster turnover rate of macroaggregates in CT compared with NT leads to a slower rate of microaggregate formation within macroaggregates and less stabilization of new SOM in free microaggregates under CT.
Maize Residue Decomposition Measurement Using Soil Surface Carbon Dioxide Fluxes and Natural Abundance of Carbon‐13
Authors: Rochette Philippe , Angers Denis A. , Flanagan Lawrence B.
Published: July 2010

The decomposition rate of crop residues in soils directly impacts organic matter content and nutrient cycling. We hypothesized that natural abundance 13C analyses could be used with soil CO2 flux measurements to quantify the short‐term decomposition rates of maize (Zea mays L.) residues under undisturbed field conditions. For this purpose, maize was grown in a sandy loam (Umbric Dystrochrept) that developed under C3 vegetation. Residues were returned to the field at the end of the growing season. During the following snowfree period (May to November), the maize residue decomposition rate was calculated for plots that were either under no‐till or moldboard plowed, using the C isotope ratio (13C/12C) of the soil CO2, the C isotope ratio of the plant and soil substrates, and the soil respiration rate. The incorporation of residue‐derived C into the soil microbial biomass was also evaluated. Maize residue decomposition increased the C isotope ratio of the soil CO2 by 2 to 7‰ relative to unamended control plots. Decomposition rates peaked in June (2–3 g C m−2 d−1) and were low at both the beginning and end of the growing season (<0.5 g C m−2 d−1). For a given soil temperature, the decomposition was more active early than late in the season because of decreased substrate availability as decomposition proceeded. The decomposition rate of maize‐derived C correlated with the fraction of the microbial biomass derived from maize residues. This active pool represented 9% of microbial biomass and showed a high level of specific activity. The total maize residue‐C losses during the study corresponded with 35% of the added residue C under no‐till plots and 40% with moldboard plowing. Natural abundance 13C analyses may be successfully used with respiration measurements to quantify crop residue decomposition rates under undisturbed field conditions.
Using Fallout Lead‐210 Measurements to Estimate Soil Erosion on Cultivated Land
Authors: Walling D. E. , He Q.
Published: July 2010

Naturally occurring fallout 210Pb is strongly adsorbed by soils and sediments and has been widely used as a tracer to establish the chronology of deposited sediments in various sedimentary environments. This paper reports an attempt to explore the potential for using fallout 210Pb to estimate rates of water‐induced soil erosion on cultivated land. Soil cores were collected from both cultivated and undisturbed areas in a small catchment in Devon, UK, and land use practices were shown to be the primary factor controlling the depth distribution of fallout 210Pb. Based on existing knowledge of the behavior of 210Pb in cultivated soils, a mass balance model has been developed that enables longer‐term (≈100 yr) rates of erosion and deposition to be estimated from values of unsupported 210Pb inventory for individual sampling points. In order to estimate longer‐term soil redistribution rates, the mass balance model was applied to an 8.54‐ha cultivated field within the study catchment from which 167 bulk cores had been collected at the intersections of a 20 by 20 m grid. Soil redistribution rates within the field ranged from −5.9 kg m−2 yr−1 (erosion) to 6.4 kg m−2 yr−1 (deposition), and the mean erosion rate for the eroding area was 1.95 kg m−2 yr−1 The pattern of soil redistribution within the study field reflected the influence of topography on sediment mobilization and transport. The results obtained confirm the potential for using fallout 210Pb measurements to estimate rates and patterns of water‐induced soil erosion on cultivated land.
Placic and Ortstein Horizon Genesis and Peatland Development, Southeastern Newfoundland
Authors: Lapen David R. , Wang Chang
Published: July 2010

There is considerable speculation about relationships between soil development and local‐scale blanket bog formation in southeastern Newfoundland. This study examined podzolization along a catena in southeastern Newfoundland. The specific objective was to investigate pedogenic processes, in particular placic and ortstein horizon development, as well as potential links between soil and peatland formation. Chemical, hydrological, and physical processes potentially responsible for pedogenesis were examined. Placic genesis appears to be linked to the precipitation of Fe at oxidizing and higher soil pH contacts at depth in the soil. Placic formation in the well‐drained heathlands is apparently precluded by constraints on Fe mobilization at the surface, in particular, Fe‐oxidizing conditions and the presence of sufficient supplies of metals neutralizing mobile organic substances. Organic‐complexed Al is the dominant cementing agent in ortstein horizons. Cementation is augmented by minimal bioturbation by roots and high coarse‐fragment content, which concentrates Fe and Al to a limited soil matrix. Weathering, podzolization, elevated water tables, and peatland processes are promoted by groundwater discharge from adjacent bogs as well as by sesquioxide pans that impede vertical drainage.
Tortuosity of Crack Networks in Swelling Clay Soils
Authors: Chertkov V. Y. , Ravina I.
Published: July 2010

Tortuosity of the crack network in a swelling clay soil determines the actual mean length of flow through the cracks and is an important factor influencing the hydraulic properties of the soil. In the literature there are works related only to tortuosity of the pore system of a nonswelling‐soil matrix. The approach to estimate tortuosity proposed here is based on an established model of crack network geometry in swelling clay soils. Dependency of the tortuosity on the connectedness of a statistically isotropic crack network is derived from the fact that connected cracks outline fragments (peds) and are their boundaries. The second parameter that characterizes the crack network, the mean spacing between cracks, does not influence the tortuosity. The estimated two‐ and three‐dimensional tortuosities vary from 1.5 to 2.2 and from 1.4 to 3.25, respectively, when connectedness decreases from unity to zero (for instance, with increasing soil depth). A proposed method for processing a two‐dimensional image of crack networks enabled us to estimate experimental two‐ and three‐dimensional tortuosities and connectedness of an assumedly isotropic crack network. This direct estimation from two‐dimensional images is practical for sufficiently large values of connectedness. Data of seventeen different two‐dimensional images (available in the literature) were used to show the applicability of the proposed dependencies of tortuosity on crack connectedness in the range 0.5 to1.
Field Bromide Transport under Transient‐State
Authors: Caron J. , Jemia S.Ben , Gallichand J. , Tre´panier L.
Published: July 2010

The contamination of groundwater by excess fertilizer and pesticides is a problem associated with modern agricultural practices. Estimating fluxes of these contaminants to groundwater requires frequent soil water sampling. Time domain reflectometry (TDR) techniques appear well‐suited to this purpose because of their potential for automation and the limited calibration work required, despite potential constraints associated with probe geometry, temperature, and the nonspecificity of the probe. The objective of this study was to compare the performance of the TDR technique with porous cup samplers for estimating solute masses and concentrations in a soil at the lysimeter scale. Potassium bromide was applied at the soil surface in a 0.91 by 0.52 m area and solute was sampled with TDR and porous cups. Recovered Br− masses were calculated based on measured water contents and Br− concentrations. When the solute was concentrated in the top 0 to 45 cm of soil, the biases for solute mass reached 2.6 and 5.3 times the applied mass for TDR and the porous cup samplers, respectively. As the solute spread out below this depth, the bias with the TDR technique decreased to between 1.17 and 1.27 times the applied mass, whereas for the porous cup samplers, it varied between 0.97 and 1.83 times the applied Br− mass. Differences in soil structure appeared the most likely explanation for the bias. The study also indicates that field calibration of TDR from porous cup samplers may be difficult to achieve under transient state conditions.
Integrated Assessment of Space, Time, and Management‐Related Variability of Soil Hydraulic Properties
Authors: van Es H. M. , Ogden C. B. , Hill R. L. , Schindelbeck R. R. , Tsegaye T.
Published: July 2010

Soil hydraulic properties have numerous sources of variability related to spatial, temporal, and management‐related processes. Soil type is considered to be the dominant source of variability, and parameterization is typically based on soil survey databases. This study evaluated the relative significance of other sources of variability: spatial and temporal at multiple scales, and management‐related factors. Identical field experiments were conducted for 3 yr at two sites in New York on clay loam and silt loam soils, and at two sites in Maryland on silt loam and sandy loam soils, all involving replicated plots with plow‐till and no‐till treatments. Infiltrability was determined from 2054 measurements using permeameters, and Campbell's a and b parameters were determined based on water‐retention data from 875 soil cores. Variance component analysis showed that differences among the sites were the most important source of variability for a (coefficient of variation, CV = 44%) and b (CV = 23%). Tillage practices were the most important source of variability for infiltrability (CV = 10%). For all properties, temporal variability was more significant than field‐scale spatial variability. Temporal and tillage effects were more significant for the medium‐ and fine‐textured soils, and correlated to initial soil water conditions. The parameterization of soil hydraulic properties solely based on soil type may not be appropriate for agricultural lands since soil‐management factors are more significant. For infiltrability, temporal factors also need to be explicitly recognized. Sampling procedures should give adequate recognition to soil‐management and temporal processes as significant sources of variability to avoid biased results.
Soil Carbon and Nitrogen Pools under Low‐ and High‐Endophyte‐Infected Tall Fescue
Authors: Franzluebbers A. J. , Nazih N. , Stuedemann J. A. , Fuhrmann J. J. , Schomberg H. H. , Hartel P. G.
Published: July 2010

Tall fescue (Festuca arundinaceaSchreb.) is an important cool‐season perennial forage for cattle production in the humid regions of the USA and throughout the world. While endophyte (Neotyphodium coenophialumGlenn, Bacon, & Hanlin) infection of tall fescue has many benefits, it also results in accumulation of toxic alkaloids in leaf tissue known to cause animal health disorders when ingested. We hypothesized that pastures containing these alkaloids may alter soil organic matter dynamics. A set of three grazed field experiments representing low (0–29%) and high (65–94%) endophyte infection of tall fescue was evaluated at the end of either 8 or 15 yr. Soil samples from 12 paddocks (0.7–0.8 ha) were collected at depths of 0 to 25, 25 to 75, 75 to 150, and 150 to 300 mm. Soil under tall fescue with high endophyte infection had 13 ± 8% greater concentrations of soil organic C and N and particulate organic N to a depth of 150 mm than with low endophyte infection. However, with high endophyte infection, microbial biomass and basal soil respiration per unit of soil organic C or particulate organic C were 86 ± 5% of those with low endophyte infection. Only small differences in soil microbial community structure, estimated via fatty acid methyl ester profiles, were observed between soils under fescue with 0 and 100% endophyte infection. Endophyte infection of tall fescue may perform an important ecological function, allowing more soil organic C and N to accumulate, perhaps because of reduced soil microbial activity on plant residues containing endophyte byproducts.
Elevated Carbon Dioxide Effects on Nitrogen Dynamics in Grasses, with Emphasis on Rhizosphere Processes
Authors: Gorissen A. , Cotrufo M. F.
Published: July 2010

Three perennial grass species, perennial ryegrass (Lolium perenne L.), colonial bentgrass (Agrostis capillaris L.), and sheep fescue (Festuca ovina L.), were grown at two CO2 concentrations (350 and 700 μL L−1) and under two N regimes: one with a minor addition of 8 kg N ha−1 and one with an addition of ≈278 kg N ha−1, both labeled with 15N. The effects of elevated CO2 on 15N and N uptake and dynamics in the plant–soil systems were determined after 32 and 55 d, with close attention to the rhizosphere. Total N uptake by the plants was not affected by elevated CO2, compared with ambient CO2, independent of N treatment and grass species. A clear decrease from 1.77 at ambient CO2 to 1.25 at elevated CO2 was observed in the shoot/root (S/R) ratio of N, resulting from a significant decrease of the N concentration in shoots, and an unchanged root N concentration. At 700 μL L−1 CO2, N concentration in the shoots decreased from 12.9 to 9.9 g kg−1, even at the low N supply, whereas the slight decrease in root N concentration for plants grown at elevated CO2 (7.9 vs. 7.3 g kg−1) was not significantly different. The relative increase of 15N found in the rhizosphere soil microbial biomass (SMB) and the rhizosphere soil residue under elevated CO2 was too small to affect plant growth, even in the low N treatment. The total amount of 15N recovered in the plants was not affected by the CO2 treatment. Although at the second harvest slightly more 15N was found in the plants than at the first harvest, probably due to turnover of the SMB, no interaction with CO2 was observed. This shows that the fertilizer 15N had not been immobilized to a larger extent or for a longer time by the SMB at elevated CO2 than under ambient CO2, even independent of N level and grass species. No evidence was found that under elevated CO2 substantial amounts of N had been immobilized by the SMB, nor that mineralization of native soil organic matter (SOM) had been stimulated by an increased supply of substrate to the SMB. We conclude that elevated CO2 has the potential to induce significant changes in plant N nutrition, modifying N allocation and tissue quality within perennial grasses, but that these effects appear to be independent of the SMB.
A Heuristic Model for the Calculation of Dinitogen and Nitrous Oxide Flux from Nitrogen‐15‐Labeled Soil
Authors: Bergsma Timothy T. , Bergsma Qiaobing C. , Ostrom Nathaniel E. , Robertson G. Philip
Published: July 2010

Very sensitive measurements of N2 and N2O flux from soil are possible when gas evolved from 15N‐labeled soil is analyzed by isotope ratio mass spectrometry. This approach is useful for studying the fate of nitrogen fertilizer and for studying soil microbial processes contributing to the atmospheric increase of nitrous oxide, a radiatively active trace gas that can contribute to global warming and ozone depletion. Most systems of equations that relate isotopic analysis to gas flux are sufficiently complex that certain limitations and potentials of the 15N approach may be overlooked. We describe a graphical representation of labeled N‐gas flux that illustrates the equations and encourages critical thinking regarding the implementation of related experiments. This model is used to interpret underestimation that occurs if flux derives from multiple pools of differing enrichment. A statistical derivation is presented for a previously published simulation of underestimation due to multiple pools. The same equations are applied to field data to explore whether temporal variation in soil nitrate enrichment is likely to cause significant underestimation. Two sampling strategies are proposed that may eliminate the assumption of pool uniformity, thereby eliminating a potential source of underestimation.
Pedology, Precision Agriculture, and the Changing Paradigm of Agricultural Research
Authors: Bouma J. , Stoorvogel J. , van Alphen B. J. , Booltink H. W. G.
Published: July 2010

Precision agriculture (PA) has recently been defined by the U.S. National Research Council as a management strategy that uses information technologies to bring data from multiple sources to bear on decisions associated with crop production. Soil information is important here, but current soil survey data do not satisfy PA requirements. In this paper, the need for soil data in PA is discussed on the basis of Dutch research. Not only operational, but also tactical and strategic aspects are considered. On the operational level, soil data, including parameters derived with pedotransfer functions, support the use of simulation models to quantify dynamically soil water regimes, N transformations, and biocide adsorption. Real time “forward‐looking” simulations incorporated in early‐warning systems assist in operational decisions on water, nutrient, and crop protection management. Backward‐looking simulations, using historic weather data, can be used to evaluate different management tactics for exploratory strategic and tactical purposes. Such simulations should balance production and environmental requirements. At the strategic and tactical level, assembled data on the performance of various farm management systems should be grouped by soil series to build a systematic database, allowing “quick and preliminary” evaluations of the effects of farm management strategies based on experiences obtained elsewhere on similar soils.
Water Table Management, Nitrogen Dynamics, and Yields of Corn and Soybean
Authors: Fisher M. J. , Fausey N. R. , Subler S. E. , Brown L. C. , Bierman P. M.
Published: July 2010

Concern about NO−3 contamination of surface waters has prompted the development of agricultural water table management systems to reduce NO−3 loss in subsurface drainage outflow by subirrigating through the existing subsurface drainage lines during the growing season and controlling off‐season outflows. We hypothesized that soil N pools, crop yields, and N uptake in a corn (Zea mays L.)–soybean (Glycine max.) rotation differ between subirrigation (water table at 40 cm) with controlled drainage (SI/CD) vs. subsurface drainage (SD) alone on Omulga silt loam (Aeric Fragiaqualfs). Mean microbial biomass N, potentially mineralizable N, dissolved organic N, and ammonia N were not affected by the water table management system. Mean NO−3–N was not affected by the water table management system at 0‐ to 15‐cm and 15‐ to 30‐cm depths, but the 2‐yr mean soil NO−3 concentration at the 30‐ to 75‐cm depth was 46% lower in SI/CD compared with SD. The average corn yield was 19% greater, and the average soybean yield was 64% greater, in SI/CD plots, compared with SD. Corn N uptake was 13% greater and soybean N uptake was 62% greater with SI/CD, compared with SD. The SI/CD water table management system increased plant N uptake and reduced deep‐profile NO−3 concentrations, thereby reducing the amount of NO−3 potentially available to move via drains to surface waters.
Crop Residue Decomposition in No‐Tillage Small‐Grain Fields
Authors: Steiner J. L. , Schomberg H. H. , Unger P. W. , Cresap J.
Published: July 2010

Conservation tillage fields provide different environments for biological and chemical processes than tilled fields. Our understanding of decomposition does not adequately account for post‐harvest residue distributions or field environment variability. We hypothesized that temperature and moisture could be used to normalize field environments to optimal conditions that produce maximum decomposition rates; and biomass density could be normalized based on the fraction of initial biomass remaining over time. Four small grains were grown at Bushland, TX, to produce high‐, medium‐, and low‐biomass densities in 36 field subplots using different seeding rate, fertilizer, and irrigation on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). During decomposition, differential irrigation increased environmental variability (13, 5, and 0 applications to sub‐subplots). Ash‐free crop residue biomass was measured seven times during 14 mo. Climate indices related field to optimal conditions, based on the daily minimum of air temperature and precipitation coefficients. First‐order decomposition coefficients, k, were determined by plot, using the cumulative climate index to represent time. Irrigation did not affect k (P < 0.45), indicating that the moisture index accounted for irrigation effects; but crops had different coefficients (P < 0.062). Initial biomass density was inversely related to k (P < 0.008), indicating that climate‐based indices inadequately normalized environments across density treatments. The k was correlated to initial biomass , fraction‐standing initial biomass , and initial N concentration in standing biomass Climate indices may allow normalization of field environments important to decomposition and other agroecosystem processes if density effects on atmosphere–soil‐residue interactions can be better quantified.
Variability in Soil Erosion Data from Replicated Plots
Authors: Nearing Mark A. , Govers Gerard , Norton L. Darrell
Published: July 2010

Understanding and quantifying the large, unexplained variability in soil erosion data are critical for advancing erosion science, evaluating soil erosion models, and designing erosion experiments. We hypothesized that it is possible to quantify variability between replicated soil erosion field plots under natural rainfall, and thus determine the principal factor or factors which correlate to the magnitude of the variability. Data from replicated plot pairs for 2061 storms, 797 annual erosion measurements, and 53 multi‐year erosion totals were used. Thirteen different soil types and site locations were represented in the data. The relative differences between replicated plot pair data tended to be lesser for greater magnitudes of measured soil loss, thus indicating that soil loss magnitude was a principal factor for explaining variance in the soil loss data. Using this assumption, we estimated the coefficient of variation of within‐treatment, plot replicate values of measured soil loss. Variances between replicates decreased as a power function of measured soil loss, and were independent of whether the measurements were event‐, annual‐, or multi‐year values. Coefficients of variation ranged on the order of 14% for a measured soil loss of 20 kg/m2 to greater than 150% for a measured soil loss of less than 0.01 kg/m2 These results have important implications for both experimental design and for using erosion data to evaluate prediction capability for erosion models.
Soil microbial biomass alterations during the maize silage growing season relative to tillage method
Authors: Staley T. E.
Published: July 2010

Tillage method can significantly alter soil microbial populations and activities. Although considerable literature exists on microbial and soil chemical alterations under various tillage methods, little information exists on soil microbial biomass C (SMB) alterations during the growing season, and especially on the relationship of SMB to crop N use. The objective of this study was to determine the effect of no‐tillage (NT) or conventional tillage (CT), and soil location, on SMB during the growing season. A maize (Zea mays L.) silage/15N field experiment, under NT or CT for 3 yr before this study, was used during the fourth growing season. Averaged over sampling times and location (within‐row or between‐row), SMB in the 0‐ to 3.8‐cm and 3.8‐ to 7.5‐cm soil layers under NT was 87 and 33% greater, respectively, than under CT. Linear regression of soil surface layer (0–3.8 cm) SMB on day‐of‐year revealed a significant (P ≤ 0.10) relationship only within‐row and under NT, with a 29% SMB decrease during the growing season. Similar regressions for the other layers and treatments were insignificant (P > 0.10) or had small seasonal differences. SMB was consistently higher in the between‐row locations under both tillage methods. Despite substantial tillage method‐induced differences in SMB (50% overall, accompanied by small differential seasonal differences) in the more surficial layers, these alterations appear to have been of little practical consequence, since previous work on these plots revealed essentially no differences in silage utilization of either fertilizer N or soil N relative to tillage method. Thus, the importance of SMB in significantly affecting crop N use in this within‐row, banded, maize silage system is questioned.