bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon and Nitrogen Mineralization Kinetics in Soil Previously Amended with Sewage Sludge
Authors: Boyle Michael , Paul E. A.
Published: July 2010

Microbial mineralization rates of organic carbon (C) and nitrogen (N) were determined on the same sludge‐amended and nonamended soil samples. The purpose of this integrated approach was to high‐light the long‐term dynamics of N release with C stabilization in sludge‐affected soil. Three application rates of digested municipal sludge, check, 45 Mg ha−1 and 180 Mg ha−1, were incorporated into field plots annually for 8 years, with no addition during the subsequent 3 years. Barley was grown on the site each spring of the 11 years. In an 87‐week laboratory incubation experiment conducted on soil samples collected 3 years after the last sludge addition, N and C mineralization rates (kn, kc) increased with sludge application rate. Soil nitrogen mineralization potentials (No) increased with sludge application, unlike carbon mineralization potentials (Co) which did not correlate with sludge application. The C/N ratio of the mineralized organic matter decreased with sludge application rate. Three years after field incorporation of sludge, decomposition of the organic fraction can be described as a set of two first‐order rate reactions. One fraction is characterized by a large stable element (high No, Co and low kn, kc); the second fraction consists of a smaller labile portion which is characterized by low No, Co and high kn, kc values. The microbial biomass decreased to less than half of its original amount after 20 weeks of incubation in all soil treatments.
Determination of Plant‐available Phosphorus by the Iron Hydroxide‐impregnated Filter Paper (Pi) Soil Test
Authors: Menon R. G. , Hammond L. L. , Sissingh H. A.
Published: July 2010

The use of iron hydroxide‐impregnated filter paper (Pi) strips as a collector for phosphorus (P) in soil suspension offers a new approach to soil testing for plant‐available P. To correlate the Pi test with crop response, four soils ranging in pH from 4.5 to 8.2 were incubated with three rates of P either as triple superphosphate (TSP) or central Florida phosphate rock (CFPR), and P was measured in these soils by the Pi, Bray 1, Bray 2, double acid, Olsen, water, and resin extraction methods. Two successive crops of maize (Zea mays L.) were grown on these soils in greenhouse pots, and the dry matter yield and P uptake by maize were correlated with the soil test values. The Pi gave highly significant correlation with crop response in all four soils. Across all soils, P source, rates of application and crops, Pi gave the best correlation (0.870) with P uptake and dry matter yield. The next best correlation with dry matter yield was that of Olsen extractable P. The Pi test showed potential as a tool for prediction of P fertilizer requirements in soils.
Soil Acidification From Ammonium‐Nitrogen Fertilization in Moldboard Plow and Stubble‐Mulch Wheat‐Fallow Tillage
Authors: Rasmussen Paul E. , Rohde C. R.
Published: July 2010

Continued use of ammonium‐based (NH4‐N) fertilizer can lower soil pH to levels deleterious to crop growth. The depth and intensity of acidification is affected by rate and type of N fertilizer, and differs with tillage systems. Change in soil pH in relation to applied N was determined for one conventional (moldboard plow) and two stubble‐mulch (offset disk, subsurface sweep) tillage treatments in a winter wheat (Triticum aestivum L.)‐fallow rotation receiving cumulative N application of 493, 728, 986, 1221, 1714, and 2207 kg N ha−1 over 44 yr. Nitrogen was applied as (NH4)2SO4 from 1940 to 1961 and as NH4NO3 from 1962 to 1983. The soil was a Walla Walla silt loam (Typic Haploxeroll) containing 200 g clay and 11 g organic C kg−1 in the upper 30 cm. Soil pH (1:2 soil/0.01 M CaCl2) decreased linearly with increasing N application in both conventional and stubble‐mulch tillage. Acidifying effects were concentrated in the top 7 cm of stubble‐mulched soil but distributed to 22 cm or below with moldboard plowing. The rate of pH decline in the top 22 cm of soil was greater for moldboard plow than for disk or sweep tillage, 0.38 vs. 0.21 and 0.28 units, respectively, per Mg of applied N ha−1. Linear regression analysis predicted that 2.7, 4.8, and 3.5 Mg N ha−1 would acidify the 0‐ to 22‐cm soil depth to a pH deleterious to wheat growth with moldboard plow, offset disk, and sweep tillage, respectively. However, the more rapid decrease in pH in the 0‐ to 7‐cm zone with disk or sweep tillage may sooner predispose stubble‐mulch systems to negative effects of acid conditions within the seed zone. Nitrogen applied as NH4NO3 produced more acidity per unit of N than did (NH4)2SO4, but NH4NO3 was applied at much higher rates at a later date so unbiased comparison is difficult.
Modeling Soil and Plant Phosphorus Dynamics in Calcareous and Highly Weathered Soils
Authors: Sharpley A. N. , Singh U. , Uehara G. , Kimble J.
Published: July 2010

Labile and organic phosphorus (P) and sorbed P are required as the minimum data set to run a soil‐plant P cycling model recently developed for continental U.S. soils. Labile and organic P and P sorption index were related to physical and chemical properties of 23 calcareous (>50 g kg−1 CaCO3 content) and 32 highly weathered soils (>30% Al saturation), to allow estimation of these P forms from readily available soil data. The P sorption or fertilizer availability index was estimated as the fraction of fertilizer P remaining as labile (resin extractable) P following incubation of soil and fertilizer. Labile P was linearly related (R2 = 0.71–0.90) to soil test P measured by Olsen (calcarous soils) and by Bray, Colwell, Mehlich III, and Truog methods (highly weathered soils). Organic P was also linearly related to organic C (R2 = 0.87) and total N (R2 = 0.89) content of all soils. Fertilizer P availability index decreased with increased incubation time from 30 to 180 d, with the decrease related to CaCO3 and extractable Fe and Al contents of calcareous and highly weathered soils, respectively. At the present time, the model uses a 180‐d incubation value of fertilizer P availability index, which can be estimated from CaCO3 and clay contents of the calcareous and highly weathered soils, respectively. Using these relationships, accurate simulations were obtained of P transformations during 60‐yr cultivation of calcareous Houston Black clay and yield of maize (Zea mays L.) on two highly weathered Hawaiian soils receiving varying amounts of fertilizer P.
Compaction and Root Modifications of Soil Aeration
Authors: Asady G. H. , Smucker A. J. M.
Published: July 2010

Soil compaction and the incipient aeration and mechanical impedance stresses are known to reduce root growth and function. Little is known, however, regarding the influence of root accumulations adjacent to a compacted area upon the aeration status of the soil profile below the root mass. This study was designed to measure plant root and soil aeration interactions with soil compaction. A clay soil was compacted to bulk densities in 1.1, 1.4 and 1.7 Mg m−3 in soil columns planted to dry edible bean (Phaseolus vulgaris L.). Mechanical resistances of these soil compaction treatments were 0.43, 2.14, and 5.50 MPa, respectively. Oxygen diffusion rates (ODR) were below the critical level for the 1.7 Mg m−3 treatment at all plant growth stages measured. As root accumulations increased at the 0.10‐ to 0.25‐m depths, ODR dropped below critical values for all bulk densities. Lower O2 concentrations above the soil surface decreased ODR both earlier and at shallower depths. Root plugging of 5% or more of the aeration pores significantly reduced the diffusion of O2 into and CO2 out of the soil regions below and adjacent to areas with the greatest accumulation of roots.
A Method to Determine Soil‐Entrapped Denitrification Products in Submerged Soils
Authors: Katyal J. C. , Holt L. S. , Gadalla A. M.
Published: July 2010

To measure the contribution of soil‐entrapped gases to denitrification in submerged soils, a soil‐filled cylindrical bag (7 cm in height by 5‐cm diam) made from stiff polyester cloth net was positioned in the center of potted Crowley silt loam soil. Denitrification of 15N‐labeled KNO3 (14.85 atom % excess, applied at 100 kg N ha−1) was complete in 16 d after fertilization; 71% of the KNO3 was denitrified, mainly as N2 gas, with 41% trapped in the soil and 30% present in the headspace. Although no significant change in denitrification occurred during the subsequent 8 d, 15N recovery from soil‐entrapped gases declined (from 41.2 to 28.4%), whereas that from gases present in headspace increased (from 29.6 to 43.9%). Regardless of time of sampling, around 90% of the 15N was recovered. These results demonstrate that in situ placement of soil‐filled polyester cloth net bags before fertilization is a practical approach for sampling submerged soils to assess the contribution of soil‐entrapped gases to denitrification loss.
Use of Oxygen Flux Density to Estimate Critical Air‐filled Porosity of a Vertisol
Authors: Hodgson A. S. , MacLeod D. A.
Published: July 2010

Waterlogging studies of Vertisols require an accurate estimate of critical aeration levels. Gaseous O2 exchange was characterized in the top 0.3 m of a furrow‐irrigated Typic Pellustert by measuring quasi‐steady state diffusion through intact soil cores sampled in the field over a range of soil‐water content. Cores were taken at 0.1‐m depth increments from below the cropped ridges at major crack sites, a quarter of the distance between major cracks, and midway between major cracks in order to sample the nonrandom heterogeneity caused by vertical cracks running across the ridges. The relationship between oxygen flux density (F) and air‐filled porosity (ε) above the 0.2‐m depth at the three positions was described by a two‐stage linear model and fitted by optimization. Values of F and ε for soil below 0.2 m were restricted largely to the first (horizontal) stage of the model. For all other combinations of depths and positions, the model fitted the data with high precision (r2 > 0.84). The F of major crack sites was not increased relative to soil at other sites having the same ε. In wet soil, crack sites were sealed by the soil swelling and hence diffusion was inhibited. In dry soil, small cracks, fissures, and pores between the major cracks allowed similar rates of diffusion to that in the major cracks at the same ε. The minimum ε at which gaseous diffusion first occurred (ε0) was 0.145 ± 0.006 m3 m−3. This exceeds the previously accepted limit of ε = 0.1 m3 m−3, and may reflect a high proportion of occluded pores in this finetextured soil. The study evaluated an improved method of quantifying the aeration status of this soil and shifted the emphasis from oxygen content to oxygen flux as a more pertinent parameter of soil aeration in cropping situations. The technique is simple, rapid, and appropriate for routine sampling.
Effect of Aluminum Treatments on Permeability and Cation Status of a Smectitic Clay
Authors: Wada Koji , Beppu Yoshihisa
Published: July 2010

Aluminum sulfate or Al2(SO4)3 and CaCO3 mixtures were added to a smectitic clay in which Al3+, Al(OH)2+, Al(OH)+2, and Al(OH)3 formed when wetted with water. The treatment increased the permeability of the soil leached with distilled water. The permeability increased in the order of Al(OH)3 < Al(OH)+2, Al(OH)2+ < Al3+ and with the amount of Al, but its relative increase decreased with increasing addition of Al. The treatment with a relatively small amount of Al3+ (e.g., 5 cmol Al kg−1) was recommended to this soil having cation exchange capacity of 29 cmol kg−1 for its efficiency in increasing the permeability and permissible decrease of exchangeable Ca, Mg, and K. The acidity and exchangeable cation status as well as cation exchange capacity should, however, be considered in the choice of the treatment for a soil. There was a correlation between the permeability and the amount of Al retained by the soil. The contribution of exchangeable Al (monomeric Al3+) to the permeability was much higher than that of nonexchangeable Al (polymeric hydroxy‐Al cations) when evaluated in terms of molar quantities, indicating the importance of electric charge on an Al atom and the location of these Al cations on the bonding between clay particles.
Phosphate Fractions in Calcareous Vertisols and Inceptisols of Spain
Authors: Solis P. , Torrent J.
Published: July 2010

Calcareous Vertisols and associated Inceptisols are abundant around the River Guadalquivir Valley, southern Spain. They support a profitable rainfed agriculture; little is known, however, about their phosphate status and fertility. For this reason the phosphate fractions in the Ap horizons of 24 of such soils were studied. The calcium carbonate equivalent of the samples ranged between 46 and 628 g kg−1 and the citrate‐dithionite‐bicarbonate (CBD)‐extractable Fe (Fe4) between 1.1 and 11.6 g kg−1 soil. Total P ranged from 331 to 1051 mg P kg−1 soil; organic P represented usually <10% of total P. Of the inorganic P, the HCl‐P (Ca phosphates) fraction was the most abundant (39–77% of total P). The fraction extracted specifically by NaOH (nonoccluded Fe‐ and Al‐bound P) was present in very small amounts. The citrate‐bicarbonate (CB)‐extractable P (P sorbed on active surfaces) ranged from 13.1 to 66.1 mg P kg−1 soil and had values similar to the resin‐extractable (labile) P. The CDB‐P (P occluded in the Fe oxides) was correlated with Fed (r = 0.92) and ranged from 7.8 to 52.0 mg P kg−1 soil. The changes in labile P associated with cropping with wheat (Triticum aestivum L.) or incubation with added P could be accounted for by changes in the CB‐P fraction. The CDB‐P and HCl‐P fractions also changed, albeit less markedly; absolute changes were similar for both fractions but relative changes were much higher for the CDB‐P. This suggests that Fe oxides (mainly as goethite) are very active in releasing and fixing P, and that occluded P is relatively mobile. The values of the Olsen and Colwell tests were correlated with labile P. The fraction of labile P extracted by these tests was negatively correlated with Fe4. Consequently labile P can be predicted, in practice, from P tests and Fed values.
Ecology of Fast‐Growing and Slow‐Growing Mesquite‐Nodulating Rhizobia in Chihuahuan and Sonoron Desert Ecosystems
Authors: Jenkins Michael B. , Virginia Ross A. , Jarrell Wesley M.
Published: July 2010

Prosopis glandulosa (mesquite) is effectively nodulated by both fast‐growing (FG) and slow‐growing (SG) rhizobia. The distribution of indigenous, free‐living, FG and SG rhizobia, and their morphological and symbiotic characteristic associated with the rooting systems of mesquite were investigated. The three warm desert ecosystems studied were an arroyo, a sand dune, and a playa in the Chihuahuan Desert of New Mexico, and a sand dune and playa in the Sonoran Desert of southern California. The FG rhizobia dominated the free‐living rhizobial population from 0‐ to 8‐m depth, at the New Mexico playa. In contrast to the New Mexico playa, the surface 1 m of soil under mesquite at the California playa was dominated by SG rhizobia, otherwise FG rhizobia dominated to 9‐m depth. Slow‐growing rhizobia dominated the lowest depths of the mesquite rooting system in both playas. Slow‐growing rhizobia dominated the entire rooting zone of both sand dune ecosystems. Fast‐growing rhizobia dominated the upper 2 m and SG rhizobia dominated below 2 m in the mesquite rooting zone at the New Mexico arroyo. Regression analysis indicated that the distribution of FG and SG rhizobia was related to the concentration of total soil salts (electrical conductivity) (r2 = 0.20). Chi‐square analysis of the distribution of colony morphologies indicated distinct rhizobial populations in each ecosystem. The FG rhizobial population at the New Mexico playa was highly effective and had a high frequency of Hup+ phenotypes. The FG rhizobia isolated from the arroyo were, in contrast, less effective and had a low frequency of Hup+ phenotypes. The SG rhizobial population at the arroyo was highly effective and had a high frequency of Hup+ phenotypes. The SG rhizobial population at the New Mexico dune system was, in contrast, mainly ineffective and had a low frequency of Hup+ phenotypes. The relationship between the variable distribution of FG and SG rhizobia and environmental factors associated with the ecosystems is discussed.
Influence of Electrolyte Concentration on Quaternary Cation Exchange by Silver Hill Illite
Authors: Thellier Catherine , Sposito Garrison
Published: July 2010

A study of Na‐K‐Ca‐Mg exchange on specimen illite in a perchlorate background of varying ionic strength is reported. Sodium‐saturated Silver Hill illite was reacted at pH 7 with perchlorate solutions of differing Na/Ca or Na/Mg ratio and total electrolyte concentration (9.2, 5, 3.6, 2 and 1 molc m−3). All soluble and exchangeable cations were measured directly. No effect of the total electrolyte concentration on the total adsorbed charge was observed. The exchange isotherms and Vanselow selectivity coefficients based on the composition data showed that Silver Hill illite exhibited more or less equal affinity for Ca and Mg. Both bivalent cations were slightly preferred to Na in the three more concentrated electrolyte backgrounds, but at concentrations of 2 and 1 molc m−3, a slight preference for Na over Ca and Mg was observed. Exchangeable K, which represented 6 to 18% of the total adsorbed charge, decreased with the content of exchangeable Ca or Mg and, at a given bivalent charge fraction, was dependent on the total perchlorate concentration. The clay exhibited a very high preference for K over the three other cations which increased as the content of exchangeable K decreased.
Influence of Electrolyte Concentration and Exchangeable Cations on the Flocculation of Silver Hill Illite
Authors: Thellier Catherine , Sposito Garrison
Published: July 2010

The light transmission and optical density of suspensions of Silver Hill illite were investigated at pH 7 in mixed Na‐K‐Ca‐Mg perchlorate solutions of variable composition, with total charge concentrations varying between 1 and 10 molc m−3. The quantitative relationship between percentage light transmission (T), a measure of flocculation, and bivalent exchangeable cation charge fraction (Eblv) was found to be independent of whether the bivalent cation was Ca2+ or Mg2+. As the total perchlorate concentration was decreased, the graph of T vs. Eblv changed gradually from an upward‐inclined line with nonzero y‐intercept, to a sigmoid curve with zero y‐intercept, to a “step function” with a definite threshold value of the bivalent charge fraction above which flocculation occurred. For total perchlorate concentrations below 5 molc m−3, a sharp rise in suspension optical density, a measure of dispersion, was observed as the charge fraction of exchangeable Na was increased from 0.05 to 0.20. For perchlorate concentrations above 5 molc m−3, only a gradual increase in turbidity with exchangeable Na charge fraction was found. These results indicate that the relation between flocculation/dispersion and exchangeable cations for illite depends sensitively on the total electrolyte concentration, but not on the type of bivalent exchangeable cation.
Accelerated Rates of Selenium Volatilization From California Soils
Authors: Karlson U. , Frankenberger W. T.
Published: July 2010

Volatilization of alkylselenides from soils spiked with labeled Se was monitored in a continuous flow system by using activated carbon traps and counting the recovered 75Se. Surface soils from a known Se‐problem area in California were used throughout this study. Inoculation with fungal isolates from these soils, including Acremonium falciforme, Penicillium citrinum, and Ulocladium tuberculatum enhanced Se evolution in nonsterile and autoclaved soils. The fraction of added Se volatilized per unit time was dependent upon Se level, soil series, Se species, and C amendment. Without C amendment, volatilization rates were up to an order of magnitude higher with Se(IV) as the Se source, when compared to Se(VI). Carbon addition in the form of pectin accelerated Se evolution 2‐ to 130‐fold, which was more pronounced with Se(VI) and with the less active soils. Hence with C amendment, Se(VI) was volatilized almost as rapidly as Se(IV) by all soils. With three pectin amendments over a period of 118 d, total Se volatilization ranged from 11.3 to 51.4% of the added Se. A minimum Se threshold for alkylselenide production was not found, applying Se additions as low as 10 µg kg−1 soil.
Nitrogen Incorporation and Flow Through a Coniferous Forest Soil Profile
Authors: Schimel Joshua P. , Firestone Mary K.
Published: July 2010

One of the major controls on N cycling in forest ecosystems is the dynamics of N in the forest floor. Uptake and movement of NH+4 by the microbial component of a mixed conifer forest soil in central California were examined by injecting 15NH+4 into either the O2 or the A horizon. Distribution of the tracer was constrained by 15 × 30 cm cylinders placed in situ 1.5 yr prior to the experiment. The 15N was followed over 1‐ and 31‐d periods to measure both the short‐term uptake and the longer‐term fate of N. Recovery of 15N was determined in coarse roots, coarse woody detritus, fine detritus, fungal strands, and the bulk soil in each horizon; microbial biomass 15N was determined in the A horizon only. Nitrogen‐dynamics in the forest floor were characterized by a period of rapid microbial NH+4‐uptake after which transformations were slower. The rate of NH+4 immobilization was approximately 200 mg m−2 d−1, giving a turnover time for the NH+4 pool of less than 1 d. In the A horizon, there was no conversion of microbial 15N into soil organic 15N, but there was extensive lateral translocation of 15N from microbial biomass in the bulk soil into coarse dead roots and coarse detritus. There was little vertical translocation up the profile from either the O2 or the A horizons. This work indicates the rapidity of N turnover in the forest floor and suggests that N sequestering in woody residues may be an important fate of N in this forest soil.
Effect of Extractant and Selected Soil Properties on Predicting the Correct Phosphorus Fertilization of Soybean
Authors: Lins I. D. G. , Cox F. R.
Published: July 2010

The rate of phosphorus required to maximize soybean [Glycine max (L.) Merr.] yields is dependent on the concentration of extractable P along with other chemical and mineralogical characteristics of the soil. Clay content, surface area, P adsorption maximum, type of clay, and extractable phosphorus were evaluated in order to enhance the prediction of the rate of P required for optimum soybean growth on seven acid soils in the greenhouse. The soil test extractants were: Mehlich‐1, Mehlich‐3, Bray‐1, and an ion exchange resin method. The critical P level by each extraction method was correlated with clay content and, in one case, also with type of clay. Clay content and surface area were the most effective additional criteria found to improve the prediction of P fertilizer rate. The Mehlich‐3 extractant was superior to Bray‐1 and the resin method; Mehlich‐1 was least predictive. From a practical standpoint, clay content and extractable P offer the best means of predicting the rate of P required.
Gypsum Occurrence in Soils on the Margin of Semipermanent Prairie Pothole Wetlands
Authors: Steinwand A. L. , Richardson J. L.
Published: July 2010

A series of three wetlands in a local recharge‐throughflow‐discharge groundwater flow system were investigated to determine factors controlling concentration of gypsum at the wetland edge. The three wetlands differ in pond size, permanence, salinity, and in their relationship to the groundwater hydrology. We believe gypsum accumulation resulted from long term hydrologic, geomorphic, and climatic factors. Wetland salinity appeared to control the distribution and amount of gypsum in soils around individual wetlands and between wetlands. In all wetlands gypsum was concentrated at the edge; presumably as a result of dissolved salt transport to an area of low water potential created by evapotranspiration and freezing (edge effect). The water flow from the edge effect converged on the peninsulas and diverged in the bays. Consequently in less saline wetlands, the bay soils contained minimal amounts of gypsum; peninsula soils were very gypsiferous. Wetlands of high salinity were surrounded by a continuous band of evaporites including gypsum. Within individual wetlands, differences in the degree and number of ponding events and groundwater recharge‐discharge resulted in variations in gypsum distribution across soils of the low prairie, wet meadow, and shallow marsh vegetation zones.
Effect of Crystalline Iron Oxides on Development and Classification of Podzolic Soils in Western Labrador, Newfoundland
Authors: Wang C. , Ross G. J. , Protz R.
Published: July 2010

Seven pedons from western Labrador with various amounts of crystalline Fe oxides in the parent material were studied to determine how Fe oxides inherited from the parent material influence Podzolic soil development in a boreal environment. Amounts of total amorphous Fe oxides did not increase with increasing amounts of crystalline Fe oxides in the soils. Consequently, the ratio of amorphous to crystalline Fe oxide contents decreased sharply with increasing crystalline Fe oxide contents. This decrease is attributed to the resistance of crystalline Fe oxides to weathering and decomposition. Goethite was the only form of crystalline Fe oxide identified in the clays of soils with low crystalline Fe oxide contents. About equal amounts of goethite and hematite were identified in the clays of soils with medium and high crystalline Fe oxide contents. Smectite and vermiculite were the major clay minerals in the E horizon of soils with low and medium crystalline Fe oxide contents. However, only small amounts of these minerals were present in the E horizon of the soil with high crystalline Fe oxide contents in spite of relatively large amounts of potentially expandable silicates such as mica. One of the current criteria of the spodic horizon, (Fe + Al)p/(Fe + Al)d, was found to be too restrictive for soils developed on materials containing medium to high crystalline Fe oxide contents and should be deleted.
Assessing Physical Conditions of Some Pacific Northwest Volcanic Ash Soils After Forest Harvest
Authors: Geist J. Michael , Hazard John W. , Seidel Kenneth W.
Published: July 2010

A study of impacts of forest harvest on volcanic ash soils was conducted on three National Forests in the Blue Mountains of Eastern Oregon and Washington. Surface soil conditions were assessed in 11 forest harvest units; sampling employed a randomly positioned grid of randomly oriented line transects. In addition, air permeameter readings were tested in seven units for correlation with bulk density values obtained from core samples. Most of the detrimental soil conditions detected were attributable to compaction. Displacement, although readily apparent during harvest or slash piling with ground‐based equipment, was nearly undetected by the methods used on these units, which ranged from 14 to 23 yr old. Detrimental compaction averaged 28 or 19% of the harvest unit area when defined as either a 15 or 20% increase in bulk density, respectively. Area percentages included skid trails and landings but not the transportation system. Statistical tests showed that either 5 or 3 of the 11 units exceeded 20% area in detrimental condition, depending on degree of bulk density increase used to define detrimental compaction. Several other units were borderline in exceeding 20% of the area. Given slow recovery from compaction, there is potential for additional area to be adversely impacted by future entries. Air permeameter readings were poorly correlated with bulk density assessments, even though six of seven correlations were statistically significant. Less than 12% of the total variability was accounted for by regression analyses. The air permeameter does not appear to be accurate enough to measure compaction in volcanic ash soils.
Iron and Trace Metals in Some Tidal Marsh Soils of the Chesapeake Bay
Authors: Griffin T. M. , Rabenhorst M. C. , Fanning D. S.
Published: July 2010

Sediments from six tidally influenced Chesapeake Bay marshes were sequentially extracted in order to determine their relative Fe, Zn, Cu, Pb, Ni and Cd content, and to ascertain the relative magnitude of the mechanisms (e.g. adsorption, sulfide occlusion, organic complexation etc., ‥) involved in their retention. The extraction sequence used, and the corresponding geochemical phases extracted were: 0.01 M DTPA (exchangeable, organic complexes); 0.1 M HC1 (monosulfide occluded); dithionite citrate bicarbonate (DCB) (Feoxide occluded); H2O2 (disulfide occluded, organically bound complexes); HF‐HNO3‐HC104 (silicate mineral component). The sediments were dated using 210Pb geochronology in an effort to evaluate historical rates of metal deposition. Marshes in the vicinity of Baltimore, MD harbor were found to contain relatively higher metal concentrations than those marshes in other areas of the bay thus indicating that the degree of metal contamination is related to the source distance. Rates of deposition were related to historical periods of industrial discharge and to the use of leaded fuels. Iron was retained in the marsh sediments mainly in the oxide and sulfide (FeS2) phases and was apparently controlled by redox conditions. Copper, Cd and to a lesser extent Zn and Ni were apparently controlled by sulfide precipitation and pyrite coprecipitation thus rendering them noninfluential and unavailable to the marsh biota. Lead however, appears to be weakly complexed by organics and is a potential ecological threat since it is more readily available to plants and organisms and thus may accumulate in the food chain.
Microbial Utilization of Carbon‐14‐Glucose in Aerobic vs. Anaerobic Denitrifying Soils
Authors: Parsons Laura L. , Smith M. Scott
Published: July 2010

In order to better characterize the behavior of denitrifying bacteria in soil and their effect on cycling of C and N, the rate of consumption and the extent of microbial assimilation of glucose were compared in aerobic and anaerobic denitrifying soils. Three soils (Bruno, a Udifluvent; Maury silt loam, and Paleudalf; and Lanton, a Haplaquoll) were amended with 14C‐glucose and excess NO‐3, then incubated for 3 to 7 d in air or anaerobically. Transient accumulations of soluble, nonglucose intermediates occurred in both aerobic and anaerobic soils. Aerobic substrate consumption rates were greater than anaerobic denitrifying substrate consumption rates. Anaerobic substrate consumption rate varied among soils more than aerobic rates, but the ratio of aerobic to anaerobic rates for a sample was not related to the presumed propensity of that soil type to denitrify. When all labelled glucose had been depleted, 8 to 10% more of the label had been mineralized to CO2 in the anaerobic than in aerobic incubations, suggesting lower efficiency of assimilation under denitrifying conditions. However, the effect of aerobic vs. denitrifying respiration on assimilation efficiency was small relative to differences among soil samples and the effects of substrate‐to‐soil ratio.
Evidence for Clay Translocation in Coastal Plain Soils with Sandy/Loamy Boundaries
Authors: Cabrera‐Martinez F. , Harris W. G. , Carlisle V. W. , Collins M. E.
Published: July 2010

Soils of the Atlantic Coastal Plain commonly have thick sandy epipedons overlying loamy subsurface horizons. The origin of these sandy/loamy boundaries is often uncertain, due to frequent lack of visible indications of clay translocation. Five soils, which varied in depth to a sandy/loamy boundary, were analyzed for evidences of lithological discontinuity and clay translocation. Four of these soils occurred in close landscape association; the fifth soil, formed in an obviously stratified parent material, was included to test the sensitivity of the methods used. No evidence of a discontinuity was found for the four associated soils. Ratios of dominant sand subfractions to total sand were relatively uniform with depth, as was heavy mineral content of very fine sand. The stratified soil, however, exhibited considerable fluctuation in these parameters. Clay translocation was indicated by (i) the presence of oriented clay coatings on ped surfaces in the Btg horizon of one soil, as verified by micromorphological techniques; and (ii) significantly higher fine‐clay to total‐clay ratios below the sandy/loamy boundary than above. Results suggest that clay illuviation is a factor in the formation of sandy/loamy boundaries in some Coastal Plain soils even when the boundary is relatively deep (>50 cm).
Use of Geostatistics in Designing Sampling Strategies for Soil Survey
Authors: Di H. J. , Kemp R. A. , Trangmar B. B.
Published: July 2010

Semivariograms are used to quantitatively assess spatial variability of depth to mottles, depth to gravels, and thickness of loamy sand and/or coarser‐textured layers, which are definitive criteria for classification of soils derived from alluvium on the Canterbury Plains near Lincoln College, New Zealand. The three properties vary anisotropically with the anisotropy ratio being highest for depth to mottles (k = 5.84), lowest for thickness of loamy sand and/or coarser‐textured layers (k = 1.58), and intermediate for depth to gravels (k = 2.43). Directions of maximum variation for depth to mottles and depth to gravels are NE‐SW across an abandoned channel hollow. This pattern is reflected in the soil map of the study area and in the smaller‐scale soil map of the adjacent region. Such variation reflects the past regional drainage patterns of channels flowing predominantly in a NW‐SE direction. The appropriate field configuration of a sampling scheme for future survey of similar adjacent soils would be rectangular with a sample spacing in the direction of least variation k (anisotropy ratio) times that in the direction of maximum variation. Suitable sample numbers and sampling intervals to achieve desired levels of precision in the direction of maximum variation are determined. These are obtained from graphs showing relationships between kriging standard error, sample spacing and sample number. This geostatistical approach is more efficient than conventional statistical methods in designing sampling strategies: less samples are needed for kriging than for the conventional method to achieve the same level of precision.
Water Relationships of Claypan and Constructed Soil Profiles
Authors: Hauser Victor L. , Chichester F. W.
Published: July 2010

Claypan soils with poor physical properties are the only surface materials available to cover and reclaim much of the spoil left by strip mining for coal in east‐central Texas. We compared an undisturbed claypan soil profile of Axtell fsl fine montmorillonitic, thermic Udertic Paleustalfs) to four constructed soil profiles and evaluated them as cover soils for toxic minespoil. We compared profiles constructed from minespoil selected for low pyrite content alone (non‐topsoiled) against the same selected spoil covered by a mixture of Axtell soil material. The rainfall intake rate and physical properties of the materials controlled forage production by kleingrass (Panicum coloratum L.). All of the constructed soils stored less water in the soil profile than the undisturbed claypan soil, and forage yield was reduced on them during drought. Infiltration rate during the first 2 cm of rainfall influenced forage yield more than final intake rate. Mulch application increased water storage and forage yield up to 15% on selected minespoil, but not on the mixed claypan soil profiles. Either selected minespoil or a mixture of Axtell soil may be used to cover toxic random soil with a nontoxic layer, but the Axtell mix had the least acid‐forming potential. Selected minespoil material was equal in value to a mixture of the 1.8 m claypan soil profile as a surface material for constructed minesoils.
Effect of Acid Treatment on Dissolved Organic Carbon Retention by a Spodic Horizon
Authors: Vance George F. , David Mark B.
Published: July 2010

Processes involving the movement of organic substances in forest soils are not well understood. This study was conducted to examine the role of acidic inputs on dissolved organic carbon (DOC) mobility, processes affecting the retention of DOC by a B horizon, and SO2‐4 adsorption. Using O and B horizon samples from a Spodosol collected in a forested watershed in Maine, acid solutions leached through O, B, and O over B (O/B) soils in small vacuum extractor columns were analyzed for DOC, DOC fractions, and anions. For the O and O/B columns, DOC in the leachates decreased (7550 to 3350 and 2380 to 850 µmol C L−1, respectively) with an increase in acidic inputs; for the B horizon, the reverse was the case (435 to 1570 µmol C L−1). The DOC in leachates from the O horizon was dominated by hydrophobic and hydrophilic acids (68 and 20% of DOC with no acid addition), which were altered by acidic inputs (46 and 36% of DOC at p[H+] = 2). The hydrophobic acid percentage in leachates from O/B horizon columns decreased from 52 to 28%, whereas hydrophilic acids increased from 27 to 47% with H2O and p[H+] = 2 treatments, respectively. Ionic strength adjustment (I = 0.01) of treatment solutions reduced C solubilization in O and O/B horizon leachates, leading to lower DOC leaching. The SO2‐4 adsorption in O over variable B horizon columns decreased with greater B horizon mass due to pH dependent SO2‐4 adsorption processes. The B horizon adsorption of DOC from field collector leachates showed that hydrophobic acids were selectively adsorbed, as indicated by initial mass isotherm coefficients. The results indicated that acidity, salt effects, and B horizon mass are significant factors in controlling both the amount and composition of DOC in surface and groundwaters.
Nature and Charge Properties of X‐Ray Noncrystalline Aluminosilicates as Affected by Citric Acid
Authors: Lou G. , Huang P. M.
Published: July 2010

The surface charge properties of x‐ray noncrystalline aluminosilicates in relation to their structural distortion by citric acid during their formation were investigated. The precipitates formed from solutions containing monomeric orthosilicic acid and AlCl3 (Si/Al molar ratio 0.5 and OH/Al molar ratio 2.0) in the presence of citric acid (citrate/Al molar ratios of 0.02 and 0.025) exhibit an IR absorption maximum at 965 cm−1, a feature similar to that of “allophane‐like constituents” or “ill‐defined fraction of the allophane‐imogolite complex” in soil. The complexation of citrate ligand with hydroxy‐aluminosilicate ions or “proto‐imogolite”, the precursor of paracrystalline to x‐ray noncrystalline aluminosilicates, promoted the development of structural defects apparently through perturbation of the regular linkage of hydroxy‐aluminosilicate fragments. The perturbation effect of citrate ligands promoted the development of positive charge and resulted in a marked increase in the point of zero charge (PZC) due to the exposure of Al‐OH0.5+2 groups around the defect sites. The role of complexing organic ligands in influencing the surface properties of short‐range ordered aluminosilicates through structural distortion thus deserves attention.
Water Transport in Unsaturated Nonisothermal Salty Soil: II. Theoretical Development
Authors: Nassar I. N. , Horton Robert
Published: July 2010

A theory describing both vapor and liquid phases of moisture transfers in porous materials is developed. The two equations included extend previous work, which only considered moisture and temperature gradients, by also including solute concentration effects. The new equations include six diffusivities to be considered in describing vapor and liquid movement in soil. Three liquid diffusivities are for liquid‐phase flow associated with water content, temperature, and solute concentration, and three vapor diffusivities are for vaporphase flow. Steady‐state heat and mass transfer laboratory experiments were performed by using moist salinized and solute‐free closed soil columns. From observations of water content, temperature, and solute distributions, five of the diffusivities (vapor diffusivities due to temperature, water, and solute concentration and liquid diffusivities due to temperature and solute concentration) are determined. The isothermal liquid diffusivity as a function of soil water content is determined in a separate experiment. In general, the liquid diffusivities are larger than the vapor diffusivities for the experimental conditions considered. For the soil conditions investigated, the water fluxes due to the solute gradients are nearly equal to the water fluxes due to the temperature gradients within salinized soil columns, but the water fluxes resulting from gradients in soil water content are small in comparison. To test the validity of the theory, two different approaches are used. The first approach involves using water diffusivities of moist solute‐free soil along with the new theory to predict steady‐state water distributions within moist salinized soil for comparison with observations. The predicted values of soil water content are in good agreement with the observed values. The second approach is to predict steady‐state soil water distributions within the moist salinized soil column while neglecting the solute effects on soil water movement. The predictions using this approach are markedly different from the experimental observations.
A Spectroscopic and Chemical Investigation on the De‐ashing of a Humin
Authors: Preston C. M. , Schnitzer M. , Ripmeester J. A.
Published: July 2010

The application of 13C cross‐polarization magic‐angle spinning nuclear magnetic resonance (CPMAS NMR) to humins has been limited because low C and high Fe contents degrade spectral quality. This study investigated the effect of de‐ashing with aqueous HCl/HF (1.16 M HCl and 2.88 M HF) on chemical properties and 13C CPMAS NMR spectra of a humin. With progressive de‐ashing, the humin became partly soluble in 0.5 M NaOH, and its ash‐free composition approached that of the humic acid fraction. The CPMAS NMR spectra showed increasing improvement in resolution and signal‐to‐noise ratio. The spectrum of the most extensively de‐ashed sample (520 g C kg−1) was very similar to that of the humid acid extracted from the same soil. The de‐ashing treatment caused variable changes in the distribution of N determined after acid hydrolysis, but little change in the molar distribution of amino acids. Some monosaccharides were lost, and there was a change in the monosaccharide composition, with glucose predominating (on a molar basis) in the most extensively de‐ashed samples. It is unlikely that major structural changes were caused by the de‐ashing, which provides a useful approach to the NMR investigation of humins.
Soil Urease Activity in Winter Wheat Residue Management Systems
Authors: Barreto Hector J. , Westerman Robert L.
Published: July 2010

Surface residue accumulation under reduced and no‐till cropping systems has been shown to cause changes in the activities of several soil enzymes. The addition of crop residues containing urease increases the rate of urea hydrolysis which can increase the potential for ammonia volatilization. Our objective was to characterize the distribution of urease activity in the surface of two Oklahoma soils (Grant silt loam, fine, silty, mixed, thermic Udic Argiustoll and Norge clay loam, fine, silty, mixed, thermic Udic Paleustoll) which had been in conventional, reduced, and no‐till wheat (Triticum aestivum L.) residue management for four consecutive years. Soil cores 60‐mm deep were taken from residue management plots that had been previously fertilized with 168 kg urea‐N ha−1 yr−1 and separated into 10‐mm increments. Urease activity was determined in the soil increments and in mature undecomposed wheat straw. Urease activity was uniformly distributed in soil to a depth of 60 mm under conventional tillage. Significant increases in urease activity were measured in the surface 10 mm of both soils where accumulation of residue had occurred. Average urease activities in the surface 10 mm of soil under conventional, reduced, and no‐till residue management systems were, 12.1, 41.4, and 45.2 µg NH4‐N g−1 h−1 for Norge clay loam and 9.7, 12.4, and 35.0 µg NH4‐N g−1 h−1 for Grant silt loam, respectively. Activity of urease in mature undecomposed wheat straw grown at the site was 376 µg NH4‐N g−1 h−1 which was 28 × larger than the average activity found in soil. Wheat straw was shown to be a major source of the observed increase in enzymatic activity. Other sources for increased urease activity include increased microbial colonization during decomposition of residue and increased urea concentration in microsites due to fertilization, particularly in combination with residue.
Crop Root Distribution as Influenced by Grain Sorghum‐Soybean Rotation and Fertilization
Authors: Roder W. , Mason S. C. , Clegg M. D. , Kniep K. R.
Published: July 2010

Soil physical, chemical, and biological changes resulting from crop rotations are likely to affect root development. Yet, crop rotation effects on root distribution have received little attention. The objective of this experiment was to measure the effect of soybean, Glycine max (L.) Merr. and grain sorghum, Sorghum bicolor (L.) Moench, rotation and fertilization on root distribution. Root samples were collected from an experiment with a 6‐yr history of (i) continuous soybean, (ii) continuous grain sorghum, (iii) soybean‐grain sorghum rotation, and (iv) grain sorghum‐soybean rotation. The experiment was conducted on a Sharpsburg silty clay loam (fine, mont‐morillinitic, mesic, Typic Argiudoll) near Mead, NE. Fertilizer treatments consisted of (i) control (no fertilizer), (ii) N at 45 kg ha−1 on soybean plots and 90 kg ha−1 on grain sorghum plots, and (iii) manure applied at 15.8 Mg dry weight ha−1 yr−1. Roots were sampled to a depth of 120 cm in 1986 and 150 cm in 1987. Root densities were reduced at most depths when soybean had been grown the previous year. Total root lengths per unit land area were 14, 21, 25, and 33 km m−2 and total root dry weights were 111, 136, 132, and 190 g m−2 for continuous soybean, soybean after grain sorghum, grain sorghum after soybean, and continuous grain sorghum, respectively. Fertilizer effects on root development were not consistent between years. Total soybean root length was positively correlated to grain yield, whereas grain sorghum root length in the 0‐ to 30‐cm zone was negatively correlated to shoot dry matter, kernel numbers, and grain yield.