bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Water Accumulation under Different Precipitation, Potential Evaporation, and Straw Mulch Conditions
Authors: Ji Shangning , Unger Paul W.
Published: July 2010

Small precipitation amounts generally have low effectiveness for crop production in semiarid regions. Our objective was to determine potential evaporation (PE; 3, 6, or 12 mm d−1) and straw‐mulch (0, 2, or 4 Mg ha−1) rate effects on water accumulation in Pullman (Torrertic Paleustoll, 37% clay) and Randall (Ustic Epiaquerts, 57% clay) soils when small amounts of water (simulated precipitation; 5, 10, or 20 mm) were applied. Water accumulation was affected in order by water‐application amount > PE > mulch > soil clay content. Mulching at 2.0 and 4.0 Mg ha−1 increased storage efficiency of 5‐mm water applications by >60 and 100%, respectively, in both soils when PE was 3 mm d−1 With 5‐mm water applications and 6 mm d−1 PE, >10% of applied water was stored in mulched soils, but not in bare soils. When PE was 12 mm d−1, little storage from 5‐mm applications occurred in bare soils, but 3 to 6% storage occurred when the mulch rate was 4.0 Mg ha−1 To obtain >10% water storage when the PE rate was 12 mm d−1, 10‐mm water applications and a 2 Mg ha−1 mulch rate were necessary. Evaporation rates were slightly higher for mulched soil than for bare soil in the late stage. Soil clay contents were correlated positively with accumulative evaporation in the late stage. Soil wetting depth increased with increases in mulch rates. Based on this study, straw mulching has potential for increasing soil water storage from small amounts of precipitation.
Detecting Treatment Differences in Soil Carbon and Nitrogen Resulting from Forest Manipulations
Authors: Homann P.S. , Bormann B.T. , Boyle J.R.
Published: July 2010

Forest management practices may alter soil properties, but experimental evaluation of treatment effects is often difficult because large soil variability yields poor statistical sensitivity. This study was conducted to determine if pretreatment soil sampling enhances our ability to detect treatment differences in Pacific Northwest forests. We used statistical simulation and data from 271 pretreatment 30‐cm‐deep soil cores taken from 70‐ to 100‐yr‐old post‐fire Douglas‐fir [Pseudotsuga menziesii(Mirb.) Franco] stands at the Siskiyou National Forest in southwestern Oregon. At this site, an unmanipulated control and six treatments of overstory species and woody debris are being established on 6‐ha plots and replicated in three blocks. If only post‐treatment measurements were made, the minimum detectable difference (MDD) between extreme treatments would be 26 to 57% of current soil C and N concentrations (g kg−1) and masses (kg m−2), with C generally having smaller relative MDDs than N. In contrast, if the differences between post‐ and pretreatment were evaluated, relative MDDs for C properties would remain the same, but those for N would decrease by as much as one‐half because N has greater pretreatment variability among plots than C. Masses of C and N, which incorporate information about rock volume and either soil mass or bulk density, have relative MDDs as small as one‐half of those associated with concentrations. Evaluation of other sites is required to determine if these observations are consistent for forests in general and, thus, applicable to the design of sampling strategies in large‐scale experiments.
Potassium‐Selective, Halloysite‐Rich Soils Formed in Volcanic Materials from Northern California
Authors: Takahashi T. , Dahlgren R.A. , Theng B.K.G. , Whitton J.S. , Soma M.
Published: July 2010

Several subsoil horizons of Andic Haploxeralfs, formed in volcanic ejecta under a xeric moisture regime in northern California, retain large amounts of exchangeable K+ and show high K+ saturation. The relationships between clay mineralogy, mineral charge characteristics, and exchangeable K+–Ca2+ selectivity were examined. Clay mineralogy and surface charge were assessed by x‐ray diffractometry (XRD), differential thermal analysis (DTA), transmission electron microscopy, x‐ray photoelectron spectroscopy (XPS), 27Al‐nuclear magnetic resonance (NMR) spectroscopy, total elemental analysis, surface area measurements, and determination of K+–Ca2+ selectivity coefficients. Kaolin minerals with a tubular morphology comprise 75 to 91% of the clay‐size fraction in the subsoil horizons. Kaolinite was prevalent in the surface horizons, while halloysite concentrations and the degree of halloysite hydration increased with depth. No detectable amounts of 2:1 layer silicates, 1:1–2:1 mixed‐layer clays, or zeolites (e.g., clinoptilolite) were found in the clay‐size fraction of the subsoil horizons. Soil samples dominated by halloysite showed a strong selectivity for K+ The clay fractions (<2 μm) have cation‐exchange capacity (CEC) values ranging from 19 to 26 cmolc kg−1 and surface areas from 90 to 112 m2 g−1 The variable and permanent charge components were 11 and 20 cmolc kg−1, respectively. The 27Al‐NMR spectrum of the halloysite‐rich clay indicates a poorly ordered kaolin and a tetrahedral Al content of ≈2%. While a disordered halloysite may be responsible for the high surface area, CEC, and K+ selectivity displayed by these soils, the contribution from 2:1 layer silicates and 1:1–2:1 mixed‐layer clays in the silt and sand fractions and Fe oxide surface coatings must also be considered.
Rheological Properties of Wet Soils and Clays under Steady and Oscillatory Stresses
Authors: Ghezzehei Teamrat A. , Or Dani
Published: July 2010

Tilled agricultural soils are in a constant state of change induced by variations in soil strength due to wetting and drying and compaction by farm implements. Changes in soil structure affect many hydraulic and transport properties; hence their quantification is critical for accurate hydrological and environmental modeling. This study highlights the role of soil rheology in determining time‐dependent stress–strain relationships that are essential for prediction and analysis of structural changes in soils. The primary objectives of this study were (i) to extend a previously proposed aggregate‐pair model to prediction of compaction under external steady or transient stresses and (ii) to provide experimentally determined rheological information for the above models. Rheological properties of soils and clay minerals were measured with a rotational rheometer with parallel‐plate sensors. These measurements, under controlled steady shear stress application, have shown that wet soils have viscoplastic behavior with well‐defined yield stress and nearly constant plastic viscosity. In contrast, rapid transient loading (e.g., passage of a tractor) is often too short for complete viscous dissipation of applied stress, resulting in an elastic (recoverable) component of deformation (viscoelastic behavior). Measured viscoelastic properties were expressed by complex viscosity and shear modulus whose components denote viscous energy dissipation, and energy storage (elastic). Results show that for low water contents and fast loading (tractor speed), the elastic component of deformation increases, whereas with higher water contents, viscosity and shear modulus decrease. Steady and oscillatory stress application to an aggregate pair model illustrates potential use of rheological properties towards obtaining predictions of strains in soils.
Deriving Hydrological Parameters for Modeling Water Flow under Field Conditions
Authors: Zavattaro Laura , Grignani Carlo
Published: July 2010

The process of deriving the hydrological characteristics of a soil to parameterize a model at the field scale is not straightforward, especially when various experimental procedures are used to estimate the parameter values. This paper shows the inconsistencies that were encountered when attempting to find the physical and hydrological parameters of two deep loam soils. The parameters were searched for with the aim, and the constraint, of compiling the input file of the LEACHM model, which implements a Campbell's modified K–θ–ψ function approach. The soil water content at saturation was not consistent with the total porosity calculated from measured bulk and particle densities. The water retention curve (RC) measured in the laboratory and the conductivity curve measured in the field were described using modified Campbell functions that were separately parameterized, and results were then compared. The optimized values obtained for the θ–ψ curve were remarkably different from those for the K–ψ curve. Considering the physical nature of a model and the measurability of its parameters as the basic requirements for extending model predictions to sites where validation cannot be provided, possible solutions are to derive all soil properties simultaneously on the same sample and/or with a cofitting procedure, to adjust the measured values of the soil properties to the functional values, in order to combine the measured soil properties with the code requirements, and to modify the code to allow a separate parameterization of the two curves.
Temporal Stability of Spatially Measured Soil Matric Potential Probability Density Function
Authors: Van Pelt R.Scott , Wierenga Peter J.
Published: July 2010

Estimation of mean water status in a field is crucial to effective irrigation water management. Problems encountered with the estimation of mean field soil water status may be attributed to spatial variability of soil physical properties. Several investigators have shown temporal stability of spatial patterns of field measured soil water content, but temporal stability of field measured soil matric potential (ψm), a measure of soil water status more appropriate for irrigation scheduling, has not previously been reported to last for more than a few days within one irrigation cycle. This study investigated the temporal stability of spatial patterns of ψm both within and between sequential irrigation cycles. Sixty locations in a 1‐ha field were outfitted with a 1‐m neutron probe access tube and three tensiometers placed at 0.15‐, 0.3‐, and 0.5‐m depths. The observations obtained from 14 d of soil water content measurements and 46 d of ψm measurements within eight irrigation cycles were analyzed with Spearman's rank correlation coefficients and a relative differencing technique. The results showed temporally stable soil water content spatial patterns and also indicated temporally stable ψm spatial patterns if assumptions of full soil wetting at the beginning of the cycle and uniform evapotranspiration among locations were satisfied. Several locations in the field estimated the field mean ψm to within 10% within a given range of potentials, and a few estimated the field mean to within 20% across the entire range of potentials tested. Other locations estimated the lower and higher percentiles of ψm with similar accuracy.
Impact of Chloride Anions on Proton and Selenium Adsorption by an Aluminum Oxide
Authors: Schulthess C.P. , Hu Zhiqiang
Published: July 2010

The quantity of protons adsorbed for each anion adsorbed by a solid surface is an essential component of surface complexation models. This reaction stoichiometry is often assumed, or it is “confirmed” based on the goodness‐of‐fit of the pH‐dependent adsorption models. This ratio can be experimentally measured, but the resulting measurement may be in error if secondary (unaccounted for) reactions are present that are also consuming or releasing protons. Using selenate and selenite adsorption isotherms on an Al oxide, the proton/anion stoichiometries were determined to be ≈2:1 at high pH values (>6), but they decreased rapidly at low pH values. The stoichiometry is ≈2:1 across a broader pH range when corrections are made for the change in Cl adsorption intensity by Al oxide in the presence of Se anions. Generalizing, if a weakly adsorbing anion is affected by another strongly adsorbing anion, then its impact on the balance of protons adsorbed (or balance of surface charge) must also be monitored. Although the Cl anion is very weakly adsorbing, the matrix needs to be considered as a ternary system consisting of H, Cl, and Se ions. A binary approach, one that views only H and Se ions, will misrepresent the H/Se adsorption ratios, particularly at low pH values.
Temperature Effects on Nickel Sorption Kinetics at the Mineral–Water Interface
Authors: Scheckel Kirk G. , Sparks Donald L.
Published: July 2010

In recent years, innovative studies have shown that sorption of metals onto natural materials results in the formation of new mineral‐like precipitate phases that increase in stability with aging time. While these findings have demonstrated the usefulness of current state‐of‐the‐art molecular‐scale methods for confirming macroscopic data and elucidating mechanisms, basic kinetic and thermodynamic parameters for the formation of the metal precipitates have not been examined. This study examined Ni‐sorption kinetics on pyrophyllite, talc, gibbsite, amorphous silica, and a mixture of gibbsite and amorphous silica over a temperature range of 9 to 35°C. Using the Arrhenius and Eyring equations, we calculated the energy of activation (Ea) and enthalpy (ΔH‡), entropy (ΔS‡), and free energy of activation (ΔG‡), related to the formation of the Ni precipitates. Based on values of Ea (93.05 to 123.71 kJ mol−1) and ΔS‡ (−27.51 to −38.70 J mol−1), Ni sorption on these sorbents was surface‐controlled and an associative mechanism. The ΔH‡ values (90.60 to 121.26 kJ mol−1) suggest, as indicated by Ea values, that an energy barrier was present for the system to overcome in order for the reaction to occur. Additionally, the large, positive ΔG‡ values suggest there is an energy barrier for product formation. Although metal precipitation reactions often occur in the natural environment, this study shows that the rate of these reactions depends strongly on temperature.
Organic Phosphorus Mineralization Studies Using Isotopic Dilution Techniques
Authors: Oehl F. , Oberson A. , Sinaj S. , Frossard E.
Published: July 2010

Soil organic P (Po) mineralization is an important process in P cycling. No accurate method for its quantification is available because any mineralized inorganic P (Pi) may be rapidly sorbed onto the soil solid phase where it cannot be separated from already present PiA method for measuring soil Pomineralization is explored using isotopic dilution techniques under conditions of constant soil respiration rates. First, the specific activity (SA) as affected by physicochemical processes was extrapolated from an isotopic exchange kinetics batch experiment. Second, the SA was assessed during incubation after labeling soil with33PO4Lower SA measured during incubation than extrapolated from the batch experiment was attributed to the release of nonlabeled Pidue to mineralization of nonlabeled PoIn order to separate biological from biochemical mineralization processes, one set of samples was γ‐irradiated to stop the microbial activity while maintaining phosphatase activity. The γ‐irradiated soil revealed higher mineralization rates than the corresponding nonirradiated soil. This was explained by an increase of the amount of easily mineralizable Poderived from killed microbial cells by γ‐irradiation. Consequently, a gross, but overestimated, biochemical P mineralization can be assessed. In the nonirradiated soil, mineralization not only of nonlabeled, but also of recently synthesized labeled Poresulting from microbial turnover, may occur. Thus, in the nonirradiated soil, after several days a gross, biologically and biochemically mediated mineralization is increasingly underestimated. During the first 7 d, the mineralization rate in the nonirradiated soil was 1.7 mg P kg−1d−1, which is an amount approximately equivalent to soil solution P in this soil, indicating that soil P mineralization is a significant process in delivering available Pi
Residue Cover and Surface‐Sealing Effects on Infiltration
Authors: Ruan Huanxiang , Ahuja Laj R. , Green Timothy R. , Benjamin Joseph G.
Published: July 2010

Surface sealing of bare soils often reduces rain infiltration, and crop‐residue cover is commonly used to reduce surface sealing. We conducted numerical experiments to quantify effects of the percentage and distribution of residue cover on infiltration, and to provide guidelines for residue management. Residue cover was simulated over the soil surface in circular patches. Excess surface water from the bare surface‐sealed areas was available for infiltration in nonsealed areas. Numerical simulations were conducted for combinations of (i) soil type, either a clay loam or loamy sand soil; (ii) percentage residue cover (Prc); (iii) saturated hydraulic conductivity of the surface seal (Kc) relative to bulk soil (Ks); (iv) residue‐patch size with a constant Prc; and (v) rainfall intensity. The Kc values had the greatest influence on infiltration as a function of Prc This influence increased with rainfall intensity. For a given Prc, smaller patches gave greater relative infiltration due to differences in the lateral redistribution of infiltrated water. The target values of Prc that provided 95% relative infiltration varied from 40 to 80% for most combinations. Changing the geometry of the residues made no significant difference. We also tested a one‐dimensional model with a spatially averaged saturated hydraulic conductivity (Kce) for both covered and surface‐sealed areas, and found that infiltration into a partially residue‐covered soil could be estimated by the one‐dimensional model for all cases of this study, when Kc > 0. Finally, simulated infiltration qualitatively agreed with data sets of two independent field experiments under similar soil and rainfall conditions.
Effect of Sediment Load on Soil Detachment and Deposition in Rills
Authors: Merten G.H. , Nearing M.A. , Borges A.L.O.
Published: July 2010

According to theory, the rate of detachment of soil particles in rills is reduced as a first‐order function of the amount of sediment load in the flow. The first objective of this study was to determine if experimental results confirmed current detachment‐transport coupling theory. The second objective was to investigate two hypothesized mechanisms responsible for any coupling effect observed: The first mechanism was that since turbulence is known to be a critical factor in detachment by flow, and since it is also known that sediment in water reduces turbulent intensity, it was suggested that sediment in flow reduces detachment via a correspondent reduction in turbulent intensities. This hypothesis was tested indirectly by adding a sediment load that was carried entirely in the suspended state. The second mechanism was that sediment covering the soil bed during the erosion process shields the soil from the forces of flow, thus reducing detachment. This hypothesis was tested by introducing bed‐load sediment. Sediment loads exiting the rill and detachment and deposition along the rill were measured. Detachment was reduced and deposition increased as a linear function of the amount of sediment introduced into the flow. Results indicated that, in general, detachment did decrease according to current theory, but discrepancies in the erosional patterns were observed, which none of the current models explain. Both hypothesized mechanisms of reduction in detachment rates were apparently active in reducing detachment rates, though the shielding mechanism appeared to have a greater impact than did the mechanism associated with a reduction in turbulent intensity.
Nutrient Retranslocation Response of Picea mariana Seedlings to Nitrogen Supply
Authors: Salifu K.F. , Timmer V.R.
Published: July 2010

The hypotheses that retranslocation is controlled by soil nutrient availability or plant nutrient reserves were tested under field conditions for one growing season using nutrient‐loaded and non‐loaded (conventional) black spruce [Picea mariana (Mill.) BSP] seedlings planted on a poor, medium, and rich fertility soil created by equivalent applications of 0, 200, and 400 kg N ha−1, respectively. Growth and nutrient uptake increased with N supply, and was consistently higher in loaded than conventional seedlings, demonstrating the advantage of nutrient loading practices to accelerate seedling growth across the range of soil N tested. Compared to the poor soil, new shoot biomass of loaded seedlings increased by 34 and 134% on the medium and rich soils, suggesting loaded seedlings may be more efficiently transplanted on more fertile sites. Net retranslocation of N, P, and K increased by 569, 185, and 102% by nutrient loading in the nursery, supporting the hypothesis of translocation driven by the magnitude of plant nutrient reserves. However, net N retranslocation diminished with time due to root system expansion that promoted uptake and reduced the need for N redistribution. Net retranslocation of N (the most limiting nutrient) declined with soil N supply, but that of P and K were relatively independent of soil fertility. Increased N availability in the soil enhanced N accumulation in the plants but lowered N retranslocation. We conclude that higher net retranslocation of N on poor soils is a phenotypic adjustment by P. mariana seedlings to maximize N use at low availability.
Estimation of Nitrate Leaching in an Entisol under Optimum Citrus Production
Authors: Paramasivam S. , Alva A.K. , Fares A. , Sajwan K.S.
Published: July 2010

Leaching of fertilizer nutrients and widespread NO3‐N contamination of drinking water wells in proximity to citrus growing regions of central Florida are a serious concern. We evaluated NO3‐N distribution in soil solution at various depths in the vadose zone, and N leaching below the root zone for two cropping seasons under the canopy of 21‐yr‐old Hamlin orange [Citrus sinensis (L.) Osbeck] trees on Cleopatra mandarin (Citrus reticulata Blanco) rootstock, on an entisol of central Florida. The treatments included 112, 168, 224, and 280 kg N ha−1 yr−1 as either dry granular fertilizer (DGF; broadcast, in 4 equal doses) or fertigation (FRT; 15 applications yr−1), and 56, 112, and 168 N kg ha−1 yr−1 as controlled‐release fertilizer (CRF; single application yr−1). Irrigation was scheduled using recommended tensiometer set points as guidelines, with a target wetting depth of 90 cm. The NO3‐N was measured in soil solutions bi‐weekly at 60‐, 120‐, and 240‐cm depths using suction lysimeters (SLs) installed under the tree canopy. The 240‐cm depth sample represented soil solution below the rooting depth of the trees, and the NO3‐N at this depth could contaminate groundwater. At the 60‐ or 120‐cm depths, the NO3‐N concentrations occasionally peaked at 12 to 100 mg L−1, but at 240 cm NO3‐N concentrations mostly remained below 10 mg L−1 The careful irrigation management, split fertilizer application, and timing of application contributed to the low leaching of NO3‐N below the root zone. Calculated NO3‐N leaching losses below the rooting depth increased with increasing rate of N application and the amount of water drained, and accounted for 1 to 16% of applied fertilizer N.
Solute Transport in Layered Soils
Authors: Zhou Liuzong , Selim H. M.
Published: July 2010

In this study, solute transport in multilayered soils where steady flow is dominant was investigated. We considered nonreactive as well as reactive solutes in layered soils with emphasis on nonlinear solute reactivity with the soil matrix. For individual soil layers, solute‐retention mechanisms considered were linear, nonlinear, Langmuir, first‐, second‐, and nth‐order kinetics, and irreversible reactions. The convective‐dispersive equation (CDE) for reactive solutes was solved using the finite difference method. First‐type and a combination of first‐ and third‐type boundary conditions (BCs) for the interface between soil layers were tested. Unlike the first‐type BC, the combined first‐ and third‐type BC always achieved a good solute mass balance in multilayered soils. Physical and chemical properties of each soil layer were assumed to differ significantly from one another. For all retention mechanisms used, our simulation results indicated that solute breakthrough curves (BTCs) were similar, regardless of the layering sequence in a soil profile. This finding is consistent with an earlier finding (Selim et al., 1977), where a linear adsorption mechanism was dominant and contrary to that of Bosma and van der Zee (1992) for nonlinear adsorption. Experimental results based on miscible displacements from soil columns of a two‐layer system [sand over Sharkey (very‐fine, smectitic, thermic Chromic Epiaquerts) clay and Sharkey clay over sand] support our simulation results. Specifically, BTCs for pulse inputs for tritium, as well as for the Ca–Mg system, support the above conclusion. All tritium and Ca–Mg BTCs were well predicted with our multilayered model where independently derived solute physical and retention parameters were implemented.
Nitrogen Response in Cotton as Affected by Tillage System and Irrigation Level
Authors: Bronson K. F. , Onken A. B. , Keeling J. W. , Booker J. D. , Torbert H. A.
Published: July 2010

More than 0.5 million ha of irrigated cotton (Gossypium hirsutum L.) are grown in the Southern High Plains of Texas. Conservation tillage cotton in terminated wheat (Triticum aestivum L.) has been shown to improve water use efficiency and reduce wind erosion. However, limited N fertilizer response research has been done in this system. The objective of this 3‐yr field study at Lubbock, TX was to characterize the response to N fertilizer (0, 28, 56, 84, or 112 kg N ha−1) at varying irrigation levels [0, 25, 50, or 75 % Evapotranspiration (ET) replacement] for conventional and conservation tillage cotton in an Acuff loam (fine loamy, mixed, superactive, thermic, Aridic Paleustoll). Additionally, we tested the chlorophyll meter as an indicator of in‐season N status of cotton and compared it to petiole NO3–N analysis. Cotton lint yields showed a quadratic response to irrigation level in 1996 and 1997, and a linear response in the drought year of 1998. Maximum lint yield varied from 71 to 97 % ET replacement. In 1997 and 1998, cotton lint yields responded to N at the 50 and 75% estimated ET replacement irrigation levels, but not at the 0 or 25% ET levels. Quadratic‐plateau models indicated that 19 to 38 kg N additional fertilizer ha−1 was needed to produce economically optimum lint yields near 1100 kg N ha−1 with conservation tillage than with conventional tillage. Chlorophyll meter and petiole NO3–N readings were positively related to N rate but were not affected by tillage system.
Soil Wetness and Traffic Level Effects on Bulk Density and Air‐Filled Porosity of Compacted Boreal Forest Soils
Authors: McNabb D.H. , Startsev A.D. , Nguyen H.
Published: July 2010

Soil compaction is a common consequence of forest harvesting that has the potential to affect several soil processes and forest productivity. Our objective was to quantify the relationships between soil trafficking, soil wetness, and soil air‐filled porosity, and the compacted bulk density and air‐filled porosity of 14 boreal forest soils in West‐Central Alberta, Canada. Bulk density and air‐filled porosity were measured on nontrafficked soil and adjacent areas immediately after the site was subjected to 3, 7, and 12 cycles of skidding with mostly wide‐tired skidders. Significant increases in bulk density (P< 0.05) occurred after three cycles at each site when the soil water potential was higher than −15 kPa; the significant increase occurred to a depth of at least 22 cm. The increase in bulk density became asymptotic between 7 and 12 cycles, but the increases were not significantly different from the bulk density at three cycles. The relationship between air‐filled porosity and trafficking was the inverse of the level of bulk density and trafficking, but the increase in bulk density of wet soil was limited by an air‐filled porosity of about 0.10 m3m−3Soil compaction only occurred when the soils were at or wetter than field capacity, which can easily be measured in the field with a hand‐held tensiometer or alternatively, estimated from a field measure of soil consistence. Managing felling operations to maximize transpiration of trees to reduce soil wetness is an effective tactic to avoid significant soil compaction by these types of equipment in this environment.
Soil and Weathered Bedrock
Authors: Hubbert K. R. , Graham R. C. , Anderson M. A.
Published: July 2010

Virtually all of the commercial forests in the southern Sierra Nevada are on granitic terrain, where bedrock may be weathered to depths >15 m while soils are <1 m thick. Because plant‐available water is depleted in these thin soils by midsummer, study objectives were to characterize the edaphic role of the weathered bedrock relative to the soil. The site was a 30‐yr‐old Jeffrey pine (Pinus jeffreyi Grev.& Balf.) plantation growing on relatively thin soils (75 cm in depth) overlying weathered granitic bedrock. The average depth to hard bedrock was 350 cm. A trench was excavated and physical and chemical properties of the soil and bedrock were evaluated. Cation‐exchange capacities (CEC) were lower in the weathered bedrock (Cr1 horizon = 4.6 cmol kg−1) than in the soil (A horizon = 13.4 cmol kg−1), but pH values were similar (4.6–5.5). Organic C content was negligible in the weathered bedrock matrix (<0.1%), but was higher within joint fractures (3.7%), where roots were concentrated, than within the soil A horizon (2.7%). Carbon/N ratios were much lower in the soil A horizon (19.6) than in the bedrock fractures (62.0). Saturated hydraulic conductivities (Ksat) of the soil and the weathered bedrock were similar and high (8–11 cm h−1). Mean root length density (RLD) was greater within the joint fractures than within the soil, but on a whole rock basis bedrock RLD was much lower (<0.08 cm cm−3). Total plant‐available water storage capacity of 48.8 cm was calculated for the 350 cm thickness of regolith, with 14.7 cm (30%) contributed by soil and 34.1 cm (70%) by weathered bedrock. Weathered bedrock underlying soils is critical to the survival of forest ecosystems, particularly with regard to water supply, and should not be neglected in ecosystem site evaluations and models.
Persistence of Soil Compaction and Effects on Seedling Growth in Northwestern Quebec
Authors: Brais Suzanne
Published: July 2010

Compaction is perceived as one of the leading causes of soil degradation resulting from forest operations. The objectives of this study were, for two contrasting soil textural groups (i) to assess persistence of compaction; (ii) to compare growth patterns of seedlings submitted to different levels of soil physical disturbance induced by harvesting, and (iii) to assess the relative importance of soil physical properties on these patterns. Six years following harvesting, penetration resistance showed significant relationships with traffic patterns while relationships between traffic patterns, soil macroporosity and bulk density were less significant. On fine‐textured soils, five years after plantation, white spruce [Picea glauca (Moench) Voss] height was 28% higher in the between track (BT) microsites and 25% higher in the wheel track areas (WT) of skid trails than in the undisturbed areas (UD). Nonetheless, mortality rate was higher in the WT area. Competition severity explained over 40% of white spruce early height and radial growth while soil physical characteristics had little effect. On coarse‐textured soils, competition severity in skid trails (WT and BT) decreased with the number of skidding cycles, resulting in significant increases in black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pinus banksiana Lamb.) growth. Growth was negatively affected by high macroporosity values or positively so by high microporosity values, indicating that water retention may be limiting on these soils. On the coarse‐textured soils, compaction was beneficial in the early establishment period. Further investigation is required to verify that these results also apply over the long term.
Tree Species and Soil Textural Controls on Carbon and Nitrogen Mineralization Rates
Authors: Giardina Christian P. , Ryan Michael G. , Hubbard Robert M. , Binkley Dan
Published: July 2010

Terrestrial ecosystem models assume that high quality litter leads to the formation of high quality organic C and N in mineral soil, and that increased soil clay content decreases soil C and N mineralization rates. Few studies in forests, however, have examined the effects of initial litter quality and clay content on C mineralization rates (g C kg−1soil C) and net N mineralization rates (g N kg−1soil N) in soil. We used 16‐mo laboratory incubations of mineral soil sampled from stands of lodgepole pine (Pinus contortaDougl. ex loud ssp.latifoliaEnglem. ex S. Wats.) and aspen (Populus tremuloidesMichx.) that varied in clay content (70 to 390 g kg−1soil) to examine how soil C and N mineralization rates relate to initial litter quality and soil texture. Aspen litter quality (C/N = 52–71; lignin/N = 26) was higher than pine litter quality (C/N = 82–111; lignin/N = 40–57), but pine soils released an average of 238 g C kg−1soil C over 16 mo compared with 103 g C kg−1soil C for aspen soils. Higher microbial biomass (mg kg−1soil C) under pine also indicates that pine soil C was of higher quality than aspen soil C. Net N mineralization rates did not relate to species or to soil C mineralization rates, and neither C nor N mineralization rates were related to soil clay content.
Diffusion Methods to Determine Different Forms of Nitrogen in Soil Hydrolysates
Authors: Mulvaney R.L. , Khan S.A.
Published: July 2010

Conventional steam‐distillation techniques for fractionating the N in soil hydrolysates have generally indicated little variation in the chemical distribution of soil organic N, regardless of soil type, cropping, cultivation, or N‐fertilization history. Nitrogen‐15 tracer studies to evaluate these techniques showed that determinations of amino sugar–N are subject to serious underestimation, and that analyses for amino acid–N are vitiated by incomplete conversion of amino acid–N to NH4–N following incomplete removal of hydrolyzable NH4 and amino sugar–N. Diffusion methods were developed for fractionating the N in soil hydrolysates that are far more accurate and specific than steam distillation, while also being much simpler and more convenient. In these methods, total hydrolyzable N is measured by Kjeldahl digestion of the hydrolysate and diffusion of the digest with NaOH; diffusion is performed with MgO to determine hydrolyzable NH4–N; (NH4 + amino sugar)–N is recovered by diffusion with NaOH, after which amino acid–N is liberated by ninhydrin oxidation at pH <1.8 and recovered by diffusion with NaOH. Analytical accuracy and specificity were evaluated using a wide variety of purified organic‐N compounds and by checking the recovery of 15N added to soil hydrolysates as (NH4)2SO4, glucosamine, or glycine. Studies using a diverse set of soils showed that distillation and diffusion usually agreed to within 10% for quantitative analysis of total hydrolyzable N, NH4–N, and amino acid–N, whereas analyses of amino sugar–N were 74 to 317% greater by diffusion than by distillation.
Phosphorus Availability in an Artificially Flooded Southeastern Floodplain Forest Soil
Authors: Wright R. B. , Lockaby B. G. , Walbridge M. R.
Published: July 2010

Studies of how flooding affects P availability in natural floodplains are rare. We examined the effects of artificial flooding on P availability in a Georgia floodplain forest. We hypothesized that P availability would increase with flooding, because of the flooding‐induced solubilization of phosphate minerals. Field mesocosms (n = 4 per treatment) were flooded with river water according to one of four treatments over ∼6 mo: (i) continuously flooded; (ii) flooded for 3 mo and then drained; (iii) flooded for 2 mo, drained for 1 mo, and repeated; and (iv) nonflooded control. Two additional sets of 3‐mo flooded–drained mesocosms (n = 4 per set) received added P or N (1 and 10 mg L−1, respectively) with flooding. Soils were collected monthly from both inside and outside of the mesocosms and analyzed by Hedley fractionation; anion‐exchange resins (AER) were used to estimate P availability in situ. As indexed by daily supply to AER, P availability was significantly greater in flooded versus control soils, and decreased significantly following drainage, in all treatments at some time during the study. Total P supply to AER was significantly greater in flooded versus control mesocosms regardless of treatment. No significant changes were observed in Fe/Al phosphate fractions. Microbial P was significantly lower in flooded versus control mesocosms during the first 3 mo of flooding and decreased significantly over time in two treatments. In this natural floodplain, biological processes are a more probable explanation for flooding‐induced increases in P availability than solubilization of mineral phosphates.
Cattle Slurry Affects Nitrous Oxide and Dinitrogen Emissions from Fertilizer Nitrate
Authors: Stevens R. James , Laughlin Ronald J.
Published: July 2010

Readily decomposable C in organic manures could enhance denitrification of NO3 existing in soil. The worst scenario occurs when farmers apply manures and NO3‐containing fertilizers at the same time to meet the nutrient requirements of the next crop. If the denitrification produced N2O rather than N2, the emission factor of 1.25% of fertilizer N used to calculate national inventories for N2O would be an underestimate for this farming practice. We used the 15N gas–flux method to measure N2O and N2 fluxes from grassland when cattle slurry (CS) containing 60 kg NH4–N ha−1 and KNO3 (60 kg N ha−1) were applied at the same time. By labeling the KNO3 and the NH4 in CS, we quantified the processes producing N2O and checked for N2 production by microbial processes other than denitrification. On average over field experiments replicated in March, May, August, and September 1997, CS increased the flux of N2O by 0.63% of the applied NO3–N in the 104 h after application, but had no significant effect on the flux of N2 The maximum flux of N2O was always observed in the first measurement period (5–7 h) after CS application. All of the N2O was formed by reduction from NO3 apart from in August when 10% was formed by nitrification in the CS treatment. There was no evidence for production of N2 by other processes such as heterotrophic nitrifier denitrification or anaerobic NH4 oxidation.
Denitrification in Maize Under No–Tillage
Authors: Rozas Hernán R. Sainz , Echeverría Hernán E. , Picone Liliana I.
Published: July 2010

Denitrification N losses from soils under no‐tillage (NT) can reduce N‐use efficiency and destroy the ozone layer if appreciable amounts of N oxides (N2O, NO) are lost. The objective of this study was to evaluate the effect of surface‐applied urea rate (0, 70, and 210 kg N ha−1) and different application times [planting (PL) and six‐leaf stage (V6)] on denitrification losses (DLs) in NT irrigated maize (Zea mays L.). The field experiment was carried out in the 1996 and the 1998 growing seasons, at Balcarce (37°45′S; 58°18′W), Argentina, on a Typic Argiudoll and a Petrocalcic Paleudoll. The annual mean rainfall in the area is 870 mm and annual mean temperature is 13.7°C. Denitrification rates (DRs; N2O) were measured using C2H2 blockage core method. The DRs were highest between PL and the V6 because of higher water filled pore space (WFPS), and were closely associated with the WFPS (r2 equal to 0.66 and 0.76 for 1996 and 1998, respectively). On average, accumulated DLs for the PL application were 7.6 and 9.8 kg N2O–N ha−1 (5.5 and 2.6% of N applied for 70 and 210 kg N ha−1, respectively). However, for application at the V6, accumulated DLs were 2.0 and 2.1 N2O–N kg ha−1 (1.0 and 0.4% of N applied for 70 and 210 kg N ha−1, respectively). The results indicate that for this soil and climatic zone, denitrification N losses were greater when the fertilizer was applied at PL than when fertilizer was applied at the V6.
Chemical and Mineralogical Properties of Kaolinite‐Rich Brazilian Soils
Authors: Melo V.F. , Singh B. , Schaefer C.E.G.R. , Novais R.F. , Fontes M.P.F.
Published: July 2010

Highly weathered kaolinitic soils in Brazil often have adequate levels of K and Mg to support plant growth. The source of K and Mg in these soils and their relationship with the dominant mineral, kaolinite, is addressed in this article. Crystallographic, chemical, and morphological properties of kaolinite, from selected highly weathered Brazilian soils, were investigated by x‐ray diffraction (XRD), analytical electron microscopy (AEM), chemical, and thermal methods. Kaolinite properties showed significant variations such as d(001) spacing ranging between 0.713 to 0.728 nm, width at half height (WHH) between 0.30 to 0.97 °2θ, and dehydroxylation temperature between 489 to 518°C. Kaolinite in the clay fraction has relatively poor crystal order with a mean crystallinity index value(CI) of 12.7. The dominant forms of the clay‐fraction kaolinite were elongated and rounded, with relatively lower proportions of hexagonal particles. The silt‐fraction kaolinite showed a tendency to form subspherical large aggregates with high stability. The average Fe2O3 level in the kaolinite of the clay fraction (19.1 g kg−1) was higher than that obtained for the silt fraction (6.6 g kg−1). The smaller kaolinite particles of the clay fraction showed a lower degree of crystal order, higher K and Mg levels, and lower dehydroxylation temperatures. From the strong relationship between the asymmetry index (AI) of the (001) diffraction line and the level of K in kaolinite from the younger soils, we believe that both K and Mg in kaolinite are part of residual micaceous layers interleaved in kaolinite crystals.
Spatial Analysis of Machine‐Wheel Traffic Effects on Soil Physical Properties
Authors: House Marcia L. , Powers William L. , Eisenhauer Dean E. , Marx David B. , Fekersillassie Daneal
Published: July 2010

Infiltration in irrigation furrows exhibits spatial variation from furrow to furrow within a field. One major contributing factor is the effect of multiple levels of machine‐wheel traffic on soil physical properties. The purpose of this study was to determine the effect of machine‐wheel traffic levels within equipment passes on a field basis. Variations in satiated hydraulic conductivity (Ks), penetrometer resistance (Rp), and bulk density (ρb) due to nine, eight‐row equipment passes were studied in three transects, crossing 72 furrows perpendicular to crop rows, on a Hord silt loam (fine‐silty, mixed, mesic, Pachic Haplustoll). Mean values, spatial patterns, and regression relationships between properties were determined. Spectral analysis was used to fit cosine curves to property data that showed significant periods at 2.7, 8.0, and 72 furrows. An additional period of 24 furrows was seen in the Rp and ρb data. All properties tested showed significant mean differences due to wheel traffic from equipment passes. Within the equipment passes it was possible to further separate treatment means for all soil properties. Results in wheel tracked furrows were different from all other treatments. Linear regression of log Ks and Rp in a 72‐furrow transect shows 58% of log Ks variability is explained by changes in Rp Predicted vs. measured log Ks in two transects shows predictions somewhat high, although the slope of the linear regression is 0.95, nearly parallel to a 1:1 line.
Nature of Clay‐Humic Complexes in an Agricultural Soil
Authors: Laird D. A. , Martens D. A. , Kingery W. L.
Published: July 2010

Soil management systems that encourage the formation and stabilization of recalcitrant clay–humic complexes will have the greatest long‐term impact on C sequestration and soil quality. The objective of this study was to determine the relationship between the chemical, biochemical, and spectroscopic characteristics of humic substances and clay mineralogy. Clay–humic complexes were separated from the Ap horizon of a Webster soil (fine‐loamy, mixed, superactive Typic Endoaquoll) by an invasive sonication–centrifugation technique. The samples were analyzed for mineralogy by XRD (x‐ray diffraction), chemical composition by inductively coupled plasma‐atomic emission spectorscopy (ICP‐AES), C and N by thermal combustion, C chemistry by solid state 13C magic angle spinning‐nuclear magnetic resonance spectroscopy (MAS‐NMR) and both gas chromatography (GC) and high performance liquid chromatography (HPLC) analyses of extractable organic compounds. The coarse, medium, and fine clay fractions are dominated by quartz, a low‐charged interstratified phase, and smectite, respectively. Extractable organic compounds, 30 to 52% of the total C, are dominated by basic amino acids and polyunsaturated fatty acids. Less than 3% of the extractable C is monosaccharides and amino sugars and only trace levels of phenolic acids were found. The C/N ratios of humic substances associated with the coarse, medium, and fine clay fractions are 17, 10, and 10, respectively. The coarse clay fraction has stronger carboxyl and O‐alkyl 13C‐NMR peaks and lower levels of extractable amino acids, fatty acids, monosaccharides, and amino sugars than humics associated with the fine clay fraction. The results indicate that the biochemistry of the clay–humic complexes differs substantially from that of whole soils and that soil clay mineralogy strongly influences humification.
Nitrogen‐15 Recovery in Soil Incubated with Potassium Nitrate and Clover Residues
Authors: Muriuki Anne W. , King Larry D. , Volk Richard J.
Published: July 2010

In the southeastern USA, legumes are used as green manure to meet crop N requirements of a following crop, but recovery is usually lower than from conventional fertilizers. We conducted a laboratory study for 26 wk under aerobic conditions to monitor recovery of15N‐labeled KNO3(fertilizer) and crimson clover (Trifolium incarnatumL.) residues (clover) in organic, inorganic, and microbial biomass N pools. Volatilization of NH3from decomposing clover residues was monitored for 12 wk. Three hundred–gram samples of a Typic Kanhapludult soil were amended with N (0.051 mg N kg−1dry soil in fertilizer and 0.049 mg N kg−1dry soil in clover). A control with no N was also included. Although inorganic N (NH4, NO2, and NO3) accumulated throughout (fertilizer > clover > control), the rate of accumulation did not differ among treatments. Organic and microbial biomass N concentration did not differ among treatments, but applied N recovery in microbial biomass was greater in clover than fertilizer (P< 0.05) throughout. Ammonia volatilized was negligible. After 26 wk, applied N recovered in soil inorganic N was 66% for fertilizer and 40% for clover; in soil organic N, 18% for fertilizer and 50% for clover; and in microbial biomass N, 0.75% for fertilizer and 1.5% for clover. Applied N presumed denitrified was 16% in fertilizer and 10% in clover. We concluded that clover green manure can meet the N requirements of a following crop from the time of emergence in the southeastern USA.