bluuebunny/crossref_metadata_2025 huggingface dataset:
Corn Residue Age and Placement Effects on Evaporation and Soil Thermal Regime
Authors: Sauer Thomas J. , Hatfield Jerry L. , Prueger John H.
Published: July 2010

Differentiation between tillage‐ and residue‐induced effects on soil moisture and thermal regimes is necessary to improve residue management practices. The objective of this research was to quantify the influence of corn (Zea mays L.) residue age and placement on evaporation from and heat flow in two soils. Soil temperature, thermal conductivity, heat flux, and moisture content were monitored in duplicate monoliths (0.45 [length] by 0.35 [width] by 0.5 [height] m) of Nicollet loam (fine‐loamy, mixed, mesic Aquic Hapludoll) and Monona silt loam (fine‐loamy, mixed, mesic Typic Hapludoll) in a controlled environment chamber. Mass changes of one monolith of each soil were measured with load cells to estimate evaporation. Surface cover types consisted of a bare soil surface (B), fresh residue (F), weathered residue (W), and weathered residue with a 0.15‐m‐wide bare strip (S). Bare‐soil evaporation averaged 9.97 ± 0.66 mm for both soils during a 96‐h period and was reduced to an average of 5.76 ± 0.70 mm with residue cover. Nicollet soil with weathered residue had an average evaporation rate of 1.33 to 1.4 mm d−1. By comparison, evaporation rates measured in a field having Nicollet and associated soils with weathered corn residue averaged 1.37 and 1.11 mm d−1. Residue cover had no significant effect on thermal conductivity measured at 0.15 m that averaged 1.22 and 1.35 W m−1 K−1 for the Nicollet and Monona soils, respectively. Phase shift in soil temperature and average daily conductive soil heat flux were similar for field and chamber measurements but the amplitude of the soil temperature wave and conductive soil heat flux were much greater in the field.
Time Domains for Early‐Time and Steady‐State Pressure Infiltrometer Data
Authors: Groenevelt P. H. , Odell B. P. , Elrick D. E.
Published: July 2010

The determination of the field‐saturated hydraulic conductivity, Kfs, using a Guelph Pressure Infiltrometer, typically relies on the establishment of steady‐state flow. For media with very low values of Kfs, such as the compacted clay liners of landfills, the establishment of steady‐state flow may take months. It then becomes opportune to rely on early‐time observations of infiltration to infer Kfs. The time domain in which early‐time data analysis is valid can, for the first time, be delineated by equating the flux from both the early‐time and steady‐state flow expressions. This new delineating boundary value will be indicated by tcr. This will be the critical time at which the early‐time behavior gradually transits into the steady‐state time domain. There is, however, a time zone around tcr in which neither the early‐time analysis nor the steady‐state analysis is appropriate, as flow is neither purely dominated by capillary forces nor gravitational forces. Results of tcr delineations are presented as a function of two field and clay liner parameters: Kfs and Δθ, the change in volumetric water content between initial and field‐saturated conditions. Graphical interpretation reveals the existence of the inversely proportional relationships: critical time vs. Kfs and critical time vs. applied pressure head. Also evident is the directly proportionate response of the critical time to change in Δθ. We find that the present form of the critical time expression can be reduced to previous formulations concerning characteristic times. We offer these derivations as proof of the validity of this new critical time parameter.
Mechanisms of Nickel Sorption on Pyrophyllite: Macroscopic and Microscopic Approaches
Authors: Scheidegger André M. , Sparks Donald L. , Fendorf Mark
Published: July 2010

Retention of heavy metal ions on soil mineral surfaces is a crucial process for maintaining environmental quality. A thorough understanding of the sorption mechanisms of heavy metals on soil mineral surfaces is therefore of fundamental importance. This study examined Ni(II) sorption mechanisms on pyrophyllite. The removal of Ni from solution was studied as a function of pH (pH = 5–8.5), initial Ni concentration (1 × 10−4 to 1 × 10−2 M), and ionic strength (0.01–1 M). The data suggest that Ni sorption behavior can be divided into two distinct pH regions. In the lower pH region (i.e., pH <7), relative Ni sorption increased with decreasing ionic strength and initial Ni concentration. The adsorption maximum at pH = 6 was significantly higher than the cation‐exchange capacity (CEC) at the same pH. Based on these findings, we propose that both specific and nonspecific adsorption are involved. In the higher pH region (pH >7), nickel sorption becomes slow and does not seem to be affected by the ionic strength and the initial Ni concentration. We employed high‐resolution transmission electron microscopy (HRTEM) to ascertain whether any alteration in the surface structure of pyrophyllite could be detected after reaction with Ni at pH >7. Surface deposits, not present on untreated samples, were found. At low Ni sorption densities, surface precipitation seems to occur preferentially along the edges of the particles. Based on the HRTEM findings, and on results from a previous x‐ray absorption fine structure spectroscopy (XAFS) study, we hypothesize that the formation of a mixed Ni‐Al hydroxide phase on the pyrophyllite surface is responsible for the sorption behavior above pH 7.
Landscape and Seasonal Patterns of Nitrous Oxide Emissions in a Semiarid Region
Authors: Corre M. D. , van Kessel C. , Pennock D. J.
Published: July 2010

As a prerequisite for quantification of annual N2O emissions at a regional scale, this study was conducted to determine the landscape‐scale patterns and seasonal fluctuations of N2O emission and to demonstrate the linking relationships between large‐scale controllers and proximal factors of N2O emission. An area of the Black soil zone of central Saskatchewan, Canada, was stratified into three main textural areas: clay loam, fine sandy loam, and sandy. Within each textural area, representative sites were selected based on land use: unfertilized and fertilized cropland, fallow, pasture, and forest sites. A consistent landscape‐scale pattern of N2O emission was observed; footslope positions had higher N2O fluxes than shoulder positions. The role of topography is attributed to its strong influence on the hydrologic and pedologic processes in the landscape, which, in turn, regulate the soil factors controlling N2O emission at the microscale level. The seasonal fluctuation of N2O emission was influenced by precipitation. Pulses of activity were observed during summer, after rainfall events following N fertilizer application, and during spring thaw. At the regional scale, the sandy area had lower N2O emissions than the fine‐textured areas. The general order of N2O evolved among the land uses was forest < pasture < fallow ≈ unfertilized < fertilized cropland. Our results showed the importance of developing spatially based, predictive relationships between N2O emission and its controlling factors. Linking these relationships with large‐scale integrative variables, such as soil texture and land use, provides a means for extrapolating N2O fluxes from landscape to regional scale.
Denitrification in Soil Profiles beneath Grassland and Cultivated Soils
Authors: Sotomayor David , Rice Charles W.
Published: July 2010

The denitrification potential of subsoils and aquifers must be characterized to assess the ultimate fate of soil N. This experiment was conducted to study changes in the subsurface distribution and activity of denitrifying bacteria as a result of cultivation. We examined soil profiles for their capacity (N addition) and potential (N + C addition) to denitrify as well as for denitrifying bacterial numbers in a Reading silt loam (fine, mixed, mesic Typic Argiudoll) soil under grassland and cultivation. Denitrifying enzyme activity was undetectable throughout the subsurface of soil profiles at both sites. Overall, the cultivated site had significantly higher NO−3 concentrations, denitrifier populations, and denitrification potential. Denitrifying bacteria were stratified in the vadose zone at the prairie site, with lowest numbers and lowest denitrification potential occurring at the interface of the water table. Although C addition enhanced denitrification at this site, the profile was not nearly as limited by C as that of the cultivated site. The results demonstrated that increased N inputs and cultivation during approximately 50 yr changed the denitrifying population and denitrification potential in the vadose and saturated zones of soils.
Nitrification and Coupled Nitrification‐Denitrification Associated with a Soil‐Manure Interface
Authors: Nielsen Tommy Harder , Nielsen Lars Peter , Revsbech Niels Peter
Published: July 2010

Nitrification and denitrification in soil often occur in close proximity so that a substantial part of the NO−3 formed by nitrification afterwards diffuses to the anaerobic denitrification zone where it is reduced to N2. The stable N isotope based isotope pairing method was used to study nitrification and coupled nitrification‐denitrification associated with a manure hot‐spot in soil contained within a diffusion chamber. During the 3‐wk incubation period, a very active nitrification zone developed within 0.7 to 1 mm from the aerobic‐anaerobic soil‐manure interface, and within this thin zone, all NH+4 liberated from the manure was oxidized. The short distance between the nitrification zone and the anaerobic manure facilitated coupled nitrification‐denitrification, which turned out to be the main sink for liberated inorganic N with maximum rates of 140 nmol N‐N2 cm−2 h−1, thereby removing 90% of the inorganic N liberated during the incubation period. The applicability of the isotopic pairing method was verified by using variable concentrations of 15NO−3 and by selectively inhibiting nitrification with acetylene. The change in 14NO−3 profile following addition of acetylene was simulated by a diffusion reaction model to obtain estimates of the underestimation of denitrification by use of the commonly used acetylene blockage technique. Incubation periods with acetylene of 1, 3, 6, and 12 h reduced the coupled nitrification‐denitrification rate to 46, 25, 16, and 10%, respectively, of the original rate, and use of the acetylene technique for determining denitrification in manure‐amended soils thus cannot be recommended.
Mycorrhizae, Phosphorus Absorption, and Yield of Maize in Response to Tillage
Authors: McGonigle Terence P. , Miller Murray H.
Published: July 2010

Maize (Zea mays L.) in the early season in no‐till (NT), compared with conventional tillage (CT), has reduced dry matter due to cooler temperatures near the seed, in spite of increased plant P absorption caused by more effective mycorrhizae in the less‐disturbed soil. We grew maize under NT and CT in a soil with 1.6 mg kg−1 NaHCO3‐extractable P, adding 0, 25, 50, or 100 kg P ha−1. A rotary cultivator (ROTO) soil‐disturbance treatment gave plots more severe disturbance than CT, and a no‐till hand‐plant (NTHP) treatment gave plots with minimal soil disturbance. Early season P uptake and mycorrhizal colonization were stimulated in the NT and NTHP treatments. The reverse was true for shoot dry mass. Early season responses to tillage treatments were the same at each of the fertilizer rates. Yields increased with increasing fertilization. At all rates of P, yields with the CT and ROTO treatments were similar to each other, as were yields with the NT and NTHP treatments. At low soil‐P fertility, NT and CT gave similar yields. However, at and above 50 kg P ha−1, yields in CT exceeded those in NT by 1000 kg ha−1. We expect that under P‐limiting conditions, NT could give increases in yield over CT, or similar yields could be achieved in NT and CT but at lower soil‐P availability in NT, but only if the early season growth depression in NT can be overcome.
Comparison of Models Describing the Vertical Distribution of Wind‐Eroded Sediment
Authors: Sterk G. , Raats P. A. C.
Published: July 2010

For the study of field wind erosion, detailed observations of windblown sediment transport in the field are needed. The objective of this study was to determine the best method to quantify the mass of wind‐blown material moving past a fixed point during four storms. Twenty‐one Modified Wilson and Cooke (MWAC) sediment catchers were installed in a pearl millet [Pennisetum glaucum (L.) R. Br.] field in the Sahelian zone of Niger, on a sandy, siliceous, isohyperthermic Psammentic Paleustalf. Each catcher trapped materials at seven heights between 0.05 and 1.00 m. The vertical profiles of measured horizontal mass fluxes were described by two different models, a three‐parameter power function and a five‐parameter combined model, which is a combination of an exponential function and a power function. For all four storms, both models described accurately the mass fluxes between 0.05 and 0.26 m, but fitted mass fluxes at 0.50, 0.75, and 1.00 m deviated from measured fluxes. Deviations were 21.1, 45.2, and 60.6% for the power function and 12.4, 18.5, and 38.0% for the combined model. Mass transport rates were calculated by integrating the mass flux profiles across height. The differences in calculated mass transport rates were small, but because of the better fit, the combined model was preferred. Correcting for the trapping efficiency of the MWAC catchers (0.49) and multiplying by the storm duration resulted in total mass transport values, which are equal to the mass of soil passing a strip of 1‐m width perpendicular to the mean wind direction. The average mass transport values were 102.7, 15.5, 31.8, and 149.8 kg m−1, respectively, for the four storms.
Exchangeable Hydrogen Explains the pH of Spodosol Oa Horizons
Authors: Ross Donald S. , Bartlett Richmond J. , David Mark B. , Lawrence Gregory B.
Published: July 2010

The chemistry of extremely acid Oa horizons does not conform to traditional pH, Al, and base saturation relationships. Results from two separate studies of northeastern U.S. forested soils were used to investigate relationships between pH in water or dilute salt solutions and other soil characteristics. In Oa horizons with pH below 4, soil pH in dilute CaCl2 solution was correlated with exchangeable H+ measured either by titration (r = −0.88, P = 0.0001, n = 142) or by electrode (r = −0.89, P = 0.0001, n = 45). Exchangeable H+ expressed as a percentage of the cation‐exchange capacity (CEC) was linear with pH and showed similar slopes for data from both studies. For all samples, pHw = 4.21 − 1.80 × H+/CEC (R2 = 0.69, n = 194). The reciprocal of the H+/CEC ratio is base saturation with Al added to the bases. Because of the low pH, exchangeable Al does not appear to behave as an acid. Exchangeable H+ remains an operationally defined quantity because of the difficulty in separating exchange and hydrolysis reactions. In a variety of neutral‐salt extractants, concentrations of H+ were correlated with 0.1 M BaCl2‐exchangeable H+ (r > 0.91, P = 0.0001, n = 26) regardless of the strength of the extract. Nine successive extractions with 0.33 mM CaCl2 removed more H+ than was removed by single batch extractions with either 1 M KCl or 0.1 M BaCl2 (average H+ of 70, 43, and 49 mmol kg−1, respectively for 26 samples). The data showed little difference in the chemical behavior of Oa horizons from a variety of geographical sites and vegetation types.
Cation and Nitrogen Contents of Organic Matter Determine Its Soil Liming Potential
Authors: Pocknee Stuart , Sumner Malcolm E.
Published: July 2010

The effect of organic matter addition to soil in relation to soil pH changes is not well understood. Organic matter additions to soil have been reported to both increase and decrease soil pH. An investigation of the effects and mechanisms involved was undertaken. Plant materials of different types were incubated with an acid Cecil topsoil (clayey, kaolinitic, thermic Typic Kanhapludult) (pHKCl 4.01) in a glasshouse experiment at rates equivalent to 50 and 200 Mg ha−1 (dry mass). Soil pH was measured with time and increases of up to 4 pH units were observed followed by attainment of a steady state at or above the original soil pH, depending on the type of organic matter added. The final pH was well correlated with the amount of basic cations present in the organic matter (r2 = 0.92). The initial short‐term fluctuations in pH were due to mineralization and nitrification of the N added in the material. A separate factorial study using simple organic sources of Ca (calcium gluconate) and N (β‐alanine) supported this contention. The short‐term organic liming effect stemming from N transformations is strongly dependent on the kinetics of the organic matter decomposition, which are, in turn, biologically mediated. Decomposition of Ca‐containing organic molecules was shown to have an effect on pH analogous to that of mineral lime (CaCO3).
Suitability of Sunn Hemp as an Alternative Late‐Summer Legume Cover Crop
Authors: Mansoer Zulfadli , Reeves D. Wayne , Wood C. Wesley
Published: July 2010

The tropical legume ‘Tropic Sun’ sunn hemp (Crotalaria juncea L.) may have potential as an alternative legume cover crop or as forage for cattle in southern temperate regions. This study determined dry‐matter production, chemical composition, and N release from sunn hemp residue under conventional and no‐tillage systems as might be used in corn (Zea mays L.) production. Sunn hemp was sown in mid‐August and mowed in early December on a Norfolk sandy loam (fine‐loamy, siliceous, thermic Typic Kandiudult) and a Lucedale fine sandy loam (fine‐loamy, siliceous, thermic Rhodic Paleudult) in Alabama (1991–1992). Mesh bags were used to determine residue decomposition and N release. Average dry‐matter production was 5.9 Mg ha−1 9 to 12 wk after planting. At mowing, residue N content averaged 126 kg ha−1. Residue overwintered on the soil surface until early April. During the first 4 wk following mowing, N release from residue was 50%. In April, N remaining in overwintered residue was only 38% of that after mowing in December (45 kg N ha−1). Nitrogen release from residue during the subsequent corn growing season was 13% in no‐tillage and 43% in conventional tillage. Sunn hemp produced sufficient dry matter to cover and protect the soil from erosion and provided sufficient N to benefit a succeeding summer crop. In addition, forage quality of leaves was suitable to provide late summer and fall grazing. Sunn hemp has potential to be managed as an alternative to winter legume cover crops in warm temperate regions.
Herbicide Losses in Runoff from Conservation‐Tilled Watersheds in a Corn‐Soybean Rotation
Authors: Shipitalo M. J. , Edwards W. M. , Owens L. B.
Published: July 2010

Soil and nutrient losses are tolerable when corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are grown in rotation on steep slopes in northern Appalachia if conservation tillage is used and a rye (Secale cereale L.) cover crop follows soybean harvest. Herbicide losses and concentrations in runoff resulting from this rotation, however, may be unacceptable. Therefore, runoff from two chiseled and two no‐till watersheds was monitored for 4 yr to determine the effect of this cropping sequence on losses of four commonly used herbicides: alachlor [2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl) acetanilide], atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine], linuron [3‐(3,4‐dichlorophenyl)‐1‐methoxy‐1‐methylurea], and metribuzin [4‐amino‐6‐(1,1‐dimethylethyl)‐3‐(methylthio)‐1,2,4‐triazin‐5(4H)‐one]. The spectrum of weeds controlled by linuron is similar to that of atrazine and their losses were compared to determine if substitution of linuron for atrazine would decrease herbicide loss in runoff. As a percentage of applied chemical, average losses were small with atrazine (0.31%) > linuron (0.20%) > metribuzin (0.14%) > alachlor (0.05%). At times, however, herbicide concentrations may be a concern. Atrazine concentrations consistently exceeded the lifetime Health Advisory Level‐Maximum Contaminant Level (HAL‐MCL) of 3 µg L−1 in the first few runoff events after application. In addition, atrazine was detectable in runoff during soybean years, at times above the HAL‐MCL. Average linuron loss was significantly less (P ≤ 0.05) than that of atrazine and linuron was rarely detected in runoff following corn harvest or during soybean years. The 2 µg L−1 MCL for alachlor was only exceeded during the first few events after application, whereas metribuzin concentrations never exceeded the HAL of 200 µg L−1.
Predicting Rainfall Erosivity in Honduras
Authors: Mikhailova E. A. , Bryant R. B. , Schwager S. J. , Smith S. D.
Published: July 2010

Iso‐erodent maps can be used in soil conservation planning to identify regions with high rainfall erosive potential. This study was conducted to determine the significance of elevation in predicting the rainfall erosivity index (R) in addition to the average annual precipitation and to develop an iso‐erodent map for Honduras. With previously calculated R‐factor values for eight climatic stations in Honduras, a regression relationship was established for estimating the rainfall erosivity index as a function of average annual precipitation and elevation with R2 of 0.972. This regression model was used to estimate the rainfall erosivity index for each of the 344 Honduran climatic stations without calculated rainfall erosivity indices. Due to the limited number of data points and their geographic clustering, the best estimates of mean rainfall erosivity indices were for stations with average annual precipitation in the range from 831 to 1313 mm and elevation between 360 and 1080 m. A provisional iso‐erodent map of Honduras at a scale 1:1 000 000 was compiled in Arc/Info format, using a basemap obtained from the digital chart of the world. Iso‐lines for the 95% prediction intervals for new rainfall erosivity indices are displayed on the map to show the accuracy of the new estimates. Elevation was found to be highly significant in predicting the rainfall erosivity in addition to the average annual precipitation. Data from Costa Rica, Sri Lanka, and the southeastern USA supported this finding.
Characterizing the Structure of Undisturbed Soils
Authors: McCoy E. L. , Cardina J.
Published: July 2010

Soil structure is often viewed as the spatial heterogeneity of component soil properties. To explore a method for determining this heterogeneity, we examined the use of spectral analysis to discern the periodic spatial variance in depth series measurements of penetration resistance and oxygen diffusion rate (ODR) in undisturbed soil cores. Mean power spectra of penetration resistance residuals for 105 moldboard‐plowed (MP) and 109 no‐tillage (NT) cores had peaks at a frequency of 0.031 cycles mm−1. The NT treatment, however, averaged 0.71 higher loge power across the frequency range of 0 to 1.0 cycles mm−1. Harmonic analysis related this to increased aggregate strength in the NT treatment. Mean power spectra of detrended ODR data from 96 MP and 95 NT cores had peaks across the frequency range of 0.017 to 0.025 cycles mm−1. The NT treatment again averaged 0.78 higher loge power across the frequency range of 0 to 0.125 cycles mm−1. Geometric mean aggregate diameters showed tillage‐induced differences of 6.8 mm for the MP and 10.8 mm for the NT treatments. The mean frequencies corresponding with maximum power for the individual spectra were not different between tillage treatments or between the independent penetrometer and ODR methods, yielding aggregate diameters of 15.3 mm. The absence of tillage‐induced aggregate diameter differences from analysis of penetration resistance and ODR data, as contrasted with the observed aggregate diameter differences from sieving, suggests that sieving may not precisely reflect the in situ aggregation of soils.
Compositional and Functional Shifts in Microbial Communities Due to Soil Warming
Authors: Zogg Gregory P. , Zak Donald R. , Ringelberg David B. , White David C. , MacDonald Neil W. , Pregitzer Kurt S.
Published: July 2010

Microbial decomposition processes are typically described using first‐order kinetics, and the effect of elevated temperature is modeled as an increase in the rate constant. However, there is experimental data to suggest that temperature increases the pool size of substrate C available for microbial respiration with little effect on first‐order rate constants. We reasoned that changes in soil temperature alter the composition of microbial communities, wherein dominant populations at higher temperatures have the ability to metabolize substrates that are not used by members of the microbial community at lower temperatures. To gain insight into changes in microbial community composition and function following soil warming, we used molecular techniques of phospholipid fatty acid (PLFA) and lipopolysaccharide fatty acid (LPS‐OHFA) analysis and compared the kinetics of microbial respiration for soils incubated from 5 to 25°C. Substrate pools for microbial respiration and the abundance of PLFA and LPS‐OHFA biomarkers for Gram‐positive and Gram‐negative bacteria differed significantly among temperature treatments, providing evidence for a shift in the function and composition of microbial communities related to soil warming. We suggest that shifts in microbial community composition following either large seasonal variation in soil temperature or smaller annual increases associated with global climate change have the potential to alter patterns of soil organic matter decomposition by a mechanism that is not considered by current simulation models.
Morphology, Porosity, and Hydraulic Conductivity of Weathered Granitic Bedrock and Overlying Soils
Authors: Graham R. C. , Anderson M. A. , Sternberg P. D. , Tice K. R. , Schoeneberger P. J.
Published: July 2010

Granitic bedrock, generally weathered several meters deep, is widespread in upland areas of California. Sound management of these areas requires knowledge of the hydraulic properties of both soils and weathered bedrock. The objectives of this research were to determine the saturated hydraulic conductivity (Ksat) of weathered granitic bedrock and overlying soils and to relate the measured Ksat to the regolith morphology and porosity. The study sites in the foothills of the San Jacinto Mountains represent common regolith conditions in granitic terrain of southern California: a coarse‐loamy Entisol <50 cm thick and a fine‐loamy Alfisol ≈ 100 cm thick, both over weathered granitic rock. The underlying bedrock (Cr horizon) at each site has a low clay content (<6%) and is weathered such that chunks of it can be excavated by chopping with a spade and crushed into grains using bare hands. In situ Ksat, measured using constant‐head permeameters, was highest (29 cm h−1) in the Entisol AC horizon, which also had the greatest macrovoid (>0.1 mm diam.) space (24%), a low clay content (6%), and abundant roots to provide pore continuity. A pedogenic horizon also had the lowest Ksat, with the Alfisol Bt horizon averaging 0.9 cm h−1. This horizon had 9% macrovoid space and 21% clay. The Cr horizons had intermediate Ksat values (1.4–3.7 cm h−1). Low clay contents, joint traces, and macrovoids (7–9%) largely unimpeded by illuvial clay help make weathered granitic bedrock an effective conductor of water under saturated conditions. On a landscape scale, water should percolate readily into regolith on Entisol sites, whereas runoff is more likely on Alfisol sites due to the low Ksat of the Bt horizon.
Derivation of Soil Properties Using a Soil Land Inference Model (SoLIM)
Authors: Zhu A‐Xing , Band Lawrence , Vertessy Robert , Dutton Barry
Published: July 2010

SoLIM (Soil Land Inference Model) is a fuzzy inference scheme for estimating and representing the spatial distribution of soil types in a landscape. This study developed the inference method a step further to derive continuous soil property maps through two case studies. The first case illustrates the derivation of soil A horizon depth in a mountainous area in western Montana. It was found that the inferred depths are a closer fit to observed depths than those derived from the conventional soil map at both spatial and attribute levels. The second case shows the derivation of soil transmissivity values across a small catchment with a gentle environmental variation in Tumut, NSW, Australia. This case shows that the derived soil transmissivity map is comparable to the results from systematic field survey over a small area. SoLIM works well in an area where there is a good understanding of the relationships between soils and their formative environment and where the soil formative environment can be characterised using current geographical information system techniques. However, we experienced difficulty with the methodology when it was applied in an area where the environmental gradient is gentle and the soil formative environment cannot be very well described using the primitive environmental indices currently employed in SoLIM.
Chemical and Mineralogical Conversion of Andisols following Invasion by Bracken Fern
Authors: Johnson‐Maynard J. L. , McDaniel P. A. , Falen A. L. , Ferguson D. E.
Published: July 2010

Andisols support ≈200 000 ha of mid‐elevation grand fir (Abies grandis [Dougl. ex D.Don] Lindl.) forests in the Pacific Northwest region that are characterized by little or no natural conifer regeneration following removal of the forest canopy. Previous work suggests that the properties of these Andisols have been altered as a result of the establishment of successional communities dominated by bracken fern (Pteridium aquilinum [L.] Kuhn) in deforested areas. In this study, we compared soil properties in a 30‐yr‐old bracken fern site (clear‐cut in 1965), a natural bracken fern site that is estimated to be centuries old, and an adjacent undisturbed forest in the Clearwater National Forest of northern Idaho. Results indicate that changes in chemical properties have accompanied establishment of successional communities. Mean weighted pH within the ash cap of the 30‐yr‐old bracken fern site (4.6) is significantly lower than that of the undisturbed forest (5.2). Mean values for Al saturation range from 27% in the undisturbed forest to 52% in the 30‐yr‐old bracken fern site; organic C is also lower in the undisturbed forest (37 g/kg) than in the 30‐yr‐old bracken fern site (54 g/kg). The dominant secondary mineralogical component of soils of the undisturbed forest is inorganic, short‐range‐order Al‐Fe minerals, while metal‐humus complexes are dominant in the bracken‐fern‐influenced soils. Data indicate that bracken fern successional communities are responsible for a shift from allophanic to nonallophanic properties in these soils, probably due to increased levels of soil organic C associated with bracken fern and a subsequent increase in formation of Al‐humus complexes. Furthermore, such a mineralogical shift may contribute to the observed problems with conifer regeneration.
Polymer Effects on Water Infiltration and Soil Aggregation
Authors: Ben‐Hur M. , Keren R.
Published: July 2010

The effectiveness of synthetic polymers as soil conditioners was found to depend on polymer properties. We hypothesized that the polymer penetration and movement into the aggregate are important factors in reduction of surface sealing. The effect of nonionic (P‐101), cationic (CP‐14), and anionic [Complete Green (CG)] commercial polymers on infiltration rate (IR) and aggregate formation was studied in a sandy loam (Typic Rhodoxeralf). Amounts of 25, 50, and 75 kg ha−1 of each polymer were spread across the soil surface. After air drying, the surface was subjected to 68 mm of distilled water with impact energy of 18.1 J mm−1 m−2 using a rainfall simulator. Soil particle association was studied in 10% (w/v) soil suspension with polymer concentration ranging from 0 to 50 g m−3. Viscosity values 3.3 109, and 165 mPa s were determined in 5 g L−1 of P‐101, CP‐14, and CG solutions at shear rate of 27 s−1, respectively. The final IR values were 63 to 30 mm h−1 at P‐101, 18 to 24 mm h−1 at CP‐14, and 18 to 30 mm h−1 at CG, compared with 8 mm h−1 in untreated soil. The critical time values in suspensions with different concentrations of polymer were 4.3 to 2.7 min for P‐101, 1.0 to 3.4 min for CP‐14, and 1.0 min for CG. The critical time indicates the size of the aggregate formed in a suspension; the lower the critical time, the larger the aggregates. It was suggested that because the particle surfaces are exposed to polymer molecules in suspension, the large molecule of CG could tie more suspended particles to form aggregates. The greater effectiveness of P‐101 in preventing sealing was probably due to its ability to penetrate into aggregates, because of its small molecular size and low viscosity in solution.
Stability and Transportability of Water‐Dispersible Soil Colloids
Authors: Seta A. K. , Karathanasis A. D.
Published: July 2010

Colloid migration in subsurface environments has attracted special attention lately due to its suspected role in facilitating transport of contaminants to groundwater. This study was conducted to evaluate the stability and potential transport of water‐dispersible colloids (WDC) through intact soil columns, and the properties of colloids and soil columns facilitating or retarding colloid stability and transportability. Water‐dispersible colloids were fractionated from six representative soil samples with diverse mineralogy and physicochemical characteristics. Their stability was evaluated from settling‐rate experiments at different pH levels. The results demonstrated that colloid stability was pH dependent. Colloid transportability was assessed by introducing colloid suspensions at a constant flux into intact soil columns representing upper Bt horizons of a Maury (fine, mixed, mesic Typic Paleudalf) and a Loradale (fine‐silty, mixed, mesic Typic Argiudoll) soil and evaluating characteristics of the suspensions that were eluted. After five pore volumes of leaching, colloid recovery in the eluents ranged from 35 to 90% depending on type of colloid, initial concentration in the influent, and soil column. The mineralogical composition of the colloid, which was correlated with particle size, appeared to have a profound effect on colloid transportability, following the sequence smectitic > mixed > kaolinitic. Total exchangeable bases (TEB) and pH of WDC also significantly influenced colloid transport. Increasing colloid concentration in the influent slightly increased colloid transportability. Soil columns with better macroporosity and less surface charge (Maury) transported more colloids than soil columns with less macroporosity and higher surface charge (Loradale).
Atrazine Adsorption by Soil Colloids and Co‐Transport through Subsurface Environments
Authors: Seta A. K. , Karathanasis A. D.
Published: July 2010

This study evaluated the potential of water‐dispersible soil colloids with diverse physicochemical and mineralogical characteristics to adsorb and mediate the transport of atrazine through macropores of intact soil columns. The soil columns were taken from the upper solum of an Alfisol (Maury) and a Mollisol (Loradale) in the Bluegrass region of Kentucky. Six different colloid suspensions mixed with atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] were introduced at a constant flux into the undisturbed soil columns. The eluents were collected and analyzed periodically for colloid and herbicide concentrations. Colloid recovery in the eluents ranged from 45 to 90%. The presence of colloids enhanced the transport of atrazine by 2 to 18%, depending on colloid type and mobility. Colloids with higher pH, total exchangeable bases (TEB), cation‐exchange capacity (CEC), organic carbon (OC), surface area (SA), and electrophoretic mobility (EM), showed greater mobility, greater affinity for atrazine, and greater potential to co‐transport atrazine. In contrast, increased levels of kaolinite, Fe, and Al inhibited atrazine adsorption and transport. Soil columns with higher hydraulic conductivity, well‐developed macropore system, and lower surface reactivity (Maury) also transported more atrazine. In spite of the increased transportability of atrazine by the presence of soil colloids, the colloid‐bound herbicide fraction contributed ≤1% to the observed increase. This suggests that matrix‐surface‐site exclusion and blocking mechanisms induced by the presence of colloids are more important than colloid sorption in promoting atrazine mobility in subsurface soil environments.
Arsenic Availability in Soil with Time under Saturated and Subsaturated Conditions
Authors: Onken B. M. , Adriano D. C.
Published: July 2010

Loss of As from solution in reduced soils has long been attributed to volatilization of As as arsines. This study was conducted to determine whether loss of As from soil solution could be accounted for by increases in surface‐bound forms of As. Pickney sand (sandy, siliceous, thermic Cumulic Humaquept) was treated with sodium arsenate and sodium arsenite and incubated under saturated and subsaturated conditions for up to 68 d. Sequential extraction of As by NH4Cl, NH4F, NaOH, and H2SO4 was performed to monitor the redistribution of As between different fractions with time. By determining the As concentration present in sequentially extractable forms, it was demonstrated that As became more recalcitrant in soil with time. Arsenic added in water‐soluble form became more tightly bound to the soil as evidenced by the necessity of stronger extractants to remove added As. The conversion (curing) of As to more insoluble forms occurred in saturated soils where the pe/pH status was in the arsenite stability field and in subsaturated soils where the pe/pH status was in the arsenate stability field. The rate at which As was converted to more insoluble (and possibly less bioavailable) forms was as rapid in saturated soils as in unsaturated soils. Arsenic was conserved during the experiment with no apparent loss of As from the system through 68 d.
Estimation of Map Unit Composition from Transect Data
Authors: Young Fred J. , Hammer R. David , Williams Frederick
Published: July 2010

We are concerned with the documentation of taxonomic variability within soil survey map units, and how that variability is expressed statistically. Twelve randomly selected transects were used to sample soil properties and classify pedons within a fluvial map unit of the Boone County, Missouri, soil survey. Map unit taxonomic variability was high, with 28 taxonomic family classes. Twenty‐five percent of the sampled soils were in the named taxonomic class of the map unit, but most were similar inclusions. Interpretive purity of the sample was 83%. Variances about this sample proportion were calculated using three methods: (i) simple random sampling, (ii) cluster sampling, and (iii) two‐stage random sampling. The simple random sampling formula provided the smallest variance, compared with the cluster formula (55% larger) or the two‐stage formula (72% larger). However, the interpretation of transect sampling as simple random sampling is questioned. The two‐stage random sampling method seemed most conceptually correct, but is computationally intensive and requires questionable assumptions about the population size. Confidence intervals based on small sample sizes drawn from binomial populations are highly suspect, and perhaps should be referred to as “approximate bounds”. It is important to carefully consider the assumptions and effects of any statistical technique chosen to analyze map unit composition.
Tillage Mulch Depth Effects during Fallow on Wheat Production and Wind Erosion Control Factors
Authors: Schillinger William F. , Papendick Robert I.
Published: July 2010

Blowing dust from summer fallow is a major soil loss and air quality concern in winter wheat (Triticum aestivum L.) production areas of the inland Pacific Northwest (PNW). The objective of our 3‐yr on‐farm study in a 286‐mm precipitation zone in eastern Washington was to determine the effects of tillage mulch depth during fallow on surface soil roughness, residue retention, seed‐zone water storage, wheat establishment, and grain yield. Soil is a Ritzville silt loam (coarse‐silty, mixed, mesic Calcidic Haploxeroll). Mulch depth combinations were created by primary spring tillage with noninversion implements at 100‐ or 160‐mm depths, and with subsequent rodweedings at 50‐ or 100‐mm depths. Tillage mulch depth during fallow did not affect seedling emergence after two wet fallow cycles, but wheat spike density was consistently greatest in deep‐tilled plots. In a dry fallow cycle, when dry soil extended beneath the rodweeder or secondary tillage layer, deep tillage increased stand establishment from 30 to 62 seedlings m‐2, grain yield from 4.4 to 5.3 Mg ha‐1, and residue production from 5.7 to 8.4 Mg ha‐1 compared with shallow tillage. Surface soil clods >50‐mm diameter, desirable for wind erosion control, increased with tillage mulch depth from 14 to 21 Mg ha‐1 in 1994, and from 22 to 37 Mg ha‐1 in 1995. A drawback to deep tillage mulches was the need to reduce tractor speed during planting. Surface residue retention was not affected by tillage mulch depth. Results show that surface clod structure and roughness during fallow can be maintained to protect the soil from erosion, mostly benefiting wheat production potential.
Estimating the Least Limiting Water Range of Soils from Properties and Management
Authors: da Silva Alvaro Pires , Kay B. D.
Published: July 2010

The least limiting water range, LLWR, is the range of soil water content within which plant growth is least limited by water potential, aeration, and mechanical resistance. Little information is available on the influence of soil property or management practice on LLWR. The LLWR calculation is based on the water release curve (WRC) and the soil resistance curve (SRC). This study tested the hypothesis that pedotransfer functions (PTF) that describe the influence of soil properties and tillage on the WRC and the SRC could be used to assess the influence of these factors on the LLWR. Thirty‐two paired sampling sites were located along two parallel transects in a side by side comparison of no‐till and conventional tillage. The transects crossed three soil types: Aquic Hapludalf, Psammentic Hapludalf, and Typic Hapludalf. Clay content (CLAY) varied from 5.8 to 37.4%, organic carbon (OC) varied from 9 to 39 g kg‐1, and the bulk density (Db) varied from 0.96 to 1.71 g cm‐3. Multiple regression analyses showed that WRC was related (R2 = 0.94) with CLAY, OC, and Db whereas the SRc was related with CLAY and OC (R2 = 0.86). Tillage had no independent effect in either of the two functions. Values of LLWR, calculated from the PTF, varied from 0 to 0.3093 cm3 cm‐3. The LLWR was negatively related with CLAY and Db and positively related with OC. The analyses supported the hypothesis illustrating the value of PTF in assessing the sensitivity of LLWR to soil properties.
Quantitative Soil‐Landscape Modeling for Estimating the Areal Extent of Hydromorphic Soils
Authors: Thompson James A. , Bell James C. , Butler Charles A.
Published: July 2010

The spatial distribution of hydromorphic soils across the landscape affects soil survey, broad‐scale wetland identification, and ecological studies. The change from upland to wetland is frequently difficult to delineate because it often occurs along a gradual continuum. We have developed a color index, the Profile Darkness Index (PDI), to assist in making these delineations. The PDI is well correlated with the duration of saturated and reducing conditions in specific Mollisol catenas in humid regions of the north‐central USA. The objective of this research was to use soil‐landscape modeling techniques to relate the variation of PDI to terrain attributes that describe the flow and accumulation of water on hillslopes. Regression models that quantify the relationships between terrain attributes and PDI on a hillslope in west‐central Minnesota indicate that variability in slope gradient, profile curvature, and elevation above local depression explained up to 65% of the variability in PDI. These models may be used to estimate the areal extent of hydromorphic soils using terrain attributes derived from a high‐resolution (10‐m resolution) digital elevation model and to quantify relationships between spatial variability of terrain attributes and of PDI. Knowledge of the terrain attributes that are statistically important according to these models, and their relative effects on PDI (e.g., as slope gradient decreases, PDI increases) may be applied to field‐scale delineations of hydric soils.
Carbon Isotope Ratios of Great Plains Soils and in Wheat‐Fallow Systems
Authors: Follett R. F. , Paul E. A. , Leavitt S. W. , Halvorson A. D. , Lyon D. , Peterson G. A.
Published: July 2010

The purposes of this study were to improve knowledge of regional vegetation patterns of C3 and C4 plants in the North American Great Plains and to use δ13C methodology and long‐term research sites to determine contributions of small‐grain crops to total soil organic carbon (SOC) now present. Archived and recent soil samples were used. Detailed soil sampling was in 1993 at long‐term sites near Akron, CO, and Sidney, NE. After soil sieving, drying, and deliming, SOC and δ13C were determined using an automated C/N analyzer interfaced to an isotope‐ratio mass spectrometer. Yield records from long‐term experimental sites were used to estimate the amount of C3 plant residue C returned to the soil. Results from δ13C analyses of soils from near Waldheim, Saskatchewan, to Big Springs, TX, showed a strong north to south decrease in SOC derived from C3 plants and a corresponding increase from C4 plants. The δ13C analyses gave evidence that C3 plant residue C (possibly from shrubs) is increasing at the Big Springs, TX, and Lawton, OK, sites. Also, δ13C analyses of subsoil and topsoil layers shows evidence of a regional shift to more C3 species, possibly because of a cooler climate during the past few hundreds to thousands of years. Data from long‐term research sites indicate that the efficiency of incorporation of small‐grain crop residue C was about 5.4% during 84 yr at Akron, CO, and about 10.5% during 20 yr at Sidney, NE. The 14C age of the SOC at 0‐ to 10‐cm depth was 193 yr and at 30 to 45 cm was 4000 yr; 14C age of nonhydrolyzable C was 2000 and 7000 yr for these same two respective depths. Natural partitioning of the 13C isotope by the photosynthetic pathways of C3 and C4 plants provides a potentially powerful tool to study SOC dynamics at both regional and local scales.
Runoff and Soil Loss Response to Vegetation Removal in a Semiarid Environment
Authors: Castillo V. M. , Martinez‐Mena M. , Albaladejo J.
Published: July 2010

The removal of vegetation is the main cause of soil degradation in semiarid areas. We hypothesized that the changes in soil properties induced by vegetation removal modified the runoff and soil erosion response in a semiarid area of Spain. To test this, two plots (15 by 5 m) were installed on a 23% slope on a Lithic Haploxeroll. Vegetation was removed by clipping from one of the plots (Plot D) and the changes in surface runoff and soil loss were compared with an undisturbed control plot (Plot N) from 1989 to 1993. Total runoff was significantly greater in Plot D (48.8 mm) than in Plot N (34.9 mm). Runoff ratios between the disturbed and natural plots increased with time from 1.4:1 in 1990 to 2.5:1 in 1993. Vegetation removal increased the soil losses in Plot D (150.2 g m−2) by 127% compared with those in Plot N (66.3 g m−2). The annual soil loss ratio between the disturbed and natural plots increased from 1.6:1 in 1989 to 4.2:1 in 1993. The observed increase in surface runoff and soil loss was attributed to a progressive deterioration of soil physical properties in Plot D. Bulk density increased by 8.4% (from 1.55 to 1.68 Mg m−3) and a reduction of total organic carbon (from 4.0 to 2.6%) and the percentage of stable aggregates (from 81.6 to 56.3%) were observed. There was no evidence of vegetation recovery, suggesting that reduced vegetal cover might lead to irreversible soil degradation in semiarid areas.