bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimum and Delayed Conservation Tillage for Wheat–Fallow Farming
Authors: Schillinger William F.
Published: July 2010

Maintaining crop residue, clods, and roughness on the soil surface during summer fallow is critical for wind erosion control in the low‐precipitation (<300 mm annual) dryland wheat (Triticum aestivum L.) production region of the inland Pacific Northwest, USA. Conventional farming practices are intensive, involving eight or more tillage operations during the fallow cycle. My objective was to evaluate fallow conservation tillage management systems for soil water storage, residue retention, surface and subsurface soil cloddiness, surface roughness, wheat stand establishment, and grain yield during 6 yr at Lind, WA. The soil is a Shano silt loam (coarse‐silty, mixed, superactive, mesic Xeric Haplocambids). Treatments were (i) conventional (tillage), (ii) minimum (herbicides and tillage), and (iii) delayed minimum (herbicides and delayed tillage). Averaged over years, precipitation storage efficiency in the soil was 51, 54, and 57% over winter, and 24, 26, and 26% at the end of the fallow cycle, for conventional tillage (CT), minimum tillage (MT), and delayed minimum tillage (DMT), respectively. Surface residue and surface clod mass were consistently reduced by 45% or more in CT compared with MT and DMT. There were no differences among treatments in seed‐zone water content at time of sowing in September nor in grain yield in any year or when averaged across years. Results show that the long‐term practice of minimum and delayed minimum tillage during fallow significantly increased surface residue and clod retention for erosion control with no adverse agronomic affects compared with conventional tillage.
Effects of Nitrogen Enrichment, Wildfire, and Harvesting on Forest‐Soil Carbon and Nitrogen
Authors: Parker Jennifer L. , Fernandez Ivan J. , Rustad Lindsey E. , Norton Stephen A.
Published: July 2010

Northern forest soils represent large reservoirs of C and N that may be altered by ecosystem perturbations. Soils at three paired watershed in Maine were investigated as case studies of experimentally elevated N deposition, wildfire, and whole‐tree harvesting. Eight years of experimental (NH4)2SO4 additions at the Bear Brook Watershed in Maine significantly reduced forest‐floor C/N ratios from 30.6 to 23.4. Forest‐floor C and N pools were lower in the treated watershed (38 Mg C ha−1, 1612 kg N ha−1) compared with the reference (75 Mg C ha−1, 2372 kg N ha−1). Fifty years after wildfire at Acadia National Park, the burned watershed with hardwood regeneration had significantly lower forest‐floor C and N concentrations (208 g C kg−1 soil, 9.9 g N kg−1 soil) than the reference watershed dominated by a softwoods (437 g C kg−1 soil, 12.8 g N kg−1 soil). Forest‐floor C and N pools were lower in the burned watershed (27 Mg C ha−1, 1323 kg N ha−1) compared with the reference (71 Mg C ha−1, 2088 kg N ha−1). At the Weymouth Point, the harvested watershed regenerated to spruce‐fir, the dominant stand type that existed before the harvest, and it had significantly lower forest‐floor C concentrations and pools (406 g C kg−1 soil, 24 Mg C ha−1) than the reference (442 g C kg−1 soil, 39 Mg C ha−1) after 17 yr. All perturbations studied were associated with lower forest‐floor C pools.
A Discussion of the Surface Complexation Modeling in the Paper by Sarkar et al. (1999)
Authors: Lützenkirchen Johannes
Published: July 2010

The application of the triple layer surface complexation model by Sarkar et al. is discussed, and it is shown that the authors obtain for gibbsite an acid/base model which is not in agreement with typical experimental data for that sorbent. Furthermore, it is concluded that experimental surface charge must be obtained data for the sorbent sample, because there is no unique surface charge for gibbsite based on the overall properties such as sorbent mass or specific surface area.
Measurement of soil aggregate density by volume displacement in two non‐mixing liquids
Authors: Sarli Guillermo O. , Filgueira Roberto R. , Giménez Daniel
Published: July 2010

Soil aggregate density is an important property influencing soil biological, chemical, and physical processes. Current methods used to estimate soil aggregate density are based on more or less restrictive assumptions or require specialized equipment. This study was conducted to develop an alternative method for measuring aggregate density of soil and other porous objects that is both simple and theoretically sound. The proposed method solves the balance of forces resulting when a kerosene‐saturated aggregate is immersed in a mix of water and glycerin. We tested the accuracy of the method by measuring the volume of 40 aggregates with diameters ranging from 4 to 20 mm and with variable densities. Soil aggregates were saturated in kerosene, drained at a tension of −30 mm, and their volume estimated using a pycnometer. Upon resaturation, aggregates were suspended from a thread and successively weighed in air, in kerosene, and in a mix of water and glycerin. Aggregate volumes and densities varied between 1.20 × 10−7 and 3.85 × 10−6 m3 and between 1.05 to 1.86 Mg m−3, respectively. On average, aggregate volumes estimated with the pycnometric method were 2.6% smaller than the volumes obtained with the proposed technique, suggesting that the new method is less aggressive in evacuating pores open to the surface than a tension of −30 mm. The new method was easier to use, did not require previous preparation of the sample, and was less time‐consuming than older methods.
Environmental Management of Soil Phosphorus
Authors: Needelman Brian A. , Gburek William J. , Sharpley Andrew N. , Petersen Gary W.
Published: July 2010

The mapping of soil P concentration is necessary to assess the risk of P loss in runoff. We modeled the distribution of Mehlich‐3 extractable soil P (M3P) in an east‐central Pennsylvania 39.5‐ha watershed (FD‐36) with an average field size of 1.0 ha. Three interpolation models were used: (i) the field classification model—simple field means, (ii) the global model—ordinary kriging across the watershed, and (iii) the within‐field model—ordinary kriging within fields with a pooled within‐stratum variogram. Soils were sampled on a 30‐m grid, resulting in an average of 14 samples per field. Multiple validation runs were used to compare the models. Overall, the mean absolute errors (MAEs) of the models were 76, 71, and 66 mg kg−1M3P for the field classification, global, and within‐field models, respectively. The field classification model performed substantially worse than did the kriging models in five fields; these fields exhibited strong spatial autocorrelation. The within‐field model performed substantially better than did the global model in three fields where autocorrelation was confined by the field boundary. However, no differences in P index classification were observed between the three prediction surfaces. The field classification model is simpler and less expensive to implement than the kriging models and should be adequate for applications that are not sensitive to small errors in soil P concentration estimates.
Field Studies of Crop Response to Water and Salt Stress
Authors: Shani U. , Dudley L. M.
Published: July 2010

Studies of crop response to water and salt stress vary either salinity with a high leaching fraction or irrigation in the absence of salinity to isolate and quantify the effects of the two types of stress. Under deficit irrigation with saline water, a water conserving practice, the crop experiences simultaneous matric and osmotic stress, and it is not known if experiments designed to isolate stress effects may be used to predict crop response to simultaneous stresses. Thus, a study was conducted wherein yields were determined under varying levels of salinity and irrigation. Corn (Zea mays L.) and melon (Cucumis melo L.) were grown at the Arava Research and Development Farm in Yotvata, Israel, and alfalfa (Medicago sativa L.) at the Utah Power & Light Research Farm in Huntington, UT. Corn and melon plots were drip irrigated at six ratios of potential evapotranspiration ranging from 0.2 to1.7 in combination with four salinity levels. Alfalfa was irrigated with water of 0.2 and 4.0 dS m−1 from a line‐source sprinkler. For all three crops, the salinity treatments consisted of a control treatment with a salinity level less than published salt‐tolerance thresholds. Interactive effects of salinity and water stress were not observed in these field experiments. At low irrigation levels (≈70% of potential evaporation), yields were unaffected by the salinity level. At the higher irrigation levels, the salinity level caused significant differences in yield. Yield data were fit to piecewise linear models that emphasized the limiting nature of the effects of salt and water stress.
Soils and Hydrology of a Wet‐Sandy Catena in East‐Central Minnesota
Authors: Reuter Ron J. , Bell Jay C.
Published: July 2010

Soil properties are strongly related to the retention and movement of water within the soil system. The purposes of this study were to document the near‐surface hydrology of a wetland–upland hillslope on a sandy glacial outwash plain in east‐central Minnesota and to describe the patterns of soil morphology with respect to observed hydrology. Water levels, soil temperature, soil‐water tension, and redox potential were monitored at seven points along a 41‐m hillslope transect composed of Psamments, Aquents, Aquods, and Saprists. In addition to standard field descriptions, particle‐size distribution, percentage of organic C, and citrate‐dithionate and ammonium‐oxalate extractable Fe (Fed and Feo, respecitively) were determined for profiles at each transect point. During the study period, the 30‐yr mean annual precipitation (MAP) was exceeded in 4 of 5 yr. Mean water levels were highest in spring and water levels typically rose from September through May. The depth to redoximorphic features increases with elevation above the peatland and the upper extent of redoximorphic features is 15 to 60 cm above the measured mean water table level. In the upper landscape positions, the redoximorphic features were located 12 cm above the maximum recorded water level. The distribution characteristics of Fe throughout the soil system indicate that Fe has been removed from the upslope soils and reconcentrated in organic‐rich horizons in the lower landscape positions. The combination of Fe distribution and the location of redoximorphic features well above the mean water table suggest that the regional water table has been lowered.
Determination of Preferential Flow Model Parameters
Authors: Logsdon S. D.
Published: July 2010

Solute transport models that include a preferential flow component require many input parameters. There are well established procedures to determine micropore parameters, but procedures to determine macropore parameters are not well established. The objective of this paper was to evaluate methods to independently measure macropore parameters. The test model used was MACRO, a transient‐state, two‐flow domain model. The key macropore parameters in the model are saturated and boundary hydraulic conductivities (Ks and Kb), the absolute value of the boundary head between macropore and micropore domains (hb), the exponent (n*) of the relation between K (variables are defined in the appendix) and water content (θ), the macropore fraction (θsma), and the half spacing (d) between equivalent parallel fractures. As an example this study used soils in the Des Moines lobe (Mollisols with textures ranging from sandy loam to silty clay). Data used to calculate model parameters included wet‐end K‐θ‐h and K(h), and results from image analysis. For the MACRO model, the parameters fit the equations best when hb was assumed to be 30 mm. For the measured data with assumed hb = 30 mm, n* had a median of 2.1 and a range from 0 to 5.2, median Kb was 15 mm h−1 with a range from 1 to 100 mm h−1, and the median Ks was 122 mm h−1 with a range from 7 to 741 mm h−1. The calculated d ranged from 1 to 847 mm, and θsma ranged from 0.001 to 0.053 m3 m−3. Depending on the data available, the various techniques can be used to determine input parameters for preferential flow models.
Correlating Manganese X‐Ray Absorption Near‐Edge Structure Spectra with Extractable Soil Manganese
Authors: Guest Christopher A. , Schulze Darrell G. , Thompson Ian A. , Huber Don M.
Published: July 2010

Manganese redox chemistry plays an important role in Mn uptake by plants, ecotoxicology of trace elements associated with Mn oxides, and the etiology of some soil‐borne plant fungal diseases. Manganese solubility is closely related to oxidation state, but direct measurement of Mn oxidation state has been difficult. We used x‐ray absorption near‐edge structure (XANES) spectroscopy to determine the relative proportions of Mn(II), Mn(III), and Mn(IV) in four soils, and correlated this with Mn solubility obtained from a sequential extraction procedure that consisted of: (i) 1MpH 7 ammonium acetate (Ac), (ii) 0.5MpH 2.9 CuSO4or 1MpH 3 NH4OAc, (iii) 0.018Mquinol in 1MpH 7 NH4OAc, and (iv) dithionite‐citrate‐bicarbonate (DCB). In moist aerated soil, most of the Mn was present as Mn(IV) and XANES spectroscopy tracked its progressive removal with increasingly aggressive extractants. Lowering the pH from 7 to 3 resulted in solid state reduction of Mn(IV) to Mn(III) within the soil Mn minerals without release of Mn to solution. After a 7‐d microbial reduction treatment, most of the Mn occurred as Mn(II), 2/3 of which was extracted by pH 7 NH4Ac, while the remaining 1/3 was extracted by pH 3 NH4Ac. The XANES spectra suggest that this acid soluble Mn(II) phase is not rhodocrosite (MnCO3), but its exact form (solid solution in calcite or MnPO4) still remains to be determined. In both aerated and reduced soils, a considerable fraction of the total Mn occurs as Mn(III), presumably incorporated into the structure of Mn and Fe oxides. Rapid air drying of a microbially reduced soil prevented reoxidation of the reduced Mn and preserved the distribution of Mn in the different extractable Mn pools.
Soil Chemical Properties Controlling Zinc2+ Activity in 18 Colorado Soils
Authors: Catlett Kathryn M. , Heil Dean M. , Lindsay Willard L. , Ebinger Michael H.
Published: July 2010

Zinc is a heavy metal of much interest since it is a plant micronutrient as well as a potential contaminant in soils. In soil solution, the speciation of Zn, and thus the free Zn activity, determines the plant availability of Zn as a micronutrient and its characteristics as a heavy metal contaminant. A better understanding of the mechanisms that control free Zn activity could improve soil treatments of Zn deficiency or toxicity. Possible controlling mechanisms for Zn activity include adsorption or precipitation. In our study, Zn2+ activity was measured by chelation and was related to soil properties for 18 alkaline soils from three farms in eastern Colorado. Soil organic C (OC) and pH were statistically significant parameters in a multiple regression with log Zn2+ activity. The significance of OC may suggest that adsorption onto organic matter controls Zn solubility in some of our soils. Log Zn2+ activities plotted with pH fell near the soil‐Zn solubility line. However, the slope of the regression line was −1 rather than an expected −2, which indicates that another mechanism besides precipitation and dissolution of soil Zn may occur. Another possibility is that there are two different regions of solubility, one below pH 8.4 and one above pH 8.4. It is suggested that free Zn ions may adsorb on organic matter in a region of low pH and may precipitate as franklinite or other minerals, such as a Zn‐containing kerolite, at high pH.
Desorption Kinetics of Yttrium, Lanthanum, and Cerium from Soils
Authors: Wen Bei , Shan Xiao-quan , Lin Jin-ming , Tang Gui-gang , Bai Nai-bin , Yuan Dong-an
Published: July 2010

Study on desorption kinetics of Y, La, and Ce from soils is of importance because it relates to the bioavailability and potential toxicity of rare‐earth elements. In the present study, a column‐flow method and three models (first‐order, two site first‐order, and log‐normal distribution first‐order kinetics models) were used to describe the desorption kinetics of Y, La, and Ce from four Chinese soils with different physicochemical properties. A high desorption percentage of Y (87.1–96.6%), La (89.9–98.5%), and Ce (57.6–96.4%) from Yingtan soil was attributed to the low soil pH 5.43 and low organic matter of 1.53%. In contrast, a low percentage of Y (27.5–45.7%), La (27.6–53.6%), and Ce (1.09–50.8%) sorbed by Beijing, Tongjiang, and Haerbin soils desorbed probably because of the higher soil pH values of 8.24, 7.16, 7.23, and increased organic matter (36.4%) in Haerbin soil. The results also suggest that the first‐order kinetics model did not offer an acceptable description of the data (R2< 0.90). However, excellent agreements were achieved between the experimental data and fits to the latter two kinetic models (R2> 0.99). The parameters derived from the kinetic equations indicated that increasing the initial sorption period from 1 to 20 wk could lead to a strong binding of rare‐earth elements, resulting in slower desorption.
Identification of Phenolic Acid Composition of Alkali‐extracted Plants and Soils
Authors: Martens Dean A.
Published: July 2010

Phenolic acids (PAs) released from plant residues have been implicated as important components in a variety of soil processes. To evaluate the role of plant PAs in soil processes, a quantitative alkaline extraction, solid‐phase purification, and gas chromatographic protocol was developed for identification of the composition and concentration of plant and soil PAs. Water‐soluble or EDTA‐exchangeable PAs were not detected in soil. Alkaline hydrolysis (1MNaOH) at ambient temperatures was required to extract ester‐linked phenolics and alkaline hydrolysis (4MNaOH) with heat extracted ether‐linked PAs present in plant and soil material. Purification of NaOH‐extracted PAs by polymeric solid‐phase extraction with gas chromatographic flame ionization and mass spectral analysis of nonderivatized extracts resulted in a highly reproducible and accurate method for the saponifiable PAs. The method quantified plant and soil PAs as ethanone (acetylbenzene), benzaldehyde, and benzoic‐ and cinnamic‐acid derivatives. The majority of soil PAs was identified as modified cinnamic acids originating from vascular plant tissue. Comparison of the described method with a standard acid digestion (12MH2SO4) and gravimetric determination of lignin in plant residues found that interferences formed by strong acid digestion of plant residues such as soybean [Glycine max (L.) Merr.] or clover (Trifolium pratenseL.) containing higher carbohydrate and protein contents resulted in an overestimation of plant lignin content when measured by the acid digestion‐gravimetric method. Since the majority of soil PAs originate from vascular plants and are not microbial in origin, the composition of ester‐linked PAs in soils may be an important indicator of the quantity of plant residue C present in soils under different management systems.
Charcoal Carbon in U.S. Agricultural Soils
Authors: Skjemstad Jan O. , Reicosky Donald C. , Wilts Alan R. , McGowan Janine A.
Published: July 2010

High levels of charcoal C resulting from repeated historical burning of grasslands, open woodlands, and agricultural crop residues have been reported in soils from Australia and Germany. In this study, five U.S. soils were selected from long‐term research plots in widely different agricultural areas. The charcoal C content was estimated on each soil using a combination of physical separation, high energy photo‐oxidation and solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy. These analyses showed that all five soils contained measurable amounts of charcoal C, <53 μm in size and ranging from 1.8 to 13.6 g C kg−1 soil and constituted up to 35% of the soil total organic C (TOC). Scanning electron microscopy showed that the charcoal material had a plant‐like morphology but were blocky and had fractured edges. These particles were similar in morphology to those separated from Australian and German soils. The implications of this material, which must be highly resistant to microbiological decomposition, to the soil C cycle are discussed.
A Spodosol‐Entisol Transition in Northern Michigan
Authors: Schaetzl Randall J.
Published: July 2010

Soils in northern lower Michigan, all formed in sandy glacial outwash, were examined to determine the effects of vegetation and fire frequency vs. climate on their development. To accomplish this, soil development was quantified for 13 pedons that span a region known as the Grayling Fingers. Next, a GIS was used to examine spatial interrelationships among the following data sets for the Fingers area: soils, climate, and presettlement vegetation. The 13 sampled pedons span a major pedologic ecotone between an area of strongly expressed spodic morphology (with hardwood forests, low fire frequencies, and deep snowpacks) and one where soils are Psamments. The Psamment area is dominated by jack pine and oak barrens, which frequently burned in presettlement time, and have much less snow cover in winter. The texture and mineralogy of all pedons are generally similar, thereby ruling out parent material as a controlling factor in their development. The relationships among vegetation patterns and soil development remain unclear in this area. Spatial relationships among snowfall amounts and snowpack thicknesses, however, correlate extremely well to soil development patterns. Thus, I conclude that in this region, patterns of soil development are related primarily to the influence of snowmelt infiltration and its previously documented impact on podzolization. Overstory vegetation may provide a strong, reinforcing influence or may be reacting in turn as a dependent variable to soil development and soil moisture during spring, as impacted directly by snowmelt infiltration.
Intraseasonal Soil Macroaggregate Dynamics in Two Contrasting Field Soils Using Labeled Tracer Spheres
Authors: Plante A. F. , McGill W. B.
Published: July 2010

Several studies have hypothesized that increased turnover of soil aggregates promotes soil organic matter losses under cultivation; while others suggest that organic matter protection requires occlusion into aggregates. However, few direct observations of aggregate dynamics are reported in the literature. A 2‐yr field study was performed to observe active organic C dynamics and soil macroaggregate dynamics in two contrasting soils. Dysprosium‐labelled tracer spheres were applied to field plots to observe soil macroaggregate dynamics, while CO2‐evolution during 10‐d laboratory incubations was used to measure active C dynamics. Results of biochemical analyses showed higher active C turnover in the low C soil, suggesting a lower proportion of incoming organic matter was protected when compared with the high C soil. No net aggregation or degradation was determined over the long‐term, suggesting the soil was at steady‐state. However, aggregation followed a cyclical pattern reset by the over‐winter period and tillage. Tracer incorporation into large macroaggregates was observed within 9 d after tillage, reaching a maximum of 40 to 60% tracer incorporation into >1‐mm aggregates after 72 d. A rapid approach to equilibrium within the study period reflected rapid dynamics of macroaggregates in both soils studied. Slower macroaggregate dynamics in the high C soil were attributed to sustained aggregate stability and resiliency at the end of the growing season. Based on observations of macroaggregate dynamics in soils with contrasting active organic C dynamics, we suggest that rapid macroaggregate turnover not only results in the exposure of labile organic matter but also provides a mechanism for the occlusion and physical protection of particulate organic matter.
Evaluation of Uncoated and Coated Time Domain Reflectometry Probes for High Electrical Conductivity Systems
Authors: Nichol Craig , Beckie Roger , Smith Leslie
Published: July 2010

High sample electrical conductivity reduces the quality of a time domain reflectrometry (TDR) waveform by the loss of signal amplitude. Two strategies are examined to obtain higher signal/noise waveforms: (i) waveform differencing by remote diode shorting and (ii) covering probe conductors with resistive coatings. Experiments using electrically conductive water solutions (0–5 dS m−1) and three‐rod Zegelin type probes show conventional dual‐tangent waveform analysis and waveform differencing using manual short circuits can accurately determine travel time but the remote diode shorting method can be systematically biased by the electrical properties of the diodes used. Three‐rod Zegelin‐type probes with a high resistance coating on the central rod permit collection of analyzable waveforms for solutions with electrical conductivities at least as high as 70 dS m−1 Dual‐tangent analysis of the raw waveform is found to be more accurate than the remote diode shorting method within water solutions and within silica sand saturated with an electrically conductive water solution. The probe coating creates a nonlinear relationship between the apparent dielectric permittivity estimated using a coated probe and the actual sample apparent dielectric permittivity. Experimental measurements of this relationship can be fitted using an equation of the form for a coaxial cell. A three‐rod coated probe with a single diode at the probe head is a practical means to collect interpretable waveforms in media with high electrical conductivity. However, measurements of travel time alone may not be sufficient to determine water content in soils with high concentrations of dissolved ions in the soil water solution.
Flow Detachment by Concentrated Flow on Smooth and Irregular Beds
Authors: Giménez Rafael , Govers Gerard
Published: July 2010

Historically, soil detachment by overland flow has mainly been studied using small samples with smooth surfaces. It may be questioned to what extent information from such experiments can be applied to predict flow detachment in actively eroding rills which are characterized by rough irregular bed surfaces. To evaluate how flow detachment on rough and smooth beds are related, two types of laboratory experiments were carried out: natural rill experiments, where a rill could freely develop; and small sample experiments, where small boxes with smooth surface were used. Soil conditions in both types of experiments were kept as constant as possible. Flow hydraulics and sediment load were recorded in detail during each experiment. Our experiments show that unit length shear force and shear stress are the most universal detachment predictor in rills (i.e., the relationship between these variables and soil detachment is independent of bed geometry). Other hydraulic variables can also be successfully related to flow detachment on a given bed type (smooth or rough), but they cannot accommodate for the effect of changing bed geometry. The fact that total shear stress controls flow detachment rather than grain shear stress or unit stream power implies that the coupling between sediment detachment and sediment transport is more complex than is presently assumed. A detachment prediction approach using hydraulic parameters based on unit length may allow a more accurate and simpler way to estimate sediment detachment in rills than a predictor, which needs an a priori calculation of flow width.
Evidence for Fungal Dominance of Denitrification and Codenitrification in a Grassland Soil
Authors: Laughlin Ronald J. , Stevens R. James
Published: July 2010

Fungi are capable of nitrification and denitrification and often dominate the microbial biomass of temperate grassland soils. We determined the contributions of bacteria and fungi to N2O and N2production in a grassland soil from Northern Ireland by combining the substrate‐induced respiration inhibition method and the15N gas‐flux method. Streptomycin (C21H39N7O12) was used as the bacterial inhibitor and cycloheximide (C15H23NO4) as the fungal inhibitor. By labeling the NH4and NO3pools, we tested the hypothesis that fungi produce N2O and N2solely by the reduction of NO3Cycloheximide decreased the flux of N2O by 89% and streptomycin decreased the flux by 23%, indicating that fungi were responsible for most of the N2O production. All of the N2O was derived from NO3reduction. Labeled N2was only detected in control and streptomycin treatments. The distribution of the15N atoms in the labeled N2indicated that the source of the labeling was predominantly the NO3pool, but that the process of formation was not dominated by denitrification. Codenitrification, where a15N atom from labeled nitrogen dioxide (NO2) combines with a14N atom from a natural abundance source, was proposed as the process forming labeled N2About 92% of the labeled N2was estimated to be due to codenitrification and 8% due to denitrification. The flux of N2O was always greater than the flux of N2, the mole fraction of N2O averaging 0.7. Fungal denitrification could be of ecological significance because N2O is the dominant gaseous end product.
Differentiating Soil Types Using Electromagnetic Conductivity and Crop Yield Maps
Authors: Anderson-Cook C. M. , Alley M. M. , Roygard J. K. F. , Khosla R. , Noble R. B. , Doolittle J. A.
Published: July 2010

Variable rate technology enables management of individual soil types within fields. However, correct classification of soil types for mid‐Atlantic coastal plain soils are currently impractically expensive using an Order I Soil Survey, yet variable rate fertilizer application based on soil type can be highly effective. The objectives of this study were to determine if apparent electromagnetic conductivity (ECa) alone or combined with previous year crop yields using global positioning system technology can provide a useful alternative to detailed soil mapping. The site contained alluvial soils ranging from Bojac 1 and 2 (coarse‐loamy, mixed, thermic, Hapludults) to Wickham 3 and 4 (fine‐loamy, mixed, thermic, Ultic Hapludalfs). The two fields totaled approximately 24 ha. A statistical nonparametric classification method, called recursive binary classification trees, was used to determine how well soil types could be classified. Electromagnetic conductivity readings and crop yields were positively correlated. Broad patterns in the relationship between soil types and ECa readings and crop yields existed for all crop combinations considered. Lower ECa readings and crop yields corresponded to the Bojac soils, while higher ECa readings and crop yields were categorized as Wickham soils. Electromagnetic induction alone correctly classified the soils into broad categories of Bojac or Wickham with over 85% accuracy. When ECa was combined with crop yield data, correct classification rose to over 90%. More precise classification into Bojac 1, Bojac 2, and Wickham soils yielded slightly lower correct classifications ranging from 62.6 to 81.2% for ECa alone, and 80.3 to 91.5% when combined with various crop yields.
Modeling Water and Soil Redistribution in a Dynamic Landscape Context
Authors: Schoorl J. M. , Veldkamp A. , Bouma J.
Published: July 2010

Soil suitability assessments for land use planning are commonly based on on‐site specific topographic, soil, and climatic characteristics, and are often neglecting the effects of physical landscape processes by water. The spatial and temporal variability of the landscape requires specific input data and modeling procedures. Existing studies aiming at the landscape level often are data‐driven and operating at detailed resolutions of seconds and hours for single slopes or catchments. This study aims at the coarser level of multiple catchments over a period of 10 yr. A dynamic modeling approach is applied to a study area for the effects of soil redistribution within a landscape (run‐on, run‐off, erosion, and sedimentation) on subsequent soil water availability. Simulation scenarios include factors of water routing, soil depth, and erodibility. Different approaches for surface run‐off routing have a major influence on the magnitude and spatial patterns of soil redistribution. Also initial conditions such as soil depth, parent material, and erodibility have spatial impacts upon soil erosion and sedimentation within the landscape. Locally decreasing water storage capacity (on‐site) may cause increased run‐off and erosion at lower positions in the landscape (off‐site). Localized soil redistribution can cause significant changes in actual soil depth and indirectly affect available soil water. The changing patterns of soil redistribution for the different scenarios are both related to modeling techniques as well as to the implemented boundary conditions. This study indicates that at the landscape scale spatial variability in for example soil properties is inherent to both the complexity of the landscape (parent material) and on‐site and off‐site effects of controlling processes.
Assessment of a Method to Measure Temporal Change in Soil Carbon Storage
Authors: Ellert B. H. , Janzen H. H. , Entz T.
Published: July 2010

Sensitive methods are essential to resolve small changes in soil C storage, such as those attained in sequestration projects, against much larger quantities of C already present. To measure temporal changes in C storage we proposed a high‐resolution method based on collecting volumetric soil cores from a microsite (4 by 7 m), marking core locations to intersperse multiple cores collected initially and in a subsequent sampling year, rigorous analytical quality control, and calculating soil C pool sizes with proper corrections for unequal soil masses. To evaluate the method, we measured the recovery of 3.64 Mg C ha−1 added as coal dust to microsites. We calculated C stored in successive soil layers of both fixed volume and equivalent mass. We inferred coal C recovery from spatial comparisons between coal‐amended and unamended plots, and from temporal comparisons between soil samples collected before and after coal addition. The comparisons among C storage showed effective recovery of added coal C, but only for paired temporal differences based on calculations of organic C storage in an equivalent soil mass. With spatial comparisons, coal C became undetectable when soil thickness exceeded 35 cm. With temporal comparisons, coal C recovery ranged from 91 to 106%, provided differences were calculated for successively thicker layers of equivalent soil mass. In contrast, recovery was only 64 to 82% when temporal differences were calculated for layers of fixed soil volume. The method is useful to quantify small temporal changes in soil organic C storage within microsites, and possibly over more extensive areas with sufficient samples to characterize spatial variability.
Leaching of Imidacloprid and Procymidone in a Greenhouse of Southeast of Spain
Authors: González-Pradas Emilio , Ureña-Amate María Dolores , Flores-Céspedes Francisco , Fernández-Pérez Manuel , Garratt James , Wilkins Richard
Published: July 2010

The leaching processes of the insecticide imidacloprid [1‐(6‐chloro‐3‐pyridinylmethyl)‐N‐nitro‐2‐imidazolidinylideamine] and the fungicide procymidone [N‐(3,5‐dichlorophenyl)‐1,2‐dimethyl‐1,2‐cyclopropanedicarboximide] in a greenhouse soil from the southeastern of Spain were investigated. Four separate pesticide applications were made at dose rates considerably higher than the recommended in normal agronomic practice, representing a worst case scenario. Soils samples were taken to a depth of 40 cm at time intervals after each application and analyzed by high performance liquid chromatography (HPLC). The partition coefficients (Kd) of the samples for imidacloprid and procymidone were calculated by carrying out batch experiments and fitting the experimental data point to the linear isotherm equation. Soil tension, water content, and temperature measurements were also determined during all the experiments. Although the results show a high degree of variability, rapid transport of pesticides through the soil occurred which increases the possibility of groundwater pollution. The leaching of these pesticides, particularly procymidone, generally thought of as immobile, might be possible through formation of stable soluble organic fraction–pesticide interactions in solution, allowing an increased groundwater contamination potential.
Extracellular Enzyme Activity Beneath Temperate Trees Growing Under Elevated Carbon Dioxide and Ozone
Authors: Larson Jennifer L. , Zak Donald R. , Sinsabaugh Robert L.
Published: July 2010

Soil microorganisms are limited by the amount and type of plant‐derived substrates entering soil, and we reasoned that changes in the production and biochemical constituents of plant litter produced under elevated CO2and O3would elicit physiological changes in soil microbial communities. To test this idea, we studied microbial activity beneath trembling aspen (Populus tremuloidesMichx.), paper birch (Betula papyriferaMarsh.), and sugar maple (Acer saccharumMarsh.) growing under experimental atmospheric CO2(ambient and 522.7 μL L−1) and O3(ambient and 54.5 nL L−1). To assess changes in microbial community function, we measured microbial biomass, respiration, and the metabolism of root‐derived substrates using BIOLOG GN microplates. We also measured the activity of phosphatase, leucine aminopeptidase, α‐glucosidase, N‐acetylglucosaminidase, cellobiohydrolase, phenol oxidase, and peroxidase enzymes, which are involved in plant and fungal litter decomposition. Microbial biomass and respiration were not significantly altered by elevated CO2and O3Cellobiohydrolase activity significantly increased under elevated CO2; however, this response was eliminated by elevated O3N‐acetylglucosaminidase activity also increased under elevated CO2, but elevated O3did not significantly alter this response. We found no difference in the metabolism of amino acids, organic acids, and simple carbohydrates, suggesting our experimental treatments did not alter the use of these substrates by soil microorganisms. Our analysis indicates that changes in plant growth in response to elevated CO2and O3alters microbial metabolism in soil.
Soil Organic Carbon Sequestration Rates by Tillage and Crop Rotation
Authors: West Tristram O. , Post Wilfred M.
Published: July 2010

Changes in agricultural management can potentially increase the accumulation rate of soil organic C (SOC), thereby sequestering CO2 from the atmosphere. This study was conducted to quantify potential soil C sequestration rates for different crops in response to decreasing tillage intensity or enhancing rotation complexity, and to estimate the duration of time over which sequestration may occur. Analyses of C sequestration rates were completed using a global database of 67 long‐term agricultural experiments, consisting of 276 paired treatments. Results indicate, on average, that a change from conventional tillage (CT) to no‐till (NT) can sequester 57 ± 14 g C m−2 yr−1, excluding wheat (Triticum aestivum L.)‐fallow systems which may not result in SOC accumulation with a change from CT to NT. Enhancing rotation complexity can sequester an average 20 ± 12 g C m−2 yr−1, excluding a change from continuous corn (Zea mays L.) to corn‐soybean (Glycine max L.) which may not result in a significant accumulation of SOC. Carbon sequestration rates, with a change from CT to NT, can be expected to peak in 5 to 10 yr with SOC reaching a new equilibrium in 15 to 20 yr. Following initiation of an enhancement in rotation complexity, SOC may reach a new equilibrium in approximately 40 to 60 yr. Carbon sequestration rates, estimated for a number of individual crops and crop rotations in this study, can be used in spatial modeling analyses to more accurately predict regional, national, and global C sequestration potentials.
Modifying FHANTM 2.0 to Estimate Phosphorus Concentrations in Runoff from Mid‐Atlantic Coastal Plain Soils
Authors: Vadas Peter A. , Sims J. Thomas , Leytem April B. , Penn Chad J.
Published: July 2010

Phosphorus lost from agricultural soils has been identified as a nonpoint source pollutant of surface waters in Delaware and throughout the Mid‐Atlantic Coastal Plain. The Field Hydrologic and Nutrient Transport Model (FHANTM) 2.0 can help identify areas with a high potential for P loss, but the method used to estimate P concentrations in runoff waters needs reevaluation. The equationPd=KPotαWβhas been proposed to predict P desorption from soil to runoff. To test this equation for use in Delaware and the Mid‐Atlantic Coastal Plain, we conducted rainfall simulations for 14 Delaware and Maryland soils packed into 5 by 20 by 100 cm boxes at a rainfall intensity of 7.5 cm h−1and a slope of 5% for 30 min. We collected all runoff and measured an average soluble P concentration in runoff for the entire simulation. We predicted P concentrations using the above equation and compared them with measured values. Predicted values were well correlated to measured values (r2= 0.78), but P concentrations were overpredicted by an average of 20 times. After we added a calibration factor to the equation based on the amount of sediment lost in runoff during the rainfall simulation, measured and predicted soluble P concentrations exhibited a nearly 1:1 relationship. Results suggest that eroded sediment in runoff may resorb P from the runoff solution, causing the desorption equation to overpredict soluble P concentrations in runoff.
Humus Index
Authors: Ponge Jean-François , Chevalier Richard , Loussot Philippe
Published: July 2010

A quantitative assessment of forest humus forms is suggested, on the basis of a scale ranging from 1 (Eumull) to 7 (Dysmoder) which is called thehumus indexRegression analyses showed that this index was well‐correlated with several morphological as well as chemical variables describing forest floors and topsoil profiles: thickness of the Oe horizon, depth of the crumby mineral horizon, Munsell hue, pHKCland pHH2O, H and Al exchangeable acidity, percentage base saturation, cation‐exchange capacity, exchangeable bases, C and N content and available P of the A horizon. The suggested humus index could be used as a cheap and rapid method for the bulk assessment of organic matter accumulation, soil acidity, and soil biological activity.
The Non‐Limiting and Least Limiting Water Ranges for Soil Nitrogen Mineralization
Authors: Drury C. F. , Zhang T. Q. , Kay B. D.
Published: July 2010

A better understanding of factors controlling N mineralization would improve our ability to estimate fertilizer requirements more accurately. Net N mineralization approaches a small reaction rate at low and high water contents, giving rise to lower and upper limiting water contents and the least limiting water range (LLWR). Within the LLWR, there is a range in water contents in which mineralization is largely independent of water content, that is, the non‐limiting water range (NLWR). An incubation study was conducted to determine the LLWR and NLWR for five soils with different properties, and two relative compaction levels with and without the addition of a legume crop residue. These soils were incubated for 1 and 3 mo at eight water contents. Net N mineralization increased with incubation time and legume addition and varied curvilinearly with water‐filled pore space (WFPS). Logistic functions were generated to establish the relationships between net N mineralization and WFPS (%) and to calculate LLWR and NLWR. The mean NLWR was 32.2% after 1 mo and decreased to 18.1% after 3 mo whereas the mean LLWR was 55% after 1 mo and increased to 70.8% after 3 mo. The LLWR increased with organic C or total N but decreased with the addition of legume residue. The NLWR decreased with clay content and with the addition of legume after 3 mo. Emissions of N2O were greatest at water contents near the upper limit of the LLWR. Use of the NLWR to differentiate soils on the basis of the sensitivity of N mineralization to variation in water content is illustrated.
Phosphorus Availability under Continuous Point Source Irrigation
Authors: Ben-Gal Alon , Dudley Lynn M.
Published: July 2010

Phosphorous fertigation applied in a microirrigation system provides increased P use efficiency relative to traditional banding. This project investigated the hypothesis that continuous, low‐intensity irrigation can provide plants with available P more efficiently than intermittent drip fertigation. Objectives of the study were to characterize water and P distribution when provided to soil by a continuous point source, and to raise P fertilizer efficiency by increasing plant available P without augmenting P application rates through maintenance of relatively constant conditions within the root zone. Plant response, soil P distribution, and soil moisture were compared for an intermittent irrigation regime, giving water for 4 h once every 2 d, to continuous application of the same amount of water in both a water‐solute simulation model (Hydrus‐2d) and in greenhouse‐lysimeter experiments with and without a corn crop on a calcareous sandy loam soil. Results from both the simulation and the lysimeter‐soil study showed that the hypothesized zones of increased available P materialized when P‐laden water was applied continuously at low application rates to an un‐cropped soil. Extractable P concentrations in the soil immediately surrounding the point source were found to be 20 to 25% higher in continuously irrigated soil as compared with pulsed irrigation. After 40 d of growth, corn plants grown under continuous fertigation yielded 20% greater biomass than plants irrigated with the same water quantity and quality once every 2 d. Phosphorus content of corn leaves was 25% greater for the continuous treatment as compared with the pulsed treatment.
Subaqueous Soil‐Landscape Relationships in a Rhode Island Estuary
Authors: Bradley Michael P. , Stolt Mark H.
Published: July 2010

Subaqueous soils occur from the lower limit of the intertidal zone to a depth of <2.5 m in protected estuarine coves, bays, inlets, and lagoons. These soils support a diverse floral and faunal assemblage and are a vital component of the estuarine ecosystem. Only recently have pedologists considered these substrates soil, thus, very few subaqueous soils have been characterized and relationships between subaqueous soils and associated subtidal landforms are unknown. In this study, we investigated shallow‐subtidal settings and associated subaqueous soils within a 116‐ha area of a Rhode Island estuary. Our objectives were to gain an understanding of soil distribution within a coastal lagoon and to elucidate subaqueous soil‐landscape relationships within differing geomorphic settings. Twelve submerged landscape units were delineated based on water depth, slope, landscape shape, and the depositional environment. Soils were sampled, described, and representative samples from each landscape unit were analyzed for pH, electrical conductivity, CaCO3, particle‐size distribution, and organic matter. The Lagoon Bottom landscape unit was mostly comprised of Typic Hydraquents (70%). These soils had the finest particle‐size distribution of all soils sampled (silt contents ranged from 23 to 64%; clay contents ranged from 16 to 30%). All the subaqueous soils found within the Storm‐surge Washover Fan Flat were classified as Typic Sulfaquents. Greater than 75% of the Barrier Submerged Beach, Mainland Submerged Beach, Shoal, and the Mid‐lagoon Channel landscape units contained Typic Endoaquents. Thapto‐histic Hydraquents were found in 60% of the Mainland Cove landscape units. These relationships suggest that landscape units can be used to model subaqueous soil distribution at the subgroup taxonomic level. Understanding of the distribution of these soils and the associated characteristics should prove valuable to coastal specialists managing these critical resources.