bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temporal Response of Soil Denitrification Rates to Rainfall and Irrigation
Authors: Sexstone Alan J. , Parkin Timothy B. , Tiedje James M. 
Published: July 2010

AbstractThe response of soil denitrification to increased soil moisture was compared in a non‐aggregated sandy loam soil and an aggregated clay loam soil using a soil core technique and the acetylene inhibition method. Elevated field denitrification rates were observed on 9 of 11 occasions on three sites following irrigation or rainfall of > 1 cm water. The denitrification rate in the sandy loam soil increased immediately after water addition and reached a maximum rate within 3–5 h and returned to preirrigation levels within 12 h. A similar, but slower denitrification response occurred in the clay loam soil, requiring 8–12 h before a maximum rate was observed and 48 h before the original background rate was restored. Maximum denitrification rates of 209 and 383 ng N g−1 d−1 occurred following water inputs of 7 and 2 cm in the sandy loam and clay loam soils, respectively. These water additions resulted in air‐filled porosities of 0.37 m3 m−3 in the two soils. Nitrogen losses from the clay loam soil were double that of the sandy loam although the sandy loam received almost twice the water input. This difference was apparently due to the longer duration of the enhanced denitrification rate in the clay loam soil following the increase in the soil moisture. In the two soils 38 and 55% of the total N loss in late spring occurred within 48 h after rainfalls greater than 1 cm. These studies confirm that significant denitrification losses can occur in bursts in response to rainfall, and illustrate that sampling schemes based on integration of denitrification rate measurements must include these episodes to obtain meaningful estimates of N loss. A denitrification response to rainfall was not always the case, however, suggesting that NO‐3 or carbon may also limit nitrogen loss.
Morphological, Physical and Chemical Properties of Major Soils from Calagua in Northwestern Uruguay
Authors: Lugo‐López M. A. , Carnelli Juan P. , Acevedo G. 
Published: July 2010

AbstractVertisols, Alfisols, and Mollisols were identified in a soil survey of the area of Calagua in northwestern Uruguay. They are generally deep, dark‐colored, with well‐developed structure, high in CEC and base saturation, and can hold and supply sufficient amounts of water and nutrients for crops. Most are developed from clay sediments derived from basalt or quaternary mudstones. Most pH values of the surface layers are around 6.0 indicating no apparent danger from either exchangeable aluminum or excess of carbonates. Potassium and phosphorus levels are strikingly low. The soils of Calagua appear to have a great potential for field crops such as rice, sugarcane, and sorghum as well as for horticultural crops such as tomatoes, melons and cabbage. Any program geared to improve crop production in the area must provide for efficient irrigation techniques at critical growth periods, drainage, and the rational use of nitrogen, phosphorus and potassium fertilizers.
Electron Spin Resonance Investigation of Copper(II) Complexation by Soil Fulvic Acid
Authors: Senesi Nicola , Bocian David F. , Sposito Garrison 
Published: July 2010

AbstractElectron Spin Resonance (ESR) spectra are reported and interpreted for Cu(II)‐fulvic acid complexes prepared by mixing Cu(ClO4)2 with a representative soil fulvic acid (FA) at Cu/FA molar ratios in the range 0.02 to 20. The data indicated the formation of anisotropic Cu(II) complexes, the metal cation being immobilized in inner‐sphere coordination with ligands arranged in a distorted octahedral environment. The soil FA showed a high potential binding capacity for Cu(II) added at various ratios in aqueous solution, the ligation being derived from both oxygenated and nitrogenated functional groups. The ESR spectra of the Cu‐FA complexes were investigated under varying conditions, among which were the Cu/FA ratio, treatment with a strongly acidic cation exchange resin, elimination of the solvent by air‐drying, and recording temperature. For the lowest Cu/FA ratio (0.02), calculated ESR parameters suggested the existence of three different coordinating environments for copper ions: (i) 4 O, (ii) 3 O, 1 N, and (iii) 2 O, 2 N. When the Cu/FA molar ratio was increased to 0.2, a small excess of Cu appeared to result in the formation of additional mixed Cu‐H2O‐FA complexes as predominant species. When the Cu/FA ratio was increased beyond 0.2, only a dipolar‐broadened ESR absorption produced by a large excess of Cu2+ aquo‐ions was observable. However, treatment of the Cu‐FA solutions with a cation exchange resin was not only able to reduce excess Cu2+ ions and leave the Cu‐FA complexes nearly unaltered, but also to yield better‐resolved ESR spectra. The ESR spectra of all the Cu/FA solutions after passage through the resin were similar and were characterized by two components consistent with 4 O and 2 O, 2 N coordinating sites for the copper ions. A highly structured pattern in the g region exhibited by the ESR spectrum at the highest Cu/FA ratio was attributed to superhyperfine coupling of the Cu2+ unpaired electron to N‐ligand nuclei. The ESR spectra of dried Cu‐FA solutions not treated with resin were similar to those of the corresponding aqueous solutions, whereas drying the solutions after resin treatment resulted in ESR spectra and spin Hamiltonian parameters consistent with a binding site involving 3 O, 1 N ligand atoms. The implied rearrangements of ligands in the complexes after the removal of water emphasize the importance of soil relative humidity to the Cu(II) complexation mechanisms of fulvic acid.
Fertilizer Nitrogen and Residual Nitrate‐Nitrogen Effects on Irrigated Corn Yield
Authors: Onken A. B. , Matheson R. L. , Nesmith D. M. 
Published: July 2010

AbstractMultirate nitrogen studies were conducted for a 6‐yr period, on an irrigated clay loam soil, to determine the influence of applied N and residual soil N on the grain yield of corn (Zea mays L.). Soil samples were taken prior to fertilizer application each year in depth increments of 0 to 0.15, 0.15 to 0.30, 0.30 to 0.60 and 0.60 to 0.90 m and analyzed for nitrate‐N (NO‐3‐N). Applied N and residual soil NO‐3‐N were found to significantly influence grain yields. Regression analyses of the data showed highly significant relationships between (i) quantities of NO‐3‐N measured in the upper portions and those measured in the lower portions of the soil profile and (ii) grain yield and applied N and residual NO‐3‐N. Highest coefficients of determination were obtained when residual NO‐3‐N was included as a separate independent variable in the regression equation. Results indicated that residual NO‐3‐N measured to 0.15 m would be sufficient for evaluation of residual N effects on irrigated corn grain yield on this soil. Fertilizer N requirements for several combinations of grain yield and residual soil NO‐3‐N were calculated using the N requirement index (NRI) and a power function, and simple and multiple linear response equations generated by regression analysis. A range of values was obtained, with NRI most frequently predicting the highest N requirement. The marginal rate of substitution of residual soil NO‐3‐N for applied fertilizer N was variable and influenced by (i) amount of residual NO‐3‐N, (ii) depth of measurement of residual NO‐3‐N and (iii) maximum grain yield. Fertilizer use efficiency (FUE) was influenced by grain yield, fertilizer N rate, and amount of residual soil NO‐3‐N. The greatest reduction in FUE resulted from residual soil NO‐3‐N. In order to maximize FUE, it is necessary to apply the amount of fertilizer N to achieve a given yield level and simultaneously leave as little as possible in the soil to carry over to the next crop year.
Spline Response Functions for Direct and Carry‐over Effects Involving a Single Nutrient
Authors: Jauregui Mario A. , Paris Quirino 
Published: July 2010

AbstractTwo continuous models which interpret the principles underlying the law of the minimum in crop response to an essential nutrient are presented. Such single‐nutrient response functions are the linear response and plateau model (LRP), and the linear, quadratic and plateau model (LQP). A spline algorithm was developed to estimate these functions. Both functions were applied to data from a field experiment carried out in Salta, Argentina, to study the response of three cuts of Rhodes grass, Chloris gayana Kunth, to N fertilization with urea. Furthermore, two associated models for carry over of available N in the soil, as well as carry‐over effects on yield, either within a growth season or between consecutive seasons, were developed. These are the platform and linear response model (PLR), and the platform, quadratic and linear response model (PQL). The LQP model, and its counterpart for carry over (PQL), imply the existence of an apparent, although restricted substitution between the limiting nutrient and the next potential limiting factor, whereas the LRP and PLR models are based on the non‐substitution assumption. It is emphasized that the restricted substitution of the LQP and PQL models is strongly situation specific, and that they can collapse into LRP and PLR fits without a quadratic domain, as they often did in this study. The quadratic polynomial equation was used throughout as a reference model with extended substitution. At worst, the spline functions performed equally well as the quadratic polynomial, and in some situations they provided a substantial increase in the goodness of fit. Hence, it is reconfirmed in this study that, while polynomial responses tend to overestimate the optimum fertilizer rate, the LRP and LQP models are better suited to provide more realistic optimum levels of fertilization. The carry‐over effect on yield was found to be more relevant within a growth season (R2 = 0.58) than between seasons (R2 = 0.38). Both the PLR and PQL models were able to explain 90 % of the variability in residual N in the soil as a function of the level of urea applied at the beginning of the growth period. The estimated minimum levels of fertilization required to attain the plateau yield showed a tendency to decrease as a result of the carryover effect. These doses were 430 and 250 kg N ha−1 for the two cuts of the first season, and 223 kg N ha−1 for the first cut of the second season. The methodological contributions of this paper are that: (i) it provides continuity for the LRP model and (ii) the knot(s) of the spline functions are endogenously obtained through an iterative procedure which maximizes the goodness of fit.
The Effect of Furrow Irrigation Erosion on Crop Productivity
Authors: Carter D. L. , Berg R. D. , Sanders B. J. 
Published: July 2010

AbstractFurrow irrigation erosion redistributes topsoil by eroding upper ends of fields and depositing sediment on downslope portions causing a several fold topsoil depth difference on individual fields. This investigation was conducted to evaluate the effects of this erosion and deposition process on crop yield and to develop crop yield‐topsoil depth relationships. Studies were conducted on 14 farmer‐operated fields and on field plots with a continuous topsoil depth gradient from 10 to 66 cm. Severe erosion on the upper ends of fields combined with tillage has mixed light‐colored subsoil with topsoil and caused these areas to become whitish in color. Crop yields have sharply decreased on these whitish areas compared to areas where the topsoil depth is 38 cm, or the original depth. Yields were increased, but less sharply, where sediment deposition has increased topsoil depth above 38 cm up to a depth of about 66 cm. Yield‐topsoil depth relationships followed the equation Y = a + b 1nX with significant correlation coefficients for wheat (Triticum aestivum L.), sweet corn (Zea mays L.), barley (Hordeum vulgare L.), alfalfa (Medicago sativa L.), dry beans (Phaseolus ssp.) and sugarbeets (Beta vulgaris L.). Yield decreases per unit loss of topsoil were greatest for wheat and sweet corn and least for sugarbeets. Yields on whitish soil areas could not be improved more than indicated by these relationships by adding additional fertilizer phosphorus or potassium.
Site Quality Evaluation for White Spruce Plantations Using Discriminant Analysis
Authors: Harding R. B. , Grigal D. F. , White E. H. 
Published: July 2010

AbstractFifty‐six study plots were established in fully‐stocked white spruce plantations, 33 to 43 yr old, in northern Minnesota. The plots were separated into three growth response groups based on site index, basal area, and mean annual biomass increment of the spruce. Discriminant analysis was used on data from 50 of the plots to determine the site descriptors that best separated the plots into their respective growth groups. The discriminant functions, based on seven descriptors, correctly classified 76% of the plots. Plots in groups 1, 2, and 3, roughly equivalent to good, medium, and poor productivity, were correctly classified 69%, 80%, and 79%, respectively. When individual plots were sequentially deleted from computation of the functions (jacknife analysis), these values dropped to 56%, 75%, and 71%, with an overall value of 68%. Three of the remaining six independent test cases were correctly classified. Slope, soil phosphorus, and nutrient synecological coordinates were all major discriminators. These discriminators represent physiographic, soil, and vegetation properties, and demonstrate the importance of the total site approach when defining site quality for white spruce.
Identification of Ammonium Thiosulfate as a Nitrification and Urease Inhibitor
Authors: Goos R. J. 
Published: July 2010

AbstractIncubation studies at 25°C with a Williams loam (Typic Argiboroll) illustrated that the thiosulfate ion is an inhibitor of nitrification. Inhibition of the nitrification of 10 mmol N kg−1 (as ammonium sulfate) ranged from 55–80% with an addition of 1 mmol S kg−1 (as sodium thiosulfate) to 82–91% with a 10 mmol S kg−1 addition. Percent inhibition was greater after 28 than 14 d of incubation. Residual soil ammonium measurements confirmed the influence of thiosulfate on nitrification. A separate study illustrated that a 5% (v/v) inclusion of commercial‐grade liquid ammonium thiosulfate (ATS) to urea‐ammonium nitrate solution (UAN) inhibited nitrification by 51% in a 28 d incubation. Another experiment also illustrates that small additions of ATS to UAN dramatically reduced the rate of urea hydrolysis. Incubations were performed for 2 and 4 d at 25°C with a Williams loam and a Bearden silty clay loam (Aeric Calciaquoll). Levels of inhibition ranged from 15–35% with a 1% (v/v) addition of ATS to UAN to 40–52% with 10% (v/v) inclusion. ATS did not inhibit urea hydrolsis by purified jackbean urease. Three commercial sources of ATS were compared to reagent sodium thiosulfate, at equal rates of sulfur, and all sources inhibited soil urease similarly. Although the nitrification and urease inhibition properties of ATS are less than have been reported for some other materials, ATS deserves further laboratory and field evaluation as a possible nitrification and urease inhibitor. As commercial batches of UAN sometimes contain ATS, each lot should be tested for ATS contamination before use in research. A procedure for such a test is described.
A Refined Soil Coring System
Authors: Ruark Gregory A. 
Published: July 2010

AbstractMaterials and construction specifications are detailed for a soil sampling system comprised of a slide hammer driver, an open probe, a core probe, and a probe puller. Intact soil cores, contained in clear plastic tubing, can be extracted from a site with minimal disturbance. Replaceable hardened steel tips facilitate sampling soils with rock fragments and high concentrations of roots. This soil sampling system is portable, versatile, and durable
Components of Rates of Ammonium Oxidation in Soil
Authors: Molina J. A. E. 
Published: July 2010

AbstractDiversity in the growth and the activity of ammonia (NH3) oxidizers in a population of 132 soil microaggregates was documented. Each microaggregate was inoculated in a poorly buffered liquid medium containing bromthymol blue and selective for NH3 oxidizers. The kinetics of ammonium oxidation was measured by monitoring the changes in percent transmittance of the medium concomitant to its acidification. Mean specific rates of NO−2 production were low: 0.321 d−1, 0.403 d−1, 0.246 d−1, and 0.069 d−1 at pH 7.50, 7.00, 6.00, and 5.50, respectively. At pH 7.5 only a few microaggregates harbored NH3 oxidizers with generation times similar to those reported for pure cultures in liquid media. Most microaggregates were still active at pH 5.9 but became inactive at pH 5.1. The lag phase before detection of activity correlated to the specific rate of ammonium (NH+4) oxidation. A statistical theory of nitrification in soil was formulated and tested. Nitrification in soil was assumed to proceed from pulses of ammonium oxidation generated by microbial clusters. The kinetics of nitrate accumulation in soil coincided with the cumulative distribution of the microaggregates' lag phase. On the average, each active microaggregate (0.036 mg) contained 2.01 clusters of NH3 oxidizers, and had generated 0.0088 g NH+‐N when their activity was stopped by self‐induced acid toxicity.
Urease Activity on a Clay‐Organic Complex
Authors: Boyd Stephen A. , Mortland Max M. 
Published: July 2010

AbstractUrease may be adsorbed on hexadecyltrimethyl‐ammonium (HDTMA)‐smectite by hydrophobic bonding. This mechanism is independent of pH and results in enzyme activity ash igh as that in homogenous solution. As much as forty percent by weight of enzyme can be bound to the clay‐organic complex before free enzyme appears in the supernatant solution. Several cycles of washing the enzyme‐clay‐organic complex at the 10% by weight level did not result in any enzyme removal. The free and bound enzyme behaved similarly with respect to kinetic parameters, pH optimum, and selectivity for substrate. Thermal stability and resistance to proteolysis were greatly decreased for urease immobilized on HDTMA smectite as compared with homogenous solution. In soils, enzymes may be immobilized on natural clay‐organic matter complexes by hydrophobic bonding.
An Application of the Maas‐Hoffman Salinity Response Model for Boron Toxicity
Authors: Bingham F. T. , Strong J. E. , Rhoades J. D. , Keren R. 
Published: July 2010

AbstractThe Maas‐Hoffman model for salinity tolerance was tested for boron toxicity (reduction in yields only) using wheat (Triticum aestivum L., var. Inia 66R), barley (Hordeum vulgare L., var. Briggs), and sorghum (Sorghum bicolor L., var. Dekalb C42A) as test crops. These crops were grown to maturity in sand cultures containing low to excessive concentrations of boron. The leaf immediately below the Y‐leaf was collected at the early spike emergence stage and analyzed for boron. At harvest, the individual grain heads were collected, dried and weighed. Relative grain and shoot yields (Y, %) were related to the boron concentration of the nutrient solution (X, mg B L−1) using the following equation Y = 100 − m(X − A), where m is the decrease in yield per unit increase in soluble boron above the threshold concentration, and A, the maximum concentration not restricting yield (the threshold). The SALT computer program (van Genuchten, 1983) was used to derive the slope and threshold parameters. The respective threshold concentrations for the grain yields of wheat, barley, and sorghum were found to be 0.3, 3.4, and 7.4 mg B L−1, respectively, which categorized these crops as being sensitive, moderately tolerant, and very tolerant to boron. The relationship between relative yield and leaf boron was linear for wheat whereas barley and sorghum followed the Maas‐Hoffman model. The threshold leaf B values with reference to grain yield were found to be 55, 768, 171 mg B kg−1, respectively, for wheat, barley, and sorghum. The study indicates that yield under the influence of soluble boron may be fitted to the Maas‐Hoffman model for salt tolerance.
Potassium‐Magnesium Interactions Affecting Nutrient Uptake by Wheat Forage
Authors: Ohno Tsutomu , Grunes D. L. 
Published: July 2010

AbstractAn important factor in the etiology of grass tetany is the role of K in suppressing the Mg concentration of the forage. A solution culture experiment was conducted to investigate K‐Mg interactions in winter wheat forage (Triticum aestivium L. ‘Centurk’). The treatments were a factorial combination of K at 0.1, 1.0, and 6.0 mM and Mg at 0.1, 0.5, 1.5, and 4.5 mM. The plants showed a growth response to nutrient solution K levels, but not to nutrient solution Mg levels. Increasing K supply depressed Mg shoot concentrations, but not Mg root concentrations. Influx rate calculations showed that the external solution concentration of K did not affect the Mg influx rate. This implies that the antagonistic K‐Mg interaction mechanism is seated in the translocation step from the root to the shoot. The Mg concentration in the nutrient solution did not affect the shoot or root concentration of K, or the K influx rate. However, increasing the Mg level decreased both the Ca concentration in the shoots and the Ca influx rates. A soil culture study was conducted to investigate the influence of the nutrient transport mechanism on the chemical composition of plants. Plants grown at 30% relative humidity had higher K/(K + Mg) ratios than plants grown at 90% humidity. This was caused partly by the greater quantities of K delivered to the root‐soil interface by mass flow, owing to greater transpiration at the lower humidity level. Calculations showed that K depletion zones formed around the root‐soil interface at the lower K fertilization levels. Thus, the K+ uptake was regulated by nutrient diffusion from the bulk soil to the root surface.
Particle Sedimentation Rates in the Linear Density Gradient
Authors: Essington M. E. , Mattigod S. V. , Ervin J. O. 
Published: July 2010

AbstractAn equation describing sedimentation times for isopycnic banding of silt and clay size particles (<20–30 µm) in linear density gradients under centrifugal force is developed. The sedimentation equation is principally applicable to the ethanol, polyvinyl pyrrolidone, tetrabromoethane gradient systems or to other gradient systems for which solution viscosity is linearly related to or invariant with respect to solution density. The equation is completely general in all other aspects and takes into consideration the gradient solution density and viscosity range, the gradient depth, the sample introducing solution depth, the particle size and density, the particles limiting approach to its isopycnic point, and the applied centrifugal force. The use of the developed sedimentation equation is illustrated.