bluuebunny/crossref_metadata_2025_split huggingface dataset:
Particulate Soil Organic‐Matter Changes across a Grassland Cultivation Sequence
Authors: Cambardella C. A. , Elliott E. T. 
Published: July 2010

AbstractMany models have been constructed in an attempt to describe the dynamics of soil organic‐matter (SOM) turnover, most of which include 2 to 3 kinetically defined organic‐matter pools. Physical and chemical definition of these conceptualized SOM pools has been difficult. We describe a simple method for dispersion of soil to isolate a particulate organic‐matter (POM) fraction that may represent an important SOM pool in grassland soils. The POM fraction was isolated by dispersing the soil in 5 g L−1 hexametaphosphate and passing the dispersed soil samples through a 53‐µm sieve. We compared POM and mineral‐associated C among three tillage treatments (20 yr under cultivation) and an undisturbed grassland at Sidney, NE. The POM C in the native sod represented 39% of the total soil organic C. Twenty years of bare‐fallow, stubble‐mulch, and no‐till management reduced the C content in this fraction to 18, 19, and 25%, respectively, of the total organic C. The mineral‐associated organic‐matter fraction showed no reduction in C content in the bare‐fallow treatment compared with the grassland soil but increased in the no‐till and stubble‐mulch treatments. Nitrogen dynamics generally mirrored those observed for C. Analysis of the POM fraction for lignin and cellulose content indicated that this fraction was 47% lignin and had a lignocellulose index of 0.7. The stable C‐isotope composition of the POM fraction suggests that wheat‐derived POM turns over faster than grass‐derived POM. We suggest the POM fraction closely matches the characteristics of a SOM pool variously described as slow, decomposable, or stabilized organic matter.
Grain Sorghum‐Soybean Rotation and Fertilization Influence on Vesicular‐Arbuscular Mycorrhizal Fungi
Authors: Ellis J. R. , Mason S. C. , Roder W. 
Published: July 2010

AbstractVesicular‐arbuscular mycorrhizal fungi (VAMF) can reduce plant stress resulting from nutrient deficiencies, drought, and other factors. The objective of this work was to measure the effect of soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] rotation and fertilization on plant response and VAMF root colonization and diversity, and relate effects to soil environment. Fertilizer treatments consisted of no fertilizer, N, and manure. Rooting densities correlated with previous crop, VAMF colonization, and soil NO3. Root colonization by VAMF was affected by previous crop, rooting density, N fertilization, soil P, and water‐filled pore space. Root colonization by VAMF ranged from 93% at 15 cm to 15% at the 120‐cm soil depth. Root density and VAMF colonization were least when soybean was grown the previous year and manure was applied. Root colonization by VAMF for control, N, and manure treatments were 54, 53, and 30%, respectively, for continuous soybean and 61, 55, and 44%, respectively, for soybean from rotation plots. Root colonization by VAMF for control, N, and manure treatments were 69, 59, and 54%, respectively, for continuous grain sorghum and 56, 48, and 31%, respectively, for grain sorghum from rotation plots. These agricultural soils contained a diverse mixture of 26 VAMF species, which is probably a major factor in the region's soil productivity. Plants stressed due to cropping system or fertilizer practice have greater VAMF colonization and VAMF activity. A diverse VAMF population could increase the ability of VAMF to respond to different stresses.
New Formulae for Mass Spectrometric Analysis of Nitrous Oxide and Dinitrogen Emissions
Authors: Arah J. R. M. 
Published: July 2010

AbstractFormulae currently used in mass spectrometric studies of N2 and N2O emissions require the initial atmosphere to be in a state of isotopic equilibrium with a 15N atom fraction equal to that of the global background (γ). This is not always the case (e.g., in sequentially sampled incubations and those conducted under artificial atmospheres). Here I present new formulae that are valid whatever the initial conditions. These formulae are simpler than previous versions. They are expressed directly in terms of the 15N atom fractions and 30N2 molecular fractions of two gas samples (taken before and after emission). I have provided secondary expressions for converting the instrumental output of any (single‐ or dual‐inlet, double‐ or triple‐collector) mass spectrometer into the atomic and molecular fractions required. In common with previous treatments, my new calculations hypothesize a homogeneous soil N pool. I have proven that where this hypothesis is false the calculated value of the apparent pool enrichment is wrong (too high where the actual enrichment exceeds that of the atmosphere; too low in the exceptional case where the atmospheric enrichment exceeds that of the pool) and the flux is invariably underestimated. Computer simulations suggest that this underestimation may be relatively constant (about 25%) if the atmosphere is initially at isotopic equilibrium with 15N fraction γ, but that it may be larger (about 40%) and more variable where this is not the case.
Maize Root Distribution between Phosphorus‐Fertilized and Unfertilized Soil
Authors: Zhang Jiancai , Barber S. A. 
Published: July 2010

AbstractPlacement of P in a fraction of the soil volume stimulates root growth in the P‐fertilized soil. Previous research on the degree of root proliferation as related to the proportion of soil fertilized with P was conducted with soils containing similar low levels of initial resin‐exchangeable P, Csi, and hence did not evaluate the influence of Csi on the degree of root proliferation in a P‐fertilized fraction of the soil. These measurements were made as part of research to determine the fractional volume of soil to fertilize with P to maximize P uptake. The objective of this research was to investigate the influence of initial soil Csi value and rate of P added on root distribution between P‐fertilized and unfertilized soil when the P‐fertilized volume is constant. Pot experiments were conducted in a controlled‐climate facility where maize (Zea mays L.) was grown on three soils varying in Csi levels and with three rates of applied P, from 50 to 300 mg kg−1, added to 0.20 of the volume of each soil. Root density, cm cm−3, in the P‐fertilized soil volume, RDF, and a comparable 0.20 volume of unfertilized soil, RDU, was measured and compared with Csi in the P‐fertilized soil, CsiF, and in the unfertilized soil, CsiU. There was a curvilinear relation between CsiF/CsiU and RDF/ROU that was described by the equation y = 1.20 + 2.74 log x (r2 = 0.97), where y is RDF/RDU and x is CsiF/CsiU. Hence, as soil Csi level increased, RDF/RDU decreased, and as rate of P applied increased, RDF/RDU increased. The relation between CsiF/CsiU and RDF/RDU can be used to predict root growth rates to use in the fertilized and unfertilized soil when using a mechanistic nutrient‐uptake model to calculate the effect of P placement on P uptake.
Role for Potassium in the Iron‐Stress Response Mechanism of Iron‐Efficient Oat
Authors: Hughes D. F. , Jolley V. D. , Brown J. C. 
Published: July 2010

AbstractAdequate soil K enhances the ability of certain Fe‐deficiency‐stressed monocotyledonous and dicotyledonous plants to obtain Fe. In dicotyledonous plants, this increased capacity to obtain Fe where adequate K is present is associated with specific Fe‐stress response mechanisms including H+ ion efflux, reductant release, and reduction of Fe3+ to Fe2+ at the root (Strategy I). A different Fe‐stress response mechanism recently identified in Fe‐efficient grasses is the release of phytosiderophore (a plant‐produced Fe3+ chelator; Strategy II). Our objective was to determine if varied K additions affect either the production and release of phytosiderophores or the uptake of Fe in oat (Avena sativa L.; a Strategy II plant). A series of hydroponic experiments was conducted imposing varying solution K concentrations on Fe‐deficiency‐stressed ‘Coker 227’ oat, an Fe‐efficient cultivar. Significantly more phytosiderophore was released by roots of oat plants grown with adequate K (84 mg K L−1) than by roots of plants grown at low concentrations of solution K (0 and 7 mg K L−1). The diminished phytosiderophore production in the absence of K corresponded significantly with greater Fe‐deficiency chlorosis and lower leaf Fe contents. Oat plants grown in adequate K successfully competed with equimolar concentrations of Fe and EDDHA [ethylene‐diamine di (O‐hydroxyphenylacetic acid)], but did not compete for Fe where excess EDDHA was added, further substantiation of a role for K in the production and release of phytosiderophore.
The Soil Survey as Paradigm‐based Science
Authors: Hudson Berman D. 
Published: July 2010

AbstractThomas S. Kuhn developed the paradigm theory of science. The soil survey is an example of paradigm‐based science. The soil‐landscape model, on which the soil survey is based, is an operative paradigm. An extreme reliance on tacit knowledge, the knowledge gained by experience, creates serious inefficiencies, both in learning the soil‐landscape paradigm and in disseminating the information resulting from its application. This article introduces concepts important to understanding paradigm theory and the nature of tacit knowledge. Among these are elements of Gestalt psychology, the theory of natural families, maps as conveyors of knowledge, and the linguistic nature of human perception. Students and field soil scientists should be provided explicit instruction concerning the paradigm on which soil mapping and interpretation are based. I also recommend that more of the soil geographic relationships discovered while making detailed soil maps be described and published so that the knowledge can be communicated to others.
Soil Erosion Effects on Corn Yields Assessed by Potential Yield Index Model
Authors: Craft E. M. , Cruse R. M. , Miller G. A. 
Published: July 2010

AbstractSoil erosion alters crop production via alteration of the soil chemical and physical environment. The objectives of this study were to: (i) develop a Potential Yield Index (PYI) model to index soil productivity based on simulated root growth, soil properties, and potential nutrient and water uptake of corn (Zea mays L.) through a growing season, (ii) utilize the PYI to estimate erosion effects on soil productivity by simulating the removal of 15 and 30 cm of soil, and (iii) simulate the impact of fertilizer additions to the eroded soil on the PYI. The PYI model independently estimates P, K, and water (W) uptake by corn. From these estimates, three separate yield indexes (PYIP, PYIK, and PYIW) are calculated. The lowest yield index is identified as the PYI for a given soil. The predicted PYIs for 45 soils in Iowa compared well to the 1984 10‐yr average corn yield (R2 = 0.83) and corn suitability rating (R2 = 0.73) for each soil. Changes in the PYI were predicted for 15 and 30 cm of simulated erosion. After 15‐cm soil loss, the PYI for all soils decreased, with all but three soils remaining within 15% of the uneroded PYI. The PYI decreased further after 30‐cm soil loss, with only 12 soils remaining within 15% of the uneroded PYI. Fertilizer additions to the plow layer of the eroded soils were then simulated. The PYI returned to within 5% of the uneroded PYI for 38 soils with 15‐cm soil loss and for 27 soils with 30‐cm soil loss. The PYI indicated that the soil factor that most limited plant yield changed with the soil, amount of soil loss, and plow‐layer soil fertility status.
Inverse Method for Determining Soil Hydraulic Functions from One‐Step Outflow Experiments
Authors: van Dam J. C. , Stricker J. N. M. , Droogers P. 
Published: July 2010

AbstractOptimization of the parameters describing the soil hydraulic functions θ(h) and K(h), in which θ is the volumetric water content, h is the soil water pressure head, and K is the unsaturated hydraulic conductivity, in a transient‐flow experiment is a promising method to derive soil hydraulic information. Laboratory outflow experiments are a typical example. However, estimates from one‐step outflow experiments, using only cumulative outflow data in the objective function, are often unreliable and non‐unique. Using the MVG model for θ(h) and K(h), the sensitivity of parameters to outflow data is shown to depend on their actual values. The one‐step outflow method was applied on samples of four soils of different texture. Additionally, the soil hydraulic functions of these soils were measured by alternative, direct methods. From the validation, it appeared that cumulative outflow data have to be supplemented with θ(h) data to get reliable estimations.
Rapid Measurement of Low Soil Water Potentials Using a Water Activity Meter
Authors: Gee G. W. , Campbell M. D. , Campbell G. S. , Campbell J. H. 
Published: July 2010

AbstractWater potential is one of the most important physical properties of soil but remains among the most difficult to measure reliably. We describe a water activity meter that can be conveniently used to measure water potentials in soils ranging in wetness from near saturation to air dry (water potentials from −0.4 to < −100 MPa). The meter senses the dew point of water vapor with a miniature cooled mirror located above a soil sample in a closed chamber. Readings for individual samples are obtained rapidly (2–5 min). Accuracy of the measurement is checked periodically using saturated soil solutions. Repeatability of measurements was found to be equal or better than the rated precision (± 0.003 activity units). Water potentials (calculated from water activities using the Kelvin equation) were obtained for soils ranging in texture from sand to clay. The meter was used on soil samples taken from sites near Richland, WA, and summertime water potentials were found to be as low as −264 MPa.
Temperature Dependence of Net Nitrogen and Sulfur Mineralization
Authors: Ellert B. H. , Bettany J. R. 
Published: July 2010

AbstractModels to express the responses of N and S mineralization to temperature are essential to predict the amounts of plant‐available N and S released from soil organic matter. We improved the methods conventionally used to describe temperature dependence by fitting, simultaneously, kinetic models and temperature‐response functions. Net N or S mineralization was defined as a function of temperature, time, and length of incubation interval. These single‐step models facilitated objective comparisons of rival temperature functions. The various functions represented rival hypotheses about the temperature dependence of mineralization. Temperature responses traditionally have been described by Arrhenius or Q10 (temperature coefficient) functions, but a quadratic function was required to describe declining responses at warm temperatures. We compared the Arrhenius and Q10 functions, and showed how indices of temperature response (activation energy and Q10) are derived from the finite differentials of the response functions. Single values of Q10 described rates that climbed exponentially with temperature, but separate values of Q10 for each temperature interval (5–15, 15–25, and 25–30 °C) were required when the responses diminished in warm soils (quadratic response). Temperature was a major factor influencing N and S mineralization in a sequence of soils under the following management regimes: native forest, recently cleared forest, and long‐term cultivation. Various combinations of kinetic equations and temperature functions were required to describe the time and temperature dependence of mineralization in soils under contrasting management. The models were proposed as multiple working hypotheses about the processes involved in mineralization.
Hypergypsic Soil Micromorphology and Landscape Relationships in Northeastern Spain
Authors: Herrero J. , Porta J. , Fédoroff N. 
Published: July 2010

AbstractThere are not many studies of hypergypsic soils and terminology describing these soils continues to develop. Hypergypsic is here applied to soils having gypsum as a major component, often more than 50%, whereas the term gypsiferous is used for soils with any amount of gypsum. The soils described here developed from gyprock, under a semiarid climate (xeric soil moisture regime). Water tables are below possible capillary rise to the soil surface and the soils do not contain salts more soluble than gypsum. Micromorphology and geomorphic positions of the soils were used to describe and relate the weathering and landscape processes. We developed models to explain the occurrence and distribution of the different kinds of gypsum. Mudflows are an important process of gypsum mobilization. Massive microcrystalline gypsum horizons are related to the gyprock weathering and mudflow deposits. Pedogenic, sand‐size sparite crystals were identified in pedofeatures named queras, and can form surface horizons. Two kinds of gypsic fabric (lenticular and microgypsic) result from the studied gypsification processes. The introduction of the hypergypsic diagnostic horizon to the taxonomic classification system would be helpful for the accurate classification of these soils.
Soils on Hillslopes in Acid Gray and Black Shales
Authors: Sobecki T. M. , Karathanasis A.D. 
Published: July 2010

AbstractThe effect of hillslope geomorphology on properties of soils formed over horizontally bedded acid gray and black shale was evaluated in the Knobs region of eastern Kentucky. The geology and geographic extent of the Knobs made it possible to apply state factor analysis by systematizing local variation in parent material, while regional climate and vegetation were held constant. Nose‐, head‐, and sideslopes truncating black shale are steeper (36–62%) than respective hillslopes truncating gray shale (20–32%). Hapludults on these hillslopes are polygenetic: colluvium overlies buried Bt horizons formed in shale residuum. This discontinuity is characterized by a zone of soil creep, differences in soil fabric, and changes in particle size and TiO2/ZrO2 depth functions. Soil chemical properties vary with hillslope geomorphic component and parent material. Although black shale strata have 20 to 30 times more organic C and up to 10 times more S than gray shale, soil material formed from the two types of strata have simllar organic C and S contents. Soil material that formed from black‐shale‐derived colluvium or residuum in noseslopes, however, has lower pH (<4) and higher Al saturation (>90%) than soil material derived from black or gray shale in other hillslope geomorphic components.
Changes in Soil Aggregation and Organic Carbon under Corn and Alfalfa
Authors: Angers D. A. 
Published: July 2010

AbstractData on rates of changes in soil structure and organic matter under different cropping systems are necessary for the development of soil and water conservation strategies. Changes in C content and water‐stable aggregation of a Kamouraska clay (fine, mixed, frigid Typic Humaquept) under continuous silage corn (Zea mays L.) and an alfalfa (Medicago sativa L.) stand were monitored monthly during five consecutive growing seasons. A bare soil (fallow) was included as a control. Under alfalfa, the mean weight diameter (MWD) of water‐stable aggregates increased from 1.5 to 2.3 mm during the 5‐yr period. An asymptotic regression explained 69% of the variation in MWD with time under alfalfa. This increase in MWD was largely attributed to an increase in aggregates >2 mm at the expense of the aggregates of 0.25‐ to 1.0‐mm diameter. Also, under alfalfa, the C content increased following a sigmoidal shape from 26 g kg−1 in the first season to 30 g kg−1 in the last year. Changes in MWD were comparatively larger and took place more rapidly than those in C. A correlation coefficient of 0.74** (significant at the 0.01 probability level) was obtained between C and MWD. Under corn and fallow (bare‐soil control), changes in MWD and C content were minimal during the 5 yr. About one‐half of the temporal variation in MWD under corn and fallow could be explained by the variation in soil water content at time of sampling. Conversely, the absence of a significant relationship between water content and MWD under alfalfa suggests that the soil aggregates under this treatment were not subject to slaking.
Tillage‐ and Traffic‐Induced Changes in Macroporosity and Macropore Continuity: Air Permeability Assessment
Authors: Roseberg R. J. , McCoy E. L. 
Published: July 2010

AbstractQuantitative analysis of macropore geometry in undisturbed soils has been hindered by difficulties in creating conditions where macropore measurements can be separated from matrix pore measurements. Such analysis is important, however, for evaluating tillage management effects on both root growth and solute movement. Inferences regarding management effects on macroporosity were made possible by combining the use of improved air‐permeability techniques with two recently developed methods to analyze air‐permeability (Ka) data, using undisturbed soil samples from a tillage study. Log10 Ka values exhibited a near‐normal distribution. In wheel‐traffic interrows (Wh), macropore air permeability was significantly less under conventional‐tillage corn (CT) than no‐tillage corn (NT) and no‐tillage alfalfa (ALF). Tillage differences were usually not significant in non‐wheel‐traffic interrows (NWh). Wheel traffic significantly decreased air permeability for CT, but not for NT or ALF. The two methods of analyzing air‐permeability data yielded similar inferences regarding macropore geometry. Conventional tillage decreased bulk density (increasing total porosity) for NWh only, but seemed to decrease the stability, number, and continuity of macropores relative to NT and ALF. Macroporosity and macropore geometric factors were affected little by traffic for NT and ALF, but traffic significantly affected CT macropores in this study where samples were taken approximately 1 mo after corn planting.
Preemergent Shoot Growth of Maize under Different Drying Conditions
Authors: Weaich Karl , Bristow Keith L. , Cass Alfred 
Published: July 2010

AbstractPoor establishment of seedlings is a problem in semi‐arid cropping regions. High drying rates that are characteristic of these regions can result in the early onset of high soil strengths and high soil temperatures, which are detrimental to seedlings. In this study, we examined the response of preemergent shoot growth of maize (Zea mays L.) to differences in the drying rate of a hardsetting red‐brown earth (fine, mixed, thermic Typic Paleustalf or Calcic Luvisol). We examined the impact of high soil strength on the constituent shoot parts (coleoptile and first internode), and used a temperature‐based shoot‐growth model to separate the effects of soil temperature and soil strength on preemergent shoot growth.Preemergent shoot growth was sensitive to small differences in drying rate. Rapid drying resulted in no emergence, moderate drying in 52% emergence, and slow drying in 78% emergence. Soil strength impeded shoot elongation at a cone index of 1.1 MPa and, at 2 MPa, growth and emergence ceased. Differences in soil strength development reflected not just the total amount of water removed from the profile, but also the distribution of water remaining within the profile. Rapid drying quickly reduced soil water content near the surface and led to the immediate development of high soil strength there.Reduction in shoot elongation at high soil strengths was largely due to the sensitivity of the first internode. The coleoptile elongation rate showed no response to treatment differences in soil strength although twisting, buckling, and rupture was more prevalent at high soil strengths.