bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Pyrophosphate on Orthophosphate Reactions in Calcareous Soils
Authors: Amer Fathi , Mostafa H. E.
Published: July 2010

Sodium pyrophosphate (NaPP) is known as a crystal growth inhibitor. Its effect on the kinetics of phosphorus (P) retention by calcium carbonate (CaCO3) and by two calcareous soils was investigated using orthophosphate (OP) solutions ranging in P concentration between 0.1 and 1 × 10−3M. Reaction of the most dilute solution with CaCO3 involved initial rapid adsorption of P followed by a gradual change in solution composition toward equilibration with hydroxyapatite (HAP). For the more concentrated solutions, the P concentration vs. time curves exhibited an initial, rapid adsorption followed by an induction period that preceded a second drop which was proportional to the initial concentration, and finally a gradual decrease toward a solubility equilibrium value. Amounts of P removed during the initial drop were close to the calculated Langmuir adsorption maximum. The second drop in P concentration was presumed to reflect precipitation involving growth of calcium phosphate nuclei adsorbed on the CaCO3 surface. Behavior of a desert soil (39% CaCO3) was quite similar to that of CaCO3, while the precipitation reaction was considerably less in an alluvial soil (4.1% CaCO3).

Addition of NaPP at a concentration of at least 2 × 10−5M P increased both the induction period and the final P concentration. Effectiveness of NaPP depended on its addition before the end of the induction period as well as on the pyrophosphate‐to‐orthophosphate ratio. Results obtained with triammonium pyrophosphate on the two soils were similar to those with NaPP.
Reduction and Reoxidation Cycles of Manganese and Iron in Flooded Soil and in Water Solution
Authors: Patrick W. H. , Henderson R. E.
Published: July 2010

Cycles of manganese (Mn) and iron (Fe) reduction and reoxidation were examined in suspensions of Crowley silt loam (a thermic Typic Albaqualf) and in water solutions. In stirred soil suspensions at a constant pH of 7.0, the redox potential was varied stepwise from reducing conditions to oxidizing conditions and then stepwise back to reducing conditions. For 50‐mV incremental changes in redox potential, similar redox potential‐pH curves were obtained for the oxidizing half of the cycle and for the reducing half of the cycle when a 2‐week incubation period at each controlled redox potential was used. A 1‐week incubation period did not result in completion of the oxidation and/or reduction reactions, and the curves obtained during oxidation did not coincide well with those obtained during reduction.

For soil‐free water solutions, the solubility of Mn was governed almost completely by pH with little effect of redox potential being evident. Iron reduction and reoxidation in water solutions were more sensitive to redox potential, especially at pH 5.0 and at pH 6.0. At pH 4.0, Fe remained in solution at all redox potentials. At pH 7.0 and 8.0, little Fe was present as soluble Fe2+ when the redox potential was decreased.
Seasonal Patterns of Growth and Soil Nitrogen Uptake by Rice
Authors: Moore P. A. , Gilmour J. T. , Wells B. R.
Published: July 2010

In order to model growth and nitrogen (N) uptake by the rice plant as well as improve nitrogen fertilizer management, a description of the temporal behavior of nitrogen in a flooded soil cropped to rice is needed. The objective of this study was to characterize the seasonal changes in soil, water, and plant nitrogen in a flooded rice culture. Lebonnet rice (Oryza sativa L.), a short‐season variety, was grown on a Crowley silt loam soil (a fine, montmorillonitic, thermic Typic Albaqualf). Twelve plots were established utilizing a randomized complete block design with six controls, and six receiving 130 kg N/ha as urea in a three‐way split. Amounts of inorganic soil nitrogen, as well as nitrogen uptake and dry matter production by the different plant fractions, were monitored at weekly intervals for 13 weeks.

Nearly 90 % of the preflood application and 95 % of all subsequent inorganic N peaks were exchangeable NH4‐N until the flood was removed. Although the preflood nitrogen application was accounted for in the soil, the midseason applications were virtually undetected. An increase in inorganic soil nitrogen occurred later in the season which was thought to be due to the decomposition of rice straw or algae. In the fertilized plants, 35% of the total dry matter production at harvest was found in the dead tissue, with 31% in the active‐vegetative tissue and 34% in the reproductive tissue. Dry matter production for control plants was 23, 34, and 43% of the total, respectively, for the dead, active‐vegetative, and reproductive tissues. Nitrogen concentrations in fertilized plants were significantly higher than controls until after tillering. Active‐vegetative tissues in fertilized and control plants showed decreases in N concentration with time, while reproductive and dead tissue nitrogen concentrations remained relatively constant after the initial sample dates. Patterns of N uptake were similar to dry matter production. Sixty kg of N per hectare accumulated in control plants and 150 kg of N per hectare in fertilized plants. At harvest, 23, 28, and 49% of the total nitrogen uptake was in the active‐vegetative, dead, and reproductive tissues of the fertilized plants, respectively. In control plants at harvest, 25, 16, and 59% of the uptake was in the active‐vegetative, dead, and reproductive tissues, respectively. In a plot of plant N vs. soil N, the efficiency of N fertilizer use was 55% for the preflood fertilizer application. A relationship was found to exist whereby N in the reproductive tissue increased as the inverse of the N in the active‐vegetative tissue increased.
A Trickle Irrigation System for Frequent Application of Nitrogen to Experimental Plots
Authors: Hairston J. E. , Schepers J. S. , Colville W. L.
Published: July 2010

The purpose of this study was to design a trickle irrigation system which could be used for frequent applications of nitrogen (N) to experimental plots. This type of system is not practical on a large scale for field crops but could be useful in determining rates and time intervals applicable on a much larger scale for specific soils. Two distribution patterns were compared, and a free‐cycling manifold system used in 1976 proved to be superior. Most field research is not conducted on perfectly level land and, according to this study, a free‐cycling manifold system is essential to minimize the effects of hydraulic pressure differences between various plots, rows within plots, or both, at different elevations. Nitrogen distribution is otherwise too erratic to produce statistically different results among treatments.
Effect of Manure and Irrigation on Sodium Bicarbonate‐Extractable Phosphorus
Authors: Pratt P. F. , Laag A. E.
Published: July 2010

Data for the NaHCO3‐extracted P in soil samples taken at the end of a 4‐year field experiment on a Hanford sandy loam (Typic Xeror‐thent) are presented. The main variables consisted of six rates of manure combined with two rates of irrigation water. The extractable P in the 0‐ to 0.3‐m depth increased for all manure rates. At the 0.3‐ to 0.6‐m and 0.6‐ to 0.9‐m depths, increases were found for only the highest rates. At the 0.9‐ to 1.2‐m depth there was a statistically significant increase only with the highest rate for the low irrigation treatment. The extractable P was consistently lower in the 0‐ to 0.3‐m depth for the high irrigation. At the lower depths there was a suggestion of higher extractable P with the high irrigation, but this effect was not consistent. The P in a fresh liquid manure appeared to move more readily into lower soil depths than a solid corral weathered material.
Phosphorus‐Enriched Soil Nodules Detected by Energy‐Dispersive X‐ray Spectrometry
Authors: McKeague J. A.
Published: July 2010

Marked enrichment in phosphorus (P) was found in 22 of 160 iron (Fe)‐rich soil nodules analyzed by scanning electron microscopy along with energy‐dispersive x‐ray analysis (SEM‐EDXRA). Estimated P levels of 10% occurred in certain areas of some nodules, and levels of 2 to 5% were common. Most of the P‐rich nodules occurred in mottled albic horizons overlying argillic horizons of imperfectly or poorly drained soils, but some were in C horizons.
Parent Materials and Paleosols in the Teays River Valley, Ohio
Authors: Thompson Michael L. , Smeck Neil E. , Bigham Jerry M.
Published: July 2010

Soils in the preglacial Teays River Valley of southern Ohio were studied to identify their parent materials and to investigate the presence of paleosols. At each of four sites, soils formed partly in a mantle identified as loess. The loess mantled the landscape to a uniform depth of 50 to 60 cm and was characterized hy 45 to 50% medium silt on a clay‐free basis as well as by Ti/Zr values of 10 to 12 in the total silt fraction. At sites near the old valley walls, the sola extended into colluvium. At sites near the center of the valley, the sola extended into silty alluvium or colluvium. Clay‐free particle‐size profiles and total silt Ti/Zr values generally supported the field identification of a lithologic discontinuity between the loess and underlying material. Finally, the soils were underlain by a third material: either lacustrine clay (Minford Clay), old alluvium (Gallia Sand), or weathered sandstone bedrock, depending on position in the valley.

Paleosols were developed in materials underlying the loess. In the field, paleosols were identified by continuous argillans on ped surfaces. Laboratory determination of total clay revealed the presence of two argillic horizons in the soils: (i) in the loess (22 to 26 % clay), and (ii) in the underlying materials (27 to 35% clay). More intense mineral weathering in the paleosol compared to overlying or underlying horizons was indicated by its higher ratios of mica weathering products to mica in the clay fractions, higher exchangeable Al, and lower K/Zr values in the fine silt fractions. The presence of a paleosol in one pedon was supported by two subsurface accumulations of amino acid nitrogen.
Growth Response of Young Douglas‐Fir to Repeated Application of Nitrogen and Phosphorus
Authors: Steinbrenner E. C.
Published: July 2010

A heavily thinned (to 200 trees/ha) stand of young Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] in southwestern Washington was treated with repeated applications of nitrogen (N) and phosphorus (P) over the 15‐year period from 1955 to 1969. Nitrogen treatments resulted in a 20‐year growth response of 24% over the controls for the lower application rates (1,120‐kg N/ha) and 46% for the higher application rates (2,016‐kg N/ha). All nitrogen treatments combined averaged 40% greater volume growth than controls. Plots that received 1972‐kg N/ha over the first 10 years of the study still showed 25% greater volume growth than the controls after 10 additional years without nitrogen applications. Phosphorus applications, either alone or in combination with nitrogen, did not increase tree growth rates.
Fallow Tillage Effects on Evaporation and Seedzone Water Content in a Dry Summer Climate
Authors: Hammel J. E. , Papendick R. I. , Campbell G. S.
Published: July 2010

Early fall establishment of winter wheat is essential for high yields and erosion control following fallow in the Pacific Northwest, USA. Successful early stands require tillage management that minimizes water loss from the seedzone during the relatively dry summer. A numerical model was developed to investigate the dynamic aspects of heat and water flow in the upper soil layers with emphasis on effects of conventional tillage fallow and no‐till (chemical fallow) on these processes and ultimately the seedzone water content. After 15‐day simulations used to verify the model with measured values of meteorological variables and soil properties, predicted and measured water content distributions across the seedzone generally agreed within 0.01 kg/kg. Exclusion of thermally induced vapor flow from the model gave a higher predicted evaporative water loss and poorer agreement between measured and simulated soil water content distributions. The values for characterizing the atmospheric boundary layer resistance were also critical for correctly simulating soil temperature and water content profiles. Evaporative water loss for no‐till over a 90‐day simulation period using measured meteorological inputs was 70% higher than for conventional tillage, resulting in water contents in the seedzone that were too low for successful stand establishment under chemical fallow. Thus, for the climatic conditions and the soil studied here, some tillage may be necessary for retention of adequate seedzone water for early fall‐winter wheat establishment.
Nonmicrobial Nitrite‐to‐Nitrate Transformation in Soils
Authors: Bartlett Richmond J.
Published: July 2010

Nitrate formation in soils equilibrated with nitrite at 0.5° C was directly related to soil level of reactive managanese (Mn) oxides. It was demonstrated that synthetic Mn oxides can oxidize nitrite to nitrate and become reduced in the process. Nitrite oxidation, nitrate formation, and MnO2 reduction were stoichiometrically related reactions in the presence or absence of atmospheric O2. Nitrite reduced Mn(IV) to either Mn(II) or Mn(III), but when MnO2/nitrite ratios were high, reduction to Mn(III) appeared to predominate. This mechanism of nonmicrobial conversion of nitrite to nitrate may explain why nitrite seldom accumulates in soils, even when Nitrobacter numbers are low and conditions for their growth are unfavorable.
Kinetic Model for Phosphate Transport and Transformation in Calcareous Soils: I. Kinetics of Transformation
Authors: Enfield Carl G. , Phan T. , Walters David M. , Ellis Roscoe
Published: July 2010

Phosphorous in concentrations exceeding those generally observed through agricultural activities has been encountered at land application wastewater treatment sites. To predict the environmental impact of these systems, a model was developed to describe the reaction of orthophosphate with mineral soils. The model is based on instantaneous reversible absorption theory plus time‐dependent solubility theory. It was assumed, in the model, that first‐order kinetics would adequately describe the formation or dissolution of phosphate minerals. Statistical regression analyses were performed on batch sorption data for 14 mineral soils where two equilibrium compounds were considered. The two compounds considered were hydroxyapatite (Ca10HPO4·2H2O) and dicalcium phosphate dihydrate (CaHPO4·2H2O). Comparisons of correlation coefficients between this model and previous models using a common data set indicate the current model with a mean correlation coefficient of 0.93 is more accurate in describing phosphate reactions in calcareous soils than earlier models with mean correlation coefficients ranging from 0.75 to 0.91.
Kinetic Model for Phosphate Transport and Transformation in Calcareous Soils: II. Laboratory and Field Transport
Authors: Enfield Carl G. , Phan T. , Walters David M.
Published: July 2010

A first‐order kinetic model was employed to predict, for selected soils, the response of the soil to phosphorus (P) applied in solution with 0.01M CaCl2 in the laboratory, and the response of P in municipal wastewater at two rapid infiltration wastewater treatment systems. The one‐dimensional steady‐state hydraulic model appears to accurately predict (±50% of estimate) both the concentration of P in the solution phase as well as the accumulation of P in the solid phase.
Thermodynamics of Potassium Exchange in Soil Using a Kinetics Approach
Authors: Sparks D. L. , Jardine P. M.
Published: July 2010

Thermodynamics of potassium (K) exchange using a kinetics approach was investigated in Ca‐saturated samples from the Ap and B21t horizons of a Matapeake soil from Delaware. Kinetics of adsorption and desorption were determined at temperatures of 0, 25, and 40°C on each soil horizon using a miscible displacement technique. Energies of activation for adsorption and for desorption (Ea and Ed, respectively) ranged from 3.83 to 5.52 kcal mol−1. The Ed values were higher than the Ea values, indicating that more energy was needed to desorb K than to adsorb K. Thermodynamic and pseudother‐modynamic parameters were determined using Gibbs' and Eyring's reaction rate theories. The free energy for K exchange (ΔG°) values were negative (ranging from 1,155 to 1,294 cal mol−1) and increased with increasing temperature. The free energy of activation values were higher for K desorption (ΔGd‡) than for K adsorption (ΔGa‡), suggesting a greater free energy requirement to desorb K. The excellent agreement between ΔG° calculated from Gibbs' theory and from Eyring's reaction rate theory indicated that pure thermodynamic parameters could be calculated using a chemical kinetics approach. The enthaply (ΔH°) values were exothermic and indicated stronger binding of K+ ions in the B21t horizon than in the Ap horizon of the Matapeake soil. The latter was related to the difference in external surface‐to‐interlayer surface‐charge ratio in the two horizons. The enthalpy of activation (ΔH‡) values in both horizons were higher for desorption (ΔH‡d), than for adsorption (ΔHa‡), suggesting the heat energy required to overcome the K desorption barrier was greater than for that of K adsorption.
Characteristic Variations in Reflectance of Surface Soils
Authors: Stoner E. R. , Baumgardner M. F.
Published: July 2010

Surface soil samples from a wide range of naturally occurring soils were obtained for the purpose of studying the characteristic variations in soil reflectance as these variations relate to other soil properties and soil classification. A total of 485 soil samples from the U.S. and Brazil representing 30 suborders of the 10 orders of Soil Taxonomy was examined. Spectral bidirectional reflectance factor was measured on uniformly moist soils over the 0.52 to 2.32 µm wavelength range with a spectroradiometer adapted for indoor use.

Five distinct soil spectral reflectance curve forms were identified according to curve shape, the presence or absence of absorption bands, and the predominance of soil organic matter and iron oxide composition. These curve forms were further characterized according to genetically homogeneous soil properties in a manner similar to the subdivisions at the suborder level of Soil Taxonomy. Results indicate that spectroradiometric measurements of soil spectral bidirectional reflectance factor can be used to characterize soil reflectance in terms that are meaningful to soil classification, genesis, and survey.
Soluble Salt Concentrations in Runoff Waters from Soils Previously Cropped to Rice
Authors: Gilmour J. T. , Marx D. B.
Published: July 2010

Soluble salt damage to rice in Arkansas has been evident in recent years. In order to adequately model salt balances for Crowley silt loam soil (Typic Aibaqualfs) cropped to rice (Oryza sativa L.) and soybean (Glycine max L. Merr.) in the Grand Prairie region of Arkansas, a description of soluble constituents in runoff water was needed. Three fields were monitored for soluble salts in runoff and irrigation water as well as runoff volume. As cumulative runoff increased, a logarithmic decline in the concentration ratio of runoff water salt concentration to irrigation water salt concentration was found for electrical conductivity (EC), Ca, Mg, Na, SO4, and Cl for the first 10 cm of runoff after removal of the rice floodwater. The equation in which the logarithm of the concentration ratio was the dependent variable and cumulative runoff was the independent variable had a common slope among fields for the solution variables studied. A common intercept was found for Ca and Na but not for EC, Mg, SO4, and Cl. A second linear relationship was developed where the intercept in the above for SO4 and Cl was found to be a function of irrigation water concentration. At one field where sufficient data were available the concentration ratio stabilized after 10 cm of runoff and could be predicted using the concentration ratio equation where cumulative runoff was set at 10 cm.
Ammonia Volatilization from Lime Urea Ammonium Nitrate Suspensions Before and After Soil Application
Authors: Winter K. T. , Whitney D. A. , Kissel D. E. , Ferguson R. B.
Published: July 2010

Limestone suspensions provide a means of uniformly applying finely divided liming materials to raise soil pH. Water has usually been the suspending medium, but N fertilizer solutions may be used.

The objective of this research was to measure ammonia (NH3) losses that might occur while a lime and urea‐ammonium nitrate (UAN) suspension is being prepared and potential losses after the suspension is applied to soil.

Ammonia volatilization was measured in the laboratory from lime‐UAN suspensions formulated with lime sources containing various amounts of CaO. Suspension pH's, rates of loss, and total NH3 losses were directly proportional to the CaO content of the lime material and ranged up to approximately 90% of the ammoniacal fraction of the UAN after 4 hours. Losses were not influenced greatly by the initial pH of the UAN materials used in the study.

Ammonia volatilization from the surface of two acid soils was also measured after lime‐UAN suspensions were applied at a rate of 840 kg/ha effective calcium carbonate [CaCO3; (ECC)] and 112 kg N/ha. Lime applied with the UAN increased NH3 volatilization, but less on Grundy sicl (Aquic Argiudoli) than on Parsons sil (Mollic Albaqualf) with a lower cation exchange capacity (CEC). Up to 17% of total N was lost with the lime‐UAN treatments on Parsons soil with a CEC of 10.2.

Results indicate substantial losses of NH3 may occur while lime‐UAN suspensions are being prepared only if the lime contains CaO. After soil application, NH3 losses can occur in the absence of CaO if the lime‐UAN is allowed to remain on the soil surface.
Wetting Moisture Characteristic Curves Derived from Constant‐rate Infiltration into Thin Soil Samples
Authors: Perroux K. M. , Raats P. A. C. , Smiles D. E.
Published: July 2010

Although procedures are available for obtaining the wetting moisture characteristics of soils, they often involve lengthy equilibration periods. A simple and quick laboratory method is described for obtaining the wetting moisture characteristic using constant flux infiltration into a thin section of soil. A theoretical analysis of the process is tested by comparing predicted and observed times for pressure heads to develop in a fine sand sample. The technique is demonstrated using a fine sand, a loam, and a silty clay loam, and comparison is made with data obtained by other methods.
Trace Metal Chemistry in Arid‐zone Field Soils Amended with Sewage Sludge: II. Comparative Study of the Fulvic Acid Fraction
Authors: Sposito Garrison , Holtzclaw Kenneth M. , LeVesque C. S. , Johnston Cliff T.
Published: July 2010

The elemental composition, infrared spectrum, and proton titration curve were determined for (i) the fulvic acid fraction of a Domino soil which had received applications of composted sewage sludge for three years in a field experiment, and (ii) a commercially available fulvic acid extracted from a spodosol. Data showed that the Domino fulvic acid more resembled a typical sludge‐derived fulvic acid than a fulvic acid extracted from natural soil organic matter. The distinguishing features of the Domino fulvic acid which led to this conclusion were: (i) a high total sulfur (S) content and the presence of sulfonyl groups, (ii) a significant content of anionic surfactants and S‐containing amino acids, (iii) a low glucosamine/galactosamine ratio, and (iv) more than two classes of acidic functional groups. However, the Domino fulvic acid had a much larger content of carboxyl and other acidic functional groups than a typical sludge‐derived fulvic acid, evidently because of partial oxidation of the sludge in the Domino soil.
Stabilization and Incorporation into Biomass of Phenolic and Benzenoid Carbons during Biodegradation in Soil
Authors: Kassim Ghiath , Stott Diane E. , Martin J. P. , Haider K.
Published: July 2010

The biodegradation, incorporation into biomass, and stabilization in humus of specific carbons of ferulic, p‐hydroxycinnamic, anisic, and benzoic acids and catechol were followed in Steinbeck loam (pH 5.0) and Greenfield sandy loam (pH 7.0). Biomass was estimated by the fumigation procedure. The least incorporation into biomass was noted for the three‐side chain carbon of ferulic acid (1.0 to 1.4%) and the greatest for the two‐side chain carbons of either ferulic or p‐hydroxycinnamic acids (10.9 to 17.6%). Greater amounts of carbon were evolved as carbon dioxide (CO2) and incorporated into the biomass in the acid soil than in the neutral soil. Approximately 74% of the ring carbons of catechol were stabilized in the neutral soil after 12 weeks but only 2% of that was in biomass. The amount of residual carbon found in the biomass decreased with time. The amount of residual ring‐carbons of anisic and benzoic acids incorporated into the biomass were 19 and 15%, respectively. As the substrate concentration increased from 1 to 10,000 ppm, the carbon released as CO2 from ferulic acid and glucose ranged from 47 to 85% and from 63 to 85%, respectively. The residual ferulic acid and glucose carbons in biomass ranged from 2.2 to 11% and 19 to 39%, respectively. The study indicated that relatively higher amounts of the phenolic carbons were stabilized in the soil humus while greater amounts of the glucose carbons were incorporated into the soil biomass, and that compared to glucose, greater amounts of the residual carbons of the phenolic compounds were not solubilized by 6N HCl hydrolysis.
Phosphorus Accumulation and Toxicity in Leaves in Relation to Zinc Supply
Authors: Loneragan J. F. , Grunes D. L. , Welch R. M. , Aduayi E. A. , Tengah A. , Lazar V. A. , Cary E. E.
Published: July 2010

The relationship of zinc (Zn) deficiency to phosphorus (P) toxicity was examined in ‘Emerald’ okra [Abelmoschus esculentus (L.) Moench] grown for 21 days (D21) in complete nutrient solution and then transferred to treatments with two levels of P (P1, P2 = 250, 2,000 µM P) and four levels of Zn (Zn1, Zn2, Zn3, Zn4 = 0, 0.25, 1, 2 µM added Zn).

No symptoms of “little leaf” or “rosetting” developed in any plants. “Mottle leaf” symptoms developed as chlorotic and necrotic patches in the interveinal areas of the older leaves of Zn1 plants at P1 and in Zn1, Zn2, and Zn3 plants at P2. Thus, increasing the level of P induced symptoms which were eliminated by adding Zn.

Treatments had little effect on dry matter at D45 and D63: at D111, low Zn depressed dry weight of P1 tops and even more markedly depressed dry weight of P2 tops, roots, and fruits.

Increasing solution P increased the concentration and amount of P in all plant parts at all harvests. At D45 it also depressed Zn concentrations in all parts of Zn1 plants but in no other Zn treatment and in no treatment at later harvests.

At Zn1, leaves had relatively low concentrations of Zn and high concentrations of P. Increasing levels of Zn enhanced their Zn concentrations and depressed their P concentrations; at D45 and D63 they also depressed the concentrations and total amounts of P in tops and whole plants but increased them in roots. Thus Zn deficiency markedly enhanced P absorption by roots, transport to tops, and accumulation in leaves.

Concentrations of magnesium in plant organs responded to treatments in the same way as did P but to a smaller degree, particularly in the leaves. No other element measured (Ca, K, Na, Fe, Cu, Mn) responded in the same way.

The development and intensity of symptoms in old leaves correlated closely with P concentrations. Leaves with faint symptoms had 0.8% P; those with marked symptoms had > 1.5% P; and dead leaves had nearly 5% P. The intensification of symptoms is attributed to accumulation of P to toxic levels in leaves.

It is suggested that Zn deficiency interferes with P metabolism enhancing the amounts of P absorbed by roots and transported to tops: under conditions of high P supply, P accumulates to toxic levels in leaves inducing or accentuating symptoms resembling Zn deficiency. This effect of Zn on P metabolism in roots seems to explain previously puzzling observations in which P treatments enhanced symptoms of Zn deficiency without any reduction in Zn contents of plant tops: there is no need to invoke any effect of P in inactivating Zn in leaves.
Quantification of Soil Loss and Sediment Produced from Eroded Land
Authors: Lewis D. T. , Lepele M. J.
Published: July 2010

Soil eroded from slopes and sediment added to stream systems as non‐point pollution from a small watershed in southeastern Nebraska were quantified. The watershed studied was within delineation of severely eroded loessial soils. Calculations of soil loss were based on horizonation and clay distribution in eroded pedons as compared to slightly eroded pedons in the same soil series. Thickness and areal extent of soil loss were used to calculate weight and volume of soil moved from the slopes as well as volume and weight of sediment that remained near its source on the landscape. Amount of soil eroded minus that remaining in local storage suggested an amount added from the watershed as non‐point sediment pollution in streams. The method described suggests a way in which soil survey mapping units may be characterized in order to quantify the amount of sediment in storage on the landscape and in stream systems due to past erosion of agricultural land.
Quality Parameters of Spring Wheat and Forage Crops Related to Topsoil and Subsoil Thickness
Authors: Power J. F. , Ries R. E. , Sandoval F. M.
Published: July 2010

Numerous factors affect the composition and quality of crops. One of these factors is soil thickness, which can affect quantity of nutrients available, availability of water, and rooting depth. This experiment was conducted in North Dakota to determine the effects of variable thicknesses of topsoil and subsoil over sodic mine spoils on nitrogen (N) and phosphorus (P) concentrations in blue grama and side oats grama (Bouteloua gracilis and Bouteloua curtipendula), crested wheatgrass (Agropyron desertorum), alfalfa (Medicago sativa), and hard red spring wheat (Triticum aestivum). Milling and baking qualities of spring wheat were also evaluated. Total phosphorus concentration in most crops was not consistently affected by subsoil thickness; however, total P in plant material was usually greatest when subsoil was covered with either 20 or 60 cm of topsoil. Mixing subsoil and topsoil in a 3:1 ratio frequently gave plant P concentrations almost as low as for treatments of no topsoil over subsoil. A notable exception was alfalfa.

Plant nitrogen concentration tended to decrease as subsoil thickness increased. Much of this decrease may have resulted from simple dilution, since total plant growth generally increased as total soil thickness increased to 90 to 120 cm. Except for alfalfa, N concentration was greater in all crops produced on 20 to 60 cm of topsoil over subsoil than on plots with no topsoil or subsoil and topsoil mixed.

Generally, milling and baking properties of the wheat grain were closely related to the grain N concentration. Based on several parameters of milling and baking quality, flour from wheat produced on plots with 20 or 60 cm of topsoil generally was superior in milling and baking properties to flour from wheat on plots with no topsoil or with subsoil and topsoil mixed.

In general, presence of topsoil affected crop quality by enhancing nutrient uptake by the plant. On the other hand, increased subsoil thickness often increased rooting depth and water availability, resulting in increased plant growth and, consequently, dilution of nutrient concentrations in the crops produced.
Subsidence and Erosion of a Histosol
Authors: Parent L. E. , Millette J. A. , Mehuys G. R.
Published: July 2010

The usual model of Histosol subsidence emphasizes the influence of the water table level on peat shrinkage and biochemical oxidation. It predicts a decrease in subsidence rate with time. However, erosion may increase the rate of subsidence significantly. The long‐term subsidence rate of the Histosol under study, where vegetable crops were grown yearly, was estimated at 2.06 ± 0.35 cm/year between 1936 and 1974. In 1974, part of the fields was sown in oats, as a conservation measure, whereas a windbreak was removed in 1976 and unusual meteorological events were recorded in 1974 and 1975. Erosion patterns were detected on the portion of the experimental site where there was no conservation measure. Between 1974 and 1978, the subsidence rate was reduced to 0.99 ± 1.59 cm/year in fields protected against erosion but increased to 4.53 ± 2.29 cm/year in unprotected fields. The decrease in subsidence rate predicted by the model was observed only in fields protected by conservation measures. Consequently, subsidence and erosion should be estimated separately for modelling adequately the subsidence process as a whole.
Portable Hand‐Operated Soil Core Sampler
Authors: Chong S. K. , Khan M. A. , Green R. E.
Published: July 2010

A simple sampling apparatus was developed to take soil cores for characterizing soil‐water relations. A portable steel frame, which is anchored to the soil surface by the operator's weight and by stakes driven into the soil, provides support for a hand‐operated 2‐ton hydraulic jack which pushes the core cylinder into the soil without impact or vibration. The method is labor‐intensive but provides highquality soil cores.
Water Adsorption and Swelling of Clay Minerals in Soil Systems
Authors: Parker J. C. , Amos D. F. , Zelazny L. W.
Published: July 2010

Volume changes of undisturbed (U) samples of Poplimento and Iredell B2 horizons, and of samples compacted at optimum (CO), below optimum (CL), and above optimum (CH) moisture were measured during wetting, drying, and re‐wetting. Poplimento contained 9% montmorillonite and 11% vermiculite while Iredell had 48% montmorillonite and 15% vermiculite on a whole‐soil basis. During the initial wetting of Poplimento samples, variations in volume change between treatments were small. This suggests that changes in soil structure with increasing moisture during compaction counteracted normal moisture‐dependent differences by reducing space for expansion into larger voids or by increasing expansion from entrapped air pressures, strain relaxation, and differential strain. Compacted Iredell samples displayed an inverse relationship between moisture at compaction and swelling during the first wetting. Undisturbed Iredell samples exhibited considerably less expansion than compacted samples.

Expansion during the second wetting followed the order U ≃ CO ≃ CH > CL for Poplimento and CO > U ≃ CH > CL for Iredell. Swelling attributable to entrapped air pressures accounted for 59, 50, 39, and 8% of the total expansion for U, CL, CO, and CH Poplimento samples and for 23, 13, 27, and 22% of similarly treated Iredell samples. These values do not appear to reflect the inverse relationship between entrapped air pressures and probable pore size which is suggested by the Laplace equation. Rate of water uptake and resistance to expansion may explain this discrepancy. Estimated osmotic adsorption accounted for 30, 61, 32, and 31% of the volume change of U, CL, CO, and CH Poplimento samples and 46, 51, 43, and 46%, respectively, for Iredell samples. Intracrystalline swelling accounted for only 3 to 6% of the total expansion in Poplimento and 8 to 9% in Iredell.

The discrepancy between these three components of swelling and measured expansion was taken as an indicator of the magnitude of swelling caused by crystal strain relaxation and differential strains between adjacent crystals or aggregates. These components appeared to increase with increasing compaction moisture for Poplimento, while in Iredell they were unaffected by treatment. For the CL Poplimento sample the sum of these components exceeded the measured swelling suggesting accommodation of osmotic swelling within relatively large pores.
Absorption of Water by Soil: The Effect of a Surface Crust
Authors: Smiles D. E. , Knight J. H. , Perroux K. M.
Published: July 2010

The one‐dimensional absorption of water by a uniform soil through a relatively impermeable surface layer is analyzed using conventional soil physics theory. The analysis permits calculation of the evolution of the water potential on the interface between the soil and the crust, the water content profiles, and the cumulative volume of water absorbed.

In the first instance the approach is tested for situations where the conductance of the crust is constant.

Extensions of the analysis to cases where the conductance is time‐dependent are foreshadowed.
Soil Pore Structural Stability and Irrigation Water Quality: I. Empirical Sodium Stability Model
Authors: Cass A. , Sumner M. E.
Published: July 2010

The use of a unique threshold concentration curve as an indication of soil pore structural stability is questionable. Not only is the choice of a particular value of relative hydraulic conductivity arbitrary but, in addition, the threshold concentration curve does not reveal soil resistance to hydraulic conductivity reductions over a range of solution composition or concentration changes. In order to overcome this deficiency an empirical sodium stability model is proposed which expresses the relationship between the slopes of the threshold concentration curves as a function of the degree of hydraulic conductivity reduction. This model provides a means of evaluating both the susceptibility to hydraulic conductivity reductions and the degree of hydraulic conductivity change as the percolate concentration is altered.
An Improved Technique for Determining Soil Electrical Conductivity‐Depth Relations from Above‐ground Electromagnetic Measurements
Authors: Corwin D. L. , Rhoades J. D.
Published: July 2010

An improved method has been developed for determining the distribution of bulk soil electrical conductivity, ECa, through the soil from electromagnetic measurements taken at the soil surface with the Geonics Limited EM‐38 device. Induced electromagnetic conductivity readings taken with the EM‐38 device's coil configuration oriented parallel and then perpendicular to the soil surface provided sufficient information, when used with equations derived from geophysical instrumentation data, to produce a soil electrical conductivity‐depth profile. The simplicity of this method further enhances the praiticability of the newly developed electromagnetic technique for field measurements of salinity and for saline seep diagnosis.
Bacterial Water Relations Using Polyethylene Glycol 4000
Authors: McAneney K. J. , Harris R. F. , Gardner W. R.
Published: July 2010

The effect of polyethylene glycol (PEG) 4000 on the growth of Arthrobacter crystallopoietes and Escherichia coli was evaluated in succinate‐limited batch culture. Arthrobacter crystallopoietes was little affected by PEG down to −1.5 MPa, and showed optima in both growth rate and cell nitrogen yield around −1.0 MPa, consistent with loss of turgor as the passive mechanistic response of this organism to matric water potential stress. The apparent growth rate (difference between the growth and death rates) of E. coli decreased 70% from 0 to −0.75 MPa, with extinction at −0.8 MPa compared to extinction at −4.0 MPa under salt stress. A relatively constant level of dissimilatory CO2 production independent of PEG (inconsistent with a substantially increased energy requirement for growth under PEG stress), together with microscopic and nitrogen balance evidence of increasing cell death and lysis under increasing PEG stress, indicated that accelerated cell death was a major factor contributing to the reduction in growth rate of E. coli caused by decreasing PEG matric water potential. Volume changes in the cell wall under PEG stress are postulated as interfering with turgor pressure modulation and maintenance of cell integrity by E. coli.

To the extent that PEG is acting purely as an impermeant osmoticum, then over the 0‐ to −1.5‐MPa range, any effect of soil matric water potential on the growth of A. crystallopoietes may be attributed to a solute‐diffusion problem. However, reductions in the soil matric water potential in the < −0.25‐MPa range are predicted to severely repress the growth of E. coli, with growth extinction at about −0.8 MPa, independent of water content‐solute transport considerations.
Mineralization of Nitrogen in Organic Soils
Authors: Reddy K. R.
Published: July 2010

The effect of fluctuating seasonal temperatures on the release of soluble NO‐3‐N, NH+4‐N, soluble organic N (SON), and solube organic C (SOC) into drainage effluent during soil organic matter mineralization was measured on organic soil profiles obtained intact from various locations in Florida. Soil columns were leached once every 25 days, followed by applying a suction of 100 cm. Soil columns were flooded for 25 days each in the months of July and August to simulate normal agronomic practices. Leachate was analyzed for NO‐3, NH+4, SON, and SOC.

The amounts of N mineralized ranged from 410 to 938 kg N·ha−1·year−1 for cultivated soils and 874 to 1,250 kg·ha−1·year−1 for virgin soils. Nitrate accounted for 48 to 81% of the total N in the effluent, while SON accounted for about 16 to 45% of the total N. Remaining 2 to 7% of the total N in the effluent was NH+4. Soluble organic C in the leachate accounted for about 1,795 to 3,516 kg C·ha−1·year−1. Seasonal fluctuations in temperatures had minimal effects on the release of SON, SOC, and NH+4, but the release of NO‐3 was increased with an increase in average daily temperature (9.4 to 30°C) with Q10 values ranging from 1.3 to 1.9. Flooding the organic soils increased the SON and SOC release into the effluents by about two‐fold, compared to drained conditions. Total N loss in 1 year as a result of organic matter mineralization was about 1.3 to 4.2% of the total soil organic N.
Distribution Patterns of Ammonium Nitrogen and 15N Uptake by Rice after Deep Placement of Urea Supergranules in Wetland Soil
Authors: Savant N. K. , De Datta S. D. , Craswell E. T.
Published: July 2010

In‐situ distribution patterns of ammonium nitrogen (NH+4‐N) and 15N uptake by wetland rice (Oryza sativa L.) were studied on the farm of the International Rice Research Institute (IRRI) during the 1979 dry season. Individual 2‐g urea supergranules were placed at 5‐, 10‐, and 15‐cm soil depths in wetland rice plots transplanted at spacings of 20 by 20 cm and 10 by 40 cm. The ammonium (NH+4) concentration gradients near placement sites showed that the NH+4 movement was slow; in the transplanted plots, NH+4 concentrations decreased with time largely due to plant uptake. Distribution patterns of NH+4 were influenced by the depth of supergranule placement and the transplanting geometry. In general, the greater the distance from the point of placement of supergranule to the plant, the slower was the depletion of NH+4‐N at the placement site. During the dry season, the NH+4 almost completely disappeared during the 40 days after transplanting, whereas during the wet season, NH+4 persisted for up to 40 days after transplanting.

The 15N uptake patterns were s‐shaped. During the first 20‐day period after transplanting, deep‐placed N was presumably physically or spatially unavailable, and negligible plant uptake occurred. After 20 days, the 15N uptake was retarded by placement of supergranules at lower depths and away from the rice hills. However, at final harvest more 15N was taken up from urea placed at the 15‐cm depth than from the 5‐cm depth. A marked lower recovery of split‐applied urea‐N (25 to 34%) than that of deep‐placed urea‐N (50 to 61%) was observed.
Spodosols Along the Southwest Oregon Coast
Authors: Nettleton W. D. , Parsons R. B. , Ness A. O. , Gelderman F. W.
Published: July 2010

Twenty‐five Spodosols and Inceptisols under forest were examined. Their climate is moist, marine, and temperate. Winters are cool and wet and summers mostly dry. The soils have some brittle horizons but should not be in duric subgroups. Pellets sand‐size or coarser and thin ortstein horizons are accessory spodic horizon features that may reliably be used for field recognition of spodic horizons. About 90% of these Spodosols can be recognized by morphology alone. The accessory spodic horizon features, however, recognize about 20% more pedons than will pass the chemical tests. Use of the accessory spodic horizon features and the relationship found between geomorphic surfaces and soils increases the quality and rate of mapping. Typic Udipsamments are in late Holocene dunes. Yaquina, an Aquic Haplorthod, is in the winter‐wet, interdune sites on the early Holocene Tenmile surface. Netarts, an Entic Haplorthod, is on summits and side slopes of the stabilized dunes of the next higher surface, Whiskey Run, which formed during the early Holocene and late Pleistocene. Blacklock, on the Pleistocene Pioneer surface, and Joeney, on the Seven Devils surface, are both Typic Sideraquods in ortstein families like most of the soils on these surfaces. The Blacklock and Joeney pedons we sampled are taxadjuncts to their respective series because they have iron/clay ratios of < 0.2.
Distribution of Available Nitrogen in Undisturbed Forest Soil Cores Following Fertilization with Urea and Ammonium Nitrate
Authors: Pang Patrick C. K.
Published: July 2010

Undisturbed soil cores collected from a 31‐year‐old Douglas‐fir (Pseudotsuga menziesii Mirb. Franco) plantation near Shawnigan Lake, B.C., were fertilized with (NH2)2CO (200 and 400 kg N ha−1) and NH4NO3 (200 kg N ha−1) and incubated for up to 5 months at 20°C/12°C (14‐hour day/10‐hour night) with air humidity of 80 to 85%. Cores with the 200 kg N ha−1 rate of fertilization were also given three monthly 24‐hour simulating precipitation treatments followed by incubation, starting 1 month after fertilization. Under conditions with or without precipitation, (NH2)2CO and/or NO‐2 were never detected in soil (forest floor plus mineral horizons) or leachates, and movement of ammonium (NH+4) beyond the forest floor was limited. In the absence of precipitation, a small amount of NO‐3 (9 to 18 µg N g−1 of dry soil) was detected in soil with (NH2)2CO fertilization, whereas up to 124 µg N g−1 of dry soil was detected with NH4NO3 fertilization. Redistribution of nitrate (NO‐3) was limited and approximately 90% of it remained in the forest floor. With precipitation, a NO‐3 concentration of 1 µg N g−1 was detected in soil over the study period after (NH2)2CO fertilization. With NH4NO3 fertilization, a maximum quantity of 32 µg N g−1 of NO‐3 was detected in the forest floor after the first precipitation treatment and only a trace (2 µg N g−1) was detected after the third precipitation treatment. Leaching of NO‐3, though small (10 mg N liter−1), was restricted to NH4NO3 fertilization. The recovery of nitrogenous fertilizers, (NH2)2CO or NH4NO3, as NH+4 plus NO‐3 never exceeded 53% of the amount applied. The incomplete recovery of the fertilizers as inorganic‐N could be due to biological immobilization of N, or interactions of organic matter with unhydrolyzed (NH2)2CO, NH+4 (from urea hydrolysis and NH4NO3 ionization), or NO‐2 (from NH+4 oxidation and NO‐3 reduction).
Long‐term Response to Phosphorus Fertilization on Selected Southeastern Coastal Plain Soils
Authors: Pritchett W. L. , Comerford N. B.
Published: July 2010

Significant response in height, diameter, basal area, and volume growth to phosphorus (P) fertilization at time of planting lasted 17 to 20 years on a variety of sites in northern and western Florida. Ground rock phosphate and the more soluble ordinary superphosphate were equally effective P sources. Comparing the residual fertilizer P in the soil to a long‐term response of slash pine (Pinus elliottii Engelm. var elliottii) helped explain lack of differences in effectiveness of P sources. The largest long‐term slash pine responses were apparent on a poorly drained Ultisol and Inceptisol while the Spodosols were more variable in their response. There were no P responses on well‐to‐excessively‐drained Entisols.