bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion Exchange and Interparticle Forces Between Clay Surfaces
Authors: Pashley R. M. , Quirk J. P.
Published: July 2010

The forces between muscovite mica surfaces have been measured in water and in NaCl and CaCl2 solutions. Above a critical electrolyte concentration, strong, short‐range repulsive forces arise which are not predicted by DLVO theory. These forces have been identified as hydration forces and have an oscillatory force superimposed with a periodicity corresponding to the diameter of the water molecule. Hydration forces are significant for the swelling of Ca‐clays. Below the critical hydration concentration exchange favors H+. Protons are so strongly adsorbed that as the surfaces are brought to a distance of separation of 2 to 3.5 nm the hydrated cations are replaced by H+ and the surfaces jump into contact due to attractive van der Waals forces. The absence of the hydration forces in the presence of H+ indicates that the water structure is not perturbed by the siloxane layer alone. The strong affinity of the H+ is attributed to the H+ proton being able to approach closely to the surface by forming H3O+ with water H‐bonded to oxygen atoms on the mica basal plane surface. The sites for adsorption are the Al tetrahedra for which the charge is confined to three surface O atoms. Other cations can only approach to within one H2O molecule of the surface because of their primary hydration shell. By comparison, the H+ associated with the surface of montmorillonite hydrate to the full extent and the crystalline swelling (d001 > 4 nm) is similar to Li‐montmorillonite. This difference must be related to the fact that the surface charge for montmorillonite is less discrete being spread over about 10 surface O atoms.
Residual Effects of Chloride Application in a Corn‐Wheat Rotation
Authors: Schumacher W. K. , Fixen P. E.
Published: July 2010

Significant correlations have been noted between soil Cl, Cl uptake, and yield response in spring wheat (Triticum aestivum L.). Little information exists, however, concerning the residual value of Cl, especially in subhumid areas. Therefore, a study was conducted to determine residual effects of Cl application on soil Cl levels and on associated crop yield in a wheat‐corn (Zea mays L.) rotation. Six Cl rates ranging from 0 to 510 kg ha−1 were applied as KCl (muriate of potash) to a soil (Udic Haploboroll) with an initial soil‐Cl content of 19 kg ha−1 in the upper 60 cm. A corn‐spring wheat rotation was practiced between two adjacent sites. Soil Cl levels were measured after the first three seasons at five depth increments to a final depth of 120 cm. Maximum Cl concentrations following the first growing season occurred at approximately 50 cm. By the beginning of the third growing season, most of the Cl had leached below 120 cm. Deep sampling to 3 m after the third growing season indicated maximum Cl accumulation between 1 and 2 m. A positive response of spring wheat to added Cl was observed for the first two growing seasons. Factors contributing to the removal of Cl from the upper 120 cm include above‐average precipitation and large precipitation events. Chloride soil testing is recommended prior to the establishment of a Cl‐responsive crop in regions where responses have been verified.
Soil Development on Stabilized Dunes in Golden Gate Park, San Francisco
Authors: Amundson Ronald G. , Tremback Brian
Published: July 2010

This paper reports the changes in soil properties that have occurred since vegetation was established on unstabilized dunes approximately a century ago in Golden Gate Park, San Francisco, CA. The static and dynamic soil properties under artificially established eucalyptus (Eucalyptus globulus Labill.), Monterey pine (Pinus radiata D. Don), cypress (Cupressus macrocarpa Hartw. ex. Gord.), as well as native live oak (Quercus agrifolia Née), were compared with those of an unstabilized dune. The O and A horizon development occurred under all the vegetated sites with differences in the horizon thickness occurring in response to vegetation type. The organic C in the vegetated sites (40 000 to 80 000 kg C ha−1) was much greater than in the dune (5000 kg C ha−1). The vegetated soils all exhibited severe water repellency in the surface horizons while the dune exhibited none. The oxalate‐extractable Fe in the A horizon of the vegetated soils (1.3–2.3 g kg−1) was greater than that in the dune (≈0.9 g kg−1) suggesting the formation of organically bound Fe and/or poorly crystalline Fe minerals. Dithionite‐citrate‐bicarbonate extracts suggest the formation of more crystalline forms of Fe oxides in the vegetated sites. Soil temperatures were lower and less variable in the vegetated sites (isomesic regime) than the dune site (mesic or thermic regime), apparently slowing biological activity and reducing the soil CO2 contents relative to the dune. Total soil respiration in the vegetated soils (350–400 mg CO2 m−2 h−1) was slightly greater than in the dune (300 mg CO2 m−2 h−1), which lacked any appreciable surface litter undergoing decomposition.
Cotton Root Growth and Soil Water Extraction
Authors: Bland William L. , Dugas William A.
Published: July 2010

The inherent productivity of many fine‐textured soils depends on timely extraction of water stored deep in the profile. Growth of crop roots and their ability to extract water are of central importance to efficient utilization of these soil resources. We observed the rate at which the soil volume was explored and water was extracted by cotton (Gossypium hirsutum L. ‘GP3774’) roots in a fine‐textured soil in a subhumid environment. Measurements of root growth and water extraction were made for 2 yr in a 2.3 m deep weighing lysimeter, 3.0 m2 in area and containing an intact core of a Frio taxadjunct silty clay loam (fine, montmorillonitic, thermic Cumulic Haplustoll). Water extraction was measured with neutron probes at 10 or 11 soil depths in the lysimeter at approximately 5‐d intervals. Root length density [Lv, cm root (cm3 soil)−1 = cm−2] was estimated at 7‐d intervals by counting roots visible against clear observation tubes installed horizontally in the lysimeter every 0.2 m between 0.5 and 2.1 m. Depth of rooting increased up to 35 mm d−1 for part of the season. Maximum Lv at 0.5 m was 1.5 and 0.8 cm−2 in 1984 and 1985, respectively; at 2.1 m comparable values were 0.24 and 0.04 cm−2. When the lysimeter surface area was divided into six 0.5‐m2 regions of soil, the coefficient of variation in Lv among the regions reached 100% both early and late in the season and both at 0.5 and 2.1 m. Crop rows did not affect the spatial distribution of Lv at depths measured. Growth of the root system required about 90 kg ha−1 d−1 for part of the season. Maximal water uptake rate per length of root was approximately 5 mm3 water (mm root)−1 d−1 and occurred at 1.7 to 1.9 m. Redistribution of dry matter invested in roots near the soil surface to deeper in the profile would probably increase total water extraction by the crop.
Submicroscopy of Clay Microaggregates in an Oxisol from Pernambuco, Brazil
Authors: Santos M. C. D. , Ribeiro M. R. , Mermut A. R.
Published: July 2010

Ultrathin sections were made from dehydrated, unoriented but undisturbed soil microaggregates (pseudosands, about 10–100 µm in size) of an Oxisol occurring in the semiarid region of Pernambuco State, Brazil. Objectives were to determine the nature and arrangements of individual particles that comprise the microaggregates. The dominant clay mineral in the microaggregate is poorly crystalline (irregular, pseudohexagonal in shape), densely packed, randomly oriented kaolinite with an average diameter of 0.2 µm. Poorly crystalline Fe oxyhydroxides, probably ferrihydrite, exist as individual aggregates filling the space between the kaolinite particles. Halloysite and Fe‐Ti‐bearing minerals also occur as accessory minerals. An attempt was made to localize organic matter by ultracytochemical reagents. Cell walls, humified hyphae, and other decomposed organic materials, which were easily identified in large pore spaces, appear to play an important role binding the clay particles in microaggregates. Concentrations of organic matter in the magnetic fraction of clays suggests that part of the humified organic matter may be locked up in organo‐Fe complexes. Ultrathin section analyses suggest that the combination of random orientation of clay particles, organic matter, and aggregates of Fe‐bearing minerals, account for the isotropic nature of the aggregates.
Nitrogen Management and Nitrification Inhibitor Effects on Nitrogen‐15 Urea: I. Yield and Fertilizer Use Efficiency
Authors: Walters D. T. , Malzer G. L.
Published: July 2010

Nitrification inhibitors (NI) are sometimes recommended for use with ammoniacal fertilizers in corn (Zea mays L.) production to improve fertilizer N use efficiency (FUE). The objectives of this experiment were to evaluate the effects of the NI nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine] application on yield and FUE of irrigated corn, and to monitor the fate of a single application of 15N‐enriched urea during a multiyear period in both soil and plant. Treatments included a factorial combination of two N rates (90 or 180 kg urea‐N ha−1 yr−1) applied during a 3‐yr period, with or without a NI and with or without incorporation, plus a zero‐N control. Twenty‐seven nonweighing lysimeters were used to quantify leaching load. Treatment effects on yield and FUE differed each year due to interactions of climate and N‐management variables. Nonincorporated urea + NI reduced grain yield when leaching load was low and increased yield at the 90 kg ha−1 N rate when leaching load was high. Maximum FUE occurred at the 90 kg ha−1 N rate when leaching load was low. The NI increased FUE only at the 90 kg ha−1 N rate when leaching load was high. Incorporation of urea + NI reduced plant recovery of fertilizer‐derived N (FDN) in the year of application, but resulted in increased uptake of residual FDN in subsequent years. Incorporation of NI with moderate N rates coupled with conservative irrigation management should reduce the risk of yield loss and minimize NO3 movement to groundwater.
Pedogenic Iron Oxide Trends in a Marine Terrace Chronosequence
Authors: Aniku Jacob R. F. , Singer Michael J.
Published: July 2010

Depth to maximum concentration and maximum horizon concentration of whole‐soil dithionite‐extractable Fe (Fed) and Al (Ald) increased from the youngest (105 000 yr) to oldest (600 000 yr) terrace in a California marine chronosequence. The ratio Fed/Fet (total Fe) for clays extracted from horizons of maximum pedogenic expression also increased with terrace age, while the clay Feo (oxalate extractable)/Fed decreased. These data suggest that there is a progressive transformation of ferrihydrite to crystalline Fe oxides with time. Relative concentrations of goethite in the clay samples were estimated from the integrated intensity of the d110 line. The intensity of the goethite d110 line increased with terrace age. Degree of Al substitution in goethite was calculated from d111 and d110 peak positions. Aluminum substitution in the geothites increased with terrace age. The relative concentrations increased from the youngest to next‐to‐oldest terrace, then decreased, but the degree of crystallinity increased from youngest to oldest terrace. Goethite was the dominant pedogenic Fe oxide in these four soils. Mean annual temperature of 14 °C, moderate precipitation (716 mm yr−1), and frequent fog appear to favor the transformation of ferrihydrite to goethite.
Soil‐Atmosphere Access Chamber and Analytical Assembly to Monitor Soil Aeration
Authors: Mukhtar S. , Baker J. L. , Kanwar R. S.
Published: July 2010

A reliable method for soil‐aeration monitoring is needed. This study was conducted to develop and test a sampling and analysis technique to be used in rapid and nondisruptive monitoring of soil atmospheres. A specially constructed soil‐atmosphere access chamber and a dual‐action syringe sampling assembly were used to obtain atmosphere samples at various depths within the soil profile in laboratory columns and field plots. The O2 contents of these samples were measured by using a portable O2 meter, a probe, and a custom‐made sample analysis reservoir. For comparison, an existing method was used to obtain simultaneous O2‐concentration measurements. Laboratory testing proved the new sampling technique to be fast and free of outside contamination. Use of the dual‐action syringe sampling assembly helped obtain representative samples at a given depth both in the field and in the laboratory. Identical O2 concentrations measured using the new technique and the previously available method suggested that this new soil‐atmosphere sampling and analysis technique is reliable. Very small standard deviations among repeated measurements of O2 concentrations at various sampling depths in both laboratory columns and field plots suggest small variations in the soil atmosphere samples obtained by using this access chamber and the analytical assembly.
Conifer Seedling Growth Response to Soil Type and Selected Nitrogen Availability Indices
Authors: Kraske Charles R. , Fernandez Ivan J.
Published: July 2010

Although N is typically a growth‐limiting factor in northeastern forest soils, few studies have demonstrated the best analytical approach for determining available N in this heavily forested region. To address this information need, seedlings of balsam fir [Abies balsamea (L.) Miller], red spruce (Picea rubens Sarg.), and white pine (Pinus strobus L.) were grown for 26 wk in the greenhouse using soil materials representative of commercial forest sites in Maine. Soils included two O horizons and two B horizons from Spodosols derived in till, and an Ap and B horizon from an Inceptisol derived in marine sediments. Six different indices of available N were evaluated for each horizon, and results were compared with seedling‐growth parameters. Three available‐N indices were chemical and three were biological. Seedlings grew markedly better in O horizons than in mineral soils. Of the species examined, white pine had the greatest dry‐weight yields, and was the only species to exhibit visible evidence of root mycorrhizal infection. Although N‐availability indices were correlated with seedling‐growth parameters, the 1‐ and 2‐wk anaerobic incubations generally exhibited the highest correlation coefficients. Of the chemical indices, the simple KCl extraction appeared best correlated with seedling growth. Of the seedling characteristics examined, foliar N concentration was not highly correlated with soil N availability due to dilution effects. In contrast, foliar N uptake was highly correlated with N availability.
Estimating Forest Soil Quality from Terrain Measurements of Apparent Electrical Conductivity
Authors: McBride R. A. , Shrive S. C. , Gordon A. M.
Published: July 2010

A portable, noncontacting electromagnetic induction meter was employed to measure the apparent electrical conductivity (ECa) of nonsaline, medium‐ and coarse‐textured forest soils on Manitoulin Island, Ontario. In simple linear regressions, bulk soil ECa was strongly correlated with ECe (saturated‐extract electrical conductivity), as well as exchangeable Ca, exchangeable Mg, and cation exchange capacity. Within the limited study area, these soil characteristics were thought to be major determinants of forest soil quality for red oak (Quercus rubra L.) production. Multiple stepwise regression showed that variations in exchangeable Ca and total Kjeldahl N concentrations accounted for a large proportion of the variation in ECa meter response (R2 = 0.871). The potential of this geophysical terrain measurement method as an integrator of edaphic properties important to forest site productivity is discussed.
Solar‐Radiation Transmittance of Flail‐Chopped Corn Residue Layers
Authors: Tanner C. B. , Shen Y.
Published: July 2010

The transmittance of solar (global) radiation through crop residues is required to model the influence of residue on the energy balance and temperature of the underlying soil in conservation tillage systems, but we could find no measurements of the transmittance of residue layers. The objective of this study was to devise ways to measure the transmittance of flail‐chopped corn (Zea mays L.) residue layers, to measure the reflectance and transmittance of the residue elements, to measure the transmittance of residue layers of different areal densities, and to see if global radiation models developed for crop canopies would be suited to predicting transmittance of residue layers. The solar reflectance of dry flail‐chopped corn stalk pieces was about 0.25 in the 400‐ to 700‐nm wave band and about 0.6 in the 700‐ to 2600‐nm band. The transmittance of residue pieces in these two bands was 0.005 and 0.02, respectively. The transmittance of layers of flail‐chopped residue was almost independent of the solar zenith angle because the bulk of the residue was comprised of stalk wall fragments that were essentially flat strips lying parallel to the surface with randomly oriented axes. The extinction coefficient of the residue for global radiation was about 1.70. This is 1.7‐fold greater than expected for randomly distributed flat, black elements. The extinction coefficient for solar radiation was not significantly different from that of thermal radiation (1.6), despite a large difference in element reflectance. We believe the large extinction coefficients resulted because residue elements were distributed uniformly rather than randomly. The similarity of extinction coefficients of solar and thermal radiation indicates forward scattering of solar radiation is negligible, probably because of the opacity and close packing of residue elements, which reduces interelement reflections. For crop radiation models to be applied to residue, they must be revised to account for both nonrandom element distribution and the close packing of residue elements on each other and on the soil.
Binary and Ternary Exchange Behavior of Potassium and Ammonium on Kentucky Subsoils
Authors: Lumbanraja J. , Evangelou V. P.
Published: July 2010

Potassium‐Ca and NH4‐Ca exchange reactions in soils are often investigated in laboratory‐type studies. In these studies, it is assumed that the results from the binary exchange systems can be extrapolated to ternary (three ion) exchange systems using appropriate models. This, however, is rarely evaluated. This study deals with K‐Ca exchange in the presence and absence of added NH4 and NH4‐Ca exchange in the presence and absence of added K on the subsoil of three Kentucky soils, Eden clay loam (fine, mixed mesic Typic Hapludalf), Lowell clay loam (fine, mixed, mesic Typic Hapludalf), and Nicholson silt loam (fine‐silty, mixed, mesic Typic Fragiudalf). The experimental approach is based on the quantity/intensity concept in order to make the findings relevant to field conditions. The added NH4 decreased the linear potential buffering capacity for the K (PBCk) more than expected and increased the equilibrium activity ratio of K (ARoK) more than expected. The addition of K stimulated the adsorption of NH4 on high‐affinity sites. Added NH4 induced expansion, rather than collapse, of the vermiculitic interlayer. This suggests that the NH4 was not occluded or trapped, but rather specifically adsorbed in the vermiculitic interlayer. In essence, the added NH4 permits a greater fraction of the total surface charge to be available for exchanging cations due to the interlayer expansion. The soil that demonstrated the greatest potential for specific adsorption of NH4 was the Eden, followed by the Lowell and the Nicholson. The same order exists with respect to intensity of interlayer expansion. The above suggest that the simultaneous addition of K and NH4 in soil systems may influence the fate of NH4, such as, for example, the quantities leached as NH4, volatilized as NH3, and oxidized to NO3.
Characterization of Chemically Fixed Liquid Anhydrous Ammonia in an Illinois Drummer Soil
Authors: He X. T. , Mulvaney R. L. , Stevenson F. J. , Vanden Heuvel R. M.
Published: July 2010

Anhydrous NH3 applied to soil is subject to chemical fixation by organic matter. A laboratory study was conducted to (i) determine the amount of N retained through chemical fixation of NH3 compared with the amount of NH4 fixed by clay, (ii) characterize the organic‐matter‐fixed NH3, and (iii) assess the biological availability of the fixed NH3. Nitrogen‐15 labeled liquid anhydrous NH3 was injected into a Drummer silty clay loam soil (2.07 g NH3‐N kg−1 soil), and the fixed 15NH3‐N was characterized by sequential extraction with Na4P2O7, KOH, NaOH, and dimethyl sulfoxide (DMSO). About 16% of the 15NH3‐N injected was fixed by the soil. Of the N fixed, 48% was accounted for by chemical fixation into the soil organic fraction, most of which was removed by sequential extraction, and 52% was accounted for as clay‐fixed NH4. Of the organic‐matter‐fixed 15NH3‐N, 55% was recovered in the fulvic acid (FA) fraction obtained by sequential extraction with Na4P2O7 and KOH; about equal amounts (17%) were recovered in the humic acid (HA) and humin fractions. The remainder (11%) was recovered in the NaOH and DMSO extracts. Most of the fixed 15NH3‐N in the FA fraction was recovered as either low‐molecular‐weight (LMW) fraction or nonhumic substances. The availability of the fixed 15NH3‐N (occurring as either organic‐matter‐fixed NH3 or clay‐fixed NH4) to soil microorganisms was estimated to be 13% after incubation with glucose for 7 d; from 20 to 22% was found to be potentially available to plants as estimated by distillation with MgO. Results indicate that NH3‐N newly fixed by organic matter occurs in forms that are less stabilized and more biologically available than the native soil N.
Statistical Comparison of SPOT Spectral Maps with Field Soil Maps
Authors: Agbu Patrick A. , Fehrenbacher Donald J. , Jansen Ivan J.
Published: July 2010

The field soil map is not the only appropriate standard for evaluating spectral maps. This study was undertaken to evaluate both the field soil map and the spectral map independently, according to the degree to which they minimize within, and maximize among, unit variability of pertinent soil properties. Two 3108‐ha areas in Ford County, east central Illinois were systematically sampled and soil properties were measured. Field and satellite‐derived maps were compared, using several approaches. The results showed that, generally, most of the variability was within map units. Of all the spectral maps, the Systeme Probatoire d'Observation de la Terre (SPOT) texture map was best, and the parameters used indicate that it was close to the field soil map. The mapping units used in the SPOT texture map were both more numerous and of a fundamentally different kind than the units on the field soil map. Units on the field soil map are defined in terms of soil properties that affect use and management, whereas units on the SPOT spectral maps are based directly on spectral properties only. Characterization of SPOT mapping units in terms of significant soil properties would be a necessary next step after generation of spectral maps, before they could be used for land management or land‐use planning. The data indicate that computer classification of SPOT digital data is a potentially useful approach to soil investigations.
Long‐Term Wheel Traffic Effects on Soil Physical Properties under Different Tillage Systems
Authors: Hill R. L. , Meza‐Montalvo M.
Published: July 2010

This study determined the effects of long‐term vehicular wheel traffic on soil physical properties for a Mattapex silt loam (fine‐loamy, mixed, mesic Aquic Hapludult) under different tillage systems. The site utilized a randomized complete‐block design with four replications of continuous‐corn (Zea mays L.) plots under no‐till and conventional till, both of which had controlled wheel traffic for 14 yr. Wheel‐traffic loads during the 14‐yr period had been confined to axle loads of <4.5 Mg. Wheel traffic generally increased bulk density and soil strength. Wheel traffic resulted in over a 50% increase in soil strength when compared with non‐wheel‐tracked areas. The relative soil strength increase from wheel traffic was less for no‐tilled soil than conventionally tilled soil, although the mean increase (∼40 kPa) was the same for both tillage systems. Wheel‐traffic effects on bulk density and soil strength decreased with depth and were largely dissipated by the 30‐cm depth. The presence of wheel traffic in the conventionally tilled interrows significantly reduced the pore volume of pores >15 µm in the upper 17.8‐cm portion of the soil, but did not cause similar reductions in the no‐tilled interrows. Conventionally tilled soil exhibited more pore space in the 15‐ to 0.1‐µm radius range that should retain plant‐available water. Wheel traffic did not exhibit statistically significant effects for the 15‐ to 0.1‐µm range. Neither tillage system nor wheel traffic adversely changed soil physical properties so much that detrimental conditions for plant growth would be encountered. Reasonable doubt exists regarding the necessity to subsoil this soil on a regular basis to alleviate the effects of wheel traffic or continuous no‐tillage management as long as small‐scale farm equipment has been used.
Nitrification Potential of Secondary‐Succession Upland Oak Forests: I. Mineralization and Nitrification during Laboratory Incubations
Authors: Donaldson Jennifer M. , Henderson Gray S.
Published: July 2010

Experiments were carried out to examine factors regulating N mineralization and nitrification in upland oak (Quercus spp.) forests of the Missouri Ozarks. Soils were collected from three sites representing secondary oak succession. Sampling dates represented different stages in the phenological development of the vegetation during a 1‐yr period. Soils were incubated in the laboratory, and changes in soil NO3‐ and NH4‐N were measured, along with changes in populations of autotrophic NH4‐oxidizing bacteria. The NO3‐production curves during laboratory incubation were used to calculate three variables that describe potential nitrification. These variables were lag prior to NO3 accumulation, and initial rate and maximum rate of NO3 production. This nitrification potential is greater in more mature oak stands. Multiple regression analyses of these data show that nitrification in these sites is indirectly regulated by soil NH4‐N availability and pH. However, the strong sampling‐date effect on soil NH4‐N levels, lags in nitrification, and populations of NH4‐oxidizing bacteria suggest interactions between soil nitrification potential and possible inhibition by vegetation.
Effective Design for Small Flood‐Irrigated Field Plots
Authors: Ghodrati Masoud , Ernst Frederick F. , Jury William A.
Published: July 2010

Many studies dealing with water flow in soil require water application through ponding. A method is described for the preparation of a large number of adjacent ponded field plots for experimental purposes. Individual plots are enclosed by corrosion‐resistant, metal strips extending 20 cm into the soil. A single border area around each group of plots functions as a buffer zone, similar to the outer zone of a double‐ring infiltrometer. Simultaneous uniform ponding of individual plots and the border area is achieved by a network of bubbler sprinkler units, with each plot having a separate water flow meter and valve unit to control the rate and amount of each irrigation episode. Such a system enabled study of the influence of macropore structure on the transport of various pesticides and dyes under continuous and intermittent flood irrigation.
Wheat Straw Decomposition and Changes in Decomposability during Field Exposure
Authors: Collins H. P. , Elliott L. F. , Papendick R. I.
Published: July 2010

Describing crop residue decomposition is important for assessing management practices that protect soil against wind and water erosion. Predicting wheat (Triticum aestivum L. em Thell) residue decomposition in conservation tillage systems requires information on C mineralization and changes in residue decomposability. The principal component of wheat residue is the stem. Wheat straw decomposition at the soil surface was followed during field and laboratory inclubation studies. Straw samples were collected on nine dates during 377 d of field exposure and analyzed for weight loss. Total C, soluble C, carbohydrate, N content, and C mineralization were measured periodically during the exposure period. Straw weight loss was 12% after 33 d and averaged 0.05% d−1 for the remaining exposure period. Cumulative weight loss was 33%. Total N, soluble C, and carbohydrate concentrations decreased 17, 73, and 66%, respectively, during field exposure. Total C concentration increased 6.2% after 94 d, then returned to the C concentration of the original straw. In the laboratory, C mineralization of straw taken from the field after ≥94 d was significantly (P < 0.001) lower than C mineralization of fresh residue. Cumulative CO2 evolution among samples that had been in the field for 94 to 377 d was not significantly different (P = 0.03). Amount and quality of soluble C was found to be important only during initial stages of fresh straw decomposition and was inconsequential for field exposed straw. Additions of cellobiose and N had no influence on C mineralization during laboratory incubation.
Indigenous Soil Factors Influencing Iron Chlorosis of Soybean in Calcareous Soils
Authors: Morris D. R. , Loeppert R. H. , Moore T. J.
Published: July 2010

Iron deficiency is the most prevalent and difficult to control of the plant‐nutrient deficiencies encountered on calcareous soils and may be especially severe for soybean [Glycine max (L.) Merr.]. This study was conducted to determine the predominant indigenous soil properties, i.e., those soil properties which are largely unaffected by environmental and management conditions, that influence Fe availability to soybean on calcareous soils. Three varieties of soybean were grown in a growth room in sand/soil mixtures of 23 calcareous soils that were selected to give wide ranges of clay, Fe oxide, CaCO3, and organic matter contents and exchange ion composition. Iron‐deficiency stress was quantified using visual chlorosis ratings in addition to chlorophyll and Fe concentrations of the plant tissue. The concentration of amorphous Fe oxide in the soil was an important factor influencing the uptake of Fe by soybean. Chlorophyll concentration of the plant tissue was negatively correlated with soil‐solution ionic strength and reactivity of the soil carbonate phase. The carbonate effect was likely due to the influence of the highly‐reactive carbonate phase on rhizosphere pH and its subsequent influence on effectiveness of the Fe‐stress response mechanism of soybean. These results differ from results of a previous study with sorghum, in which concentration and reactivity of the carbonate phase of calcareous soils had no influence on the incidence of Fe chlorosis. The different behavior of soybean and sorghum with respect to carbonate reactivity may be attributed to the different predominant Fe‐stress response mechanisms of these crops.
Portable Laser Scanner for Measuring Soil Surface Roughness
Authors: Huang Chi‐hua , Bradford Joe M.
Published: July 2010

Soil surface elevations are commonly measured along a profile at relatively large grid spacings between 5 and 50 mm. This limitation in measurement technique allows the description of surface roughness due to tillage marks and large clods only on the order of ≥20 mm. A portable scanner was designed to measure soil topography at variable grid spacings down to submillimeter scales. The scanner consisted of an optical transducer for measuring soil surface elevation, a motor‐driven X‐Y traversing frame, a set of processing and control electronics, and a personal computer. The optical transducer was mounted on the carriage of the X‐Y traversing frame and was programmed to scan a maximum area of 1 by 1 m. The personal computer controlled the scanning and recorded elevation data. The system had no static noise and the combined frame vibration and spot size produced a positional and elevational resolution on the order 0.1 to 0.3 mm. This scanner can be used to digitize surfaces at fine grid spacings and the detailed surface topography can then be used to study surface boundary processes such as soil erosion.
Ammonia Volatilization from Flooded Soil Systems: A Computer Model. II. Theory and Model Results
Authors: Jayaweera G. R. , Mikkelsen D. S.
Published: July 2010

Our theory to describe the process of NH3 volatilization from flooded systems is that the rate of NH3 loss is principally a function of two parameters, floodwater NH3(aq) concentration and the volatilization rate constant for NH3, kvN. These parameters are governed by five primary factors, floodwater NH4‐N concentration, pH, temperature, depth of floodwater, and wind speed. The NH3‐volatilization model is executed with five primary factors as input variables. With the input of time, it predicts the NH3 loss for a specified period. The interactive effects of these factors were studied by individually varying one factor while maintaining the four other factors at their mean values; the same factor was also studied by maintaining a second factor at its highest and lowest values while the other three factors were kept constant at their mean values. It is seen that, by changing the existing conditions, the NH3‐volatilization losses are increased or decreased appreciably. The sensitivity analysis shows that pH is the most sensitive and temperature and water depth are the least sensitive determinants affecting NH3 volatilization.
A Wick Tensiometer to Measure Low Tensions in Coarse Soils
Authors: Gee Glendon W. , Campbell Melvin D.
Published: July 2010

A wick tensiometer was constructed to measure soil water pressures or tensions in coarse sands and gravelly soils. The tensiometer is similar in design to a conventional tensiometer except that a flexible wick material is used instead of a ceramic cup. Soil matric potential (reported as tension) or water pressure is sensed by the wick and monitored with a pressure transducer or hanging water column. Several wick materials were tested. Absorbent toweling, rolled to form a tight cylinder and sealed into a tensiometer body by a compression fitting, measured tensions up to 90 cm successfully. Glass‐fiber filter paper and wettable plastic sheeting were also tested successfully. Initial tests indicated that the wick sensor was as responsive to tension changes in gravelly soil as ceramic cup units and was less likely to break during placement.
Soil Denitrification and Nitrification Potentials during the Growing Season Relative to Tillage
Authors: Staley T. E. , Boyer D. G. , Caskey W. H.
Published: July 2010

Soil management practice, through the alteration of various biological processes, can have a profound effect on nutrient availability to crops. During the growing season, the effect of no‐tillage (NT) or conventional tillage (CT), location (between or within row), and N rate (0 or 56 kg N ha−1) on soil potential denitrification activity (PDA) and potential nitrification activity (PNA) was investigated. A Gilpin silt loam (fine‐loamy, mixed, mesic Typic Hapludults) was selected and maize (Zea mays L.) was planted. For both PDA and PNA, most of the activity was concentrated in the soil surface (0–3.8‐cm) layer, especially under NT, and decreased to barely detectable levels in the deepest (15–30‐cm) layer examined. Significant main effects were found for tillage, season, and location for PDA in the soil surface layer. Tillage interacted only with season, resulting in an increase in PDA under NT, and a lack of response under CT, during the growing season in both the soil surface and the 3.8‐ to 7.6‐cm layers. For PNA in the soil surface layer, significant main effects were found for all treatments. Only location interacted with tillage, resulting in a 50% increase in PNA from within rows to between rows under NT, and a lack of response under CT. In the 3.8‐ to 7.6‐cm layer, the lowest order interaction was significant. In the 7.6‐ to 15‐cm layer, PNA increased more rapidly under CT than NT during the growing season. These results demonstrate the importance of considering spatial distribution and time when these microbial activities are examined in tillage studies, and suggest that N losses under NT should exceed those under CT.
Occurrence and Correction of Manganese Deficiency in Histosol‐Grown Rice
Authors: Snyder G. H. , Jones D. B. , Coale F. J.
Published: July 2010

Rice (Oryza sativa L.) production is seldom limited by availability of Mn in mineral soils. Manganese deficiency of seedling rice was suspected, however, in drained Histosols with pH values near or exceeding 7.0 in the Everglades Agricultural Area. Several greenhouse and field studies were conducted to verify the occurrence of Mn deficiency, to document its effect on rice growth, and to explore methods for alleviating the deficiency in Histosols. Manganese deficiency was determined to limit the growth of rice seedlings drill‐planted in several drained Histosols having pH values ranging from 6.9 to 7.7. Approximately 3 wk after seedling emergence, deficiency symptoms were evident as interveinal chlorosis on fully expanded leaves. Affected seedlings were shorter, had fewer leaves, weighed less, and had less root mass and length than unaffected seedlings. Affected seedlings contained <20 mg Mn kg−1 tissue. The deficiency also reduced grain yield in the field. In the greenhouse, several methods were investigated for preventing the deficiency. These included soaking seeds in Mn solutions, foliar application of Mn, flooding, or placing Mn fertilizer with the seed at planting. The latter proved to be the best method for preventing the deficiency. The results of the field studies indicated that application of approximately 15 kg Mn ha−1 as MnSO4 with the seed prevented the deficiency and provided near‐maximum grain yields.
Origin of Silt‐Enriched Alpine Surface Mantles in Indian Basin, Wyoming
Authors: Munn L. C. , Spackman L. K.
Published: July 2010

Three soil profiles developed over different bedrock (intrusive mafic pods and granite gneiss) in the Wind River Range, Wyoming were examined to determine the origin of their high‐silt‐content surface horizons. Particle‐size distributions and clay mineralogy support the hypothesis that the soils have formed in surficial deposits derived from local bedrock materials. The soils are the product of physical (gelifraction) and chemical weathering, influenced by colluvial and (local) eolian transport processes. Mineral weathering has produced vermiculite and illite with an alteration or loss of chlorite and interstratified smectite‐kaolinite. The silt‐enriched mantles are distinctly different from loess. Frost action has resulted in silt and clay production in surface horizons and in mixing of materials throughout the profiles.
Acidification Induced by Different Nitrogen Sources in Columns of Selected Tropical Soils
Authors: Stumpe John M. , Vlek Paul L. G.
Published: July 2010

Sustainability in agriculture is a rising concern in the tropics where fertilizers are introduced to meet increasing food demands. The adverse effects of long‐term fertilizer use were monitored through changes in the soil exchange complex in packed columns of an Oxic Paleustalf, a Typic Paleudult, and a Tropeptic Haplustox. Following each application of N at rates of 0, 50, or 100 kg ha−1 as urea, ammonium sulfate (AS), or calcium ammonium nitrate (CAN), the soils were flushed with distilled water, representing the water draining from these soils in their respective tropical environments during a growing season. The procedure was repeated 30 times during 2 yr with 6‐wk rest periods after each five cycles. The rate of acidification reflected the rate of application and acid‐producing capacity of the N source. In the Oxisol and Ultisol, further acidification resulted in an increase in exchangeable Al and Mn, which were eventually found in the effluent, suggesting mineral dissolution. In the Alfisol, acidification resulted in a loss of cation‐exchange sites and the increasing predominance of Al and Mn. This acid‐consuming process caused the development of a descending acidification front, in which soil pH dropped from 6.7 to 5.0. Leachates remained neutral until the acidification front reached the bottom of the soil column. Applied N was quantitatively recovered in the leachates of all soils. Although plant growth would moderate these processes, the results show that indiscriminate N use on such fragile soils may eventually cause soil degradation and groundwater pollution.
Temporal Effects of Subsoil Compaction on Soil Strength and Plant Growth
Authors: Lowery B. , Schuler R. T.
Published: July 2010

In recent years, scientists have become concerned that heavy farm equipment is causing soil compaction below the nominal depth of tillage. Compaction this deep may not be ameliorated after one season's freeze‐thaw and wet‐dry cycles. Experiments were conducted on a Kewaunee (fine, mixed, mesic Typic Hapludalf) and Rozetta (fine‐silty, mixed, mesic Typic Hapludalf) soil to determine the duration and effect of subsoil compaction on soil strength and corn (Zea mays L.) growth. Soil at two sites was compacted with 8 and 12.5 Mg axle loads in the spring of 1983. Cone‐penetration resistance of compacted soil was significantly higher than that of uncompacted soil below the plow zone. Plant heights, at physiological maturity averaged across both sites, were reduced 13 and 26% on the 8‐ and 12.5‐Mg compaction treatments, respectively, compared with the control in 1983. In 1984, average mature plant heights were 2.4, 2.3, and 2.3 m for the control, 8‐, and 12.5‐Mg compaction, respectively. Three years after the compaction was applied (1986), the average mature plant height for the 8‐ and 12.5‐Mg compacted sites were reduced 3.1 and 4.3% compared with the control. Nitrogen and K uptake was reduced by compaction. Iron, Al, and Mn uptake increased with increasing levels of compaction on the Kewaunee soil in 1983. In 1983, yields for the 8‐ and 12.5‐Mg treatments on the Rozetta soil were reduced 4 and 14%, respectively, relative to the control. Similarly, yields for the Kewaunee soil were reduced 14 and 43%. Yields for the Kewaunee soil were not reduced by compaction in 1984, although 5 and 9% reductions were observed at the Rozetta site. Yields were not affected the following 2 yr (1985 and 1986), whereas the resistance to cone penetration was significantly higher in the compacted plots compared with the control.
Productivity Index Model Modified to Estimate Variability of Montana Small Grain Yields
Authors: Wilson J. P. , Sandor S. P. , Nielsen G. A.
Published: July 2010

The productivity index (PI) model estimates crop productivity by characterization of the soil rooting environment and evaluates a soil's vulnerability by simulated removal of surface soil and consideration of three soil properties, available water‐holding capacity, bulk density, and pH. Although the PI model has performed well in the Corn Belt and elsewhere, further testing is required to demonstrate its applicability in northern Great Plains small‐grain environments. Evaluation of PI model performance in Cascade County, Montana, revealed a weak relationship between PI and small‐grain yield that may have been due to shortcomings in the SOILS‐5 database. Therefore, soils and crop data were collected in August and September 1987 from four fields in Hill and Jefferson Counties to evaluate model performance and indicate appropriate changes in the model's design to allow its use in Montana. Results indicate that model performance can be improved by addition of the content and location of organic matter and CaCO3 in the soil profile. Productivity indices were first generated with the original model. The regression of small‐grain yield against PI accounted for 64, 67, 63, and 1% of the variability in yield within Fields 1 through 4, respectively. When the modified PI values were used, R2 increased an average of 44% and accounted for 77, 69, 60, and 75% of the variation in grain yield within Fields 1 through 4, respectively. Moreover, R2 increased slightly (0.69 to 0.75) for all fields collectively when cropping history was considered. These results have encouraged further efforts to develop a modified and improved version of the PI model that uses the SOILS‐5 database for county‐scale assessments in northern Great Plains small‐grain environments.
Cover Crop Management of Polysaccharide‐Mediated Aggregation in an Orchard Soil
Authors: Roberson Emily B. , Firestone Mary K. , Sarig shlomo
Published: July 2010

Soil carbohydrates, including microbial extracellular polysacchrides, stabilize soil aggregates and improve soil structure. This study examined whether short‐term managment of C inputs by cover crops and tillage affected polysaccharide‐mediated macroaggregation. Soil was sampled from a Californa prune (Prunus domestica L.) orchard where an experiment comparing four management techniques, permanent grass cover crop, mowed cover crop, no‐till herbicide, and conventional tillage, had been in place for two seasons. Cover crops significantly increased saturated hydraulic conductivity, acid‐ex‐tractable heavy‐ fraction carbohydrates (those in soil denser than 1.7 g/mL), and macroaggregate slaking resistance over clean‐cultivated or herbicide treatments. Heavy‐fraction carbohydrates are probably mainly composed of microbial extracellualr polysaccharides produced in response to cover‐crop C inputs. Heavy‐fraction carbohydrates were significantly correlated with aggregate stability and satureated hydraulic conductivity, while total organic C and lightfraction carbohydrates were not. There were no differences between soil under herbicide and clean‐cultivation treatments, showing that tillage alone did not measurably affect carbohydrate or soil structure. Heavy‐fraction carbohydrates were shown to be important in the initial improvement of soil structure by cover crops.
Nutrient Flux to Mixed‐Bed Ion‐Exchange Resin: Temperature Effects
Authors: Yang J. E. , Skogley E. O. , Schaff B. E.
Published: July 2010

The phytoavailability soil test (PST) is designed to assay plant‐available nutrient quantity as a function of diffusive ion movement to a spherical, mixed‐bed ion‐exchange resin sink. Temperature is known to alter many parameters relating to nutrient availability and plant uptake. This study was conducted to determine PST sensitivity to temperature‐induced changes in availability of NO‐3‐N, NH+4‐N, P, K, and S. Nutrient flux to resin accumulators was measured during 96 h at 25, 35, and 45 °C. Fluxes of P, K, S, and NH+4‐N all increased with increasing temperature, while the flux of NO‐3‐N decreased. The size of the temperature effect was nutrient and soil specific. Nutrient‐accumulation characteristics were significantly represented by quadratic equations, corresponding to diffusion‐controlled processes. Initial flux (0.5 h) of each nutrient to the resin was rapid and highly related to nutrient ion activity in saturated‐paste soil solutions equilibrated for 24 h. The slope of the accumulation curve decreased after the initial rapid flux. This is interpreted to suggest that diffusion characteristics of the soil control, to a large degree, the flux of nutrients to the resin accumulator after an initial rapid phase related to high nutrient activity in the soil solution. These results provide strong evidence that the PST system is diffusion controlled and that it is sensitive to conditions known to influence nutrient availability in soils, such as temperature and nutrient ion activities.