bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen Mineralization from Soil Organic Matter and Crop Residues: Field Validation of Laboratory Predictions
Authors: Honeycutt C. Wayne
Published: July 2010

Accurate prediction of N mineralization under field conditions would promote optimal N‐use efficiency from both organic and inorganic sources. This study was conducted to assess the utility of microplot cylinders with mixed‐bed exchange resins for monitoring field N mineralization, to compare laboratory predictions with field measurements of N mineralization, and to determine the impact of using ground (≤1 mm) crop residues in the laboratory to predict N mineralization of unground (≤25 mm) residues in the field. Nitrogen mineralization from soil organic matter and hairy vetch (Vicia villosa Roth) residues was followed in the laboratory at 15, 20, and 25 °C with 0, 2150, 4300, and 6450 kg vetch ha‐1 equivalent loading rates of ≤1 mm particle‐size residue. Ground and unground residues were added to microplot cylinders at loading rates equivalent to 0, 4028, and 5010 kg vetch ha‐1 and installed in potato (Solanum tuberosum L. Norwis) crop rows in two growing seasons. Nitrogen mineralization from soil organic matter under field conditions was overestimated by laboratory predictions; however, field measurements of N mineralization from both ground and unground vetch residues were closely predicted by a complementary laboratory study. These data indicate vetch residue N mineralization under these modified field conditions (i.e., microplot cylinders) can be predicted from laboratory studies that use ground residues, constant temperatures, and variable residue quantities. This finding may advance our ability to model and account for residue N mineralization when developing N management recommendations.
Disturbances During Minirhizotron Installation Can Affect Root Observation Data
Authors: Joslin J. Devereux , Wolfe Mark H.
Published: July 2010

Use of minirhizotrons in forested ecosystems has produced considerable information on production, mortality, distribution, and the phenology of root growth. But installation of minirhizotrons severs roots and disturbs soil, which can cause root proliferation in perennial plants. We compared the magnitude and vertical distribution of root growth observations in a mature hardwood forest during the growing season immediately after minirhizotron installation with observations more than two years later. We also compared the vertical root growth distribution during these two different years with the preinstallation distribution of fine root biomass. Before minirhizotron installation and again two years later, about 74% of fine root biomass was in the upper 30 cm of soil, but immediately after installation, 98% of the root elongation was in the upper 30 cm. Large differences in the quantity of root elongation were observed across different slope positions in the minirhizotron data from the first growing season (approximately four times greater on the upper slope as the lower slope). Such differences with slope position were not seen in the later minirhizotron data, nor in the preinstallation fine root biomass data. The evidence suggests that the minirhizotron data collected immediately after installation can be biased by disturbance of roots and soil during installation, which result in excessive root proliferation, particularly near the soil surface. Root proliferation appears to be the result of a response to both root pruning and to nutrient release in microsites near the newly installed minirhizotron.
General Model for Unsaturated Hydraulic Conductivity for Soils with Lognormal Pore‐Size Distribution
Authors: Kosugi K.
Published: July 2010

Describing water flow in unsaturated soils requires knowledge of the unsaturated hydraulic conductivity. This study was conducted to develop a general conductivity model for soils with lognormal pore‐size distribution based on the Mualem‐Dagan pore‐scale model. The derived model has three parameters other than parameters for a retention model: the parameters α and β, both of which are related to the soil pore tortuosity, and the parameter γ to describe how to evaluate the effective pore radius. The proposed model was applied to observed retention and conductivity data sets for 200 soils. Results showed that both α and β should be treated as fitted parameters for accurate descriptions of conductivity, whereas estimation results were insensitive to γ as long as α and β were optimized. Consequently, a simplified form of the general conductivity model was suggested which uses the constant γ value of unity. Based on the simplified general conductivity model, two predictive methods (AB and FN) were developed. The method AB uses the constant α and β values to minimize the average prediction error. The method FN uses an empirically derived relationship between β and the dimensionless parameter of the retention model, and the constant α value to minimize the average prediction error. Both methods reduced the average prediction error more than 77% compared with the Burdine and Mualem predictive models. The method FN provided slightly better predictions than the method AB, reducing the average prediction error by 28%.
Defining the “Ideal” Soil Structure in Surface Soil of a Typic Fluvaquent in the Netherlands
Authors: Bouma J. , Droogers P. , Peters P.
Published: July 2010

Traditional soil structure descriptions are static and qualitative. However, measurement of basic physical and chemical characteristics of a given soil structure followed by simulation modeling of crop yields and water and nutrient regimes results in a dynamic and quantitative soil structure characterization. Within any given soil series, different types of structure may occur as a result of different management practices, and each structure type can thus be characterized. This, however, is a reactive approach in which soil structures are presented as given fact. This paper explores a proactive approach in which measurement of basic soil characteristics on a series of standardized structure samples and exploratory simulation modeling are used to define an “ideal” structure, using plant growth and nutrient‐use efficiency as indicators. Management practices to realize such an “ideal” structure remain to be designed by others. Quantitative indicators for the “ideal” structure in the 0‐ to 30‐cm surface soil of a loamy, mixed, mesic Typic Fluvaquent (a prime agricultural soil in the Netherlands) were based on simulated yields and associated nitrate leaching. Simulations considered water supply capacity, occurrence of by pass flow and internal catchment, leaching of nitrates as a function of fertilization scenarios, accessibility of water to roots, and trafficability in spring. Exploratory simulations, using a validated model for a period of 30 yr to express temporal variability for a complete soil profile with varying topsoil structures, showed a structure consisting of 0.5‐cm aggregates and a bulk density of 1.6 g cm‐3 to be “ideal” for the agricultural land use being considered.
Water‐Use Efficiency and Carbon Isotopic Composition in Reduced Tillage Systems
Authors: Walley F. L. , Matus A. , Lafond G. P. , van Kessel C.
Published: July 2010

Cropping systems that influence soil water availability are expected to influence the C isotopic composition (δ13C) of crop residues and consequently, the δ13C of soil organic matter. We hypothesized that the δ13C of plant residues and soil organic matter in three tillage systems (zero [ZT], minimum [MT], and conventional tillage [CT]) and three, 4‐yr crop rotations would vary and would relate to water‐use efficiency (WUE). The study was conducted on an Indian Head heavy clay (Udic Haploboroll) in Saskatchewan, Canada. The three crop rotations were fallow‐spring wheat (Triticum aestivum L.)‐spring wheat‐winter wheat, spring wheat‐spring wheat‐flax (Linum usitatissimum L.)‐winter wheat, and spring wheat‐flax‐winter wheat‐field pea (Pisum sativum L.). Water use was estimated yearly using mass balance. The δ13C of the standing crop residue, roots, and soil organic matter was determined 9 yr after the study was initiated. Although crop water use was higher in ZT (31.2 cm yr‐1) and MT (30.9 cm yr‐1) than in CT (28.8 cm yr‐1), corresponding differences in WUE and δ13C of plant tissue and soil organic matter were not detected. In one instance, within the most diversified rotation, WUE was reduced in ZT compared with CT; however, observed variations in WUE did not conform to theoretical expectations of the δ13C of plant residues and soil organic matter. Factors other than WUE, including soil fertility and timing of moisture deficits, may have influenced the degree to which C isotope discrimination was expressed in the plant residues and soil organic matter.
Availability of Nitrogen in 15N‐Labeled Ruminant Manure Components to Successively Grown Crops
Authors: Jensen B. , Sørensen P. , Thomsen I. K. , Christensen B. T. , Jensen E. S.
Published: July 2010

To improve crop N use efficiency of animal manures, the availability of N in individual manure components must be better understood. This microplot field study quantifies crop offtakes of N in four similar batches of ruminant manure containing 15N‐labeled urine, feces, or straw, or unlabeled components only. The urine and feces were from a sheep first fed unlabeled hay and then 15N‐labeled hay. Manures (≈ 19 g total N m‐2) were incorporated into two coarse‐textured soils before planting to spring barley (Hordeum vulgare L.) undersown with perennial ryegrass (Lolium perenne L.). Manures with one 15N‐labeled component were supplemented with unlabeled NH4NO3 (7.3 g N m‐2), while unlabeled manure was given 15NH415NO3. Labeled and unlabeled N were determined in the spring barley at maturity and in six cuts of ryegrass taken during the succeeding 2.5 yr. The homogeneity of feces and urine 15N‐labeling was high. Dry matter yields and crop N offtakes were similar in all treatments. Barley (grain and straw) recovered 40, 26, 10, and 6%, respectively of 15N added with mineral fertilizer, urine, straw, and feces. Weighted mean recovery of the combined manure and fertilizer dressing was 22% of the added 15N. Crop recovery of urine and feces 15N was smaller and that of straw 15N higher than reported in previous studies on individual components, indicating that the N mineralization‐immobilization turnover (MIT) of the manure components interacted. In the second and third growth seasons, 2.7 to 4.4% and 1.1 to 2.0% of the 15N was recovered in grass cuts, respectively. Total recovery ranged from 84 to 95% of the added 15N, suggesting small N losses from this cropping system.
Phosphate Removal Capacity of Palustrine Forested Wetlands and Adjacent Uplands in Virginia
Authors: Axt J. R. , Walbridge M. R.
Published: July 2010

We examined the ability of soils in six nontidal palustrine forested wetlands (PFOs) in Virginia's Piedmont (PD) and Coastal Plain (CP)to remove dissolved inorganic P from solution, and we compared the P sorption capacities of wetlands with those of streambanks (within wetlands) and adjacent uplands. We hypothesized that wetland soils would have higher P sorption capacities than streambank and upland soils due to the higher concentration of noncrystalline (oxalate‐extractable) Al and Fe (Aloand Feo) favored by periodic flooding. We found that P sorption capacities varied both as a function of landscape position and soil depth. Wetlands had higher P sorption capacities than uplands in surface soils (0–15 cm), while below 50 cm the relationship was reversed. Streambank areas within wetlands generally had the lowest P sorption capacities. As hypothesized, Alowas correlated with P sorption capacity in wetland soils, but so was soil organic matter (as estimated by mass loss on ignition [LOI]); in fact, Aloand organic matter were positively correlated in wetland soilsIn contrast, clay and silt content were the two soil parameters most highly positively correlated with P sorption capacity in upland soilsOverall, these results suggest that differences in soil chemistry exist among landscape positions (wetland, streambank, upland) that have important implications with regard to P sorption capacity. Since wetlands and uplands may remove P from different hydrologic sources (i.e., surface runoff in wetlands and groundwater in uplands), hydrology may be a key factor in determining water quality functioning.
Characterization of Particle‐Size Distribution in Soils with a Fragmentation Model
Authors: Bittelli Marco , Campbell Gaylon S. , Flury Markus
Published: July 2010

Particle‐size distributions (PSDs) of soils are often used to estimate other soil properties, such as soil moisture characteristics and hydraulic conductivities. Prediction of hydraulic properties from soil texture requires an accurate characterization of PSDs. The objective of this study was to test the validity of a mass‐based fragmentation model to describe PSDs in soils. Wet sieving, pipette, and light‐diffraction techniques were used to obtain PSDs of 19 soils in the range of 0.05 to 2000 μm. Light diffraction allows determination of smaller particle sizes than the classical sedimentation methods, and provides a high resolution of the PSD. The measured data were analyzed with a mass‐based model originating from fragmentation processes, which yields a power‐law relation between mass and size of soil particles. It was found that a single power‐law exponent could not characterize the PSD across the whole range of the measurements. Three main power‐law domains were identified. The boundaries between the three domains were located at particle diameters of 0.51 ± 0.15 and 85.3 ± 25.3 μm. The exponent of the power law describing the domain between 0.51 and 85.3 μm was correlated with the clay and sand contents of the soil sample, indicating some relationship between power‐law exponent and textural class. Two simple equations are derived to calculate the parameters of the fragmentation model of the domain between 0.51 and 85.3 μm from mass fractions of clay and silt.
Measuring Saturated Hydraulic Conductivity using a Generalized Solution for Single‐Ring Infiltrometers
Authors: Wu L. , Pan L. , Mitchell J. , Sanden B.
Published: July 2010

Saturated hydraulic conductivity is a measure of the ability of a soil to transmit water and is one of the most important soil parameters. New single‐ring infiltrometer methods that use a generalized solution to measure the field saturated hydraulic conductivity (Ks) were developed and tested in this study. The Ks values can be calculated either from the whole cumulative infiltration curve (Method 1) or from the steady‐state part of the cumulative infiltration curve by using a correction factor (Method 2). Numerical evaluation showed that the Ks values calculated from the simulated infiltration curves of representative soil textural types were in the range of 87 to 130% of the real Ks values. Field infiltration tests were conducted on an Arlington fine sandy loam (coarse‐loamy, mixed, thermic, Haplic Durixeralfs). The geometric means of the Ks values calculated from the field‐measured infiltration curves by Method 1 and Method 2 were not significantly different. The geometric mean of the Ks calculated from the detached core samples, however, was about twice that of the Ks calculated from the infiltration curves, which was consistent with earlier findings. Unlike the earlier approaches, Method 1 calculates Ks values from the whole infiltration curve without assuming a fixed relationship between saturated hydraulic conductivity and matric flux potential ϕm
Microbial Biomass and Activities in Soil Aggregates Affected by Winter Cover Crops
Authors: Mendes I. C. , Bandick A. K. , Dick R. P. , Bottomley P. J.
Published: July 2010

Winter cover crops may increase soil organic matter (SOM) and improve soil structure in intensively managed summer vegetable cropping systems. Our study examined the influence of three cover crop treatments (fallow, cereal, and legume within a summer crop rotation of sweet corn and broccoli) on microbiological properties associated with five soil aggregate‐size classes (<0.25, 0.25 to 0.5, 0.5 to 1.0, 1.0 to 2.0, and 2.0 to 5.0 mm) of a Willamette silt loam (Pachic Ultic Argixerolls). The distributions of total organic C (TOC), total Kjeldahl N (TKN), soil microbial biomass C (SMBC), readily mineralizable C and N, and two enzyme activities (β‐glucosidase and fluorescein diacetate [FDA] hydrolysis) were compared among aggregate‐size classes of surface (0–20 cm) soils at seedbed preparation (June 1996) and after harvest of either broccoli (September 1995) or sweet corn (September 1996). Although cover cropping did not significantly influence aggregate‐size distribution, TOC, nor TKN on any sampling date, it did significantly (P< 0.05) influence SMBC in September 1995, mineralizable C and N and FDA hydrolysis and β‐glucosidase activities in June 1996, and levels of mineralizable C and N and β‐glucosidase activity in September 1996. Significant (P< 0.01) interactions occurred among the cover crop treatments and aggregate‐size classes for SMBC in September 1995, and among mineralizable C and N and FDA hydrolysis in June and September 1996. Mineralizable C and N and FDA hydrolysis differed (P< 0.01) among aggregate‐size classes between June and September 1996; these changes were significantly (P< 0.01) affected by cover crop treatment. These studies identified focal points for further research on the effects of aggregate‐size classes and cover cropping on the activities and dynamics of their respective microbial communities.
Long‐term Effects of Gypsum on Crop Yield and Subsoil Chemical Properties
Authors: Toma M. , Sumner M. E. , Weeks G. , Saigusa M.
Published: July 2010

In hot humid climates with highly leached, variable charge soils, the yields of many crops are limited due to subsoil acidity. Although surface‐applied gypsum has been shown to be effective in ameliorating this acidity in ferruginous and aluminous soils, the length of time that the effect is likely to last has not been satisfactorily established. A number of long‐term experiments with gypsum incorporated into the topsoil at 10 and 35 Mg ha−1were sampled to evaluate its effects on soil profile chemical properties and yields of corn (Zea maysL.) and alfalfa (Medicago sativaL.). Even after 16 yr, the gypsum effects were still clearly visible. Exchangeable Ca and SO4were higher down the soil profile in the gypsum than in the control treatment. A complementary reduction in exchangeable Al was observed in the gypsum treatment to the 80‐cm depth. However, pH was not greatly altered down the profile. This amelioration of the effects of subsoil acidity was reflected in improved crop yields of both corn (29–50%) and alfalfa (≈50%) on the gypsum treatments. Because the gypsum effect is so long‐lasting, its use as a subsoil acidity ameliorant becomes highly economic because the initially high cost can be amortized over an extended period of time.
Soil Organic Carbon Storage and Distribution in Arctic Tundra, Barrow, Alaska
Authors: Bockheim J. G. , Everett L. R. , Hinkel K. M. , Nelson F. E. , Brown J.
Published: July 2010

Soil organic C (SOC) levels were determined to a depth of 100 cm for the nine units designated on a 1957 1:20000 soil map of Barrow, AK prepared by J.V. Drew. The legend was updated by converting Drew's map units into the recently adopted Gelisol order in U.S. soil taxonomy and field verified. The SOC varied from 2.5 kg m−3 in modern beach sediments to >73 kg m−3 in Typic Sapristels in high‐centered, ice‐wedge polygons developed in reworked organic‐rich lake sediments. The SOC averaged 50 kg m−3 for the entire 64‐km2 area (excluding open water). Considerable variability in SOC exists within individual soil map units. For example, SOC levels in a Typic Aquiturbel (formerly classified as a Meadow Tundra, Normal Phase soil) ranged from 24 to 109 kg m−3 Substantial variation in SOC occurs within individual patterned‐ground units. For a high‐centered, ice‐wedge polygon with a diameter of 15 m, SOC levels are 24, 32, and 64 kg m−3 for the wedge trough, rim, and center, respectively. In a low‐centered, ice‐wedge polygon, SOC levels are 28 and 83 kg m−3 for the trough and center. The variation in SOC within soil map units and individual patterned‐ground units is due primarily to differences in the amount of ground ice. Active‐layer thickness varies within and between soil map units, ranging from 31 cm in Typic Sapristels to >100 cm in modern beach sediments. About 47% of the SOC in the upper meter of soil was in the active layer at the time of sampling; the remainder occurring in frozen ground, much of it meeting the definition of permafrost. Some of the SOC originates from past reworking of organic‐rich lake sediments. Carbon stocks in near‐surface permafrost may be of global significance and should be inventoried in other tundra regions.
Effects of Soil Morphology on Hydraulic Properties I. Quantification of Soil Morphology
Authors: Lin H. S. , McInnes K. J. , Wilding L. P. , Hallmark C. T.
Published: July 2010

Utilization of existing soil survey databases for characterizing water flow and solute transport in field soils has practical value. However, the lack of a proper means for quantifying soil morphology limits the incorporation of soil structural information into models. In this study, we examined basic relationships between five major soil morphological features (texture, initial moisture, pedality, macroporosity, and root density) and steady infiltration rates for 96 soil horizons of varying structure. Based on these relationships, a point scale system was developed as an approach to quantify soil morphology. Descriptive morphological classes were first rated with respect to their potential impacts on soil water flow rate. Points that provided the best correlation with the measured steady infiltration rates were then obtained for each morphological class through a computer optimization program. The optimal points assigned to each morphological feature were divided by the maximum value to yield a morphometric index of 0 to 1. Such an approach permitted the determination of interrelationships among different morphological features that would otherwise be difficult with qualitative descriptors. The proposed morphology quantification system also has potential in facilitating pedotransfer studies of estimating water flow and chemical transport parameters from soil survey databases including structural descriptors.
Soil Quality Assessment of Tillage Impacts in Illinois
Authors: Wander M. M. , Bollero G. A.
Published: July 2010

Successful soil quality assessment strategies are needed to improve our ability to manage soils sustainably. Our objective was to use a multivariate data set to determine whether recent adoption of no‐tillage (NT) practices had altered soil quality in Illinois. In 1995 and 1996, we sampled thirty‐six farm fields under conventional tillage (CT) or NT practices and relatively nondisturbed (ND) areas. Soils were Mollisols or Alfisols. Tillage or region affected 20 of the 23 parameters characterized. Soil chemical parameters were less variable than biological or physical measures. Principal component analysis (PCA) was used to assess soil quality overall. Principal component 1 (PC1) scores, which explained 39% of the total variance of the overall data set, were affected by tillage (ND > NT > CT) and increased with particulate and organic C and total N, biological activity, mineralizable N, and wet aggregate stability, and decreased with bulk density and dry aggregate mean weight diameter. The only significant factor contributing to PC2 was penetration resistance; PC2 explained 13% of the variance and decreased as follows: NT ≥ ND > CT. Multivariate assessment of soil quality indicated use of NT practices improved the biological and physical condition of the soil (0–15 cm) despite increased consolidation. It also showed that those biological and physical aspects of soils influenced by organic matter were the properties most altered by agronomic practices. Particulate organic matter (POM) was identified as a promising soil quality measure. A next step is to determine the biological and environmental relevance of a refined set of soil quality measures in conjunction with soil processes of regional concern.
Relationship between the Hydraulic Conductivity Function and the Particle‐Size Distribution
Authors: Arya Lalit M. , Leij Feike J. , Shouse Peter J. , van Genuchten Martinus Th.
Published: July 2010

We present a model to compute the hydraulic conductivity, K, as a function of water content, θ, directly from the particle‐size distribution (PSD) of a soil. The model is based on the assumption that soil pores can be represented by equivalent capillary tubes and that the water flow rate is a function of pore size. The pore‐size distribution is derived from the PSD using the Arya‐Paris model. Particle‐size distribution and K(θ) data for 16 soils, representing several textural classes, were used to relate the pore flow rate and the pore radius according to , where qi is the pore flow rate (cm3 s−1) and ri is the pore radius (cm). Log c varied from about −2.43 to about 2.78, and x varied from ≈2.66 to ≈4.71. However, these parameters did not exhibit a systematic trend with textural class. The model was used to independently compute the K(θ) function, from the PSD data for 16 additional soils. The model predicted K(θ) values from near saturation to very low water contents. The agreement between the predicted and experimental K(θ) for individual samples ranged from excellent to poor, with the root mean square residuals (RMSR) of the log‐transformed K(θ) ranging from 0.616 to 1.603 for sand, from 0.592 to 1.719 for loam, and from 0.487 to 1.065 for clay. The average RMSR for all textures was 0.878.
Practical Aspects of Salinity Effect on TDR‐Measured Water Content A Field Study
Authors: Nadler Arie , Gamliel Abraham , Peretz Isaac
Published: July 2010

It is possible to use the reflected electromagnetic time‐domain reflectometry (TDR) pulse for measuring water content (θ), for conventional probes, only when the soil electrical conductivity (EC) is low. The exact limiting level, above which the reflection is unnoticeable, depends on soil texture, salinity, θ, and probe geometry. Recently, the validity of θTDR, measured in saline soils, was questioned and overestimation was attributed to it. This study tested such a possible bias by simultaneously measuring the soil‐water content by the TDR and neutron scattering techniques, in two field experiments. The experiments lasted 150 d, and were irrigated with saline waters. In the Zeelim sandy site, peanut (Arachis hypogaea L.) was sprinkler irrigated at a rate of 6500 to 7500 m3 ha−1 with 1.9 dS m−1 irrigation waters. In the Nirim loamy site, cotton (Gossypium hirsutum L.) was drip‐irrigated at a rate of 3010 to 4580 m3 ha−1 with waters of EC ranging 3.6 to 4.0 dS m−1 The objective of this study was to observe if salinity increased θTDR relative to θneutron Measured θneutron values were found to be up to 0.02 or 0.08 m3 m−3 above and below θTDR for the sandy or loamy tested soils, respectively, with no significant effect of the salinity. Similarly, both, under‐ and over estimation were related to the effect of salinity on θTDR in over 20 previously published studies comparing θTDR to θgravimetric under wide ranges of clay, organic matter, and salt contents. The EC effect, expressed as bulk soil EC (σa), may depend also on texture and geometric parameters like particle aspect ratio. At field capacity, for the two soils tested, no detectable effect of salinity was found.
Characterization of Macropore Flow Mechanisms in Soil by Means of a Split Macropore Column
Authors: Ghodrati Masoud , Chendorain Michael , Chang Y. Jason
Published: July 2010

Naturally occurring macropores such as root channels and earthworm holes have been shown to affect water flow and solute transport processes in soils. To further our understanding of the specific processes that are involved in macropore flow, we have developed a Split Macropore Column (SMC) which consists of a semi‐cylindrical soil column with a semi‐cylindrical macropore at the main axial of its planer surface. The SMC allows one to control a number of important physical parameters such as the size, density, and continuity of the macropores for miscible displacement studies, as well as an opportunity to observe visually the macropore's impact on flow processes at the critical matrix‐macropore interface. After rigorous testing, we found that this system is a useful instrument to study macropore flow mechanisms. Using these SMCs, we performed a series of miscible displacement experiments to study the effects of soil type, flux rate, macropore size, and macropore to matrix size ratio. Our initial results show three zones of flow through the column: (i) film flow at the matrix–macropore interface, (ii) in the matrix directly adjacent to the macropore, and (iii) in the remaining matrix. The initial data suggest that macropore flow is influenced more by the matrix–macropore size ratio than by the macropore size.
The Effect of Hysteresis on Microbial Activity in Computer Simulation Models
Authors: Whitmore Andrew P. , Heinen Marius
Published: July 2010

Microbial activity in soils depends on the status of the soil water, which is expressed by pressure head (h) or water content (θ). There is no unique relationship between θ and h because moisture relations exhibit hysteresis. For convenience microbial activity has usually been related to the main drying curve but in general this will lead to bias in computer models that aim to simulate microbial activity. This article aims to evaluate the magnitude of the bias resulting from the use of computer simulation models of mineralization coupled to a model that follows the hysteresis of water relations in soil. Simulations of mineralization were found to accumulate a bias of more than 15% of the mean annual mineralization by harvest. This bias was found to be most serious where soil is continually subject to severe wetting and drying cycles such as can be found in irrigated and tropical agriculture.
Interaction of Tillage and Soil Texture Biologically Active Soil Organic Matter in Illinois
Authors: Needelman B. A. , Wander M. M. , Bollero G. A. , Boast C. W. , Sims G. K. , Bullock D. G.
Published: July 2010

Several long‐term studies suggest that no‐till (NT) practices do not increase soil organic matter (SOM) sequestration in all situations. We evaluated the interaction of tillage and soil texture effects on SOM in Illinois Mollisols and Alfisols by characterizing particulate organic matter (POM), potentially mineralizable N (PMN), and soil microbial biomass (SMB). Thirty‐six fields were sampled during spring and summer of 1995 and 1996. Each field had been under either conventional tillage (CT) (disc, moldboard plow, and/or chisel plow) or NT management for at least 5 yr. No‐till fields contained 15% (3.0 g C kg−1soil) more soil organic C (SOC) than CT fields in the 0‐ to 5‐cm depth; however, tillage did not affect SOC contents in the 5‐ to 15‐ or 15‐ to 30‐cm depths, or in the overall sampling depth (0–30 cm). Fields under NT contained 33% more POM (1.4 g C kg−1soil) and 54% more PMN in the 0‐ to 5‐cm depth, but there was no tillage effect on POM (0–15 cm) or PMN (0–30 cm) contents overall. Average POM contents were 29% lower (0.73 g C kg−1soil) in the 5‐ to 15‐cm depth of the NT than of the CT soils. At sand contents below ≈50 g kg−1soil, NT fields contained greater SOC, total N, and POM contents in the 0‐ to 5‐cm depth and lower POM contents in the 5‐ to 15‐cm depth than CT fields. In soils with sand contents higher than ≈50 g kg−1soil, tillage practices did not affect the vertical distribution of SOC, total N, or POM.
Forest Nutrient and Carbon Pools at Walker Branch Watershed Changes during a 21‐Year Period
Authors: Trettin C. C. , Johnson D. W. , Todd D. E.
Published: July 2010

A 21‐yr perspective on changes in nutrient and C pools on undisturbed upland forest sites is provided. Plots originally representing four cover types have been sampled three times. On each plot, forest biomass, forest floor, and soil, to a depth of 60 cm, were measured, sampled, and analyzed for Ca, Mg, C, N, and P. Exchangeable soil Ca and Mg have declined in most soils. Despite the low exchangeable Ca, cumulative sequestration in the biomass has exceeded the soil pool, suggesting that soil supplies below 60 cm are satisfying the biomass demand. Extractable soil P also declined, with means ranging from 4.2 to 18.2 kg ha−1, as a result of reductions in the mineral soil and Oi horizon. The loss of extractable soil P exceeded biomass sequestration in all but one plot, suggesting abiotic soil processes as the removal mechanism. Soil C and N were either stable, although highly variable, or declined, which was unexpected in these undisturbed sites. The net C balance of these sites was controlled by aboveground sequestration, which offset changes in the soil and forest floor. Soil parent material and geomorphic setting strongly influenced the changes in soil properties during the 21‐yr period, reflecting the importance of those factors in assessing soil nutrient and C cycles over that of forest cover type. The variability encountered in the periodic soil measurements highlights the difficulty in detecting temporal changes in soil chemical properties.
George Nelson Coffey, Early American Pedologist
Authors: Brevik Eric C.
Published: July 2010

George Nelson Coffey joined the Bureau of Soils in 1900, the second year of its existence, and worked in the program for about 11 years. During those years he worked on soil surveys in many parts of the United States. Those surveys exposed him to a wide variety of soils. Because of his experience and knowledge, he was chosen to supervise soil classification and correlation after five years with the Bureau. During the time that he was in charge of soil classification and correlation, Coffey became acquainted with earlier soil studies, such as those of E.W. Hilgard in Mississippi, T.C. Chamberlain in Wisconsin, and the Dokuchaiev school in Russia. From those sources and his own field experience, Coffey developed and promoted his ideas of soil genesis and classification. Coffey's ideas were in marked contrast to the prevailing idea in this country that soils were simply a function of the underlying rocks. Coffey presented his ideas in journal articles for several years, culminating with the publication of USDA Bureau of Soils Bulletin No. 85 in 1912. Bulletin 85 is now recognized as a classic, but like Coffey's journal articles, it fell on deaf ears in 1912. Coffey left the soil survey program before Bulletin 85 was published and worked at the Ohio Agricultural Station, where he worked on soil mapping, an erosion study, and fertilizer trials. Later, Coffey moved on to the University of Illinois. In 1922 Coffey left soil science as a career but retained his interest in soils and geology. After he left the soil survey program Coffey's publications on soil genesis and classification were largely forgotten. About a decade later a profound change in the concept of soil and in the understanding of soil genesis began in the United States. Championed by Curtis F. Marbut, the change occurred gradually in the 1920s, 1930s, and beyond. A new group of American pedologists emerged who had learned of and from the Dokuchaiev school and had the benefit of the profound changes that had occurred in the United States. Those pedologists rediscovered Bureau of Soils Bulletin No. 85 and earlier publications by Coffey and recognized the advanced nature of Coffey's ideas of soil genesis and classification. Those ideas mark Coffey as one of the first, if not the very first, of the American pedologists.
Small‐Scale Measurement of Soil Water Content Using a Fiber Optic Sensor
Authors: Garrido Fernando , Ghodrati Masoud , Chendorain Michael
Published: July 2010

Many water flow and solute transport studies require accurate measurement of water content within small soil volumes. We have examined the feasibility of using fiber optic mini‐probes (FOMPs) for in situ measurement of water content in relatively small soil volumes (<15–20 mm3) in real time and on a continuous basis. The system consists of transmitting a constant beam of light through the input leg of a fiber optic mini‐probe to a location of interest within the soil matrix. At the tip, the light exits the probe, interacts with the soil volume directly in front, and partially reflects back into the probe. The reflected signal is transmitted through the output leg to a photodetector and quantified. The output signal, which is constant during steady state (i.e., dry soil), decreases as the water content in soil increases. A calibration is necessary to convert the output light intensity to water content. In developing calibration curves for the three soils used in the study, we consistently found an excellent correlation (r2 > 0.98) between the soil light reflectivity and the water content. Calibration of the FOMP depends on the individual probe, soil type (largely due to texture), and bulk density. The FOMP system may be ideal in situations where water content is dynamic and changing at small spatial scales, especially where these changes have a large impact on other processes.
Preferential Flow through Intact Soil Cores Effects of Matric Head
Authors: Langner H. W. , Gaber H.M. , Wraith J. M. , Huwe B. , Inskeep W. P.
Published: July 2010

Continuous soil pores may act as pathways for preferential flow depending on their size and water status (filled or drained), the latter being largely controlled by the soil matric head (h). The literature contains a wide range of proposed minimal pore sizes that may contribute to preferential flow. The objective of this study was to examine the relationship between h (and corresponding pore sizes) and preferential solute transport in a naturally structured soil. Tracer (3H2O and pentafluorobenzoic acid, [PFBA]) miscible displacement experiments were performed at several h values in intact soil cores (15‐cm diameter, 30‐cm length) using an apparatus especially suited to maintain constant h while collecting large effluent volumes. To test for the occurrence of preferential flow, observed breakthrough curves (BTCs) were evaluated for physical nonequilibrium (PNE) using a comparison between fitted local equilibrium (LE) and PNE models. Fitting results of the observed BTCs indicated absence of PNE in all solute transport experiments at h ≤ −10 cm. Experiments at h ≥ −5 cm consistently exhibited PNE conditions, indicating the presence of preferential flow. These results suggest that soil pores with effective radii of 150 μm and smaller (water‐filled at h = −10 cm) do not contribute to preferential flow. Observed pore water velocities were not indicative of the presence or absence of preferential flow conditions. Continuous measurements of soil water content (θ) using time domain reflectometry (TDR) revealed that at h = −10 cm, <2% of the soil volume (1–5% of θ at saturation) had drained.
Measurement of fixed ammonium and nitrogen isotope ratios using dry combustion
Authors: Liang B. C. , Mackenzie A. F. , Gregorich E. G.
Published: July 2010

Clay‐fixed NH4–N can represent up to 18 percent of the total soil N for Canadian agricultural soils. A modification of the Silva and Bremner's method for determining clay‐fixed NH4was developed. The Silva and Bremner procedure incorporates dissolution of mineral residues by a HF–HCl digestion in order to release bound NH4, following removal of exchangeable NH4and organic N. Steam distillation is used to recover NH4from the soil digest. The procedure presented in this paper substitutes combustion in an automated elemental analyzer for the HF–HCl digestion step. Combustion with an elemental analyzer follows removal of exchangeable NH4with 0.5MKCl and organic N with wet digestion using KOBr. The elimination of the HF–HCl digestion and steam distillation steps shortens the time required for analysis and avoids the use of strong reagents. The procedure is also suitable for15N studies when combined with a mass spectrometer. The two techniques gave virtually the same results for 17 soils with the slope of the regression of 1.03 and a coefficient of determination of 0.97. Simultaneous measurements of fixed NH4and N isotope ratios using continuous flow mass spectrometry can be carried out.
Accuracy and Reliability of Pedotransfer Functions as Affected by Grouping Soils
Authors: Pachepsky Ya. A. , Rawls W. J.
Published: July 2010

Pedotransfer functions (PTFs; i.e., dependencies of soil water retention and soil hydraulic conductivity on basic soil parameters available from soil surveys) are widely used to predict soil functioning in agricultural and environmental systems. The reliability of PTFs needs to be assessed by examining the correspondence between measured and estimated data for data set(s) other than the one used to develop a PTF. Our objective was to see whether grouping according to taxonomic unit, soil moisture regime, soil temperature regime, and soil textural class would improve both PTF accuracy and reliability. We estimated soil water contents at matrix potentials of −33 kPa and −1500 kPa for the 447 soil samples from the Oklahoma National Resource Conservation Service database. Dry bulk density, the ratio of cation‐exchange capacity (CEC) to clay content, and contents of clay, sand, coarse fragments, and organic matter were used as predictors. The Group Method of Data Handling (GMDH) was used to develop PTFs. To assess accuracy and reliability of the PTFs, we used cross‐validation; i.e., repeated random splitting of the data set into subsets for development and validation. The PTF accuracy and reliability was quantified by the root mean square error in the development and validation data set, respectively. Grouping improved the accuracy of PTFs in most cases. None of the grouping criteria proved to be clearly superior. Although PTFs developed from the groups were more accurate than the PTFs developed from the whole database, they were not more reliable. Improving PTF reliability may be an issue distinctly different from improving PTF accuracy.
Viability of Permanently Installed Platinum Redox Electrodes
Authors: Austin W. E. , Huddleston J. H.
Published: July 2010

Electrodes used continuously in the field for up to 5 yr were removed, examined visually, and tested in both a quinhydrone solution and a 1:5 soil–water slurry. Comparison with pre‐installation quinhydrone readings showed that all but 3 of 102 electrodes tested were still within ±10 mV of the standard value. Water observed inside more than half the electrodes had no apparent adverse impact on electrode performance. The post‐removal quinhydrone test correctly identified one electrode that developed faulty readings in the first year of field use. Test values for two other potentially defective electrodes fell within acceptable standards after rinsing them in an HCl–HNO3 solution and retesting. Platinum poisoning with coatings could not be detected visually, and we conclude that poisoning, though possibly present at minimal levels, did not significantly impair electrode performance after 5 yr. Post‐removal testing in a constantly stirred slurry gave readings that were a little more variable than quinhydrone readings but were much less variable than actual field readings. Anomalous slurry readings within replicated electrode sets suggest that, despite good quinhydrone readings, some electrodes may not have responded properly under actual field use. Field data from one such set confirmed the presence of a defective electrode. We conclude that the slurry test provides valuable information that complements the quinhydrone test and could be used as a pre‐installation test to help identify potentially faulty electrodes.
Changes in Aggregate Stability and Concentration of Glomalin during Tillage Management Transition
Authors: Wright S. F. , Starr J. L. , Paltineanu I. C.
Published: July 2010

Improvement in structure of degraded soils or prevention of degradation of structure in healthy soils requires an understanding of processes contributing to aggregate stability. The impact of cropping systems on a specific molecule that contributes to aggregate stability is part of the process that has not been elucidated. The relationship between aggregate stability and glomalin, a glycoprotein produced by arbuscular mycorrhizal (AM) fungi, was studied during the first 3 yr in transition from plow tillage (PT) to no tillage (NT) maize (Zea mays L.). Results showed a high linear correlation between glomalin concentration in aggregates and aggregate stability. Increases in both aggregate stability and glomalin were measurable from year to year in NT plots, but NT was significantly higher than PT after 2 or 3 yr (P < 0.05). Comparison of NT plots after 3 yr with nearby soil in grass cover indicated that there was 20% greater stability and 45% higher concentration of glomalin in the grass‐covered soil. Comparison of PT and NT (3 yr) interrow samples with intrarow samples indicated that plant roots and NT management may have a synergistic effect on aggregate stabilization. These results show that cropping systems should be evaluated for the impact on production of glomalin by AM fungi.
Lime‐induced loss of soil organic carbon and effect on aggregate stability
Authors: Chan K. Y. , Heenan D. P.
Published: July 2010

We investigated the decline in soil organic C on an Oxic Paleustalf (red earth) as a result of lime application (1.5 t CaCO3ha−1) in New South Wales, Australia and determined how loss of organic C was related to soil aggregate stability changes. Organic C lost as a result of liming was mainly (up to 84% of total loss) in the form of light fraction (specific gravity <1.8) bound to macroaggregates. With liming, a given level of aggregate stability was achieved at a lower soil organic C level in limed soil (e.g., total C level for a 50% aggregate stability was 13.0 and 17.8 g kg−1for limed and unlimed soils, respectively). Increased aggregate stability in limed soils suggested formation of new bonding involved Ca bridges.
Horizons and Humus Forms in Beech Forests of the Belgian Ardennes
Authors: Ponge Jean-Franc¸ois
Published: July 2010

Forest soil organic horizons are named on the basis of visual observations made directly in the field, thus this is often subjective. To find more objective bases for their classification, humus form horizons in 13 beech stands (Fagus sylvatica Ehrh.) were compared. Test sites were located in the Belgian Ardennes (western Europe), which encompasses a wide range of ecological conditions. I used a semi‐quantitative micromorphological method for the description of horizons, and a multivariate method for data analysis. These methods helped to discern objective discontinuities among Oi, Oe, and Oa horizons, adding new criteria for their characterization, such as the root system of trees. Within these horizons, transitions between sub‐horizons are gradual and thus do not lie on clear‐cut criteria. The transition between Oa and A horizons was also gradual. The composition of Oa and A horizons varies according to humus form. The vertical distribution of soil organisms and their vertical movements were considered the origin of discontinuous and continuous processes taking part in the transition from one horizon to another. The observation of horizons under a dissecting microscope may help to find more reliable bases for their nomenclature, even without the use of costly soil sections.