bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Nitrogen Dynamics following Harvesting and Conversion of Red Alder and Douglas Fir Stands
Authors: Van Miegroet H. , Homann P. S. , Cole D. W.
Published: July 2010

Drastic reductions in NO3‐ leaching have been observed after harvesting of mature red alder (Alnus rubra Bong.) stands. Our objective was to examine whether these reduction were linked to changes in soil N dynamics. Adjacent alder and Douglas fir [Pseudotsuga menziessii (Mirbel.) Franco] stands on young glacial soils (Alderwood; a loamy‐skeletal, mixed, mesic, ortstein Aquic Haplorthod) in western Washington were harvested and replanted with either alder or Douglas fir seedlings; reference plots were established in nearby undisturbed stands. Three years after site conversion, when NO3‐ leaching declined most drastically in the harvested alder plots, net N mineralization and net nitrification in the upper soil were determined seasonally by in situ incubation using the buried‐bag technique. There were no significant increases in soil NH4‐N during incubation, indicating that nitrification rates closely followed net N mineralization in all plots. In the N‐poor soils of the harvested and uncut Douglas fir plots, nitrification was consistently <2 µg N g−1 per 30 d. In the N‐rich alder reference plot, nitrification was highest in summer (52 µg N g−1 per 30 d), lowest in winter (4 µg N g−1), and intermediate in spring (20 µg N g−1). Seasonal fluctuations in nitrification diminished in the harvested alder plots. Nitrification rates were significantly lower than in the uncut alder plot in summer only (5–9 µg N g−1 per 30 d), but this difference was insufficient to account for the lower NO3‐ leaching rates in the conversion plots. Soils in the harvested plots were drier and experienced greater temperature extremes, but these changes did not correlate well with the variability in N‐mineralization rates between uncut and harvested alder plots. Nitrification was positively correlated to soil temperature in the uncut alder plot only. The establishment of red alder seedlings did not appear to have influenced the N dynamics in either N‐poor or N‐rich soils.
Infiltration into Sealed Soils as Influenced by Gravel Cover
Authors: Valentin C. , Casenave A.
Published: July 2010

The influence of stone gravel on water infiltration is not thoroughly understood, in that previous studies led to contradictory results. This field work was conducted to determine the effect of gravel on infiltration into sealed soils and to develop a regression model for infiltration based on the areas of the exposed and covered surfaces. Data were collected on 11 soils from three great groups from the fringe of the Sahara to the wet savanna zone of West Africa. A portable rainfall simulator was used to simulate rainfall on 28 undisturbed 1 by 1 m plots. Surface slope (P), portions of surface areas covered by grass vegetation (V), coarse fragments partly embedded in a surface seal (E), free coarse fragments (F), and sealed patches (S) were assessed as well as mean diameters (MD) of coarse fragments. The surface coverage by free surface gravel alone accounted for 68% of the variance of the cumulative infiltration/rainfall ratio, denoted as the infiltration ratio (IO). A simple nonlinear model taking into account S, F, and MD resulted in a high coefficient of determination of IO (R2 = 0.95). This model tested with three other sets of data was regarded as satisfactory to predict IO (r2 = 0.87). The results suggest that infiltration rate (IR) could be better related to the effective infiltrating annulus (AN) along the perimeter of free gravel than to the whole area under the free gravel (F). Moreover, simulated results indicated that IR increased with increasing F for MD < 0.029 m. For higher values of MD, IR decreased with increasing F. Thus, in the regions where large gravel‐size coarse fragments prevail, infiltration decreases with increasing stone cover, especially if the stones are embedded in a surface seal, as in desert pavements. Conversely, infiltration is enhanced by stone cover where small free coarse fragments are dominant, like those originating from a dismantled Fe pan.
Water Transport in an Unsaturated Medium to Roots with Differing Local Geometries
Authors: Petrie C. L. , Hall A. E. , Kabala Z. J. , Simunek J.
Published: July 2010

Pearl millet [Pennisetum glaucum (L.) R. Br.: syn. P. americanum (L.) Leeke] develops substantially lower predawn leaf water potentials than cowpea [Vigna unguiculata (L.) Walp.] under conditions of soil dehydration, but overall root length densities are greater in millet than in cowpea. The hypothesis was tested that, due to differences in root geometry and root length density, root systems of millet become less efficient in water uptake than those of cowpea as soil dries. Plants were grown in an artificial medium in pots or 1.15‐m tubes in a greenhouse and subjected to soil drying. Root geometries, root length densities, and water potentials of cowpea and millet were measured as the rooting medium dried. Distribution of roots was quantified by calculating a clumping ratio (total root length density divided by the root length density in the region surrounding individual root segment axes) at several depths within the profile. Overall root length densities were higher in millet than in cowpea, and root distributions differed. Millet roots were clumped locally along the root axis and globally within the profile, with the highest root length densities at the surface. Cowpea root lengths were one‐half as dense as millet along the root axis and distributed fairly uniformly throughout the profile. These data were used in two‐dimensional modeling of horizontal water transport from soil to branched segments of root axes of cowpea and millet to test the hypothesis. Simulations in which millet water potential became substantially lower than cowpea, and millet root length was twice as great as cowpea, predicted little difference in cumulative water flow to the roots of millet or cowpea during soil dehydration. This prediction is consistent with observations. Simulated water velocity vector fields indicated that millet's dense and clumped local root geometry became less efficient in water uptake under soil water deficits than cowpea's less dense and more evenly distributed root geometry because water uptake by millet was mainly at the root tips; in contrast, most of the root length of cowpea contributed to water uptake. Simulations conducted with millet root axes having different root length densities indicated that the low efficiency of millet in water uptake was due to the combined effects of local clumping and high root length density. When input parameters for roots and soil were varied, conclusions from the simulations remained the same.
Modeling the Hydraulic Properties of a Multiregion Soil
Authors: Wilson G. V. , Jardine P. M. , Gwo J. P.
Published: July 2010

Numerical techniques for modeling transport of solutes in multiple porosity systems have recently been developed to better represent the physical attributes of structured soils. Multiregion flow modeling requires characterization of the water content (θ) and hydraulic conductivity (K) as a function of pressure head (h) for each region of the system. A technique is presented for determining the θ(h) and K(h) relationships for a three‐region soil system based on a typical water retention data base. The demarcation between Region 1 (macropore) and Region 2 (mesopore) was assumed to occur at h = −10 cm. The effect of this assumption was evaluated against criteria of h = −2 and −25 cm, with h = −10 cm giving the best results. The θ(h) function was described as a Fermi function for Region 1 and combined with the van Genuchten model for describing Regions 2 and 3 (micropore). Continuity in θ(h) and K(θ) between regions was achieved and an excellent agreement between predicted and measured values was obtained for each region. However, the derivative of the θ(h) and K(θ) functions were occasionally not continuous through the junction points. The Fermi function based on measured and assumed parameters gave erroneous predictions of K(θ) when a large (25‐cm) range in h was used for Region 1. A modified Fermi function was developed that gave an excellent prediction of K(θ) based on assumed parameters.
Interpretation of Solute Transport Data Obtained with Fiberglass Wick Soil Solution Samplers
Authors: Poletika N. N. , Roth K. , Jury W. A.
Published: July 2010

The fiberglass wick soil solution sampler has shown potential for use in unsaturated soil, but its effect on determination of transport properties is not fully characterized. This study investigated transport behavior in the sampler of Br‐, simazine [2‐chloro‐4,6‐bis(ethylamino)‐s‐triazine], and MS‐2 coliphage. Travel‐time moment analysis for several steady flow experiments involving narrow pulse inputs of these components showed rapid breakthrough with well‐defined peaks and negligible adsorption. Assuming a convection‐dispersion process in a two‐layer system consisting of homogeneous soil overlying a sampler, moment analysis suggests that, for the flow rates tested, both expected travel time and its variance are little influenced by transport through the porous wick for layer thicknesses commonly used in solute transport studies.
Plant and Soil Composition as Affected by an Alternative Lime Source Containing Sulfate
Authors: Marsh Brian H. , Grove J. H.
Published: July 2010

The reduced crude oil conversion system uses a fluidized bed combustion system for in situ SO2 removal. The reduced crude conversion spent lime (RCCSL) that results contains mostly CaO, CaSO4, and MgO. This material was evaluated as an alternative lime source in greenhouse studies with tobacco (Nicotiana tabacum L.) and corn (Zea mays L.). Equivalent amounts (CaCO3 basis) of RCCSL, reagentgrade Ca(OH)2, and agricultural‐grade (ag) dolomitic limestone were applied at rates of 0, 0.33, 0.67, 1.0, and 1.33 times the 50 mmol CaCO3 kg−1 soil lime requirement (LR) to an acid Maury silt loam (fine, mixed, mesic Typic Paleudalf). The RCCSL and Ca(OH)2 were equivalent in raising the soil pH and reducing active Al3+, H+, and Mn2+. Ag lime was less effective. Soil solution electrical conductance increased with increasing rate for Ca(OH)2 and RCCSL, but not for ag lime. After 5 wk, plant dry matter was highest at 0.33 and 0.67 LR. Dry matter was reduced for both crops by the highest application rate of all lime sources. Leaf tissue N, K, S, B, and Zn generally declined with increasing lime rates. Chloride accumulation increased with rate and was higher with RCCSL. No deleterious or unusually high amounts of Cd, Pb, Ni, or V were detected. The overliming response could not be ascribed to impaired P, Mg, or Zn nutrition in either species and was speculatively attributed to Al toxicity at near‐neutral pH. The results indicate that field evaluations of the RCCSL material are warranted.
Erosion Effects on Soil Water Storage, Plant Water Uptake, and Corn Growth
Authors: Andraski B. J. , Lowery B.
Published: July 2010

Many investigators have suggested that the greatest negative effect of erosion on soil productivity is the decrease in available water‐holding capacity, but few have attempted to evaluate this relation directly. In this 4‐yr study, we evaluated the effects of past erosion on soil water storage, plant water uptake, and corn (Zea mays L.) growth on a linear slope of Dubuque silt loam soil (fine‐silty, mixed, mesic Typic Hapludalf) in southwestern Wisconsin. Levels of past erosion were based on depth to red clay (2Bt horizon): slight, 0.95 m; moderate, 0.74 m; and severe, 0.45 m. The total quantity of plant‐extractable water that could be stored in the upper 1 m of slightly eroded soil (181 mm) was 7% more than that for moderately eroded soil (169 mm) and 14% more than that for severely eroded soil (159 mm). For all erosion levels, water retained in the 0.5‐ to 1.0‐m soil depth was utilized by corn. Erosion level had no negative effect on early‐season plant growth. As plant‐extractable water decreased to <55 to 60% of total, evapotranspiration (ET) and vegetative‐growth rates decreased as erosion level increased. The greatest differences in ET rates among erosion levels were observed during a 35‐d period in the drought year of 1988 when rates averaged 3.7 mm d−1 for slight erosion, 2.6 mm d−1 for moderate erosion, and 2.2 mm d−1 for severe erosion. For the 3 yr in which plant water stress was observed, maximum plant heights for the slight erosion level averaged 7% more than those for moderate erosion and 13% more than those for severe erosion. Although the soil's capacity to store and supply water decreased as erosion increased, the observed effects of erosion level on grain and stover yields, grain‐yield components, and harvest populations typically were not significant.
Hydraulic Compaction Device for Making Soil Cores
Authors: Torbert H. A. , Prior S. A. , Elkins C. B.
Published: July 2010

It is now well established that soil compaction of agricultural land used for crop production is a major problem. For basic laboratory investigations of soil compaction, it is important that multiple soil cores of varying bulk densities be reproduced within statistically acceptable ranges. A device was designed, constructed, and tested to consistently compact soil cores of varying dimensions and bulk densities. The device uses two opposing hydraulic cylinders to evenly compress soil samples. The compactor is designed to generate compacted cylinders varying from 50 to 100 mm in diameter and 25 to 150 mm in length. Bulk density values for 10 replications of a 150‐mm soil cylinder with a 50‐mm diameter did not vary significantly when compacted under a single pressure. Pressures of 0.35, 1.04, and 2.07 MPa produced cores having bulk densities of 1.66, 1.76, and 1.86 g cm−3, respectively. Approximately 10 cylinders per hour can be prepared with this device.
Fertilizer Placement for Conventional and No‐Tillage Barley in the Subarctic
Authors: Cochran V. L. , Schlentner S. F.
Published: July 2010

Banding all fertilizer near the seed at planting saves time and often increases nutrient uptake and yields of small grains, but adds to the cost of the drill. Some growers have successfully banded all of the fertilizer with barley (Hordeum vulgare L.) in cold soils. This study compares banding 100, 66, 34, and 0% of the fertilizer with the seed and placing the remainder in a deep band between rows and broadcasting all fertilizer. Fertilizer rates were 90, 20, 37, and 18 kg ha−1 of N, P, K, and S, respectively; urea was the N source. Both tilled and no‐till treatments were included on a Volkmar silt loam (coarsesilty over sandy or sandy‐skeletal, mixed Aquic Cryochrept) at Delta Junction, AK. Banding 100% of the fertilizer with the seed in field studies reduced emergence 2 of 3 yr for both tillage treatments, but did not affect nutrient uptake or yields. Nitrogen uptake and grain yields were reduced by broadcasting the fertilizer in no‐till but was not affected in the tilled treatments. Seedling injury from urea applied with barley seed at soil temperatures of 5, 15, and 25 °C was evaluated in root‐zone temperature chambers using Tanana silt loam (loamy, mixed, nonacid Pergelic Cryaquept). These studies confirmed that percentage of emergence increased with reduced soil temperature when urea was placed with the seed, but that emergence rate was delayed at all temperatures. This indicates that the risk of injury from banding urea with the seed is less in cold soil than in warm soil, but there is still danger of injury to the crop.
New Mass‐Based Model for Estimating Fractal Dimensions of Soil Aggregates
Authors: Rasiah V. , Kay B. D. , Perfect E.
Published: July 2010

Values of the fractal dimension, D, for soil aggregates may vary with the model used and the assumptions invoked in formulating the model. The objectives of this study were to: (i) develop a new mass‐size‐based model, not assuming that probability of failure, P, and bulk density, ρ, are scale‐invariant for the estimation of D (defined DR), and (ii) compare the values of DR with those obtained using three other procedures. In the first procedure, manually counted aggregate numbers were used in the number‐size relation model for the estimation of D (defined Dn). Aggregate numbers were computed, assuming scale‐invariant ρ, in the second procedure and these numbers were used in the same number‐size relation model for the estimation of D (defined Dm). In the third procedure, a mass‐size‐based model, which has an upper limit to D and assumes scale‐invariant ρ, was used for the estimation of D (defined DT). Aggregate‐size distributions and P for different sizes of aggregates arising from fragmentation during wet sieving in water were obtained for three soils under two cropping treatments (CT) using a modified form of the Yoder apparatus. The P of soil aggregates ranged, depending on soil type, CT, and aggregate size, from 0.30 to 0.91. Values of DR ranged from 2.02 to 3.19 and those for Dm and DT ranged from 2.32 to 3.28 and from 2.46 to 2.84, respectively. Significant 1:1 linear correlations existed only between DR and Dm and between Dm and Dn. Values of DR, Dm, and DT were strongly influenced by soil type, CT, and the estimation model used. The interaction between clay and organic matter contents and CT accounted for 74% of the variability in DR, compared with 54% for DT and 52% for Dm.
Seasonal Variations in Denitrification and Nitrous Oxide Evolution at the Landscape Scale
Authors: van Kessel C. , Pennock D. J. , Farrell R. E.
Published: July 2010

This study was conducted to examine the seasonal and spatial variability of denitrification in various landform elements in a pea (Pisum sativum L.) field at Blaine Lake, Saskatchewan, Canada. The distributions of denitrification activity and N2O evolution were highly skewed, and could not be log‐transformed to yield normal distributions. Consequently, ordinary statistical procedures (i.e., those based on a normal distribution) were considered inappropriate for this study, and nonparametric statistics were used to describe the data. Denitrification activity and N2O evolution exhibited similar temporal and landscape‐scale patterns and were highly correlated, suggesting that denitrification was the main source of N2O evolution. In general, N2O evolution accounted for ≅41% of the denitrification activity. Maximum rates of denitrification were low prior to spring tillage and seeding, increased during the first half of the growing season (following the addition of fertilizer N), and decreased toward the end of the growing season; denitrification had essentially ceased by the fall sampling. Statistical outliers for denitrification activity, i.e., hotspots of activity, occurred predominantly at low levels of denitrification activity and were completely absent when denitrification activity was at its maximum. Therefore, the importance of hotspots of activity for estimating seasonal rates of denitrification appears to be limited. Soil water content was the most dominant factor controlling denitrification activity, followed by the concentration of NH+4, total soil respiration, and NO−3. The intensity of denitrification was controlled largely by hydrologic processes, which, in turn, were influenced by the topography of the landscape. Nevertheless, the landscape‐scale patterns of denitrification and N2O evolution were intensity‐independent and remained consistent throughout the season.
Evaluation of Pedo‐Transfer Functions
Authors: Tietje O. , Tapkenhinrichs M.
Published: July 2010

Measuring unsaturated hydraulic properties, including water retention vs. tension relationships, is expensive, time consuming, and labor intensive. Several attempts have been made to estimate these relationships from available soil data such as particle‐size distribution, organic C content, and bulk density. An estimation method that describes the soil water retention relationship based on other soil characteristics is referred to as pedo‐transfer function (PTF). The PTF approach will supply data for water and transport models for the unsaturated zone. Pedo‐transfer functions were evaluated by comparing estimated with measured water retention values using test data sets with a broad range of soils. Accuracy of the retention prediction is quantified by the root of the mean squared difference (RMSD) between the measured and predicted retention function. After the application of several PTFs to many soils in a data set, the average 〈RMSD〉 was found in the range of 0.04 to 0.13 m3 m−3 depending on the PTF. When the RMSD was calculated in the range from 0.1 J kg−1 to wilting point, the lowest 〈RMSD〉 was found to be about 0.05 m3 m−3. Using a PTF to supply the water retention for unsaturated soil water flux models (Richards equation), the most practical (and the most accurate) method is to predict retention function parameters (e.g., the parameters of the van Genuchten equation). But, the prediction of the van Genuchten retention function parameters α and θr (residual water content) using a PTF was found to be inaccurate, even when the PTF is based on nonlinear regression analysis and principle factor analysis.
Nutrient Availability and Foliar Nutrient Status of Sugar Maple Saplings following Fertilization
Authors: Paré D. , Meyer W. L. , Camiré C.
Published: July 2010

Foliar analysis of maple sugar (Acer saccharum Marsh.) saplings having low foliar K (5.4 g kg−1) and P (1.2 g kg−1) was carried out for 3 yr to investigate the effects of a single application of fertilizer P triple superphosphate [TSP], K (K2SO4) and Ca [Ca(OH)2]. Also, soll, water‐saturated soil extract, resin sacks buried in situ, and lysimeter solution analysis methods were used. Potassium and P additions significantly increased foliar K (1.81 g kg−1 increase) and P (0.25 g kg−1 increase) for the 3 yr that the observations were conducted. Calcium addition had no effect on foliar element concentrations. A Diagnosis and Recommendation Integrated System (DRIS) analysis corroborated the foliar analysis: K indices increased with increased K fertilization (from −47 to ‐23) and P indices increased with increased P fertilization (from ‐25 to −15). Calcium application significantly increased the effective cation‐exchange capacity (CEC), exchangeable Ca and Mg and water‐extractable Ca and decreased the acidity in the rooting zone for a 3‐yr period. Conventional soil analysis and resin sacks detected significant effects of P and K fertilizers on their respective elements. However, these effects did not last more than 2 yr after fertilizer application in the surface soil horizon (Ah). Lysimeter solution analysis showed that K2SO4 fertilizer caused short‐term increases in SO4 and Ca leaching. The duration of fertilizer P and K on foliar nutrition and the behavior of soil nutrients suggested that biochemical cycles are important mechanisms perpetuating fertilizer effects.
Competition in Adsorption between Phosphate and Oxalate on an Aluminum Hydroxide Montmorillonite Complex
Authors: Violante A. , Gianfreda L.
Published: July 2010

A study was conducted to provide information on phosphate and oxalate sorption on an Al(OH)x‐montmorillonite (chlorite‐like) complex under changing conditions of pH, total solution ligand concentrations, and order of anion addition. The competitive adsorption of phosphate and oxalate on a chlorite‐like complex (3.3 mol Al kg−1 montmorillonite) was influenced by pH (5.0–9.0), order of anion addition, and initial oxalate/phosphate molar ratio (Ri). In systems containing a constant amount of phosphate (500 or 400 mmol kg−1) and increasing quantities of oxalate (Ri from 0.5 to 3.34), more phosphate than oxalate was adsorbed even when the initial concentration of oxalate was much higher than that of phosphate. Of the sites on the clay surface that were available for adsorption by both anions, 51 to 79% were occupied by phosphate at Ri = 3.34 in the range of pH studied. Minimum reduction in phosphate adsorption occurred when phosphate was added to the clay mineral before oxalate, whereas maximum reduction occurred when oxalate was introduced before phosphate. The efficiency of oxalate in inhibiting phosphate adsorption was stronger at pH 5.0 than at pH 7.0 or 9.0. At pH 5.0, by increasing Ri from 0.5 to 3.34, phosphate sorption decreased from 20 to 44% when OX was added before phosphate. Many sites of the clay mineral were highly specific for phosphate, whereas some others, common to both the anions, had a higher affinity for phosphate than for oxalate. However, some sites were specific for oxalate anions.
Soil Solution Chemistry: Effects of Bulking Soil Samples
Authors: Giesler R. , Lundström U.
Published: July 2010

Bulking of soil samples is commonly used to obtain a spatially averaged measure of soil properties. This study investigated whether bulking can affect the chemistry of soil solution extracted by the centrifuge drainage technique. The short‐range variation within a 1‐m‐wide pit face was also investigated. Systematic differences were found between the chemistry of soil solutions taken from bulked and unbulked soil samples. The soil samples studied were taken on several occasions from the upper and lower part of a Bs horizon. Samples of soil solution extracted from replicate bulked soil samples contained significantly (P ≤ 0.05) larger amounts of Si, Na, Mg, and K as well as significantly (P ≤ 0.05) smaller amounts of Al and Fe than soil solution from unbulked samples. Bulking reduced the variation in all solutes measured, although a variation remained in replicates from the bulked sample. The variation between individual core samples taken just a few tens of centimeters apart can be considerable, although the magnitude of variation differs depending on the solute studied. The results suggest that unbulked soil samples may be preferable, especially when Al or Fe chemistry is studied and a centrifuge drainage technique is used.
Simulated Aerobic Pedogenesis in Pyritic Overburden with a Positive Acid—Base Account
Authors: Doolittle James J. , Hossner L. R. , Wilding L. P.
Published: July 2010

Reclamation of surface‐mined land is often hindered by the excess salts and acidity produced by the weathering of pyritic overburden. This study was conducted to document the initial transformations that occur when pyritic overburden containing excess acid neutralizing potential is used as parent material in minesoil construction. An overburden containing 0.8% FeS2 (pyrite) and 1.6% inorganic carbonate (predominantly dolomite) was collected from the highwall of an active lignite surface mine in Panola County, Texas. The overburden was lightly crushed through a 13‐mm sieve and packed into three replicate lysimeters (0.75 by 0.75 by 1.2 m). The lysimeters were leached monthly with 63.5 mm of deionized water for 24 mo. The initial material had a pH of 8.3 and an excess acid neutralizing potential. Progressive FeS2 oxidation released H2SO4 and the pH decreased to 6.8. The dolomite dissolved, neutralizing the acidity, with subsequent release of Ca and Mg ions into solution. Leachate Ca2+ and SO2−4 concentrations exceeded the ion activity product of gypsum in the lower 60 cm of the lysimeters. Thin‐section analysis revealed that gypsum crystals precipitated along margins of residual pyrite particles and in conductive vughs and channels. The continued accumulation of gypsum in minesoil development could eventually lead to the formation of a gypsic or a petrogypsic horizon. A restrictive layer such as this would decrease vertical movement of water and O2, which would reduce vegetative growth, increase runoff and erosion, and thus increase the probability of reclamation failure.
Transport of Solutes as Affected by Irrigation Method
Authors: Jaynes D. B. , Rice R. C.
Published: July 2010

The leaching behavior of agricultural chemicals depends on the application method of both the chemical and water. This study investigated the leaching behavior of conservative tracers under intermittent flood and drip irrigation on a clay loam soil. Slug applications of conservative tracers were applied sequentially to a single 37‐m2 plot and leached under the two irrigation regimes with the same daily application rate. Suction lysimeters, installed at seven depths (0.3, 0.6, 1.0, 1.4, 1.8, 2.4, and 3.0 m) and replicated four times, were used to withdraw daily soil solution samples during leaching. Pore water velocities, v, and dispersion coefficients, D, for a one‐dimensional advection‐dispersion model were fit to the resulting concentration vs. time curves by nonlinear least squares. Pore water velocities were slightly greater on average under drip irrigation and were more uniform across the plot (smaller variance) than under flood irrigation. Preferential flow was observed under both irrigation regimes. Breakthrough curves showed considerably more spreading under intermittent flood irrigation than under drip, indicating greater hydrodynamic dispersion under flood irrigation. Fitted D values were, on average, nearly three times greater under flood irrigation than under drip. Allowing free water at the soil surface during flood irrigation increased the dispersion of tracer compared with the drip irrigation system, where water was applied at a rate less than the saturated conductivity. The increase in D is most likely due to small‐scale spatial variability of the soil's hydraulic properties.
Hydraulic Properties of Surface Seals in Georgia Soils
Authors: Chiang S. C. , Radcliffe D. E. , Miller W. P.
Published: July 2010

To predict infiltration in a sealing soil, the seal hydraulic conductivity as a function of time or cumulative rainfall must be known. Few studies have reported measured seal hydraulic conductivities in soils from the southeast USA. Seven Georgia soils packed in columns were subjected to simulated rainfall at an intensity of 50 mm h−1. The sandy loam soils were easily disrupted by rainfall. The calculated seal hydraulic conductivities (Kc) dropped sharply in 10 min of rain and were less than 10% of the initial saturated hydraulic conductivity (Ki) after 45 min. The sandy loam soil with low aggregate stability and Fe content was especially prone to sealing in that Kc dropped to 4% of Ki after 10 min. The well‐structured soil with a clay texture declined in Kc gradually with time, indicating a high resistance to rainfall energy. The sandiest soil showed intermediate resistance to raindrop impact, and Kc leveled off at a high value after 20 min due to the low clay content. The loamy soil with smectitic clay had the lowest Ki and showed little change in Kc with time. Relative seal hydraulic conductivity after 10 or 60 min of rain were good indices differentiating the relative resistance of these soils to surface sealing. A soil stability factor, used to characterize the decrease of Kc in an exponential decay equation, was significantly correlated with water‐dispersible clay on a soil basis.
Reevaluation of the Evaporation Method for Determining Hydraulic Functions in Unsaturated Soils
Authors: Wendroth Ole , Ehlers W. , Hopmans J. W. , Kage H. , Halbertsma J. , Wösten J. H. M.
Published: July 2010

Understanding of soil water and solute transport processes requires knowledge of the soil hydraulic properties. A simple evaporation method for the determination of the hydraulic conductivity function and the water retention characteristic was developed and applied to a range of soils with different texture and structure. During evaporation from the top of a 6‐cm‐high soil core, soil water pressure head at 1.5 and 4.5 cm below the soil surface was measured with tensiometers several times. At the same time, evaporative water loss was determined by weighing the soil column. The procedure for calculation of hydraulic functions was evaluated via numerical simulations. Results from the numerical experiment confirm the underlying theory. A limitation of the evaporation method is the fact that, at water contents near saturation where hydraulic conductivity is high, hydraulic gradients cannot be determined with sufficient accuracy. Other measurement techniques are suggested that can supplement the evaporation method in the wet range.
Fiberglass Wick Preparation for Use in Passive Capillary Wick Soil Pore‐Water Samplers
Authors: Knutson J. H. , Lee S. B. , Zhang W. Q. , Selker J. S.
Published: July 2010

Passive capillary samplers (PCAPS) use the capillary potential generated by hanging fiberglass wicks to exert a sampling suction on soil water. Impurities on the fiberglass affect the capillary properties of the wick and the chemical properties of the samples collected. To determine the need, and a method, for cleaning the wicks, capillary rise and moisture contents were measured using four preparations: uncleaned, detergent washed, acetone extracted, and combusted. Wicks were made with fibers produced by PPG Industries and Manville Company. Results showed that wicks made from PPG fibers lost up to 3.4% of original mass during combustion while Manville fiber wicks lost <0.6%. These losses are assumed to have been due to combustion of organic compounds applied by the manufacturers. All cleaning methods had higher capillary rise than obtained with uncleaned wicks. Combustion at 400 °C for 4 h was the best cleaning method, removing 98 to 100% of impurities.
Horizontal and Vertical Movements of Two Expansive Soils in Mississippi
Authors: Cheng Yaan , Pettry D. E.
Published: July 2010

Expansive soils create severe problems for road construction and maintenance, building foundations, and agricultural and industrial operations. Quantification of soil movement under natural field conditions has received little attention and is not well understood. Horizontal and vertical movements were measured for 20 mo by surveying rods placed at various depths in field plots of Typic Chromuderts and Vertic Hapludalfs of the Mississippi Blackland Prairie. Vertical soil movement was a function of soil depth, soil water content, and rainfall. Greatest vertical soil movement occurred in the upper 50 cm of both soils, with a maximum of 27 mm in the Vertisol and 24 mm in the Alfisol. Soil swelling occurred in winter and shrinking occurred in late spring and summer. Horizontal soil movement was not related to soil depth, but was related to soil water content and rainfall. Maximum horizontal movement was 36 mm in the Vertisol and 20 mm in the Alfisol. Horizontal and vertical movements in expansive soils are reversible, dynamic processes under natural field conditions. Horizontal movement appears more dynamic than vertical movement, and it reflects short‐term response to precipitation events followed by drier periods. Vertical movement reflects long‐term precipitation‐evapotranspiration distribution and is probably related to movement along master slickensides.
Foliar Nutrients in Sugar Maple Forests along a Regional Pollution‐Climate Gradient
Authors: Burton Andrew J. , Pregitzer Kurt S. , MacDonald Neil W.
Published: July 2010

Stressing agents such as defoliation, adverse climatic conditions, and pollutant deposition have the potential to alter forest nutrition. Several recent instances of sugar maple (Acer saccharum Marsh.) decline and dieback have been associated with foliar nutrients deficiencies. This study assessed foliar nutrient status and cycling in five sugar maple dominated northern hardwood forests along a Great Lakes pollution‐climatic gradient. Concentrations and contents in mid‐July foliage and litterfall were determined at each site for N, P, S, Ca, Mg, K, Al, Fe, Mn, B, Zn, and Cu. Where differences existed among sites in foliar nutrient concentrations, they could be predicted primarily from soil properties. Two notable exceptions were foliar S, which was strongly related to SO4 deposition, and foliar Al, which could be predicted by a combination of soil nutrient cation availability and SO4 deposition. Nutrient content of mid‐July foliage and litterfall increased from northwest to southeast along the gradient for N, S, Mg, Al, Fe, B, and Cu. This was the result of an increase in foliage and litterfall biomass, combined in some cases (S, Al, Fe, and B) with increasing foliar nutrient concentrations. Reproductive effort significantly affected total litter return of all nutrients and 43 to 62% of mid‐July foliar N, P, K, and S were conserved through retranslocation prior to litterfall. Sugar maple foliar nutrient concentrations for the five sites revealed no obvious nutrient deficiencies or toxicities, and provide a regional baseline against which the effects of long‐term pollutant deposition and other stresses can be assessed in the future.
Optimal Spacing of Surface‐Banded Nitrogen on Fescue
Authors: Vigil M. F. , Kissel D. E. , Cabrera M. L. , Raczkowski C. W.
Published: July 2010

A recommended N application method for approximately 0.2 million ha of tall fescue (Festuca arundinacea Schreb.) grown in Kansas is topdress banding in early spring. Optimal spacing of N fertilizer bands increases N use efficiency, thereby reducing expenditures for fertilizer and the potential for environmental contamination. The objective of this study was to develop and test a model to determine optimal spacing of surface‐banded N from tall fescue dry matter measured on plots fertilized with single bands. A major assumption in the development of the model was: the yield at any point between two fertilizer bands is the sum of yield responses from adjacent bands. In 1985 tall fescue yields measured at various distances from single bands of N fertilizer (applied at rates of 30, 60, 90, and 180 kg ha−1) were used to develop the model. The yields on another set of plots fertilized in a complete factorial arrangement at rates of 60 or 180 kg N ha−1, with band spacings of 25 and 50 cm, were used to test the model in 1984 and 1985. Measured and model‐predicted yields indicated that optimal band spacing was near 25 cm. The model predicted a decrease in optimal band spacing with increasing N rates. The fitted regression of measured yield on predicted yield had a slope and an intercept not significantly different from one and zero, respectively, indicating a good fit between measured and modeled yields. This research provides a practical tool to predict fertilizer band spacings that maximize fescue yields at N rates between 30 and 180 kg N ha−1.
The Distributed Recharge Mechanism in the Australian Arid Zone
Authors: Barnes C. J. , Jacobson G. , Smith G. D.
Published: July 2010

We developed a model to describe fluctuations in historical records of well water levels in the Australian arid zone in order to determine the average recharge rate and specific yield of the phreatic aquifer. The model was used to explore the degree to which variations in solute concentrations are preserved in the deep unsaturated zone during convection to the water table during recharge of rainwater. An examination of historical water levels in wells gives support to the hypothesis (obtained from an earlier study on NO3 contamination of groundwater) that distributed recharge is the primary source of groundwater renewal. Detailed comparison of the hydrograph records suggests a nonlinear response to rainfall, with an “initial loss” of approximately 130 mm mo−1 (five times the mean rainfall). The best estimate of the long‐term recharge rate is about 20 mm yr−1, although the last 10 yr appear to have been somewhat wetter than usual, due mainly to a very large rainfall event in 1989. This recharge mechanism implies that historical environmental tracer signals in recharge waters moving through deep unsaturated zones in unstructured soils will be largely unaffected, when recharge rates are low, by dispersion or even diffusion below a depth that depends on the variability of the rainfall.
Changes in Surface Runoff and Sediment Production after Repeated Rangeland Burns
Authors: Emmerich William E. , Cox Jerry R.
Published: July 2010

Prescribed burning of vegetation may increase the potential for surface runoff and erosion. Changes in surface runoff and sediment production were evaluated with time following fall and spring burns at two different soil and vegetation type locations in southeastern Arizona. Rainfall simulations were conducted immediately after prescribed burns on four replicate areas and 1 yr later following a repeat burn on the same areas, and compared with paired unburned areas. The burn treatment and evaluation sequence was repeated in a second year on new areas to evaluate differences in years. After the first burn, runoff and sediment production on unburned and burned areas were similar within locations, and were greater at one location than the other. One location showed significantly more runoff and sediment production in the fall season on both unburned and burned areas after the first burn treatment. There was significantly greater runoff and sediment production from the burned areas after the second burn and the burned areas were now similar between locations. Runoff and sediment production for the fall season and for the second year on the 1‐yr‐old areas was higher at both locations, regardless of treatment. The increases in runoff and sediment production were greater from the burning than the season or year effects after 1 yr. The management implications for these locations and conditions are that, immediately after a rangeland burn, runoff and sediment production maybe unchanged, but within 1 yr significant increases can occur and significant seasonal and yearly differences may occur irrespective of a burn.
Variability in the Growth of Faidherbia albida: The Soils Connection
Authors: Geiger S. C. , Vandenbeldt R. J. , Manu A.
Published: July 2010

Variability in the growth of Faidherbia albida (Del.) A. Chev. (syn. Acacia albida [Del.]) in the Sahelian zone of West Africa is a common observation. The “albida effect” has been attributed to the amelioration of soil chemical, physical, and microbiological properties by the direct action of the tree, resulting in enhanced crop production beneath the mature canopy. Crop yields within fields without F. albida can also be highly variable within short distances. A study was conducted to observe the association between the variability in soil properties and the variable growth of young (2‐yr‐old) F. albida trees planted at the ICRISAT Sahelian Center located near Niamey, Niger. The results of this study indicate that the variability in F. albida growth is caused, in large part, by variability in soil properties across relatively short distances. Good growth sites had higher clay contents and base saturations, and lower exchangeable acidity than poor growth sites within the field. The tallest trees in the field were associated with the proximity to abandoned termite mounds and other microhigh sites. Seedlings planted on sheet‐eroded sites caused by runoff from micro‐topographical high sites within the field grew poorly. The variability in F. albida growth in plantations within Niger is hypothesized to be due, in part, to preexisting soil conditions. These results also suggest that the albida effect might be partially caused by these preexisting “islands of fertility”. This site‐determined variable growth of F. albida could be exploited with proper seedling placement strategies.
Statistical and Fractal Evaluation of the Spatial Characteristics of Soil Surface Strength
Authors: Folorunso O. A. , Puente C. E. , Rolston D. E. , Pinzón J. E.
Published: July 2010

In order to understand processes causing soil crusting and to optimize sampling schemes, improved understanding of crust spatial characteristics is needed. For this purpose, statistical and fractal analyses of soil surface strength, as measured by a 1.59‐mm‐diam. flat‐tipped micropenetrometer, were carried out for a variety of soils and under a variety of sampling schemes. Specifically, this work considered maximum penetration forces sampled at intervals of 0.005, 0.01, 0.05 and 0.5 m along four parallel transects 0.25 m apart, for nine different sites within California's Central Valley. Force measurements were non‐homogeneous in space. For eight of the nine sites, both the mean and the variance were non constant; and for all sites, the range and nugget variance of fitted semivariograms were scale dependent. Fractal analysis of the measurements allowed qualitative discrimination among soils, despite small variations across scales. For all sites, fractal dimensions of sampled series at alternative scales were similar, but the smallest deviations across scales were observed on high‐strength silt loam, and the largest on low‐strength loamy sand soils. Multifractal spectra (for data sets normalized and interpreted as probability measures) gave similar entropy dimensions for all sampling schemes, with very small deviations across scales for silt loam soils and largest again for loamy sands. Results suggest that the fractal attributes (fractal and entropy dimensions), being scale‐independent attributes, may be relevant qualifiers of the intrinsic variability of penetration measurements and that this variability can be modeled as a fractal process.
Nondestructive Determination of Hydrogeometrical Characteristics of Soil Macropores
Authors: Wang D. , Norman J. M. , Lowery B. , McSweeney K.
Published: July 2010

Hydrological and geometrical parameters of macropores are essential for modeling water and solute transport through soils containing macropores. This study was conducted to develop a fast and nondestructive technique for determining the hydrological and geometrical characteristics of soil macropores. We measured the rate of water flowing into ant and earthworm burrows with a macropore infiltrometer and estimated burrow diameter, volume, and depth from the measured flow rate and a water flow model. To evaluate the estimated burrow parameters, we made castings of the ant and earthworm burrows with a dental plaster. The burrows had similar diameters (2.1 mm for laminar flow; 2.9 mm for turbulent flow) but different volumes and depths (281‐cm3 volume and 0.60‐m depth for ant burrows; 210‐cm3 volume and 0.82‐m depth for earthworm burrows). This technique is reasonable for ant burrows because the root mean square difference (RMSD) between casting and infiltrometer‐calculated volumes is 17%; however, errors are larger for earthworm burrows (RMSD is 73%). Saturated soil matrix hydraulic conductivity (Ks) estimated from the infiltrometer measurement of earthworm burrows were comparable to matrix Ks of the bulk silt loam. The matrix Ks values estimated for ant burrows were about eight times smaller than matrix Ks of the bulk sandy soil. Such large decrease in Ks is probably caused by infilling of burrow walls by ants with fine materials. Combining the macropore infiltrometer measurements with the model is a useful means of estimating the hydrological and geometrical parameters of ant and possibly earthworm burrows.
Automatic Atomized Water Spray System for Soil Hydraulic Conductivity Measurements
Authors: Dirksen C. , Matula S.
Published: July 2010

Soil hydraulic conductivity, K, as function of volumetric water content, θ, must be known accurately for any quantitative investigation of water and solute transport in unsaturated soil. Direct measurements of K(θ) are hampered by lack of a suitable apparatus to apply small and spatially uniform water flux densities to soil surfaces for extended periods of time. We developed an automatic atomized water spray system that meets these requirements. Results indicate that, with this water spray system, soil hydraulic conductivities between saturation and values approaching 0.1 mm/d can be measured easily, quickly, and accurately. Hydraulic conductivities were a single‐valued function of water content, measured simultaneously with time‐domain reflectometry, but not of pressure head.