bluuebunny/crossref_metadata_2025_split huggingface dataset:
Soil Productivity Index: Predictions of Site Quality for White Spruce Plantations
Authors: Gale M. R. , Grigal D. F. , Harding R. B. 
Published: July 2010

AbstractVery few site‐quality models have incorporated the biological effects of multiple soil properties on optimum root growth. One such model that was originally developed for agronomic crops and has been used for naturally forested stands is the soil productivity index (PI) model. Our objectives for this study were to determine if the PI model could be used to estimate site quality for white spruce (Picea glauca [Moench] Voss) plantations and to compare the use of PI vs. site index in equations describing changes in aboveground biomass with age. The PI model includes an estimate of optimum vertical root distributions that is used to weight the relative effects of mineral‐soil characteristics (bulk density, pH, available water capacity, and aeration) on aboveground biomass. Relative topographic (percent slope) and climatic (precipitation and evaporation potential) information are also used in the model. Results indicated that site index and PI were not significantly correlated. However, PI was more highly correlated with aboveground stand biomass and mean annual biomass increment than was site index. Site index was more highly correlated with biomass estimates in older plantations (35–43 yr), whereas PI was more highly correlated to biomass estimates in younger plantations (19–34 yr). To further assess the relationships between estimates of biomass and site quality, adjusted for age, a Schumacher‐type equation was used. Comparable results were observed between stand‐biomass equations using PI vs. site index.
Soil‐Core Break Method to Estimate Pine Root Distribution
Authors: Escamilla J. A. , Comerford N. B. , Neary D. G. 
Published: July 2010

AbstractRoot‐distribution studies are tedious and time consuming; there‐fore, root systems of forest ecosystems are one of the least studied components. Yet they are essential in order to assess belowground effects of forest‐management activities. This study used the soil core‐break method to measure the number of roots crossing a horizontal unit area (N, expressed in no. cm−2) as an alternative to measuring the more time consuming root‐length density (Lv, expressed as cm root length cm−3 soil volume). Soil core samples were taken from the surface horizon of a 7‐yr‐old slash pine (Pinus elliottii Engelm.) stand growing on a Pomona sand (sandy, siliceous, hyperthermic Ultic Haplaquod). Soil cores, 15.2‐cm diameter by 30 cm long, were extracted from two microsite locations within the check and complete‐weed‐control plots. Root‐length density and roots per square centimeter were measured at 2‐cm depth increments. The roots‐per‐square centimeter measure was a useful predictor of root‐length density only when treatment means were used, and even then the data did not fit the theoretical relationship of Lv = 2N. An Lv/N slope of ≈1 suggested that roots have a preferential vertical orientation in the A horizon. However, depth trends of root‐length density and roots per square centimeter were similar regardless of management practices or microsite. Roots measured as roots per square centimeter was also a less variable measure of root quantity than was root‐length density. Although roots per square centimeter can only be used to calculate root‐length density on an empirical basis, the more easily obtained value of roots per square centimeter can be used to depict root response to belowground competition.
Spatial and Temporal Fine‐Root Distribution in Three Louisiana Forest Soils
Authors: Farrish K. W. 
Published: July 2010

AbstractThe distribution of fine plant roots (≤3‐mm diam.) in three northern Louisiana forest soils was investigated. Two upland mixed pine‐hardwood sites and one bottomland hardwood site were sampled periodically for a year. Fine‐root biomass and surface area were determined on root samples extracted using wet sieving of soil corings. Both fine‐root biomass and surface area decreased abruptly with increasing depth on all sites, with 60 to 64% of the biomass and 63 to 70% of the fine‐root surface area occurring in the top 20 cm of soil. Prolonged soil wetness or dryness during the growing season caused reductions in fine‐root‐biomass concentrations. A contradictory increase in fine‐root surface area occurred, however, during prolonged soil saturation in the bottomland site, suggesting a possible change in fine‐root morphology during inundation. Total fine‐root biomass was similar on the three sites, averaging 8.4 and 10.5 Mg ha−1 on the two upland sites, and 9.9 Mg ha−1 on the bottomland site. Total fine‐root surface area was much higher on the bottomland site, however, averaging 1.48 × 105 m2 ha−1 vs. 9.5 × 104 and 7.0 × 104 m2 ha−1 on the upland sites. These data indicate that fine‐root concentrations in these forest soils decrease rapidly in response to unfavorable soil environmental conditions such as prolonged saturation or drying. These data also indicate that maximum root concentrations generally occur in the spring and early summer, with minimums during late summer, fall, and winter.
Phosphate Mineralogy and Equilibria in Two Kentucky Alfisols Derived from Ordovician Limestones
Authors: Karathanasis A. D. 
Published: July 2010

AbstractThe phosphate mineral distribution as it relates to in situ soil solution composition of two Alfisols developed from phosphatic Ordovician limestones in the inner Bluegrass Region of Kentucky was investigated. At both sites, microcrystalline apatite appeared to be the primary source of P. Surface weathering under a moderate pH (5.7–6.7) and a carbonate‐free environment has apparently induced apatite transformations to wavellite, crandallite‐like, and barrandite‐like minerals as indicated by x‐ray diffraction (XRD), differential scanning calorimetry (DSC) or scanning electron microscopy (SEM) analyses. The possible stability of othe phosphate minerals such as millisite, montgomeryite, variscite, strengite and MnPO4·1.5H2O was supported by solution‐composition data, but it was not confirmed by XRD, DSC, or SEM analyses. Sequential‐fractionation extractions suggested the presence of significant amounts of discrete or occluded Al‐ and Fe‐phosphates in soil and nodular materials, mostly in amorphous or poorly crystalline forms. The solution ion‐activity products in most cases were consistent with amorphous Fe‐ or Al‐phosphates approaching the stoichiometry, but exceeding the solubility, or strengite or variscite‐like minerals. Solution data and SEM observations suggested that the formation of secondary Ca‐Al‐, Al‐, and/or Fe‐phosphates in these soils may occur through an apatite congruent‐dissolution stage, which is followed by gradual adsorption and precipitation of P on chemically etched clay‐mineral and amorphous‐hydroxide surfaces.
Using an Electro‐Optical Switch to Measure Soil Water Suction
Authors: Cary J. W. , Gee G. W. , Simmons C. S. 
Published: July 2010

AbstractA simple and inexpensive electro‐optical switch (infrared light‐emitting diode; IR LED) was used to show that soil water suctions can be measured accurately by employing nylon filter disks with different pore sizes. Nylon filter disks that become translucent when water is absorbed were shown to open or close an electro‐optical switch at specific soil water suctions associated with the air‐entry suction of a disk, thereby demonstrating the principle of a digital tensiometer. Sensors constructed by inserting a nylon filter disk in a switch were shown to operate across a suction range of 0.004 to 2.4 MPa and were tested in a silt loam soil under drying and wetting conditions. The switch‐sensor's performance was compared with a second type of sensor (CdS photoresistor with LED) made with a layered fritted‐glass disk instead of nylon. This second sensor was able to continuously detect changes of water content from air dry to saturated. We concluded, however, that the first type of sensor was superior for precisely measuring soil water suction.
Saturated Hydraulic Conductivity Reduction Caused by Aerobic Bacteria in Sand Columns
Authors: Vandevivere Philippe , Baveye Philippe 
Published: July 2010

AbstractBacterial reductions of the saturated hydraulic conductivity, Ks, of natural porous media have been traditionally associated with the development of anaerobic conditions and the production of large amounts of extracellular polymers by the bacteria. Various researchers have also reported that these reductions occur predominantly at or very near the surfaces of injection of nutrients within the porous media. Attempts to describe mathematically the resulting clogging process have, in the past, been based on the assumption that bacterial cells form impermeable biofilms uniformly covering pore walls. A series of percolation experiments was carried out to determine the extent to which an obligately aerobic bacterial strain, Arthrobacter sp., is able to clog permeameters filled with fine sand. A second objective was to elucidate the mechanism(s) responsible for this process. The experimental results indicate that strictly aerobic bacteria are able to reduce Ks by up to four orders of magnitude. Rapid reductions in Ks are associated with the formation of a bacterial mat at the inlet boundary of the sand columns. When the colonization of the inlet is prevented, clogging proceeds within the bulk of the sand at a noticeably slower rate. Under O2‐ or glucose‐limited growth conditions, this decrease in Ks within the sand does not appear on scanning electron micrographs to be caused by exopolymers, which are entirely absent, but rather seems to be due to the presence of large aggregates of cells that form local plugs within the pores. Under conditions of severe N limitation, the same mechanism seems to be largely responsible for the observed clogging, in spite of the production by the cells of extracellular substances, visible under light microscopy and on scanning electron micrographs. In all cases, the coverage of the solid surfaces by the bacterial cells is sparse and heterogeneous, contrary to the basic tenets of the biofilm model.
Simulation of Surface Energy Balance and Soil Temperature under Strip Tillage: II. Field Test
Authors: Hares Mohammad A. , Novak Michael D. 
Published: July 2010

AbstractStrip tillage may be a viable management technique for annual crops in northern latitudes, since the mulch strip should conserve soil and water while higher temperatures in the bare strip should yield good germination. The object of our research was to identify the processes that determine surface energy‐balance components and soil temperatures under strip tillage and simulate them using a physically based numerical model. We tested the model with micrometeorological data collected at Vancouver, BC. Soil temperatures and evaporation rates in bare and uniformly covered straw‐mulch plots were predicted reasonably well, except for the bare plot when evaporation was soil limited. The disagreement was attributed to variability associated with patchy soil drying and inadequacy of the simple surface‐resistance model used to calculate evaporation. Good agreement for evaporation rates under 10 and 20 t ha‐1 mulches was achieved by enhancing transfer rates within the mulch layers by at least a factor of 4.5 above molecular diffusion rates. For the strip‐tillage plots, the model underestimated (energy‐limited) evaporation rates and soil temperatures in 0.1‐m‐wide bare strips separated by 0.3‐m‐wide mulch strips. This disagreement was attributed to micro‐scale advection of warmer and drier air from the mulch strips to the bare strips, a phenomenon neglected in the model (and in all such models in the literature). The measurements showed that springtime soil temperatures in bare strips oriented in various directions were nearly equal to those in an adjacent bare plot. Therefore, considerable erosion protection should be possible without deleterious soil thermal regimes for seed germination.
Rainfall Intensity Affects Transport of Water and Chemicals through Macropores in No‐Till Soil
Authors: Edwards W. M. , Shipitalo M. J. , Owens L. B. , Dick W. A. 
Published: July 2010

AbstractWater that infiltrates through cropland soils can carry agricultural chemicals through and below the root zone, possibly reaching groundwater. We investigated the effect of rainfall intensity on movement of water and chemicals through no‐till soil containing earthworm (Lumbricus terrestris L.) burrows and other macropores. Nine 30 by 30 by 30 cm blocks of soil from the surface of a no‐till corn (Zea mays L.) field received a surface application of 7.7 kg ha‐1 atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) and 105 kg ha‐1 SrBr2·6H2O and were subjected to simulated rainfall treatments of 30 mm (2700 mL) of water applied in 15‐, 30‐, or 120‐min periods. Percolation through the blocks during and after the rainfall treatments was collected in 64 3.75 by 3.75 cm cells at the base of each block. Average time to start of percolation was 2.2, 4.4, and 51.5 min for the 15‐, 30‐, and 120‐min rainfall treatments, respectively. For the same treatments, percolation volumes averaged 468, 334, and 33 mL block‐1. Of the 64 possible percolation sampling cells, the average number of cells that collected percolate was 13.3 for the fast, 5.3 for the medium, and 3.3 for the slow treatments. The largest percolate sample for each block averaged 34, 60, and 51% of the total percolate for these intensity rates, emphasizing the lack of homogeneous flow through soils containing macropores. Average concentration of atrazine in the percolate ranged between 7 and 9 mg L‐1 and was not affected by rainfall intensity. A second 30‐min‐intensity storm was applied 1 wk later to all blocks, producing more percolate with lower chemical concentrations. Transport of each chemical was dominated by percolate volume rather than by rainfall intensity.
Contribution of Nitrogen Fixation to Sugar Cane: Nitrogen‐15 and Nitrogen‐Balance Estimates
Authors: Urquiaga Segundo , Cruz Kátia H.S. , Boddey Robert M. 
Published: July 2010

AbstractContinuous sugarcane (Saccharum spp.) culture in Brazil, with low N inputs and almost total removal of plant biomass at each harvest, has not depleted soil N reserves. This, and high numbers of N2‐fixing bacteria associated with the plants, suggests that the crop may be obtaining considerable N from biological nitrogen fixation (BNF). This 3‐yr study assessed the importance of such contributions to three sugarcane species (S. officinarum L., S. barberi Jesw., and S. spontaneum L.), and seven commercial Brazilian hybrids. The plants were grown in a concrete tank containing 15N‐labeled soil in order to use 15N isotope dilution to estimate the BNF contributions. A grass, Brachiaria arrecta (cv. IRI 442), was included as a non‐N2‐fixing control. All aerial tissue was harvested annually, and the roots and stem bases were removed at the end of the experiment. For all 3 yr, the commercial hybrids and the S. spontaneum cultivar (Krakatau) accumulated more N at significantly lower 15N enrichments than the control. These data suggest that the plants obtained considerable BNF contributions, but interpretation of the 15N data was prejudiced by (i) the steadily declining 15N enrichment of the soil mineral N, (ii) carry‐over of N from one harvest to the next in the roots and stem bases, and (iii) shading of the control crop by the tall cane plants. Several of the sugarcane cultivars had significantly positive N balances, however, and there was good agreement between the estimates of BNF contributions derived from N balance and isotope dilution. Krakatau and the commercial hybrids CB 45‐3 and SP 70‐1143 obtained the largest contributions from BNF, but methodological problems did not allow exact determinations.
Soil Water and Crop Yield Spatial Variability Induced by Irrigation Nonuniformity
Authors: Or Dani , Hanks R. J. 
Published: July 2010

AbstractExperimental evaluation of different irrigation management practices under similar conditions of soil variability often requires several plots having similar soil variability. These types of field plots are difficult to find or not available for experimental use. This study examined crop yield and soil water variability resulting from nonuniform irrigation applications as a surrogate for soil variability within an otherwise homogeneous field. The study conducted at Logan, UT, in 1989 on a Millville silt loam soil (coarse‐silty, carbonatic, mesic Typic Haploxeroll) used a drip irrigation system with spatially variable application rates. The mean dripper application rate was 5.6 L/h with a standard deviation of 3.18 L/h and a spatial‐correlation range of 5.3 m. Corn (Zea mays L.) was grown in 0.75‐m‐wide rows at a plant density of 8.9 plants/m2 in 30 by 15 m plots. Irrigation‐scheduling treatments were (i) a predetermined calendar schedule (NPT), and (ii) optimized for the nonuniformity of the irrigation system (OPT). There were three replicates. Soil water, crop height, and crop‐yield variability exhibited spatial structures similar to the applied‐irrigation variability, but crop‐yield variability (mean CV of 0.227) was less than the irrigation variability (CV of 0.57). Crop yield was highly correlated to the dripper flow rate and was 13% higher on the OPT than on the NPT schedule. Nonuniform irrigation can be used to induce a desired spatial pattern of available soil water. Irrigation scheduling methods should consider soil variability and irrigation uniformity.
Surface Sealing and Hydraulic Conductances under Varying‐Intensity Rains
Authors: Giménez D. , Dirksen C. , Miedema R. , Eppink L.A.A.J. , Schoonderbeek D. 
Published: July 2010

AbstractIn the past, investigations on surface seals developing under simulated rains usually were performed with uniform rainfall intensities. Recent studies, however, showed that varying‐intensity rains affect erosion and volumes of runoff. We conducted a study on surface sealing under varying‐intensity rains using physical and morphological methods. Four 1‐h‐duration rainfall patterns were used: S1, S2, S3 and S4, with mean rainfall intensities of 83, 69, 65, and 51 mm h‐1, respectively, and highest intensities of 148, 120, 111, and 100 mm h‐1, respectively. Two experiments were performed in triplicate: (i) in packed soil columns, pressure heads at 1‐cm depth were measured, and runoff (Rt) and wash sediment (St) collected at short time intervals during S1, S3, and S4 patterns; and (ii) packed shallow soil flumes were successively exposed to 10, 15, 30, 40, and 60 min of S2 and S4 patterns, and the surface was then characterized by micromorphological analysis of thin sections (S2) and top‐view photographs (S2 and S4). The largest differences between rainfall patterns occurred during the intensity peaks (10–30 min): at the end of these periods, measured surface seal hydraulic conductances (β) attained values of 0.80, 0.25, and 0.51 h‐1 for S1, S3, and S4, respectively. These relative β values are thought to be due to partially open surfaces as a result of microrill erosion (S1), complete sealing without erosion (S3), and incomplete sealing (S4). Presented Rt, St, and morphological data support these conclusions. After 5 min of the intensity peaks of S2, surface seals attained maximum observed thickness and minimum macroporosity (>30 µm). Planar voids (>500 µm) were eliminated at this point. Under continuing rain, erosion reduced the seal thickness and increased macroporosity, mainly as planar voids.
Field‐Scale Bromide Transport as Affected by Tillage
Authors: Agus F. , Cassel D. K. 
Published: July 2010

AbstractTillage alters soil physical properties and modifies the rates of many physical, chemical, and biological processes. The purpose of this study was to determine if subsoiling increased the depth of leaching of the nonreactive Br‐ anion in a Norfolk soil (fine‐loamy, siliceous, thermic Typic Kandiudult) having a tillage‐induced pan. Three tillage treatments, replicated three times, were selected: (i) current‐year subsolling (S88); (ii) one‐year subsoiling carry‐over (subsoiled in 1987: S87); and (iii) double disk tillage (DD). Mechanical impedance was measured at 35 d after tillage with a recording cone penetrometer to a depth of 60 cm on transects normal to the soybean (Glycine max [L.] Merr.) row. Cone index exceeded 3000 kPa for the DD treatment at the 20‐ to 45‐cm depth; current‐year subsoiling reduced cone index at that depth to 1300 to 2500 kPa. Six days after planting soybean, KBr was uniformly broadcast on the soil surface at the rate of 280 kg Br‐/ha. Soil samples were taken after the plots received 130, 260, 545, and 1217 mm of cumulative rain and/or irrigation (28, 64, 128 and 351 d, respectively, after applying KBr). Soil samples were collected using a hydraulic probe at seven positions on duplicate transects normal to the soybean row in each plot. Bromide concentration measured with a specific‐ion electrode was highly variable at all depths. For the four consecutive sampling dates, the center of Br‐ mass occurred at the 11‐, 17‐, 51‐, and 90‐cm depths, respectively, for Treatment DD; at the 19‐, 27‐, 71‐, and 1002‐cm depths for Treatment S88; and at the 13‐, 20‐, 57‐, and 108‐cm depths for Treatment S87. Both subsoil treatments loosened the soil and increased the depth of Br‐ transport. Although the depth of Br‐ transport was slightly deeper for the subsoiled treatments, it leached below the rooting depth for all treatments. No definitive relationship between cone index and Br‐ leaching depth was observed.
Soil Dispersibility, Rain Properties, and Slope Interaction in Rill Formation and Erosion
Authors: Shainberg I. , Warrington D. , Laflen J. M. 
Published: July 2010

AbstractSoil erosion increases with slope steepness. We hypothesized that the rate at which short‐slope soil erosion increases with slope steepness depends on the prevailing erosion mechanism, which in turn depends on soil dispersibility and rain properties (impact energy of drops and water quality). Soil dispersion, as a function of exchangeable sodium percentage (ESP) and water quality, was determined by shaking soil samples in deionized water (DW) or tap water (TW). Clay dispersion increased with increases in soil ESP and was prevented by the electrolyte concentration in TW. We studied the effect of soil ESP, water quality, and the impact energy of rain on soil erosion while maintaining similar runoff. To do so, we first exposed the soil samples to DW rain on a 5% slope until a surface seal developed. Then we increased the slope to 35% and changed the water quality and impact energy of the rain. Runoff volumes were unaffected by rain properties at the 35% slope. Soil losses increased with increases in the ESP of the soil. Soil losses varied with rain properties in the following order: DW rain > TW rain = DW rain with low energy (mist) > TW mist. Rills were formed by both DW rains (high impact energy and mist). The extent of rilling increased with soil ESP. No rills were formed by TW rains. Under dispersive conditions (sodic soils and DW), runoff was sufficient to initiate rilling and soil losses increased sharply with slope.