bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady‐State Funnel Flow: Its Characteristics and Impact on Modeling
Authors: Ju S.‐H. , Kung K.‐J. S.
Published: July 2010

Preferential flow could dictate the leaching of contaminants in unsaturated soils. The objectives of this study were to: (i) numerically determine the characteristics of steady‐state funnel‐type preferential flow and how would it be influenced by infiltration rate, soil layer density, and textural combinations; and (ii) explore the validity of several basic assumptions used in different models to incorporate pesticide leaching through preferential flow paths. Water movement and pesticide transport in 12 two‐dimensional hypothetical profiles were numerically simulated. Results showed that there was an induction zone where water was gradually congregated into preferential flow paths and its movement could be conceptualized as a network of tributaries merging into rivers. Beneath the induction zone, water moved through several distinct flow domains without lateral interaction. The frequency distribution of normalized water fluxes would spread out when the layering density increased or the pore discontinuity across a textural boundary increased. There existed a critical number beyond which any further increase in layer density would not influence the frequency distribution of normalized water fluxes. Frequency of water fluxes in the stationary region was not lognormally distributed. Pesticide leaching depended primarily on the last 20% of the water flux distribution. If a profile was made of regions with different layer densities, the water fluxes of the entire unsaturated profile might be neither spatially stationary nor vertically invariant. It was possible to numerically derive the worst‐case scenario (i.e., the widest spreading of the water fluxes). Because it is impossible to measure the frequency distribution of normalized water fluxes in a field, it is prudent to predict pesticide leaching according to this worst‐case frequency distribution.
Nitrogen Contribution of Pea Residue in a Hummocky Terrain
Authors: Stevenson F. C. , van Kessel C.
Published: July 2010

Topography influences the distribution of soil water and inorganic N, which could affect the availability of N from legume residue to the subsequent crop. A study assessed the landscape‐scale variability of the N contribution by pea (Pisum sativum L.) to the soil (N2 fixation in residue minus seed N derived from the soil) and the subsequent wheat (Triticum aestivum L.) crop. In situ 15N‐labeled pea residue was used to monitor the contribution of pea residue to the succeeding crop. A 100‐point sampling grid, with 10‐m spacings, was established in a field with hummocky terrain. Each sampling point was classified as a shoulder or a low‐catchment or high‐catchment footslope. The N contribution by pea to the soil was 45 kg ha−1 in the shoulders and 63 kg ha−1 in the footslopes. Recovery of 15N in the microbial biomass was greater in the footslopes (71%) vs. the shoulders (51%), and related to greater soil water content in the footslopes. The N contribution by pea to wheat, as assessed by the 15N that wheat derived from the residue of the preceding wheat crop, was 11% and similar among landform complexes. Therefore, the N contribution of pea to wheat did not explain the greater N accumulation by wheat in the high‐catchment areas than the other landform complexes. The N contribution of pea to a succeeding wheat crop apparently will be a small component of the rotation benefit by pea in a hummocky terrain.
Evaluation of an In Situ Net Soil Nitrogen Mineralization Method in Dryland Agroecosystems
Authors: Kolberg R. L. , Rouppet B. , Westfall D. G. , Peterson G. A.
Published: July 2010

Direct quantitative measurement of soil net N mineralization in agricultural soils under field conditions has not been widely used. A potential method of in situ net N mineralization was investigated in the fallow phase of a 3‐yr no‐till crop rotation at two sites. Undisturbed soil cores (5 by 15 cm) with anion‐ and cation‐exchange resins (Sybron Ionac ASB‐1P and C‐249) at the bottom were incubated in situ. Nitrate‐N plus NH4+‐N extracted from soil was added to extracted amounts from resin bags to determine net N mineralized during each of three incubation periods (3–4 wk each). Total net N mineralization was 33.7 and 26.5 kg N ha−1 during 84 and 75 d of incubation at Sterling and Stratton, respectively. Relative amounts of resin did not affect N captured but cores placed midway between old corn (Zea Mays L.) rows tended to accumulate more (P > F = 0.13) N than cores placed in rows. This in situ method appears to be a reliable method for measuring net N mineralization in the field; however, variation is large and many observations are required to obtain net N mineralization rates within an acceptable confidence interval.
Spatial Patterns of Carbon and Texture on Drumlins in Northeastern Wisconsin
Authors: Kabrick J. M. , Clayton M. K. , McSweeney K.
Published: July 2010

The objective of the study was to determine if there is a consistent and pervasive spatial pattern to organic C and particle‐size distribution for drumlin summits of the Nicolet National Forest, Wisconsin. Accordingly, a method for estimating confidence intervals was developed and used to assess variogram similarity and variation. Organic C and particle‐size distribution were determined for the upper 20 cm of mineral soil at nodes of sampling grids on each of six drumlin summits. The aeolian cap thickness was also measured at each node. Variograms and confidence intervals were constructed for each attribute on each drumlin. A systematic comparison of variograms and their confidence intervals revealed that C and clay content each had similar variograms from drumlin to drumlin. Thus, composite variograms for each C and clay content were then constructed. Organic C appeared to be nearly spatially random, while clay content is spatially dependent. Sand and silt variograms each varied from drumlin to drumlin and thus were not combined into composite variograms. Variogram dissimilarity for sand and silt appeared to be related to aeolian cap thickness; greater sill variances occurred on drumlins with thinner aeolian caps. The approach and methods described here have utility for identifying attributes that have similar patterns on a particular landform and show promise for more rigorously quantifying soil attribute patterns for soil surveys and related land information systems.
Anthraquic Conditions in Nonagricultural Soils: A Proposal and Case Study
Authors: Evans C. V.
Published: July 2010

As soil scientists develop recommendations for the classification and interpretation of anthropogenic soils, many altered soils will need to be described and classified, probably at a variety of taxonomic levels. One agent of alteration may be the application of liquid wastes to soils for extended periods of time, with the potential of creating aquic conditions in those soils. Although such conditions could logically be termed anthraquic, no provision exists for recognizing anthraquic conditions in nonagricultural soils. As these morphological characteristics may be reversed if the spraying were discontinued, it is important that future land‐use planners be given such information. The most logical venue is to include anthraquic designators at appropriate levels of classification that may also be applied to nonagricultural soils. An example is given of a wooded plot in New Hampshire that has received secondary Cl‐treated wastewater for >15 yr.
Rapid Laboratory Calibration of Time Domain Reflectometry Using Upward Infiltration
Authors: Young M. H. , Fleming J. B. , Wierenga P. J. , Warrick A. W.
Published: July 2010

We propose an upward infiltration method to calibrate a time domain reflectometry (TDR) system. The method is rapid, allows the soil to remain unchanged during the experiment, and provides hundreds of data points. Three experiments were conducted using 18.7‐cm‐long probes in soils of three textures (nine experiments total). Calibrations also were performed by packing soil cores with soil at progressively higher water contents. The data from the two methods were fitted using regression techniques to two published models of the dielectric constant‐water content relationship. The results show that the calibration curves of all three soils, fitted simultaneously to replicate experiments, were similar in shape and statistically the same. A single calibration curve, fitted simultaneously to the replicate experiments of the three soils, was compared with Topps equation and was statistically the same. The results support the conclusion that the upward infiltration method provides a fast and repeatable calibration method, consistent with conventional calibration.
Uniform Separation of Concentric Surface Layers from Soil Aggregates
Authors: Santos D. , Smucker A. J. M. , Murphy S. L. S. , Taubner H. , Horn R.
Published: July 2010

It is well accepted that soil organic matter improves soil structure; however, current methods limit our knowledge of the many physical‐chemical mechanisms that control the temporal processes of soil aggregation. A soil aggregate erosion (SAE) apparatus was designed to uniformly remove concentric surface layers of soil aggregates in an enclosed erosion chamber. The SAE was used to test for the presence of concentration gradients within aggregates of different soil types. The SAE method generally improved the separation of ion concentrations between the external and internal layers. Concentrations of C, Ca, and Mg were 8 to 19, 20 to 21, and 29 to 33% lower, respectively, at the external layers of aggregates for Haplaquoll and Hapludalf soils. Removal of surface layers had no effect on the tensile strength of soil aggregates. Therefore, we concluded that the SAE apparatus improves the separation of ion gradients within natural soil aggregates. Identification of the mineralogical, physical, chemical, and biological properties of this improved separation of concentric layers from soil aggregates should lead to further advancements in our knowledge of the functional mechanisms associated with the development and stability of soil aggregates.
Nitrogen Dynamics and Balance in Intensified Rainfed Lowland Rice‐Based Cropping Systems
Authors: Tripathi B. P. , Ladha J. K. , Timsina J. , Pascua S. R.
Published: July 2010

Nitrogen dynamics and balances in intensive and diversified lowland rice (Oryza sativa L.)‐based cropping systems that receive heavy fertilization, tillage, and irrigation have not been explored. Such information is essential to improve the efficiency of N fertilizer, an input based on a nonrenewable energy resource and whose oxidized products pose hazards to human health and the environment. Field experiments at an experimental farm on an Inceptisol and in two farmers' fields, one with an Inceptisol and one with a Vertisol soil, quantified (i) NO‐3‐N and NH+4‐N in different soil layers in relation to water‐filled pore spaces (WFPS), (ii) N balance, and (iii) systems‐level N efficiencies in several cropping patterns. Nitrate‐N and NH+4‐N were quantified monthly from July 1993 to June 1994. The WFPS remained <0.80 mL mL‐1 in the beginning of the wet season and throughout the dry season that enhanced nitrification. Ammonium‐N in the 100‐cm layer was 20 to 40 kg ha‐1 in the wet season and <10 kg ha‐1 in the dry season. Nitrate‐N, however, ranged from 27 to 54 and from 67 to 195 kg ha‐1 in the two seasons; it was higher in farmers' fields (192–195 kg ha‐1) than in the experimental farm (67–112 kg ha‐1). Total N loss was 34 to 549 kg ha‐1 across sites, with the largest in rice‐sweetpepper (Capsicum annuum L. var. annuum) and rice‐tomato (Lycopersicon esculentum Miller). Despite a lack of a consistent trend in N efficiency among the different cropping systems, it was higher with tobacco (Nicotiana tabacum L.) and garlic (Allium sativum L.). There appears an opportunity to grow a NO‐3 catch crop during the dry‐wet transition in rice‐sweetpepper and rice‐tomato systems to capture and recycle soil NO‐3‐N.
Rice Plant Growth and Nitrogen Accumulation in Drill‐Seeded and Water‐Seeded Culture
Authors: Bufogle, A. , Kovar J. L. , Bollich P. K. , Norman R. J. , Lindau C. W. , Macchiavelli R. E.
Published: July 2010

Nitrogen fertilization strategies for flooded rice (Oryza sativa L.) depend on understanding plant N demand. Seasonal N accumulation research in general is limited, and is nonexistent in water‐seeded (WS) culture. A field study was conducted for 3 yr in Louisiana and 1 yr in Arkansas to characterize plant growth and N accumulation by rice at different development stages, and to compare these factors in drill‐seeded (DS) and WS culture. ‘Cypress’ rice was grown on a Crowley silt loam (fine, montmorillonitic, thermic Typic Albaqualf). Straw, grain, roots, and soil were collected at eight growth stages. Nitrogen‐15‐labeled urea was applied to 75 by 75 cm microplots enclosed by stainless steel retainers. Total dry matter increased each season, and grain dry matter was similar each year. In 1994 and 1995, both surface and subsurface root growth increased linearly until 90% heading. Fertilizer N accumulation increased to the four‐leaf plus 21‐d or panicle differentiation (PD) stages. Native soil N and remobilization of N from straw provided N needed for maturing grain. From heading plus 21 d to maturity, factors did not differ under either DS or WS each year. At early and late stages of development, factors did not differ under DS and WS in Louisiana. Differences in N accumulation and fertilizer N recovery were seen in Arkansas. This suggests that, under Louisiana conditions, results from experiments in DS and WS are interchangeable. Variation of the measured factors among years was significant, suggesting that even when labeled N is used, results from multiple seasons are required for accurate interpretation.
Field‐Scale Variability of Phosphorus and Potassium Uptake by No‐Till Corn and Soybean
Authors: Borges R. , Mallarino A. P.
Published: July 2010

Use of precision farming technologies requires better understanding of nutrient variability in soils and plants. This study assessed patterns of spatial variability of plant P and K content of no‐till corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] on eight fields that had varied histories of fertilization. One hundred composite whole‐plant samples (five corn plants and 10 soybean plants at V5 to V6 growth stages) were collected in late spring from 2.2‐m2 areas spaced 3.05 m along two intersecting transects. Dry weight (DW) and total P and K concentrations were measured in all samples. Plots of observed values, variography, and fast Fourier transform (FFT) analyses revealed clustering of values and periodic patterns of DW and nutrient content in most fields. The patterns of variability varied greatly among fields and directions within a field. The diversity of patterns probably results from nonuniform distribution of fertilizers and animal manures. Patterns of plant K uptake (KU) followed patterns of plant K concentration (KC) in some fields and those of DW in others. Patterns of plant P uptake (PU), however, usually followed those of DW. Implementation of plant analysis for no‐till fields should address situations with high spatially structured variability of cyclic or clustered structure. The results show that the structure of the variability in P and K uptake is site specific and that both the sampling scheme and the optimal separation distance between sampling positions would vary greatly among fields. The results suggest that plant analysis would have similar sampling problems to those of soil testing for representing the P and K supplies of corn and soybean fields.
Optimizing Corn Production and Reducing Nitrate Losses with Water Table Control‐Subirrigation
Authors: Drury C. F. , Tan C. S. , Gaynor J. D. , Oloya T. O. , van Wesenbeeck I. J. , McKenney D. J.
Published: July 2010

Water table control‐subiriggation (WTC) systems have increased crop production and improved water quality; however, the relationship between N management, water table depths, and corn production has not been well defined. We hypothesized that optimizing water table depth would increase corn (Zea mays L.) growth, improve N fertilizer efficiency, and reduce NO‐3 losses. A greenhouse incubation study with three water table depths (30, 60, and 80 cm) and four N rates (0, 0.7, 1.4, and 2.1 g N plant‐1) was conducted using undisturbed soil columns (Fox sandy loam, Typic Hapludalf) planted to corn. The 30‐cm WTC treatment had the greatest NO‐3 loss through tile drainage (715 µg N column‐1). The 60‐cm WTC treatment reduced these losses by 54%. Nitrate losses through tile drainage were proportional to drainage volume, which followed the order 30 cm > 60 cm > 80 cm WTC. The 60‐cm WTC treatment increased crop yields (95 g plant‐1) compared with the 30‐cm (68 g plant‐1) and 80‐cm WTC (18 g plant‐1) treatments at the optimal N rate of 1.4 g N plant‐1. After the first simulated rainfall event, N2O production was increased by 12.7 times with the 30‐cm WTC treatment (825 µg N column‐1 d‐1) compared with the 60‐ and 80‐cm WTC treatments. Water stress imposed by the 80‐cm WTC treatment limited crop growth, N uptake, leaching, and N2O emissions. However, up to 28% of added N (664 mg N column‐1) remained in the soil after corn was harvested from the 80‐cm WTC treatment, which would be susceptible to leaching between cropping seasons.
Determination of Soil Sorptivity and Hydraulic Conductivity from the Disk Infiltrometer
Authors: Zhang Renduo
Published: July 2010

A simple two‐term infiltration equation was used to determine soil sorptivity and hydraulic conductivity from cumulative infiltration data from the disk infiltrometer. Parameters of the equation were obtained by fitting the equation to cumulative infiltration data. The parameters of the first and second terms in the equation were related to soil sorptivity and hydraulic conductivity, respectively. By using the twoterm infiltration equation, sorptivity and hydraulic conductivity were estimated for various soils, radii and tensions of the disk infiltrometer, and initial infiltration conditions. Sorptivity and hydraulic conductivity values calculated using the method and simulated cumulative infiltration data resulted in excellent agreement with the theoretical results. The relative error of estimation of sorptivity and hydraulic conductivity was within 5% for most cases. The method can be used to determine the soil hydraulic properties from infiltrometer infiltration for a wide range of soils, having a retention function of the type of either van Genuchten, Russo, or Zhang and van Genuchten.
A Model Describing Pesticide Bioavailability and Biodegradation in Soil
Authors: Shelton Daniel R. , Doherty Michael A.
Published: July 2010

A model is proposed for describing pesticide‐substrate bioavailability and rates of biodegradation in soil. The model accounts for sorption to soil surfaces, diffusion into the internal matrix of soil organic matter or aggregates, and microbial growth. Rates of sorption and diffusion are approximated by first‐order kinetics while microbial growth is approximated by Monod kinetics. Model verification was performed using 2,4‐D (2,4‐dichlorophenoxyacetic acid) degradation data from high and low organic matter soils inoculated with pure cultures of 2,4‐D degrading bacteria. Estimates of sorption, diffusion, and Monod constants were obtained sequentially by fitting the defining differential equations to the data using nonlinear regression techniques. Independent estimates of initial biomass (X0) and growth yield (Y) were required, although X0 could be approximated from the number of colony‐forming units assuming a bacterial weight of 0.1 pg cell−1. The model could account for the partitioning of 2,4‐D between soluble and sorbed phases and provided estimates of the Monod constants, µmax and KS, which were generally consistent with values previously determined in pure culture. In conjunction with pest toxicology data, the model may be useful in predicting the time between application and loss of efficacy (i.e., window of efficacy) for biodegradable pesticides.
Spodosol Development as Affected by Geomorphic Aspect, Baraga County, Michigan
Authors: Hunckler Robert V. , Schaetzl Randall J.
Published: July 2010

In midlatitude locations with steep slopes, geomorphic aspect can be an important factor in determining spatial variations in soil development. This study examines the influence of aspect on soil development in Baraga County, Michigan, as a means of explaining within‐landform variability. The soils are sandy and have spodic morphologies. All are located on steep slopes (45–73%) of contrasting aspect. Ten pedons each from backslopes on north‐to‐northeast‐(N‐NE) and south‐to‐southwest‐(S‐SW) facing slopes were described, sampled, and compared using standard techniques.

Variation in slope gradient was not, statistically, a determining factor in the differential soil development found here. Aspect has strongly influenced soil development, however, with soils more strongly developed (i.e., more podzolized) on N‐NE slopes than on S‐SW slopes. Several soil characteristics indicative of strong podzolization were found on N‐NE slopes, including higher values of solum thickness and POD index, greater losses of extractable Fe and Al from E horizons and concomitant gains in B horizons, and darker and redder B horizon colors. Soils were generally cooler on N‐NE slopes in summer, with essentially similar temperatures under snowpacks in winter. Cooler temperatures and greater amounts of infiltrating water in soils with N‐NE aspects may have accelerated podzolization by allowing more organo‐metallic complexes to be formed and translocated. Podzolization driven by translocation of amorphous, inorganic compounds appears, however, to be nearly equivalent on sites of differing aspect.

Of the ten pedons on N‐NE slopes, nine classified as Spodosols (Entic or Typic Haplorthods) and the other was an Entisol. Seven of the 10 pedons on S‐SW slopes classified as Entisols (Udipsamments or Udorthents), and the remaining three were Spodosols.
Aggregate Stabilities of Some Southeastern U.S. Soils
Authors: Levy G. J. , Miller W. P.
Published: July 2010

Soils from humid regions have traditionally been considered to have stable aggregates. Some humid southeastern U.S. soils have demonstrated poor structural stability. We hypothesized that a sensitive measure of aggregate stability of southeastern U.S. soils would demonstrate that stability of macroaggregates may depend on some soil properties and may not correlate with soil erosivity. This study evaluated the stability of aggregates from southeastern U.S. soils employing a sensitive aggregate stability test, and compared it with previously published data for the same soils. Stability of 0.5‐ to 1.0‐ mm aggregates of 11 Georgia topsoils were determined using the high‐energy‐moisture‐characteristic method, where the destructive force used to break the aggregates is a controlled wetting process. Aggregates were wetted either rapidly by a matric potential of 0.0 J kg−1, or slowly where they were initially subjected to a matric potential of −2.0 J kg−1, which was then gradually increased to 0.0 J kg−1. Two water qualities were used for wetting: tap water (electrical conductivity [EC] 0.097 mS cm−1) and a saturated CaSO4 solution (EC 2.24 mS cm−1). Stability ratio (ratio of fast to slow structural indices) of the soils ranged between 0.40 and 0.95. Six soils had a stability ratio of ≤0.5 (low aggregate stability). Aggregate stability in unstable soils with pH >6.5 rose to ≥0.62 when saline solution was used. The measured aggregate stability indices significantly correlated with published infiltration rate data (R = 0.622), but not with soil splash or soil loss.
Resin Capsules for On‐Site Assessment of Soil Nutrient Supply in Lowland Rice Fields
Authors: Dobermann A. , Pampolino M. F. , Adviento M. A. A.
Published: July 2010

Using ion‐exchange resin capsules for assessing nutrient supply in lowland rice (Oryza sativa L.) fields requires strategies for estimating field means of resin adsorption quantities (RAQs). To develop recommendations for on‐site use of capsules, we conducted two experiments in rice fields on Typic Tropaquepts and Tropaqualfs in the Philippines. Resin capsules were placed in situ (ISI) or inserted into composite soil samples for on‐site incubation (OSI). Capsules were retrieved after 1, 2, 4, 7, and 14 d and RAQs of NH4‐N, P, K, Ca, Mg, Na, Fe, and Mn were measured. In ISI or OSI of single soil cores, coefficients of variation in RAQs of N, P, and Fe ranged from 17 to 71%, whereas those for K and Ca ranged from 10 to 20%. Between one and five capsules per 0.25‐ha field were required to estimate the average RAQ of P, K, and Ca after 14 d with a precision of ± 10%, compared with four to 10 capsules per field for estimating the RAQ of NH4‐N and Fe after 14 d. Soil core sampling and OSI of composite soil samples reduced microvariability in RAQs. About eight to 10 soil cores (0–15‐cm depth) were required per field for resin capsule OSI. Because of soil physical changes, degassing, and oxidation during soil mixing, RAQs of P, Fe, K, and Ca were lower for OSI than for ISI. The ISI method is recommended for routine soil testing in lowland rice fields. The OSI requires fewer capsules but more labor. Its reliability depends on the extent to which mechanical disturbance, degassing, and exposure to air can be minimized.
Sesbania Phosphorus Requirements When Used as Biofertilizer for Long‐Term Rice Cultivation
Authors: Ventura W. , Ladha J. K.
Published: July 2010

Green manures may affect the long‐term nutrient supplying capacity of soils. In a long‐term trial that compared the performance of azolla (Azolla microphylla Lam.), sesbania (Sesbania rostrata Bremek. & Oberm.), urea, and no fertilizer N on rice (Oryza sativa L.), a progressive decline in the growth of and N accumulation by sesbania was observed after the ninth crop. This study examined the reasons for sesbania decline with emphasis on the effect of fertilizer P on sesbania performance in relation to soil available P, cropping history, and moisture regime. In the 1992 dry season (14th crop), sesbania performance with and without P was determined in (i) field microplots within main long‐term plots, and (ii) pots containing soil monoliths from long‐term plots. Without P fertilizer, sesbania grew poorly and accumulated <40 kg N ha−1. But addition of 28.4 kg P ha−1 increased sesbania N accumulation 3 to 11 fold and the greater N availability increased rice production. Addition of P improved sesbania biomass and N accumulation in dried‐flooded and continuously flooded regimes but not in the dried‐moist regime. Sesbania P requirements were greater than for rice. Continuous rice‐sesbania cropping without addition of P limited sesbania growth, N accumulation, and green manure value even though it did not limit rice production, suggesting that the P requirements will be greater for a long‐term rice cropping system that depends solely on green manure N than for rice grown with fertilizer N.
Mineralogical Variations of Bulk and Rhizosphere Soils from a Norway Spruce Stand
Authors: Courchesne François , Gobran George R.
Published: July 2010

The mineralogy of bulk and rhizosphere soil materials was compared to assess the effect of roots on mineral weathering in a Podzol supporting a homogeneous Norway spruce [Picea abies (L.) Karst] stand. Six horizons were sampled in two profiles at the Skogaby site in southwestern Sweden. The soil adhering to the roots after shaking was considered as rhizosphere soil, a layer <3 mm thick intimately associated with root surfaces. The remaining material was regarded as bulk soil. The mineralogy of the clay‐sized particles of both fractions was determined by x‐ray diffraction (XRD) and normalized with respect to quartz (I/IQZ). Amorphous solid phases were estimated by extracting Fe and Al with acid‐ammonium oxalate (AlO, FeO). Mineral abundance (I/IQZ) near roots differed consistently from that in the bulk soil. The rhizosphere contained significantly lower amounts of amphiboles and expandable phyllosilicates (α = 0.10) relative to the bulk soil. This trend was paralleled by a systematic increase in AlO and FeO (α = 0.10) at the root‐soil interface. Lower amounts of plagioclase were also seen in the rhizosphere samples from five of the six horizons, but the difference from the bulk soil was not significant when all horizons were integrated in the comparison. No rhizosphere effect was detected for K‐feldspars. This study provides converging results that emphasize the pedogenic significance of the rhizosphere zone and the role of roots as dynamic weathering agents.
Applicability of Analytical Solutions for Flow from Point Sources to Drip Irrigation Management
Authors: Eugenio Coelho F. , Or Dani
Published: July 2010

The design and management of drip irrigation systems requires understanding of water distribution and dynamics within the wetted soil volume. This information can be obtained by means of analytical or numerical solutions of the multidimensional Richards equation. Though steady‐state solutions have been advocated as design tools for drip irrigation, very little information about their performance under practical field conditions is available. The objective of this study was to evaluate the applicability of analytical solutions for steady and transient flows from point sources to practical drip irrigation management. The emphasis was on the adaptive and dynamic aspects of management vs. conservative design considerations. Experiments were carried out in containers and in the field to determine steady‐state attainment rates and to provide information on spatial and temporal dynamics of water content and matric potential during irrigation cycles. The main results were: (i) analytical solutions for steady and transient flow conditions predicted reasonably well measured distributions of water content and matric potential in the absence of plants; (ii) steady flow conditions were seldom realized under practical drip irrigation; (iii) transient flow solutions provided a more realistic description of soil water dynamics; and (iv) introducing uptake terms into transient analytical solutions provided a simple and effective framework for capturing soil water dynamics in the presence of plant roots.
Use of Pseudo‐Crossvariograms and Cokriging to Improve Estimates of Soil Solute Concentrations
Authors: Zhang R. , Shouse P. , Yates S.
Published: July 2010

Estimating mass and distributions of chemicals in soils is one of the key steps to study chemical transport in the vadose zone and groundwater systems. In this study, solute mass and distributions were computed in an 800 by 800 by 1.8 m soil volume using kriging and cokriging with nonsymmetric pseudo‐crossvariograms. Among the measured chemicals of Cl−, SO2−4, Ca2+, Mg2+, Na+, P2O−5, K+, and NO−3 in the three‐dimensional system, Cl− was used as the model to show the estimation process and results. Using pseudo‐crossvariograms maximized the use of available information at different soil depths and improved solute estimation. All sample pseudo‐crossvariograms between depths were modeled successfully with common variogram functions such as spherical and linear. Therefore, it was relatively easier to test the positive definiteness of the cokriging coefficient matrix adapted to pseudo‐crossvariograms. Cokriging allows easily obtained information at shallower depths to be used to improve solute estimations at deeper depths. Compared with kriging, cokriging reduced the mean squared errors of estimations between 30 and 60% at different depths, and reduced the mean kriging variances between 35 and 58%. In the total mass estimation of Cl− in the soil, cokriging with nonsymmetric pseudo‐crossvariograms used less than half the data; potentially it could reduce more than half the sampling cost of kriging estimation. Meanwhile, cokriging reduced the estimation error by about 18%, when compared with kriging estimates using all observations. Using the same data at each layer, cokriging would reduce the estimation error 40% more than kriging because cokriging efficiently incorporated information at upper layers without increasing the sample requirement. Cokriging with nonsymmetric pseudo‐crossvariograms is an accurate and economical way to calculate solute distributions and total mass in a large field.
Soil Nitrogen and Carbon Response to Maize Cropping System, Nitrogen Source, and Tillage
Authors: Reeves Margaret , Lal Rattan , Logan Terry , Sigarán Juan
Published: July 2010

These experiments were conducted to evaluate the combined effects of intercropping and N source and the interaction of these two factors with tillage on N dynamics. Maize (Zea mays L.) was planted in two consecutive years in Costa Rica to measure changes in soil mineral N, soil C, and maize grain N in response to monoculture or polyculture and legume residues or NH4NO3 fertilizer under conventional (CT) or minimum (MT) tillage. Soil mineral N levels were greater with fertilizer than with residues at the end of the first season and greater with residues at the beginning of the second season, reflecting a residual effect from the previous season. There were no treatment interactions. The dominant form of mineral N shifted from NO−3‐N (first season) to NH+4‐N (second season). The shift corresponded to an overall increase in soil C (from 27.6 to 30.2 g kg−1), which was significantly greater under monoculture and with residues (33.2 and 33.4 g kg−1, respectively) than under polyculture and fertilizer (31.1 and 30.9 g kg−1, respectively). A positive cropping system × N source interaction resulted in 67% greater maize grain N in the polyculture under residues than with fertilizer N. Maize response to polyculture and legume residues, together with soil N and C data, were used to propose a mechanistic explanation for how these strategies may help maintain productivity (and minimize N loss) in low‐input farming systems.
Comparison of Sampling Methods for Estimating Pit and Mound Microtopography
Authors: Kabrick J. M. , Meyers N. L. , McSweeney K.
Published: July 2010

We developed a method for making rapid estimates of pit and mound microtopography for characterizing research sites, soil map units, and ecological land types. We conducted this study in the drumlinized uplands of northeastern Wisconsin, where pit and mound microtopography is extensive. We established one 10 by 30 m grid and one 300‐m transect on each of four drumlins and identified a pit, a mound, or neither at nodes 1 m apart (300 observations per grid or transect). Pit and mound microtopography was estimated by calculating the proportion of pits, mounds, and points lacking evidence of pit and mound microtopography at nodes within each grid or transect. The optimal node spacing for grid and transect sampling methods was determined by repeatedly subsampling data derived from each method and identifying the lowest mean square error. The precision of grid sampling vs. transect sampling was determined by comparing the standard errors estimated with each method. Transects were more precise and time‐efficient than grids for estimating pit and mound microtopography percentages. Satisfactory results were obtained with 300‐m‐long transects with 3‐m node spacing. Transect methods appear applicable to the quantification of other types of microtopography.
Quantitative Aspects of Weathering and Neoformation in Selected Costa Rican Volcanic Soils
Authors: Nieuwenhuyse A. , van Breemen N.
Published: July 2010

Gains and losses of major elements in eight soil profiles developed on volcanic parent material in the perhumid tropical Atlantic lowland of Costa Rica were calculated from total element contents, assuming Ti to be immobile. Initially soil formation (0–500 yr) in Tropopsamments involves dilation of the sandy deposits by incorporation of organic matter and formation of structure and biopores, without detectable gains or losses of elements. In 2000‐ to 5000‐yr‐old sandy Hapludands, primary minerals are still abundant, but up to 20% of the mineral soil consists of x‐ray amorphous materials. Dilation continues and losses of Mg, Ca, Na, and K, and to a lesser degree Si, become measurable. Within 18 000 yr, a Melanudand develops, which is depleted of primary minerals and especially volcanic glass in the fine‐earth fraction. A mixture of short‐range order material, metal‐humus complexes, and gibbsite and kaolin minerals dominate its upper horizon, while gibbsite, halloysite, and short‐range order material are the most important secondary minerals at greater depths. Dilation of the soil mass prevails in the A horizon, while collapse has occurred in the B horizon. The Melanudand has lost considerable amounts of mobile elements: 50 to 85% of Si, Mg, Ca, Na, and K have been leached from the fine‐earth fraction. Within 125 000 yr, a Haploperox has formed (thought to have formed from Andisols); it is strongly collapsed and is dominated by gibbsite, kaolin minerals, and Fe (hydr) oxides. The upper meters are devoid of primary minerals except for small opaques. Under the prevailing environmental conditions, weathering and neoformation of primary volcanic minerals lead to almost complete dissolution and leaching of basic cations, probably within 20 000 to 50 000 yr. The Si and P mineral reserves are depleted considerably, but part is still present after such long time periods.
A Source of Systematic Error in Transient‐Flow Air Permeameter Measurements
Authors: Smith James E. , Robin Michel J. L. , Elrick David E.
Published: July 2010

The data from transient‐flow air permeameters often exhibit curvature in the theoretically linear plots of the natual log of pressure vs. time. This was originally attributed to errors in water manometer data caused by the inertia of the water in the manometer. The resulting recommendation was to ignore the early time data when calculating the air permeability of a soil by these methods. We have demonstrated and quantified that the exhibited curvature is a direct consequence of small changes in temperature in the source air tank as a result of the cooling of the expanding air during the permeability determination. This was accomplished by interfacing the air permeameter with a computer to collect pressure and temperature data at a relatively high frequency. The data acquisition procedure facilitated the calculation of the change in pressure and temperature with respect to time, which allowed the direct solution of the differential form of the equations describing the mass flux of air from the tank through the core. The data is compared with the theoretical relationship expected for the core based on air permeability determined using a steady‐state method.
Mechanisms of Acifluorfen Interaction with Humic Acid
Authors: Celi Luisella , Gennari Mara , Khan Shahamat U. , Schnitzer Morris
Published: July 2010

The interaction of the herbicide acifluorfen (AC; 5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]2‐nitrobenzoic acid) with a humic acid (HA) extracted from an undisturbed Ah horizon of a Haploboroll, was studied at different pHs. Both the HA and AC were methylated to determine the possible role of O‐containing functional groups in the adsorption process. Fourier‐transform infrared spectroscopy (FT‐IR) was employed to establish the mechanism of interaction. The interaction was affected by the pH of the system and by the methylation treatment, as they changed the polarity of both the HA and AC. A nonpolar environment at low pH or HA after methylation increased retention of AC by the humic materials. Carboxyl and phenolic groups of the HA negatively affect the interaction by repulsing the herbicide, as indicated by the increased adsorption by the methylated HA over the unmethylated HA. The herbicide appeared to interact with the HA by physical adsorption or weak chemical bonding that could readily be broken by extraction with water. The FT‐IR spectra suggested limited involvement of H bonding in the interaction processes.
Silica‐Cemented Terrace Edges, Central California Coast
Authors: Moody L. E. , Graham R. C.
Published: July 2010

The morphologic development of soils on marine terraces is a function of terrace age and geomorphic evolution. In this study, interrelationships between terrace landscape evolution and pedogenic silica cementation were investigated. Soil morphology, micromorphology, selective dissolution, penetration resistance, and hydraulic conductivity were used to determine the nature and extent of the cementation and evaluate the effect of cementation on soil properties. Soils on the interior part of the terrace (coarse‐loamy, mixed, thermic Typic Epiaquolls) contain plinthite, continuous throughout the entire terrace, cemented to the extent that it is only slowly permeable. A seasonally perched water table develops above the plinthite, and water seeps out of soils at the terrace edges. Some of these soils are cemented by opaline silica, in both channels and interstitial voids. The silica cementation extends inward into the terrace soils only 4 m, but at the terrace edge is strong enough to result in block fall as the predominant mechanism of scarp retreat. Redoximorphic Fe depletions are prominent in deeper horizons at the edge, but are absent from the interior. These depletions are formed through seasonal saturation and Fe reduction, by water seeping laterally through preferential flow paths in and adjacent to shrinkage cracks above the regolith‐bedrock contact. Contrasting morphology and chemistry between terrace interior and edge both result from, and cause, the interaction of pedogenic processes and landscape evolution. Contrasts between interior and edge soils suggest that caution is essential in using edge exposures as representative of soils under a geomorphic surface.
Tillage and Cover Crop Effects on Saturated and Unsaturated Transport of Fluometuron
Authors: Wilson G. V. , Yunsheng L. , Essington M. E. , Tyler D. D. , Selim H. M.
Published: July 2010

This study compared flow parameters for no‐till (NT) and tilled (T) soils from Louisiana and Tennessee, with hairy vetch (Vicia villosa Roth ssp. villosa) or no winter cover crop, under saturated and unsaturated conditions and the multireaction characteristics of fluometuron [N,N‐dimethyl‐N′‐[3‐(trifluoromethyl) phenyl] under unsaturated conditions. Miscible displacement experiments were conducted under saturated flow at a rate of 2.13 cm h−1, and under unsaturated conditions with a matric head of −50 cm at a flow rate of 0.21 cm h−1. Preferential flow through these loessial soils was evident by asymmetric breakthrough curves (BTC) under saturated conditions for both NT and T systems. The dispersion coefficients describing the nonreactive BTC under saturated conditions for the NT columns were generally lower than for the T columns. Dispersion was substantially higher for saturated flow, with Peclet numbers nearly an order of magnitude lower than for unsaturated flow. The dispersion coefficients under unsaturated conditions were generally two times larger for NT than T systems. Nonreactive solute transport characteristics for the T‐vetch cover systems were similar to NT systems with no cover crop under both saturated and unsaturated conditions. Adsorption was enhanced by NT in Louisiana, whereas adsorption was enhanced by vetch cover in Tennessee columns. Tillage and cover crops did not affect the instantaneous reactivity (Kd), whereas the irreversible rate coefficient (Kirr) was four times higher under the vetch system than the no‐cover system. The forward and backward kinetic adsorption coefficients were two times higher under NT than T systems.
Analytical Solution for One‐Dimensional Heat Conduction‐Convection Equation
Authors: Shao Mingan , Horton Robert , Jaynes D. B.
Published: July 2010

Coupled conduction and convection heat transfer occurs in soil when a significant amount of water is moving continuously through soil. Prime examples are rainfall and irrigation. We developed an analytical solution for the heat conduction‐convection equation. The solution for the upper boundary of the first type is obtained by Fourier transformation. Results from the analytical solution are compared with data from a field infiltration experiment with natural temperature variations. The predicted temperature values are very similar to the observed values. Temperature changes with time for different soil depths are predicted from conduction‐convection theory and from conduction theory alone. During infiltration, convective heat transfer contributed significantly to the temperature changes at all soil depths monitored. The theory also quite accurately predicts temperature effects on surface infiltration.
Proton Adsorption on an Aluminum Oxide in the Presence of Bicarbonate
Authors: Schulthess C. P. , Wijnja H. , Swanson K.
Published: July 2010

The aqueous species of CO2 [CO2(aq), H2CO3, HCO−3 and CO2−3] are often ignored in adsorption studies despite the fact that CO2 in soil air can be hundreds of times greater than in the atmosphere. Adsorption studies that do not account for CO2 species may be under‐estimating proton adsorption in natural environments. The objective of this study was to discern the effect CO2 species have on proton adsorption to an Al oxide. The backtitration method was used to produce proton adsorption curves as a function of pH for samples of Al oxide with and without aqueous bicarbonate. Sodium chloride was used to vary the ionic strength. Proton adsorption increased in the presence of the bicarbonate below pH 9.7. The greater the concentration of bicarbonate, the greater the proton adsorption. The point of zero salt effect (PZSE = 8.30) was unaffected by the bicarbonate. The data presented show an approximate 1:1 stoichiometry for proton removal with inorganic‐C (HCO3 plus all other species) adsorption data. That is, this research directly quantified that every inorganic C adsorbed (expressed as HCO3 adsorbed) is accompanied by the removal of one proton (more precisely, 1.10 ± 0.28) from the aqueous phase by the Al oxide. Thus, the net removed from the liquid phase is equivalent to one H2CO3 in mass‐balanced terms. The use of traditional titration methods, rather than the backtitration method, resulted in a questionable pH‐dependent pattern that reflects the impact of Al dissolution on these measurements.
Interaction of Mugineic Acid with Iron (Hydr)oxides: Sulfate and Phosphate Influences
Authors: Hiradate S. , Inoue K.
Published: July 2010

Interactions of 100 µmol L−1 mugineic acid (MA) with synthetically produced Fe (hydr)oxides (goethite, hematite, lepidocrocite, and ferrihydrite) as influenced by 100 mmol L−1 SO2−4 and phosphate were studied at equilibrium in the pH range from 3 to 11. In the presence of SO2−4, the concentrations of total MA [i.e., free MA + Fe(III)‐MA complexes] and Fe(III) dissolved by MA in the filtrates were higher than those in the presence of 100 mmol L−1 Cl− at pH < 7. Sulfate increased the formation of Fe(III)‐MA complexes indirectly by reducing the adsorption of MA and Fe(III)‐MA by the Fe (hydr)oxides. The adsorption of MA by the Fe (hydr)oxides and consequently the MA‐promoted dissolution of Fe(III) from ferrihydrite and lepidocrocite were greatly inhibited by the adsorption of phosphate. The slight dissolution of Fe(III) between pH 5 and 9 is partly attributed to the formation of soluble Fe(III)‐phosphate complexes. Although MA does not react directly with Fe (hydr)oxides in the presence of excess phosphate, MA would promote the dissolution reaction of Fe(III) by phosphate. The sequence of adsorption affinity for the Fe (hydr)oxides was found to be: phosphate >> MA > Fe(III)‐MA, SO2−4 > Cl−. Our results suggest that SO2−4 and especially phosphate applied as fertilizers may inhibit the MA‐promoted dissolution of Fe(III) from Fe (hydr)oxides in soils mainly by displacement of MA from the surface of Fe (hydr)oxides.