bluuebunny/crossref_metadata_2025 huggingface dataset:
Applicability of the Four‐Probe Technique under Extremely Variable Water Contents and Salinity Distribution
Authors: Nadler A. , Frenkel H. , Mantell A.
Published: July 2010

A drip‐irrigated cotton field was used to test the applicability of the four‐probe technique for measuring the salinity of the soil solution. The formation factor (F), which relates measured bulk soil electrical conductivity (ECa) to calculated salinity (ECw), is highly dependent on soil water content. Good results were obtained even though soil water content is extremely variable in drip‐irrigated soil. Only 15% of the calculated salinity values deviated from a range chosen as a reasonable criterion (± 20% of water‐content‐corrected soil extracts), and this deviation was attributed to an unrepresentative water content value of the sampled soil. The calculation procedures produced similar values when slightly different parameters were used in calculating ECw from ECa.
Bicarbonate Directly Induces Iron Chlorosis in Susceptible Soybean Cultivars
Authors: Coulombe B. A. , Chaney R. L. , Wiebold W. J.
Published: July 2010

Four soybean [Glycine max (L.) Merr.] cultivars differing in susceptibility to iron (Fe) chlorosis in wet calcareous soils were grown in nutrient solutions to characterize the effects of phosphate (P) and bicarbonate (HCO‐3) in inducing chlorosis. NaHCO3 (0 or 10 mM), P (10 or 400 µM as NaH2PO4, and NH+4 (0 or 300 µM) as (NH4)2SO4 were factorial treatments in a nutrient solution. Low Fe availability was maintained by supplying 5 µM Fe + 10 µM EDDHA, and excess CaCO3(pH 7.5). With no HCO‐3 added, ‘T203’ (extremely chlorosis susceptible) was green at 10 µM P, but severely chlorotic at 400 µM P; ‘Wayne’ (chlorosis susceptible) was green at both P levels. Addition of HCO‐3 caused chlorosis in T203 and Wayne at 10 or 400 µM P. Chlorosis resistant ‘AP9’ and ‘Hawkeye’ remained green with added P or HCO‐3. Chlorosis ratings (1 = green to 5 = severely chlorotic) in the 0 HCO‐3 + 10 µM P, 0 HCO‐3 + 400 µM P and 10 HCO‐3 + 400 µM P treatments, respectively, were: 1.0, 1.0, and 1.5 for AP9; 1.0, 1.0, and 1.4 for Hawkeye; 1.0, 1.2, and 3.9 for Wayne; and 1.0, 4.2, and 4.6 for T203. Low Fe concentrations in young leaves corresponded with high chlorosis ratings. Phosphorus concentration in young leaves did not change with HCO‐3 at 10 µM P, but decreased with HCO‐3 at 400 µM P. In the absence of HCO‐3, Wayne was not chlorotic at either concentration of solution P, although this cultivar is known to be highly susceptible to chlorosis in the field. Bicarbonate‐induced chlorosis in Wayne was not a result of increased solubility or plant uptake of P. Thus, HCO‐3 was a direct factor in causing soybean chlorosis, and likely is also a cause in soils.
Effects of Water and Salt Stress on Growth and Acetylene Reduction in Alfalfa
Authors: Keck T. J. , Wagenet R. J. , Campbell W. F. , Knighton R. E.
Published: July 2010

The interactive effects of three irrigation water salinities (1.0, 3.0, and 9.0 dS/m) and three quantities of water applied per irrigation (2.3, 4.7, and 7.0 cm) on plant growth and N fixation by alfalfa (Medicago sativa L. cv. Resistador) were assessed in the greenhouse. Salt and water treatments were started after nodulation had been established in young plants and samples were harvested at 10, 30, and 50 d thereafter. Alfalfa top growth was limited by both salt and water stresses. Irrigation water salinity had a greater effect on top growth than root growth while root distribution was unaffected by either the quantity of water applied or by water salinity. The effects of salinity on plant growth were masked by water stress. Specific nodule activity (µmol C2H4 s−1 kg−1) was enhanced by increasing quantity of water applied at each irrigation and was adversely affected by increased irrigation water salinity. In contrast, both nodulation and total nodule mass were insensitive to salt stress and sensitive only to severe water stress. Alfalfa plants continued to reduce acetylene at the third sampling even under severe water and salt stress. These data indicate that the Resistador cultivar of alfalfa apparently continues to fix N2 during periods of substantial environmental stress.
Fiber Size Distribution, Bulk Density, and Ash Content of Peats in Minnesota, Wisconsin, and Michigan
Authors: Nichols Dale S. , Boelter Don H.
Published: July 2010

Boelter (1969) described the physical characteristics of some undrained organic soils in northern Minnesota. This paper expands upon Boelter's work. Bulk density, ash content, and percent (dry weight basis) of rubbed and unrubbed fiber > 2.0 mm, 1.0 – 2.0 mm, 0.5 – 1.0 mm, 0.25 – 0.5 mm, and 0.1 – 0.25 mm were determined for 176 peat samples from 38 peatlands in northern Minnesota, Wisconsin, and the Upper Peninsula of Michigan. When the distribution of various sizes of plant fibers in the peat is used as an index of the stage of peat decomposition, the increase in bulk density that accompanies increasing decomposition is easily seen. Fibers > 0.5 mm predominate in low bulk density peats, but are quickly lost as decomposition proceeds and bulk density increases. Curvilinear regression equations between bulk density and rubbed and unrubbed fiber >0.5, >0.25 and 0.1 mm were developed that represent improvements over such equations previously calculated for northern Minnesota peats only. At the same bulk density, moss peats contained larger amounts of fiber than herbaceous peats; the unrubbed fiber content of the woody peats studied was higher than that of moss peats, but fell to an intermediate level between moss and herbaceous peats when subjected to rubbing. When a dispersing agent such as sodium metaphosphate (NaPO3) is used before sieving and percent fiber is calculated on a dry weight basis, the traditional rubbed fiber content appears to have little advantage over unrubbed fiber content as a descriptive criterion for characterizing organic soil.
Soil Survey Interpretations from Water Retention Data: II. Assessment of Soil Capability Ratings and Crop Performance Indices
Authors: McBride R. A. , Mackintosh E. E.
Published: July 2010

A water retention model developed for Ontario soils is used to estimate the preseason plant‐available moisture‐holding capacity (Θva) of the soil root zone in equilibrium with a phreatic surface and the air‐filled porosity (ε) of the surface 30 cm. Preliminary soil capability class ratings are then assessed from a set of regional guidelines based on class intervals of Θva and ε. Crop performance indices are determined for capability classes 1 to 5 inclusive using a statistical corn productivity model which relates long‐term mean grain corn yields in Ontario to a seasonal soil moisture deficit or surplus. Total seasonal field water supply is budgeted against potential crop evapotranspiration to estimate the extent to which plant water stress from excess or deficit soil water availability limits the attainment of regional agro‐climatic potential yields. Advantages in using a water retention model as a basis for agronomic interpretations of soil survey data for land evaluation purposes are discussed.
Fragipan Bonding in a Late‐Wisconsinan Loess‐Derived Soil in East‐Central Ohio
Authors: Norton L. D. , Hall G. F. , Smeck N. E. , Bigham J. M.
Published: July 2010

A fragipan developed in a late‐Wisconsinan, loess‐derived soil was studied in detail to determine if its brittleness could be related to a specific chemical bonding agent. Three approaches were used in the study. The first involved an attempt to create fragipan brittleness and consistence by adding solutions containing Fe, Al, or Si to non‐fragipan, loess material. Secondly, a destructive approach utilizing various dissolution techniques was used to extract fragipan material under vacuum in an attempt to selectively remove the cementing agent. Lastly, the fragipan fabric was observed and analyzed in situ by scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDXRA). Solutions containing Si or Al added to acid, nonfragipan loess material increased the rupture strength. Na‐citrate‐bicarbonate‐dithionite (CBD) and Na‐citrate‐dithionite solutions destroyed fragipan peds under vacuum and eliminated the slaking properties of the residue. Pyrophosphate also destroyed the ped fabric and dispersed clay, but the residue retained its ability to slake in water. Differential infrared spectroscopy and differential thermal calorimetry revealed that CBD selectively removed an inorganic fraction unique to the fragipan. SEM study demonstrated that bridges occurred between silt grains in the fragipan and EDXRA revealed that these bridges contained considerably more Si than identifiable argillaceous plasma in either the fragipan or nonfragipan horizons. In conclusion, the key bonding agent in the fragipan studied appears to be a hydrous aluminosilicate, possibly associated with clay, which formed bridges between skeletal grains.
Genesis and Morphology of Soils Associated with Formation of Laramie Basin (Mima‐Like) Mounds in Wyoming
Authors: Spackman L. K. , Munn L. C.
Published: July 2010

Small mounds of varied origin are a common microrelief feature over much of the western United States. In Wyoming's Laramie Basin, soil genesis and mound formation were studied in a 27.5 m long trench dug to expose intermound soils with strongly developed horizonation (Borollic Haplargids) and two mounds with weakly developed soils (Borollic Camborthids). Fossil permafrost sand wedges, common along the trench exposure, are believed to be evidence of a mid‐ to late‐ Wisconsin periglacial environment. The intermound soils date from pre‐ to early Wisconsin and were formed by a sequence of alluvial deposition, argillic horizon development, carbonate accumulation, sand wedge formation, and development of a second argillic horizon with weak carbonate accumulation. Mound formation occurred as a result of upwellings of gravelly substrata induced by cryostatic pressure. The gravelly pipes broke through large fossil sand wedges to the soil surface forming the mounds. Subsequent soil formation on the mounds has involved cambic horizon development, leaching of salts, and weak carbonate accumulation.
Statistical Analysis of Crop Yield‐Soil Water Relationships in Heterogeneous Soil under Trickle Irrigation
Authors: Russo David
Published: July 2010

Field data of bell pepper (Capsicum frutescens ‘Maor’) yield (Y), soil water pressure potential (P), and salinity (EC) obtained under trickle irrigation, and of two soil hydraulic parameters (K1 and α), were used to analyze spatial variability of these properties and its impact on relationships between crop yield and soil properties. Both conventional statistical analysis methods and spatial structure analysis methods were used. With the conventional methods, observations of each property were considered as statistically independent regardless of their spatial position in the field. Results of multiple regression analysis suggest the variability in K1 and α is responsible for about 25% of the variabilities in both P and EC, which in turn, are responsible for < 25% of the variability in Y, when experimental data from the entire field are considered. With the spatial structure methods, a variogram was used to investigate spatial structure of different properties, and a cross‐variogram was used to investigate spatial dependence of P and EC on K1 and α and spatial dependence of Y on P and on EC. Results show field spatial structure affects the relationships between different properties over distances which were related to the respective ranges of direct variograms of pertinent properties. The characteristic length of field spatial structure (in terms of integral scale, J) varied between J = 25 m (K1) and J=78 m (α) with an average of J=43 m. The direct variograms of properties were used to calculate kriging estimates of pertinent properties, which in turn, were used for two subsequent analyses. In the first analysis, kriging estimates obtained for a square domain (43 by 43 m in size) moving over the entire field were used to calculate the correlation between different properties at different parts in the field. The analysis showed that in some parts of the field variability in K1 and α was responsible for about 90% of the variabilities in both P and EC, which in turn, were responsible for about 90% of the variability in Y. In the second analysis, kriging estimates of Y, P and EC obtained for regions in the field which are associated with a constant saturated zone in the vicinity of the trickle emitter (in terms of its radius ru = ru (K1, α; Q); Q being trickle emitter discharge) were used to analyze the dependence of Y on P and on EC. The analysis showed that in regions which were associated with relatively small values of ru (ru < 0.05 m) the variability in P and EC is responsible for > 0.8 of the variability in Y. In regions which were associated with relatively large values of ru (ru>0.08 m) and a relatively large leached zone, it was not soil water pressure or salinity, but other factors that most influenced yield.
Temporal Response of Soil Denitrification Rates to Rainfall and Irrigation
Authors: Sexstone Alan J. , Parkin Timothy B. , Tiedje James M.
Published: July 2010

The 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

Vertisols, 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

Electron 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

Multirate 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

Two 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

Furrow 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

Fifty‐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

Incubation 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

Materials 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

Diversity 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

Urease 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

The 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

An 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

An 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.
Production of Thiocysteine (Sulfide) in Cysteine Amended Soils
Authors: Morra M. J. , Dick W. A.
Published: July 2010

Little information is currently available concerning the formation in soils of hydrogen sulfide, an important intermediate in the cycling of sulfur within the earth's environment. Studies were performed in which 3 g of air‐dry soil were treated with 10 mM cysteine HCl (pH 6.0) and incubated for 24 h at 37°C. Results indicated that a dithio sulfur compound, thiocysteine (2‐amino‐2‐carboxyethyl hydrodisulfide), was produced. Production of thiocysteine occurs as a result of cystathionine γ‐lyase (EC 4.4.1.1) activity and the actual substrate of the enzyme is cystine, the oxidized form of cysteine. The procedure to measure thiocysteine involved a second addition of cysteine, used as a reagent, after the 24‐h incubation. Cysteine causes a nonenzymatic breakdown of thiocysteine, producing hydrogen sulfide, which was then collected in zinc acetate and determined colorimetrically. The amount of thiocysteine (sulfide) measured in the four soils studied after the 24‐h incubation period ranged from 7.8 to 16 mg kg−1 soil. The biological nature of the reaction was demonstrated when the production of thiocysteine (sulfide) was inhibited when soils were treated with 0.1 mL of 0.5 M sodium azide or steam sterilized for 1 h at 121°C. Complete inhibition also occurred upon the addition of 0.2 mL of toluene or formaldehyde. Addition of 10 mM propargylglycine (16.7 µmol g soil−1), a specific inhibitor of cystathionine γ‐lyase, reduced thiocysteine (sulfide) production by 58 to 91%. The formation of hydrogen sulfide as a result of the combination of cystathionine γ‐lyase activity and the nonenzymatic degradation of thiocysteine to produce hydrogen sulfide may represent an important pathway in the cycling of sulfur through the soil system.
Phosphorus Cycling in Unfertilized and Fertilized Agricultural Soils
Authors: Sharpley A. N.
Published: July 2010

Surface soil samples (0–50 mm depth) were taken from several grassed and cropped, unfertilized and P‐fertilized soils at monthly intervals for 2 yr, to investigate seasonal variations in amounts and forms of P and relative importance of inorganic and organic P as sources of plant available P. Although no consistent seasonal variation in inorganic P content was observed for the unfertilized soils, amounts increased after fertilizer P addition. Organic P content was higher in the winter (Oct.–Mar.) than spring months (May–June) for both unfertilized and fertilized soils. Consequently, mineralization of organic P during the growing season, which contributed similar amounts of P (20–74 kg P ha−1) as added in fertilizer (13–100 kgP ha−1), was not inhibited by fertilizer P addition. Organic P variation was mainly due to changes in moderately labile organic P, with more labile and resistant pools remaining constant. The most labile organic P pool was maintained at a constant level possibly by mineralization and formation from moderately labile organic P. Little change in P content of unfertilized subsurface soil (50–150 mm) was observed, although inorganic and available P contents increased slightly following fertilizer P application. Available P (Bray‐I P) was closely correlated with organic P in unfertilized soils and with inorganic P in fertilized soils. Slopes of these relationships were related to phosphatase enzyme activity and P sorption maximum for organic and inorganic P, respectively. The importance of organic P as a source of available P in both unfertilized and fertilized soils was demonstrated. The need to include organic P in soil‐P fertility tests, especially with the increasing use of reduced‐tillage practices, is emphasized.
Soil Bulk Density Recovery on Compacted Skid Trails in Central Idaho
Authors: Froehlich H. A. , Miles D. W. R. , Robbins R. W.
Published: July 2010

In west‐central Idaho, the bulk densities of soil in major skid trails were compared with those of adjacent undisturbed soil in order to determine rates of recovery. Five study sites on each of two soils, one formed from granitic material (mixed, frigid, Typic Xeropsamments) and the other from volcanic material (fine‐loamy, mixed Dystric Cryochrepts), provided two chronosequences (five 5‐yr periods) of time since logging. Bulk density was measured at 5.1‐, 15.2‐, and 30.5‐cm depths. The percent increase in bulk density of soil on a skid trail over that on an adjacent undisturbed area was greater in the volcanic than the granitic soil, but recovery rates (slope of the regression line) for the two soils were not significantly different. Linear regression models showed a significant (p < 0.05) recovery trend for all depths except the 15.2‐cm depth on the volcanic site. Except for the surface 5.1 cm of the granitic soil, none of the bulk densities in skid trails had returned to the undisturbed values in the 23 yr since logging.
Soil and Stand Characteristics and Elemental Concentration of Tall Shrub Twigs
Authors: Kernik L. K. , Grigal D. F.
Published: July 2010

Woody twigs (⩽ 3 mm diam) of tall shrubs were collected during winter in 18 forest stands in the Superior National Forest of northeastern Minnesota. Elemental concentration of the twigs was examined with respect to variation due to site characteristics including vegetation type, soil properties, management history, and stand age. The stands ranged from young Pinus resinosa Ait. plantations to natural pine and hardwood stands to lowland conifer stands on organic soils. Levels of most elements in twigs were not significantly related to soil properties. Twigs from stands on organic soils were higher in Mg and Zn concentration than were twigs from the stands on mineral soils, and Ca was lower in twigs on soils with coarser texture. Although significant differences were found in elemental concentrations of Ca, Mg, Zn, Fe, and Mn among stands classified by vegetation type, these differences were small among the upland stands. There were no differences in concentration related to differences in site preparation; K, Ca, and Zn varied with method of release of plantations. Stand age did not appear to have a major influence on elemental concentration, but twigs in younger stands had higher K and lower Fe concentrations than did twigs in older stands. Two consistent trends emerged from the analysis, those of differences in Ca and Zn associated with vegetation and soil, and of differences in K associated with stand development. The relatively small size of the study area, 185 km2, may have led to few differences.
Aging of Partially Neutralized Aluminum Solutions of Sodium Hydroxide/Aluminum Molar Ratio = 2.2
Authors: Tsai Ping Ping , Hsu Pa Ho
Published: July 2010

Aluminum hydroxide developed in all solutions in this study (0.02 M in AlCl3, NaOH/Al molar ratio in preparation = 2.2) after prolonged aging. The induction period and the rate of aluminum hydroxide [Al(OH)3] crystallization varied greatly among solutions, however. The Al ions in the freshly prepared solutions were predominantly OH‐Al polymers that reacted with ferron rapidly and yielded tetrahedral crystals of basic aluminum sulfate, of composition Na0.08Al(OH)2.46(SO4)0.31(H2O)x, upon the addition of sodium sulfate. During aging, the initial OH‐Al polymers gradually converted to either more stable polymers of similar basicity or Al(OH)3 precipitate. The conversion of metastable to stable polymers probably proceeded through internal structural rearrangement, but the development of Al(OH)3 proceeded through redissolution and crystallization. The variation in the induction period was attributed to the initial number of nuclei present as a result of localized high alkalinity during solution preparation. The variation in the rate of Al(OH)3 crystallization was attributed to the distribution of metastable and stable OH‐Al polymers at the time of crystallization. The crystallization of Al(OH)3 was faster from metastable polymers than from stable ones.
Collecting and Testing Barrel Sized Undisturbed Soil Monoliths
Authors: Brown K. W. , Thomas J. C. , Aurelius M. W.
Published: July 2010

A procedure was developed for encasing undisturbed soil monoliths in a 0.57‐m diam, 0.85‐m deep steel casing. The casings are available from barrel manufacturing companies, and other equipment is easily made or leased locally. This equipment includes a specially designed frame that holds the thin walled casings during filling. The technique has been successfully used in soils with textures ranging from sandy loam to clay. Bromide breakthrough curves were symmetric for the majority of the encased monoliths. This suggests that side wall boundary flow contributes little to solute mobility through the encased soils. This simple test will allow the user to discard defective monoliths.
Spatial Variability of Field‐measured Soil‐water Characteristics
Authors: Greminger P. J. , Sud Y. K. , Nielsen D. R.
Published: July 2010

One hundred neutron access pipes were placed 1‐m apart along a 100‐m transect together with tensiometers located at soil depths of 0.3 and 0.6 m. After ponding the experimental site with water for at least 4 d, the site was allowed to drain and covered with 0.3 m of straw to reduce evaporation. Measurements of soil‐water content θ and soil‐water pressure head (h) initially made at 2‐h intervals were made less frequently as redistribution proceeded. The (θ,h|t)—observations were fitted to the five‐parameter van Genuchten model. Spatial autocorrelations and cross‐correlations of θ, h, and percentage sand manifested significant coefficients for distances as great as 10 m. The practical significance of this research is that it addresses the impact of the separation distance between a tensiometer and a neutron meter access tube on the precision of the measured soil‐water characteristic curve. Greater precision is obtained for separation distances < 10 m.
Colonization of Winter Wheat Roots by Inhibitory Rhizobacteria
Authors: Fredrickson J. K. , Elliott L. F.
Published: July 2010

Colonization of the winter wheat (Triticum aestivum L.) rhizoplane by root‐inhibiting nonfluorescent pseudomonads was investigated in laboratory and greenhouse studies with genetically marked (rifampicin resistant) isolates. Colonization was similar at root zone temperatures of 5, 10, and 15°C but was dependent on soil type, with higher populations occurring in the soil with lower organic matter and microbial biomass. Rhizoplane populations of test strains were over tenfold higher on roots in pasteurized soil than in non‐pasteurized soil or vermiculite. Deleterious effects on growth of winter wheat were related to the extent of rhizoplane colonization by the bacteria; approximately 106 colony forming units (cfu) mg−1 root were required for significant inhibition of root growth. The shoots and roots of winter wheat were significantly shorter on plants inoculated with the inhibitory bacteria in pasteurized or methyl bromide fumigated soil as well as in nonpasteurized Ritzville soil (Calciorthidic Haploxerolls). The difference in early stages of plant growth, especially shoots, between bacterized (seed treated with antibiotic‐resistant inhibitory bacteria) and nonbacterized winter wheat increased with time. The antibiotic‐resistant bacteria maintained a high population on the roots during this period. The bacteria were observed to extensively colonize winter wheat roots (rhizobacteria) and are considered a potential constraint on winter wheat yield in the Pacific Northwest.