bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency Distributions of Soil Properties on a Loess‐mantled Missouri Watershed
Authors: Young F. J. , Hammer R. D. , Larsen D.
Published: July 2010

Frequency distributions of soil property values are largely unknown, yet they are important to studies of soil variability. Our objectives in this paper were to (i) evaluate the distributional normality of soil properties within and among upland geomorphic surfaces, and (ii) interpret these distributions in terms of pedogenic factors and processes. Sixty soil properties were measured from 257 pedons along point transects in a 40‐ha upland Missouri pasture. Five of the 60 tested variables approximated normality. About three‐quarters of the distributions were asymmetric (skewed), and over four‐fifths were misshapen (kurtotic). Partitioning the samples by geomorphic surface (ridge, shoulder and backslope) improved the normalities, symmetries and shapes of many, but not all, distributions. A priori assumptions of normality are not warranted for most soil properties. Care should be taken when applying statistical tests that are sensitive to departures from normality. However, asymmetric or misshapen distributions provide meaningful information. Extended tails in skewed distributions represent outliers or inclusions in soil survey map units. These distributions result from variation in depositional environments or the asymmetric effects of pedogenic or hydrologic processes. Kurtotic distributions may indicate the presence within the sample of subpopulations with differing means or variances. Distributions provide important clues to understanding spatial variability.
Iron Oxidation States on Root Surfaces of a Wetland Plant (Phragmites australis)
Authors: Wang Tiangen , Peverly John H.
Published: July 2010

Iron in root plaque is usually thought to be Fe(III) because of rhizosphere oxidation. This study was conducted to examine Fe oxidation states on root surfaces of the common reed [Phragmites australis (Cav.) Trin. ex Steudel]. Using an EDTA‐BPDS method, Fe(II) and Fe(III) on the surfaces of roots sampled from various environments were stabilized, extracted and determined simultaneously. The proportion of extracted Fe(II) to total Fe ranged from 0.17 to 0.65 for the roots grown in constructed wetlands, fields, and hydroponic culture; and from 0.34 to 0.70 for different sections of wetland plant roots. The observed results suggested that Fe plaque is caused not only by rhizosphere oxidation, but also by Fe(II) compound formation on the root surfaces.
Soil Phosphorus Fractions in Unfertilized Fallow‐Maize Systems on Two Tropical Soils
Authors: Maroko Jeremiah B. , Buresh Roland J. , Smithson Paul C.
Published: July 2010

The rotation of crops with either legumes or natural regrowth of native vegetation is known to supply N to crops in tropical land‐use systems, but little is known about the effect of such rotations on P supply to crops. An experiment was conducted on two soils in Kenya, an Oxisol (very fine, isohyperthermic Kandiudalfic Eutrudox), and an Alfisol (mixed, isothermic Kandic Paleustalf), to determine the effect of unfertilized, organic‐based land‐use systems on fractions of soil inorganic P (Pi) and organic P (Po). The land‐use systems involved growth of three maize (Zea mays L.) crops (18 mo total duration) after 17 mo of either (i) Sesbania sesban (L.) Merr. tree growth (sesbania fallow), (ii) natural regrowth of vegetation without cultivation (natural fallow), (iii) three crops of unfertilized maize (maize monoculture), or (iv) bare uncultivated soil (bare fallow). Soil (0–15 cm deep) was collected before post‐fallow maize and after the three post‐fallow maize crops. Sesbania and natural fallows increased the amount of P in light fraction soil organic matter (OM) (>150 µm, <1.13 Mg m‐3) and macroorganic matter (250–2000 µm) on each soil and increased chloroform extractable P on the Oxisol. Land‐use systems had no effect on extractable Pi (bicarbonate, Bray‐1, iron‐oxide impregnated paper), except for resin P on the Oxisol. Unfertilized sesbania and natural fallows cycled soil P through plant residues, resulting in increased P in soil microbial biomass immediately after the fallows and increased P in light fraction soil OM for three post‐fallow cropping seasons.
Comparison of Methods for Determining Bulk Densities of Rocky Forest Soils
Authors: Page‐Dumroese Deborah S. , Brown Robert E. , Jurgensen Martin F. , Mroz Glenn D.
Published: July 2010

Measurement of forest soil bulk density is often hampered by coarse fragments. In this study, five methods to determine total and fine bulk density and coarse‐fragment content of a rocky forest soil in western Montana were evaluated. Two methods of core sampling (small and large diameter cylinders), two methods of soil excavation and volume determination (water and polyurethane foam), and a nuclear source moisture gauge were tested at two depths (0–10 cm and 10–20 cm) on a soil with a 35% slope and 45% rock content. In the surface 10 cm, total and fine soil bulk density values were greatest from the nuclear gauge. The two excavation techniques gave similar results. Volumetric rock‐fragment content calculations using the small diameter cylinder were significantly lower than those using the other methods. At the 10‐ to 20‐cm depth, all methods except the large diameter cylinder gave comparable results for total soil bulk density. The small diameter core method gave the highest estimate of fine bulk density at this depth. All methods are easy to use. Soil excavation using the polyurethane foam for volume determinations is the simplest method and has low standard errors.
Retention of Nitrogen by a Nitrogen‐Loaded Scotch Pine Forest
Authors: Johannisson C. , Högberg P. , Myrold D. D.
Published: July 2010

The capacity of forests to store added N and how this excess N might interact with other nutrients is not well understood. We studied N retention in a Scotch pine (Pinus sylvestris L.) forest that had received two decades of annual additions of N as NH4NO3 at four rates (N0‐N3, equivalent to 0, 36, 72 and 108 kg N ha‐1 yr‐1), with and without supplementary additions of P and K. The highest N treatment (N3) was suspended three years before this study. Leaching of inorganic N was measured beneath lysimeters with and without living tree roots inside them, and the fate of 15N injected into the mor layer was traced by sampling understory vegetation, soil to 20‐cm depth, and leachates. Leaching of inorganic N increased with increasing N dose and was dominated by NO‐3 on plots to which N had been added. In the suspended N3 treatment, leaching of N was lower than in the N2 treatment. The presence of tree roots greatly reduced leaching of N. The occurrence of labeled NO‐3 under lysimeters to which labeled NH+4 had been added showed that nitrification was important in treatment N2, but not in N1, suggesting that additions of >30 kg N ha‐1 yr‐1 are needed to induce larger net nitrification at this site. Our data showed (i) that trees were an important sink for N, (ii) that additions of P and K had a marginal positive effect on N retention, and (iii) that leaching from previously N‐loaded forest rapidly decreased when the N load was removed.
Discrimination of Soil Phases by Dual Energy X‐ray Tomography
Authors: Rogasik H. , Crawford J.W. , Wendroth O. , Young I.M. , Joschko M. , Ritz K.
Published: July 2010

Numerous soil ecological functions are influenced by soil structure through its impact on spatial and temporal distributions of soil particles, water, and air within the soil profile. The nondestructive technique of x‐ray computed tomography (CT) was used for studying soil structure. X‐ray attenuation determined for two energy levels (80 kV and 120 kV) was used to calculate distributions of water, air, and solids, as well as the voxel dry bulk density for two silt loam subsoils. The spatial resolution during scanning was 0.25 mm in the horizontal and 1 mm in the vertical direction. For different voxel sizes, the weighted mean of the derived volumetric water, air, and solid contents, and the dry bulk densities agreed with the sample's phase composition and dry bulk density obtained by weighing. The use of dual energy scanning to study the heterogeneity of soil structure and the spatial distribution of water, air, and solids is discussed.
A Dielectric–Water Content Relationship for Sandy Volcanic Soils in New Zealand
Authors: Tomer M. D. , Clothier B. E. , Vogeler I. , Green S.
Published: July 2010

To measure soil water content (θ) by time domain reflectometry (TDR), one must know the relationship between the soil's dielectric constant (Ka) and θ. Our objective was to determine Ka–θ calibrations for sandy volcanic soils on the North Island of New Zealand. We collected samples from 24 horizons and 6 soil profiles. The soils were sandy loam and loamy sand textured, with bulk densities between 0.55 and 1.34 Mg m−3 Samples were air‐dried and packed to their field bulk density in plastic boxes. Time domain reflectometry probes (100 mm long) were inserted, and TDR waveforms were recorded and analyzed. Water contents were increased in approximate steps of 0.05 m3 m−3 volume to the liquid limit, which varied between 0.33 and 0.57 m3 m−3 Samples were then submerged to obtain water contents as great as 0.646 m3 m−3 Measured water contents were greater that those predicted by the Topp equation, but the differences varied according to soil texture. Pooled data from 17 of the samples provided a third‐order polynomial calibration with an R2 of 0.977 and root mean square error (RMSE) of 0.026 m3 m−3 A third‐order mixing model and a linear Ka–θ expression gave greater mean errors. Although the calibration applied to a range of sandy volcanic soils, there were also two small groups of samples that showed distinct calibrations. These were coarser tephras, with at least 75% of particles >0.125 mm diam. by mass, and with bulk densities >1.0 Mg m−3
Differential Effects of Earthworms on Nitrogen Cycling from Various Nitrogen‐15‐Labeled Substrates
Authors: Bohlen Patrick J. , Parmelee Robert W. , Allen Michael F. , Ketterings Quirine M.
Published: July 2010

Earthworms incorporate organic matter into soil but their influence on cycling of N from incorporated materials is not well understood. This study examined the role of earthworms in the turnover of N from different15N‐labeled inputs. We incubated intact soil cores with or without earthworms (Lumbricus terrestris) and with15N‐labeled KNO3, rye litter (Secale cerealeL.), or cow manure, added to the soil surface at a rate of 150 kg N ha−1The cores were destructively sampled after 2, 6, and 10 wk and assayed for total soil N, KCl‐extractable N, microbial‐biomass N (MBN), two size fractions (53–2000 μm and >2000 μm) of particulate organic matter (POM), and15N enrichment of all N pools. Earthworms increased the incorporation of15N into the soil in organically treated cores but had little effect on the distribution of15N in the inorganically fertilized cores. The percentage of initial15N that was incorporated into the soil after 10 wk was 71 and 45% in cores with earthworms and 34 and 25% in cores without earthworms, in the manure and rye treatments, respectively. Earthworms incorporated the manure more rapidly than the rye, as shown by temporal patterns of incorporation of total N and POM. Earthworms increased MBN in the manure treatment by about 20 to 30%, but slightly decreased MBN on one sample date (2 wk) in the rye treatment. Interactions between earthworms and organic materials of different quality influence both the rate at which the materials are incorporated into the soil and the subsequent mineralization of N from those materials.
Release of Natural Organic Matter Sorbed to Oxides and a Subsoil
Authors: Kaiser K. , Zech W.
Published: July 2010

Sorption to mineral surfaces is an important process controlling the mobility and stability of natural organic matter (NOM) in soil, yet only knowledge of the reversibility of this process enables the prediction of element cycling and NOM‐induced transport in soils. We have elucidated the desorption of mineral‐bound NOM in batch experiments with amorphous Al(OH)3, goethite, and a subsoil low in organic C. These sorbents were equilibrated with increasing amounts of water‐extractable NOM from the Oa horizon of a mor forest‐floor layer and then extracted with solutions of different ionic strengths, pH, and concentrations of inorganic anions (Cl−, SO2−4, H2PO−4). Sorbed NOM was extracted after 24, 48, 72, and 120 h. We investigated structural and functional characteristics of the desorbed NOM by XAD‐8 (macroporous resin) fractionation and by13C‐NMR spectroscopy. Desorption of NOM from minerals and soils was negligible (<3%) under solution conditions similar to those during the sorption (hysteresis). It was not influenced by increasing concentrations of noncompeting inorganic anions such as Cl−Increased concentrations (≤0.1M) of competing anions like SO2−4or H2PO−4increased the NOM desorption. Though H2PO−4was most efficient in desorbing NOM, the extractability was only ≤60% at the highest H2PO−4concentration. The most significant desorption occurred when solution pH was raised. For goethite, NOM desorption reached a maximum at a pH above the point of zero charge (PZC) of the mineral. With increasing surface coverage of the sorbent by NOM, the proportion of desorbable NOM decreased for all extractants. Increased sorption hysteresis was also observed with an increasing time period between sorption and desorption. The desorption was more pronounced for NOM compounds that exhibit hydrophilic properties and have low contents of aromatic structures and carboxyl groups. The irreversible binding of NOM, especially of the lignin‐derived portion, to soil minerals seems to result from its polyelectrolytic nature. This may favor the formation of multi‐site coordinative bonds and effective shielding of the binding ligands by other parts of the sorbed molecule.
Soil Water Recharge under Uncropped Ridges and Furrows
Authors: Bargar B. , Swan J. B. , Jaynes D.
Published: July 2010

Nitrate leaching to ground and surface water is an increasing concern in agriculture. Ridge tillage and associated residue management offer potential for modifying the pattern of soil water and solute movement to reduce NO3 leaching from corn (Zea mays L.) production. To test this idea we used time domain reflectometry (TDR) measurements of volumetric soil water content (θ) at 0.5‐h intervals following natural rainfall events to determine the pattern of infiltration and soil water recharge for uncropped row and furrow positions in long‐term ridge‐tillage fields. Soil water content was measured under adjacent rows and three adjoining furrows for 103 d in 1992 on a Clarion loam (fine‐loamy, mixed mesic, Typic Hapludoll) near Boone, IA and 96 d on Monona silt loam (fine‐silty, mixed mesic, Typic Hapludoll) near Treynor, IA. During rainfall, infiltration occurred primarily in furrows, as indicated by greater and more rapid initial increases in θ for furrow than for row positions at the same elevation. Following redistribution and evaporation, row and furrow positions at the same elevation had θ values differing by <0.03 m3 m−3 Changes in profile average θ of rows and furrows between rainfall events were closely correlated (R2 > 0.94). Storage between rainfall events decreased with increasing initial θ and time interval between events (R2 > 0.68), consequently soil water recharge occurred as a series of stepwise increases of θ. These results support the conclusion that water infiltrated in furrows and primarily moved laterally to row positions, minimizing downward water movement under the row. These results explain greater solute movement under furrows than under rows, as found in several short‐term studies.
Erosion and Productivity of Vegetable Systems on Sloping Volcanic Ash–Derived Philippine Soils
Authors: Poudel D. D. , Midmore D. J. , West L. T.
Published: July 2010

Soil erosion is a major constraint to the sustainability of sloping‐land vegetable systems. Little information is available on the effectiveness of soil conservation measures under sloping intensified vegetable systems on volcanic ash–derived soils. We hypothesized that contouring, strip cropping, and high‐value contour hedgerows — asparagus (Asparagus officinalisL.), pineapple [Ananas comosus(L.) Merr.], pigeonpea [Cajanus cajan(L.) Huth], and lemongrass [Cymbopogon flexuosus(Nees ex Steudel) J. F. Watson] — reduce soil loss compared with the farmer's traditional practice of up‐and‐down cultivation on sloping lands. A field experiment tested these soil conservation technologies from 1995 to 1998 in a completely randomized block design on a 42% natural slope on a clayey, halloysitic, isothermic, Typic Kandiudox. The greatest annual soil loss (65.3 t ha−1) was in the up‐and‐down system and comparative values were 37.8 t ha−1for contouring, 43.7 t ha−1for strip cropping, and 45.4 t ha−1for high‐value contour hedgerows. Three rain events alone caused 47% of the total soil loss. All erosion–runoff plots showed large differences in soil properties and crop yields between the upper and the lower slope. Crop yields downslope were greater by 40% for tomato (Lycopersicon esculentumMiller), 36% for corn (Zea maysL.), and 78% for cabbage (Brassica oleraceavar.capitataL.) than for upslope. In the contour hedgerow treatment, rapid terrace development changed soil properties, and crop yields for the bottom portions of bioterraces were greater by 121% for corn and 50% for tomato than yields of top portions.
Separation of Root Respiration from Total Soil Respiration Using Carbon‐13 Labeling during Free‐Air Carbon Dioxide Enrichment (FACE)
Authors: Andrews Jeffrey A. , Harrison Kevin G. , Matamala Roser , Schlesinger William H.
Published: July 2010

Soil respiration constitutes a major component of the global carbon cycle and is likely to be altered by climatic change. However, there is an incomplete understanding of the extent to which various processes contribute to total soil respiration, especially the contributions of root and rhizosphere respiration. Here, using a stable carbon isotope tracer, we separate the relative contributions of root and soil heterotrophic respiration to total soil respiration in situ. The Free‐Air Carbon dioxide Enrichment (FACE) facility in the Duke University Forest (NC) fumigates plots of an undisturbed loblolly pine (Pinus taeda L.) forest with CO2 that is strongly depleted in 13C. This labeled CO2 is found in the soil pore space through live root and mycorrhizal respiration and soil heterotroph respiration of labile root exudates. By measuring the depletion of 13CO2 in the soil system, we found that the rhizosphere contribution to soil CO2 reflected the distribution of fine roots in the soil and that late in the growing season roots contributed 55% of total soil respiration at the surface. This estimate may represent an upper limit on the contribution of roots to soil respiration because high atmospheric CO2 often increases in root density and/or root activity in the soil.
Numerical Analysis of the Effect of the Lower Boundary Condition on Solute Transport in Lysimeters
Authors: Flury Markus , Yates Marylynn V. , Jury William A.
Published: July 2010

Field lysimeters are often used to assess environmental behavior of agrochemicals. Most lysimeters used to date have a free‐draining lower boundary where leaching out of the lysimeter occurs by gravity alone. In this case, the lower boundary of a lysimeter is open to the atmosphere, and consequently, leachate is collected only if the bottom of the lysimeter becomes water saturated. In a field soil, such local water saturation does not occur. The objective of this study was to evaluate the effect of the lower boundary condition on chemical leaching. Numerical simulations were used to compare solute transport in field soils and in lysimeters. Simulations were carried out in homogeneous sandy and loamy soils under steady‐state, unsaturated water flow conditions. Water flow was described by the Richards equation and solute transport by the advection–dispersion equation. The effect of linear and nonlinear and instantaneous and kinetic sorption was investigated. The results showed that for a conservative solute the differences between field soil and lysimeter increase as the coarseness of the soil increases. Decreasing water flux increases the difference between field soil and lysimeter. In general, solute transport in the lysimeter is characterized by a slower mean velocity, a larger spreading, and smaller concentration values. For solutes subject to linear equilibrium sorption, the sorption mechanism compensates for the effects of the lower boundary condition. The larger the sorption coefficient, the less the difference between lysimeter and field soil. However, large differences are found in the case of strongly convex nonlinear sorption isotherms.
Small‐Scale Variability in Solute Transport Processes in a Homogeneous Clay Loam Soil
Authors: Garrido Fernando , Ghodrati Masoud , Chendorain Michael , Campbell Chris G.
Published: July 2010

Small‐scale variations in transport parameters may have a profound influence on larger scale flow processes. Fiber‐optic miniprobes (FOMPs) provide the opportunity to continuously measure solute resident concentration in small soil volumes. A 20‐channel multiplexed‐FOMP system was used in repeated miscible displacements in a repacked clay loam soil column (20 cm long and 10‐cm diam.) to examine small‐scale, point‐to‐point variability in convective–dispersive transport processes. Transport parameters, measured 10 cm below the surface, were compared at two drip irrigation point densities and two fluxes. Irrigation densities of one irrigation drip point per 4 cm2 and 11 cm2 of column surface area produced similar results. The breakthrough curves measured at 0.10 cm h−1 had a larger immobile phase than at a flux of 1.07 cm h−1 In the clay loam soil the mobile–immobile model fit the breakthrough curves better than the convective–dispersive equation (CDE), with r2 values of 99.6 and 97.1, respectively. This analysis demonstrated that dispersion and mass recovery were much more variable than pore water velocity in this repacked clay loam soil. However, even in the most variable transport conditions encountered, only 17 sampling points were necessary to describe the column average transport parameters within 20% of the mean.
Phosphorous and Potassium Fertilizer Recommendation Variability for Two Mid‐Atlantic Coastal Plain Fields
Authors: Anderson-Cook C. M. , Alley M. M. , Noble Robert , Khosla R.
Published: July 2010

Fertilizer recommendations for variable rate treatments developed from grid soil sampling protocols are unproven for mid‐Atlantic Coastal Plain soils. The objectives of this study were to compare soil test results for P and K fertilizer recommendations for two fields utilizing two grid sampling sizes (0.33 ha and 0.83 ha), sampling by soil type, and standard composite sampling. The study location contained alluvial soils ranging from a loamy sand to a silt loam. The two fields totaled approximately 21 ha and were sampled on grids 18.5 by 30.4 m. Samples consisted of composites of eight cores to a 20‐cm depth that were analyzed for Mehlich I extractable P and K. Two statistical models were developed for comparing the extractable P and K data and the resulting fertilizer recommendations. The first model, following a precision farming approach, implies sources of variation are systematic and attributable to narrow geographic locations. The second model, associated with composite sampling, utilizes less specific patterns of variability. Comparisons showed that the smaller grid (0.33 ha) produced more precise estimates of extractable K in only one field (with 67% of tested locations receiving appropriate fertilizer rates), with no improvement for extractable P in either field. Both grid‐sampling systems improved estimate precision for extractable P and K (with a smaller average misapplication rate) compared with a whole‐field composite. The composite‐by‐soil‐type approach was superior to the whole‐field composite for estimating extractable P and K with a lower average misapplication and higher percentage receiving appropriate fertilizer rates. The composite‐by‐soil approach produced the most precise fertilizer recommendations for small systematic variation and required fewer laboratory measurements. It approached the grids‐sampling system precision of fertilizer recommendations for large in‐field variation. Only when strong trends in extractable P and K exist would grid sampling be recommended over the composite‐by‐soil‐type sampling approach.
Role of Hydrophobic Components of Soil Organic Matter in Soil Aggregate Stability
Authors: Piccolo Alessandro , Mbagwu Joe S. C.
Published: July 2010

Little is known about the effects of the individual components of organic matter (OM) on aggregate stability (AS). We hypothesized that AS of a Typic Haplustalf from which native OM was either removed or retained would be affected by incubation periods and application rates of a hydrophilic polysaccharide gum (G) and a hydrophobic stearic acid (S) with or without pretreatment with a hydrophobic humic acid (HA). Removal of OM reduced AS of unmodified soil by ≈40 and 20% after soil incubation for 7 and 40 d, respectively. In both soil samples, AS was best at the highest rate of G (5.0 g kg−1). Its effect was better on Soil A (where OM was removed) than Soil B (where OM was retained) but diminished rapidly during 40 d. At this rate, G increased AS by 750% in Soil A and by 335% in Soil B compared with no addition. With S, aggregate stability increased more with time in Soil B than in Soil A. Its maximum effect was also at the highest application rate (5.0 g kg−1), where AS increased 100% on Soil A and 131% on Soil B. At the highest rate (0.2 g kg−1), HA increased AS by 73% on Soil B and 27% on Soil A. The effect of HA alone did not vary with time. Soil pretreatment with HA before addition of G reduced significantly both the state of aggregation and AS of both soils. The reverse occurred when HA was applied before S. After 40 d, S+HA increased AS in Soil B by 34%, whereas G and G+HA decreased AS by 14 and 4%, respectively. We found that soil AS was improved and maintained with time more by hydrophobic than by hydrophilic components of organic matter. Long‐lasting aggregate stability of soils can be thus achieved by addition of hydrophobic humic material with hydrophobic organic wastes.
Fertilizer Banding Influence on Spatial and Temporal Distribution of Soil Inorganic Nitrogen in a Corn Field
Authors: Zebarth B. J. , Younie M. F. , Paul J. W. , Hall J. W. , Telford G. A.
Published: July 2010

Fertilizer N is commonly applied as a sidedress band application in corn (Zea maysL.) fields. The objectives of this study were to determine the implications of fertilizer band application on spatial and temporal variations in soil inorganic N and to evaluate different sampling strategies for their suitability in estimating the average soil inorganic N concentration of a field. Treatments were 0, 60, and 120 kg N ha−1in 1994, and 0, 120, and 240 kg N ha−1in 1995, replicated three times at each of two sites. Fertilizer was applied as a band of NH4NO315 cm on each side of each corn row at the corn six‐leaf stage. Soil samples taken at eight interrow locations 0, 5, 10, 15, 20, 25, 30, and 35 cm from the corn row and at depth increments of 0 to 15, 15 to 30, and 30 to 60 cm and on five sampling dates were analyzed for soil NO3and NH4concentrations. Random sampling and five systematic sampling strategies were evaluated with respect to bias in estimation of field soil NO3and NH4concentration for three depth increments, and with respect to the number of samples required to achieve a given precision and probability level combination for soil NO3concentration for the 0‐ to 15‐cm depth. All systematic sampling strategies provided adequate estimates of the true soil inorganic N concentration as estimated based on uniform sampling across all interrow locations. There was no consistent benefit to using any one systematic strategy with respect to the number of cores required to obtain a given level of precision in soil NO3concentration at a given level of probability. Systematic sampling strategies were at least as good as, or superior to, random sampling, particularly after fertilizer band application and at high N rates. The apparent insensitivity of estimated field soil NO3concentration to sampling strategy was attributed to the relatively high mobility of NO3in soil and variation in placement of the fertilizer band relative to the corn row during sidedressing.
Induration of C Horizons by Allophane and Imogolite in Costa Rican Volcanic Soils
Authors: Jongmans A.G. , Denaix L. , van Oort F. , Nieuwenhuyse A.
Published: July 2010

Little is known about the contribution of allophane and imogolite to induration of soil horizons in the perudic tropics. In this study we observed, to a depth of 10 m, indurated sandy C horizons that contained isotropic translucent fine‐textured coatings in Holocene and Pleistocene alluvial andesitic deposits situated in the perudic moisture regime in Costa Rica. The horizons have a firm to extremely firm consistence and do not slake in water. Optical microscopy showed that the coatings cover and bridge primary minerals, forming a three‐dimensional framework in the horizons, which indicates a post‐depositional origin. Bulk chemical analyses show the presence of allophane in the indurated horizons. Scanning electron microscopy (SEM) of undisturbed mineral surfaces confirmed the existence of the coating framework. Chemical analyses, obtained by SEM energy‐dispersive x‐ray, indicate an alumino‐silicate coating with Al/Si ratios ranging from 1.6 to 2.1. Coatings were studied by TEM, carried out on an ultra‐thin section (50 nm) cut from a coating that was in situ sampled by microdrilling in an uncovered thin section. All clay material in the horizons consists of coatings of allophane and imogolite. Rapid weathering of the andesitic parent material released large amounts of Al and Si, which accumulated as amorphous gels due to oversaturation of the soil solution near the wetting front or in deeper water‐conducting layers. We conclude that the mechanisms for soil horizon induration include changes in moisture conditions due to short seasonal drying, climatic changes, tectonic uplifting, and erosion, which lead to irreversible drying of allophane and imogolite.
Environmental Factors Controlling Soil Respiration in Three Semiarid Ecosystems
Authors: Conant Richard T. , Klopatek Jeffrey M. , Klopatek Carole C.
Published: July 2010

Previous research suggests that soil organic C pools may be a feature of semiarid regions that are particularly sensitive to climatic changes. We instituted an 18‐mo experiment along an elevation gradient in northern Arizona to evaluate the influence of temperature, moisture, and soil C pool size on soil respiration. Soils, from underneath different tree canopy types and interspaces of three semiarid ecosystems, were moved upslope and/or downslope to modify soil climate. Soils moved downslope experienced increased temperature and decreased precipitation, resulting in decreased soil moisture and soil respiration (as much as 23 and 20%, respectively). Soils moved upslope to more mesic, cooler sites had greater soil water content and increased rates of soil respiration (as much as 40%), despite decreased temperature. Soil respiration rates normalized for total C were not significantly different within any of the three incubation sites, indicating that under identical climatic conditions, soil respiration is directly related to soil C pool size for the incubated soils. Normalized soil respiration rates between sites differed significantly for all soil types and were always greater for soils incubated under more mesic, but cooler, conditions. Total soil C did not change significantly during the experiment, but estimates suggest that significant portions of the rapidly cycling C pool were lost. While long‐term decreases in aboveground and belowground detrital inputs may ultimately be greater than decreased soil respiration, the initial response to increased temperature and decreased precipitation in these systems is a decrease in annual soil C efflux.
Chemical Evaluation of Nutrient Supply From Fly Ash–Biosolids Mixtures
Authors: Schumann Arnold W. , Sumner Malcolm E.
Published: July 2010

Prediction of plant nutrient supply from fly ash and biosolids (sewage sludge and poultry manure) may enhance their agricultural use as crop fertilizer. Two mild extraction methods (42‐d equilibration with ion‐exchange resins; 2‐d equilibration with pH 4.8 buffered nutrient solution) and analysis of nutrient data by the Diagnosis and Recommendation Integrated System (DRIS) were tested with 29 fly ash samples, four biosolids samples, and their mixtures. The resin method was useful for major nutrient (N, P, K, Ca, Mg, S) extraction from fly ashes and organic materials, particularly where mineralizable fractions of N and P under aerobic conditions are required. However, resins were inefficient in extracting P from high‐Fe sewage sludges because organic waste samples caused premature failure of semipermeable membranes and fouling of resins. Extraction of fly ash with dilute buffered nutrient solution was more successful because micronutrient recovery was improved, major nutrients were correlated to the resin method, both addition and removal of nutrients were recorded, DRIS analysis was possible, and equilibration was rapid (2 d). The overall nutrient supply from these extremely variable fly ashes was:(high micronutrient, low major nutrient supply). For biosolids, the major nutrients ranked: P > N ≈ Ca > S > Mg > K (sewage sludges), and N > Ca ≈ K > P > Mg > S (poultry manures). In mixtures of fly ash with 26% sewage sludge the order was: Ca > S > N > Mg > P > K, while in mixtures of fly ash and 13% poultry manure, the nutrients ranked: Ca > K ≈ N ≈ S > Mg > P. Optimal plant nutrition (especially N–P–K balancing) should be possible by mixing these three waste materials.
Effect of Cable Length on Time Domain Reflectometry Calibration for High Surface Area Soils
Authors: Logsdon S. D.
Published: July 2010

Time domain reflectometry (TDR) has been used by soil scientists to determine soil water content (θ). A waveform analysis determines an apparent dielectric number (ϵa) which can often be empirically related to ϵ. “Bound water” near colloid surfaces has different properties than free water. At the gigahertz frequencies used for TDR, free water has a negative temperature effect but bound water has a positive temperature effect on dielectric number. Long coaxial cables reduce the higher frequencies of the TDR equipment, which can influence the frequency dependent ϵa of bound water. The objective of this study was to determine the effect of coaxial cable length and temperature on apparent dielectric properties for samples with and without large amounts of bound water. Two undisturbed columns of Okoboji mucky silty clay loam (fine, smectitic, mesic cumulic Endoaquoll) with a specific surface area of 286 m2 g−1 and two packed sand samples with calculated surface areas of 0.01 m2 g−1 were used for the experiment. The ϵa was determined at four cable length combinations, three temperatures, and a range of θ. The temperature correction factors for Okoboji ranged from 0.008 to 0.012 θ/°C, depending on cable length. Long cables increased the rise time 41%, which decreased the frequency bandwidth. The Okoboji samples had a bulk electrical conductivity as high as 0.14 S m−1, which hampered determination of the final part of the waveform. In summary for Okoboji, cable length and temperature had a greater effect on ϵa than did θ. High surface area samples should be calibrated using the same cable length used for measurements, and the temperature effect should be incorporated.
Time Domain Reflectometry Measurements of Solute Transport across a Soil Layer Boundary
Authors: Nissen H.H. , Moldrup P. , Kachanoski R.G.
Published: July 2010

The mechanisms governing solute transport through layered soil are not fully understood. Solute transport at, above, and beyond the interface between two soil layers during quasi‐steady‐state soil water movement was investigated using time domain reflectometry (TDR). A 0.26‐m sandy loam layer was packed on top of a 1.35‐m fine sand layer in a soil column (0.15‐m i.d.). Soil water content (θ) and bulk soil electrical conductivity (ECb) were measured by 50 horizontal and 2 vertical TDR probes. A new TDR calibration method that gives a detailed relationship between apparent relative dielectric permittivity (Ka) and θ was applied. Two replicate solute transport experiments were conducted adding a conservative tracer (KCl) to the surface as a short pulse. The convective lognormal transfer function model (CLT) was fitted to the TDR‐measured time integral–normalized resident concentration breakthrough curves (BTCs). The BTCs and the average solute‐transport velocities showed preferential flow occurred across the layer boundary. A nonlinear decrease in TDR‐measured θ in the upper soil toward the soil layer boundary suggests the existence of a 0.10‐m zone where water is confined towards fingered flow, creating lateral variations in the area‐averaged water flux above the layer boundary. A comparison of the time integral–normalized flux concentration measured by vertical and horizontal TDR probes at the layer boundary also indicates a nonuniform solute transport. The solute dispersivity remained constant in the upper soil layer, but increased nonlinearly (and further down, linearly) with depth in the lower layer, implying convective‐dispersive solute transport in the upper soil, a transition zone just below the boundary, and stochastic–convective solute transport in the remaining part of the lower soil.
Estimating Soil Hydraulic Properties During Constant Flux Infiltration Inverse Procedures
Authors: Si B. C. , Kachanoski R. G.
Published: July 2010

There is a need for accurate and cost‐effective methods to estimate the hydraulic properties of soils. Past work indicated measurements of a single hydraulic response will not necessarily result in unique and stable estimates of hydraulic parameters when the number of unknowns is more than two. Prior information regarding the parameters or additional measurements are needed for the estimation problem to be well posed. However, accurate prior information is seldom available due to variations of the hydraulic properties in space and time. This paper presents a method for estimating hydraulic properties from simultaneous measurements of soil water storage to a fixed depth as a function of time during constant flux infiltration, and steady‐state pressure head readings using vertically installed multi‐purpose time domain reflectometry probes (MTDR). Multi‐purpose TDR probes have a porous steel cup at their ends allowing soil water storage and ψ to be simultaneously measured at the same location. Our parameter estimation is formulated by an inverse procedure which combines a weighted nonlinear least square method with analytical solutions for soil water content and pressure head as functions of depth and time during one dimensional infiltration. We analyze the possibility of using water storage data combined with the initial and steady‐state pressure head readings for the purpose of estimating soil hydraulic properties. The uniqueness problem was analyzed by studying the behavior of response surfaces. The combination of water storage measurements during constant flux infiltration with an initial and a steady‐state pressure head reading yielded unique and stable solutions of the inverse problem. The utility of the parameter estimation procedure is demonstrated using experimental and theoretical data.
Facilitated Transport of Napropamide by Dissolved Organic Matter Through Soil Columns
Authors: Williams C. F. , Agassi M. , Letey J. , Farmer W. J. , Nelson S. D. , Ben-Hur M.
Published: July 2010

Contamination of groundwater by pesticide percolation is of great concern. Field observations have revealed that some pesticides move deeper into the soil profile than would be expected from predictions made by solute transport models. The discrepancies have been attributed to preferential flow of water carrying pesticides via macropores in field soils. The same phenomenon may also be explained by transport facilitated by a carrier such as dissolved organic matter (DOM). A laboratory study was conducted to evaluate the transport of napropamide [2‐(a‐naphthoxy‐N,N‐diethylpropionamide] through soil via DOM. Soils were sieved, packed in columns, and treated at the surface with14C‐labeled napropamide. Water was applied to the columns by flooding and leachate was collected. It was found that14C‐labeled napropamide was present in the first 0.22 cm of leachate. The14C and DOM concentrations were highest in the initial leachate and decreased with increasing leachate. Napropamide concentration fell below detection at some depth in all columns and recovery in the soil averaged 95% of the applied napropamide. Gas chromatographic analyses verified that14C activity in the leachate was associated with napropamide. A dialysis equilibrium technique determined that 17 to 56% of the napropamide in the leachate was retained inside a 500‐Da dialysis membrane. The rapid leaching of a small fraction of napropamide was not a result of preferential flow in our experiments but is due to DOM‐facilitated transport. Thus, under field conditions rapid pesticide leaching could be the combined effects of preferential flow and facilitated transport.
Update and recorrelation of soil surveys using gis and statistical analysis
Authors: Brannon G. R. , Hajek B. F.
Published: July 2010

The introduction of U.S. soil taxonomy and the increased pressure on land use and development has generated the need to update soil surveys that were published before 1965. A portion of a pre‐1965 soil survey from Montgomery county in Alabama was selected to evaluate an update approach using geographic information system (GIS) and statistical analysis. The update included map recompilation, correlation, interpretation, and presentation methods. Sampling points were identified with a stratified random sampling and data obtained at each point were analyzed by traditional statistical methods. The taxonomic accuracy was 75 to 83% at a confidence level of 90%. Interpretative reliability was 90 to 95% for dwellings without basements, 95 to 98% for septic tank absorption fields, and 93 to 98% for local roads and streets. Updating old soil surveys by using GIS technology and statistical evaluation can produce a quality soil survey that meets or exceeds National Cooperative Soil Survey (NCSS) standards. Using this method, an experienced soil scientist can update, recorrelate, and recompile ≈40180 ha (100000 acres) yr−1 This is an increase in production of 22090 to 24100 ha (55000–60000 acres) or ≈120 to 150% compared with conventional remapping methods.
Alfalfa Root and Shoot Mulching Effects on Soil Hydraulic Properties and Aggregation
Authors: Rasse Daniel P. , Smucker Alvin J. M. , Santos Djail
Published: July 2010

Although alfalfa (Medicago sativa L.) stands have been reported to improve soil physical properties, little is known about the specific influences of above‐ and belowground alfalfa components on soil physical properties. A 2‐yr study was conducted to investigate alfalfa root and shoot mulch modifications of soil physical properties and water movement in the root zone of a Kalamazoo loam soil (fine‐loamy, mixed, mesic Typic Hapludalf) in southwest Michigan. Four treatments were considered: bare fallow (BF), bare fallow with alfalfa shoot mulch (BFSM), alfalfa with shoots removed and roots remaining (AR), and alfalfa with alfalfa shoot mulch (ASM). Volumetric soil water contents were measured by time domain reflectometry (TDR). Development of fine roots was monitored by minirhizotron technology. Alfalfa root systems increased saturated hydraulic conductivity (Ksat) by 57%, total and macroporosities by 1.7 and 1.8%, respectively, and water recharge rate of the soil profile by as much as 5.4% per day. These effects of alfalfa roots on soil porosity were mainly attributed to increased amplitudes of wetting and drying cycles and high rates of root turnover in the Ap horizon. Ksat was significantly correlated with macroporosity Mean weight diameter (MWD) of aggregates from bare fallow soils was 20% higher when alfalfa shoot mulch was applied. Our results suggest that aggregate stability was more affected by C sources from shoot mulch and root turnover than by factors specific to root activities such as physical enmeshment of aggregates and increased soil wetting and drying cycles.
Nitrous Oxide Emission from an Agricultural Soil Fertilized with Liquid Swine Waste or Constituents
Authors: Whalen S. C.
Published: July 2010

Large scale swine production facilities that land‐apply liquid waste are rapidly expanding in the southeastern USA. This study evaluated controls on N2O emission in a Goldsboro loamy sand (fine‐loamy thermic, aquic Typic Paleudult) receiving field in North Carolina that was planted to winter wheat (Triticum aestivumL.). Two experiments were conducted in April–May 1997 where field plots were fertilized with liquid swine waste, individual chemical constituents of waste (NH4, available C), NO3, or deionized water. Temporal changes in N2O efflux and soil physicochemical properties were assessed over 8 and 11 d.. Treatments that included N (75–165 kg ha−1) showed N2O fluxes exceeding 4000 μg N2O–N m−2h−1within 1 d of fertilization, but emissions declined to prefertilization values (∼10–25 μg N2O–N m−2h−1) within a few days as soils drained. Treatments that did not include N (deionized water, glucose) showed no increase in N2O emission over unfertilized controls. Time‐integrated N2O emission was significantly lower for plots amended with swine waste (8.5 mg N2O–N m−2) compared with plots comparably fertilized with NH4–N plus glucose‐C (20.8 mg N2O–N m−2), suggesting that some component of the waste adversely affected the microbial N cycling community. The immediate increase in N2O emission following fertilization and accumulation of NO3–N without lag indicated that repeated fertilization throughout the growing season maintained active and responsive nitrifying and denitrifying communities. Percentage fertilizer loss to N2O to the point where fluxes had returned to prefertilization values was low, <1.0%. However, simulated rainfall gave pulsed N2O emission from denitrification of accumulated NO−3–N, indicating that further emissions will occur with an increase in soil moisture.
Sulfate Pools in the Weathered Substrata of a Forested Catchment
Authors: Manderscheid B. , Schweisser T. , Lischeid G. , Alewell C. , Matzner E.
Published: July 2010

The mitigating effect of decreasing anthropogenic SO4 deposition on acidified soils and waters can be delayed by the release of previously stored soil SO4. We investigated SO4 pools and desorption in the weathered substrata (0.5–10 m depth) of a forested catchment on granite to quantify the importance of these layers to SO4 dynamics. Solid‐phase materials from 10 boreholes to a maximum depth of 10 m were analyzed for water‐ and phosphate‐extractable SO4, SO4 desorption, cation‐exchange capacity (CEC), pH, and dithionite‐ and oxalate‐extractable Fe (Fed and Feo) and Al (Ald and Alo). Seven of the investigated boreholes were used to monitor water table depth and to obtain samples for measurement of solution SO4 concentrations. The storage of phosphate‐extractable SO4 in the weathered substrata was estimated at 90 kmol ha−1, of which ≈50 kmol ha−1 were water soluble. Sulfate pools and their desorption behavior were highly variable, which could partly be explained by the variation of pH and extractable Fe and Al contents of the samples. Sulfate concentrations in groundwater were dependent on the depth of groundwater table and corresponded with the depth gradients of solid‐phase SO4. The SO4 pools of the substrata were apparently regulating solution concentrations. Thus, groundwater acidification in such aquifers will not be easily reversed by decreasing SO4 deposition because of the release of previously stored SO4.