bluuebunny/crossref_metadata_2025 huggingface dataset:
Movement and Distribution of Ammonium‐N Following Deep Placement of Urea in a Wetland Rice Soil
Authors: Savant N. K. , De Datta S. K.
Published: July 2010

The vertical distribution of NH4+‐N following subsurface placement of different forms of urea was studied in incubated, undisturbed wetland soil cores. For prilled urea, supergranule urea, and prilled urea in mudballs placed at the 10‐cm depth, peak concentration of NH4+‐N was near the placement site and decreased with time, whereas after placement of sulfurcoated urea (SCU‐21) at the same depth, peak concentration of NH4+‐N increased over a period of 4 weeks. With time, the NH4+‐N tended to move downward more than upward from the placement sites, probably because of the mass flow of percolating water.

In another experiment, the movement and spatial distribution of NH4+‐N were studied following application of 2‐g supergranules of urea (SGU) and sulfur‐coated supergranules of urea (SC‐SGU) at a depth of 10 cm in transplanted and cultivated wetland fallow plots. After 2 weeks, NH4+‐N concentration gradient for SGU was 1,850 to 32 µg N/cm3 wet soil, over a distance of 10–12 cm from the placement site. The corresponding gradient for SC‐SGU was 287 to 32 µg N/cm3 wet soil, over a distance of 5–7 cm from its placement site. For SGU in transplanted plots, the concentration gradient decreased steadily through 8 weeks, whereas for SC‐SGU it increased during the first 4 weeks and then decreased. The disappearance of NH4+‐N with time and distance from the site of application is attributed to diffusive transport or convective transport, or both, and root‐sink effect. The general movement of NH4+‐N was downward > lateral > upward. The apparent benefits of deep placement of urea in a wetland rice soil are discussed.
Translocation of Nutrients in Soybeans
Authors: Scott H. D. , Brewer D. W.
Published: July 2010

Transport of nutrients in plants represents an important area in the pursuit of a greater understanding of plant nutrition. A mathematical model was developed to describe the changes in accumulation of nutrients in soybean [Glycine max L. Merr.] plants during the growing season. The model uses the compartmental approach to describe transport of nutrients between three compartments: soil (including roots), plant (including stems, petioles, and leaves), and pod (including seed). The validity of the model was tested using published data for soybeans grown in the field. The results show that nutrient translocation in soybeans varies with the type of nutrient, growth stage, and growing season.
Soil Aggregates and Primary Particles Transported in Rill and Interrill Flow
Authors: Alberts E. E. , Moldenhauer W. C. , Foster G. R.
Published: July 2010

The size distribution of soil particles detached and transported in rill and interrill flow was determined on a silt loam soil in northcentral Indiana. Eroded soil was separated by field and laboratory sieving into > 2‐, 2‐ to 1‐, 1‐ to 0.5‐, 0.5‐ to 0.21‐, 0.21‐ to 0.05‐, and < 0.05‐mm size classes. The amount of primary clay (< 0.002 mm) transported as discrete particles in rill and interrill flow was also determined.

Large differences were found in the size of soil aggregates and primary particles in rill and interrill sediment. Rill flow transported a greater proportion of larger particles as compared with interrill flow because of basic differences in the detachment and transport mechanisms. Less than 5% of the rill and interrill sediment was composed of primary clays, indicating that most eroded clay was transported within soil aggregates.

The primary particle composition of the eroded aggregates was also determined. For all sizes > 0.05 mm, the percentage of sand in rill and interrill sediment was considerably higher than that in the matrix soil. The high sand content decreased the percentage of silt in some size classes more than the percentage of clay, indicating that primary clays may either flocculate or adsorb to the surfaces of larger aggregates during transport.

Water was added to the top of preformed rills at several rates to simulate various upland slope lengths. Discharge and rill erosion rates were not related for this soil that had not been tilled or cropped for 1 year.
Nutrient Uptake in Fertilized Plantations of American Sycamore
Authors: Wittwer R. F. , Immel M. J. , Ellingsworth F. R.
Published: July 2010

Annual applications of ammonium nitrate (169 kg/ha elemental N), alone and in combination with concentrated superphosphate (112 kg/ha elemental P), increased biomass of 4‐ and 5‐year‐old American sycamore (Platanus occidentalis L.) by approximately 45 and 205% on a bottomland and a terrace site, respectively, in the Ohio River Valley region of western Kentucky. Growth response and nutrient contents of trees fertilized with N and P were not significantly different from those receiving N only. After 5 years, N fertilization has increased elemental content of aboveground tree components by 189% for N, 48% for P, 90% for K, 93% for Ca, and 106% for Mg. Initial spacing of the seedlings in these closely‐spaced (0.3 by 0.9 m, 0.9 by 0.9 m, 1.8 by 0.9 m) trials did not have a significant effect on nutrient contents. Recovery of added N, as indicated by increased above ground tree contents after 5 years, represented 11 and 14% of the quantity added in fertilizer applications on the bottomland and terrace, respectively. After 5 years, levels of available P in soils receiving annual P fertilization had increased by 140 kg/ha, representing about 25% of the total P added. After 5 years exchangeable Ca had decreased in the bottomland soils and exchangeable K, Ca, and Mg had decreased in the less fertile terrace soil.
Iron Coatings on Rice Roots: Mineralogy and Quantity Influencing Factors
Authors: Chen C. C. , Dixon J. B. , Turner F. T.
Published: July 2010

Rice (Oryza sativa L.) root coatings were investigated to determine the amounts and mineralogical properties of the coatings during plant growth and in different soils under field conditions. X‐ray diffraction, electron microscopy, high gradient magnetic separation, and chemical methods were employed. Determinations of oxygen transport by different rice cultivars were made in vitro.

Rice cultivars, growth stage, and soil type were significantly related to the amount of iron oxyhydroxide (FeOOH) on field‐grown rice roots. Accumulation of FeOOH was < 2% of dry root weight 7 days after flooding of the soil, increased to a maximum of about 10% at plant maturity and decreased slightly thereafter. Of the four soils studied, two Vertisols had less FeOOH accumulation on root surfaces than two Alfisols. Of the four cultivars characterized (‘Brazos’, ‘Labelle’, ‘Lebonnet’, and ‘Bluebelle’), Brazos had the largest amount of O2 released from the roots and precipitated the largest amount of FeOOH on the roots when field grown in three of four soils. Lake Charles clay was the only soil in which Brazos rice did not rank highest in percent FeOOH on roots and in grain yield.

Goethite (α‐FeOOH) and lepidocrocite (τ‐FeOOH) were identified in rice root coatings that were ultrasonically dispersed and concentrated by high gradient magnetic separation.
Mineralogy of Saudi Arabian Soils: Southwestern Region
Authors: Aba‐Husayn M. M. , Dixon J. B. , Lee S. Y.
Published: July 2010

Mineralogical properties of soils along a 500‐km north‐south transect in the mountainous Asir region were investigated. The transect represented areas of wide variations in climate, parent material, and topography. Soils developed on stable landscapes at higher elevation (> 2,000 m) have well‐developed profiles and near neutral soil pH's. Soils developed on alluvial terraces near wadi banks at lower elevations (> 1,500 m) have deep but less developed profiles, and slightly greater than neutral pH's with carbonates present. Quartz, feldspars, and micaceous minerals are the major components of the silt and sand fractions of the soils. Clay fractions of the soils are composed mainly of kaolinite, smectite, vermiculite, mica and chlorite minerals. Kaolinite is the most abundant clay mineral of the soils developed on well‐drained highland areas. Smectite is the most abundant clay mineral in the alluvial soils developed on lower terrace areas.
Experimental and Mathematical Description of Nonadsorbed Solute Transfer by Diffusion in Spherical Aggregates
Authors: Rao P. S. C. , Jessup R. E. , Rolston D. E. , Davidson J. M. , Kilcrease D. P.
Published: July 2010

Diffusion of nonadsorbed solutes (3H2O and 36Cl‐) out of two sizes of porous ceramic spheres (0.55‐ and 0.75‐cm radius) was measured. These data were analyzed to provide independent estimates of the input parameters required in two simulation models for describing solute transport in aggregated porous media with distinct mobile and stagnant pore‐water regions. Tracer‐saturated porous spheres were placed in tracer‐free 0.01N CaCl2 solution and the rate of tracer diffusion out of the porous spheres was measured by monitoring the increase in tracer concentration with time in the external electrolyte solution. Experimental results were analyzed using two mathematical models. Fick's second law, written in spherical coordinates, formed the basis for Model I. In Model II, the time‐rate of solute transfer into or out of the porous spheres was assumed to be proportional to the difference in tracer concentration inside and outside the porous spheres. The analytical solution to Model I for given initial and boundary conditions was substituted into Model II, to derive an explicit expression relating the empirical mass transfer rate coefficient (α) in Model II and known physical constants of the system. This theoretical analysis indicated that the α value is dependent upon the sphere radius, time of diffusion, volumetric water contents inside and outside the sphere, and the molecular diffusion coefficient. Over a range of experimental conditions, excellent agreement was found between measured α values and those calculated using the analytic expression developed here.
Effect of Particle Surface Roughness on Densification of Coarse‐Textured Soil
Authors: Cruse R. M. , Cassel D. K. , Averette F. G.
Published: July 2010

It has been observed that soils on the Atlantic Coastal Plain compact to different bulk densities under the same compactive effort. It is hypothesized that densification differences observed among Ap horizon materials of these soils are partially due to variations in soil particle surface roughness. Surface roughness of Coastal Plain soil materials and sand size fractions derived from these materials were photographed and/or characterized by measuring the dense soil angle of response (DSAR) over a range of bulk densities. Altering the particle size distribution of a given material did not significantly influence the DSAR vs. Db (soil bulk density) relationship; the slopes and intercepts of these linear plots were not statistically different. However, plots of DSAR vs. Db for materials with different particle surface roughness had similar slopes, but different intercepts. It is proposed that the intercept of the DSAR vs. Db curve, or the value of DSAR at a given Db, be used to characterize soil particle roughness for coarse‐textured materials.

It was further hypothesized that the DSAR at a given Db was directly related to particle packing arrangement stability, or resistance to further densification, of the soil material. To test this hypothesis, different levels of vibrational energy were applied to materials with different particle roughness but similar particle size distributions. Soil materials with the smoothest particles, i.e., those with the lowest DSAR at each Db, consistently produced the highest Db at each vibrational energy level.
Studying Dried, Stored Soil Samples — Some Pitfalls
Authors: Bartlett Richmond , James Bruce
Published: July 2010

Dried, pulverized, and sieved soil samples are prepared and stored for laboratory research convenience. Drying and increasing time of storage both tend to push soil, which is metastable, toward increased surface acidity, reduced Mn, and increased solubility and oxidizability of soil organic matter. Reformation of metastable moist soil is a slow process mediated by environmental conditions interacting with life in the soil. Similar effects undoubtedly occur in the field as soils are dried.

Two sets of problems confront the researcher using dried soil samples: those associated with drying itself and those associated with remoistening. The behavior of a dried sample immediately after adding water to it is different from that of the continuously moist soil. Remoistening for a longer period is followed by a microbiological explosion. The behavior of the soil for an extended period, perhaps more than a month after rewetting, may be anomalous, or at least unpredictable. Keeping a soil moist and aerobic, though certainly inconvenient, is the most satisfactory method of storage for many research uses.
Nitrogen Mineralization in Florida Histosols
Authors: Terry Richard E.
Published: July 2010

The N‐mineralization rates of several Florida Histosols and the effects of soil moisture tension and organic C amendments on these rates were measured in the laboratory with an 15N‐tracer technique. An enhancement of microbial activity by crop residues was exhibited by greater N mineralization in cropped vs. uncropped soils. Nitrogen mineralization was not affected by soil moisture tension over the range of 0.1 to 3.0 bar. Exogenous C supplies such as glucose or St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntz] stimulated mineralization of native soil organic matter. Mineralization of soil organic N was increased by 91% in glucose amended soil samples. The N‐mineralization rate for a 75‐cm profile of Pahokee muck was estimated to be 686 kg N/ha for each centimeter of soil lost to microbial oxidation.
The Partial Inactivation of Degradative Soil Enzymes by Residual Fertilizer Copper in Histosols
Authors: Mathur S. P. , Sanderson R. B.
Published: July 2010

Samples of 14 neighboring fields of Histosols (organic soils) were similar in all but one of their 24 physical and chemical properties examined. The Cu content of these soils varied from 18 to 275 µg/g. Activities of C1‐cellulase, Cx‐cellulase, cellobiase, xylanase, amylase, inulase, lichenase, and lipase enzymes in the air‐dried and stored soil samples were found to correlate posiitvely with soil respiration and negatively with soil Cu content. Similarly, when samples from many border strips kept free of plants by cultivation in the same 14 fields were collected, air‐dried at about 23°C, and assayed within 1 week in summer, soluble Cu content of the soils was found to be negatively correlated with the cellobiase and invertase activities, and the enzyme activity levels similar to those of the air‐dried samples in storage for 2 years. Evidence presented therefore supports earlier suggestions that Cu may restrain the mineralization and subsidence of some organic soils through inactivation by the Cu of certain extracellular soil enzymes which normally facilitate biochemical oxidation of nonhumic soil organic matter.
Nitrate Movement Under Corn and Fallow Conditions
Authors: Long F. Leslie , Huck Morris G.
Published: July 2010

Nitrate movement under corn (Zea mays L.) and fallow conditions was studied in a simulated field soil profile of Dothan loamy sand (Plinthic Paleudults) in the Auburn rhizotron. The rates of N applied were 250 and 500 kg N/ha. The nitrate movement was monitored by analysis of soil solution samples taken at 48‐ to 72‐hour intervals over a 120‐day period from the 20‐, 40‐, 60‐, 80‐, 100‐, and 140‐cm depths. Nearly all the nitrate applied to the surface of fallow plots moved with percolating water and was leached below the 100‐cm depth within 65 days; this was true for both N rates. Actively‐growing corn roots intercepted nitrate from the 250 kg N/ha treatment before it reached the 80‐cm depth and from the 500 kg N/ha treatment before it reached the 100‐cm depth. At maturity the above‐ground portion of the corn contained 20% more N than was applied at the 250 kg N/ha rate and 75% of that applied at 500 kg N/ha. Corn roots effectively prevented leaching of nitrate.
Predicting the Effects of Changing Water‐Table Levels and Associated Soil Moisture Regimes for Soil Survey Interpretations
Authors: Bouma J. , de Laat P. J. M. , van Holst A. F. , van de Nes Th.J.
Published: July 2010

A one‐dimensional computer model for simulating the soil moisture regime was used to calculate evapotranspiration and equivalent productions of grass for six different soils. Input data consisted of rooting depths, moisture retention curves and hydraulic conductivity curves. Physical boundary conditions were derived from climatic data and depths to water table. Average relative production was calculated for actual water table fluctuations and for lowered levels, thus simulating the effects of ground water extraction. Productions for the six soils reacted quite differently to lowering of the water table. A classification was developed to characterize the different reactions. A SYMAP computer program was used to produce maps (which were based on soil maps) showing the effects in different soils to lowering of the water table. Storage of basic data on tape allows the production of many maps on demand for natural conditions and for conditions changed by man. Soil survey interpretation thus becomes a matter of offering many choices rather than a qualitative judgement based on actual conditions. The model can be used to express variability of mapping units on a soil map by simulating moisture regimes for the range of soil properties observed within the mapping unit.
Rebound of Five One‐Dimensionally Compressed Unsaturated Granular Soils
Authors: Stone J. A. , Larson W. E.
Published: July 2010

Rebound (decrease in bulk density after removal of mechanical stress) of five agricultural soils from four soil orders was measured at stresses of 1,000, 5,000 and 10,000 g cm−2 and pore water pressures from 0 to −1 bar.

Rebound was usually < 0.05 g cm−3. It was larger in soils containing expanding clays than in soils containing nonexpanding clays. It increased with stress in soils containing expanding clays but not in soils containing nonexpanding clays. Rebound decreased with repeated loading. It could not be delineated in terms of soil type, pore water pressure, or water content. In the prediction of bulk density of unsaturated agricultural soils based on their compression characteristics, rebound is usually small enough that it can be neglected.
Estimating Water Used by Irrigated Corn in West Central Minnesota
Authors: Dylla A. S. , Timmons D. R. , Shull H.
Published: July 2010

Irrigation development in Minnesota is expanding rapidly on the sandy and droughty soils of which there is considerable area. Construction of suitable wells into underlying gravel aquifers has facilitated the rapid growth. The objective of this study was to measure water use by irrigated corn in west central Minnesota for comparing with current estimating methods for irrigation scheduling. Lysimeters, 1.75 m diam by 1.22 m deep, located in irrigated corn (Zea mays L.) plots were used to measure water use or evapotranspiration (ET) amounts. Four years of comparisons were made of measured ET to amounts calculated with the standard and refined Jensen‐Haise potential ET equations and corn crop coefficients from southeastern North Dakota data. Measured ET was also compared with ET estimates determined by the Lundstrom‐Stegman “checkbook method,” and by crop coefficients with pan evaporation. Crop coefficients with pan evaporation provided the better ET estimates, however, the “checkbook method” was the simplest and was about as accurate for estimating ET as the Jensen‐Haise potential ET equation with southeastern North Dakota crop coefficients.
A Closed‐form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils
Authors: van Genuchten M. Th.
Published: July 2010

A new and relatively simple equation for the soil‐water content‐pressure head curve, θ(h), is described in this paper. The particular form of the equation enables one to derive closed‐form analytical expressions for the relative hydraulic conductivity, Kr, when substituted in the predictive conductivity models of N.T. Burdine or Y. Mualem. The resulting expressions for Kr(h) contain three independent parameters which may be obtained by fitting the proposed soil‐water retention model to experimental data. Results obtained with the closed‐form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties. The unsaturated hydraulic conductivity is predicted well in four out of five cases. It is found that a reasonable description of the soil‐water retention curve at low water contents is important for an accurated prediction of the unsaturated hydraulic conductivity.
First Integrals of the Diffusion Equation; An Extension of the Fujita Solutions
Authors: Parlange J.‐Y. , Braddock R. D. , Chu B. T.
Published: July 2010

In general, solutions of the nonlinear diffusion equation have to be obtained by numerical or analytical iterative integration. It is shown here that if the diffusivity has a dependence on the water content which obeys a power law, then iterations can be avoided, and the solution obtained at once. This unique case results from the existence of a first integral of the diffusion equation. Previously known analytical results, i.e., the constant diffusivity solution, the delta‐function solution, and the Fujita solutions belong to that general class.

For this general class of solutions it is also possible to show that the sorptivity has a dependence on the surface water content which obeys a power law. This represents the only known case when such an analytical relationship exists. This relationship is used to discuss the representation of the square of the sorptivity as an integral of the diffusivity, when the latter has an arbitrary dependence on the water content.
Prediction of Diffusion Coefficients from the Electrical Conductance of Soil
Authors: Palmer C. J. , Blanchar R. W.
Published: July 2010

Electrical conductance may be used to predict salt movement through soil by diffusion. A two‐component model was used which considers electrical conductance in soil to be a combination of a solution and a surface process. It has the form: ECa = ECwθT8 + EC8 where ECa is the specific conductance of the soil, ECw is the conductance of the solution, θ is the volumetric moisture content, ECr is the surface conductance, and T8 is the tortuosity. It was assumed that T8 and EC8 did not vary with changes in solution concentration, and these two parameters were calculated by measuring ECa and ECw on two soil samples which differed only in electrolyte concentrations. These values were used to calculate the equivalent conductance and the diffusion coefficients for Na+ and K+.

The alternating current measurement of conductivity was frequency (f) dependent due to electrode‐electrolyte interactions known as the Warburg impedance. The specific conductance was found by plotting the measured conductance against f‐0.5 and extrapolating to zero. At low electrolyte concentrations, the conductivity of the soil varied as a linear function of the logarithm of frequency and this factor was evaluated before predicting diffusion coefficients from the conductance of the soil.

The diffusion coefficient for K+ in four soils with 0.0133M KCl varied from 1.64 × 10−6 to 0.50 × 10−6 cm2/sec when computed from electrical conductivity but varied from 1.84 × 10−6 to 0.33 × 10−6 cm2/sec when computed from self‐diffusion. The fraction of the electrical current carried by the 0.0133M KCl in the soil solution varied from 0.85 to 0.13 and was inversely related to the cation exchange capacity. A comparison of diffusion coefficients estimated from the self‐diffusion of 42K and 24Na in concentrated and dilute systems indicates good agreement except for 0.0133M K+ in the Mexico Ap soil. The data suggest that diffusion measurements made by electrical conductance are more reproducible than those made by self‐diffusion, but give estimates of the diffusion coefficient that are of similar magnitude.
A Comparison of the Use of Phenolase and Peroxidase for the Synthesis of Model Humic Acid‐type Polymers
Authors: Martin J. P. , Haider K.
Published: July 2010

Yields of HA (humic acid) and FA (fulvic acid) fractions of mushroom phenolase‐catalyzed humic acid‐type polymers varied considerably. The higher yields from 4 g of phenol mixture alone or with 1 g of various amino acids, glucosamine, or protein; and with 150 to 300 mg of phenolase varied from 1.5 to 2.5 g with about equal amounts in both fractions. As determined by use of 14C‐labeled compounds, about 33% of the ferulic acid; 55% of catechol; 5 to 14% of glycine, lysine, and glucosamine; 50% of cysteine; and 100% of the protein present in the reaction mixtures were recovered in the ploymers. Using an adaptation of the peroxidase — H2O2 method for preparing model lignins the yields of humic polymers were more consistent, varied from 2.5 to 3.5 g, and about 80% of each polymer was recovered as HA. Also about 77% of the ferulic acid; 95% of catechol; 23 to 34% of glycine, lysine, and glucosamine; 63% of cysteine; and essentially all of the protein present in the reaction mixtures were recovered in the polymers. All model polymers were resistant to biodegradation in the soil. During 12 weeks 4 to 8% of benzene ring carbons and 8 to 25% of ferulic acid side group, amino acid, glucosamine, and protein carbons were evolved as CO2.
Plant Effects on Soil Manganese Availability
Authors: Godo Gnahoua H. , Reisenauer H. M.
Published: July 2010

Relationships differ greatly between soil Mn solubility and pH, between plant uptake of Mn and soil pH, and between plant uptake of Mn and nutrient solution pH. The discrepancies suggest that soil Mn availability is controlled by neither soil nor plant characteristics per se but by the combined effects of soil properties, plant characteristics, and the interactions of plant roots and the surrounding soil.

Experiments were done to evaluate the contributions of root/soil interactions, specifically those of root exudates, to Mn availability. The solubility of soil Mn and of MnO2 in root exudates and in rhizosphere and bulk soils was measured over the pH range of 4.5 to 6.5. The relationships between pH and MnO2 solubility in solutions of root exudates and selected root exudate components closely resembled those between plant uptake of Mn and soil pH. Similarly, the relationship between CaCl2‐soluble Mn in the rhizosphere soil and soil pH resembled that between plant uptake of Mn and soil pH. The pattern with pH of the CaCl2‐soluble Mn of the bulk soil was that of soil alone and fell below that of the rhizosphere soil. These relations establish that root exudates make an important contribution to plant uptake of soil Mn. Exudate compounds, such as hydroxy‐carboxylates, increase soil Mn solubility through reducing MnO2 and complexing the divalent Mn released. The effect is particularly marked in systems more acid than pH 5.5 and explains many of the apparent anomalies of soil Mn availability.
Utilization of Fertilizer Nitrogen‐Nitrogen‐15 by Field‐grown Alfalfa
Authors: Feigenbaum Sala , Hadas Aviva
Published: July 2010

Although legumes are usually not fertilized with N, response of irrigated alfalfa (Medicago sativa L.) to N fertilization has been observed frequently. More precise information is required, however, on the time and extent of the fertilizer‐N utilization by alfalfa and its distribution in the soil.

Uptake of ammonium fertilizer by alfalfa, its rate of nitrification and its recovery in a clay and sandy soil, were studied under field conditions using labeled ammonium sulfate as a fertilizer source. The fertilizer, enriched to 10.28 atom % 15N, was applied to microplots, with and without plants, in a commercial alfalfa field at a rate of 100 kgN/ha. Plant tops were analyzed for total N and soil samples for mineral N. Excess 15N content in plants and soil was also determined.

Alfalfa recovered 40 to 45% of the applied fertilizer during the whole growth period on both soils, but in the first cut the recovery was higher in the sandy than in the clay soil. The 15N atom % in the alfalfa indicated a large effect of fertilizer on N uptake in the first two cuts only.

The decrease in NH4‐15N recovery in the soil with time during the first 20 days after fertilization was exponential, indicating first‐order kinetics of the nitrification process. The rate constant was 0.13 day−1 and the half‐life of ammonium in the field was 5 days, which is considerably faster than reported in the literature for laboratory incubation experiments at similar temperatures.
Extraction of Phosphatase, Urease, Proteases, Organic Carbon, and Nitrogen from Soil
Authors: Nannipieri Paolo , Ceccanti Brunello , Cervelli Stefano , Matarese Emilio
Published: July 2010

Extractions of three soils at different incubation times demonstrate that 0.14M sodium pyrophosphate at pH 7.1 extracts phosphatase, urease, casein, and benzoylarginamide hydrolyzing proteases. Extraction yields of phosphatase and casein‐hydrolyzing proteases are remarkably high. The most efficient length of extraction depends both on the type of soil and on the selected enzyme.

Correlation analyses of extracted enzymes and extracted C and organic N content generally show a significant correlation (p = 0.05 and 0.01).
Predicting the Most Efficient Phosphorus Placement for Corn
Authors: Anghinoni I. , Barber S. A.
Published: July 2010

Yield increase from P fertilizer application depends on the efficiency of utilization of the added P. Placing added P in part of the soil volume rather than mixing it with all the soil may increase P uptake because of less tie‐up of P by the soil, however, the degree of benefit from P placement has been difficult to predict. The objective of this paper is to use data from P placement experiments with corn (Zea mays L.) together with a simulation model to develop a procedure for estimating the P placement that will maximize P recovery and plant yield. The Claassen‐Barber simulation model gave predicted P uptake by corn that compared favorably with observed P uptake and hence was used in this study. The model uses parameters describing root growth and morphology, kinetics of P uptake, and kinetics of P supply by the soil. Measurements of corn root growth as affected by P placement, of P influx into corn roots as influenced by P concentration, and of soil P supply as affected by rate of P addition to three soils were used to provide data to use in the simulation model. Predicted P uptake by corn was calculated for a range of fractions of the soil volume treated with five rates of added P per pot for two soils and with one P rate on an additional soil. Uptake of P from P‐treated soil was added to uptake from untreated soil to get total P uptake. As the volume fraction of P treated soil increased from zero, calculated P uptake increased to a maximum then decreased with further dilution of added P with soil. The optimum fraction of the soil that had to be P‐treated to get the greatest predicted P uptake increased with rate of application. Where one rate was applied to three soils, the greater the adsorption of P by the soil, the lower the fraction of P‐treated soil needed to maximize P uptake. The principles illustrated in this paper may be useful for developing the most efficient fertilizer placement for crops grown in the field.
Soil Properties and Chemical Composition of Tree Leaves in Southern Indiana
Authors: Crum J. R. , Franzmeier D. P.
Published: July 2010

Soils developed from gray‐green shale in southeastern Indiana and neighboring states have low forest site quality and low productivity for farm crops. In this study the Rarden soil, formed from gray‐green shale, was compared with the Trappist soil (moderately productive), developed from black carbonrich shale, and the Hickory soil (highly productive), developed from Illinoian till. The soils were on westerly‐facing shoulder and backslope landscape positions. Crystals occurring as small patches in the B3 of Rarden were identified as barite (BaSO4) in prismatic, hexagonal‐tabular, or octagonal‐tabular shapes. A pedon of the Rarden soil contained about two‐thirds as much extractable Ba as Ca. Leaves from three hardwood species were analyzed for 15 elements at each site. Flowering dogwood (Cornus florida L.) leaves accumulated Ca and, especially, Al to a much greater extent than sugar maple (Acer Saccharum Marsh) or white oak (Quercus alba L.), whereas sugar maple tended to accumulate Mn. Leaf samples collected in July and September showed no significant differences in concentration of the major nutrient elements P, K, and Ca, but did show differences in concentration of several of the minor nutrients. No evidence was found that Ba or other minor elements caused toxicities or deficiencies. The contents of extractable Ca and Al in the soil were reflected in their concentrations in flowering dogwood leaves.
A Variable‐Depth Ground‐Water Sampler
Authors: Galgowski C. G. , Wright W. R.
Published: July 2010

An inexpensive variable‐depth ground‐water sampler for 4‐cm i.d. PVC well casing is made from readily available materials. The sampler will extract water samples at any selected depth from a shallow aquifer via a perforated well casing without mixing water from different strata. Water samples can be obtained from a depth of about 10 m with standard vacuum equipment.
Estimating Critical Stress in Unsaturated Soils from Changes in Pore Water Pressure During Confined Compression
Authors: Larson W. E. , Gupta S. C.
Published: July 2010

The objective of this study was to describe the changes in pore water pressure as a function of initial soil water content and applied stress. A hypothesis is developed that relates pore water pressure of unsaturated soils during application of applied mechanical stress to changes in soil structure.

During compression of unsaturated agricultural soils, the pore water pressure decreases to a minimum (becomes more negative), and then increases as the applied mechanical stress increases. The pore water pressure‐log applied stress curves for a given soil with different water contents are similar in shape but vary in scale. The degree of water saturation at which minimum pore water pressure occurs appears to be a constant for a given soil. This degree of saturation increases with soil clay content up to about 33% clay and then remains nearly constant at 0.60. The pore water pressure‐log applied stress curves for different water contents of a given soil, when normalized, fit a common curve. For different soils, the log of applied stress corresponding to the minimum pore water pressure, when normalized with respect to the log of stress at saturation, increases with clay content up to about 33% clay and then remains constant at 0.78. It appears that, as the applied stress increases beyond the point of minimum pore water pressure, soil aggregates are sheared and their integrity destroyed. The stress corresponding to the point of minimum pore water pressure is, we think, the maximum stress that should be applied to a soil during cultivation or by vehicular traffic. Finally, this paper describes a procedure for estimating the critical stress for other soils from a soil's clay content using the relationships developed in this study.
Coupling Phenomena in Saturated Homo‐ionic Montmorillonite: IV. The Dispersion Coefficient
Authors: Groenevelt P. H. , Elrick D. E. , Laryea K. B.
Published: July 2010

The movement of NaCl through the clay paste examined in this series of articles is analyzed in terms of dispersion and convection. The dispersion coefficient is proven to be velocity independent, i.e. the “hydrodynamic/lateral diffusion” part of the dispersion coefficient is negligible in comparison to the “molecular‐diffusion” part.

Subsequently the thermodynamic equations for the salt flux and the liquid flux are reformulated for the condition of zero electric current. The salt flux equation is then further transformed in order to conform with the transport equation for the salt commonly used in dispersion studies, such that one recognizes a dispersion term and a convection term. The dispersion coefficient appears to contain an element due to salt sieving. The convection term appears as the product of the volume flux, the equilibrium salt concentration and a term involving the reflection coefficient.
Immobilization of Diammonium Phosphate and Monocalcium Phosphate in Calcareous Soils
Authors: Amer Fathi , Shams M. S. , Awad K. M. , Khalil M. A.
Published: July 2010

Immobilization of monocalcium phosphate (MCP) and diammonium phosphate (DAP) was investigated in an alluvial soil (4.1% CaCO3) and in a desert soil (39% CaCO3). Laboratory experiments were performed to study P solubility in the fertilized soils as affected by wetting and drying cycles and by moisture tension. In addition, the relationship between NH3 volatilization and P solubility was evaluated for DAP, and the agronomic effectiveness of the two fertilizers was tested in a greenhouse experiment. At 4,900 ppm P both fertilizers saturated the alluvial soil during the first 10 cycles with respect to dicalcium phosphate dihydrate (DCPD). The MCP‐treated desert soil was DCPD‐saturated for the first cycle then suffered a sharp decline in soluble P, but maintained DCPD saturation with the addition of organic matter. DAP, on the other hand, failed to saturate the desert soil with DCPD and a negative relationship was obtained between NH3 volatilization and P solubility. In soil columns soluble P increased with depth for DAP while for MCP it was dependent on the moisture tension, the lower the tension the higher the solubility. Greenhouse results were in agreement with the laboratory findings. DAP and MCP were equally effective in the alluvial soil but MCP was superior in the highly calcareous desert soil, especially when combined with organic matter application.
Calculating Cation Exchange in a Salt Transport Model
Authors: Robbins C. W. , Jurinak J. J. , Wagenet R. J.
Published: July 2010

A cation exchange subroutine that can be expanded to include any number of cations was developed and interfaced with a water flow‐salt transport model that also contained a lime and gypsum precipitation‐dissolution chemistry subroutine. The exchange subroutine was required by the complete model to satisfactorily predict EC, SAR, and specific ion concentration changes with time and depth for a gypsiferous and a non‐gypsiferous soil irrigated with waters containing three different CaSO4 concentrations at two leaching fractions. In his sudy, exchangeable Ca, Mg, Na, and K were considered. Exchangeable K was included for use with high exchangeable and soluble K soils and high K irrigation waters. The additional cation exchange coefficient values needed for K exchange and a method for their calculation is given.
Measurement of Fertilizer Phosphorus Residues and Its Utilization
Authors: Spratt E. D. , Warder F. G. , Bailey L. D. , Read D. W. L.
Published: July 2010

A values and sodium bicarbonate (NaHCO3) extraction soil tests were used to determine phosphorus (P) levels over 8 years on four soils which had been treated with 0, 100, 200, and 400 kg P/ha. The tests correlated highly with each other and indicated the decline of residual fertilizer‐P over years as the soils were cropped. Reliable predictions for the duration of the beneficial effects of large amounts of fertilizer‐P could be made for the two Manitoba soils where cropping was continuous (wheat‐flax) but not for the Saskatchewan soils where fallow was included (wheat‐fallow). By using the linear equation of NaHCO3 soil tests vs. time (years), it was predicted that 100, 200, and 400 kg P/ha would last about 6, 9, and 13 years, respectively, before further fertilizer‐P inputs were needed to maintain wheat production. Longer durations were predicted for 200 and 400 kg P/ha when curvilinear relationships were used, averaging 11 and 22 years, respectively, giving better economic feasibility. These soil testing techniques may be used on calcareous soils to minimize current fertilizer‐P inputs for wheat where residual fertilizer‐P has accumulated.
Liming and Lime‐Phosphorus‐Zinc Interactions in Two Nigerian Ultisols: II. Effects on Maize Root and Shoot Growth
Authors: Friesen D. K. , Miller M. H. , Juo A. S. R.
Published: July 2010

Two greenhouse experiments, the first a complete factorial comprising six rates of lime, four of phosphorus (P) and three of zinc (Zn) on two kaolinitic Ultisols, and the second involving factorial combinations of lime at four levels or gypsum at two chemically equivalent levels with three levels of P on one Ultisol, examined lime‐nutrient interactions in the growth of maize (Zea mays L.) shoots and roots in relation to interactions in nutrient availability in the soil.

Strong, highly significant interactions in maize growth were observed on both soils. The lime‐P interaction was positive and occurred only at lime rates less than equivalent to the KCl‐exchangeable Al content. Both total P uptake and root surface area per unit length increased substantially with liming to pH 5.5, but P uptake per unit root surface area was not altered. Total P uptake was linearly correlated with root surface area at each level of applied P and with the product of root surface area and available P, suggesting that the lime‐P interaction was due primarily to the effect of lime on improving root exploitation of available P in the soil.

The third‐order lime × P × Zn interaction was observed at high lime rates in the pH range of 6 to 7. Overliming depressed yields only where Zn was not applied; shoot yields were closely related to Zn activities in soil solution. total P uptake was not reduced by liming soils to neutrality but total Zn uptake was linearly correlated with the product of Zn activity (controlled by soil pH) and root weight (influenced by P nutrition).

Aluminum toxicity was shown to be the primary growth‐limiting factor for maize grown in the two Ultisols under greenhouse conditions. Plants did not respond to gypsum treatments even though tissue concentrations and gross uptake rates of Ca were raised to levels comparable to equivalent lime treatments. Maize shoot yields were closely related to exchangeable Al saturation and total Al concentration in soil solution and declined at levels in excess of 28% and 4 µg/ml, respectively. Maximum shoot yields occurred at comparatively low rates of lime sufficient to raise soil pH to about 5.0 in the fertilized soils.
Decomposition of Aflatoxin in Soil
Authors: Angle J. S. , Wagner G. H.
Published: July 2010

Corn infected by Aspergillus flavus and A. parasiticus is frequently contaminated with aflatoxin. If the contamination exceeds 20 ppb, the corn is considered unfit for animal consumption and is often plowed into the soil. This study was undertaken to determine the fate of aflatoxin in the soil. Aflatoxin B1 was added to soil at a rate of 10,000 ppb. The soil was periodically extracted with acetone, and the quantity and species of aflatoxins were determined using thin‐layer chromatographic procedures. The rate of decomposition was also monitored by adding 14C‐aflatoxin to the soil and periodically measuring the evolution of 14CO2.

Aflatoxin B1 was observed to be rapidly reduced to aflatoxin B2 when added to the soil. The speed of this reaction suggests a chemical mechanism. The resulting aflatoxin B2 decomposed at a much slower rate, declining to a level where it could no longer be detected at 77 days. Aflatoxin G2 was also detected 2 days after the addition of aflatoxin B1 to the soil. Its concentration remained, however, well below that of the other aflatoxins observed. Aflatoxin G2 reached a maximum concentration at 14 days after the addition of aflatoxin B1 to the soil and was no longer detectable at 49 days. Microbial decomposition of 14C‐aflatoxin B1, as measured by CO2 evolution, accounted for 14% of added 14C in 112 days of incubation. When wheat straw or sugar was added to the soil, the amount of aflatoxin C liberated as CO2 was less.
Evaluation of Selected Processes Controlling Nitrogen Loss in a Flooded Soil
Authors: Reddy K. R. , Patrick W. H. , Phillips R. E.
Published: July 2010

The roles of NH4‐N diffusion, NH4‐N oxidation, NO3‐N diffusion, and NO3‐N reduction in controlling N loss from continuously flooded soil were evaluated in independent experiments. Applied NH4‐N moved from zones of high NH4‐N concentration to the zones of low NH4‐N concentration. The average diffusion coefficient (D) for NH4‐N in flooded soil ranged from 0.059 to 0.216 cm2 day−1 for different soils. Diffusion coefficients were influenced by soil type and soil‐water content. Rate of NH4‐N oxidation in the aerobic layer of flooded soil range from 1.2 to 3.5 µg g−1 day−1 in different soils. Nitrate diffusion into the anaerobic soil layer ranged from 0.96 to 1.91 cm2 day−1, whereas NO3‐N reduction rates were 0.32 to 0.52 day−1. The slow rate of NH4‐N diffusion from the anaerobic soil layer to the aerobic soil layer and the slow rate of NH4‐N oxidation in the aerobic soil layer indicate that these two processes are limiting steps in controlling N loss. Nitrate diffusion into the anaerobic soil layer and NO3‐N reduction in the anaerobic soil layer were found to proceed at a faster rate and are not likely to limit N loss from flooded soil.
An Aerobic‐Anaerobic Interactive System for Soil Suspensions
Authors: Hunt P. G. , Matheny T. A. , Parsons J. E. , Campbell R. B.
Published: July 2010

A system was developed that allows for the simultaneous batch study of aerobic and anaerobic soil suspensions. It is a modification of earlier systems that allowed for the investigation of homogeneous suspensions at desired oxidative‐reduction potentials. This system allows for the contents of aerobic and anaerobic reaction vats to be mixed at desired proportions by using a peristaltic pump connecting the two systems. A desktop computer‐based data acquisition system is used to control the pumping time and to monitor the redox potential in the respective vats. By using the HP 9825 calculator and the HP‐IB bus, one can program the pumping, based on time, Eh readings, or other monitorable parameters. Gas samples taken from the air space of each unit permits one to study biological and chemical processes as they are affected by interaction of components from aerobic and anaerobic suspensions.
Relation Between pHc and Sodium Adsorption Ratio (SAR) and an Alternative Method of Estimating SAR of Soil or Drainage Waters
Authors: Suarez D. L.
Published: July 2010

The relation between the sodium adsorption ratio (SAR) and pHc derived here predicts SAR of the drainage water (SARdw) better than existing empirical equations. Inaccuracies in SAR estimates from the new relationship can be anticipated by the extent to which the derived conditions are valid. Empirical equations provide no understanding of why they are sometimes inaccurate. Due to the relative insensitivity of SAR to calcium concentrations, SAR predictions of most drainage waters (where Ca ≅ ½ HCO3) are satisfactory when the Ca concentration of the drainage water is assumed to be constant at any fixed PCO2. Prediction of SAR in drainage or soil water in the absence of gypsum precipitation requires knowledge of PCO2, irrigation water composition, HCO3/Ca ratio, and the leaching fraction. SARdw can be simply and accurately calculated from the derived equation and a table accounting for ionic strength and HCO3/Ca ratio.