bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Study of Podzolization on Tephra and Bedrock
Authors: Singer Michael , Ugolini F. C. , Zachara J.
Published: July 2010

A study was initiated in the Washington Cascades to examine processes of soil genesis in situ through the analysis of soil solution chemistry. Suction plate lysimeters were used to continuously extract soil solution held below 0.1 atm from the O2, A2, IIB2hir, and IVB32 horizons of a forest soil. Movement of elements was in the order Si > Al > Fe > Mn. The O2 and A2 were the source of the Fe, Al, and Si which entered the IIB2hir. Most of the Mn originated in the A2. Virtually all of the Fe, 48.5% of the Al, 50% of the Mn, and 15% of the Si which left the A2 remained in the IIB2hir. According to the soil's morphology, it appears to be a Spodosol, and the lysimeter data indicates that podzolization is the major process of soil formation. The soil does not meet the criteria of a Spodosol in Soil Taxonomy. Two explanations for this are: (i) the soil has not become a Spodosol yet because the intensity of weathering is low or (ii) soil taxonomy criteria for the Spodosol order are not broad enough and need to be broadened to include soils of this type.
Sulfur Status of Some Central Oregon Pumice Soils
Authors: Will G. M. , Youngberg C. T.
Published: July 2010

In a fertilizer experiment established in a 45‐year‐old stand of ponderosa pine (Pinus ponderosa Laws) on a pumice soil, 112 kg S/ha added as gypsum resulted in a small increase in tree growth in the first 5‐year period. The combination of S with 224 kg N/ha gave a greater response. Over a 10‐year period, basal area growth was 50% greater than in untreated plots. The soil layers in the tree rooting zone at this and four other sites were collected for a pot trial bioassay of their S status. In all cases the growth of Monterey pine (Pinus radiata D. Don) seedlings was improved by the addition of S. At all sites the soil layer least deficient in S was the A1 horizon which varied from 5 to 15 cm in thickness. Although the results indicated that the field trial site is more S deficient than the others, they also show that many of the pumice soils in central Oregon are marginally deficient in S. Forest management operations, such as site preparation, which remove the surface soil, will seriously lower the S as well as the N and P levels of the soil and if productivity is to be maintained, the use of fertilizers will be essential.
Relationships of Soils to Mountain and Foothill Range Habitat Types and Production in Western Montana
Authors: Munn L. C. , Nielsen G. A. , Mueggler W. F.
Published: July 2010

Soils at 23 sites representing eight western Montana mountain and foothill range habitat types were characterized and classified in accordance with Soil Taxonomy. The soils ranged from Borollic Calciorthids at the dry end of a moisture and soil development gradient to Pachic Cryoborolls on the moist end. Corresponding vegetation was a Stipa comata‐Bouteloua gracilis community on the dry end and a Festuca idahoensis‐Agropyron caninum community on the moist end. Soil taxonomic units and vegetation habitat types were ordered along the moisture gradient. Multiple linear regression analysis was used to model above‐ground dry‐matter productivity of the sampled sites. Eighteen significant variables were identified including thickness of the mollic epipedon, total soil organic matter, total N content, elevation, depth to free carbonates, estimated annual precipitation, aspect, solum thickness, summer soil temperature at 50 cm, percent coarse fragments in the A horizon, and extractable K. The thickness of the mollic epipedon was the variable most highly correlated with productivity (r=0.89**) and the best regression model accounted for 90% of the variability in total productivity between sites (based on 2 years' productivity data). Soil morphological characteristics proved more useful in models of site productivity than estimated climatic data or site nutrient data.
A Study of a Deep Weathering Profile on Granite in Peninsular Malaysia: I. Physico‐Chemical and Micromorphological Properties
Authors: Eswaran H. , Bin Wong Chaw
Published: July 2010

To facilitate description and study, the deep profile is divided into several morphological zones, via., α, γm, γp and δ zones. Clay content progressively increases from the rock zone δ to the soil zone α. The silt/clay ratio increases from the δ to the upper part of the γp zone and then decreases again. These changes are explained in terms of the fragmentation or aggregation of various minerals during the clay separation procedure. Estimates of the mineralogical composition in the fine earth shows differences in the zones, and the charge characteristics are related to these.

Changes in the microfabric are monitored with thin‐sections. Micrographs are presented showing fabric characteristics and some examples of pseudomorphic alteration. A brief discussion on the genesis of the profile is given.
Rapid Estimate of Unsaturated Hydraulic Conductivity Function
Authors: Bresler E. , Russo D. , Miller R. D.
Published: July 2010

From results of Reichardt, Nielsen, and Biggar and of Russo and Bresler, it is inferred that a laboratory horizontal infiltration experiment with air‐dry soil yields an estimate of the saturated‐unsaturated hydraulic conductivity function given by K(h) = 0.27 m4 (he/h)2.6 or K(θ) = 0.27 m4 [(θ − θd)/(θw − θd)]7.2. Here m = dx/d (t1/2); x is distance to the wetting front and t is infiltration time; θd and θw are water contents of air‐dry and “saturated” soil; h is pore water pressure head, and he is the air entry value of h. These relationships can serve as a general approximation of K(θ) and K(h) in nonsodic stable soils. Field measurements of he and saturated K can also be used to derive K(θ) and K(h).
Hydrodynamic Dispersion During Absorption of Water by Soil
Authors: Smiles D. E. , Philip J. R. , Knight J. H. , Elrick D. E.
Published: July 2010

The paper reports an experimental study of hydrodynamic dispersion of low concentration solutions during absorption into horizontal columns of soil with initially uniform moisture and solute contents. The initial soil solutions were of relatively high salt concentration. It was found that both the water and salt concentration profiles preserved similarity in terms of distance divided by the square root of time. This observation implies that the longitudinal dispersion coefficient is insensitive to pore water velocity and may be taken as a function of the volumetric water content only, at least for a given initial (low) moisture content.

The formulation which follows is frankly phenomenological. It provides a simple means of predicting dispersion during flow in unsaturated soils which promises to be sufficiently accurate for most purposes.
The Distribution of Micronutrient Cations in Soil Under Conditions of Varying Redox Potential and pH
Authors: Sims J. L. , Patrick W. H.
Published: July 2010

A laboratory study was conducted to determine the influence of redox potential and soil pH on the distribution of Fe, Mn, Zn, and Cu in Mhoon silty clay loam soil (Typic Fluvaquents) and to provide insight into factors affecting micronutrient dissolution and mobility in soil. Generally, greater amounts of Fe, Mn, Zn, and Cu were found in the Na acetate (exchangeable) and pyrophosphate (organic) extractions at low pH and Eh than at high pH or Eh. In contrast, the amounts (except Mn) in the water‐soluble, NH2OH·HCl, and oxalate fractions were greater at high pH or Eh. Although the micronutrients were brought into solution at low pH and Eh, much of the soluble cations soon associated with the exchangeable and organic fractions. After reduction, mobilized Fe associated about equally with the exchangeable, organic, and NH2OH·HCl fractions; mobilized Mn with the exchangeable and water‐soluble fractions; mobilized Zn with the organic fraction; and the mobilized Cu with the organic and water‐soluble fractions. Separation of the water‐soluble fraction into free ions and those complexed by soluble organic matter indicated that micronutrient cations were complexed by organic matter to a greater extent in reduced soil.
Measurement of Exchangeable NH4+ in Tropical Rice Soils
Authors: Sahrawat K. L. , Ponnamperuma F. N.
Published: July 2010

Measurement of exchangeable NH4+ by two methods—steam distillation of the filtrates of KCl extracts and of soil‐KCl suspensions with MgO—was compared for 17 tropical soils covering a wide range in texture, pH, and organic matter. Distillation of soil suspensions gave significantly higher values for NH4+ both for aerobic and anaerobic soils, but the differences were much greater in the anaerobic soils. The higher values obtained by direct distillation of KCl‐soil suspensions were probably due to hydrolysis of soil organic matter at the high pH values (9.9 to 10.7) brought about by the boiling MgO suspensions. We recommend the use of a filtered KCl extract instead of a soil suspension to measure exchangeable NH4+ in tropical rice soils.
Phosphodiesterase Activity of Soils
Authors: Browman M. G. , Tabatabai M. A.
Published: July 2010

An improved method to assay phosphodiesterase activity in soils is described. It involves extraction and colorimetric determination of the p‐nitrophenol released when 1 g of soil is incubated with 5 ml of 1mM buffered [0.05M tris (hydroxymethyl) aminomethane (THAM), pH 8.0] bis‐p‐nitrophenyl phosphate solution at 37°C for 1 hour. The reagents (0.5M CaCl2 and 0.1M THAM pH 12) used for extraction of the p‐nitrophenol released give quantitative recovery of p‐nitrophenol added to soils and do not cause chemical hydrolysis of the substrate, bis‐p‐nitrophenyl phosphate. Results showed that this soil enzyme has its optimum activity at buffer pH 8.0. The initial rates of p‐nitrophenol release obeyed zero‐order kinetics. The phosphodiesterase activity of six surface soils studied ranged from 16 to 147 µg p‐nitrophenol released · g−1 soil · hour−1. Steam sterilization and formaldehyde destroyed and toluene increased the activity of this enzyme. At 5mM, PO43‐, EDTA, and citrate inhibited phosphodiesterase activity. The inhibition by orthophosphate showed competitive kinetics. The temperature dependence of the rate constant conformed to the Arrhenius equation up to the point of enzyme inactivation (70°C). The activation energy of phosphodiesterase of the six surface soils studied ranged from 7,860 to 10,390 (avg. = 8,720) calories · mole−1. By using the Lineweaver‐Burk plot, the Km values ranged from 1.26 to 2.02 (avg. = 1.69)mM and the Vmax ranged from 52 to 530 (avg. = 303) µg p‐nitrophenol released · g−1 soil · hour−1. Phosphodiesterase activity was significantly correlated with organic C in each soil profile and in the surface soils studied.
Nutrient Effectiveness in Relation to Rates Applied for Pot Experiments: II. Phosphorus Sources
Authors: Mortvedt J. J. , Terman G. L.
Published: July 2010

Three greenhouse pot experiments were conducted with corn (Zea mays L.) grown on infertile soils to evaluate four fertilizers as sources of P. The granular sources were concentrated superphosphate (CSP, 90% of P water‐soluble), monoammonium phosphate (MAP, 100% of P water‐soluble), a mixture of 30% of the P as CSP and 70% as dicalcium phosphate (DCP, water‐insoluble), and a 10‐90% mixture of CSP and DCP. Rates of 0, 50, 200, 400, and 800 mg of P/pot from each source were compared in Exp. 1; and 0, 60, 120, and 480 mg rates of P in Exp. 2 and 3. These P sources and rates were compared at various levels of N and K. The order of effectiveness was the same at all levels of applied N and K: MAP ≥ CSP > 30% CSP + 70% DCP > 10% CSP + 90% DCP. This indicates that on these soils, P was the chief limiting nutrient at all levels of N and K. However, yield levels and the precision of determining differences in effectiveness among sources relative to experimental error increased greatly at higher rates of applied N and K.

These results show that effectiveness of P sources and also source differences relative to experimental error are greater at adequate than at deficient levels of nontest nutrients or other growth‐limiting factors. Adequate levels of nutrients for greenhouse pot experiments are much higher per pot equivalent than the normal recommended application rates for crops grown under field conditions.
Loess Deposits of the Eastern Shore of Maryland
Authors: Foss J. E. , Fanning D. S. , Miller F. P. , Wagner D. P.
Published: July 2010

A silty mantle on the upper Eastern Shore of Maryland was studied to determine its origin and characteristics. Thickness of the silts was studied by selecting traverses in an east‐west direction from the Chesapeake Bay and also scattered borings between traverses. These deposits are believed to be loess; they are characterized by 50 to 75% silt‐sized particles. The material is also carbonatefree, nonstratified, and yellowish brown in color. In addition, the silty mantle shows a reduction in thickness and particle size with increasing distance from the Chesapeake Bay, which was the probable source area. In areas of thin loess (< 90 cm), increasing amounts of sand were apparently incorporated into the loess at the time of deposition. Based on 14C date of a 11A1b horizon of a buried paleosol below the loess, deposition of the silts took place after 10,520 ± 240 years B.P. Profile characteristics of soils developed in the loess show moderately well expressed argillic horizons with the soil in this study having an increase of 9% clay from the A to the B2t horizon or a B2t/A clay ratio of 1.65.
Soils of a Grassland‐Forest Ecotone in Eastern Nebraska
Authors: Al‐Barrak Saad , Lewis David T.
Published: July 2010

In Otoe County, in eastern Nebraska, loessal soils on very steep slopes along the bluffs of the valley of the Missouri River exhibit weakly developed characteristics that are often associated with soils formed under deciduous forests. While these soils are Mollisols and show the dominant effects of the prairie, they have superimposed on the Mollisol characteristics what appear to be effects of having existed under forests for some time. In spite of the fact that these soils are on very steep slopes, they appear to be more highly weathered than adjacent soils on the divides. Evidence of this weathering includes a weakly developed A2 horizon and an argillic horizon, discontinuous cutans in the argillic horizon, gray coatings on ped surfaces to a depth of over 120 cm, and a much deeper solum than nearby soils within the Marshall and Monona Soil Series that show none of the above characteristics. Data suggest that the soils on the bluffs accumulate more moisture than those on the divides. The additional moisture, plus the effects of the forest may be the factors that are related to the differences in morphology.
A Technique for Studying the Kinetics of Adsorption in Suspensions
Authors: Zasoski R. J. , Burau R. G.
Published: July 2010

Experimental techniques are described for study of both the kinetics and equilibria of metal sorption in colloidal managanese dioxide suspensions. The techniques and apparatus appear not to contaminate the reactants or to sorb metal ions onto the reaction vessel walls, even at pH's as high as 8 and metal concentrations in parts per billion. Products and reactants can be monitored simultaneously, and a complete accounting made of the ions thought to participate in the reaction. This system allows description of the sorption process from mixing to equilibrium. Repeated sequential sampling does not alter the ratio of solution to suspension, and accurate equilibrium data can be obtained from kinetic experiments over extended periods.
An Analysis of Sensible and Latent Heat Flow in a Partially Frozen Unsaturated Soil
Authors: Fuchs M. , Campbell G. S. , Papendick R. I.
Published: July 2010

A heat flow theory has been developed which can be used to predict freezing and thawing cycles of a temperate soil. The latent heat of fusion is incorporated into the classical heat flow equation with the heat capacity and the thermal conductivity of the soil modified to include terms which account for the phase transformation. Computations for a Palouse silt loam soil show that the ice‐liquid phase transformation occurs over a defined temperature range where the apparent heat capacity and the apparent thermal conductivity may take on values which are several orders of magnitude larger than those either in the unfrozen or in the near completely frozen soil. The computations also indicate that the presence of solutes in the soil water significantly lowers the temperature range over which the freeze‐thaw zone develops and may allow considerable transport of water and heat at lower temperature than in the absence of solutes.
Development of a DTPA Soil Test for Zinc, Iron, Manganese, and Copper
Authors: Lindsay W. L. , Norvell W. A.
Published: July 2010

A DTPA soil test was developed to identify near‐neutral and calcareous soils with insufficient available Zn, Fe, Mn, or Cu for maximum yields of crops. The extractant consists of 0.005M DTPA (diethylenetriaminepentaacetic acid), 0.1M triethanolamine, and 0.01M CaCl2, with a pH of 7.3. The soil test consists of shaking 10 g of air‐dry soil with 20 ml of extractant for 2 hours. The leachate is filtered, and Zn, Fe, Mn, and Cu are measured in the filtrate by atomic absorption spectrophotometry.

The soil test successfully separated 77 Colorado soils on the basis of crop response to Zn, Fe, and Mn fertilizers. Critical nutrient levels must be determined separately for each crop using standardized procedures for soil preparation, grinding, and extraction. The critical levels for corn using the procedures reported herein were: 0.8 ppm for Zn, 4.5 ppm for Fe, and tentatively 1.0 ppm for Mn, and 0.2 ppm for Cu.

Development of the soil test was based, in part, on theoretical considerations. The extractant is buffered at pH 7.30 and contains CaCl2 so that equilibrium with CaCO3 is established at a CO2 level about 10 times that of the atmosphere. Thus, the extractant precludes dissolution of CaCO3 and the release of occluded nutrients which are normally not available to plants. DTPA was selected as the chelating agent because it can effectively extract all four micronutrient metals. Factors such as pH, concentration of chelating agent, time of shaking, and temperature of extraction affect the amount of micronutrients extracted and were adjusted for maximum overall effectiveness.
Greenhouse Evaluation of Residual Phosphate by Four Phosphorus Methods in Neutral and Calcareous Soils
Authors: Bowman R. A. , Olsen S. R. , Watanabe F. S.
Published: July 2010

Four determinations of phosphorus—Olsen‐P, Colwell‐P, total exchangeable P, and resin‐extractable P—were evaluated in terms of total plant P uptake in a 3‐year continuous greenhouse study of 23 high P calcareous and neutral soils. All methods were highly correlated with the total P taken up from the soils by 5–8 successive greenhouse crops. The Olsen‐P procedure extracted an average of nearly 50% of the total plant P while the Colwell procedure extracted nearly 80%. Resin‐extractable P and total exchangeable P values approximated the total plant P uptake, and served as good biological measures of the total plant‐available P in the soil. No significant differences were observed between the carrier and carrier‐free 32P methods on the 23 test soils.
Straw‐mulch Rate Effect on Soil Water Storage and Sorghum Yield
Authors: Unger Paul W.
Published: July 2010

A field study was conducted to determine the effects of straw mulch rates on soil water storage during fallow and on subsequent grain sorghum [Sorghum bicolor (L.) Moench] production. Wheat [Triticum aestivum (L.)] straw at rates of 0 (check), 1, 2, 4, 8, or 12 metric tons/ha was placed on field plots in July 1973, 1974, and 1975. A different area, previously cropped to dryland wheat, was used each year. Atrazine [2‐chloro‐4(ethylamino)‐6‐(isopropylamino)‐s‐triazine] was applied for volunteer wheat and weed control before mulch placement. Soil water content was measured periodically from July until the following May, when grain sorghum was planted, and during the sorghum growing season. Available soil water at planting averaged 12.3 and 21.4 cm for the 0‐ and 12‐metric tons/ha mulch treatments, respectively. The additional water, along with greater infiltration and lower evaporation during the growing season, increased grain yields, which averaged 1,780 and 3,990 kg/ha for the respective treatments. Water‐use efficiency increased from 55.6 kg/ha‐cm for no mulch to 115.0 kg/ha‐cm for 12 metric tons mulch/ha.
A Soil‐Water‐Nitrogen Model for Irrigated Corn on Sandy Soils
Authors: Watts D. G. , Hanks R. J.
Published: July 2010

A model was developed which describes the net changes of nitrogen amounts due to transformations and the movement, uptake, and loss of nitrogen from the root system of irrigated corn (Zea mays L.) grown on sandy soils. A potential nitrogen uptake function developed from field data is used to determine the maximum uptake for nonlimiting soil water and nitrogen availability. Actual uptake is calculated as less than potential when soil water content and/or mineral nitrogen concentration and distribution limit convective and diffusive movement of nitrate to the root system. Separate calculations are made for uptake resulting from each of these two mechanisms. Seasonal nitrogen uptake was computed within ± 15% of measured uptake on field plots where uptake by above ground plant material ranged from 105 to 218 kg/ha. Computed nitrate leaching losses compared favorably with losses estimated by multiplying percolation loss determined from a weekly water balance, by measured nitrate concentration at 150 cm depth. Field leaching losses estimated by the water balance‐concentration method ranged from 37 to 154 kg/ha.
Alterations of Micas and Feldspars During Microbial Formation of Basic Ferric Sulfates in the Laboratory
Authors: Ivarson K.C. , Ross G.J. , Miles N.M.
Published: July 2010

During the oxidation of ferrous iron in solution by the iron‐oxidizing bacterium, Thiobacillus ferrooxidans, formation of jarosite [KFe3(SO4)2(OH)6] occurred in the presence of glauconite, illite and microcline whereas natrojarosite [NaFe3(SO4)2(OH)6] was formed in the presence of albite. The required K and Na were supplied by these minerals and considerable amounts (up to 12%) of jarosite were formed during four months of reaction. When NH4 ions were present in solution, K release from the minerals appeared to be blocked and ammoniojarosite [NH4Fe3(SO4)2(OH)6] was formed. In the absence of NH4 ions or K‐ and Na‐bearing minerals an amorphous precipitate formed. X‐ray diffraction and chemical data indicate that interlayer K was preferentially removed from glauconite which resulted in an expanding phase having a d(001) spacing of 18Å with Mg and glycerol saturation. There was little preferential removal of interlayer K from illite as most of the K was removed by approximately stoichiometric dissolution. The K from microcline and the Na from albite were also removed stoichiometrically during jarosite and natrojarosite formation. The K released for jarosite formation followed the order glauconite>illite>microcline. The availability of Na from albite was somewhat greater than the availability of K from microcline.

The results show that in acid sulfate soils where ferrous iron, Thiobaccillus ferrooxidans and basic ferric sulfates are abundant, clay minerals can supply the alkali cations for the formation of these sulfates.
Prediction of Phosphorus Diffusion from Fertilizer Source
Authors: Hira G. S. , Singh N. T.
Published: July 2010

Rate of P diffusion from fertilizer applied at the soil surface was studied using Fick's law of diffusion. The diffusion coefficient of P was determined from a knowledge of the tortuosity factor and P adsorption isotherm. Phosphorus diffusion coefficient calculated from Nye's equation did not prove suitable at very low or high concentration of P at the soil surface. The phosphorus diffusion coefficient calculated from experimental data increased linearly with the square root of P concentration applied at the source. Phosphorus diffusion coefficient could be calculated from the equation,
urn:x-wiley:03615995:saj2sssaj197803615995004200040005x:equation:saj2sssaj197803615995004200040005x-math-0001 Predicted P concentration‐distance profiles were very close to the experimental values estimated by employing a sectioning technique.
Phosphate Desorption from Kaolinite Suspensions
Authors: Bar‐Yosef B. , Kafkafi U.
Published: July 2010

Phosphate desorption from soil minerals is one of the factors which determine the rate of P uptake by plants. Under laboratory conditions desorption is usually obtained by drastic dilution or leaching of the clay, thus inducing its dissolution. The objective of this work was to study the effect of the desorption method used, equilibration time and the dissolved silica on the desorption of P from kaolinite. Two desorption methods were used: (i) diluting 1% suspensions by various volumes of the same electrolyte, and (ii) immersing a dialysis tube containing 0.25% suspension (+P) in an identical suspension initially free of P. The desorption process in both cases could be divided into a rapid and a slow first‐order reaction. The rapid reaction rate constant was similar in both systems (about 4.65 × 10−3hours−1 at 25°C). The slow reaction constants were 0.3 × 10−3hours−1 and 1.15 × 10−3hours−1 for cases (i) and (ii), respectively. The activation energy of the desorption process in case (ii) was 16.2 Kcal/mole for the rapid and 4.8 Kcal/mole for the slow reaction. The amount of silica dissolved from kaolinite due to dilution with 0.01M KCl depended on the dilution ratio and reached 16 mg SiO2/g kaolinite when the suspension was diluted 100‐fold. Readsorption of part of the dissolved silica is stipulated to contribute to the fast P desorption process.
Use of K/Rb Ratio to Characterize Potassium Uptake by Plant Roots Growing in Soil
Authors: Baligar V. C. , Barber S. A.
Published: July 2010

Interaction between the plant root and the soil on cation influx into the root is not well understood. Use of the ratio of K/Rb, two ions absorbed interchangeably by the root, enables measurement of the K ion medium influencing K flux into the root. In experiments with corn (Zea mays L.) grown in eight soil‐K systems in a growth chamber, the K/Rb ratio of uptake was similar to the K/Rb ratio of the ions on the exchange sites, and not the K/Rb ratio of the solution cations. The data may be interpreted to indicate that K and Rb on the exchange sites had more influence on K and Rb flux into the root than K and Rb in solution. Diffusion of K and Rb from the soil to H‐saturated exchange membranes was in the ratio of K/Rb in solution.
Factors Affecting Denitrification in a Sonoran Desert Soil
Authors: Westerman R. L. , Tucker T. C.
Published: July 2010

Incubation studies were conducted to determine the effect of temperature, moisture content, organic C, soil depth, and time on transformations of added 15NO3‐N to a Sonoran Desert soil in open and closed systems. In open system studies, increasing temperature from 20° to 37°C, adding organic C, and increasing moisture content from field capacity to saturation increased denitrification losses 16, 22, and 2%, respectively. There were no apparent differences in immobilization of 15NO3‐N due to temperature, time, moisture content, or soil depth without organic C amendments. However, immobilization of 15NO3‐N soils with organic C amendments was increased markedly with increased temperature and time, but initial moisture content had little effect. At C/N ratios of 150:1 only traces of 15N appeared in NH4‐N, however, at C/N ratios of 15:1 to 45:1 ammonification and immobilization occurred simultaneously.

Closed system investigations with organic C and 15NO3‐N amendments showed 79% loss in 5 days with the remaining 21% accumulating as organic‐15N. Denitrification losses in open systems with soil moisture contents representative of saturated conditions were 70% of the loss observed under closed systems at the same moisture content.
Potassium Uptake by Onion Roots Characterized by Potassium/Rubidium Ratio
Authors: Baligar V. C. , Barber S. A.
Published: July 2010

A common belief is that plant roots absorb cations from the solution phase of the soil. Experiments with corn (Zea mays L.) using K/Rb ratio to evaluate the source of K and Rb absorbed indicated the plant roots absorbed these ions in the ratio of exchangeable K and Rb. The objective of this research was to study the source of K and Rb absorbed from soil by onion (Allium cepa) roots since they do not have root hairs and this may influence the uptake mechanism. Onions absorbed K/Rb with a ratio which was intermediate between the ratio of exchangeable K and Rb and the ratio of these cations in solution. In comparison with corn, onions absorbed K at one‐third the rate, but absorbed water three times faster so that mass flow contributed a greater proportion of K absorbed by onions than that by corn. This, rather than differences in root hairs may be the reason for the observed differences in K uptake between corn and onions.
Salt Outflows from New and Old Irrigated Lands
Authors: Carter D. L. , Robbins C. W.
Published: July 2010

Three water application treatments with low salt water were applied to previously nonirrigated soil and to a similar soil which had been irrigated for 67 years. The total soluble salt content of these soils initially, and after one and two seasons of treatment, was measured to determine salt outflow. Residual soluble salts were essentially removed from the previously nonirrigated soil after 30 cm of water/m depth of soil had passed from the soil as leachate, regardless of the number of seasons required for that amount of leaching. The total quantity of residual salt removed from soil 5 m deep was 70 metric tons/ha, with about 38 metric tons/ha being leached out by the first 14 cm of leachate. After the residual salt was removed, the salt content of the newly irrigated soil was the same as that of the soil which had been irrigated for 67 years. Subsequent salt outflow from the soil was directly related to the quantity of water leaching through the soil, indicating that more minerals dissolved with more leaching. Soils irrigated for many years and then not irrigated for up to 10 years had no measurable reaccumulation of soluble salts during the period of nonirrigation. Results of these investigations provide a basis for estimating salt outflows from newly developed and old irrigated lands, and for assessing the impact of these salts on surface and groundwater supplies.
A Soil Moisture Budget Model Accounting for Shallow Water Table Influences
Authors: Stuff R. G. , Dale R. F.
Published: July 2010

Soil moisture balance programs developed on well‐drained soils were found to be unsatisfactory for a soil underlain by shallow water tables, a condition typical of about 9 million acres of cropland in Indiana. Capillary rise past a 105‐cm root zone boundary was estimated as the difference between estimated evapotranspiration (ET) and changes in soil moisture under corn (Zea mays L.) on a tile‐drained Typic Argiaquoll at West Lafayette, Ind. during three growing seasons, 1971–1973. Capillary water was found to supply an average of 27% of the ET in periods with little or no precipitation. Computer model estimates showed capillary water to furnish about 17% of the total ET over a 100‐day period from 49 days before silking to 50 days after.

Evapotranspiration was based on measured pan evaporation adjusted with crop development and moisture stress factors from the literature. Soil moisture in the root zone was measured by neutron counting and expressed as deficits from a variable holding capacity which was allowed to change in time depending upon the depth of the shallow water table. Water table levels were measured in open wells, and water table changes were statistically related to the estimated amounts of capillary rise for use in the model. The factors used to estimate capillary rise were the soil moisture deficit in the root zone and depth of the water table.

The derived relationships with those obtained from literature sources and assumptions regarding runoff and recharge were programmed in a computer model for simulating the daily moisture status and changes in the corn root zone. Model inputs were pan evaporation, precipitation, soil moisture characteristics, corn silking date, and initial soil moisture conditions. The model was found to closely track measurements of both soil moisture and water table depths in four independent seasons: early and late plantings in 1970 and 1974.
Coupling Phenomena in Saturated Homo‐ionic Montmorillonite: III. Analysis
Authors: Groenevelt P. H. , Elrick D. E. , Blom T. J. M.
Published: July 2010

The data presented in the first paper of this series are analyzed using the theoretical transport equations and the analytical expressions for the transport coefficients developed in the second paper of the series.

When the electrodes of the system presented in Part 1 of this series are not shorted the predicted behavior corresponds precisely with the actual behavior.

Upon shorting the electrodes, the data indicate that the actual shorting of the clay‐water system is not perfect, an indication that the electrodes cannot release and absorb Cl‐ ions infinitely fast. From the data the shorting efficiency is calculated. The flux of cations through the clay‐water system while the electrodes are shorted can then be calculated. The absolute value of this flux appears to be slightly larger than the value calculated from the decrease in time of the salt concentration difference in the two liquid compartments. This is likely due to the buildup of a salt concentration gradient in the membranes.
Solute Travel‐time Estimates for Tile‐drained Fields: III. Removal of a Geothermal Brine Spill from Soil by Leaching
Authors: Jury W. A. , Weeks L. V.
Published: July 2010

The time required to leach a slug of saline, sodic geothermal brine from the point of injection to the tile outlet of an artificially drained field is calculated. Sprinkler, complete, and partial ponding leaching methods are compared as a function of drain spacing and initial location of the spill. Calculated results are presented as dimensionless parameters which scale the drainage system dimensions and the soil water transport properties. Ponded leaching required more water, but less time to leach brine out of the system for all situations except where the brine spill occurs near the midpoint between tile lines.

A simple calculation is proposed to estimate the leaching fluid volume required to remove excess Na+ from the exchange complex. Good agreement was attained between simulated and experimental results involving a laboratory soil column. For fine‐textured soils in the Imperial Valley of California it may require up to 30 pore volumes of leaching fluid to replace Na+ with Ca2+ if saturated gypsum solution is used in reclamation. Application time per pore volume was calculated to be in excess of 1 year for all cases except ponded leaching directly over a tile line.
A Mathematical Treatment of Infiltration from a Line Source into an Inclined Porous Medium
Authors: Zachmann D. W.
Published: July 2010

An exact mathematical solution is obtained for two‐dimensional steady infiltration from a line source into an inclined porous medium with an impermeable lower boundary. Unsaturated hydraulic conductivity is assumed to be an exponential function of pressure head. Equations for a stream function and the pressure head are developed and stream lines and contours of constant pressure head are plotted for a sandy soil and a clay soil using inclinations of 5° and 20° from horizontal.
The Spectrophotometric and Fluorometric Determination of Aluminum with 8‐Hydroxyquinoline and Butyl Acetate Extraction
Authors: Bloom P. R. , Weaver R. M. , McBride M. B.
Published: July 2010

A spectrophotometric method and a fluorometric method for the determination of Al by the extraction of the Al‐hydroxyquinolate complex with butyl acetate were evaluated. The Al complex was found to be very stable in butyl acetate. Since butyl acetate is less dense than water the extractions could be done in screw top tubes and it was not necessary to dewater the solvent phase.

The spectrophotometric method was found to be useful for the analysis of solutions containing 2 × 10−6M (50 ppb) Al or greater. The spectrophotometric response was linear up to absorbance = 1.1. The relative error in midrange was < 2.5%. The quantity of Al determined in soil extracts was shown for some soils to be strongly dependent on the time of contact with the complexing reagents before extraction with butyl acetate. This was attributed to the complexation of Al by organic matter in the soil solutions.

The flourometric method was found to have a detection limit of about 1 × 10−8M (0.3 ppb) Al. The fluorometric response was nearly linear in the most sensitive range of the fluorometer but was less linear for higher Al concentrations. The relative error was < 8% except near the detection limit.

There was no interference with either method from Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Fe2+, Fe3+, F‐, PO43‐, SO42‐, and SiO32‐ at the levels found in most soil extracts.
Adsorption and Extractability of Molybdenum in Relation to Some Chemical Properties of Soil
Authors: Karimian N. , Cox F. R.
Published: July 2010

Development of a practical soil test for molybdenum (Mo) will depend on selection of the proper extractant. To achieve this, more knowledge is needed about Mo adsorption and its extractability, especially in relation to other soil properties.

Adsorption of Mo from aqueous solutions was determined for eight soils from the Atlantic Coastal Plain and Piedmont regions. The data followed the Freundlich isotherm more consistently than the Langmuir. Adsorption increased as the organic matter and/or Fe oxide contents of the soils increased. Adsorption from an aqueous solution that was initially 0.3 mM Mo (AdMo) also was determined on 32 soils collected from the regions. The AdMo level was positively correlated with Fe oxide and organic matter contents and negatively correlated with pH and P levels.

The level of Mo extracted with acid ammonium oxalate (Grigg Mo) and an anion exchange resin (resin Mo) were also determined and related to soil chemical properties and a lime treatment. Grigg Mo was positively correlated with amorphous and free Fe oxide contents, probably as a result of the strong dissolution of Fe oxide by oxalate. Resin Mo was positively correlated with pH but not with other soil properties. Incubating soils with CaCO3 increased the level of resin Mo.
Genetic Association of Properties of Soils of an Area in the Upper Amazon Basin of Peru
Authors: Tyler E. J. , Buol S. W. , Sanchez P. A.
Published: July 2010

Soil properties of a 400‐ha area in the Upper Amazon Basin of Peru were found to be related to the nature of the parent material and to occurrence of defined geomorphic surfaces. The soils are developed from unconsolidated sandy to clay textured river sediments, originating in the Andes Mountains. The oldest surface is presently on the level hill tops. A surface which cuts the higher older surface and grades to the intervening valley floors of the same age and the recent flood plain is the youngest geomorphic surface.

The Typic and Aquic Paleudults of the oldest surface generally have lower pH values, lower base saturation, and contain less weatherable minerals, but contain greater amounts of clay‐sized kaolinite than the soils of the younger surface. The soils of the erosional surface are Ultisols, Inceptisols or Alfisols. Genetic control of these soils appears to depend upon the location of an impervious layer which controls ground water depth. The Alfisols, Inceptisols, and Entisols of the flood plain contain about 15% weatherable minerals and high amounts of well crystalized smectite clay minerals that have probably undergone limited pedologic alteration.
Clay Minerals of Montana Soils Formed on Volcanic Parent Materials
Authors: Klages M. G.
Published: July 2010

Samples were taken of soils formed on volcanic materials varying in age from Cretaceous to Recent. The soil samples were analyzed for particle size distribution, pH, organic matter, cation exchange capacity, and exchangeable cations. Clays were separated and identified by X‐ray diffraction supported by chemical analysis. Clay mineralogy varied with age of the parent material. Recent ash in western Montana from sources in Washington and Oregon gave rise to amorphous clays in eight of nine samples. Soils on Quaternary volcanics near Yellowstone National Park had amorphous or poorly crystalline 2:1 clays. Clays of soils from Tertiary age volcanics were dominated by smectite. Cretaceous volcanics gave rise to mixed 2:1 clays similar to soils on Cretaceous sediments in the Northern Great Plains. Exchangeable cations in the soils varied with the dominant clay minerals.
Errors in Gamma‐ray Measurements of Water Content and Bulk Density in Nonuniform Soils
Authors: Nofziger D. L.
Published: July 2010

Recent experimental study of freezing soils has shown gamma‐ray measurements of water content and bulk density are in error when the water content and bulk density are not uniform throughout the gamma‐ray beam. Many gamma‐ray measurements involve nonuniform soils. This study was conducted to determine the magnitude of errors due to nonuniform bulk density and water content. Errors in gamma‐ray water content and bulk density were determined for soil‐water systems with linear and step‐function changes in water content and bulk density and for measurements of water absorption by a nonswelling porous medium. Both single‐energy and dual‐energy gammaray systems were analyzed.

Large errors in water content and bulk density determined by dualenergy gamma‐ray measurements can occur for highly stratified soils. The calculated values may fall outside the range of values within the gamma‐ray beam. Relatively small errors occur if the bulk density and water content change linearly in the collimated beam. Both single‐ and dual‐energy systems accurately measure the average water content in the collimated beam if the bulk density of the soil is constant. However, the average water content in the beam may not represent the water content at the middle of the collimated beam and the middle of the preset time period. Errors due to nonuniform soils can be evaluated using the equations and graphs presented.
Field Measurement of Denitrification: I. Flux of N2 and N2O
Authors: Rolston D. E. , Hoffman D. L. , Toy D. W.
Published: July 2010

Absolute amounts and rates of denitrification from a Yolo loam (Typic Xerorthents) field profile were studied in relation to the influence of soil‐water content, organic C source, and soil temperature. Field plots were intensely instrumented with soil atmosphere samplers, tensiometers, and thermocouples. Soil‐water contents were maintained constant with a spray irrigation system activated at frequent time intervals. The upper 15 cm of soil was maintained at soil‐water pressure heads (h) of −15 and −70 cm of water for the two different water regimes of the experiment conducted at a soil temperature (5 cm depth) of 23°C. Soil‐water pressure heads were maintained at −8 and −50 cm for the two water regimes conducted at 8°C. Plots cropped with ryegrass, uncropped plots, and plots to which manure was mixed in the top 10 cm of soil were used to establish three different C levels. Fertilizer was applied at the rate of 300 kg N ha−1 as KNO3 enriched with 20 and 40% 15N for the h = −15 or −8 and h = −70 or −50 cm treatments, respectively. The flux of gases at the soil surface was measured from the accumulation of N2O and 15N2 beneath an air‐tight cover placed over the soil surface for 1 or 2 hours per day. Denitrification from gas fluxes occurred for the 23°C experiment in order of decreasing magnitude in manure (h = −15 cm), manure (h = −70 cm), cropped (h = −15 cm), cropped (h = −70 cm), uncropped (h = −15 cm), and uncropped (h = −70 cm) plots. Approximately 70% of the fertilizer N was denitrified for the manure (h = −15 cm) treatment. Approximately 1% of the added fertilizer was denitrified in the uncropped (h = −70 cm) treatment. Denitrification from gas fluxes for the 8°C experiment occurred in the same order as that of the 23°C experiment except that rates and absolute magnitudes were much smaller. Approximately 11% of the fertilizer N was denitrified for the manure (h = −8 cm), and no measurable denitrification occurred in the uncropped (h = −50 cm) treatment. The amount of N2 produced was much greater than N2O for all plots. The N2O flux at the soil surface was dependent upon time and degree of anoxic development and varied between 5 and 26% of total denitrification.
Oxygen Flux Measurement in Unsaturated Soils
Authors: Rankin J. M. , Sumner M. E.
Published: July 2010

Because in unsaturated soil systems the plateau of the current‐voltage curve is not well developed or is absent, O2 reduction at the platinum microelectrode is not diffusion controlled and consequently measured current depends continuously on applied potential. To overcome this difficulty an O2 flux meter has been designed which carefully controls and measures the applied potential and enables the effective potential at the electrode to be measured precisely. The instrument, which has facilities for measuring soil electrical resistance, electrode redox potential, and O2 reduction current is fully described together with a circuit diagram. Because the surface oxide condition of the microelectrode is crucial to reproducible results, electrode pretreatment involving gentle abrasion in wet fine sand is necessary to standardize conditions prior to measurement. The results show that the instrument is suitable for measuring O2 flux in unsaturated systems, and that measured current is closely related to soil airspace.
Nitrogen Mineralization and Denitrification in Organic Soils
Authors: Guthrie T. F. , Duxbury J. M.
Published: July 2010

The quantities of N mineralized when columns of Histosols were incubated at field capacity for periods up to 28 days corresponded to 500‐600 kg N/ha per year without correction for N lost by denitrification.

An absorption train utilizing molecular sieve 5Å to collect N2O was used in denitrification experiments. Under an argon stream, 52‐53% of the added NO3‐‐N was recovered as N2O, whereas the maximum concentration of N2O accumulating in the headspace of closed vessels amounted to 65% of the added NO3‐‐N. The quantity of N2O either collected or accumulating in a headspace was reduced to 15‐41% of the NO3‐‐N denitrified when a second addition of NO3‐ was made to the soils. Denitrification occurred in both drained and flooded soil columns amended with NO3‐. The N2O recovered ranged from 2.5‐9% and 9‐19% of the NO3‐‐N denitrified in the drained and flooded columns, respectively. From 78‐98% of the N2O was recovered in leachate from the flooded columns and the corresponding range for the drained columns was 11‐52%.