bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium Trends in Red Pine Plantations at Pack Forest, New York
Authors: Nowak C. A. , Downard R. B. , White E. H.
Published: July 2010

Trees are believed to cause improvement of nutrient availability in impoverished soils; however, evidence for this ameliorative capacity has generally been only circumstantial. Long‐term monitoring of chemical changes in forest soils on nutrient‐poor, agriculturally degraded sites may provide evidence of amelioration by trees. At the Pack Forest in the southeastern Adirondack Mountains of New York, soil and foliar K were periodically measured from 1949 to 1987 in red pine (Pinus resinosa Ait.) plantations established in the late 1920s to early 1930s. These plantations were established two decades after the area had been abandoned following a century of exploitive agriculture, when the inherently nutrient‐poor site was further impoverished for K by crop removal. For unfertilized plantations, both Ap horizon exchangeable K and K in current‐year foliage increased from the 1950s to the 1980s; the rate of soil K increase was 250 g ha−1 yr−1. For K‐fertilized stands, Ap horizon and foliar K were constant throughout the measurement period. High potential for the parent material to supply K, coupled with conservative biogeochemical cycling, can account for the increase and maintenance of K in this agriculturally degraded system.
Seasonal Variation in Solution Composition and Mineral Stability of Two Kentucky Alfisols
Authors: Karathanasis A. D.
Published: July 2010

Seasonal variations in the soil solution composition of two Maury soils (fine, mixed, mesic Typic Paleudalf) of the inner bluegrass region in Kentucky were investigated by monitoring solution chemistry changes of Ap, Bt, and BC horizons during the spring, fall, and winter of 1988. During the summer, the soils were too dry for soil solution extraction. Temporal soil moisture variations accounted for only a small portion of the variability in solute activities. The resultes demonstrated that, for most solutes, there were significant seasonal differences as well as differences between horizons and between soils. Many solute activities spanned a temporal range of ≈ ±5 times the mean, with Al showing one of the highest (≈10 times) and H4SiO4 one of the lowest (≈3 times) variations. The highest solute activities were attained during early fall and the lowest during the spring or winter seasons. The contrasting behavior of pH and certain solutes (Al, Na, Mn, H2PO4) within and between soils was attributed to stratification effects of the weathered limestone beds. Seasonal fluctuations of Al, Si, Mg, K, and H in solution apparently have moderate effects on illite → vermiculite/smectite → kaolinite weathering relationships, with kaolinite formation being favored during Si‐depleted spring periods and vermiculite/smectite during Si‐enriched fall (and probably summer) months. Temperature decreases during the winter appeared to enhance the stability of lower order kaolinite, gibbsite, and quartz mineral phases. Even though the consistency of the observed relationships is subject to the uncertainty of the thermodynamic data used and the variability from year to year, the results of this study point out that temporal variations in solution chemistry have indeed a significant impact on chemical weathering and nutrient‐availability patterns.
Measurement of Cadmium Activities in Slightly Acidic to Alkaline Soils
Authors: El‐Falaky A. A. , Aboulroos S. A. , Lindsay W. L.
Published: July 2010

The solid phases that control Cd2+ solubility in soils are poorly understood. This study was made to measure Cd2+ activity in nine slightly acidic to alkaline soils using competitive chelation, which avoids errors that may be caused by unknown Cd‐organic complexes that may be present. The Cd2+ activities measured in these soils varied widely, ranging from 10−6.61 to 10−9.31 M, and were inversely related to soil pH with a correlation coefficient (r2) of 0.95. The activities of Cd2+ in the soils could be predicted from the equation (Cd2+) = 106.5(H+)2. A solubility diagram was constructed for various Cd minerals using the thermodynamic data selected from the literature. The equilibrium constant (Ko) for the reaction of CdFe2O4(c) was derived assuming that the entropy (So) value of CdFe2O4(c) is similar to that of ZnFe2O4(c). The diagram suggests that CdFe2O4(c), in equilibrium with soil Fe, is a likely solid phase controlling Cd2+ activities in these soils.
Diffusion and Automated Nitrogen‐15 Analysis of Low‐Mass Ammonium Samples
Authors: Kelley K. R. , Ditsch D. C. , Alley M. M.
Published: July 2010

Conventional steam‐distillation techniques for concentrating inorganic N in soil extracts prior to 15N analysis are time‐consuming and labor‐intensive procedures. Diffusion procedures have been proposed as alternatives to steam distillation, but incomplete recovery and isotope dilution have been reported. We evaluated a procedure for diffusing low masses of 15NH4‐N from 2 M KCl solution to determine the effects of NH4 and 15N concentrations on recovery and isotope‐ratio analysis of diffused N. A series of solutions were prepared containing from 0.5 to 2.5 mg N L−1 at 1.1461 atom % 15N. Forty‐milliliter aliquots were placed in plastic containers, equipped with acidified glass‐fiber disks, and allowed to diffuse for either 6 d at room temperature or 5 d at 55 °C. Nitrogen recovery in glassfiber disks averaged 100.5% of the added N. Quantitative recovery of added N was also obtained in a second study in which 30‐mL aliquots of standard solutions containing from 25 to 100 µg N at 15N concentrations varying from 0.1030 to 1.1461 atom % 15N were diffused for 10 d at 55 °C. Significant dilution of 15N concentration for low‐mass N samples occurred. Differences in 15N concentrations between diffused and nondiffused samples were attributed to background N at a 15N concentration of natural abundance. Close agreement was obtained between diffused and nondiffused samples when an isotope‐dilution equation was used to calculate the atom % 15N concentration of the sample N. These studies indicate that the diffusion method is suitable for preparing low‐mass N samples for 15N analysis if appropriate blanks are determined and used to correct for background N.
Soil Phosphorus Extracted By Iron‐Aluminum‐Oxide‐Impregnated Filter Paper
Authors: Sharpley Andrew N.
Published: July 2010

The use of Fe‐Al‐oxide‐impregnated paper strips may allow estimation of plant‐available P contents of soils with widely differing properties. Little information is available on the forms of P extracted by paper strips (SP). Relationships between SP and Olsen, Bray I, Mehlich III, and P fractions were investigated for 203 surface soils representing all soil orders. Soils were divided into calcareous, slightly weathered, and highly weathered groups, based on taxonomy and weathering. Amounts of P extracted by paper strips were closely correlated (r2 of 0.89 to 0.93, P > 0.001) with soil‐test P (Olsen, Bray I, and Mehlich III), for soils on which use of the test is recommended. It is suggested that the paper strips removed primarily physically bound extractable P from all soils (approximate 1:1 relationship), with little extraction of amorphous Al and Fe or Ca compounds indicated. A potential general applicability of Fe‐Al‐oxide‐impregnated paper strips to estimate plant‐available soil P is suggested.
Micromorphology of the Soil‐Saprolite Transition Zone in Hapludults of Virginia
Authors: Stolt M. H. , Baker J. C. , Simpson T. W.
Published: July 2010

Most residual soils occurring in the southeastern USA have formed in saprolite. Between the saprolite and the argillic horizon lies a zone that divides material undergoing pedogenesis from that undergoing geochemical processes. We examined the physical, chemical, mineralogical, and micromorphological properties and characteristics of representative soils and saprolite formed from schistose or gneissic rocks of Virginia in order to describe and define the soil‐saprolite transition zone. Argillic horizons showed considerable oriented clay (3–16%), strong to moderate subangular blocky microstructure, porphyric coarse/fine related distribution patterns (c/f RDP), low (<0.5) coarse/fine ratios separated at 20 µm (c/f20µ ratios), and many planar voids. Oriented clay was absent from C horizons and microstructure was termed rock controlled to describe the apedal nature of these horizons. The c/f RDP was chitonic or gefuric, with the c/f20µ ratio at least double that of the argillic horizon. Microstructure of transition horizons was moderate subangular blocky to weak subangular blocky/rock controlled. The c/f20µ ratios and c/f RDP were intermediate between the argillic horizons and the saprolite. Transition horizons were designated as BCt, BC, or CB depending on percent oriented clay, rates of change with depth of clay, dithionite‐citrate‐bicarbonate (DB) extractable Fe, and sand contents. Weathering of mica grains showed slight to almost total pellicular and parallel linear alteration to hydroxy‐interlayered vermiculite (HIV), kaolinite, and an interstratified component of these minerals. Alteration of feldspar grains was generally <25% and occurred in the form of pellicular, or parallel, or cross‐linear patterns to kaolinite or gibbsite.
Repeated Fertilization Effects on Nitrogen Fluxes Measured by Sequential Coring
Authors: Whynot Tim W. , Weetman Gordon F.
Published: July 2010

Improving site quality is an important goal of optimum‐nutrition trials where fertilizer is applied repeatedly to a site. Site quality is often measured by the rate of N mineralization, but commonly used agronomic methods for assessing N availability are often not suitable for forestry use; therefore, the merits of other methods need to be examined. To determine if four repeated N fertilizations at four rates in a young lodgepole pine (Pinus contorta [Dougl.] var. latifolia) stand had changed soil N‐mineralization rates, and to compare field and laboratory techniques for measuring N mineralization, the results of in situ sequential coring and anaerobic incubation were compared. Estimates of gross potential mineralizable N (laboratory‐incubated mineral N concentration) were consistent with field estimates, while net potential mineralization N (gross mineralizable N minus initial N concentration) estimates were not. While the data suggested increases in N fluxes, repeated N and P+K fertilization did not produce statistically significant increases (P > 0.05) in either N mineralization or uptake. Because sequential coring results in minimal soil disturbance and is sensitive to environmental processes, it is useful for evaluating other techniques for measuring N mineralization in forests, but requires intensive spatial and temporal sampling, which will limit its use. Because of variable flux rates following fertilization, mineralization should be measured two or more years following fertilization to determine if a significant change in site quality has occurred.
Iron Oxides in Selected Brazilian Oxisols: I. Mineralogy
Authors: Fontes M. P. F. , Weed S. B.
Published: July 2010

Twelve Oxisols from the Triangulo Mineiro region, Minas Gerais state, Brazil, derived from four different parent materials were studied to provide insight into their Fe‐oxide mineralogy. The clay fraction (<2 µm) of all soils consisted of kaolinite and Fe oxides (hematite and/or goethite); gibbsite and anatase were found in most of the soils; maghemite was detected in several of them. Citratedithionite (CD) treatment of the soil clays showed hematite preferentially dissolved compared with goethite, and a higher dissolution rate for poorly crystalline than for well‐crystalline goethite. The calculated values for Al substitution in the Fe oxides, based on the CD extracts of the total clay corrected for Al soluble in acid ammonium oxalate, and of clay treated for gibbsite removal gave fair to good agreement with Al substitution determined by differential x‐ray diffraction (DXRD) for those samples in which the Fe‐oxide fraction was dominated by either goethite or hematite. Aluminum‐substituted maghemite, detected by DXRD, was present only in soils from mafic rocks, suggesting its formation through oxidation of the magnetite present in the parent material. Aluminum substitution, determined by DXRD, varied from 17 to 36 mol % for goethites, 6 to 15 mol % for hematites, and 16 to 26 mol % for maghemites. The mean crystallite dimension (MCDkkl) of some hematite samples determined from DXRD showed preferential crystal development in the X‐Y direction, suggesting a platy nature.
Synthetic Allophanes Formed in Calcareous Environments: Nature, Conditions of Formation, and Transformations
Authors: Farmer V. C. , McHardy W. J. , Palmieri F. , Violante A. , Violante P.
Published: July 2010

Synthetic allophanes were prepared by adding excess CaCO3 to solutions containing Al(NO3)3 and Si(OH)4 (concentrations ≤1.5 mM) with molar Si/Al starting ratios ranging from 1:8 to 4:1. The systems were incubated at 20 and 80 °C until the concentration of Si(OH)4 in solution approached stability after 6 to 10 wk, when the allophanes were isolated and characterized by infrared (IR) spectroscopy and electron microscopy. At 20 °C, proto‐imogolite allophane, rather than Al(OH)3 species, formed when Si in solution exceeded about 50 µM, but hydrous feldspathoids, containing tetrahedral Al, were progressively formed when Si in solution exceeded about 150 µM. At 80 °C, partial or nearly complete transformation of these products to proto‐halloysite occurred for Si in solution above 50 µM. The presence of 1 mM Mg and K in the starting solutions did not affect the allophanes formed at 20 °C, but modified those formed at 80 °C. For starting Si/Al ratios of 1:2 and 1:1, the formation of proto‐halloysite was partially inhibited, but for starting ratios of 2:1 and 4:1, evidence for the initiation of 2:1 trioctahedral layer silicate saponite was obtained. It is postulated that an alkaline environment favors the transformation of allophanes to layer silicate clays, and that this may account for the scarcity of reports of allophanes in calcareous horizons. A marked decrease in Si in solution when acid soils are limed is explained.
Balloon and Core Sampling for Determining Bulk Density of Alluvial Desert Soil
Authors: Andraski B. J.
Published: July 2010

Samples were collected from major strata in the upper 5 m of an alluvial soil profile in the Amargosa Desert of southern Nevada to compare rubber‐balloon and drive‐core bulk‐density measurement methods. For strate where the fine soil was <82% sand and <15% clay, differences between total and fine‐soil bulk‐density values determined by the two methods were typically <10 and 15%, respectively, even where rock‐fragment content was as great as 48% by volume. Outside this range of fine‐soil texture, where soil consistency was either very loose or very hard, the core method appeared to sample inaccurately, resulting in bulk‐density values >0.30 Mg m−3 less than those determined by the balloon method. Under the severe sampling conditions encountered, large decreases in the relative accuracy of the core method were not directly related to rock‐fragment content, but were related to extremes in the cohesiveness of the strata sampled.
Anthropic Epipedons in Oyster Shell Middens of Maryland
Authors: Kaufman Ian R. , James Bruce R.
Published: July 2010

Citric acid extractable P is the principal criterion used in the taxonomic classification of soils to distinguish mollic and anthropic epipedons, but the method has not been standardized or evaluated for soils strongly influenced by low‐P, high‐CaCO3 shells in oyster middens. This method was used on oyster‐midden‐affected A horizon samples associated with Ultisols along the Chesapeake Bay in Maryland to clarify its utility for this type of human‐influenced soil. Five of six midden‐soil A horizons contained >250 mg of extractable P2O5/kg. The soil horizon meeting mollic criteria was clearly human influenced, with deposition of shells and other evidence of human settlement. The citric acid test appeared appropriate in most cases, but an anthropic subgrouping would aid in classifying these soils, especially for those soils with mollic epipedons that are visually identified as anthropogenic.
Physical and Morphological Characterization of Bypass Flow in a Well‐Structured Clay Soil
Authors: Booltink H. W. G. , Bouma J.
Published: July 2010

Bypass flow governs solute movement in well‐structured clay soils. Combined use of physical and morphological methods was made in this study to better characterize the process. Flow processes in five 200‐mm‐long undisturbed cores of 200‐mm diameter were monitored at 11‐min intervals by using 102 small transducer tensiometers, divided among five samples and installed at three depths. Flow patterns along macropores were stained with methylene blue. Twenty‐five tensiometers in or within a distance of a few millimeters of stained macropores reacted very quickly when 10 mm of simulated rain was applied at an intensity of 13 mm h−1, and showed a drying pattern after the end of the simulated rainfall. Forty‐three tensiometers inside peds reacted more slowly and showed continued wetting after the end of the simulated rainfall indicating internal catchment of water in the bottom of discontinuous macropores followed by redistribution of water. Internal catchment increased with depth in the samples, as indicated by both physical and morphological data. Using tensiometer measurements as a point count, it is estimated that 33% of the soil volume was in close contact with continuous macropores, while 42% was influenced by the effects of internal catchment. An average of 5.2 ± 0.96 mm of the applied 10 mm of water left the cores through bypass flow, while an estimated average of 3.3 ± 0.96 mm contributed to internal catchment. The observed patterns of water movement illustrate the inadequacy of the concept of mobile/immobile water.
Zinc Sorption by Manganese‐Oxide‐Coated Sand as a Function of pH
Authors: Stahl Randal S. , James Bruce R.
Published: July 2010

Manganese oxides in soils may be sites for sorption of heavy‐metal cations, but the roles of pH‐dependent charge and oxide mineralogy remain unclear as controls on exchangeability of the metals. A model soil‐oxide system tested the effect of pH on the amount and form of Zn retained in exchangeable or nonexchangeable fractions on birnessite‐hausmannite‐coated sand or pyrolusite‐coated sand. Two Zn treatments, 250 and 2500 µmol/kg sand, were used to determine the effect of Zn concentration on the form of Zn retained. Surface charge for the birnessite‐hausmannite‐coated sand and pyrolusite‐coated sand increased across the pH range from 4 to 7.6, but surface charge was found to be a poor predictor of the amount and form of Zn retained even though the oxides increased Zn sorption by the sand. The distribution between the exchangeable and nonexchangeable Zn fractions changed from predominantly exchangeable to predominantly nonexchangeable Zn due to the oxide coatings and higher pHs. The difference in the exchangeable and nonexchangeable Zn retention by the two sands was attributed to mineralogical constraints on the type of surface functional groups. The mechanisms proposed to account for the nonexchangeable retention of Zn on both oxide‐coated sand surfaces were hydrolysis of the Zn followed by chemisorption to the oxide surface.
Sodium‐Calcium Exchange on Brazilian Soils: Modeling the Variation of Selectivity Coefficients
Authors: Rieu M. , Touma J. , Gheyi H. R.
Published: July 2010

Because routine experimental determination of exchangeable cations is time consuming, models allowing for the prediction of the composition of the adsorbed phase based on that of the solution are of great interest. Thermodynamically based models allow the determination of exchange equilibrium constants from the variation of selectivity coefficients, as defined by Vanselow, Gapon, or Gaines‐Thomas, and usually modeled by a direct fit of experimental data. Empirical models, based on the relationship between the sodium adsorption ratio (SAR) and either the exchangeable sodium ratio (ESR) or the exchangeable fraction ratio (EFR) provide an estimate of adsorbed cation ratios. Both thermodynamically based and empirical models were tested on 74 Na‐Ca exchange equilibria measurements, carried out on calcic Cambisols representative of the Paraiba region of northeast Brazil. Because of their sensitivity to errors in measurement, questionable selectivity‐coefficient values were obtained by a direct fit of experimental data, so models involving these values appeared roughly approximate. Selectivity‐coefficient values calculated from empirical relations between SAR and either ESR or EFR were more accurate. Therefore, models of the variation of selectivity coefficients were derived from these relationships. Linear relations enabled consideration of the constancy of the selectivity coefficients across a range of SAR ≤60, as implicitly assumed by the well‐known relationship between SAR and ESR. Parabolic relations exhibited a restricted range of application, whereas power‐law relationships appeared very simple and accurate for producing both a direct estimate of the composition of the adsorbed phase and the calculation of the equilibrium exchange constant.
Determination of the Copper2+ Activity Required by Maize Using Chelator‐Buffered Nutrient Solutions
Authors: Bell Paul F. , Chaney Rufus L. , Angle Jay S.
Published: July 2010

Hydroponics is a useful method to study micronutrient deficiencies in plants. Problems in using this method to study Cu deficiencies are: (i) control of Cu supply to induce any degree of deficiency is difficult, (ii) purification of reagents is required to induce severe deficiency; and (iii) when chelators are added to induce Cu deficiency, the chelators may inactivate Fe, making Fe unavailable to plants. Mild to severe Cu deficiencies were induced in maize (Zea mays L.) without the purification of reagents using chelators HEDTA [N‐(2‐hydroxyethyl)ethylenediamine triacetate] with and without BPDS (4,7‐diphenyl‐1,10‐phenanthrolinedisulfonic acid) to bind and inactivate Cu. GEOCHEM‐PC was used to calculate the quantity of free and chelate‐bound Cu. A wide range in leaf and root Cu concentrations was observed from plants grown in HEDTA solutions with calculated solution Cu2+ activities of 10−15.4 to 10−12.4 M. The calculated Cu2+ activity associated with a 20% reduction in yield was 10−14.5 M (control plants yielded 15 g dry matter at 18 d). Solutions containing HEDTA with BPDS and the lowering of nutrient‐solution Ca concentrations were evaluated as means of inducing severe Cu deficiency. Maize grown in BPDS‐added solutions were severely stunted regardless of Ca treatment, and had significantly lower shoot Cu, Mn, and Fe concentrations than those found in other treatments. Results indicated Cu availability to maize was controlled by Cu2+ and not Cu+ activity. HEDTA, especially in combination with BPDS, can effectively induce Cu deficiency and supply adequate Fe to maize.
Liming Effects on the Stability and Erodibility of Some Brazilian Oxisols
Authors: Castro C. , Logan T. J.
Published: July 2010

The effects of liming on the aggregate stability and erodibility of three Oxisols in Parana State, southern Brazil, were studied. Two soils from Londrina, one in a 10‐yr coffee (Coffea sp.) plantation (LC), and the other in a secondary mixed hardwood forest (LM), were compared with a third Oxisol from Cascavel, also under secondary mixed hardwood forest (CA), to give a range of surface organic‐C contents in the order CA > LM > LC. Lime was applied to replicated field plots at each site to neutralize 0, 25, 50, 100, 200, and 400% of total exchangeable acidity. Acid was also added to the Londrina soils to reduce initial soil pH to that of the Cascavel soil. Changes in aggregate stability, soil splash, and water erosion were measured. Lime application decreased the weight percentage of 2.0 to 4.0‐mm‐diam. aggregates and mean weight diameter (MWD) of aggregates in Cascavel soil, but had no effect on the other two soils. Liming decreased the apparent clay content of all three soils, and increased water‐dispersible clay on the LC soil. There were no significant effects of liming on soil splash, in part because of the high experimental variability of measurement. Soil erosion, measured on the field plots with a portable rainfall simulator, was in the order LC > LM > CA, a trend that corresponded to the decreasing organic‐C contents of the soils. Liming significantly decreased erosion on the LC soil, and had no effect on the other two soils. The study suggests that, while there may be some short‐term structural degradation caused by liming, the long‐term effect is to reduce water erosion.
Soil Response to Acid Deposition, Wind River Mountains, Wyoming: II. Column Leaching Studies
Authors: Clayton James L. , Kennedy Debora A. , Nagel Terry
Published: July 2010

Both base exchange and SO4 adsorption were important proton consuming processes in a laboratory leaching study of western, high‐elevation Inceptisols. Two soils formed from granitic parent materials are present in the watershed: a highly organic Humic Cryaquept (HCA) located adjacent to streams and on lake margins, and an upland Dystric Cryochrept (DCO). Large, single‐horizon soil columns were leached sequentially with deionized H2O (six pore volumes [PV]), pH 4 H2SO4 (12–16 PVs), and pH 3 H2SO4 (11–16 PVs). These treatments were equivalent to 3 to 6 yr of runoff and 50 to 100 times annual S‐deposition rates. Proton exchange for base cations was very effective at buffering all horizons for the distilled H2O and pH 4 treatments. Following three to five PVs of pH 3 H2SO4, leachate pH dropped to 5 in the B horizon and 4.2 in the C horizon of the DCO. The Al(OH)3 dissolution then stabilized the pH in those two experiments. The A horizon of the DCO and both HCA horizons had sufficient cation‐exchange capacity (CEC) and base saturation to resist large pH depressions during the pH 3 treatment. Cation exchange was the dominant neutralization process, accounting for 56 to 96% of total proton consumption. Sulfate adsorption was important in DCO horizons (20–35% of protons consumed), but not in the organic HCA soil. Postleaching analysis of soils indicated that exchangeable Na and Mg decreased to about one‐half of original values, but Ca and K remained unchanged. Apparently, hydrolysis of abundant primary minerals can resupply these cations under the conditions of these experiments.
Phosphate Rocks Compacted with Superphosphates vs. Partially Acidulated Rocks for Bean and Rice
Authors: Menon R. G. , Chien S. H. , Gadalla Abd el Nabi
Published: July 2010

Phosphate rocks (PR), which have low reactivity and contain large amounts of Fe and Al oxides, may be both ineffective as direct‐application fertilizers and unsuitable for partial acidulation. Such PRs can be made more effective by mixing them with soluble phosphates and compressing the mixture into pellets. The agronomic effectiveness of such pelletized mixtures was compared with that of partially acidulated phosphate rocks (PAPR), in pot trials with upland rice (Oryza sativa L.) and kidney bean (Phaseolus vulgaris L.) as indicator crops. Capinota PR, (CPR) which is low in reactivity and contains 8.8% Fe2O3 + Al2O3, and moderately reactive Huila PR (HPR), with 2.3% Fe2O3 + Al2O3, were mixed with triple superphosphate (TSP) to provide 50% of the total P in water‐soluble form in the mixture. The mixtures were then compacted into pellets. A Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult, pH 4.5) was used in the study. With TSP as the standard (assuming 100% effectiveness), pelletizing it with CPR increased the CPR's relative effectiveness from 43% before treatment to 80% after for rice grain production and from 51% before treatment to 92% after for bean biomass yield. Likewise, P uptake by rice increased from 47 to 79% and uptake by beans from 51% to 92% of that of TSP for CPR compacted with TSP. The moderately reactive HPR, low in Fe2O3 + Al2O3, the Huila PAPR (HPAPR), and the compacted HPR pus TSP were 83 to 86% as effective as TSP in increasing grain yield of rice and 75 to 81% as effective in promoting P uptake. For bean, the relative effectiveness of HPR, HPAPR, and compacted HPR plus TSP was 88 to 95% for biomass yield and 80 to 88% for P uptake. This study confirms that, for some PRs that have low reactivity and high Fe2O3 + Al2O3 contents, compaction with soluble P fertilizers is agronomically more effective than partial acidulation.
Field Measurement of Solute Travel Times Using Time Domain Reflectometry
Authors: Kachanoski R. G. , Pringle E. , Ward A.
Published: July 2010

A limiting step in our understanding of solute transport through unsaturated field soils is the lack of experimental data. Field solute transport characteristics such as the travel‐time density functions, FL(T), for different soil depths are often very difficult and time‐consuming to measure. The objective of this study was to develop a method to measure FL(T) for a conserving tracer added as a pulse under conditions of constant surface water flux density. The method uses vertically installed time domain reflectometry (TDR) probes. At constant soil volumetric water content, ϑ, the TDR estimate of bulk electrical conductivity, ECE, is related to the average pore water concentration of an added solute tracer, which in turn is related to the total specific mass (g m‐2) of the tracer between the TDR probes. The change in EC*E with time is shown to be linearly related to the mass flux of the solute past the ends of the TDR transmission rods. Solute mass flux out of a laboratory column was very similar to that measured using the TDR method. Excellent agreement was also obtained between solute‐mass‐flux measurements in the field (0.2‐m depth), using ceramic solution samplers, and the new TDR method. The method measures mass flux of the solute at a particular depth and not solute concentration. Thus, no assumptions about local water flux density are necessary in estimating FL(T). The method also has the advantage that ϑ can be measured at the same location (soil volume) where the solute mass flux is measured. The method is limited to soils where addition of a solute pulse will cause a measurable reduction in the reflected signal. This depends on steady‐state soil water content, ECE at steady state, and the depth of measurement.
Solution Sulfate Chemistry in Three Sulfur‐Retentive Hydrandepts
Authors: Wolt J. D. , Hue N. V. , Fox R. L.
Published: July 2010

Highly S‐retentive Hydrandepts frequently contain large quantities (> 200 mmol kg‐1) of sorbed S while exhibiting low S intensities in soil solution. Solution‐solid phase S relations for three representative Hydrandepts from Hawaii were investigated in terms of the nature of sorption isotherms and the role of basic Al hydroxysulfate precipitation as a mechanism for S retention. Sorption data were fit to linear, Langmuir, and multisite Langmuir isotherms using a modeling routine that performed parameter estimates and model optimization using weighted nonlinear fitting. Best‐fit models indicated sorption data were adequately described by Langmuir isotherms. Total P‐extractable SO4‐S increased markedly at depths > 45 cm and tended to decline at depths > 120 cm. Extractable SO4‐S was strongly regressed on gravimetric moisture content, a relative indicator of reactive surface for these thixotropic soils. Soil solution SO4‐S concentrations were consistent with alunite or basaluminite solubility when gibbsite controlled solution Al3+.
Evaluation of Direct/Delayed Response Project Soil Sampling Classes: Northeastern United States
Authors: Adams M. B. , Turner R.S. , Schmoyer D. D.
Published: July 2010

The Direct/Delayed Response Project (DDRP) identified approximately 600 soils on 145 watersheds in the northeastern USA. Soils were assembled into 38 sampling classes, based on soil characteristics thought to influence surface water chemistry. Multivariate analysis techniques were used to evaluate the utility of the sampling classes. Hydrologic and chemical properties of soils were determined to be the most important for discriminating among the sampling classes. Although sampling class was a statistically significant effect for most soil chemistry variables, only a few sampling classes were particularly distinct (some Entisols, Histosols, and Inceptisols with high base saturation). For most variables, within‐sampling‐class variability was less than or equal to between‐class variability, although this was not true for all of the characteristics evaluated. No better classification approaches were identified in this analysis. The DDRP sampling classes provide a means for grouping soils for efficiency in regional soil sampling, characterization, and aggregation to mapped areas.
Proton Effects on Quaternary Cation Exchange and Flocculation of Silver Hill Illite
Authors: Thellier Catherine , Sposito Garrison , Holtzclaw Kenneth M.
Published: July 2010

The investigation of quaternary cation exchange and flocculation in dilute suspensions of illite with mixed Na‐K‐Ca‐Mg perchlorate solutions was extended to consider the effect of aqueous protons. The exchange reactions and flocculation of Silver Hill illite at inial pH (pHi) = 6 or 8, three total perchlorate concentrations (9, 5, or 2 molc m−3), and varying initial Na/Ca or Na/Mg ratios in the aqueous solution phase were studied. It was found that pHi had little or no effect on exchangeable cation selectivity or total adsorbed metal charge. The degree of flocculation, as described by the percentage light transmission through the illite suspensions, was found to be highly pHi dependent. The effect of pHi was greatest in the 5 molc m−3 perchlorate background, where, at an exchangeable bivalent charge fraction near 0.3, the suspension was almost completely flocculated at pHi = 6 but dispersed at pHi = 8. Overall, at a given exchangeable bivalent charge fraction, the illite suspensions became less flocculated, and showed greater sensitivity to exchangeable Ca vs. Mg, as pHi increased from 6 to 8. Changes in pHi thus produced colloidal effects just the inverse of changes in the total perchlorate concentration. Analysis of the pH dependence of the light‐transmission data suggested that the mechanism of illite flocculation was affected greatly by the adsorption‐desorption reactions of a small number of protons on the edge surfaces of suspended particles.
Soil Drying and Rewetting, or Freezing and Thawing, Affects Soil Solution Composition
Authors: Walworth J. L.
Published: July 2010

Analysis of soil solution is a useful tool for soil fertility characterization and environmental studies, yet little is known about the effects of soil storage and handling on the solution collected. A laboratory study was conducted to determine the effects of time of extraction and preextraction freezing and thawing, or drying, rewetting, and incubating on centrifugally collected soil solutions. The relationship between electrical conductivity (EC) and ionic strength (I) also was studied. Samples of Bt horizons of three Hapludults were centrifuged at 750 g and solutions were collected after 20, 60, 120, and 240 min. Solutions were collected from fresh soils and from soils that had been frozen and thawed, or air dried and rewetted to their original water content, and then incubated for various periods of time. Solutions were analyzed for EC, pH, NH4, Ca, K, Mg, Na, Cl, F, NO3, and SO4. Significant changes in soil solution composition were found as centrifugation time was varied, indicating the importance of this parameter in soil solution extractions. The relationship between EC and I was very close to those previously described; EC can provide a good estimate of I of soil solutions. Soil solution composition was substantially altered by preextraction drying‐rewetting or freezing‐thawing. Following incubation, the composition of soil solutions from rewetted soils did not approach that of fresh soils. Neither of the methods studied here provided a good means of storing soil samples prior to soil solution extraction.
Quantity‐Intensity Relationships of Soil Ammonia in Long‐Term Rotation Plots
Authors: Thompson T. L. , Blackmer A. M.
Published: July 2010

Reports of release of nonexchangeable NH+4 from soils under some conditions and reports that management practices can change the affinity of the exchange complex for NH+4 indicate a need to reevaluate the commonly accepted practice of determining exchangeable NH+4 to assess the availability of NH+4 to plants. To address this need, quantity‐intensity (Q/I) relationships were studied in soil samples from two Iowa soils, a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) and a Galva silty clay loam (fine‐silty, mixed, mesic Typic Hapludoll) in long‐term experiments having various crop‐rotation and N‐fertilizer treatments. The observed Q/I relationships gave no evidence for release of nonexchangeable NH+4. Potassium‐exchangeable NH+4 concentrations were well correlated with measurements of labile NH+4 (r = 0.91, P < 0.01) and equilibrium activity ratios for NH+4 (r = 0.89, P < 0.01). No significant relationship was found between relative affinity of the exchange complex for NH+4 and organic C within each soil. Soil management practices influenced NH+4 availability as evaluated by KCl‐exchangeable NH+4 and Q/I parameters, but did not change the relative affinity of the exchange complex for NH+4. Overall, indexes of NH+4 availability based on determinations of K‐exchangeable NH+4 were similar to those derived from studies of Q/I relationships.
Leaching of Inorganic Phosphorus from Litter of Southern Pine Plantations
Authors: Polglase P. J. , Jokela E. J. , Comerford N. B.
Published: July 2010

A study was conducted to quantify leachable nutrients in needles of the litter layer of intensively managed southern pine plantations. The study site used for sampling of litter was a 2 × 2 × 2 factorial (three replicates) of species (slash [Pinus elliottii Engelm. var elliottii] and loblolly [P. taeda L.] pines), weed control (with or without complete and sustained weed control) and fertilizer application (with or without annual applications of essential elements). Fresh, intact needles collected in September and December 1989 and in March 1990 were soaked in distilled water (4°C, pH 4.9) for 5 d and measured for pools of soluble inorganic and organic P and N. Of these nutrients, only inorganic P (Pi) was detected in leachates. About 5 and 15% of the total P content was leached from Oi horizon needles in nonfertilized and fertilized plots, respectively. Because fertilizer application also doubled the total P content of Oi horizon needles, direct leaching losses will be important only in plots amended by fertilizer. A 5‐d time‐course experiment demonstrated that Pi was continuously leached from Oi horizon needles of the combination treatment, whereas the small amounts of Pi available for leaching in the Oe1 and Oe2 horizon needles were extracted immediately. In fertilizer‐amended plots, at least, the Oi horizon provides the majority of potentially leachable Pi.
Infiltration Simulations among Five Hydraulic Property Models
Authors: Alessi Sam , Prunty Lyle , Schuh W.M.
Published: July 2010

Analytical functions are used within computer models to give continuous representation of discrete data obtained from measurement. Functionally different equations have been used for soil hydraulic properties without concern for their smoothing effect on the data or their relationship to the stability of the numerical algorithm. This study evaluates the effect of five different power‐function representations of the soil water‐retention function and corresponding poreinteraction hydraulic‐conductivity representations on numerical solutions of Richards' equation. The functions were curve‐fit to 46 data sets for Hecla loamy fine sand (sandy, mixed Aquic Haploboroll). Minimum, median, and maximum function parameters (Campbell's b coefficient and air entry) were used to identify data sets from which one‐dimensional finite‐difference infiltration simulations were conducted. The wetting‐front location varied 6.0 to 8.0 cm (T = 6 min) among models, whereas variation within a model due to soil‐series‐imposed parameter variability was slightly larger (5.5–8.5 cm). Infiltration amounts varied −27 to 12% from the average among models. The results quantify sources of error due to curve‐fitting soil waterretention data to analytical functions assuming pore‐interaction theory.
Coupled Diffusion of Exchangeable Cations in Soil
Authors: Rhue Dean
Published: July 2010

Although coupling of transport processes in soil has been studied for some time using the principles of irreversible thermodynamics, its importance with respect to coupled diffusion of cations in soil has not yet been fully determined. The purpose of this study was to evaluate the importance of coupled diffusion of cations in a sandy soil in which the pH‐dependent charge from organic matter represented a major proportion of the total cation‐exchange capacity. The degree of coupling was evaluated by determining what effect counterdiffusion of exchangeable K and Ca had on the distribution of exchangeable Na when the latter was initially at a uniform concentration throughout the system. Coupling was evidenced by a Na flux that was counter to, and ranged from 16 to 28% as large as, the K flux. The simultaneous diffusion of Ca, K, and Na was modeled by assuming that the coupling resulted from a diffusion potential arising from the counterdiffusion of K and Ca. Intrinsic diffusion coefficients required in the model were estimated from conductance data. Predicted and measured cation concentrations showed a highly significant linear correlation, with predicted concentrations averaging 96% of measured concentrations for all three cations.
Significance of Soil Chemical Heterogeneity for Spatial Behavior of Cadmium in Field Soils
Authors: Boekhold Alexandra E. , Van der Zee Sjoerd E.A.T.M.
Published: July 2010

To investigate the spatial behavior of Cd in an arable field and to analyze its dependency on pH and organic carbon content (OC), soil was sampled on a 0.5‐ha field and analyzed for HNO3‐extractable Cd and Zn contents (CdT and ZnT, respectively), soluble Cd and Zn contents (Cds and Zns, respectively), pH, and OC. All parameters were spatially variable and anisotropic. Within the sampled area the measurements became independent of each other for OC, for CdT and ZnT in the east‐west direction, and for Cds in the north‐south direction at distances of 5 to 20 m. For the other variables and directions, no range was observed. Similarity between anisotropy of HNO3‐extractable heavy metal contents and OC, as well as between soluble contents and pH, suggested a functional (spatial) relationship between these parameters. Because the field was anisotropic, the spatial structure of the parameters was different from the spatial structure obtained from transect analysis in the same field. Correlation between Cd and Zn contents was high, both in soluble and in HNO3‐extractable form. No correlation was observed between HNO3‐extractable and soluble heavy metal contents. Soluble Cd and Zn were highly correlated with pH. A significant correlation was found between CdT and ZnT and pH, and between HNO3‐extractable contents and OC. Using a scaled sorption model, variability of pH and OC was explicitly accounted for when calculating Cds from HNO3‐extractable Cd contents. Predicted Cd concentrations in the soil solution correlated well (r = 0.87) with measured Cd concentrations, whereas prediction when homogeneity of the sorption parameters is assumed yielded no significant correlation. Apparently, pH and organic‐matter content are the most important soil parameters that regulate Cd sorption in this soil.
Landscape‐Scale Variations in Denitrification
Authors: Pennock D. J. , van Kessel C. , Farrell R. E. , Sutherland R. A.
Published: July 2010

Denitrification from agricultural ecosystems is regarded as a major contributor to atmospheric N levels, but the actual rates of denitrification and the controls on these rates remain poorly understood. This study was conducted to examine landscape‐scale patterns of denitrification and the soil properties that control these patterns. A 110 by 110 m sampling grid was established in an irrigated field in an aridic Boroll (Brown Chernozemic) soil in southern Saskatchewan. The measured soil properties (denitrification rate, respiration rate, volumetric water content, bulk density, soluble organic and inorganic C, total and mineral N, in situ pH, and in situ redox potential) were correlated to the derived landform elements at the site to determine landscapescale patterns and relationships. The soil properties occurred in one of three spatial patterns: (i) a random pattern for mineral N; (ii) a diagonal pattern for pH, soluble organic and inorganic C, and total N; and (iii) a depression‐centered pattern for denitrification, bulk density, moisture, respiration, and redox potential. Denitrification activity displayed a distinct landscape‐scale pattern and statistically distinct rates of denitrification were associated with the different landform elements: rates were lowest in the shoulder elements, intermediate in the footslope and level‐convex elements, and highest in the level‐concave elements. Hot spots of denitrification activity, i.e., sampling sites with denitrification rates identified statistically as outliers, were all associated with the level elements and, predominantly, the level‐concave elements. For the data set as a whole, denitrification was most highly correlated with volumetric water content (rs = 0.448**) and soil redox potential (rs = −0.335**). In the level landform elements, volumetric water content was the soil variable most highly correlated with denitrification; in the shoulder and footslope elements, respiration and bulk density, respectively, were the soil variables most highly correlated with denitrification. These data indicate that (i) topography has a strong influence over in situ denitrification, (ii) different controls are at work in the various landform elements, and (iii) landscape analysis should be incorporated in the process of modeling total N losses through denitrification.
Water‐Use Efficiency of Grasses as Affected by Soil, Nitrogen, and Temperature
Authors: Stout W. L.
Published: July 2010

Forage grass production in the northeastern USA is limited by soil water availability, but little is known about water use by forage grasses in this region. The purpose of this study was to assess the effects of soils, temperature regime, and N fertilization on water‐use efficiency of a C3 and a C4 forage grass. The study was conducted from 1987 to 1989 on four sites in central Pennsylvania selected for soil water‐holding capacity and temperature regime. Plot areas of orchardgrass (Dactylis glomerata L. cv. Pennlate) were treated with a split application of 0, 84, and 168 kg N ha−1 of 15N‐depleted NH4NO3. Plot areas of switchgrass (Panicum virgatum L. cv. Cave‐n‐Rock) were treated with a single application of 0 and 84 kg ha−1 unlabeled NH4NO3. Soil water was measured with a neutron probe on each plot biweekly during the growing season and monthly during the rest of the year. At heading stage (approximately 31 May), the orchardgrass plots were harvested for yield at a 7.5‐cm stubble height and all herbage removed from the plot. These plots were refertilized and sampled again on 31 October. Switchgrass was harvested at a 15‐cm stubble height at heading stage (approximately 15 July). Water‐use efficiency was 126 kg ha−1 cm−1 H2O for spring‐growth orchardgrass and 44 kg ha−1 cm−1 H2O for summer‐fall‐growth orchardgrass and was affected by N fertilization and temperature regime. Water‐use efficiency was 250 kg ha−1 cm−1 H2O for summer‐growth switchgrass and was also affected by N fertilization and temperature regime, but the effect of temperature was not as pronounced as in the case of orchardgrass.