bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Soil Organic Matter Accumulation on Potassium and Ammonium Quantity‐intensity Relationships
Authors: Evangelou V. P. , Karathanasis A. D. , Blevins R. L.
Published: July 2010

Quantity‐intensity (Q/I) relationships for potassium (K+) and ammonium (NH4+) in a Maury silt loam soil (fine‐silty, mixed, mesic, Typic Paleudalfs) under long‐term conventional and no‐tillage management were investigated to determine changes in solute‐soil interactions brought about by differential organic matter accumulation. To obtain differences in organic matter content, representative soil samples were collected from a field experiment that was established in the spring of 1970, involving treatments of conventional tillage with no nitrogen (N) fertilizer (CT‐control) and no‐tillage with 336 kg N ha−1 applied annually (NT‐high N). The results of the study reveal that K+ and NH4+ equilibrium concentration ratios (CRk*, CRNH*4) along with the linear potential buffering capacities (PBCK, PBCNH4) were greatly affected by soil organic matter accumulation resulting from no‐tillage and N addition. CRK* and CRNH*4 were higher in the NT‐high N than the CT‐control system (19.61 and 12.11 vs 6.61 and 2.15 [(mol L−1)1/2 × 103], respectively). Furthermore, the PBCk was slightly greater but not significantly different in the NT‐high N (28.4) than the CT‐control system (26.3) [cmol(+) kg−1)/(L mol−1)1/2]. Potential buffering capacity for NH4+ (PBCNH4) was significantly smaller in the NT‐high N (17.5) than the CT‐control system (26.0). The affinity of the NT‐high N soil exchange phase for both K+ and NH4+ was significantly lower than that of the CT‐control exchange phase. The affinity for K+ exhibited by NT‐high N system was significantly greater than that for NH4+ (1.71 vs. 1.23). In CT‐control systems only slight differences (statistically nonsignificant) were observed in affinities for NH4+ and K+ (2.62 vs. 2.47). Potential buffering capacity for NH4+ and K+ appeared to be a function of the affinity of the exchange phase for each cation and the magnitude of the cation exchange capacity (CEC). Despite higher CEC values in the NT‐high N system, a proportional increase in the PBC was not observed because the NT‐high N exchange phase exhibited a lower affinity for NH4+ and K+ ions than the CT‐control did.
Nature and Micromorphology of Carbonate Glaebules in Some Vertisols of India
Authors: Mermut A. R. , Dasog G. S.
Published: July 2010

The mineralogical and chemical nature, size, shape, distribution, and orientation of carbonate glaebules in two Chromusterts and two Pellusterts of India were studied. Micromorphology and 14C analysis of these features indicated their pedogenic origin. X‐ray diffraction and chemical analyses showed that calcite was the only carbonate mineral present and that there were inclusions of primary minerals and other soil constituents. Two morphological groups consisting of black and white glaebules were observed. Black carbonate glaebules had relatively older 14C dates (26 000 yr BP) and higher amounts of Fe and Mn, and were usually smaller (0.5‐cm diam) than the white ones (1.0‐cm diam, 4000–14 000 yr BP). Since the black carbonate glaebules were coated by Fe and Mn oxides, they therefore had a smoother surface morphology. The majority of the glaebules had cavities that were partly or entirely filled by carbonate neoformations. Intersecting sets of glaebules with an inclined, banded orientation pattern in the subsoil were interpreted as a sign of stress phenomena, and the quantitative distribution and orientation pattern of these features suggested a self‐mixing process. The study also indicated the possibility of using carbonate glaebules as a criterion in the classification of Indian Vertisols.
A Portable Constant‐rate Cone Penetrometer
Authors: Lowery Birl
Published: July 2010

A portable, constant‐rate, recording cone penetrometer was designed and field tested to eliminate operator‐associated variability with hand‐pushed penentrometers and to overcome the limited portability of tractor‐mounted penetrometers. An average penetration rate of 8.3 mm s−1 was achieved with a small high‐torque DC motor connected to a rack‐pinion gear system. The motor and gear system was mounted on a tripod that allowed the unit to be leveled and provided for a maximum penetration depth of 0.61 m. Force of penetration, as a function of depth, was determined with four strain gages mounted on a proving ring and a rotary encoder. The encoder provided a remote signal to drive a x‐y plotter providing 0.61 mm of chart per millimeter of soil penetrated. The coefficient of variation for the rate of penetration was 3.4%. The rate of penetration remained approximately constant when tested over a range of soil densities from 0.9 to 1.9 Mg m−3.
Topsoil and Subsoil Thickness Requirements for Reclamation of Nonsodic Mined‐land
Authors: Halvorson G. A. , Melsted S. W. , Schroeder S. A. , Smith C. M. , Pole M. W.
Published: July 2010

Eight trenches were excavated to a depth of 4.6 m and filled with one of three different textures of spoil to evaluate topsoil and subsoil thickness requirements for crop production on nonsaline, nonsodic spoil material. Yields of wheat (Triticum aestivum L.) in 1979 and 1982, barley (Hordeum vulgare L.) in 1980, and corn (Zea mays L.) in 1981 and 1983 were compared on plots with 0.23, 0.46, or 0.69 m of topsoil replaced over loamy sand spoil with and without subsoil, over clay loam spoil, or over silty clay loam spoil. Crop yields increased with increasing thickness of replaced topsoil, especially on trenches filled with loamy sand spoil. Crop yields were greater when subsoil was replaced than when no subsoil was replaced on loamy sand spoil at a given topsoil thickness. Average yields from the trenches were equal to or better than average yields from undisturbed plots in 1979 and 1983. On irrigated plots in 1983, response of silage and corn grain to subsoil/spoil treatments was similar to the nonirrigated plots. Wheat grown on irrigated plots in 1982 did not respond significantly to topsoil thickness or subsoil/spoil treatments. At least 0.69 m of topsoil plus subsoil was required to achieve highest yields on nonsodic, nonsaline, loamy sand spoil, but 0.46 to 0.69 m of topsoil was sufficient for highest yields on clay loam and silty clay loam nonsaline, nonsodic spoil. Crop yields were not increased by broadcast applications of N and P fertilizer.
Effects of Subsoiling and Mechanical Impedance on Tobacco Root Growth
Authors: Vepraskas M. J. , Miner G. S.
Published: July 2010

Relationships between mechanical impedance and root growth have not been extensively defined for field conditions, and as a result, it is usually impossible to know with certainty when soil layers of high mechanical impedance are limiting root growth or where subsoiling is needed to improve root development. The primary objective of this investigation was to describe relationships between mechanical impedance and root concentration for both subsoiled and nonsubsoiled tillage treatments in field studies. Experiments were conducted at three locations in the North Carolina Coastal Plain on soils that were coarse‐textured Typic and Arenic Paleudults with tillage pans. At each site, flue‐cured tobacco (Nicotiana tabacum L.) was grown in subsoiled and nonsubsoiled (moldboard plow/disk) tillage treatments replicated four times. Penetrometer readings were made in the row and 0.30 m to the side of the row at 6‐ to 14‐d intervals for periods of 28 to 42 d; these data were averaged by depth and position and were expressed as mean cone index (CI). At approximately 52 and 75 days following transplanting, roots were counted by the trench‐profile method. At all locations, numbers of roots below the Ap horizon were significantly greater for the subsoiled, as compared to nonsubsoiled treatments for both root count dates. Mean CI was significantly correlated with root concentration in the Ap and E‐B horizons at all locations with r values ranging from −0.79** to −0.88** for both root count dates. The three tillage pans examined had mean CI's between 2.8 to 3.2 MPa. Subsoiling reduced the CI of the tillage pans for up to 47 d from transplanting and permitted significantly greater root penetration of the subsoil.
Extent and Persistence of Subsoil Compaction Caused by Heavy Axle Loads
Authors: Voorhees W. B. , Nelson W. W. , Randall G. W.
Published: July 2010

Wheel traffic of heavy farm machinery is causing increased concerns about soil compaction. To offset the increasing weight of large equipment, tires have increased in both size and numbers in an effort to keep constant the contact pressure on the soil surface. Recent research has indicated, however, that increasing axle load can cause increasing and deeper compaction irrespective of surface contact pressure. Axle loads of 9 and 18 Mg were applied in replicated field experiments initiated in 1981 and 1982 in Minnesota as part of an international cooperative study on the effects of high axle loads on deep soil compaction and plant response. Such axle loads are typical of modern harvest and transport equipment. These heavy axle loads were applied only at the beginning of the experiment, and are compared with check treatments where axle loads are limited to ≤4.5 Mg. Various soil parameters were measured to assess the extent and persistence of subsoil compaction. When the subsoil was relatively dry, axle loads of 9 and 18 Mg did not cause significant changes in bulk density, penetrometer resistance, or hydraulic conductivity deeper than about 20 to 30 cm, the normal depth of tillage. However, when the subsoil was relatively wet, bulk density increased about 0.08 Mg m−3 from about the 30‐ to 50‐cm depth. Saturated hydraulic conductivity decreased from 2 to 0.2 cm h−1 due to 18‐Mg axle load on a Webster clay loam (Typic Haplaquolls). A similar relative decrease was measured on a Nicollet clay loam (Aquic Hapludolls). Evidence of subsoil compaction persistence was measured 4 yr after initial heavy axle loading in spite of annual winter soil freezing to depths up to 90 cm.
Changes in Void Distribution and Volume During Compaction of a Forest Soil
Authors: Lenhard Robert J.
Published: July 2010

Bulk density and water retention measurements were conducted after 0, 1, 2, 4, 8, 16, and 32 trips with a rubber‐tired skidder on a forest soil whose surface was formed from volcanic ash. Changes in these measurements were used to evaluate effects of travelling intensity with heavy equipment on some soil physical properties. Bulk density reached a maximum after four trips and remained statistically constant with additional trips. A parameter indexing the poresize distribution, however, changed after four trips. The distribution of flow channels, therefore, was altered even with no significant change in mass per unit volume relationships. Compression of the soil during each skidder pass and elastic rebound thereafter was identified as the mechanism resulting in changes of the pore‐size distribution while bulk density remained constant. Effects of heavy equipment operation on the pore‐size distribution and water retention properties should be recognized in forest management.
Evaporite Mineralogy Associated with Saline Seeps in Southwestern North Dakota
Authors: Timpson M. E. , Richardson J. L. , Keller L. P. , McCarthy G. J.
Published: July 2010

Saline seepage in western North Dakota occurs when water in excess of crop use leaches soluble salts from the root zone and transports them laterally to lower landscape positions. Evapotranspiration moves these dissolved salts upward through the soil, resulting in salt crust formation at the surface. This study was undertaken to detail the mineralogic changes occurring as saline waters migrate through the soil profile, and to determine the mineralogic composition of the saline efflorescences present at the soil surface of four saline seeps in Hettinger County, North Dakota. Mineralogic changes resulting from upward water movement in soils were accurately predicted using the Hardie‐Eugster model of closed basin brine evolution. The sequence calcite‐gypsum‐ and mixed Na‐Mg‐(SO4) minerals occurs as saline waters migrate upward through the profile. The following minerals occur in surface efflorescences; mirabilite, thenardite, epsomite, hexahydrite, bloedite (Na2Mg(SO4)2·4H20), konyaite (Na2Mg(SO4)2·5H20), loewite Na12Mg7(SO4)13·15H2O), and gypsum. Hydration state, mineral occurrence, and mineral solubility were seasonally dependent.
Air Encapsulation: I. Measurement in a Field Soil
Authors: Fayer M. J. , Hillel D.
Published: July 2010

Encapsulated air is an important component of shallow water table fluctuations. Our objective was to measure the quantity and persistence of encapsulated air in a field setting. Using sprinkling rates of either 3.5 × 10−6 or 3.8 × 10−5 m s−1, we brought the water table in a field soil from a depth of 1.5 m to the surface on several occasions. Moisture contents during and after sprinkling were monitored with a neutron probe. Twice following sprinkling, the water table was maintained at the surface for more than 20 d, during which time we continued to monitor moisture contents. With the water table at the surface, differences between the porosity and the measured moisture content were attributed to encapsulated air. Encapsulated air contents ranged from 1.1 to 6.3% of the bulk soil volume, depending on the rate of sprinkling, soil depth, and initial soil moisture content. During ponding, encapsulated air persisted at the 0.3m depth for up to 28 d. The results indicate that encapsulated air is measurable in a field situation and that its quantity and persistence should be considered in analyzing the results of similar field experiments.
Nitrification Rates in Profiles of Differently Managed Soil Types
Authors: Hadas Aviva , Feigenbaum Sala , Feigin A. , Portnoy Rita
Published: July 2010

The variation of nitrification rates among soils and within soil profiles has received little attention compared with the well‐established relations with soil moisture and temperature. In this study, the rate of nitrification was determined in profiles of various soil types and under different agricultural management. Verhulst's equation was used to express the accumulation of nitrate (NO‐3) with time and modified to describe the rate of ammonium (NH+4) decrease. The maximal rate of nitrification (Kmx) and the delay period (t′) were derived from the equation and used to characterize quantitatively the nitrification process in various soil samples. The Kmx and t′ of surface soil samples were from 5 to 70 mg kg−1 d−1 and from 0.2 to 8 d, respectively. The Kmx decreased and t′ increased with soil depth. Soil factors mostly affecting the rate parameters were: pH decreasing from 7.8 to 6.6 or HCO‐3 decreasing below 1 mol m−3, previous agricultural management, and soil depth. Data obtained from 15N studies indicated that mineralization rate of soil organic N in NH+4‐treated soils was not always negligible relative to nitrification.
Desiccation Tolerance of Clover Rhizobia in Sterile Soils
Authors: Fuhrmann J. , Davey C. B. , Wollum A. G.
Published: July 2010

Procedures were developed to examine the effect of low soil moisture on clover rhizobia (Rhizobium leguminosarum biovar trifolii, formerly R. trifolii). A study was then conducted to determine the feasibility of identifying desiccation‐tolerant rhizobia as a possible means of improving inoculant quality for cool‐season, annual clovers (Trifolium L.). Five clover rhizobia isolates were tested for response to three water potential regimes in two sterile soils over a 42‐d incubation period. Initial soil water potential for all treatment combinations was −0.1 MPa. The three water potential regimes imposed were a constant −0.1‐MPa treatment and two progressive desiccation treatments having equilibrium potentials of ca. −70 and −500 MPa, respectively. These treatments were obtained by using sulfuric acid solutions to manipulate the relative humidity levels of the atmosphere surrounding the inoculated soils. The two soils used (0–10 cm) were an Altavista (Aquic Hapludults) loamy sand and a Cecil (Typic Hapludults) sandy clay loam. Overall survival of the rhizobia was highest, and relative persistence of the isolates was similar, in both soils at the −0.1 MPa treatment. Population levels were generally lowest under the −70 MPa desiccation regime. Population trends under the desiccation regimes were strongly affected by soil type and appeared to reflect the differential desiccation rates observed between the physically dissimilar soils. Although soil type also affected relative survival among the rhizobia, one isolate exhibited excellent survival at all treatment combinations. The more consistent estimates of relative desiccation tolerance were obtained with the finer‐textured Cecil soil, −500 MPa desiccation regime, and a minimum 21‐d incubation period.
Pedogenic Imogolite and Soil Environments: Case Study of Spodosols in Quebec, Canada
Authors: Wang C. , McKeague J. A. , Kodama H.
Published: July 2010

Spodosols similar in parent material, relief, and age but different in soil climate and vegetation were studied along two transects in Quebec, Canada. Soils of the northern transect (between 50 and 52°N) were under spruce (Picea mariana) forest in a colder region than that of the southern transect (at 46°N) where the forest was mainly deciduous, dominantly maples (Acer sp. L.) with greater rooting depth. Major differences in properties of pedons between the two transects were: total organic C in B horizons of the northern pedons was less than half that in southern pedons, and ratios of inorganic to organic amorphous Al and Fe in B horizons of the northern pedons were 5 to 10 times that of the B horizons of the southern transect. Both the lower organic C content and the higher ratios of inorganic to organic amorphous Al and Fe in the pedons of the northern transect may be attributed to the differences in vegetative cover, soil temperature, and biological activities of the two transects. Pedogenic imogolite was detected in all B and some C horizons of the northern transect but in none of the pedons of the southern transect. The high organic C content in the pedons of the southern transect is thought to retard the formation of imogolite. The domination of inorganic forms of amorphous Al and Fe in the spodic and spodic‐like horizons of the northern transect support the hypothesis that much Al and probably some Fe are translocated and deposited as inorganic complexes with Si in some Spodosols. It indicates the desirability of basing the chemical criteria of a spodic horizon on an extractant that removes both organic and inorganic amorphous products of pedogenesis. The currently‐used pyrophosphate extractant removes mainly organic‐associated forms of Al and Fe.
Transformations of Biotite to Kaolinite During Saprolite‐Soil Weathering
Authors: Rebertus R. A. , Weed S. B. , Buol S. W.
Published: July 2010

Biotite transformations in 10 pedons representing a developmental sequence of soils formed from coarse‐grained regional metamorphic rocks in the Piedmont and lower elevations of the Blue Ridge provinces of North Carolina are reported. Kaolinite is common to abundant in sand fractions of six of the pedons and is found to some extent in nine of the 10 pedons. Most of the kaolinite is derived from the pseudomorphic (isomorphic and largely isovolumetric) alteration of biotite. Biotite first alters to interstratified biotite‐vermiculite in which the vermiculite is hydroxy‐Al interlayered. The kaolinization of biotite extends throughout the grain, the pseudomorphs retaining the morphology of the biotite precursor but having the optical and structural properties of kaolinite. The koalinite pseudomorphs can be considered as single crystals because unit cells within the individual grains are all aligned crystallographically. A transformation model is proposed that accounts for most of the properties observed in weathering biotite. The degree of kaolinization of biotite increases with nearness to the soil surface and with increased degree of soil development. In the saprolite of the shallowest Dystrochrept biotite is relatively unweathered. In the sola of deeper Dystrochrepts and fine‐loamy Hapludults most of the biotite is kaolinized. Sand‐sized kaolinite pseudomorphs are less elastic and tenacious than fresh biotite and begin to physically disintegrate in the upper sola of fine‐loamy soils under the influence of processes of pedoturbation. In deeply developed clayey soils, kaolinite pseudomorphs may be absent from the sola. The increased clay content of clayey soils over that of fine‐loamy soils is largely a result of claysized kaolinite added from the comminution of sand‐sized kaolinite pseudomorphs of biotite.
Characterization of Hydroxy‐Aluminum Solutions by Aluminum‐27 Nuclear Magnetic Resonance Spectroscopy
Authors: Bertsch Paul M. , Thomas Grant W. , Barnhisel Richard I.
Published: July 2010

Laboratory synthesized hydroxy‐Al solutions were characterized by nuclear magnetic resonance (NMR) spectroscopy. Solutions ranging in Al concentration from 3.4 × 10−3 to 1.0 mol L−1 at OH/Al ratios (ñ) of 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.25, and 2.50 prepared with base injection rates of 0.6 and 1.2 cm3 min−1 were investigated. For concentrated solutions (0.5 mol L−1), two polymeric species produced observable resonance peaks, the [AlO4Al12(OH)24(H2O)2]7+ polynuclear (i.e., “Al13”) species with a chemical shift (δ) 63‐ppm downfield of the hexaaquaaluminum species, and the dimer Al2(OH)2(H2O)4+8, which displayed a broad resonance ≅ 3‐ppm downfield from the hexaaqua‐Al cation. In solutions of much lower Al concentration (3.4 × 10−2 mol L−1), the Al13 polynuclear species was observed at ñ>0.25 and its concentration was found to increase linearly as a function of ñ. For ñ = 2.5, the concentration of the Al13 polymer decreased at the 1.2 cm3 min−1 base injection rate; however, this was not the case at the 0.6 cm3 min−1 neutralization rate where the concentration continued to increase linearly. The data suggest that the distribution of Al species in partially neutralized solutions are acutely sensitive to Al concentration and neutralization rate.
Determining the Saturated Hydraulic Conductivity of a Soil Containing Rock Fragments
Authors: Brakensiek D. L. , Rawls W. J. , Stephenson G. R.
Published: July 2010

Many rangeland soils contain various amounts of rock fragments (>2 mm and <75 mm), which influence soil hydraulic and water storage properties. Most published data on these properties are only for the fine earth fraction (<2 mm). Determining properties for soils containing rock fragments requires either in situ measurements or procedures that adjust fine earth fabric properties for the coarse fraction content. The hydraulic conductivity is a major determinant of the infiltration and water movement properties of soils. Additionally, the saturated conductivity is used as a scaling parameter in modeling partially saturated flow in porous media. In this Note, literature is reviewed on calculating the saturated hydraulic conductivity for soils containing rock fragments. The two most widely used methodologies are based on knowing either the volume fraction of the rock fragments or the void ratio of the field soil and the fine earth fabric. Both of these soil properties require somewhat laborious laboratory procedures. We show that a calculation of the saturated conductivity of the bulk soil can be accomplished by using only the rock fragment fraction on a weight basis. For many soils the rock fragment fraction on a weight basis is routinely determined and published. For example, the Soil Conservation Service pedon data files list the rock fraction on a weight basis. We test our calculation of the saturated hydraulic conductivity with published data on the saturated conductivity of a stony soil. We show that our simple formulation using the rock fraction on a weight basis duplicates the observed data. Furthermore, it is as accurate as the more complicated procedure requiring void ratio information.
Preferential Flow and Hydraulic Conductivity of Forest Soils
Authors: Moore I. D. , Burch G. J. , Wallbrink P. J.
Published: July 2010

Macroscopic analytical methods, based upon the capillary rise formula and the Hagen‐Poiseuille equation, were used to quantify the combined effects of soil‐pore size and preferential flow on the hydraulic conductivity of forest soils. A density function was derived that relates effective pore diameters of heterogeneous soil‐pore systems to measured hydraulic conductivity. Density functions derived for soils from sites with different topographic influences and disturbance effects characterized the effect of preferential flow on their hydraulic conductivity. It was shown that macroscopic methods can describe preferential flow without having to resort to microscopic examination of individual pores. If the required properties of the undisturbed parent soil (hydraulic conductivity and equivalent pore size) have been characterized, then these methods can predict the effect of disturbance on the hydraulic behavior of the soils.
Infiltration and Water Extraction from Trickle Irrigation Source: The Effective Hemisphere Model
Authors: Ben‐Asher J. , Charach Ch. , Zemel A.
Published: July 2010

Infiltration from a point trickle source in the presence of water extraction is investigated using an approximate hemispherical model. Analytic expressions for the position of the wetting front are derived. In the short‐time limit the wetting front follows a simple t1/3 dependence. The rate of advance of the wetting front depends on a single soil parameter, closely related to the saturated water content. At larger times the effects of water extraction modify the solution to an exponential approach to a limiting radius, which is determined by the balance between the competing discharge and extraction processes. The results are consistent with available experimental data and with predictions of various existing models.
Saturation, Aeration, and Color Patterns in a Toposequence of Soils in North‐central Indiana
Authors: Evans C. V. , Franzmeier D. P.
Published: July 2010

The purposes of this study were to determine how geomorphology and stratigraphy influence soil water and O2 regimes, how water and O2 regimes are reflected in soil color patterns, and how soil color patterns can be used to predict soil behavior and suitability for various uses. We measured water table depths, soil‐water O2 levels, and saturated hydraulic conductivity (Ksat), and described soil color patterns in soils formed in silty loess and loam glacial till in two forested toposequences. In both sequences, Aqualfs and Aquolls are on the swells and swales, respectively, of the till plain summit, and Udalfs occupy hillslope shoulder and backslope positions along drainageways cutting back into the till plain. Compact glacial till C horizons had very low Ksat values, which forced subsurface water to flow laterally, through more permeable B horizons, to lower landscape positions. In this manner, stratigraphy and shape of the land surface controlled water movement in the landscape. Udalfs had deeper water tables, shorter saturation periods, higher soil‐water O2 levels, and higher chroma colors than Aqualfs and Aquolls. Udalfs, however, were periodically saturated above a depth of 1 m. Soils with dominant chroma of 2 or less in B horizons had water‐oxygen regimes of saturation and reduction consistent with the aquic moisture regime. Soils with no chromas ≤2 but with some three or four chroma colors had water‐oxygen regimes of saturation and oxidation. Such chromas should be recognized as indicators of soils that are occasionally saturated but not reduced. These saturated‐oxidized soils are not properly recognized in soil interpretation records and published soil surveys. They can be farmed without artificial drainage but they have definite limitations for many nonagricultural uses such as on‐site waste disposal.
Estimating Generalized Soil‐water Characteristics from Texture
Authors: Saxton K. E. , Rawls W. J. , Romberger J. S. , Papendick R. I.
Published: July 2010

Soil‐water potential and hydraulic conductivity relationships with soil‐water content are needed for many plant and soil‐water studies. Measurement of these relationships is costly, difficult, and often impractical. For many purposes, general estimates based on more readily available information such as soil texture are sufficient. Recent studies have developed statistical correlations between soil texture and selected soil potentials using a large data base, and also between selected soil textures and hydraulic conductivity. The objective of this study was to extend these results by providing mathematical equations for continuous estimates over broad ranges of soil texture, water potentials, and hydraulic conductivities. Results from the recent statistical analyses were used to calculate water potentials for a wide range of soil textures, then these were fit by multivariate analyses to provide continuous potential estimates for all inclusive textures. Similarly, equations were developed for unsaturated hydraulic conductivities for all inclusive textures. While the developed equations only represent a statistical estimate and only the textural influence, they provide quite useful estimates for many usual soil‐water cases. The equations provide excellent computational efficiency for model applications and the textures can be used as calibration parameters where field or laboratory soil water characteristic data are available. Predicted values were successfully compared with several independent measurements of soil‐water potential.
The Temperature Dependence of Isothermal Moisture vs. Potential Characteristics of Soils
Authors: Nimmo J. R. , Miller E. E.
Published: July 2010

A method has been developed for rapid, transient measurement of hysteretic soil‐moisture characteristics as a function of temperature. While a varying soil‐water pressure was imposed on a thin sample by means of flexible membranes held in firm contact with the soil, water content was measured by gamma‐ray attenuation, and matric potential was measured with tensiometers. The applied pressure was cycled through a program designed to obtain hysteretic θ(ψ) main and scanning curves. Isothermal characteristics were measured for 181‐µm glass beads, Plainfield (Typic Udipsamments) sand, and an undisturbed core of Plano (Typic Argiudolls) silt loam at several temperatures in the 4° to 50°C range. At each temperature the measurements included main drying and wetting curves covering the θ range from 0.30 to 0.05 m3 water/m3 for glass beads, 0.30 to 0.17 for sand, and 0.45 to 0.37 for silt loam. A model has been developed to quantify the temperature dependence as a function of θ. Combined with an isothermal hysteresis model of Mualem, this model requires only three characteristic functions to represent all hysteretic θ(ψ) curves for a given medium at all temperatures. Model calculations for the sand and silt loam data indicate that except near saturation, the temperature effect is greater than can be accounted for by the temperature dependence of the surface tension of pure water. The results rule out several possible explanations but they support the hypothesis that the concentration and effectiveness of dissolved surfactants increases with temperature.
Heat and Moisture Transfer in a Partly Frozen Nonheaving Soil
Authors: Kung Samuel K. J. , Steenhuis Tammo S.
Published: July 2010

The purpose of this research was to develop a computer model to simulate water and heat movement in the soil under freezing conditions. The model was based on the theory of coupled heat and mass transport, which was derived from the theory of irreversible thermodynamics. A finite difference scheme was used to solve the coupled‐fluxes equations in space. The difference scheme used only first‐order derivatives to facilitate the simulation of steep gradients of hydraulic potential at the freezing front. The simulated results were compared against two sets of laboratory experiments in which soil columns were suddenly cooled below freezing at one end. Thermal and hydraulic soil properties used in the simulation model were either obtained from independent measurements on the soil or by well‐established estimating procedures. The simulated results agreed well with the observed values in the first experiment, and in the second experiments the simulated data followed the trend, but a too low ice content was predicted and the freezing front prediction lagged behind. Overall it seems that although the model in its present form is limited to nonheaving conditions, the theory of irreversible thermodynamics is a promising approach to simulate heat and moisture transfer in partly frozen soils.
Temporal Variability of Soil Hydraulic Properties with Wetting and Drying Subsequent to Tillage
Authors: Mapa R. B. , Green R. E. , Santo L.
Published: July 2010

Modeling of water movement in soils requires mathematical representation of hydraulic conductivity and water retention functions. Hydraulic properties of soils are expected to vary over time during a cropping cycle, especially soon after tillage. Field experiments were conducted on two soils, a Typic Torrox and a Vertic Haplustoll, to evaluate the effect of soil deformation from repeated wetting and drying on soil properties such as hydraulic conductivity, sorptivity, and the water content‐suction relationship. Hydraulic conductivity near saturation was the most sensitive measure of temporal changes of hydraulic properties, decreasing 100‐fold with wetting and drying after tillage. Sorptivity measured with negative head, a simple and rapid method, was also sensitive to temporal changes and was judged the most appropriate for variability studies requiring a large number of samples. The impact of temporal changes in hydraulic functions on soil‐water movement was demonstrated by a comparison of water content profiles predicted with a simulation model using input functions obtained before and after irrigation.
Kinetics of Calcite Precipitation in the Presence of Water‐soluble Organic Ligands
Authors: Inskeep William P. , Bloom Paul R.
Published: July 2010

The rate of precipitation of calcite is an important geochemical process which can influence the saturation state of natural waters with respect to pure calcite. The present study was established to determine the influence of water‐soluble soil organic ligands on the rate of calcite precipitation. A reproducible seeded growth method was used to measure the rate constant for calcite precipitation at pH = 8.4 and 25°C, in the presence of varying amounts of total soluble organic carbon (CTS) added as a water‐soil extract (WSE) or Seward fulvic acid (FA). The rate equation which described the rate of calcite precipitation in the present experiments was: R = kfs γ22 ([Ca2+][CO2‐3]‐Ksp γ‐22), where R = rate of calcite precipitation (mol L−1s−1), kf = precipitation rate constant (L2 mol−1m−2s−1), s = surface area of calcite seeds (m2L−1), γ2 = divalent ion activity coefficient, brackets represent concentrations (mol L−1), and Ksp is the solubility of pure calcite at 25°C. Rate constants decreased to zero in the presence of 0.15 mM and 0.028 mM CTS added as the WSE and FA, respectively. The organic C surface coverage on the calcite seeds corresponding to complete inhibition of calcite precipitation was 90 and 30 atoms C nm−2 for the WSE and FA, respectively. The efficacy of inhibition of calcite precipitation in the presence of soluble soil organic matter explains why many natural waters, including soil solutions of Calciaquolls, are oversaturated with respect to pure calcite. Soluble polymeric carbon constituents which adsorb onto potential calcite seeds, render these surfaces inactive as sites for crystal growth.
Competitive Coefficients for the Adsorption of Arsenate, Molybdate, and Phosphate Mixtures by Soils
Authors: Roy W. R. , Hassett J. J. , Griffin R. A.
Published: July 2010

The adsorption behavior of anionic mixtures (binary‐solute combinations of arsenate, molybdate, and phosphate) by three soils (Cecil clay [Typic Hapludults], EPA‐14 [Ultisol], and Catlin silt loam [Typic Argiudolls]) was investigated using the Sheindorf‐Rebhun‐Sheintuch (SRS) equation. The SRS equation is a multicomponent Freundlich‐type adsorption equation. Most of the isotherm data were found to conform to linear SRS expressions, making it possible to derive competitive coefficients on a concentration basis for each binary‐solute system. The adsorption of arsenate and molybdate by all three soils were significantly reduced by the presence of phosphate, which was attributed to competitive interactions. In each solute‐soil system, the adsorption of phosphate was not greatly suppressed by either arsenate or molybdate. The adsorption of arsenate by Cecil clay and EPA‐14 was reduced in the presence of molybdate, whereas arsenate did not compete strongly with molybdate adsorption. In contrast, the adsorption of arsenate by Catlin appeared to be independent of molybdate, while the presence of arsenate lowered molybdate adsorption. In general, the associated competitive coefficient for each solute‐soil system appeared to be consistent with qualitative observations, and was viewed as a single‐valued term indicative of the relative affinity of each soil for a given anion with respect to a competing anion from a binary‐solute mixture.
Soil Nitrogen Availability after Long‐term Continuous No‐tillage and Conventional Tillage Corn Production
Authors: Rice C. W. , Smith M. S. , Blevins R. L.
Published: July 2010

Several short‐term studies of no‐tillage (NT) vs. conventional tillage (CT) have suggested that N availability is lower in NT. Less is known about the long‐term effects of NT on soil processes and N availability. Recent observations of a NT vs. CT experiment, initiated in 1970 on a Maury silt loam (Typic Paleudalfs), are presented here. During the first 9 yr of this study corn (Zea mays L.) yields with no N fertilizer were consistently greater in CT than NT, but at high N rates yields were approximately equal. Since 1979, there have been no consistent differences between the tillage systems with regard to yield without N or in relative response to N. Inorganic soil N during 1981 and 1982 was usually equal but occasionally greater in NT compared to CT, in contrast to previous observations during the early years of this experiment. Soil N mineralization was estimated in 1982 by a laboratory soil core incubation technique and by observing dilution rates of labeled N added to field microplots. Both of these approaches suggested that N mineralization was at least as great in long‐term NT plots as in long‐term CT plots. We suggest that the lower availability of N frequently observed in NT soils, in some cases can be a transient effect. In this experiment availability of soil N in NT apparently approached that of CT after approximately 10 yr.
Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum
Authors: Sumner M. E. , Shahandeh H. , Bouton J. , Hammel J.
Published: July 2010

Highly weathered soils in the southeastern USA often have very acid, hard, infertile subsoils not readily penetrated by crop roots. An experiment on a Typic Hapludult involving deep liming, subsoil disturbance and mixing, and surface application of gypsum was conducted to investigate the possibilities of ameliorating such subsoils. Results with alfalfa (Medicago sativa L.) over 4 yr show that liming to 1 m can increase yields by 50% while merely mixing the subsoil without lime incorporation resulted in a substantial yield decline. Surface application of gypsum with sufficient time for it to penetrate the subsoil resulted in 25% yield increases. Deep liming resulted in the complete precipitation of soluble Al and increased the level of soluble Ca allowing roots to freely penetrate the subsoil. Gypsum resulted in a progressive reduction in soluble Al and an increase in soluble Ca creating a similar but lesser effect than liming. Water extraction patterns corroborated the fact that roots were penetrating chemically ameliorated subsoil. Saturation extract studies indicated that gypsum reduced the activity of Al3+ and increased that of Ca2+ substantially. These results suggest that by‐product gypsum from phosphate acid manufacture would be a feasible amendment for acid subsoils.
Silicon Fertilization of Rice on Everglades Histosols
Authors: Snyder G. H. , Jones D. B. , Gascho G. J.
Published: July 2010

Rice (Oryza sativa L.), one of the world's most widely grown grain crops, is seldom grown on Histosols, in part because of many problems related to plant nutrition. Studies were conducted on Terra Ceia muck (Typic Medisaprists) in the Everglades to determine the effect of calcium silicate slag on ‘Lebonnet’ rice production. Grain yields were increased in excess of 30% in each of 3 yr by preplant application of slag at 10 Mg ha−1 or more. Rice in plots receiving slag had greater height, greater number of panicles per square meter, heavier grains, and less disease. Although the slag contained a number of plant nutrients, Si appeared to be the factor most responsible for the observed results. A positive linear relationship was observed in all years between straw Si and grain yield. First crop straw averaged 1.3, 5.0, and 5.9 dag Si kg−1 in plots receiving 0, 10, and 20 Mg slag ha−1, respectively. A first crop straw Si concentration <3.0 dag Si kg−1 was associated with reduced rice yield. Perhaps Si application should be considered in other regions when difficulties are encountered with rice production on Histosols.
Organic Carbon in Montana Soils as Related to Clay Content and Climate
Authors: Sims Z. R. , Nielsen G. A.
Published: July 2010

Data describing 130 A horizons were extracted from the Montana Soil Pedon Database to determine whether there is a relationship between soil clay content and organic C. All sites sampled had either frigid or cryic temperature regimes. The pedons were grouped according to land use, soil classification, temperature regime, and horizon position. Correlations between organic C and clay content were not significant for any group. Apparently clay content has much less influence on organic C accumulation in cool soils of Montana than it does in warmer soils of the southern Great Plains. In Montana, organic C content is better predicted by elevation and mean annual precipitation. The r value for a multilinear regression equation using these variables was 0.88.
Differentiation of Closely Related Xerolls that Support Different Sagebrush Plant Communities in Nevada
Authors: Nettleton W. D. , Brasher B. R. , Spencer E. L. , Langan L. N. , Peterson F. F.
Published: July 2010

We studied 20 pedons and four composite A horizon samples in the Tuscarora Mountain Area in northern Nevada in an effort to differentiate between two morphologically similar Xerolls (Donna and Stampede series) that support strongly contrasting kinds of sagebrush (Artemisia sp.) plant communities. We found no differences between surface horizons by laboratory analyses, but there are significant differences between the soils in clay content of AB, BA, and Bt horizons and in most related properties such as linear extensibility, cation exchange capacity, and 1.5‐MPa water. Thickness of the A horizon has the highest utility as a mapping criterion for the Donna and Stampede soils. Water retention difference between 0.03 and 1.5 MPa and depth of rooting best explain the differences in kind and amount of vegetation found on the two soils.
Measuring Sediment Movement at Low Erosion Rates Using Cesium‐137
Authors: Lance J. C. , McIntyre S. C. , Naney J. W. , Rousseva S. S.
Published: July 2010

New and innovative methods for measuring soil loss and its impact on productivity are needed to accurately assess the value of soil lost by erosion. Cesium‐137 (137Cs), a radionuclide from nuclear weapons tests which is strongly adsorbed to clay, can be used to trace sediment movement. Measurements of 137Cs concentrations in uneroded soils across the southern United States indicated that the 137Cs input was proportional to the average annual precipitation. Distribution of 137Cs within the profile was related to soil properties rather than to rainfall. Cesium‐137 measurements on a small native grass watershed in Oklahoma showed considerable spatial variability in the 137Cs concentrations, but the variability was random and was not correlated with changes in slope. Cesium‐137 concentrations measured on a 10‐m grid in an adjacent small watershed that had been cultivated for 8 yr showed differences with slope positions even though only 17.8 Mg/ha sediment had been removed from the watershed during an 8 yr measurement period. Also, 137Cs concentrations in the cultivated watershed were significantly lower than in the uncultivated watershed. These data show that 137Cs measurements can be used at low erosion rates if enough samples are analyzed. Further research is needed to determine the number of samples needed for different watersheds and to refine the method.
Foliar and Soil Tests for the Prediction of Phosphorus Response in Loblolly Pine
Authors: Wells C. G. , Craig J. R. , Kane M. B. , Allen H. L.
Published: July 2010

Loblolly pine (Pinus taeda L.) fertilization studies in the southeast USA were used to relate tree growth response to soil tests and foliar analyses data. In the Lower Coastal Plain, a needle P concentration of 0.80 g kg−1 and less indicated a severe P deficiency, and 5‐yr height growth increased by 50 to 140% after fertilization of young stands with 50 kg P ha−1. Stands with foliar P from 0.80 to 1.0 g kg−1 generally responded 15 to 50% in height growth to fertilization. Height and volume response to P fertilization in the Upper Coastal Plain and Piedmont were not correlated to P concentration of needles. Soil drainage class of the Lower Coastal Plain was useful in separation of soils responsive and unresponsive to P. Loblolly pine growth on 12 of 13 very poorly and poorly drained soils was stimulated 15% or more by P fertilization, whereas this level of response was found on only two of 11 better drained soils. Soils influenced by phosphatic deposits and previous P application should be excluded when using drainage alone as an indicator of P responsiveness. Total soil acidity separated P responsive and unresponsive soils in the Lower Coastal Plain. Where total soil acidity was 5 cmol (+) L−1 and less, height response to P fertilization varied from 15 to 138%. Extractable P as measured was not useful. A maximum volume response of 30% was obtained from P fertilization in the Upper Coastal Plain. When Mehlich 1 extractable P of the 0‐ to 20‐cm depth was <3 mg L−1 the 5‐yr volume response generally was from 14 to 30%. Improved separation of P‐responsive stands appeared possible by using soil acid saturation and pH. As acid saturation increases and pH decreases, the response to P fertilization tends to increase. Phosphorus response in the Piedmont ranged from a negative 19 to positive 21% and no relationship was found for prediction of response within the range of 2 to 6 mg L−1 of Mehlich 1 extractable P.
Soil Response to Trampling Under Intensive Rotation Grazing
Authors: Warren S. D. , Nevill M. B. , Blackburn W. H. , Garza N. E.
Published: July 2010

The impact of short‐term, high intensity livestock trampling on selected properties of a silty clay soil was determined at the Texas Agriculture Experiment Station located near Sonora, TX. Intensive livestock trampling typical of multi‐pasture rotational grazing systems had a negative impact on soil physical properties. The deleterious effects tended to increase as stocking rate increased. Trampling on dry soil caused disruption of naturally occurring aggregates and compaction of the surface soil layer. Trampling on moist soil deformed existing aggregates and led to the creation of a flat, comparatively impermeable surface layer composed of dense, unstable clods.