bluuebunny/crossref_metadata_2025 huggingface dataset:
Vegetation Management and Interrill Erosion in No‐Till Corn Following Alfalfa
Authors: Gallagher A. V. , Wollenhaupt N. C. , Bosworth A. H.
Published: July 2010

No‐till corn (Zea mays L.) following alfalfa (Medicago sativa L.) is recommended for reducing soil erosion; however, killing alfalfa in the fall may result in insufficient crop residue cover for Conservation Compliance soil erosion goals. We hypothesized that soil conservation effectiveness was related to burn‐down spray date and final harvest date influence on cover. A Wisconsin field study to test this hypothesis included fall and spring burn‐down spray dates in combination with either August or September final alfalfa harvests. Soils included Plano and Saybrook silt loams (fine‐silty, mixed, mesic Typic Argiudolls) on 2 to 9% slopes and Palsgrove silt loam (fine‐silty, mixed, mesic Typic Hapludalf) and Reedsburg silt loam (fine‐silty, mixed, mesic Aquic Paleudalf) on 7 to 14% slopes. Simulated rainfall (72 mm h−1 for 1 h) was applied following corn planting. The fall spray‐September harvest (FS‐SH) averaged 25% residue cover, measured after planting, with soil loss of 257 g m−2. The spring spray‐August harvest (SS‐AH) averaged 79% residue cover and 24 g m−2 soil loss. Of the 72 mm of rain applied on each of the treatments, 34 mm ran off the two FS treatments, 23 mm ran off the SS‐SH treatments, and 19 mm ran off the SS‐AH treatments. Treatment runoff amounts and final infiltration rates related in part to surface macroporosity and surface sealing. Fall herbicide application resulted in too little residue cover to adequately reduce soil erosion.
The Fate of Sludge Phosphorus in Soil‐Plant Systems
Authors: Frossard E. , Sinaj S. , Zhang L‐M , Morel J. L.
Published: July 2010

Sewage sludges have been used for many years as sources of P for agricultural crops, but there is a lack of information regarding the proportion of sludge P that can be used by crops. The aim of this work was to assess the importance of soil available P and sludge origin on the utilization of sludge P by plants. First, the changes in soil P isotopically exchangeable within 1 min (E1min) were measured in incubated soil‐sludge mixtures using two soils and four sludges. Then, the uptake of sludge P by ryegrass (Lolium perenne L.) was measured on the same sludge‐amended soils. The application of sludges increased E1min to values lower or equal to those obtained following the application monocalcium phosphate. Similarly the utilization of sludge P by ryegrass was systematically lower than the utilization of P derived from a water‐soluble fertilizer. In both soils, the lowest utilization of sludge P was observed for the two FeSO4 flocculated and anaerobically digested sludges, while the primary sludge and the aerobically digested sludge released somewhat higher quantities of P to ryegrass. In the clayey soil, the amount of sludge P taken up by the crop was significantly related both to the sludge and soil available P content, whereas no such relation was observed in the loamy soil because of its high available P content. The origin of the sludge and the soil available P content must therefore be taken into account when advising sludge application to crops to adjust P inputs to plant needs.
A Modified Number‐based Method for Estimating Fragmentation Fractal Dimensions of Soils
Authors: Kozak E. , Sokołowska Z. , Stępniewski W. , Pachepsky Ya. A. , Sokołowski S.
Published: July 2010

Fractal theory has been applied to the characterization of particle‐ and aggregate‐size distributions in soils. We used a number‐based method for estimating fragmentation fractal dimensions from these distributions. This method has several inconsistencies. The objectives of our study were to: (i) propose a modified number‐based method, (ii) evaluate the modified method using published data on particle‐ and aggregate‐size distributions, and (iii) apply the modified method to a large particle‐size distribution data base to analyze the validity of fractal scaling. Assuming scale‐invariant fragmentation to be a valid model of particle‐size distribution within size ranges of fractions, we derived a formula expressing the characteristic grain size as a function of the fractal dimension and limits of the grain size range. Parameters of Turcotte's fractal fragmentation model were found by minimizing the sum of squares of differences between measured and calculated masses of grain fractions. Comparison between original and modified number‐based methods showed that the modified method generally resulted in lower fragmentation fractal dimensions than the original method. The modified method was applied to a data set of particle‐size distributions of 2600 soil samples. In 80% of samples, the fractal scaling was not applicable across the whole range of particle size between 0.002 and 1 mm, since errors of the fractal fragmentation model were statistically significantly larger than measurement errors, and estimates of the fractal dimension were larger than 3. It appears that models more sophisticated than scale‐invariant fragmentation are required to simulate soil particle‐size distributions.
Solute Transport under Transient Flow Conditions Estimated Using Time Domain Reflectometry
Authors: Risler P. D. , Wraith J. M. , Gaber H. M.
Published: July 2010

Improved methods having high resolution in space and time are needed to monitor transport of soluble chemicals in soils. We used time domain reflectometry (TDR) to measure breakthrough curves (BTCs) for Br− during miscible displacement in repacked soil columns under nonsteady water flow conditions. A simple linear model was used to estimate soil solution electrical conductivity (σw) based on TDR‐measured bulk soil electrical conductivity (σa) and volumetric water content (θ). An efficient calibration method was developed whereby required model parameters were estimated in the same soil volume and under the same flow conditions as were used in subsequent transport experiments. Breakthrough curves measured using TDR were similar to those based on electrical conductivity or Br− concentration in effluent fractions, although peak σw were substantially lower for TDR than for effluent from two of the four soils. Effluent σw BTCs were adequately predicted based on TDR σa and θ for all four soils when parameters of the simple linear model or two alternative models were optimized to the effluent data. Time moments and convection‐dispersion equation (CDE) transport parameters based on time moments of measured BTCs were similar for TDR and effluent analyses. Our results indicate that TDR has potential to monitor the status of representative concentrations of ionic solutes under laboratory and field conditions, without the need to impose steady water flow.
Determination of Arsenic Species in Soil Solution under Flooded Conditions
Authors: Onken B. M. , Hossner L. R.
Published: July 2010

Greenhouse experiments were conducted to evaluate the relationships between the species and concentrations of As in the soil solution of flooded soils with other parameters including soil pe, pH, Fe, Mn, and type and amount of As added. Two soils were treated with 0, 5, 15, 25, 35, and 45 mg As kg−1 soil added as either Na‐arsenate or Na‐arsenite and planted with rice (Oryza sativa L.). Soil solution samples were collected during a period of 60 d and analyzed for As. Selective hydride generation was employed to evaluate both type and quantity of As present in the samples. Inorganic As in the form of arsenate and arsenite was found in the soil solution of both soils. The conversion of added arsenite to arsenate occurred within the first 10 d of the experiment when the pe/pH of the soil was not conducive to arsenite stability. Added arsenate was converted to arsenite during the course of the experiment as the pe/pH of the soil declined due to flooding. Arsenate reached a maximum in soil solution at 10 to 20 d after flooding while maximum arsenite concentrations occurred at 20 to 30 d after flooding. The total concentration of As in soil solution generally reached a maximum at 20 to 30 d after flooding, after which time precipitous losses of As from soil solution occurred in all but the highest As treatments. Soil solution As concentrations were not statistically different between planted and unplanted controls.
Aspartase Activity of Soils
Authors: Senwo Z. N. , Tabatabai M. A.
Published: July 2010

The enzyme aspartase [L‐aspartate ammonia‐lyase, Enzyme Commission (EC) 4.3.1.1] catalyzes the hydrolysis of L‐aspartate producing fumarate and NH3. The detection of this enzyme in soils is reported, and a simple and precise method is described for assaying its activity in soils. The method involves determination, by steam distillation, of the NH4+‐N produced when soil is incubated with potassium aspartate in 0.1 M THAM [tris(hydroxymethyl)aminomethane] buffer (pH 8.5) and toluene at 37°C for 24 h. Results showed that soil aspartase has its optimum activity at buffer pH 8.5 and is inactivated at temperatures above 40°C. Preheating soil samples for 2 h before assay of aspartase activity showed that the enzyme is stable up to 40°C in field‐moist samples and up to 70°C in air‐dried samples. The Km values of the aspartase activity in three soils ranged from 0.173 to 0.208 M. The Arrhenius equation plot for aspartase activity in three soils was linear between 20 and 40°C. The activation energy values of the reaction catalyzed by this enzyme ranged from 40.1 to 50.7 kJ mol−1, and the temperature coefficients (Q10) ranged from 1.50 to 2.44 (avg. = 1.89). Treatment of soils with formaldehyde, dimethylsulfoxide, and HgCl2 decreased the aspartase activity but toluene increased this activity. The use of sulfhydryl reagents suggested that a free sulfhydryl moiety is present in the active sites of this enzyme. The coefficients of variation of the proposed method for assay of aspartase activity in soils was <2.5%.
Tillage and Nitrogen Placement Effects on Nutrient Uptake by Potato
Authors: Westermann D. T. , Sojka R. E.
Published: July 2010

Deep tillage of compacted soils can improve potato (Solanum tuberosum L.) tuber yield and quality if no other production factors are limiting. We hypothesized that within‐row subsoiling and N placement would affect tuber yields and availability of plant nutrients. Potato (cv. Russet Burbank) was grown after winter wheat (Triticum aestivum L.) in 1989 and after dry bean (Phaseolus vulgaris L.) in 1990 on a furrow irrigated Portneuf silt loam (coarse‐silty, mixed, mesic Durixerollic Calciorthid). Fall tillage treatments (disking, chiseling, and moldboard plowing) were split with zone subsoiling after planting. Nitrogen was broadcast before planting or banded beside the seed piece at planting across all tillage combinations. We estimated plant nutrient status and uptake each year with whole‐plant and petiole samplings during tuber growth. Final tuber yield and quality were determined in early October. Fall tillage did not influence nutrient concentration and uptake, tuber yield, or quality. Zone subsoiling increased average plant dry weights 9%, total tuber yields 10% (4 Mg ha−1), and quality, and increased P uptake an average of 11.6% (1.8 kg P ha−1) without appreciably changing whole‐plant or petiole P concentrations. Banding N increased average plant dry weight 6.4%, total tuber yield 9%, and N uptake 28% compared with broadcast N. Petiole NO3‐N, P, K, and Zn concentrations were higher where N was banded. There were no consistent zone subsoiling × N placement interactions. Higher nutrient applications may be required with zone subsoiling or to compensate for soil compaction problems.
Spatial Variability Patterns of Phosphorus and Potassium in No‐Tilled Soils for Two Sampling Scales
Authors: Mallarino Antonio P.
Published: July 2010

The increasing use of grid soil sampling methods and variable‐rate fertilization requires better understanding of patterns and causes of lateral variability of nutrients. This study assessed patterns of spatial variability of P and K for two scales of sampling on eight no‐tilled corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] fields. The fields had received no P or K fertilization since the last harvest but had varied histories of fertilization. Fifty 10‐core (0‐ to 15.2‐cm depth) composite samples were collected from 2.2‐m2 areas separated 3.05 m from each other along each of two 150‐m intersecting transects laid out across and along old crop rows. Sixty‐seven single‐core samples spaced 7.6 or 15.2 cm were collected from 7.85‐m segments of the transects across rows. Variography revealed high random and spatially structured variability for most fields. The structure of the variability differed among fields and directions within a field. Plots of soil‐test P and soil‐test K values, fast Fourier transform analyses, and semivariograms showed clusters and periodic patterns of variable regularity and size across fields. The cyclic patterns were more defined across crop rows. Small‐scale cyclic patterns with a period of ≈ 1 m revealed for some fields probably resulted from repeated banded fertilizer applications. Large‐scale cyclic trends with periods of 15 to 18 m or a multiple of this distance were probably the result of broadcast fertilization with commercial bulk spreaders. Sampling methods should be developed for fields with high spatial variability of cyclic structure at various scales. Producers should pay more attention to uniform application of fertilizers and manure.
Water‐Holding Characteristics of Metasedimentary Rock in Selected Forest Ecosystems in Southwestern Oregon
Authors: Zwieniecki Maciej A. , Newton Michael
Published: July 2010

On sites characterized by shallow soil in semiarid climates, lack of bedrock description may lead to underestimates of total storage capacity of water available for plants, and therefore of potential site productivity. Sample rocks from southwestern Oregon soil‐rock profiles excavated beneath typical forest plant communities were examined for pore volume distribution by means of mercury intrusion porosimetry and oversolution equilibrium. Four ranges of pore size were distinguished: gravitational water, available water content (AWC), slowly available water (SAW), and nonavailable water. Pore volume for AWC and SAW was associated with bulk density and in low density rock, was 20% of volume. Results suggest that metasedimentary rock has the potential to be a major reservoir of plant available water in semiarid climates.
Limitations of Bioassays for Monitoring Forest Soil Productivity: Rationale and Example
Authors: Burger James A.
Published: July 2010

Sustaining forest soil productivity is a common goal of forest landowners in the Southeast, but determining the effects of forest management practices on soil and site quality has not been easy. An unbiased measurement is needed to monitor sustained soil and site productivity. Growth cycle comparisons, traditional measures of forest productivity, are not very timely, are often biased, and do not always account for changes in soil quality due to management. This was demonstrated by comparing growth curves of two successive loblolly pine (Pinus taeda L.) rotations, and by comparing growth curves influenced by two site preparation treatments within the last rotation. The growth cycle comparison between rotations was not a definitive indicator of sustained soil quality because stand response could have been confounded by differences in genotype and vegetation management from the first to the second rotation. Stand responses due to soil treatment in the last rotation were confounded by the influence of different levels of competing vegetation. Because stand response is a function of many confounding non‐soil factors as well as soil quality, soil sustainability and the effects of management should be determined by measuring soil properties and processes directly.
Field Evaluation of Passive Capillary Samplers
Authors: Brandi‐Dohrn Florian M. , Hess Mario , Selker John S. , Dick Richard P.
Published: July 2010

Soil solution samplers have certain inadequacies that limit their range of possible applications. Passive capillary samplers (PCAPS), which apply suction to the soil pore water via a hanging water column in a fiberglass wick, have shown promising results in preliminary experiments in regard to collection efficiency of water and Br tracers. The objectives of this study were to evaluate PCAPS with respect to (i) effect of installation procedure and operational characteristics; and (ii) ability to estimate the soil‐water and solute flux. We installed 32 PCAPS and 32 ceramic suction cup samplers at a depth of 1.2 m in an undisturbed silt loam soil. For the first year, water flux, NO3‐N and Br concentrations in the part of the PCAPS closest (0.3 m) to the refilled trench were 15, 14, and 34% less, respectively, than in the part farthest (0.9 m) away from the refilled trench. This was attributed to installation procedure, since the bias ceased for the second year. Soil‐water flux measurements of PCAPS underestimated those determined by a water balance by 20 to 34%. Some of the discrepancy is thought to be due to the lack of accounting for runoff, which was observed but not quantified. The recovery of a Br tracer was low with an average of 29%, ranging from 5 to 77%, which was attributed to lateral water movement due to prominent lateral stratification. To estimate the mean Br concentration with a 30% bound at the 0.05 confidence level on this 1‐ha field site, 25 PCAPS and 37 suction cup samplers are necessary. Sampling a more evenly distributed solute such as residual fertilizer NO3 requires only eight PCAPS for this level of confidence.
BTEX Sorption by Organo‐Clays: Cosorptive Enhancement and Equivalence of Interlayer Complexes
Authors: Jaynes W. F. , Vance G. F.
Published: July 2010

Aqueous organic contaminants, such as gasoline‐derived aromatics, are effectively sorbed by organo‐clays. Organo‐clays were prepared from montmorillonite (SWy‐1, SAz‐1) and vermiculite (VSC) clay minerals by exchanging quaternary, alkylammonium cations for the inorganic exchange cations; thus, a variety of clay‐charge/organic‐cation combinations were formed. Dodecyltrimethylammonium (DTMA), hexadecyltrimethylammonium (HDTMA), didodecyldimethylammonium (DDDMA), and dioctadecyldimethylammonium (DODMA) organic cations were used. An aqueous mixture of BTEX (benzene, toluene, ethylbenzene, xylenes) consistent with unleaded gasoline was used to relate organo‐clay sorptivity to structure. Greater sorption of the BTEX mixture constituents than the pure compounds occurred when total sorbed BTEX loadings on the organo‐clays exceeded 10 g/kg. A cosorption effect caused curvilinear isotherms and enhanced BTEX mixture sorption; BTEX sorption increased the organo‐clay organic matter content, which promoted additional BTEX sorption. The sorptivities of the organo‐clays were generally proportional to the organic C contents; although SAz‐DDDMA and VSC‐HDTMA, with 20 to 30% less C, had twice the BTEX sorptivity of SAz‐DODMA and VSC‐DDDMA. No relationship was found between surface area and BTEX sorption. A straight‐chain alkyl cation conferred five times greater BTEX sorption to an organo‐clay than did a comparable cyclic alkyl cation. This suggests that rearrangements in the alkyl groups may facilitate sorption in a manner analogous to solvation. Organo‐clay BTEX sorptivity was governed by the type of alkylammonium complex; a paraffin complex with a 25.4 to 27.6 Å basal spacing was optimal. Organo‐clays of similar basal spacing prepared using different clays and alkylammonium cations had equivalent sorptive phases. Selection of an appropriate combination of clay and organic cation can optimize contaminant sorption by organoclays.
Fractal Dimension of Humic Acids in Aqueous Suspension as a Function of pH and Time
Authors: Senesi N. , Rizzi F. R. , Dellino P. , Acquafredda P.
Published: July 2010

The fractal dimensions of soil and peat humic acids equilibrated for various lengths of time in aqueous suspension at different pH values were determined by measuring their turbidity as a function of wavelength, with collaboration by scanning electron microscopy (SEM). Particle‐size distributions of the humic acid systems were also determined. The analysis of the power‐law dependence of the turbidity on the wavelength revealed that soil and peat humic acids may exhibit either a nonfractal or a mass fractal nature. Peat humic acid could also be described as a surface fractal. The passage from one regime to another depended on the pH and equilibration time. With an increase of either factor, the mass fractal dimension of humic acids decreased from about 2.8 to values close to 1.0. This trend, supported by SEM observations, suggested that humic particles in suspension evolve from compact, almost space‐filled structures with smooth surfaces, to less compact, fragmented and elongated structures with increasingly rough and irregular surfaces as the pH or time increases. Values of the mass fractal dimension close to 2.5 would reflect diffusion‐limited aggregation (DLA), whereas values close to 2.1 would suggest a reaction‐limited cluster‐cluster (RLA) aggregation model for humic acid. The fractal dimension thus represents a numerical parameter able to describe quantitatively the morphological features assumed by humic particles in suspension and to provide information on the underlying aggregation processes.
A Landscape‐Scale Assessment of the Nitrogen and Non‐Nitrogen Rotation Benefits of Pea
Authors: Stevenson F. C. , van Kessel C.
Published: July 2010

The inclusion of a pulse crop in a rotation often leads to an increase in seed yield of the succeeding cereal crop. Landscape‐scale and small‐plot studies were established in 1993 to assess the N and non‐N rotation benefit by pea (Pisum sativum L.) to the subsequent wheat (Triticum aestivum L.) crop. In the second rotation phase, wheat seed yields were 982 kg ha−1 greater and total N accumulation increased by 46 kg ha−1 in the pea‐wheat rotation. Reduced leaf disease severity and grassy weed infestation were related to 91% of the yield advantage in the pea‐wheat rotation, the non‐N rotation benefit. A 129 N kg ha−1 increase in the A value (soil N supplying power) was related to 9% of the yield advantage in the pea‐wheat rotation, the N benefit. In both rotations, seed yield was about 400 kg ha−1 lower in the high‐catchment footslopes than the low‐catchment footslopes and shoulders. The landform effect on seed yield in the pea‐wheat rotation was related to greater soil water and N content in the high‐catchment footslopes. Increased grassy weed infestation in the high‐catchment areas of the wheat‐wheat rotation was related to lower seed yields in this same area. The rotation benefit of pea to wheat was 34% greater in the landscape‐scale vs. the small‐plot study. Topographic variation interacted with factors responsible for the non‐N rotation benefit. A landscape‐scale assessment of the rotation benefit from legumes can be used to develop site‐specific management strategies that consider the effect of crop rotation.
A Rule‐based System to Map Soil Properties
Authors: Cook S. E. , Corner R. J. , Grealish G. , Gessler P. E. , Chartres C. J.
Published: July 2010

Conventional soil mapping is limited in its capabilities in that it presents a summary of the soil surveyor's conceptual view of soil variation. As such, the method conveys little regarding what is known about the variation of individual soil properties, or the quantitative nature of their variation. We developed a new method for soil mapping, based on the concepts employed in the PROSPECTOR mineral exploration system, which builds on existing soil surveyor knowledge to construct quantitative statements about individual soil properties via the development of a network of rules. These rules operate within a system of Bayesian inference to assign the varying probability of occurrence of a soil property of interest within an area, given evidence that relates to it in a known way. Permissible evidence includes the range of attributes normally used by a soil surveyor, such as landform, vegetation, land use, or parent material, and can also include remotely sensed digital data. Evidence is weighted according to the uncertainty associated with it, and combined to produce a single estimate of probability of a given attribute. The relationship between the evidence and prediction is stated explicitly at each stage of the procedure and is thus repeatable in a consistent manner. The system has the advantage that while it does not discard the evidence and knowledge used in conventional soil survey, it produces quantitative estimates of the distribution of soil properties, which can be used for a wide range of applications. The data produced is amenable to storage in geographic information systems and related data bases. As such, it can be updated or enhanced as new information or knowledge becomes available.
Experimental Soil Acidification and Recovery at the Bear Brook Watershed in Maine
Authors: Rustad L. E. , Fernandez I. J. , David M. B. , Mitchell M. J. , Nadelhoffer K. J. , Fuller R. B.
Published: July 2010

The response and subsequent recovery of soils (Typic Haplorthods) to acidification by dilute H2SO4 (2000 and 4000 molc ha−1 yr−1 of SO4), HNO3 (2000 and 4000 molc ha−1 yr−1 of NO3), and combined H2SO4‐HNO3 (2000 molc ha−1 yr−1 each of SO4 and NO3) were studied at the Bear Brook Watershed in Maine. Treatments were delivered to eighteen 15 by 15 m plots (three plots per treatment) during four field seasons from 1988–1991. Recovery was monitored for the ensuing two years. Changes in soil and soil solution chemistry were evaluated using tension lysimeters and buried mineral soil bags. Soil solutions responded rapidly to all treatments with increased concentrations of SO4 (four to eight times ambient) and NO3 (39 to 88 times ambient), depending on treatment, accompanied by increased concentrations of Ca and Mg (three to five times ambient) from the upper B horizon. As solutions passed through the upper 25 cm of the pedon, concentrations of SO4 and the sum of base cations decreased significantly. Results from buried mineral soil bags located directly below the forest floor indicated that a relatively reversible SO4 sorption mechanism was responsible for attenuating most SO4 losses from these soils. Following 4 yr of acid inputs and 2 yr of recovery, soil and soil solution chemistry were remarkably unchanged, demonstrating that this hardwood forest soil was not irreversibly altered and could quickly recover.
Mineralogical Properties of a Collapsible Lateritic Soil from Minas Gerais, Brazil
Authors: de Brito Galvão T. C. , Schulze D. G.
Published: July 2010

Soils weathered from limestone and sediments of the Bambuí Formation in parts of Minas Gerais, Brazil, are prone to near‐surface subsidence, resulting in damage to buildings and roads, and loss of life. Engineers consider them “collapsible soils” because they exhibit large decreases in volume and associated settlements with no increase in applied stress when wetting occurs. The objective of this study was to determine a possible mineralogical or chemical basis for this behavior. Three horizons to a depth of 170 cm from a Rhodic Hapludox near Sete Lagoas were analyzed by x‐ray diffraction, infrared absorption, electron microscopy, and wet chemical methods. All horizons were mineralogically very homogeneous, with kaolinite, gibbsite, and hematite dominant, but (dioctahedral) mica, hydroxy‐interlayered vermiculite, goethite, anatase, rutile, quartz, and perhaps cristobalite also present. More than 850 g kg−1 of each horizon consists of minerals with particles <2 µm, but aggregation of particles by Fe oxides results in a silt content of about 300 g kg−1. The pH of each horizon is at or very near to its zero point of charge. The physical properties of this soil are apparently dominated by: (i) the residual nature of the soil, which has weathered in place a very long time, resulting in high porosity and low bulk density, (ii) the aggregation of kaolinite and gibbsite by Fe oxides to form silt‐sized aggregates, and (iii) the variable surface charge of the dominant minerals. Future soil mechanics research on these soils should consider the consequences of chemical changes that might alter interparticle forces important in soil stability.
Modeling the Probabilities of Groundwater Contamination by Pesticides
Authors: Di H. J. , Aylmore L. A. G.
Published: July 2010

Field soils show significant spatial variations in properties, such as organic matter content, bulk density, and moisture content, that can affect the mobility and persistence and thus fate of organic pesticides in the soil environment. A simple model incorporating the variations in soil and pesticide parameters has been developed to assess the groundwater contamination potential of pesticides. The model is based on linear, equilibrium, and reversible sorption, first‐order degradation, and steady piston flow, and allows the unsaturated soil zone to be divided into a number of layers of different thickness and properties. For each input parameter, 500 random data were generated from normal distributions that characterize the variability of the parameters. The fate of 29 pesticides were assessed using soil and environmental conditions of the Swan Coastal Plains of Western Australia and pesticide properties reported in the literature. The predicted pesticide residue fractions remaining at 150‐, 300‐, and 500‐cm depths were described by beta distributions, and the corresponding travel times by normal distributions. Fourteen out of the 29 pesticides are predicted to reach 150 and 300 cm and 13 are predicted to reach the 500‐cm depth with mean residue fractions ≥ 0.01%. The predicted mean travel times for pesticides that may reach 300 cm vary from about 2 mo to about 18 yr. Significant standard deviations are associated with these mean residue fractions and travel times. Six pesticides, fenamiphos, simazine, metribuzin, linuron, fenarimol, and metalaxyl, have been identified as having high cumulative probabilities of 0.82 to 1.00 for residue concentrations to be >0.01% at the 300‐cm depth.
Seasonal Variation of Hydraulic Properties of Soils Measured using a Tension Disk Infiltrometer
Authors: Angulo‐Jaramillo R. , Thony J. L. , Vachaud G. , Moreno F. , Fernandez‐Boy E. , Cayuela J. A. , Clothier B. E.
Published: July 2010

For sound land management, it is important to understand the temporal changes that soil hydraulic properties undergo. Estimation of the unsaturated characteristics of the hydraulic conductivity, sorptivity, and mean pore radius was performed using tension‐disk infiltrometers in two different soils of the Mediterranean region: a sandy soil (Xerochrept) and a heterogeneous, stony, and sandy soil (Alfisol). Both soils were cropped with maize (Zea mays L.) and underwent conventional tillage and different irrigation practices, namely furrow irrigation and gun irrigation. The mobile water content was also deduced from soil samples extracted underneath the disk following a period of infiltration with the tension infiltrometer filled with a Cl− tracer. Results are presented here of measurements made after plowing and again at the end of the growing season. During the growing season, the sandy soil under furrow irrigation showed a significant decrease in its hydraulic properties. This followed an increase in the bulk density and was a result of sealing of the small interconnected pores at the soil surface. Strong nonlinearity in the hydraulic conductivity was found for the stony soil, yet there was no significant change in this nonlinearity during the growing season. However, from the tracer results, it is stated that for this soil, the structure of the fine fraction changes from a well‐interconnected microporous network to a poorly connected one. This results in an increase of the mobile water content during the growing season. It is shown that a good understanding of the porous network can be obtained from tension infiltrometers and can explain changes in both the hydraulic conductivity and the sorptivity. These changes were also partially corroborated by the mobile water content measurements obtained from tracer observations under the disk.
Image Analysis for Determination of Dye Tracer Concentrations in Sand Columns
Authors: Aeby P. , Forrer J. , Flühler H. , Steinmeier C.
Published: July 2010

Dye tracers can be used to visualize flow paths in soils. We used digital image analysis to determine the spatial distribution of dye concentrations in a quartz sand column. Color slides and near‐infrared black‐and‐white photographs were taken from a sand column that was cut in halves longitudinally after a point‐source dye infiltration experiment. In a separate calibration experiment, sand samples were prepared with known water content and dye concentration. Photographs of such sample arrays were used as training areas for image analysis. Image analysis is a viable way for obtaining a high spatial resolution of tracer concentrations and provides a quantitative basis for describing different solute mixing regimes.
Combining Scanning Tunneling Microscopy and Computer Simulation of Humic Substances: Citric Acid, a Model
Authors: Bailey George W. , Shevchenko Sergey M. , Yu Y. Shane , Kamermans Heleen
Published: July 2010

Citric acid (CA) is a model for soil humic substances and an important participant in many biochemical processes. Humic and humic‐like materials play crucial roles in the bioavailability and mobility of organic and inorganic pollutants in aquatic and terrestrial ecosystems. Scanning tunneling microscopy (STM) was used to image and analyze the morphological character of CA aggregates on graphite. Nano‐scale images of CA also were simulated and interpreted using a molecular mechanics technique. The effects of intermolecular association and hydration on the electronic properties and chemical reactivity of CA were analyzed in relation to the behavior of similar compounds in natural processes. Computer‐assisted STM proved to be a powerful technique to investigate structure, morphology, and chemical reactivity of soil organic matter components and their aggregates. The CA molecule aggregation and hydration do not affect the electronic properties significantly. However, electrostatic potential is highly sensitive to the conformation of the molecule and the morphology of the ensuing molecular aggregate.
Effects of Adsorbed Humic Acid on Surface Charge and Flocculation of Kaolinite
Authors: Kretzschmar Ruben , Sticher Hans , Hesterberg Dean
Published: July 2010

The behavior of clays in soils, groundwater aquifers, and aquatic environments is controlled to a large extent by flocculation and dispersion phenomena. Dispersed clay particles can become mobile and facilitate the translocation of strongly sorbed pollutants in the environment. In this study, the adsorption of a soil humic acid to Na‐kaolinite and the resulting effects on surface charge and colloidal stability of kaolinite were investigated in dilute aqueous suspensions. The pH dependence (pH 3–11) of humic acid adsorption to kaolinite in a NaClO4 background electrolyte was studied with batch experiments at three different ionic strengths (0.001, 0.01, and 0.1 M). Sorption of humic acid increased with decreasing pH or increasing ionic strength, a behavior that is typical for anionic polyelectrolytes with carboxylic functional groups. Electrophoretic mobility measurements showed that pure kaolinite had positive net total particle surface charge at low pH and negative surface charge at high pH, with an isoelectric point at pH 4.8 (in 0.01 M NaClO4). With increasing amounts of humic acid sorbed to the kaolinite surface, the electrophoretic mobility was continuously shifted to more negative values. At low pH, this resulted in charge reversal from positive to negative net total particle surface charge. Additions of small amounts of humic acid to the kaolinite suspensions resulted in large increases in colloidal stability. At low pH, this was probably due to reversal of edge charge from positive to negative preventing edge‐to‐face flocculation. In addition, a general increase in negative surface charge density and steric stabilization effects may contribute to the influence of adsorbed humic acid on the colloidal stability of kaolinite.
A Model of the Physical Protection of Organic Matter in Soils
Authors: Hassink Jan , Whitmore Andrew P.
Published: July 2010

Current computer simulation models do not treat the physical protection of organic matter in soil mechanistically. A model is presented that describes physical protection explicitly as a function of the capacity of clay particles and aggregates to hold organic matter. The net rate of decomposition of organic matter depends not simply on soil texture but on the degree to which the protective capacity of the soil is already occupied. The rate at which organic matter becomes protected depends on both the amount of free organic matter and the degree to which the protective capacity is filled. The rate at which organic matter is released from protection depends only on the amount of protected organic matter. The model closely followed the buildup and decline of organic matter in 10 soils to which grass residues were added each year for a period of 10 yr and then left without addition for a further 10 yr. An estimate made with the model of the maximum capacity of each of these soils to protect organic matter was closely correlated with the clay fraction in the soils. With this model, we were better able to predict the buildup and decline in amounts of soil organic matter in soils of different textures and initial organic matter contents than with conventional, implicit descriptions of protection. Our model accounted for 80% of the variance in the experimental data compared with 77 and 75% using the other two models. Secondly and importantly, the capacity of soil to protect organic matter was found to be positively and well related with the clay content of the soil in our model, whereas similar relationships were not found between soil texture and the parameters controlling protection in the other models.
A Chloride‐Deficient Leaf Spot Syndrome of Wheat
Authors: Engel R. E. , Bruckner P. L. , Mathre D. E. , Brumfield S. K. Z.
Published: July 2010

A leaf spot complex that results in tissue necrosis and whose origin is unknown frequently damages selected winter wheat (Triticum aestivum L.) cultivars in Montana and neighboring regions. This study was undertaken to determine leaf spot origin (physiologic or pathogenic), cultivar susceptibility, and response to Cl nutrition. Winter wheat studies at seven sites (1993–1995) compared cultivars (Redwin, Tiber, CDC Kestrel, Manning, Stephens, Sierra, and Promontory), propiconazole (1‐[[2‐(2,4‐dichlorophenyl)‐4‐propyl‐1,3‐dioxolan‐2‐yl]methyl]‐1H‐1,2,4‐triazole) fungicide treatments, and multiple Cl fertilizer rates (0–90 kg ha−1). Chlorotic or necrotic lesions developed at all sites, but not all cultivars were affected similarly. CDC Kestrel was the most susceptible cultivar. Flag leaf spot severity (portion of tissue area affected) was as great as 40% in this cultivar. Redwin, Sierra, and Promontory were the next most susceptible cultivars, followed by Stephens and Manning. Tiber, a variant line row selection of Redwin, was leaf spot tolerant. Multiple propiconazole applications had no effect on leaf spot severity, and infectious organism(s) could not be isolated from symptomatic tissue. Thus, leaf spot origin was probably physiologic and not infectious. Chloride fertilization (11–22 kg ha−1) greatly suppressed or eliminated leaf spotting, and increased yield in one or more cultivars at six of seven sites (up to 998 kg ha−1). Physiologic leaf spot occurrence and severity in affected cultivars was linked to inadequate Cl nutrition, and a possible osmotic imbalance in leaf mesophyll cells. Damage was usually minor when whole‐plant Cl at head emergence was ≥ 1.0 g kg−1. Leaf spot damage increased exponentially as plant Cl dropped below this concentration. The name Cl‐deficient leaf spot syndrome is proposed to describe this phenomenon in wheat.
Yield and Nitrogen Uptake Prediction by CERES‐Maize Model under Semiarid Conditions
Authors: Pang X. P. , Letey J. , Wu L.
Published: July 2010

Quantitative relationships between N and irrigation management on crop yield and NO3− leaching is urgently needed for economical and environmental analyses. Validity of the CERES‐Maize (version 2.10) model under arid conditions was evaluated for 3‐yr irrigation and fertilizer management trials conducted at Davis, CA. The N was applied at rates of 0, 90, 180, and 360 kg N ha and irrigation amounts were 20, 60, and 100 cm. The slope of the regression line between measured and simulated grain yield was 1.003 with r2 = 0.936. The slope of the regression line between measured and simulated N uptake was 1.013 with r2 = 0.946. We concluded that the CERES‐Maize model may be applied with confidence to study effects of N and irrigation management on corn (Zea mays L.) yield and N uptake under irrigated semiarid or arid conditions.
Effect of Compaction on Soil Physical and Hydraulic Properties: Experimental Results and Modeling
Authors: Assouline S. , Tessier D. , Tavares‐Filho J.
Published: July 2010

Soil compaction affects soil physical properties and, eventually, crop production. A severe drop in the productivity of the state of Parana, southern Brazil, was observed due to soil compaction. Two oxisols from this region, a Haplic Acrothox from the site of Cascavel and a Haplic Eutrothox from the site of Palotina, presenting different compaction behaviors in the field, are studied under laboratory conditions. Uniaxial compressive pressures, from 50 to 1000 kPa, are applied to soil samples at different initial matric potentials, varying from −0.1 to −1000 kPa. The bulk density of the Palotina soil is always higher than that of the Cascavel soil and is the highest when the initial matric tension is − 32 kPa. Differences in pH, cation‐exchange capacity, organic matter, and clay particle thickness also tend to explain the different compaction behaviors. A model of the soil bulk density increase during compaction is proposed and compared with a multiplicative model and a logarithmic model. The performances of the proposed and the multiplicative models are practically similar and better than those of the logarithmic model. The major advantage of the proposed model is that it has one fitting parameter less than the multiplicative model. Compaction affects the soil water retention curves for the whole range of matric tensions, up to − 100 MPa. An approach that allows the evaluation of the hydraulic conductivity functions of the compacted samples is proposed. Applied to the Brooks and Corey relationship, the main drying curves of the compacted samples are well reproduced using one fitting parameter only.
Changes of Soil Phosphorous Fractions under Long‐Term Corn Monoculture
Authors: Zhang T. Q. , MacKenzie A. F.
Published: July 2010

Corn (Zea mays L.) monoculture is a common management practice due to high production levels with economic and agronomic advantages. Phosphorus reactions in soil affect sustainable, economic corn management and environmental quality. Our objectives were to quantify changes in soil P fractions as related to additions of manure and inorganic P with time using a modified Hedley fractionation scheme. A field experiment was conducted on a Chicot sandy clay loam soil (fine‐loamy, mixed, frigid Typic Hapludalf) from 1984 to 1993. With an annual rate of 60 kg P ha−1 manure P plus 44 kg P ha−1 inorganic P, labile inorganic P (Pi; Bicarb‐Pi) increased and moderately labile Pi (NaOH‐Pi) decreased. A higher annual P rate of 132 kg P ha−1 plus manure P increased soil Pi through Bicarb‐Pi, NaOH‐Pi, and stable Ca‐bound Pi (HCl‐Pi). Inorganic P at either rate combined with manure P decreased labile Bicarb‐Po fractions and increased moderately labile NaOH‐Po, with the result that total extractable soil organic P (Po) increased. Without manure, 44 kg P ha−1, approximately equal to P removal by the crop, resulted in no change in soil P fractions except for residual P (Res‐P), which decreased. Soil Po and Pi levels increased continuously in soil fertilized with 132 kg P ha−1 yr−1 inorganic P only. With the manure‐inorganic system, 86% of the Bicarb‐Pi was supplied from added inorganic P, indicating reduced P fixation compared with the inorganic P system. The NaOH‐Pi and Res‐P were soil P sinks, with Res‐P being supplied from both the NaOH‐Po and HCl‐Pi fractions. In contrast, NaOH‐Pi in the inorganic P system was the major source for Bicarb‐Pi.
Tillage‐Induced Horizontal Periodicity of Preferential Flow in the Root Zone
Authors: Petersen C. T. , Hansen S. , Jensen H. E.
Published: July 2010

Flow patterns for water and solutes in the root zone are often heterogeneous. Understanding the spatial variability of flow is essential in solute‐transport studies and for management of chemical movement. We hypothesized the occurrence of effects of past tillage operations (plowing and seed bed preparation with and without rotovation) on flow patterns and that such effects could be determined from dye tracing. High‐resolution, digitized images of flow patterns on 221 vertical soil profiles (1 m2) perpendicular to the direction of plowing in two sandy loam soils (Typic Agrudalfs) were analyzed using time series analysis. Significant (P < 0.01) horizontal periodicity with a characteristic length equal to the furrow width for the plow (35 cm) was found for the degree of dye coverage in the 0‐ to 25‐cm topsoil layer (12 out of 15 plots) and for the number of stained channels in the 25‐ to 100‐cm subsoil layer (11 out of 15 plots) after plowing and conventional seed bed preparation (harrowing). The 35‐cm‐scale periodic variability of flow patterns in the subsoil was linearly related to the variability of patterns in the topsoil in three out of 17 plots (P < 0.01). Significant (P < 0.05) linear trends with horizontal distance were found for the degree of dye coverage in the topsoil (11 out of 20 plots), and for the number of stained channels in the subsoil (10 out of 17 plots). Rotovating after seedbed harrowing (five plots) reduced the number of stained flow pathways in the subsoil.
Light Fraction Soil Organic Matter and Available Nitrogen following Trees and Maize
Authors: Barrios E. , Buresh R. J. , Kwesiga F. , Sprent J. I.
Published: July 2010

Trees grown for 2 to 3 yr in rotation with crops (tree fallows) are a potential technology for increasing soil fertility in maize‐based cropping systems in sub‐Saharan Africa. The objective of our study was to determine the effect of contrasting fallow options, compared with continuous maize (Zea mays L.), on light fraction soil organic matter (SOM), inorganic N (NO3 and NH4), and N mineralization. Soil was collected 2 and 3 yr after the establishment of fallow and maize systems on a sandy clay loam (Ustic Rhodustalf) in Zambia. Total soil C, N, and P were not different among the fallow and maize systems. Soil inorganic N and amount of light fraction N (150–2000 µm, <1.13 Mg m‐3) were higher for the mean of five N2‐fixing trees than the one non‐fixing tree. Inorganic N, anaerobic and aerobic N mineralization, and light fraction N were (i) higher for the mean of the two trees with lowest (lignin + polyphenol)/N ratios in leaf litter than the two trees with highest ratios in leaf litter and (ii) higher for Sesbania sesban (L.) Merr. than the mean of other trees. Sesbania and fertilized maize monoculture resulted in similar soil inorganic N, but N mineralization and light fraction N were greater after sesbania. Comparable effects of the systems on light (<1.13 Mg m‐3) and light + intermediate fraction (<1.37 Mg m‐3) SOM suggest that light and intermediate fractions can be combined to simplify the fractionation procedure. Tree species vary greatly in effect on N availability and hence their suitability for soil fertility replenishment.