bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in Phosphorus Fractions in Soils under Intensive Plant Growth
Authors: Guo F. , Yost R. S. , Hue N. V. , Evensen C. I. , Silva J. A.
Published: July 2010

The total quantity of P and plant‐available P often differ greatly in soils of the tropics, which typically range in weathering intensity. Assessing available P is fundamental to managing P in many of these soils. Phosphorus availability in some soils has been inferred from the Hedley sequential extraction assuming that each P fraction reflects similar plant availability in different soils. However, experimental measurements of plant P availability were either of short duration or involved multiple P applications, which complicates assessment of the plant availability of P fractions. The objectives of this study were to examine the changes in P fractions under exhaustive cropping on diverse soils and to discern the differences in plant availability among P fractions. Eight soils ranging in weathering from Vertisols and Mollisols to Ultisols and Oxisols were amended with Ca(H2PO4)·H2O to raise soil solution P to 0.2 mg L−1and planted for 14 crops to remove available P. The results indicated that the Fe‐impregnated strip–P and inorganic NaHCO3–P (NaHCO3–Pi) decreased the most in response to plant P withdrawal in all soils. The inorganic NaOH‐P (NaOH‐Pi) also declined with plant P uptake in all soils. The HCl‐P and residual P seemed to act as a buffer for the strip‐P and the NaHCO3–Piin the slightly weathered soils, whereas NaOH‐Piseemed to act as a buffering pool for strip‐P and NaHCO3–Piin the highly weathered soils. Residual P in the slightly weathered soils was plant‐available on a relatively short time scale. In contrast, residual P in the highly weathered soils accumulated in the presence of intensive plant P removal, indicating that it was unavailable to plants. Organic P (NaHCO3‐ and NaOH‐Po) fractions were not significant contributors to available P in these soils that received high levels of inorganic P. Phosphorus fractions separated by the same sequential method were not of equal availability to plants in all soils.
Fragipan Degradation and Nodule Formation in Glossic Fragiudalfs of the Lower Mississippi River Valley
Authors: Lindbo D. L. , Rhoton F. E. , Hudnall W. H. , Smeck N. E. , Bigham J. M. , Tyler D. D.
Published: July 2010

Glossic Fragiudalfs comprise several million hectares of agronomically important soils within the silty uplands of the lower Mississippi River Valley (Major Land Resource Area [MLRA] 134). These soils are typified by a fragipan within 100 cm of the surface overlain by a 5‐cm‐thick, or more, glossic horizon containing bleached coatings (albic material) along primary ped faces, indicating fragipan degradation. Concentrations of Fe–Mn nodules also occur in horizons above the fragipan. There is limited documentation regarding the in situ morphology of the nodules or their relationship to the underlying fragipan. The objectives of this study were to document (i) the profile distribution of nodules, (ii) variations in nodule morphology with depth, and (iii) the role of fragipans in nodule formation. Nodules were most common and largest directly above the fragipan horizons. Field and micromorphological observations suggested the nodules formed in remnants of the brittle fragipan matrix as a result of the conversion of Btx material to E′ material (albic material) that isolated and surrounded brittle fragipan peds. The brittle peds that are the precursors to nodules appeared to decrease in size and became more highly impregnated with Fe and Mn oxides with distance above the fragipan. Spatial relationships of Fe concentrations and argillans within the nodules illustrated that the nodules were being formed in place and were not transported despite having distinct borders. With time the glossic horizon expands at the expense of the fragipan, resulting in a horizon consisting of Fe–Mn nodules and a few isolated brittle peds in a matrix of albic material.
Ten‐Year Responses of Soil Quality and Conifer Growth to Silvicultural Treatments
Authors: Périé Catherine , Munson Alison D.
Published: July 2010

The development of sustainable forestry practices and credible certification systems relies on continuous monitoring of indicators. In the present study, carried out at the Petawawa Research Forest (Ontario, Canada), we evaluated the impacts of three intensive silvicultural treatments: scarification, fertilization, and herbicide treatment, applied alone or in combination—on indicators of organic layer quality, foliar nutrition, and tree growth—10 yr after establishment of eastern white pine (Pinus strobusL.) and white spruce [Picea glauca(Moench) Voss] plantations. We compared these 10‐yr results with measurements made 3 to 4 yr after plantation establishment. In both 1989 and 1996, the herbicide treatment had the greatest effect on organic layer quality. In 1996, compared with the no‐treatment control, herbicide application reduced organic C mass by 46%, total N mass by 15%, and acid phosphatase activity by 64%. These negative effects were offset when herbicide was applied in combination with fertilizer. The negative impact of herbicide on microbial biomass C noted in 1990 was no longer evident in 1996. In herbicide‐treated plots, the nitrate‐dominated cycle observed 1989–1990 was replaced by an ammonium‐dominated cycle in 1996. Although herbicide application negatively affected soil quality, it increased tree growth and generally improved foliar nutrition; thus organic layer and tree responses were not correlated. The indicators used were sensitive to changes in the ecosystem over time and signaled soil impacts that could have consequences for long‐term productivity.
Soil Color as an Indicator of Slash‐and‐Burn Fire Severity and Soil Fertility in Sumatra, Indonesia
Authors: Ketterings Quirine M. , Bigham Jerry M.
Published: July 2010

Fire is widely used as a tool for converting forest to agricultural land in many developing countries, and correlations are thought to exist between fire severity, burned soil color, and soil fertility. To test this hypothesis, field experiments were conducted in Sepunggur, Jambi Province, Sumatra, Indonesia. Field burning a slashed 12‐ to 15‐yr‐old secondary forest caused Munsell values and chromas to decrease and hues to become yellower with increasing heat severity, especially in the top 5 cm of the soil. However, at peak surface temperatures >600°C, soil C was mostly depleted and the soil matrix was reddened. Laboratory studies showed similar results with static heating. Moreover, color changes were highly dependent on the duration of exposure at a given temperature. Fire induced the formation of aggregates with exteriors that had lower values and chromas and slightly redder hues than the interiors. Laboratory removal of organic matter from burned samples by chemical oxidation did not alter the color. Soil exchangeable Ca, Mg, and K increased with fire severity, while exchangeable acidity and Al decreased 2 wk after the burn. Soil C and N were reduced at high burn severity only. Phosphorus showed an increase in availability at low to medium fire severity and a decrease in availability at the most intense burn levels. Colors of burned areas in the field did not change significantly during the 12 wk following the burn. However, within 12 wk following the field burn exchangeable Ca had decreased to preburn levels and Al saturation had increased markedly. Using postburn color measurements to predict the spatial patterns in soil fertility was limited by the fact that fertility changed rapidly following the burn, whereas color parameters did not.
Carbon Distribution in Subalpine Forests and Meadows of the Olympic Mountains, Washington
Authors: Prichard Susan J. , Peterson David L. , Hammer R. David
Published: July 2010

Estimates of C storage in mountainous regions are rare. Forest–meadow ecotones in subalpine ecosystems, which contain a mosaic of forests and meadows, may be particularly sensitive to future changes in climate and are therefore important to include in estimates of terrestrial C storage. In this study, we quantified soil C and ecosystem C pools in subalpine forest and meadow soils of the northeastern (NE, dry climate) and southwestern (SW, wet climate) Olympic Mountains. Carbon concentrations of mineral soil are relatively high in upper horizons, ranging from 43 to 142 g kg−1in NE soils and 27 to 162 g kg−1in SW soils. Northeastern meadow soils store more C than NE forests, while SW forest soils store more C than SW meadowsEcosystem C storage is greater in forests than in meadows. Under a warmer climatic scenario with drier summers and wetter winters, subalpine C storage may decrease in the NE and increase in the SW, and changes in C storage will be closely related to vegetation distribution, ecosystem productivity, decomposition rates, and local disturbance regimes. Because ecosystem processes and associated C storage differ between high‐ and low‐elevation ecosystems, it is important that data from both high‐ and low‐elevation sites are included in estimates of C storage in terrestrial ecosystems.
A Simple Treatment of Physical Nonequilibrium Water Flow in Soils
Authors: Ross P. J. , Smettem K. R. J.
Published: July 2010

Water flow in soils with sufficiently large aggregate size or pore‐class heterogeneity may exhibit a nonequilibrium between the actual water content and that given by the water retention curve. The result is deeper penetration of infiltrating water than predicted using classical infiltration theory. Models of this process usually divide the soil into two or more exchanging flow regions. A simpler treatment is possible by combining Richards' equation with a dynamic description of the approach to equilibrium. We present a first‐order time constant equilibration model of infiltration into a hypothetical structured soil and use the model to describe published outflow responses to constant rate rainfall on six large, undisturbed cores. Using measured hydraulic properties and varying only the A and B horizon time constants, the model was fitted to cumulative outflow from one particular soil core that had measured time domain reflectometry (TDR) water contents at the 0.05‐ and 0.5‐m depths recorded during the experiment. Cumulative outflow was fitted using time constants of 4 and 5 h for A and B horizons, respectively, and this also gave good agreement with TDR measured water contents. Cumulative outflow and runoff from a further four of the six cores was described using the same A and B horizon time constants and varying only the macropore hydraulic conductivity. The remaining core contained a decayed root, which conducted water rapidly with little opportunity for lateral exchange. A description of cumulative outflow required both the macropore hydraulic conductivity and the time constant to be altered.
A Note on Calculating Hysteretic Behavior
Authors: Poulovassilis A. , Kargas G.
Published: July 2010

A computational procedure for approximating the hysteretic relationship between pore water content and pressure head in porous bodies is described. A distribution function F is introduced that retains the features of the distribution function F of the independent domain model, but its values are obtained by partitioning the slopes of the wetting boundary curve of a reproducible hysteresis loop proportionately to the slopes of the drying boundary curve or vice versa. With the help of data provided by a primary drying scanning curve the procedure can be extended to approximate the hysteretic curves in the presence of nonindependent water elements. Calculated scanning curves were compared with experimental ones and satisfactory agreement between calculated and experimental scanning curves was observed.
Effect of Dissolved Organic Matter in Treated Effluents on Sorption of Atrazine and Prometryn by Soils
Authors: Seol Yongkoo , Lee Linda S.
Published: July 2010

The apparent enhanced transport of soil‐applied atrazine following irrigation of treated effluents has been hypothesized to be from complexation of atrazine with effluent‐borne dissolved organic matter (DOM). Under long‐term effluent irrigation, even small DOM‐induced decreases in pesticide sorption can result in significant enhanced pesticide movement due to cumulative effects. The effect of atrazine and prometryn association with DOM extracted from municipal wastewater (MW), swine‐derived lagoon wastewater (SW), and dissolved Aldrich humic acid (HA) on sorption by two soils was measured in batch equilibration studies. Individual association of pesticides to DOM, sorption of DOM to soil, and pesticide sorption by soil were also quantified. Pesticide association to DOM normalized to organic carbon (OC) ranged from 30 to 1000 L/kg OC. DOM sorption by soil ranged from 1.5 to 10 L/kg with a silt loam having a higher affinity for the DOM than the sandy loam. DOM up to 150 mg OC/L did not significantly suppress sorption by soils of either atrazine or prometryne in agreement with predictions using the independently measured binary distribution coefficients in a model that assumed linear equilibrium behavior among pesticide, soil, and DOM. A sensitivity analysis was performed using the same model to identify what combination of soil, pesticide, and DOC variables may suppress sorption, resulting in facilitated transport. Results from the sensitivity analysis are presented and the potential for effluent properties other than DOM to facilitate pesticide transport is discussed.
Soil Nitrogen Dynamics in Organic and Mineral Soil Calcareous Wetlands in Eastern New York
Authors: Van Hoewyk Douglas , Groffman Peter M. , Kiviat Erik , Mihocko Gail , Stevens Gretchen
Published: July 2010

Calcareous wetlands are of great interest in conservation biology. Previous research has suggested that there are significant differences in soil microbial N cycle processes between calcareous wetlands developed on organic vs. mineral soils. In the study presented here, we measured potential net N mineralization and nitrification, denitrification enzyme activity and soil inorganic N levels at 25 calcareous wetland sites with variable substrate types. We also evaluated the response of N cycling to livestock grazing by sampling at two sites with heavy grazing activity. All N cycle variables were significantly higher in organic soils than mineral soils on a weight basis; however, there were very few differences when results were expressed on an areal (volume) basis because of the low bulk density of the organic soils. The areal results suggest that organic and mineral soil calcareous wetland sites have similar N water quality maintenance values, that is, the ability to absorb N from upland land areas. Heavily grazed sites had significantly decreased pH and increased NO−3 levels relative to undisturbed sites, but the differences were small. The lack of strong differences in N cycle variables between mineral and organic soil sites raises questions about the need to make a classification distinction between calcareous peatlands (fens) and calcareous mineral soil wetlands in nutrient cycling and water quality maintenance contexts.
Impact of Climate and Parent Material on Chemical Weathering in Loess‐derived Soils of the Mississippi River Valley
Authors: Muhs D. R. , Bettis E. A. , Been J. , McGeehin J. P.
Published: July 2010

Peoria Loess‐derived soils on uplands east of the Mississippi River valley were studied from Louisiana to Iowa, along a south‐to‐north gradient of decreasing precipitation and temperature. Major element analyses of deep loess in Mississippi and Illinois show that the composition of the parent material is similar in the northern and southern parts of the valley. We hypothesized that in the warmer, wetter parts of the transect, mineral weathering should be greater than in the cooler, drier parts of the transect. Profile average values of CaO/TiO2, MgO/TiO2, K2O/TiO2 and Na2O/TiO2, Sr/Zr, Ba/Zr, and Rb/Zr represent proxies for depletion of loess minerals such as calcite, dolomite, hornblende, mica, and plagioclase. All ratios show increases from south to north, supporting the hypothesis of greater chemical weathering in the southern part of the valley. An unexpected result is that profile average values of Al2O3/TiO2 and Fe2O3/TiO2 (proxies for the relative abundance of clay minerals) show increases from south to north. This finding, while contrary to the evidence of greater chemical weathering in the southern part of the transect, is consistent with an earlier study which showed higher clay contents in Bt horizons of loess‐derived soils in the northern part of the transect. We hypothesize that soils in the northern part of the valley received fine‐grained loess from sources to the west of the Mississippi River valley either late in the last glacial period, during the Holocene or both. In contrast, soils in the southern part of the valley were unaffected by such additions.
Soil Solution Response to Nitrogen and Magnesium Application in a Scots Pine Forest
Authors: Vestgarden Live S. , Abrahamsen Gunnar , Stuanes Arne O.
Published: July 2010

High inputs of N to N‐limited forests may disturb the nutrient balance of the plant‐soil system. The objective of this study was to quantify the effects of N and Mg applications on soil water chemistry in a 35‐ to 45‐yr‐old Scots pine (Pinus sylvestris L.) forest in southern Norway. Fertilizer applications began in 1990 and soil water sampling was carried out in May through October 1997 to 1999. Nine years with annual (one dose) inputs of 30 kg N ha−1 yr−1 increased the annual average nitrate N (NO3–N) leaching below the B horizon to ≈2.1 kg ha−1, compared with ≈0.1 kg ha−1 in the control plots. An input of 90 kg N ha−1 yr−1 resulted in symptoms of N saturation. The soil water concentration of NO−3 and ammonium (NH+4) increased, and the annual average leaching of inorganic N from May to October during the years 1997 to 1999 was ≈15 kg N ha−1 The N addition significantly reduced the concentrations of dissolved organic carbon and N (DOC and DON), but the contribution of DON to the total N leaching from the plots receiving the highest N dose was still large. Addition of 1.5 kg ha−1 yr−1 of Mg increased the DOC and DON concentrations. The reason for this is unknown, and further studies are needed to understand DOC and DON dynamics. Even though applications of high single N doses are not directly comparable to chronic N depositions of small doses in precipitation, the results indicate future consequences to pine forests growing under similar conditions.
Evaluating Chemical and Physical Indices of Nitrogen Mineralization Capacity with an Unequivocal Reference
Authors: Wang Weijin , Smith Chris J. , Chalk Phillip M. , Chen Deli
Published: July 2010

After decades of searching for a rapid method to estimate the N mineralization capacity of soil, there is still no consistent recommendation. It is legitimate to examine the causes for the often‐conflicting results in literature. The efficacy of various references that have been used as benchmarks for assessing chemical and physical indices in the literature is critically reviewed in this paper. Gross N mineralization and consumption during waterlogged and aerobic incubations were estimated in a wide range of soils. It was found that equivalent to 17 to 90 and 23 to 59% of the mineralized N was consumed during the waterlogged and aerobic incubations, respectively. As net N production rate represents the balance between N‐producing and N‐consuming processes, it appears difficult to find a simple method that could be used to predict the net effect of several concurrent processes. We used the gross N mineralization as a reference criterion for N mineralization ability. Total organic N, water‐soluble organic N, alkali‐hydrolyzable N, acid‐hydrolyzable N, hot salt‐hydrolyzable N and N in the light organic matter fraction were assessed against this reference criterion. All indices except light fraction N were significantly related to gross N mineralization. Water‐soluble organic N had the highest correlation of all the indices tested. None of the chemically hydrolyzed N fractions consistently showed closer relationships with N mineralization than total organic N, suggesting that these chemical methods are ineffective in extracting a biologically labile fraction of soil organic N.
Stabilization of Fertilizer Nitrogen‐15 into Humic Substances in Aerobic vs. Waterlogged Soil Following Straw Incorporation
Authors: Devêvre Olivier C. , Horwáth William R.
Published: July 2010

This study was undertaken to investigate and quantify the interactive effects of flooding and straw incorporation on key microbial processes, principally stabilization of fertilizer N into various soil organic matter (SOM) pools. The fate of fertilizer15N in a paddy soil was examined at 5, 15, and 25°C, with and without rice (Oryza sativaL.) straw added, and under flooded and nonflooded conditions. After a 160‐d incubation, three fractions of the SOM were separated and defined as directly alkali‐extractable humic substances (DAEHS), reducible metal‐bound humic substances (RMBHS), and non‐alkali‐extractable organic matter (NAEOM). The DAEHS had the highest percentage, up to 50%, of fertilizer15N recovered at 160 d, indicating that this SOM fraction was the most dynamic fraction of the SOM. On the other hand, the RMBHS is considered the least dynamic pool, containing up to 12% fertilizer15N after 160 d. The NAEOM was surprisingly highly enriched, up to 28% fertilizer15N, and showed a significant treatment effect, suggesting that some active components of N cycling were present in this SOM fraction. The addition of rice straw increased the recovery of fertilizer15N in the above SOM fractions. Flooding significantly reduced the stabilization of fertilizer N compared with the nonflooded treatment. Indices of recalcitrance of the stabilized N confirm that the soil N supply capacity does not decrease with flooding. The total alkali‐extractable organic matter (AEOM = DAEHS + RMBHS), as the NAEOM, appears to be a complex and dynamic mixture of potentially mineralizable and recalcitrant forms of N. Our data show that long‐term N availability and stabilization into humic fractions is a function of rice residue input and temperature; however, the effects of residue and temperature are inversely related. With increase in temperature of incubation, less fertilizer N becomes stabilized into humic fractions, presumably from increased microbial activity, microbial consumption of potential humic precursors (N‐containing precursors of humic substances turned over faster at higher temperatures), and/or formation of different end‐products with less humification potential.
Tidal Inundation of Transgressive Coastal Areas
Authors: Hussein A.H. , Rabenhorst M.C.
Published: July 2010

Two transects were selected across submerging landscapes in Dorchester County, Maryland, to study the impact of the frequency of tidal inundation on salinization and alkalinization. The frequency of high tides of a particular elevation increases over time due to rising sea level to create dynamic environments in submerging coastal soils. The constructed frequency distribution curves of high tide at Hell Hook and Cedar Creek revealed that the frequency pattern was logarithmic and increased with lower elevation. This distribution enhances the relative importance of tidally induced pedogenic processes at elevations approaching mean high water. For pedons above mean high water, the effect of salinization and alkalinization processes follows the logarithmic frequency distribution pattern. However, for pedons below mean high water, the effect of these pedogenic processes is expected to decline toward a steady‐state condition. In marsh environments, the pH‐dependent acidity of submerging Al‐buffered soils (Ultisols) is not replaced upon permanent inundation, and increasing electrical conductivity (EC) of the soil solution enhances the selectivity of the colloidal complex for Al. Therefore, in response to sea‐level rise, low‐lying Ultisols transform directly to Histosols. Due to high exchangeable acidity associated with Atlantic coastal soils, the assumptions underlying the relationship between the exchangeable sodium percentage and the sodium adsorption ratio are not valid. Thus, exchangeable sodium percentage should be used to assess soil alkalinity.
Phosphorus Sorption Dynamics in Soils and Coupling with Surface and Pore Water in Riverine Wetlands
Authors: Bridgham Scott D. , Johnston Carol A. , Schubauer-Berigan Joseph P. , Weishampel Peter
Published: July 2010

Adsorption to soils is one of the dominant mechanisms of P storage in wetlands. We examined P sorption dynamics in soils collected at 12 sample points with diverse hydrology, geomorphic position, mineralogy, and plant communities in two riverine wetlands in northern Minnesota and Wisconsin. Phosphorus sorption parameters from these 12 sample points were correlated with corresponding biogeochemical variables and subsequently extrapolated across 157 sampling points in the two wetlands, based upon a large spatial dataset. We then used a series of single and stepwise regressions to determine the best set of predictive variables for surface water, soil, and plant P pools. Intrasite variation in P sorption dynamics was greater than intersite variation between the two wetlands and rivaled the variation found in the literature for both upland and wetland soils. An essentially constant final P concentration occurred at moderate P additions (≤32 μmol P L−1), indicating extreme soil buffering capacity of porewater P concentrations. Spatial variation in soil P pools across each wetland were predicted very well in stepwise regressions, particularly in the summer (R2= 0.49–1.00). Variables that were important in explaining this variation included the amount of P sorbed at equilibrium, maximum P sorption capacity, percentage of P sorption sites occupied at equilibrium, organic matter content, bulk density, and oxalate‐extractable Fe and Al content. Phosphorus concentrations in surface water were predicted less well by stepwise regression (R2= 0.04–0.46), suggesting only weak‐to‐moderate spatial coupling between soils and surface‐water P dynamics. Plant P pools were predicted poorly. Our results indicate the importance of geochemical sorption in controlling P dynamics in riverine soils. We suggest that nutrient studies in spatially diverse wetlands must be designed in a manner that adequately captures the rich spatial dynamics of the system.
Fertilization Effects on Soil Solution Chemistry in Three Eucalypt Plantations
Authors: Smethurst P.J. , Herbert A.M. , Ballard L.M.
Published: July 2010

Concentrations of nutrients in soil solution may by important indicators of nutrient availability for forest plantations, but we were unaware of the extent to which these concentrations varied temporally and were affected by fertilizer treatments at various sites. The effect of fertilizing eucalypt plantations on the concentrations of NH4, NO3, and inorganic phosphate (Pi), and on electrical conductivity (EC) and pH in paste extracts was assessed at three sites in Tasmania, Australia. Nitrogen and P fertilizers were broadcast at elemental rates in the range 0 to 600 kg ha−1 as (NH4)2SO4 and triple super‐phosphate within 2 mo of planting, and again at 26 mo at two of the sites. Nutrient concentrations in undiluted soil solution were inferred by adjusting for the effects of dilution and buffering. Both fertilization events decreased pH by up to one‐half a unit, and increased conductivity and the concentrations of NH4 and Pi by up to 10‐fold in the 0‐ to 60‐cm depth at all sites. Even at the highest rate of application, values of all parameters generally returned to unfertilized values before the second application of fertilizer. Rates of decrease in concentrations of NH4 and Pi after fertilization were unaffected by the age of the crop. When broadcast, applications of fertilizers may be needed at 2‐ to 4‐yr intervals to maintain high nutrient availability. A single application of (NH4)2SO4 to these soils at a typical rate of 200 kg N ha−1 will have minimal effect on pH, but multiple applications could decrease pH and adversely affect Ca, K, and Mg availability.
Flow Interruption Effects on Intake Rate and Rill Erosion in Two Soils
Authors: Sirjacobs D. , Shainberg I. , Rapp I. , Levy G.J.
Published: July 2010

Efficiency of surface irrigation is often low because of poor infiltration uniformity, resulting from relatively long periods of infiltration at the upstream end and short periods of infiltration at the downstream end of the field. Surge irrigation, the intermittent supply of water to furrows, generally reduces soil intake rate (IR) and improves moisture uniformity over the entire field. However, IR reduction varies from one irrigation scheme to another, depends on soil and water properties, and is difficult to predict. A laboratory study using miniflumes was designed to investigate the effect of interrupted flow on IR and soil loss from short rills. Two soils differing in their textures, a silt loam (Calcic Haploxeralf) derived from loess and a clay soil (Typic Haploxerert), were studied. Intake rate in the clay soil was greater than that in the silt loam. Therefore, different inflow rates were applied to the two soils to achieve similar runoff flow rates from the two soils. Cumulative infiltration decreased from 646 mL in continuous flow to 539 mL in interrupted flow for the silt loam and from 1142 to 1068 mL in the clay soil. Interrupted flow also reduced cumulative soil loss by 84% in the clay soil but had only a small effect on soil loss from the silt loam. However, when flow rate was increased from 80 to 320 mL min−1, interrupted flow reduced soil loss in the silt loam as much as in the clay soil. Consolidation of the soil surface and formation of cohesive forces between soil particles of the silt loam with unstable structure during flow interruption was suggested as the explanation for the effect of flow interruption on intake rate and soil detachment. These results need to be verified in field experiments.
Evaluation of Nitrate‐Nitrogen Transport in a Potato–Barley Rotation
Authors: Delgado Jorge A. , Riggenbach Ronald R. , Sparks Richard T. , Dillon Merlin A. , Kawanabe Lawrence M. , Ristau Randall J.
Published: July 2010

Well water NO−3–N concentrations have been found to exceed 10 mg L−1 of NO−3–N for some areas of the San Luis Valley (SLV) of South‐Central Colorado. The region's predominant soils are sandy soils, with a dominant potato (Solanum tuberosum L.) followed by malting barley (Hordeum vulgare L.) crop rotation. There is limited knowledge about how much NO−3–N is lost by leaching from these systems, and protocols need to be developed to evaluate the NO−3–N transport out of these coarse textured soils from these arid and semiarid irrigated cropping systems. Management information, N content at harvest, initial and final NO−3–N in the soil profile, and other supportive data were collected at 14 commercial fields and used as inputs for the Nitrate Leaching and Economic Analysis Package (NLEAP) model, version 1.20. NLEAP simulated available soil water for the root zone as well as the transport of NO−3–N in the soil profile, and can be used as part of the protocol to evaluate the NO−3–N transport of these systems. Best recommended practices in this region, such as application of N fertilizer rates on the basis of soil test analysis and split applications of N fertilizers, kept the net transport of NO−3–N out of the potato–barley systems to a minimum. Our approach of applying simulation models to assess management scenarios showed that barley served as a scavenger for the NO−3–N that was added with irrigation water and the residual soil nitrate from the potato growing period.
An inexpensive, portable meter for measuring soil moisture
Authors: O'Brien Joseph J. , Oberbauer Steven F.
Published: July 2010

Until now, dielectric‐based soil moisture measurements required expensive cable testers or commercial systems to read probes. Here we describe a method of constructing an inexpensive meter from a multimeter and a simple power supply. When coupled with a Campbell Scientific (Logan, UT) CS615 probe, the entire system costs ≈$350 US. A single meter can be used to measure multiple probes and the entire system is quite small and portable. The new system reads soil moisture probes capable of measuring a soil's dieclectric constant. Measurements taken with the meter described here and a CR10 data logger recommended by the probe manufacturer did not differ significantly. Nor was there any measurement offset between the data logger and the meter.
Selectivity Sequence and Competitive Adsorption of Heavy Metals by Brazilian Soils
Authors: Gomes Paulo C. , Fontes Mauricio P.F. , da Silva Aderbal G. , de S. Mendonça Eduardo , Netto André R.
Published: July 2010

Heavy‐metal cations can be introduced into agricultural soils by application of fertilizers, liming materials, sewage sludge, composts, and other industrial and urban waste materials. Therefore, heavy‐metal adsorption reactions, in a competitive system, are important to determine heavy‐metal availability to plants and their mobility throughout the soil. This study was conducted to evaluate the selectivity sequence and estimate the competitive adsorption of several heavy metals in seven soils with different chemical and mineralogical characteristics. Distribution coefficients (Kd), which represent the sorption affinity of metals for the solid phase, were obtained for each soil and heavy‐metal cation. On the basis of these Kd, the selectivity sequence was evaluated. The most common sequences were Cr > Pb > Cu > Cd > Zn > Ni and Pb > Cr > Cu > Cd > Ni > Zn. Chromium, Pb, and Cu were the heavy‐metal cations most strongly adsorbed by all soils, whereas Cd, Ni, and Zn were the least adsorbed, in the competitive situation. Selectivity sequences related to valence for the trivalent Cr. For metals of the same valence, sequences did not exactly follow the order of electronegativity. For individual elements, the Misono softness parameter and hydrolysis properties of the heavy‐metal cations may have influenced the sequences. Correlation analysis showed that soil characteristics that may have affected the heavy‐metals adsorption, represented by the distribution coefficients, were pH and cation‐exchange capacity (CEC) for Cd and Cr; organic carbon, clay, and gibbsite contents for Cu; pH and CEC for Ni and Pb.
A Soil Organic Nitrogen Fraction that Reduces the Need for Nitrogen Fertilization
Authors: Mulvaney R. L. , Khan S. A. , Hoeft R. G. , Brown H. M.
Published: July 2010

The need to estimate mineralization has long been recognized in making N fertilizer recommendations, but little progress has thus far been made in identifying a specific fraction of soil organic N that affects crop responsiveness to N fertilization. After eliminating major defects in the methodology employed to fractionate the N in soil hydrolysates, a study was conducted to compare N‐distribution analyses for soils differing in N‐fertilizer responsiveness by corn (Zea maysL.). Hydrolyses with 6MHCl were performed on composite soil samples (0–30 cm) that had been collected in late March or early April of 1990, 1991, or 1992, from 18 sites in a N‐response study involving 75 site–years throughout Illinois with different soil types, crop rotations, and N management practices. Concentrations of amino sugar N were 33 to 1000% greater (P< 0.001) for 11 nonresponsive than for seven responsive soils, whereas no consistent difference was observed in their content of total hydrolyzable N, hydrolyzable NH4–N, or amino acid N. Upon aerobic incubation for 3 mo with biweekly leaching, production of (NH4+ NO3+ NO2)‐N averaged 260% greater for three nonresponsive soils than for two responsive soils, and was accompanied by a net decrease in amino sugar N but not in amino acid N. Soil concentrations of amino sugar N were very highly correlated with check‐plot yield (r= 0.79***) and fertilizer‐N response (r= −0.82***). On the basis of amino sugar N, all 18 soils were classified correctly as responsive (<200 mg kg−1) or nonresponsive (>250 mg kg−1) to N fertilization.
Tillage and Row Position Effects on Water and Solute Infiltration Characteristics
Authors: Vervoort R. W. , Dabney S. M. , Römkens M. J. M.
Published: July 2010

Biological channels and wheel track compaction zones increase heterogeneity of soil properties affecting infiltration, runoff, erosion, and solute movement. We hypothesized that crop, tillage system, and position relative to the plant row would alter the rate and pattern of water infiltration into a Grenada silt loam (fine‐silty, mixed, active, thermic, Oxyaquic Fraglossudalfs). We compared plant row (ROW), nontrafficked (UTK) and trafficked interrow (TRK) positions for cotton (Gossypium hirsutum L.) and grain sorghum [Sorghum bicolor (L.) Moench] grown with chisel plow, disk, or no‐tillage in the fourth year of a cropping system and tillage study. We used ring and tension infiltration measurements 3 to 10 wk after planting to determine infiltration rate and pore‐size distribution. Infiltration patterns and mobile water contents were studied by ponding Brilliant Blue FCF dye [(N‐ethyl‐N{4‐[(4‐{ethyl[(3‐sulfophenyl)methyl]‐amino}phenyl)(2‐sulfophenyl)methylene]‐2,5‐cyclohexadien‐1‐ylidene}‐3‐sulfoben‐zenemethanaminium hydroxide inner salt, disodium salt)](PYLAM products Co., Garden City, NY) and excavation. Neither tillage nor crop affected ponded infiltration rates that averaged 86.5 mm h−1 for the ROW, 18.6 mm h−1 for the UTK, and 2.4 mm h−1 for the TRK position. Sorghum had more pores (0.04 m3 m−3) between 1.0 and 0.2 mm diam. than cotton (0.02 m3 m−3). Deeper and less uniform dye penetration reflected lower mobile water contents under no‐tillage (0.04 m3 m−3) compared to tillage (0.20–0.27 m3 m−3). This research confirmed the importance of continuous macropores in solute movement, but ponded infiltration rates were only weakly correlated with maximum dye depth and did not reflect tillage system differences in dye patterns.
Design and Ammonia‐Recovery Evaluation of a Wind Speed‐Sensitive Chamber System
Authors: Cabrera M. L. , Kissel D. E. , Davis R. C. , Qafoku N. P. , Segars W. I.
Published: July 2010

A previously developed system to measure NH3volatilization in the field consists of a vacuum pump, volatilization chambers, and acid traps to capture NH3The vacuum pump of the system draws air through each chamber at a constant rate, which may be faster or slower than the wind speed outside the chamber. Because wind speed affects NH3volatilization, it would be desirable to draw air through the chambers at a wind speed similar to that outside the chambers. The objective of this work was to improve the existing design by adding the capability of adjusting the speed at which air is drawn through each chamber. A hot needle anemometer was placed next to each chamber to measure wind speed at 1 cm above the soil surface. Wind speed was used to adjust an electronic valve so that the rate at which air was drawn through the chamber would match the external wind speed. Three N recovery studies were conducted with a sand–CaCO3mixture in the field to determine if the system could be used to obtain quantitative estimates of NH3volatilized. The NH3volatilized in each study was estimated from (i) the loss of soil inorganic N and (ii) the N captured in the acid traps. In all three studies, the NH3volatilized estimated from the acid traps (10–15% of applied N) was not different from the NH3volatilized estimated from the loss of soil inorganic N. These results indicate that the system can be used to obtain quantitative measurements of NH3volatilized under the conditions of these studies.
Temporal Dynamics of Preferential Flow to a Subsurface Drain
Authors: Jaynes D. B. , Ahmed S. I. , Kung K.-J. S. , Kanwar R. S.
Published: July 2010

We conducted a sequential tracer leaching study on a 24.4 by 42.7 m field plot to investigate the temporal behavior of chemical movement to a 1.2‐m deep field drain during irrigation and subsequent rainfall events over a 14‐d period. The herbicides atrazine [6‐chloroN‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine], and alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)acetamide] along with the conservative tracer Br were applied to a 1‐m wide strip, offset 1.5 m laterally from a subsurface drain pipe, immediately before an 11.3‐h long, 4.2‐mm h−1 irrigation. Three additional conservative tracers, pentafluorobenzoate (PF), o‐trifluoromethylbenzoate (TF), and difluorobenzoate (DF) were applied to the strip during the irrigation at 2‐h intervals. Breakthrough of Br and the two herbicides occurred within the first 2‐h of irrigation, indicating that a fraction of the solute transport was along preferential flow paths. Retardation and attenuation of the herbicides indicated that there was interaction between the chemicals and the soil lining the preferential pathways. The conservative tracers applied during the later stages of irrigation arrived at the subsurface drain much faster than tracers applied earlier. The final tracer, applied 6 h after the start of irrigation (DF), took only 15 min and 1 mm of irrigation water to travel to the subsurface drain. Model simulations using a two‐dimensional, convective, and dispersive numerical model without an explicit preferential flow component failed to reproduce Br tracer concentrations in the drain effluent, confirming the importance of preferential flow. This study showed that preferential flow in this soil is not a uniform process during a leaching event.
An algorithm for generating cation exchange isotherms from binary selectivity coefficients
Authors: Bloom S. A. , Mansell R. S.
Published: July 2010

An algorithm for simulating ion exchange batch mode experiments utilizing a known binary or ternary linear or nonlinear selectivity matrix and disequilibrium concentrations in exchange and solution phases was developed, and can be used to calculate initial equilibrium conditions for the initiation of numerical transport simulations, to generate binary isotherms (by repeated applications), and to separate ion‐exchange from other solute reactions in soils. The algorithm is an iterative process utilizing a binary search to determine the sorbed phase concentrations defined by the selectivity values and dissolved phase concentrations while maintaining the correct total mass of all ions. It was developed to aid in the separation of ion‐exchange from other retention processes when empirical determination of exchange isotherms are difficult or impossible.
A Chloride Deficient Leaf Spot of Durum Wheat
Authors: Engel R. E. , Bruebaker L. , Emborg T. J.
Published: July 2010

A leaf spot complex of ‘WB881’ durum (Triticum turgidum L. var. durum), similar to symptoms observed in winter wheat (Triticum aestivum L), was greatly suppressed by Cl at a field site in Montana. The objectives were to determine: (i) if this leaf spot phenomenon could be reproduced under hydroponics; (ii) the effect of Cl on leaf spot severity, water use, and plant growth; (iii) whether Br could substitute for Cl; and (iv) whether other durum cultivars were susceptible to leaf spotting under Cl deficiency. WB881 durum was grown at four halide (Cl and Br) levels of 1.5, 3.0, 6.0, and 30.0 mmole pot−1, plus a control. Three cultivars (WB881, Kyle, and Monroe) were grown at Cl levels of 0, 1.2, and 24.0 mmole pot−1 Withholding Cl from starter and refill solutions reproduced leaf spotting in WB881 similar to symptoms observed in the field. Leaf spotting was suppressed by Cl up to the 30.0 mmole pot−1 dose, but was aggravated by Br. Plant water use increased with Cl up to the 30.0 mmole pot−1 dose and was related to the beneficial effect of Cl in suppressing tissue necrosis. Leaf spot severity was closely related to shoot Cl concentration. Tissue necrosis was minor if Cl concentration was ≥1.0 g kg−1, but increased exponentially below this level. Withholding Cl from the hydroponic cultures reduced shoot and grain yield 58.2 and 98.9%, respectively. Bromide did not substitute for Cl by improving shoot and grain yield. Monroe was less susceptible to this Cl‐deficient leaf spot than was WB881 or Kyle. Cultivar susceptibility or tolerance to leaf spotting could not be explained by differences in Cl partitioning within the plant (e.g., roots, shoots, leaves).
Map Quality for Site‐Specific Fertility Management
Authors: Mueller T. G. , Pierce F. J. , Schabenberger O. , Warncke D. D.
Published: July 2010

The quality of soil fertility maps affects the efficacy of site‐specific soil fertility management (SSFM). The purpose of this study was to evaluate how different soil sampling approaches and grid interpolation schemes affect map quality. A field in south central Michigan was soil sampled using several strategies including grid‐point (30‐ and 100‐m regular grids), grid cell (100‐m cells), and a simulated soil map unit sampling. Soil fertility [pH, P, K, Ca, Mg, and cation‐exchange capacity (CEC)] data were predicted using ordinary kriging, inverse distance weighted (IDW), and nearest neighbor (NN) interpolations for the various data sets. Each resulting map was validated against an independent data (n= 62) set to evaluate map quality. While soil properties were spatially structured, kriging predictions were marginal (prediction efficiencies ≤48%) at high sample densities and poor at lower densities (i.e., 61‐ and 100‐m grids; prediction efficiencies <21%). The average optimal distance exponent at each scale of measurement was 1.5. The performance of kriging relative to IDW methods (with a distance exponent of 1.5) improved with increasing sampling intensity (i.e., IDW was superior to kriging for 100% of cases with the 100‐m grid, 79% of the cases with the 61.5‐m grid scale, and 67% of the cases with the 30‐m grid). Practically, there was little difference between these interpolation methods. Grid sampling with a 100‐m grid, grid cell sampling, and simulated soil map unit sampling yielded similar prediction efficiencies to those for the field average approach, all of which were generally poor.
Models for Estimating Soil Particle‐Size Distributions
Authors: Hwang Sang Il , Lee Kwang Pyo , Lee Dong Soo , Powers Susan E.
Published: July 2010

An accurate mathematical representation of particle‐size distributions (PSDs) is required to estimate soil hydraulic properties or to compare texture measurements from different classification systems. The objective of this study was to evaluate the ability of seven models (i.e., five lognormal models, the Gompertz model, and the Fredlund model) to fit PSD data sets from a wide range of soil textures. Special attention was given to the effect of texture on model performance. Several criteria were used to determine the optimum model with the least number of fitting parameters when other conditions are equal. The Fredlund model with four parameters showed the best performance with the majority of soils studied, even when three criteria that impose a penalty for additional fitting parameters were used. Especially, the relative performance of the Fredlund model in regard to other models increased with increase of clay content. Among all soil classes, the lognormal models with two or three parameters showed better fits for silty clay, silty clay loam, and silt loam soils, and worse fit for sandy clay loam soil.