bluuebunny/crossref_metadata_2025 huggingface dataset:
Variation of Soil Water Storage across a Sand Plain Hillslope
Authors: Tomer M. D. , Anderson J. L.
Published: July 2010

Although landscape variations in soil properties and productivity are often attributed to soil water conditions, landscape‐scale studies of soil water are rare. This study describes variability of soil layering and soil water storage on a sand plain hillslope. According to a nested grid (with spacings from 2 to 16 m), soil cores were collected by horizon, and soil water profiles were measured with a neutron probe during the 1992 growing season. Particle‐size analysis was conducted on the soil samples. A topographic survey of the hillslope was conducted, and elevation, slope, and slope curvature maps were constructed. Fine aeolian sand overlies medium sand of alluvial origin. The fine sand is thickest at upland positions, indicating the hill is a dune remnant. Lamellae only occur in the finer upland soils. Surface water storage (0–0.7‐m interval) is greatest at the toeslope, where the epipedon is mollic. Subsurface storage (0.7–1.7‐m interval) is greatest at upland positions, where perching of soil water is associated with lamellae and the depositional discontinuity. Regression modeling showed that combinations of elevation (cubic trend), slope, and plan curvature explain 51 to 77% of the variability in profile water storage, depending on depth interval. When topographic trends are removed, spatial correlation of water storage only occurs within distances <6 m. Topographic trends can be used to model variability in soil water storage for this landscape, even though surface runoff is not significant.
Reassessment of Polynov's Ion Mobility Series
Authors: Hudson Berman D.
Published: July 2010

Polynov (1937) calculated the relative mobilities of important elements in landscapes: Cl > SO4 > Ca > Na > Mg > K > Si > Fe > Al. This series depicts a general weathering sequence that is essential to understanding many aspects of soil genesis and soil geography. It is argued on tbeoretical grounds that Ca and Na are out of proper sequence in Polynov's series. Polynov estimated ion mobilities by comparing the average content of elements in igneous rock to the average content of the same elements in river waters. However, an estimated 80% of the rocks at the earth's surface, which supply most of the leachate to rivers, are sedimentary. Accordingly, Polynov's mobility series was recalculated after adjusting rock chemical composition for the dominance of sedimentary rock types at the earth's surface. By using the elemental composition of igneous rocks in his calculations, Polynov greatly overestimated the amount of Na relative to Ca in rocks providing leachate to rivers. As a result, he significantly underestimated the mobility of Na relative to Ca. It is recommended that Polynov's ion mobility series be modified to the following: Cl > SO4 > Na > Ca > Mg > K > Si > Fe > Al. This study showed that Na is much more mobile (relative mobility 18.0) than Ca (8.1), Mg (5.4), or K (3.5). Therefore, it is recommended that Na be placed in a distinct mobility phase (II) second in relative mobility to Cl and SO4 (I).
Effects of Cultivation and Abandonment on Soil Organic Matter in Northeastern Colorado
Authors: Ihori Tamiko , Burke Ingrid C. , Lauenroth William K. , Coffin Debra P.
Published: July 2010

The influence of climate and soil texture on soil organic matter losses due to cultivation are rarely addressed due to lack of appropriately paired sites. In addition, soil organic matter recovery on previously cultivated fields is not well understood. In this study, we identified seven sites that have native and abandoned fields and five sites that have native, abandoned, and cultivated fields. All sites are in the northeastern Colorado shortgrass steppe, crossing a precipitation range from 320 to 370 mm, and have sand contents from 36 to 67%. Historical cultivation reduced soil C and N across this region by between 16 and 42%. Although variation in native soil C and N at these sites correlates with climate and soil texture, variation among sites in soil losses due to cultivation is not explained by these variables. We used a statistical model and a simulation model to estimate patterns of soil loss across sites; neither model predicted variation among sites adequately (P > 0.05). We suggest that local‐scale variability in organic matter losses due to cultivation are strongly dependent on management practices. With a simulation model and the data from native, abandoned, and cultivated fields, we estimated that 25 to 120 g C m−2 have been recovered on the abandoned fields during the past 50 yr. Such rates of recovery are small compared with loss rates due to cultivation. Rates of soil organic matter recovery are constrained by natural pedogenic processes, which cannot reverse disturbance processes at a comparable rate in this semiarid environment.
Relationship between Buffelgrass Survival, Organic Carbon, and Soil Color in Mexico
Authors: Ibarra‐F. Fernando A. , Martin‐R. Martha H. , Cox Jerry R. , Crowl Todd A. , Post Donald F. , Miller Raymond W. , Rasmussen G. Allen
Published: July 2010

T‐4464 buffelgrass (Cenchrus ciliaris L.), a perennial bunchgrass from Africa, has been extensively seeded throughout Mexico. After establishment and grazing, T‐4464 either persists with time and actively invades surrounding areas (spreads), persists with time but does not increase (persists), or declines with time and all plants die (dies). To help land managers select high‐potential seeding sites, we classified 139 seeding sites in three survival regimes: (i) spreads, (ii) persists, and (iii) dies. In previous research, we identified a relationship between plant survival and organic C. This research was designed to identify relationships between organic C and soil color. Single comparisons between organic C and Munsell hue, value, chroma, and reflectance in dry and moist soils were poor predictors of plant survival. To predict buffelgrass survival among the three survival regimes and between spreads and dies, we used discriminant function analyses. In dry soil, a model including value and chroma correctly classified 53% (Wilke's λ = 0.8) of the seeding sites in the three survival regimes, while in moist soils, value and reflectance components correctly classified 61% (Wilke's λ = 0.7) of the seeding sites. A dry soil model including value, chroma, and reflectance correctly classified 81% (Wilke's λ = 0.7) of the seeding sites between spreads and dies, while a moist soil model, including the same components, correctly classified 83% (Wilke's λ = 0.6) of the seeding sites. Survival regime selection with multiple soil color components prior to brush control and sowing will reduce adverse economic and environmental consequences and enhance long‐term beef production.
Water Management Effects on Mineralization of Soil Organic Matter and Corn Residue
Authors: Kimmelshue J. E. , Gilliam J. W. , Volk R. J.
Published: July 2010

Water table control is being used on large areas of poorly drained Atlantic Coastal Plain soils during the winter to reduce N losses to surface waters. This study was conducted to determine the effect of water table depth (WTD) and control on N mineralization of added corn (Zea mays L.) residue. Soil columns (15‐cm‐diam.) were extracted to 70‐cm depth from a Portsmouth loam (fine‐loamy over sandy or sandy‐skeletal, mixed, thermic Typic Umbraquult), placed in polyvinyl chloride (PVC) water table columns, and buried even with the surrounding soil surface. Labeled corn residue (18.01 atom % excess 15N) was incorporated in the upper 15 cm of the PVC columns and WTDs of 0, 15, 30, and 45 cm maintained. Soil microsamples were taken over time for N analyses. After 209 d, approximately 8 to 13% of the inorganic N came from the N added as plant residue, even though the added N was only 1.1% of the total soil N. Although the 0‐ and 15‐cm WTD treatments accumulated little 15NO3‐N, they contained appreciable 15NH4‐N. In contrast, the 30‐ and 45‐cm WTD treatments accumulated primarily 15NO3‐N as inorganic N accumulation increased with time and rising soil temperatures. It was concluded that WTD control could be used during the winter to promote denitrification of available NO3‐N and thus to minimize NO3‐N lost to drainage water.
Land Subsidence in Drained Histosols and Highly Organic Mineral Soils of California
Authors: Rojstaczer Stuart , Deverel Steven J.
Published: July 2010

This study was conducted to determine historical trends in subsidence in the Sacramento‐San Joaquin Delta and their environmental controls. Historical subsidence was determined by measuring soil surface elevation loss near electrical tower foundations and by evaluating survey data between 1922 and 1981. The data indicated that subsidence slowed with time. In the western Delta, average subsidence rates were 2.3 cm yr−1 from 1910 to 1988 and 1.5 cm yr−1 from 1952 to 1988. Spatially variability in subsidence was correlated with organic matter content of the soil (r2 = 0.62), which in turn was related to the depositional and drainage history of the Delta. Subsidence rates appeared to be independent of crops grown.
Nitrogen Mineralization in Humid Tropical Forest Soils: Mineralogy, Texture, and Measured Nitrogen Fractions
Authors: Motavalli P. P. , Palm C. A. , Elliott E. T. , Frey S. D. , Smithson P. C.
Published: July 2010

Chemical and physical stabilization of soil organic matter by the interaction of organic compounds with soil clay minerals may affect N mineralization in tropical forest soils. Nitrogen mineralization rates during long‐term incubation were determined on soils of several mineralogies collected from native forests in Costa Rica, Colombia, Peru, and Brazil. Amounts of N mineralization were related to soil mineralogy, texture, and N fractions in order to determine the effects of these soil components on N mineralization and to evaluate measurements of these components for their use as potential N availability indices. Allophanic soils produced higher cumulative levels of mineralized N and had higher initial levels of several N fractions than soils with smectitic, oxidic, and kaolinitic mineralogies. This mineralogical effect was attributed to greater initial N stabilization in allophanic soils followed by greater N release after the addition of nutrient solution during incubation. Total soil N had the strongest correlation with N mineralization among the N measurements considered in this study. The active N pool, as calculated by a two‐pool regression model of cumulative mineralized N, had the highest positive relationships with NH+4‐N evolved in a 1‐wk anaerobic incubation and soluble N. The stable N pool had the strongest correlations with total N and light‐fraction N. The relationships between soluble N or NH+4‐N evolved after a 1‐wk anaerobic incubation and N mineralization were affected by soil mineralogy, which suggests the need for further evaluation of potential N availability indices for the effects of soil mineralogy.
Co‐Occurrence of Hydrophobicity and Allelopathy in Sand Pits under Burned Slash
Authors: Everett Richard L. , Java‐Sharpe Bonnie J. , Scherer George R. , Wilt F. Martin , Ottmar Roger D.
Published: July 2010

Prescribed burning of slash following tree harvest is a standard practice to reduce fire hazard and prepare seed beds for planting conifers. This study examined the co‐occurrence and intensity of hydrophobic and allelopathic layers created in sand pits under burned slash piles and broadcast slash. Following slash burning, 24 sand cores were taken from the sand pits and analyzed for water repellency and allelopathic effects on germination, emergence, and height growth of a bioassay species, blue wildrye (Elymus glaucus Buckley). Water drop penetration that was instantaneous in untreated sand cores was delayed in sand cores from burn treatments for 5 to 90 s in seven cores and for >270 s in five cores. Seedling emergence and height of the bioassay species declined in both the created hydrophobic sand layer and in an allelopathic zone of wettable sand immediately below the hydrophobic layer. Lack of allelopathic response when free water was present suggests that allelopathic effects are exhibited only under unsaturated soil conditions. Results indicate that nonwettable soils and allelopathy effects will act in unison to reduce water penetration and slow plant establishment following wildfires or prescribed burns.
Forms of Phosphorus in Soil Profiles from Dairies of South Florida
Authors: Nair V. D. , Graetz D. A. , Portier K. M.
Published: July 2010

Soil P fractions of current and abandoned dairy systems in South Florida's Lake Okeechobee watershed were evaluated to develop an understanding of the stability of P in this basin. Land use within the dairies was classified as intensive (high cattle impacted) and pasture, forage, or native (low cattle impacted) areas. All soils (Spodosols) were characterized for labile P (1 M NH4Cl), Fe‐Al‐associated P (0.1 M NaOH), Ca‐Mg‐associated P (0.5 M HCl), residual P, and organic P in the NaOH fraction. The A horizons of the intensive areas had ≈9% of total P as labile P, though most of the Ca‐Mg‐associated P (≈70% of total P) in these particular systems could also be removed by sequential NH4Cl extractions. Therefore, almost 80% of the P in the surface horizons of the high cattle impacted areas had the potential to move eventually with drainage water into the lake. The P in the E horizons of the intensive areas consisted primarily of labile P and Ca‐Mg‐associated P forms as well, though the total P in these horizons was <5% of that for the A horizons. About 80% of the total P in the spodic (Bh) horizons was extractable by NaOH, of which only 4 to 18% was associated with organic matter. The total P contents for all horizons of the soil profiles from the low cattle impacted areas were considerably less than those from the high cattle impacted areas. There were apparently no major shifts of P to more stable P forms, with time, for soils of high cattle impacted areas. Therefore, the possibility of P release from high cattle impacted soils, even after dairies were abandoned for more than 12 yr, cannot be ruled out.
New Method for Assessment of Long‐Term Phosphate Desorption from Soils
Authors: Freese D. , Lookman R. , Merckx R. , van Riemsdijk W. H.
Published: July 2010

A new method was developed to study P desorption kinetics. This new technique uses dialysis membrane tubes, filled with hydrous ferric oxide (ferrihydrite) acting as an “infinite” P sink. This system is mechanically stable for very long reaction periods, provided that a microbial inhibitor, e.g., chloroform, is added to the soil suspension to prevent hydrolysis of the membrane. The pH of the soil solution during desorption remains almost constant. After the desired time of contact between soil suspension and P sink, the sink can be easily separated from the soil suspension with practically no loss of soil material. As such, the new technique has important advantages to the Fe oxide impregnated filter paper P extraction method. The system is capable of maintaining a constant low P activity in solution, necessary to study long‐term P desorption kinetics of soils. This method was tested on six sandy soil samples and a comparison made with the amount of P desorbed by a single Fe oxide impregnated filter paper extraction (Pi). An important finding from this experiment was that P desorption continues for long periods. No desorption maximum was reached within 500 h, as is often suggested by desorption results based on repeated extractions with Fe‐impregnated filter paper. Furthermore, relatively large differences were observed between different soils with respect to the quantity of oxalate‐extractable phosphate released by the soils after a specified time of desorption.
Time of Nitrogen Application: Effects on Winter Wheat and Residual Soil Nitrate
Authors: Boman R. K. , Westerman R. L. , Raun W. R. , Jojola M. E.
Published: July 2010

Rate and time of N fertilizer application can affect winter wheat (Triticum aestivum L.) forage and grain yield and quality, and may influence residual NO3‐N concentration and distribution in the soil profile. Objectives of this experiment were to determine the effects of N fertilizer rate and time of application on forage and grain yield, N uptake, and distribution of residual soil NO3‐N. Field experiments were conducted for four consecutive years on a Teller sandy loam (fine‐loamy, mixed, thermic Udic Argiustoll) cropped to winter wheat under conventional tillage. Urea‐ammonium nitrate (UAN) was broadcast and incorporated before planting (PPI) or topdressed in December (Feekes 3), January (late Feekes 3), February (Feekes 4), or March (Feekes 5–6) at rates of 34, 67, 101, and 134 kg N ha−1. Soil samples were taken from each plot after each grain harvest to 1.2 m and analyzed for NH4‐N and NO3‐N. Forage yield response (measured in late March to mid‐April) to January and December N application was comparable to PPI when adequate precipitation was received after N was applied. Applying N in February and March resulted in plant tissue damage and lower forage yields due to less early‐season growth than with other applications. Apparent fertilizer N recovery in forage was highest when N was applied at or before mid‐January. Date of N application had minimal influence on grain yields. Quadratic response surface models suggest the optimum time of N application for maximum forage and grain yields to be mid‐November and early January, respectively. Timing of N application had no effect on residual NH4‐N and little influence on residual NO3‐N concentration and distribution in the soil profile at the end of each cropping cycle.
Landscape Evolution and Shallow Groundwater Hydrology of a Till Landscape in Central Iowa
Authors: Steinwand A. L. , Fenton T. E.
Published: July 2010

Deciphering the effects of land use on environmental quality requires detailed knowledge of the processes governing soil and landscape genesis. The objective of this study was to describe the landscape evolution and shallow groundwater hydrology of a glaciated landscape in Iowa and to relate the soil color pattern to water table fluctuations. Stratigraphic and geomorphic maps and cross sections were prepared using characterization data from 128 soil cores collected from a 32‐ha site. One transect crossing several hillslopes was instrumented with 47 piezometers to determine groundwater flow direction. Three strata of surficial sediments overlying till were identified. The upper two strata were slope alluvium deposited after 4300 YBP, which limits the age of the soils to the late Holocene or younger. The lower sediment resembled alluvium and may be supraglacial sediment draped on the till and later eroded from adjacent hillslopes. The hydrology was characterized by recharge under topographic highs, lateral groundwater flow on sideslopes and discharge in swales. During dry periods, however, portions of higher swales acted as recharge areas and groundwater flow was directed between swales. Morphologic indicators of wetness are better expressed and shallower in soils at footslope and toeslope positions, but some of these features are relict because of the lowering of the water table by artificial drainage.
Residual Deep Plowing Effects on Irrigation Intake for Pullman Clay Loam
Authors: Allen R. R. , Musick J. T. , Schneider A. D.
Published: July 2010

Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) and related soils predominate in the southern High Plains of the USA. They are slowly permeable but respond to deep tillage with increased irrigation water intake. A one‐time deep moldboard plowing to 0.4‐, 0.6‐, or 0.8‐m depths was performed in 1966 to evaluate the inversion and mixing of the slowly permeable Bt1 horizon with the Ap horizon. We hypothesized that these deep tillage effects would still be present after 25 yr. We report irrigation intake effects with 5 yr (four growing seasons) of cropping to winter wheat (Triticum aestivum L.) beginning in 1988. After moldboard plowing to 0.2 m to restore surface tillage layer permeability, residual effects from the 1966 deep plowing caused an average increase in intake of 26% (129–163 mm) for the 0.4‐m plow depth, compared with the 0.2‐m check, for the first irrigation after tillage from 1988 to 1992. Irrigation intake increased 40% (52 mm) with 0.6‐m deep plowing; however, there was no additional increase for 0.8‐m plowing. Grain yields increased from 4.2 to 5.0 Mg ha−1 (19%) for the 0.4‐m or deeper plowing. The 1966 deep tillage also increased deep soil water storage between the 1‐ and 2.3‐m depths during 1988 to 1992. Water use efficiencies were ≈8% greater for the deep plowing treatments.
Tillage Effects on Corn Production and Soil Physical Conditions
Authors: Cassel D. K. , Raczkowski C. W. , Denton H. P.
Published: July 2010

Row crop production on highly erodible soils of the Piedmont in the southeastern USA is often limited by surface sealing, excessive surface water runoff, soil erosion, and low crop yields. The effects of four tillage practices on corn (Zea mays L.) growth and soil properties on two crust‐prone soils were evaluated. Tillage treatments at two Piedmont locations, Oxford and Reidsville, NC, were no‐till (NT), in‐row subsoiling (IRS) (1987 only), chisel plow (CP), and moldboard plow‐disk (MP). Residue cover was 1% for MP and ranged from 75 to 87% for NT and 38 to 27% for CP. The interaction between tillage, soil properties, and plant performance was complex. Mean bulk density of the Ap horizon at Reidsville for the 2‐yr period was 1.56 Mg m−3 for NT, compared with 1.48 Mg m−3 for CP and 1.46 Mg m−3 for MP. Cone index was not affected by tillage but was greatest in the trafficked interrow, 3.50 MPa, compared with 1.91 and 1.09 MPa in the row and nontrafficked interrow, respectively. Mean corn grain yield for the four year‐locations was least, 1.23 Mg ha−1, for MP, compared with 2.97 Mg ha−1 for NT and 2.44 Mg ha−1 for CP; mean yield for IRS in 1987 was 3.69 Mg ha−1. Tillage practices leaving crop residues on the soil surface, such as NT, CP, and IRS, can reduce or eliminate surface crusting, increase infiltration, and reduce surface runoff and soil loss while increasing crop yield.
Evaluating Shrub‐Associated Spatial Patterns of Soil Properties in a Shrub‐Steppe Ecosystem Using Multiple‐Variable Geostatistics
Authors: Halvorson Jonathan J. , Bolton Harvey , Rossi Richard E. , Smith Jeffrey L.
Published: July 2010

Geostatistics are often calculated for a single variable at a time, even though many natural phenomena are functions of several variables. The objective of this work was to demonstrate a nonparametric approach for assessing the spatial characteristics of multiple‐variable phenomena. Specifically, we analyzed the spatial characteristics of resource islands in the soil under big sagebrush (Artemisia tridentata Nutt.), a dominant shrub in the intermountain western USA. For our example, we defined resource islands as a function of six soil variables representing concentrations of soil resources, populations of microorganisms, and soil microbial physiological variables. By collectively evaluating the indicator transformations of these individual variables, we created a new data set, termed a multiple‐variable indicator transform or MVIT. Alternate MVITs were obtained by varying the selection criteria. Each MVIT was analyzed with variography to characterize spatial continuity, and with indicator kriging to predict the combined probability of their occurrence at unsampled locations in the landscape. Simple graphical analysis and variography demonstrated spatial dependence for all individual soil variables. Analysis also showed that ensembles of variables were not randomly distributed, but rather were correlated systematically within the landscape. Maps derived from ordinary kriging of MVITs suggested that the combined probabilities for encountering zones of above‐median resources were greatest near big sagebrush. As the selection criteria for defining a resource island became more stringent, the area of the resource island decreased. Cross‐variography revealed that big sagebrush was more positively correlated with MVIT resource islands than were grass species, the other major plant type.
Authigenic Dolomite in a Saline Soil in Alberta, Canada
Authors: Kohut Connie , Dudas M. J. , Muehlenbachs K.
Published: July 2010

The formation of dolomite is poorly understood and highly controversial, since well‐ordered dolomite has never been synthesized under earth surface conditions and natural occurrences of modern dolomite have been reported only rarely from restricted sedimentary environments. It is generally accepted that dolomite does not form in soils. This study investigates the characteristics and origin of dolomite in a sulfatic saline soil in east‐central Alberta, Canada, in which dolomite makes up more than half of the <2‐µm fraction. X‐ray diffraction analysis shows that the dolomite is stoichiometric and ordered, with only slight deviations in unit cell parameters relative to ideal dolomite. The clay‐sized dolomite is enriched in 18O and depleted in 13C relative to detrital dolomite and dolomite present in larger size fractions, and has a radiocarbon age ranging from 1270 to 5270 yr before present, clearly indicating an authigenic origin. The very small dolomite particle size and differences in isotope content from coexisting calcite suggests that the dolomite formed by direct precipitation in the soil rather than by dolomitization of a preexisting calcite.
Predicting Phosphate Adsorption‐Desorption in a Soilscape
Authors: Scheinost A. C. , Schwertmann U.
Published: July 2010

Modeling the P availability in a soilscape requires knowledge about the three‐dimensional variability of the phosphate adsorption‐desorption (AD) curves. The high variabilities of soil parent material and of agricultural P input in a 1.5‐km2 study area were taken into account by taking 2555 samples at the intersections of a 50‐m grid. To reduce the necessary laboratory work, pedotransfer functions (PTFs) were developed that could predict the AD curves from more easily obtainable soil characteristics. Therefore, AD curves were measured for only 40 representative samples. The AD curves were fitted with an extended and rearranged Freundlich equation with a constant adsorption energy parameter k = 0.29. The adsorption capacity parameter A of this equation was predicted from clay, dithionite‐extractable Fe (Fed), and pH using a nonlinear regression method. With increasing pH, A decreased for 4 < pH < 6.5 but increased for 6.5 < pH < 7.5. The Fed could be replaced by the soil color yellowness component b*, which was easily determined with a chroma meter. The equilibrium P concentration of the soil solution, ceq, was closely related to a one‐point measurement of the AD curves, c1.2 (the final concentration after adding 1.2 mg L−1 P). Thus, only the four soil properties clay, Fed (or b*), pH, and c1.2 were necessary to predict complete AD curves using the developed equations. The equations proved to be reliable when tested by an independently selected subset of the 2555 samples and by a functional validation. The developed equations can therefore be used as PTFs.
Tillage and Crop Effects on Seasonal Soil Carbon and Nitrogen Dynamics
Authors: Franzluebbers A. J. , Hons F. M. , Zuberer D. A.
Published: July 2010

Seasonal changes in the active fractions of soil C and N are important in understanding mineralization‐immobilization processes that influence soil N availability. Our objective was to determine the effect of tillage (conventional tillage [CT] and no tillage [NT]) in monoculture sorghum [Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.] on the seasonal dynamics of in situ inorganic soil N, potential C and N mineralization, and soil microbial biomass C (SMBC). A Weswood silty clay loam (fine‐silty, mixed, thermic Fluventic Ustochrept) located in south‐central Texas was sampled to a depth of 200 mm 57 times during a 2‐yr period. In situ soil NO3− accumulated at a rate of ≈0.03 g N m−2 d−1 following harvest when temperature and moisture were adequate. Potential soil C mineralization was 35, 39, and 53% greater under NT than under CT when averaged across months in wheat, sorghum, and soybean, respectively. However, following harvest of each crop, potential soil C mineralization increased at a faster rate under CT than under NT and differences between tillage regimes were reduced for several months, which caused temporary N immobilization in CT. Periods of net N immobilization at the end of the growing season and beginning of the fallow period were often associated with an increasing SMBC pool. Large seasonal changes in active soil C and N pools could be related to rhizodeposition, crop residue addition, and the long fallow period. The type, placement, and timing of residue input significantly altered the seasonal dynamics of the active soil C and N pools and their effect on soil N availability.
Phosphorus Soil Test Correlation to Sugarcane Grown on Histosols in the Everglades
Authors: Korndörfer G. H. , Anderson D. L. , Portier K. M. , Hanlon E. A.
Published: July 2010

Sugarcane (Saccharum spp.) in Florida is principally grown on Histosols in the Everglades Agricultural Area. Soil‐test‐based P fertilization recommendations have not been addressed since the 1970s. The objectives of this research were to evaluate the most acceptable soil test P extractant that best correlates to crop yield, and to define soil test P groupings associated with crop response to applied P. Results will be used in the future to recalibrate soil test data to yield and rate of P application. Phosphorus trials were conducted at four sites on organic soils between 1968 and 1972 and additionally at eight sites on organic soils between 1982 and 1990. Phosphorus applications ranging from 0 to 98 kg P ha−1 were broadcast or row‐applied in combination with different cultivars, and/or K, Si, or S rates at 12 sites (multiple experiments used per site per crop). The effectiveness of water, acetic acid, and Mehlich‐1 extractable soil P as yield response predictors was determined. Acetic acid extractable P was more highly correlated to sugar and cane yields (r = 0.72* and 0.63**, respectively) than water‐extractable P (r = 0.27** and 0.39**, respectively). Mehlich‐1 extractable P was poorly correlated to sugar (r = 0.25*) and cane (r = 0.05ns) yields. Acetic acid extractable P was selected as the best‐suited extractant related to crop yield response to P fertilization. Soil test calibration curves (i.e., relative yield as a function of acetic acid extractable P) were determined from the choice of seven types of regression models, in which the reciprocal function was chosen with the highest coefficient of determination (R2) and minimized residuals. Soil acetic acid extractable P criteria were developed to define soil test level groups associated with yield response conditions: low soil test levels ranged from 0 to 9 mg L−1, medium from 9 to 39 mg L−1, and high exceeded 39 mg P L−1.
Nitrogen Use Efficiency of Winter Wheat among Landscape Positions
Authors: Fiez T. E. , Pan W. L. , Miller B. C.
Published: July 2010

Spatially variable N fertilizer application may reduce environmental impacts and increase the economic return of N fertilization. To achieve these benefits, N recommendations must account for within‐field differences in the amount of N required to produce a unit of yield (unit N requirement, UNR). Component analysis was used to determine the sources of variation in the UNRs of winter wheat (Triticum aestivum L.) among landscape positions. The UNRs were divided into two components, N uptake efficiency (plant N/N supply) and N utilization efficiency (grain yield/plant N) observed in N rate trials (0–140 kg N ha−1 fall applications) established on footslope, south backslope, shoulder, and north backslope positions of two farms for 2 yr. Variation in the UNR among the 16 landscape positions studied was most associated with differences in N uptake efficiency (r = −0.80), although N utilization efficiency (r = −0.62) also contributed to the variation. Nitrogen uptake efficiency among landscape positions declined as more fertilizer was required to reach optimum yield (r = −0.56) due to low N fertilizer uptake efficiencies (Δplant N/ΔN fertilizer). Nitrogen fertilizer uptake efficiency was related to the degree of apparent N loss (r = −0.87), indicating that N availability limited N uptake efficiency among landscapes. Overall, low N fertilizer uptake efficiencies (<50%) and high N loss percentages (>50%) indicate the need to reduce N losses and lower UNRs, particularly on north‐facing backslopes susceptible to N leaching.
Phosphorus Forms in Particle‐Size Fractions of a Toposequence from Northeast Brazil
Authors: Agbenin J. O. , Tiessen H.
Published: July 2010

A previous study of this toposequence from semiarid northeastern Brazil concluded that processes of P transformation in semiarid tropical landscapes with steep slopes are difficult to describe with concepts developed in temperate regions. In these soils, derived from syenitic rocks, particle‐size fractions reflect increasing effects of weathering processes from sands to clays. We therefore document the association of P and different sequentially extracted P fractions with particle‐size fractions along the toposequence to further investigate P transformations during pedogenesis in the tropics. Total P was exceptionally high in these soils and in all particle‐size fractions. Total P increased with decreasing particle size and decreased downslope. Total P in sand and silt correlated with total Ca in these fractions. The Ca‐bound phosphate, largely of primary origin, was most abundant in sands and decreased downslope in all particle‐size fractions. At the lower slope, all particle‐size fractions were dominated by resistant inorganic P forms that correlated with total Fe. Comparison of the proportion of Ca‐associated and resistant P between different profile depths and with the underlying saprolite at the mid and lower slopes indicated increased transformations and P losses in deeper horizons and substantial weathering and leaching extending through the solum into the saprolite underlying the soil. The interpretation of P transformations with soil development and landscape position is complicated by intense weathering, highly variable leaching, and colluvial mixing that results from the complex interactions of lithology, weathering, and colluvial action in this semiarid tropical environment of steep slopes, annual moisture deficits, and intense rainfalls.
Aggregate Stability under Oak and Pine after Four Decades of Soil Development
Authors: Graham R. C. , Ervin J. O. , Wood H. B.
Published: July 2010

The development of water‐stable aggregates is an important soil genesis process because it strongly influences important soil characteristics, including infiltration, aeration, and erodibility. We studied a 41‐yr‐old biosequence of lysimeter soils at the San Dimas Experimental Forest in southern California to assess water‐stable aggregates as a function of the imposed scrub oak (Quercus dumosa Nutt.) and Coulter pine (Pinus coulteri B. Don) communities. Significantly different aggregate stabilities developed in these initially identical and homogeneous soils. Earthworms under the oak produced a 7‐cm‐thick A horizon composed almost entirely of worm casts. Casts were also deposited within the litter of the Oi horizon. The A horizon and the Oi horizon worm casts had aggregate stabilities near 90%, ≈35 g kg−1 organic C, and abundant fungal hyphae, as observed by scanning electron microscopy. The 1‐cm‐thick A horizon under pine contained no worm casts and had 78% water‐stable aggregates, 12.9 g kg−1 organic C, and abundant very fine roots and fungal hyphae. Subsoils under both oak and pine had 43 to 51% water‐stable aggregates, attributable to inorganic binding mechanisms since organic C contents were ≤4 g kg−1, roots were relatively few, and no fungal hyphae were observed. After 41 yr of soil formation, aggregate stability was ≈15% greater and the volume of stable aggregates was seven times larger under scrub oak than under Coulter pine.
Effects of Pine Plantations and Adjacent Deciduous Forests on Soil Calcium
Authors: Wilson David M. , Grigal D. F.
Published: July 2010

Potential depletion of soil Ca and forest sustainability continue to be concerns. Previous studies from the north‐central USA have reported depletion of Ca in soil but increased amounts in the overstory of deciduous compared with coniferous forests, with total system Ca remaining constant. To determine if those reports were generalizable, we sampled 38 pairs of red pine (Pinus resinosa Ait.) plantations and adjacent deciduous stands across the area. Records indicated site similarity before plantation establishment. Neither the texture of the rooting zone (0–32 cm), nor the texture, pH, or Ca content of the 32‐to 100‐cm soil layer differed between forest types, further supporting site similarity. Stands were similar in biomass, but because of lags in plantation establishment, the deciduous stands were older (60 vs. 45 yr). The deciduous stands had greater mass of Ca in the overstory and higher Ca concentration in the 0‐ to 4‐cm mineral soil layer. Both Ca concentration and mass were greater in lower layers of the rooting zone (to 32 cm) under pine. Neither mass of Ca in the forest floor nor in mineral soil to 100 cm differed between types. Contrary to earlier reports, total system Ca was greater in deciduous stands. Our results and others from glaciated areas suggest that deeper soil layers provide minimal Ca to forest stands during a normal rotation. The initial quantity of Ca in the near‐surface soil and the input‐output balance determine Ca status of a site, but the role of deciduous forests in conserving the inputs deserves further scrutiny.
Soil Sampling Technique for Band‐Fertilized, No‐Till Fields with Monte Carlo Simulations
Authors: James D. W. , Hurst R. L.
Published: July 2010

Band application of P fertilizer in no‐till fields results in extremely variable soil test P (STP) along lines perpendicular to the bands. This variation may be represented by two interlaced populations, each with a unique STP mean and standard deviation. The objectives of this research were to: (i) characterize STP populations in a band‐fertilized field; (ii) use these population characteristics to calibrate a Monte Carlo based model to simulate STP populations; and (iii) use simulated STP populations to evaluate different soil sampling procedures. A corn (Zea mays L.) field was band fertilized with P, and 1 yr later STP (mg P kg−1) was measured on individual soil cores with the bicarbonate extraction procedure. Out‐band STP mean and standard deviation (SD) were 13.9 ± 4.75, in‐band STP mean and SD were 127.4 ± 29.7, and composite STP mean and SD were 23.3 ± 28.69. A computer simulation model based on the Monte Carlo technique reproduced the observed populations very closely. The results show that the number of completely random soil cores needed to represent a band‐fertilized field is prohibitive. Rapid collection of a single representative composite sample with equipment capable of taking a slice of soil across the fertilizer band and accurately weight in‐band and out‐band STP by volume is recommended.
Phosphorus Sorption Characteristics of Everglades Soils along a Eutrophication Gradient
Authors: Richardson C. J. , Vaithiyanathan P.
Published: July 2010

We examined the P sorption characteristics of northern Everglades peat soils along a eutrophication gradient to understand the P retention efficiency of the soils. The amount of phosphate adsorbed on the soils (Q) and the zero equilibrium phosphate concentration supported by the soils (EPCo) exhibited a linear decrease with distance from the inflow structures supplying agricultural drainage (r2 = 0.74 and 0.71, respectively; P < 0.05; n = 18). Values of Q and EPCo for the enriched soils are an order of magnitude higher than for unenriched soils. Estimated Q values of the soils compare well with the exchangeable P fraction determined by KCl and HCO3 extraction. Comparison of soil EPCo and pore water PO4‐P values with the surface water PO4‐P concentrations suggests that soils may serve as an additional internal source of P to the overlying water column in nutrient‐enriched areas. Linear phosphate adsorption coefficient (K) of the alkaline Everglades soils is higher than that of acidic pocosin bog peat soils of North Carolina but lower than wetland soils and sediments with a high mineral content. Phosphorus sorption characteristics of the Everglade soils are most likely regulated by CaCO3.
Properties and Variability of Soil and Trench Fill at an Arid Waste‐Burial Site
Authors: Andraski B. J.
Published: July 2010

Arid sites commonly are assumed to be ideal for long‐term isolation of wastes. Information on properties and variability of desert soils is limited, however, and little is known about how the natural site environment is altered by installation of a waste facility. During fall construction of two test trenches next to the waste facility on the Amargosa Desert near Beatty, NV, samples were collected to: (i) characterize physical and hydraulic properties of native soil (upper 5 m) and trench fill, (ii) determine effects of trench construction on selected properties and vertical variability of these properties, and (iii) develop conceptual models of vertical variation within the soil profile and trench fill. Water retention was measured to air dryness (ψ = 2 × 106 cm water suction). The 15 300‐cm pressure‐plate data were omitted from the analysis because water‐activity measurements showed the actual suction values were significantly less than the expected 15 300‐cm value (avg. difference = 8550 ± 2460 cm water). Trench construction significantly altered properties and variability of the natural site environment. For example, water content ranged from 0.029 to 0.041 m3 m‐3 for fill vs. 0.030 to 0.095 m3 m‐3 for soil; saturated hydraulic conductivity was ≈ 10‐4 cm s‐1 for fill vs. 10‐2 to ≈ 10‐4 cm s‐1 for soil. Statistical analyses showed that the native soil may be represented by three major horizontal components and the fill by a single component. Under initial conditions, calculated liquid conductivity (Kl) plus isothermal vapor conductivity (Kv) for the upper two soil layers and the trench fill was ≈ 10‐13 cm s‐1, and Kl was ≤ Kv. For the deeper (2–5 m) soil, total conductivity was ≈ 10‐10 cm s‐1, and Kl was >Kv. This study quantitatively describes hydraulic characteristics of a site using data measured across a water‐content range that is representative of arid conditions, but is seldom studied.
Characterizing the Dependence of Gas Diffusion Coefficient on Soil Properties
Authors: Jin Yan , Jury William A.
Published: July 2010

Knowledge of the gaseous diffusion coefficient is necessary to properly model gas movement in porous media. In this study, a nonreactive tracer (freon‐12) and a reactive tracer (hexafluorobenzene) were used to evaluate the relationship between the ratio of the gas diffusion coefficient in soil (Dsg) to that in free air (Dag) and the volumetric air content (a) with a two‐chamber diffusion system. The measured Dsg/Dag values in our experiments (i.e., the relative gas diffusion coefficients) showed a similar relationship to air content as data obtained from various studies reported in the literature. Our data and values taken from other studies were used to test the validity of various models. When compared with data obtained from experiments with disturbed soils, the Penman model Dsg/Dag = 0.66 a was found to overestimate the measured relative diffusion coefficient, whereas the Millington‐Quirk model Dsg/Dag = a10/3/ϕ2, where ϕ is the soil porosity, underestimated it. Another Millington‐Quirk relationship Dsg/Dag = a2/ϕ2/3, which has been largely overlooked in the literature, was found to provide significantly better agreement with measured relative diffusion coefficients in various disturbed soils of different texture. On the contrary, no universal relationship was found when data from both disturbed and undisturbed soil experiments were evaluated. The Troeh model Dsg/Dag = [(a − u)/(1 − u)]v had the flexibility to fit all of the experimental data when both of the model parameters were varied simultaneously; however, no obvious correlation was found between soil properties and the parameters. The limitations of any universal form for gas tortuosity model in natural soils were analyzed with percolation theory.
Adsorption Isotherms of Poly(vinyl alcohol) on Silicon Oxide
Authors: Schulthess C. P. , Tokunaga S.
Published: July 2010

Poly(vinyl alcohol), PVA, is a water‐soluble polymer that is made up of repeating alcoholic and acetate units. Because this polymer is sometimes applied to soils, it is advantageous to fully understand the relative impact on the adsorption behavior of this polymer by each of the functional groups on the polymer. Using adsorption isotherm data, our objective was to elucidate the effect of the alcoholic and acetate groups on the macromolecule's affinity for a Si oxide surface. Seven PVA polymers were chosen for this study to cover a range of polymer sizes (10 000–128 000 g mol‐1) and degree of hydrolysis (78–99%). As the percentage of hydrolysis of the polymer increases (increase in the alcoholic groups, decrease in the acetate groups), the adsorption of the polymer decreases on a mass basis. We propose that the acetate functional groups on the PVA chains encourage the formation of loops by the polymer on the Si surface, which also increases the amount adsorbed on a mass basis. The larger polymers also adsorbed more than the smaller ones. Conformity of the polymer to the Langmuir isotherm indicates that the adsorption is site‐specific. The Langmuir equilibrium constant (K) was determined for the polymer above low surface coverage conditions because the energy of adsorption was stronger at low surface coverage. As the hydrolysis percentage of the polymer was lowered, K increased; this was semi‐independent of the polymer size. Consequently, the acetate functional groups on the PVA chains also enhance the affinity of the polymer toward the surface.
Micromorphologies and Stabilities of Chromium (III) Surface Precipitates Elucidated by Scanning Force Microscopy
Authors: Fendorf Scott E. , Li Guangchao , Gunter Mickey E.
Published: July 2010

Ascertaining the stability of immobilized contaminants in soils is necessary to assess their potential risk in the environment. The composition, structure, and surface morphology are the principal determinants of a sorbate's reactivity. We investigated Cr(III) precipitates on goethite (α‐FeOOH) and silica (amorphous SiO2) using scanning force microscopy to ascertain the morphology of the surface precipitates. Imaging was performed on both colloidal and single‐particle solids. The colloidal materials were used to simulate solids found within soils, while the single particles provide in situ investigations. Scanning force micrographs reveal that Cr(III) forms a precipitate on α‐FeOOH that distributes over the surface, while on SiO2(amorphous) discrete surface clusters are observed. Based on these results, one would predict that at coverages exceeding monolayer capacity, Cr(III) precipitates on silica would be more reactive and thus have a greater potential for remobilization in the environment than Cr(III) precipitates on goethite. To test this hypothesis we reacted the surface precipitates with oxalate, a common root exudate, and measured the rate and extent of Cr(III) dissolution. The expected greater reactivity of Cr(III) on silica relative to Cr(III) on goethite was supported by the more rapid and extensive oxalate‐induced dissolution of Cr(III); initial dissolution rates were 0.166 mol L‐1 h‐1 for Cr(III)‐silica while only 0.0420 mol L‐1 h‐1 for Cr(III)‐goethite.