bluuebunny/crossref_metadata_2025 huggingface dataset:
Maize Root Distribution between Phosphorus‐Fertilized and Unfertilized Soil
Authors: Zhang Jiancai , Barber S. A.
Published: July 2010

Placement 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

Adequate 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

Thomas 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

Soil 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

Optimization 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

Water 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

Models 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

There 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

The 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

Data 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

Quantitative 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

Poor 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.
Crop Species, Amendment, and Water Quality Effects on Selected Soil Physical Properties
Authors: Bauder J. W. , Brock T. A.
Published: July 2010

Saline and sodic soils have developed in some irrigated areas of Montana. Cropping systems that promote maximum efficacy of surface‐applied amendments for reclamation need to be identified. Effects of crop species, amendment, and water quality on alteration of selected physical properties of a Haverson silty clay (fine‐loamy, mixed [calcareous], mesic Ustic Torrifluvent) were compared. Crops grown in lysimeters and compared with a noncropped control were alfalfa (Medicago sativa L.), barley (Hordeum vulgare L.), and sorghum‐sundangrass [Sorghum bicolor (L.) Moench‐ S. × drummondii (Steudel) Millsp. & Chase], commonly referred to as sordan. Soil amendments included a check, gypsum (CaSO4·2H2O), phosphogypsum (CaSO4·2H2O with <1% [w/w] P), and MgCl2. Lysimeters were irrigated with water having either a total dissolved solids (TDS) concentration of 0.75 g L−1 and a sodium adsorption ratio (SAR) of 1.15 or TDS of 1.65 g L−1 and SAR of 7.01 until three barely crops were successively grown. The presence of a crop caused a significant increase in bulk density in all lysimeters and a significant decrease in total porosity, compared with the uncropped control treatments. Barley caused the greatest decrease in total porosity, followed by alfalfa, then sordan. Total porosity decreased nearly 0.1 m3 m−3. The result was a significant increase in number of micropores (<0.149 × 10−2 mm radius) and a disproportionately greater decrease in number of macropores (>1.49 × 10−2 mm radius). Soil water release characteristics differed among the different crop treatments. Neither amendment treatment nor irrigation water quality had a significant effect on either porosity, pore‐size distribution, or bulk density. Results of this study indicate that crop selection and rotation may affect the significance of surface‐applied amendments used for reclamation and leaching of Na‐ and salt‐affected soils.
Dynamic Oxygen and Carbon Dioxide Exchange between Soil and Atmosphere: II. Model Simulations
Authors: Ouyang Y. , Boersma L.
Published: July 2010

An important general objective for modeling gaseous transport through unsaturated soils is to provide better understanding of gas exchange between the terrestrial ecosystem and the atmosphere. A more specific objective is the evaluation of problems of soil aeration. We present sensitivity analyses of a mathematical model developed for the dynamic exchange of O2 and CO2 between soil and atmosphere. We also present simulations to evaluate changes in concentrations during cycles of infiltration, evaporation, and redistribution during which simultaneous transport of water, heat, O2, and CO2 was involved. Simulation was also used to evaluate possible effects of O2 and CO2 concentrations on the rate of root growth; effects of a compacted layer on the simultaneous transport of water, O2, and CO2; effect of the presence of a crop canopy on concentrations of O2 and CO2 in the soil; and an evaluation of possible nonideal behavior of CO2 molecules in the gas phase of the soil. Results emphasize the important effects of rainfall, evaporation, and root respiration on O2 and CO2 concentrations in the soil. Simulations show that root growth below a compacted soil layer may be restricted by low O2 concentrations resulting from limited diffusion through the compacted layer. The presence of a crop canopy has a decisive effect on concentrations of O2 and CO2 at the soil surface, thereby affecting the concentrations of those gases in the root zone.
Transport of Imazethapyr in Undisturbed Soil Columns
Authors: O'Dell J. David , Wolt Jeff D. , Jardine Philip M.
Published: July 2010

The disappearance of imazethapyr [(±)‐2‐[4,5‐dihydro‐4‐methyl‐4‐(1‐methylethyl)‐5‐oxo‐1H‐imidazole‐2‐yl]‐5‐ethyl‐3‐pyridinecarboxylic acid] from soil solution was investigated to evaluate the transport of imazethapyr in undisturbed soil columns. Soil treated with imazethapyr was incubated for 0.15, 1, 2, 4, 8, and 16 d, at which times soil solution was obtained by vacuum displacement. Bromide and imazethapyr were then applied to the surface of undisturbed soil columns followed by application of deionized water at approximately 3 cm d−1. The removal of imazethapyr from solution (i.e., sorption) exhibited biphasic kinetics and was well described (R2 = 0.99) by two simultaneous first‐order reactions. The initial reaction was essentially instantaneous and the secondary reaction was time dependent. The classical convective‐dispersive (CD) equation was used to describe solute transport through undisturbed soil columns. Bromide and imazethapyr breakthrough curves (BTCs) were displaced to the left of one pore volume and showed considerable tailing, with imazethapyr BTCs retarded in relation to Br‐. This was indicative of preferential solute mobility in the soil. Imazethapyr BTCs were similar to model simulations using transport parameters determined from Br‐ BTCs, kinetic parameters from the imazethapyr solution concentration decay curves, and retardation factors calculated from the distribution coefficient at the 1‐d incubation time. Model simulations using retardation factors from later times predicted increasingly delayed imazethapyr breakthrough with lower peak concentrations than measured. Preferential flow paths apparently reduced attenuation of imazethapyr as predicted from equilibrium adsorption measurements.
Predicting Calcium and Magnesium Precipitation in Saline Solutions following Evaporation
Authors: Miyamoto S. , Pingitore N. E.
Published: July 2010

Salt precipitation associated with water evaporation from saline water is a fundamental process occurring in irrigation and drainage waters and aquaculture ponds. This study examined five different methods of predicting Ca and Mg precipitation in saline solutions following evaporation: (i) Ca precipitation as calcite; (ii) Ca precipitation as metastable CaCO3, such as vaterite; (iii) CaCO3 plus Mg precipitation as magnesite or nesquehonite; (iv) formation of homogeneous magnesian calcite and resulting changes in solubility; and (v) formation of heterogeneous magnesian calcite particles having various levels of Mg substitution and solubility. Computed results were then compared with laboratory data in which 10 saline solutions simulating irrigation waters were concentrated up to 30‐fold through evaporation at 25 °C. Precipitated salts from selected cases were also analyzed by x‐ray diffraction and an electron probe. Results indicated that Ca precipitation is extensive, and that Mg precipitation or substitution is minimal, except when HCO3 concentrations greatly exceed Ca concentrations. The presence of Mg reduced the rate of precipitation in evaporating solutions, and provided quasi‐stable dissolved Ca concentrations following evaporation, which were significantly higher than calcite solubility. X‐ray diffraction analyses indicated the formation of magnesian calcite with a Mg molar content up to 7% with some aragonite. Electron probe microanalyses supported a theoretical prediction (based on Method v) that magnesian calcite particles are heterogeneous, having higher Mg contents toward the particle surface. Calcium and Mg concentrations in the saline solutions following evaporation were best estimated by Method v, which incorporated the coevolution of the composition of solution and solid phases.
Light‐Fraction Organic Matter in Soils from Long‐Term Crop Rotations
Authors: Janzen H. H. , Campbell C. A. , Brandt S. A. , Lafond G. P. , Townley‐Smith L.
Published: July 2010

Light‐fraction (LF) material, comprised largely of incompletely decomposed organic residues, may provide a sensitive indicator of the effects of cropping practices on soil organic matter. The objective of our study was to determine the influence of agronomic variables on soil LF content, and to evaluate the LF as a measure of labile organic matter. Soils from three long‐term crop rotation studies in Saskatchewan, Canada, were analyzed for LF content and composition. The experiments, established at Indian Head (Udic Boroll), Melfort (Udic Boroll), and Scott (Typic Boroll), included wheat (Triticum aestivum L.) based rotations varying in fertilizer application, frequency of summer fallow, and cropping sequence. The LF of the surface soil (0–7.5 cm) accounted for 2.0 to 5.4%, 3.3 to 7.1%, and 7.1 to 17.5% of the organic C at Indian Head, Melfort, and Scott, respectively. Within each site, the LF content was generally highest in treatments with continuous cropping or perennial forages and lowest in those with a high frequency of summer fallow. Fertilizer application generally favored LF accumulation. Differences in LF content among sites and treatments were attributed to variable residue inputs and rates of substrate decomposition. The respiration rate and microbial N content of soils was strongly correlated with the LF content, suggesting that the LF is a useful indicator of labile organic matter. Nitrogen mineralization was also correlated with LF content, though the relationship was less consistent, presumably because the high C/N ratio of the LF induced temporary N immobilization. The LF content is a sensitive indicator of the effects of cropping on soil organic matter content and composition but, because of its transient nature, probably reflects primarily short‐term effects.
Soil‐Based Irrigation and Salinity Management Model: I. Plant Water Uptake Calculations
Authors: Cardon G. E. , Letey J.
Published: July 2010

A new soil‐based model for irrigation and soil salinity management has been formulated to rectify deficiencies in existing soil‐based models with respect to mass balance, numerical stability, and the treatment of plant growth and water uptake dynamics. The advantages of the new model are: (i) the treatment of temporal variation in potential transpiration (TP) and rooting depth and distribution, (ii) the adjustment of TP based on feedback from simulated crop water uptake, (iii) the provision for treating growth‐stage‐specific crop tolerance to salinity and water stress, and (iv) the provision for multiseasonal simulation through the treatment of noncropped periods. A sensitivity test and a comparison of model calculations to experimental data were conducted. The model tended to overpredict relative crop yield from a field experiment based on relative crop water uptake calculations. The mean simulated relative yield was 7% higher than observed with a root squared error (RMSE) of 8.8% relative yield. Willmott's d index (a statistical index of agreement between measured and observed data) result was high 0.79 (perfect agreement = 1.0).
Crusting, Runoff, and Erosion Response to Soil Water Content and Successive Rainfalls
Authors: Bissonnais Yves Le , Singer Michael J.
Published: July 2010

Soil crusts reduce the water infiltration rate and may induce the erosion process by increasing runoff. We investigated the effects of initial soil water content and successive rainfalls on soil crusting, subsequent runoff, and erosion. Surface samples of Capay silty clay loam (fine, montmorillonitic, thermic Typic Chromoxerert) and Solano silt loam (fine‐loamy, mixed, thermic Typic Natrixeralf) were packed into 0.37‐m2 plots inclined at 9% slopes and subjected to simulated rainfall applied at 40 mm h−1 as 3.2‐mm‐diam. drops falling 2.5 m. Three successive 1‐h rainfalls were applied to initially air dried or prewetted soils. Water splash, runoff, soil splash, and wash materials were collected at 5‐min intervals. Post‐rainfall photographs of crusted soil surfaces provided additional morphological evidence to support conclusions drawn from quantitative data. Prewetting reduced crust development, runoff, and erosion and the differences remained significant even during the third rainfall. For the initially air dry soils, erosion rates and runoff reached steady state after 25 mm of rain during the first rainfall, and were the same for the second and third rainfalls. For prewetted soils, runoff and erosion were lower, did not reach steady state during the first event, and increased during each subsequent rainfall. The infiltration rate for initially air dry soils was 20 times lower than for prewetted soils after 40 mm of the first rainfall, and remained 10 and 2 times lower after the second and third rain, respectively. The crust was still not completely developed on prewetted soils after 120 mm of cumulative rainfall.
Seed‐Zone Temperature and Moisture Conditions under Conventional and No‐Tillage in Alaska
Authors: Bidlake W. R. , Campbell G. S. , Papendick R. I. , Cullum R. F.
Published: July 2010

Identification of tillage and residue management options that favor crop production and promote soil conservation is an important research objective. A study was conducted to compare seed‐zone temperature and moisture conditions under conventional and no‐tillage regimes during stand establishment of spring barley (Hordeum vulgare L.) in interior Alaska. The approach was to monitor soil temperature and moisture conditions in a conventional tillage and a no‐tillage plot, and to develop and apply a mechanistic model of heat and moisture transport for partially frozen soil‐crop residue systems. The model simulates temperature and vapor density profiles and radiation transfer within the crop residue canopy and soil temperature and soil water matric potential. Both measured and simulated results indicated that the no‐tillage soil was cooler and wetter than the conventional tillage soil. The average daily difference between simulated temperature at the 6‐cm depth was 2.5°C during the 54‐d simulation period. Simulated matric potential of unfrozen soil at the 6‐cm depth varied between −12 and −45 J kg−1 for conventional tillage and between −3 and −5 J kg−1 for no‐tillage. Simulations indicated that the average difference in soil temperature at the planting depth was reduced by 31% when the no‐tillage planting depth was decreased to 3 cm, and this practice may be used to exploit the greater moisture availability under that management to obtain more favorable seed‐zone conditions.
Oxygen Concentration and Redox Potential Gradients in Unsaturated Model Soil Aggregates
Authors: Zausig Jörg , Stepniewski Witold , Horn Rainer
Published: July 2010

Anoxic microsites in unsaturated soils are often discussed in the context of denitrification or favorable conditions for plant root growth. To verify the existence of such anoxic microsites in the center of aggregates in unsaturated soils, O2 partial pressure, and redox potential were studied in model soil aggregates of spherical shape with microelectrodes. Soil material was taken from six soil horizons varying in texture and content of organic C. The measurements showed significant changes of the aeration status of these soil aggregates (diameter of 23 mm) as a function of pore water pressure in the range of pm = −1 to −6 kPa. At pore water pressures less than −4 kPa, all aggregates exhibited oxic centers. At higher soil moisture contents, the radii of anoxic centers at different pore water pressures could be related to soil respiration as the sink for O2, with parameters such as air‐filled porosity and pore continuity controlling the O2 flux to the aggregate center. The values of diffusion constant covered the range from 4 × 10−16 to 40 × 10‐16 mol Pa−1 m−1 s−1 and were related closely to pore water pressure, but didn't show a close relation to air‐filled porosity. The occurrence of anoxic aggregate centers was not always accompanied by a decrease in redox potential. It was assumed that these effects are induced by different microbial activities as well as by a different redox buffering of the six soils investigated.
Pyrite Oxidation, Carbonate Weathering, and Gypsum Formation in a Drained Potential Acid Sulfate Soil
Authors: Ritsema C. J. , Groenenberg J. E.
Published: July 2010

To quantify the rate of pyrite oxidation, weathering of carbonates and the formation of gypsum in a potential acid sulfate soil exposed to drainage, a column experiment was executed for 175 d. During the experiment, 24 g of FeS2, of the originally present 1327 g, oxidized within 70 d. Weathering of carbonates prevented acidification; an estimated 21 g of CaCO3 and 17 g of CaMg(CO3)2 dissolved simultaneously within the first 70 d. Rising Ca2+ and SO2−4 concentrations initiated gypsum precipitation from around Day 70 until the end of the experiment. A numerical model was used to simulate the experimental results. Estimated and simulated quantities of pyrite oxidation and carbonate weathering, and measured and simulated soil solution concentrations appeared to agree well. Model simulations indicate the formation of 63 g CaSO4 between Days 70 and 175 in the upper 60 cm of the soil profile.
Automated Determination of Nitrogen‐15‐Labeled Dinitrogen and Nitrous Oxide by Mass Spectrometry
Authors: Stevens R. J. , Laughlin R. J. , Atkins G. J. , Prosser S. J.
Published: July 2010

The 15N content of N2 and N2O emitted from 15N‐enriched soils conveys information about their sources; such information can only be obtained by mass spectrometry. Conventional dual‐inlet isotoperatio mass spectrometry (IRMS) involve complex gas sampling and inlet systems, which limit the use of the technique. Continuous‐flow IRMS was evaluated for the automated analysis of 15N‐labeled N2 or N2O. A gas sample is flushed from a vial by a He carrier stream. Carbon dioxide, NO, and water are chemically removed prior to chromatographic separation of N2 from N2O. For N2 analysis, the carrier stream is passed through a Cu reduction column to remove O2. A triple‐collector isotope‐ratio mass spectrometer analyzes a portion of the carrier stream for N2 at m/z 28, 29, and 30. Accurate values for ratio (29/28 and 30/28) differences in normal and enriched atmospheres were obtained from enrichments up to 2 atom % 15N with coefficients of variation (CVs) ranging from 0.07 to 1.37%. The reduction column is bypassed for the analysis of N2O at m/z 44, 45, and 46. From the 45/44 ratios, the 15N content of the N2O could be determined accurately with enrichments up to 40 atom %. Precision depended on concentration and enrichment, with CVs ranging from 10% for 15 µL N2O L−1 at natural abundance to <1% for 100 µL N2O L−1 at 10 atom % 15N. The concentration of N2O could be quantified from the ion currents at m/z 44, 45, and 46 with a detection limit of 2.1 µL N2O L−1. A batch of 132 samples can be analyzed automatically for N2 or N2O at a rate of six determinations per hour. Automation of 15N determination in N2 and N2O should aid the study of the processes resulting in evolution of these gases from soil.
Decomposition of Nitrogen‐15‐Labeled Wheat and Cellulose in Soil: Modeling Tracer Dynamics
Authors: Hadas Aviva , Feigenbaum Sala , Sofer M. , Molina J. A. E. , Clapp C. E.
Published: July 2010

The decomposition of heterogeneous plant material could be described more generally if it were based on decomposition rates of defined materials. In this study, mineralization of 15N‐labeled wheat (Triticum aestivum L.) and 15N turnover linked with the decomposition of cellulose in soil were measured and compared with simulated kinetics computed by the model NCSOIL. Dried wheat shoots (2 g C kg−1) with a C/N ratio of 14.4, or cellulose with (15NH4)2SO4 at the same C rate and C/N ratio, were added to two soils and incubated for 32 wk at 30 °C and 60% water‐holding capacity. Inorganic and Kjeldahl N and 15N were measured and compared with simulated data. Cellulose induced net immobilization of 70 mg N kg−1 within 2 wk; thereafter, net N mineralization was greater than for untreated soils. The decomposition rate constant of cellulose, computed by optimization of the model, was 0.024 d−1. The model underestimated N immobilization, the subsequent rate of net N mineralization, and the isotopic dilution of inorganic N. These discrepancies probably resulted from slower turnover of microbial biomass than simulated. Wheat decomposition was divided into three stages, corresponding to soluble, cellulose‐like, and resistant fractions that decomposed with rate constants of 3.0, 0.024, and 4 × 10−8 d−1 and accounted for 19, 45, and 36%, respectively, of organic wheat N. The computed gross mineralization of wheat N after 32 wk totaled 64% of added organic N, whereas 15N recovery as inorganic N was 40 to 50%, depending on the soil. The difference was attributed to concurrent assimilation of labeled N by soil microbial biomass that depended partly on native soil N concentrations and should be considered in interpreting tracer experiments.
Radiocarbon Signatures of Turnover Rates in Active Soil Organic Carbon Pools
Authors: Hsieh Yuch‐Ping
Published: July 2010

Identifying turnover rates in active soil organic carbon (SOC) pools is a critical step toward the understanding of soil nutrient cycling and global C cycles. The mean residence times (MRT) of the dominating active SOC pools in surface soils are usually less than a few decades. This range of MRT is difficult to determine because it is too short for radiocarbon dating and too long for most tracer techniques. I developed a procedure to construct radiocarbon signatures for identifying MRT in active SOC pools based on the residue bomb 14C in the atmosphere. The radiocarbon signature is specific to the year when a soil sample is taken. The sensitivity of the radiocarbon signatures is a function of MRT and the time when a soil sample is taken. This method is sensitive to MRT of active SOC pools in a range from 1 to 80 yr at the present time. Using those radiocarbon signatures, the MRT of active SOC pools in the Morrow Plots (Urbana, IL) and Sanborn Field (Columbia, MO) were estimated at 67 and 34 yr, respectively.
Short‐ and Long‐Term Phosphorus Dynamics in a Fertilized Ultisol under Sugarcane
Authors: Ball‐Coelho B. , Tiessen H. , Stewart J. W. B. , Salcedo I. H.
Published: July 2010

In Brazilian sugarcane production systems, P fertilizer represents a substantial input cost, yet it is used with low efficiency. Furthermore, extractants currently used to estimate available P in highly weathered soils are not satisfactory. Understanding soil P transformations is a prerequisite to improving estimates of available P and fertilizer use efficiency. We used a sequential P fractionation procedure to examine short‐term dynamics of P from fertilizer, residue returns, and soil, and long‐term changes in forms and quantities of soil P as a result of fertilization. Mulch and burn systems of residue management were imposed as treatments in field‐grown sugarcane (Saccharum officinarum L.) in northeast Brazil. Both treatments had similar inputs of P from residues (8.7 kg ha−1) but, despite the higher “available” P content of the ashes, more of the added P was mobilized and taken up by the plant in the mulch system, probably due to the presence of roots within the decomposing litter and more intense root exploration of the topsoil as a result of an improved moisture regime. This improved moisture and P supply was reflected in a 45% higher ratoon yield in the mulch treatment. Fertilizer P applied in a furrow 20 cm deep with the plant crop was concentrated in the more labile fractions, and had a residual effect on the first ratoon of about 30%. Over the long term (10 yr) there was accumulation (about 144 kg ha−1) of fertilizer P in the top 30 cm (in both labile and stable fractions). Nearly one‐half of the increase was in the first 7.5 cm of soil, a reflection of limited mixing of broadcast applications and uptake from the 7.5‐ to 15‐cm layer.
Kinetics of Microbial Respiration and Nitrogen Mineralization in Great Lakes Forests
Authors: Zak Donald R. , Grigal David F. , Ohmann Lewis F.
Published: July 2010

Recent attention has focused on organic matter storage in forested ecosystems because climate change could potentially alter this process. Labile organic matter pools are especially important because they may be most strongly influenced by changes in soil temperature and water availability. We measured rates at which C and N were released from labile organic matter within the forest floor and mineral soil of jack pine (Pinus banksiana Lambert), red pine (P. resinosa Aiton), balsam fir [Abies balsamea (L.) Miller], sugar maple (Acer saccharum Marshall), and quaking aspen (Populus tremuloides Michaux) forests. Forest floor and mineral soil samples were assayed for microbial respiration and N mineralization using a long‐term (32 wk at 35 °C) laboratory incubation. Cumulative amounts of respired C and mineralized N were fit to first‐order rate equations; pools and rate constants were compared among forests. Labile (respired) C pools in forest floor ranged from 67 (jack pine) to 92 g C m−2 (sugar maple), four to six times less than that measured in mineral soil. Rate constants for microbial respiration were statistically different among forest types, but means ranged narrowly in forest floor (0.269–0.299 wk−1) and mineral soil (0.303–0.350 wk−1). Labile (mineralized) N pools ranged from 2.2 (red pine) to 4.1 g N m−2 (sugar maple) in forest floor, an order of magnitude less than those in mineral soil. Rate constants for N mineralization varied from 0.326 to 0.556 wk−1 in forest floor and from 0.043 to 0.069 wk−1 in mineral soil. Regional climatic variables were weakly correlated with labile C and N pools and with rate constants. Annual in situ estimates of microbial respiration and N mineralization were far less than respired C and mineralized N pools, suggesting that only a fraction of labile soil organic matter is annually metabolized within these forests. Local climate, rather than the chemistry of labile organic matter, appears to be an important factor constraining the annual in situ flux of C and N from this pool.
Nitrogen and Phosphorus Fate from Long‐Term Poultry Litter Applications to Oklahoma Soils
Authors: Sharpley Andrew N. , Smith S. J. , Bain W. R.
Published: July 2010

With the rapid growth of the poultry industry in eastern Oklahoma, information is needed on the impact of land application of associated litter on the area's soil and water resources. The effect of broiler litter application on the N and P content was investigated by sampling 12 soil profiles to 150 cm under ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] to which litter had been continually applied for 12 to 35 yr. Litter application averaged 6 Mg ha−1 yr−1 (dry wt.), which contributed approximate N and P amounts of 270 and 90 kg ha−1 yr−1. Adjacent soil profiles under idle native grass, which received no litter or mineral fertilizer, were sampled at the same time to a 150‐cm depth. On average, soil pH and organic C were 0.5 and 21 g kg−1 greater and bulk density 0.2 Mg m−3 lower in the surface 5 cm of treated than untreated soils. Below 25 cm, litter had little effect on these properties. The effect of poultry litter on N and P content was greatest in the surface 5 cm of soil, with NO3‐N and Bray‐I P (BP) averaging 49 and 188 mg kg−1 in treated and 13 and 9 mg kg−1 in untreated soils. Below 5 cm, N and P content decreased rapidly, with only slight NO3‐N accumulations (5 mg kg−1) between 50 and 100 cm and no movement of P below 30 cm observed. Poultry litter application decreased P sorption to a depth of 30 cm. Average 1.2‐ and 2.5‐fold increases in the total N and NO3‐N content of treated compared with untreated 0‐ to 100‐cm profiles were observed. For P, 2‐ and 13‐fold increases in total P and BP were found, with little accumulation as organic P. Overall, BP increased 22 mg kg−1 for each 100 kg P ha−1 added in litter. The greater portion of litter P (72%) than N (44%) retained in the soil profile reflects the differing sorption of these nutrients by soil, and greater plant uptake of N than P. It also emphasizes the need to carefully manage continual land applications of poultry litter to minimize potential environmental impacts.
Analyses of Slope and Runoff Factors Based on the WEPP Erosion Model
Authors: Huang Chi‐hua , Bradford Joe M.
Published: July 2010

Under process‐based erosion model development, the source of sediment transported off a field is separated into that from interrill and rill areas, and separate detachment equations are developed. Limitation of this spatial separation is that, in many conditions, rill and interrill areas are not clearly defined a priori. We interpreted the erosion and deposition equations used in the current Water Erosion Prediction Project (WEPP) in an alternative fashion such that spatial separation of rill and interrill areas is no longer required. Analytic solutions were derived for the WEPP erosion and deposition equations under general conditions. Simplified solutions for a specific case, uniform rain on uniform slope, were examined closely for slope and runoff effects on sediment delivery. Under both erosion and deposition conditions, analytic solutions show a linear relationship between sediment yield, qs and slope, S. The dependency of qs on runoff, qw, is either linear or quadratic depending on whether the system is dominated by an erosion or deposition regime. These analytic findings explain results obtained from laboratory studies in which sediment yield was collected under variable slope and rain intensities.