bluuebunny/crossref_metadata_2025 huggingface dataset:
Erodibility Indices Compared to Measured Values of Selected Trinidad Soils
Authors: Lindsay J. I. , Gumbs F. A.
Published: July 2010

The most suitable erodibility index for tropical soils has not been determined. This study was therefore carried out with 10 selected Trinidad soils to compare three erodibility indices previously used with soils in different parts of the world. The erodibility of the soils was determined by the USDA Erodibility Nomograph, the Australian Erodibility Index, and the Modified Raindrop Technique and their suitability evaluated by comparison with the erodibility measured directly on four of the 10 soil types in the field.

The USDA Erodibility Nomograph correctly predicted the erodibility class of the four soil types; the Australian Index in two of the four soil types; and the Raindrop Technique did not prove to be a suitable method. The number of drops required to break the soil aggregate in the Raindrop Technique depended on the wetting and drying history of aggregate. The erodibility of the four soil types determined by the Nomograph were all classified as slight.
Ammonia Volatilization and Soil Nitrogen Changes after Urea and Ammonium Nitrate Fertilization of Pinus Taeda L.
Authors: Craig Joseph R. , Wollum A. G.
Published: July 2010

From 3.9 to 13.1% of the nitrogen (N) was lost to the atmosphere when 200 kg/ha of N as (NH2)2CO were applied to an undisturbed forest soil during each of the four annual seasons. There were no measurable losses from a comparable NH4NO3 treatment. The majority of the loss occurred within the first 2 weeks after fertilizer application. During this time volatilization of NH3 from the (NH2)2CO‐amended soils appeared to depend more on moisture in the soil and time and amount of precipitation after fertilizer application than on season of fertilizer application. Conditions of light precipitation providing adequate moisture for (NH2)2CO hydrolysis but insufficient to leach the (NH2)2CO resulted in the greatest NH3 losses. Heavy precipitation leached the urea or NH3 deeper into the soil profile where it was retained. Although differences were not significant among seasons, winter loss < fall < summer ≃ spring. Precipitation trends and seasonal temperature differences may be responsible for these differences.

Ammonium‐N from (NH2)2CO remained in the forest floor and top few centimeters of mineral soil. In contrast, the NH4+ produced by the ionization of NH4NO3 was carried deeper into the soil profile.
Effect of Nitrogen Fertilization of Dryland Wheat on Grain Selenium Concentration
Authors: Soltanpour P. N. , Olsen S. R. , Goos R. J.
Published: July 2010

This study was undertaken to (i) determine the effect of nitrogen (N) fertilization on selenium (Se) content of wheat grain (‘Scout 66’) grown under the dryland fallow system of eastern Colorado and (ii) determine the relationship between grain Se and ammonium bicarbonate‐DTPA soil test levels of Se.

Nitrogen fertilization did not affect grain Se where yield was increased significantly in only one out of 10 locations. The ammonium bicarbonate‐DTPA‐extractable level of soil Se was a good indicator of grain Se if 0‐ to 90‐cm soil samples were used (r2 = 0.82). Surface (0 to 30 cm) soil Se levels were weakly related to Se concentration of the grain (r2 = 0.13).
A Modified Line Source Sprinkler Technique for Continuous‐Variable Leaching Studies
Authors: Stark J. C. , Jarrell W. M. , Letey J.
Published: July 2010

An irrigation system designed to produce a continuous range of leaching fractions is described. The leaching variable is produced by supplementing standard sprinkler irrigation with line source irrigation. The advantages of this modified line source technique include (i) the capability of applying a continuous leaching variable to plots receiving uniform applications of sprinkler‐applied fertilizers or pesticides, (ii) the ability to adjust the slope of the water application gradient to produce the desired range of leaching fractions, and (iii) the option of a back‐up irrigation system when wind speed is too great for line source irrigation.
Calibration and Field Testing of a Two‐probe Gamma Gauge
Authors: Rawitz E. , Etkin H. , Hazan A.
Published: July 2010

A series of laboratory and field calibration tests was carried out with a commercial double‐probe gamma gauge in an attempt to resolve difficulties encountered in routine field use of the equipment. The laboratory tests showed that transmitted count rate is affected by the extent of the medium surrounding the beam path, indicating that linearity between log of count rate and sample density is not sufficient proof of monochromatic radiation. The equipment was also found to be sufficiently sensitive to require the use of separate attenuation coefficients for soil solids and for water. A universal calibration equation for wet density can therefore not be used with this equipment. Due to the above two phenomena, the calibration stand supplied with the instrument does not yield a calibration curve adequate for accurate work in the field range of soil moisture. A valid calibration therefore requires measurements of moisture and density in a large soil volume over a range of conditions. In view of the technical difficulties in meeting these conditions in the laboratory, empirical field determination of a multipoint calibration curve appears to be the best choice. Once such a curve has been developed, simple two‐point calibration checks of unknown soils could be performed in the laboratory, provided the assumptions of linearity between log of count rate and medium density, and of the effective universality of the attenuation coefficient of soil may be taken as valid. When properly calibrated, the equipment tested is sensitive and reliable for the determination of soil bulk density in the field.
Ion Exchange and Diffusive Mass Transfer During Miscible Displacement Through an Aggregated Oxisol
Authors: Nkedi‐Kizza P. , Rao P. S. C. , Jessup R. E. , Davidson J. M.
Published: July 2010

Effluent breakthrough curves (BTCs) for four tracers (3H2O, 14CH3OH, 36Cl, and 45Ca) were measured over a wide range of porewater velocities (3 to 164 cm/hour) using water‐saturated columns of Ione soil, an aggregated Oxisol. Increasing asymmetry of the measured BTCs for all tracers with increasing pore‐water velocity was attributed to decreasing residence time for solute transfer by diffusion between inter‐ and intra‐aggregate regions. The measured BTCs for 36Cl and 45Ca illustrated the role played by the pH‐dependent soil surface charge in determining the retention and transport of ionic species.

Measured BTCs were compared with those calculated using a simulation model where (i) convective‐dispersive solute flow was limited to the inter‐aggregate regions, (ii) solute transfer into and out of equivalent spherical aggregates was described by Fick's second law of diffusion, and (iii) isotopic exchange was considered to be an instantaneous reversible process and was described with a linear exchange isotherm. For the slightly sorbed solutes (3H2O and 14CH3OH), all model parameters were independently estimated. Owing to the strong pH‐dependence of isotopic exchange and the inability to exactly duplicate in batch experiments the chemical environment (pH and ionic strength) of the soil columns, exchange coefficients (KD) for 36Cl and 45Ca were estimated by curve‐fitting the model to BTCs measured at the low pore‐water velocity (3 cm/hour). These KD values and all other independently estimated parameters were then used to simulate 36Cl and 45Ca BTCs for the high pore‐water velocity (120 cm/hour). Good agreement was found between measured and calculated BTCs for all tracers. These data and simulations demonstrated the coupling between physical processes (convective‐dispersive flow, diffusive mass transfer) and chemical processes (ion exchange, pH‐dependent charge) in determining the shapes and positions of BTCs obtained from water‐saturated aggregated soils with a variable surface charge.
Soil Pore Structural Stability and Irrigation Water Quality: III. Evaluation of Soil Stability and Crop Yield in Relation to Salinity and Sodicity
Authors: Cass A. , Sumner M. E.
Published: July 2010

A method is proposed for quantitative evaluation of the relationship between irrigation water quality and soil structural stability under a specified set of climatic conditions. Quantitative criteria for pore structural stability are provided by a family of threshold concentration curves determined empirically for each soil. After estimating the variation in composition and concentration of soil water as a function of rainfall, evapotranspiration, and soil drainage, intersection of the sodium stability curve with the irrigation water‐soil solution rectangle provides the necessary quantitative index. A similar approach for evaluating crop response to salinity is presented. The method provides quantitative evaluation of irrigation water quality in relation to soil structural stability and crop salinity tolerance.
Transport of Rhizobium and Pseudomonas through Soil
Authors: Madsen Eugene L. , Alexander Martin
Published: July 2010

A study was made of the vertical movement of Rhizobium japonicum and Pseudomonas putida added to the surface 2.4 cm of nonsterile soil. Recovery of low numbers of these bacteria was possible because the strains were resistant to combinations of inhibitors that prevented growth of most soil microorganisms on agar media. Viable cells of the two bacteria were not transported below 2.7 cm in moist soil in the absence of some transporting agent or in the presence of developing roots of soybeans (Glycine max (L.) Merr.) or beans (Phaseolus vulgaris L.). Percolating water and a burrowing earthworm (Lumbricus rubellus) enhanced the vertical transport of P. putida but had a smaller effect on R. japonicum. Dispersal of both bacteria was more extensive in the presence of percolating water together with L. rubellus or developing roots. Pseudomonas putida was transported farther and in greater numbers than R. japonicum. However, <1 and 4% of the recovered viable cells of R. japonicum and P. putida, respectively, were present below 2.7 cm.
Agronomic Effectiveness of Pyrophosphate as an Additive to Monocalcium Phosphate and Diammonium Phosphate in Calcareous Soils
Authors: Amer Fathi , Khalil M. A. , Diab G. S.
Published: July 2010

Recovery of phosphorus (P) from monocalcium phosphate (MCP) and from diammonium phosphate (DAP), in the presence and the absence of sodium pyrophosphate (NaPP), was determined in the greenhouse on two calcareous soils which had been cropped successively with wheat (Triticum aestivum L.), corn (Zea mays L.), and clover (Trifolium alexandrinum L.). Addition of NaPP to MCP at a pyro‐P/ortho‐P ratio of 1:49 or 5:45 markedly increased wheat grain yield on the desert soil (39% CaCO3), and responses to 50 ppm P with additive were not statistically different from those to 100 ppm P without additive. Sodium pyrophosphate tended to increase P recovery from MCP by the wheat and by the following corn on the alluvial soil (4.1% CaCO3), and only by the wheat on the desert soil. By the end of the cropping experiments total P recovery was considerably lower on the desert than on the alluvial soil, especially with DAP. The highest recoveries were obtained with the additive treatments. At the rate of 50 ppm P, total recovery from MCP increased with 1 ppm additive from 48.1 to 55.4% on the desert soil and from 57.5 to 71.6% on the alluvial soil. With DAP, the beneficial effect of the additive was not significant at the 0.05 level. In soil columns, addition of NaPP enhanced mobility of MCP to a greater extent than that of DAP. The results suggest that DAP may not be recommended for soils high in CaCO3 content.
Characteristics of the Colo Soil Series as Mapped in the North Central Region
Authors: Collins M. E. , Fenton T. E.
Published: July 2010

The Colo soil series (fine‐silty, mixed, mesic Cumulic Haplaquoll) was sampled and studied in areas mapped as Colo in the North Central Region (NCR). Within this broad geographic area, there are variations in climate, vegetation, parent material, relief, and time—the five soil‐forming factors. This soil is mapped on floodplains of streams and in drainageways of various size. Forty‐seven soil profiles from five states were described and sampled to determine selected physical, chemical, and mineralogical properties and the ranges of these properties in this series.

The principal objectives of this investigation were to (i) study one soil series and characterize the series as mapped, (ii) compare Colo soil properties with associated upland soils, and (iii) develop a model to better understand the genesis of soils derived from alluvial sediments in the NCR.

Depth distribution of selected chemical and physical properties in some Colo profiles indicated some degree of horizon differentiation. Clay, total phosphorus (TP), inorganic phosphorus (IP), and available phosphorus (AVP) depth distributions in many profiles had a zone of eluviation and illuviation, indicating redistribution of these constituents within the profile. One possible interpretation of the redistribution is that the soils are on landforms that have been stable for some period of time. Total carbon (TC) content usually decreased regularly with increasing depth. Clay mineralogical analyses indicated a dominance of interstratified clay minerals. Smectite, kaolinite‐chlorite, and illite are minor clay minerals in these soils as interpreted from relative peak heights. For most profiles, clay mineralogy was similar with increasing depth.

Statistical model equations involving several physical, chemical, and mineralogical parameters, as dependent or independent variables, were developed.
Genesis of Maryland Soils Formed from Serpentinite
Authors: Rabenhorst M. C. , Foss J. E. , Fanning D. S.
Published: July 2010

Four pedons developed over serpentinite were characterized. Eluvial and illuvial processes have caused formation of weak‐to‐moderately‐expressed argillic horizons. Magnesium‐rich parent materials are responsible for the dominance of Mg on the exchange complex, except in surface horizons where H+ prevailed. Also due to the Mgrich parent materials, extractable Ca/Mg ratios decreased with depth ranging from 0.8 to 2.45 at the surface to 0.03 to 0.17 above the bedrock. The pH values increased with depth from 4.9 to 5.6 at the surface to 6.6 to 6.8 above the bedrock. Total nickel and chromium concentrations were between 180 and 18,900 ppm and 400 to 5,850 ppm, respectively.

Weathering of serpentine minerals tends toward the formation of smectite, which, with vermiculite, dominates the fine (clay) fractions. These are often interstratified with hydroxyinterlayered minerals. Serpentine minerals, while absent from the <0.2‐µm fraction, occurred with chlorite and vermiculite in the 2‐ to 5‐ and 0.2‐ to 2‐µm fractions. The presence of the silicon‐rich minerals, mica, feldspars, and quartz in the upper portions of the pedons indicates that some eolian materials have been added to the serpentinite residuum. This is substantiated by elemental analyses of the silt fractions.
Determining and Evaluating Nutrient Losses Following Whole‐tree Harvesting of Aspen
Authors: Silkworth D. R. , Grigal D. F.
Published: July 2010

Nutrient loss following whole‐tree harvesting of aspen (Populus tremuloides Michx.) was assessed on coarse‐loamy Typic Fragiochrepts in northeastern Minnesota. We used a methodology that could be applied to other systems to roughly estimate the impact of harvesting on nutrient capital. Ceramic cups collected soil solution through the frost‐free season at 130 cm on sites harvested 1, 2, and 5 years before and on undisturbed sites (total = 24). Nutrients in vegetation, soil, and forest floor were also determined. An evapotranspiration model predicted the flux of water moving through the soil. Soil solution concentrations peaked in midsummer. Nitrogen concentrations in solution were below detection limits, and P concentrations were not related to harvesting. Potassium in soil solution decreased, and Ca and Mg increased on harvested sites compared to undisturbed sites. After adjusting for leaching flux, only Ca showed a statistically significant loss associated with harvest in the first 5 years after the harvest (60 kg/ha). Over a 60‐year rotation, precipitation and normal weathering will replace N, P, and K lost by product removal and deep leaching, will replace about one‐half the Mg, but will not replace Ca. Because of their initial abundance in the soil, Ca and Mg will probably not become nutritionally deficient, but their loss may lead to accelerated soil acidification and associated secondary effects.
The Influence of Anthropogenic Sulfur Inputs upon Soil Properties in the Copper Basin Region of Tennessee
Authors: Wolt J. D. , Lietzke D. A.
Published: July 2010

Anthropogenic sulfur (S) released from historical copper‐sulfide ore smelting in the Copper Basin of Tennessee provides an example of acid‐sulfate weathering from which the long‐term impact of acid‐sulfate precipitation upon soils of the Southern Appalachians may be inferred. Three similar soils (clayey and fine‐loamy, oxidic, mesic Typic Hapludults) were described and sampled downwind from smelter operations in the Copper Basin along a gradient of diminishing S input. The soil at the site of high S input, in the heart of the Copper Basin, contained twofold greater total S in the B2t horizon in comparison to the soil at a site of low S input approximately 11 km downwind. Decreased soil pH and increased exchangeable acidity were also associated with high levels of S input. Comparison of the clay fractions isolated from soils sampled from sites of varied S input indicated decreased gibbsite and total potassium (K) contents and increased kaolinite contents for soils subjected to higher levels of S input. The trends in total K, kaolinite, and gibbsite distributions are consistent with a mechanism whereby gibbsite was destroyed and K‐mica weathered to kaolinite in the past environment of the Copper Basin. The formation of an Al‐hydroxy‐sulfate compound as a consequence of the weathering processes may account for the greater levels of S retention by soils subjected to higher levels of S input.
Soil Solution Nutrient Concentrations Sampled with Tension and Zero‐Tension Lysimeters: Report of Discrepancies
Authors: Haines B. L. , Waide J. B. , Todd R. L.
Published: July 2010

Lysimeters were used to sample soil solutions in an ecosystem‐level study of nutrient cycling in a southern Appalachian deciduous forest watershed. Four lysimeters were installed at each of 16 randomly designated locations. At each location, first at the litter‐soil interface and again 30 cm beneath the litter‐soil interface, one tension and one zero‐tension lysimeter were installed side by side. Samples for 13 time intervals over a 15‐month period were analyzed for water volume, H+, NH+4, K+, Na2+, Ca2+, Mg2+, NO‐3, Cl‐, SO2‐4, H2PO4‐, and dissolved silica. The sums of cations, the sums of anions, and the anion deficit (unmeasured anions) were calculated for each collection. Estimates of soil solution composition and water flow differed according to lysimeter type. At the litter‐soil interface the zero‐tension lysimeters collected 7 times more water flow which had significantly higher concentrations of H+, Ca2+, and SO2‐ and significantly lower concentrations of Na+, K+, and Cl‐ than collections from tension lysimeters. At a soil depth of 30 cm, zero‐tension lysimeters collected 2.1 times less water which had significantly higher concentrations of NH+4, K+, NO‐3, Cl‐, SO2‐4, sums of cations, and sums of anions but significantly less silica than collections from tension lysimeters. A testable hypothesis is advanced to account for these observed discrepancies.
Effect of Pyrophosphate on Phosphate Sorption and Ammonia Volatilization by Calcareous Soils Treated with Ammonium Phosphates
Authors: El‐Zahaby E. M. , Chien S. H. , Savant N. K. , Vlek P. L. G. , Mokwunye A. U.
Published: July 2010

Techniques are needed to simultaneously reduce phosphorus (P) precipitation and ammonia (NH3) volatilization from MAP and DAP (monoammonium‐ and diammonium phosphate). The purpose of this study was to investigate the inhibitory effect of sodium pyrophosphate (NaPP) on P precipitation and NH3 volatilization in a pure calcium carbonate (CaCO3) system and in two calcareous soils from Egypt.

In the CaCO3 system, additions of NaPP‐P equivalent to 4 and 8% of MAP‐P and DAP‐P, respectively, reduced the amounts of P sorption and NH3 volatilization. Solution ammoniacal‐N was higher with PP than without it for both MAP and DAP. Pyrophosphate acts as a nucleation and/or crystal growth inhibitor for dicalcium phosphate dihydrate (DCPD), thereby maintaining higher solution P concentrations. Because NaPP inhibits the formation of DCPD, the pH of the solution was lowered by its addition, which, in turn, reduced NH3 volatilization. Pyrophosphate did not affect NH3 volatilization from NH4Cl in the CaCO3 system since no insoluble reaction products were formed. The solution pH values were about the same for NH4Cl with or without NaPP in the CaCO3 system. The reaction of DAP with CaCO3 did not directly affect NH3 volatilization but indirectly increased solution pH which, in turn, controlled NH3 volatilization.

In the soil system the inhibitory effect of NaPP was relatively more effective in reducing P sorption and NH3 volatilization from MAP than from DAP, and its effect lasted longer in the soil with less CaCO3 content than in the other soil. The effect of NaPP increased when the rate of PP‐P was increased from 2 to 4% of MAP‐P, but no further reduction in NH3 volatilization was noted between 4 and 8% on either soil. The inhibitory effect of PP on P sorption from MAP, however, did increase with an increase in PP‐P from 4 to 8%. Sodium pyrophosphate reduced the P sorption and NH3 volatilization from DAP more efficiently if applied in solution form or applied to the dried soil surface followed by the addition of water than if NaPP was applied to the premoistened soil surface. This is probably related to the dissolved PP concentration in the soil solution. In summary the results obtained with the soil system are in agreement with the results obtained with the pure CaCO3 system.
The Effect of Soil Drainage on Phosphorus Status and Availability to Corn in Long‐term Manure‐amended Soils
Authors: Kuo S. , Baker A. S.
Published: July 2010

The effect of soil drainage on phosphorus (P) transformation and availability in soils was examined in a field that received annual manure applications for more than 20 years. The soil in the field ranged from well‐drained Briscot loam (Typic Fluvaquents) to poorly drained Schalcar muck (Terric Medisprists) and was planted with corn (Zea mays L.) in 1979. Ten weeks after planting, soil and plant tissue samples were collected for P analysis.

Manure applications increased the P content of the soils considerably. Most of the added P from manure remained in the surface soils (0 to 30 cm), though some downward movement of P did occur. Poor soil drainage increased the accumulation of P in the organic matter (NaOCl‐extractable) and in the amorphous Fe‐Al oxide (oxalate‐extractable) soil fractions, but reduced the amount of P in the acid (0.5N H2SO4)‐soluble soil fraction. Drainage affected the P desorption and availability to corn plants as well. The poorly drained Schalcar muck soil, for instance, had less P extractable by dilute HCl‐H2SO4 or NaHCO3 solution than the well‐drained Briscot loam soil, despite the higher total P content of the muck soil. The rate of P desorption by NaHCO3 can be described by two zero‐order rate equations after an initial rapid desorption. The rate constant of desorption for the poorly drained soil (0.058 µg ml−1 min−1) was lower than for the well‐drained soil (0.082 µg ml−1 min−1).

The marked influence of soil drainage on P availability and transformation in the manure‐amended soils observed in this study suggests that the selection of appropriate soils for manure disposal is necessary for better recycling of this nutrient by plants.
Oxygen Consumption and Denitrification Kinetics in Soil
Authors: Cho C. M.
Published: July 2010

Oxygen consumption and CO2, N2O, and N2 production from a slurry of a slightly acidic soil incubated in a closed container with several different concentrations of NO‐3 were investigated using a mass spectrometer. Under unshaken conditions, the rates of O2 consumption and CO2 production changed with time. Nitrous oxide and N2 gases were produced even though there was ample O2 in the atmosphere above the stagnant water. Under these conditions the rates of O2 consumption and N2O, N2, and CO2 production were controlled by the kind and rate of supply of electron acceptors to the sites of denitrification. When well shaken, the rate of O2 consumption was constant. The CO2 production rate had two distinctive values. The rate of CO2 production when O2 was still in the system was greater than the value obtained after O2 in the system was all depleted. Nitrous oxide started to appear only when O2 was completely consumed. Under the shaken conditions, the measured rates of O2 consumption, CO2, and N2O production were independent of NO‐3 concentration; however, the average life and the maximum concentration of N2O were directly related to initial NO‐3 concentration.

It is useful to define a parameter, denitrification intensity (DNI), which is proportional to the potential maximum rate of electron production for a soil with constant microbial activity under fixed temperature. Determination of the DNI must be made when the rate of electron acceptor (NO‐3 or NO‐2) supply is not limiting the reaction. Under these conditions, the inhibition of conversion of N2O to N2 results in the rate of N2O‐N production which is greater than the rate of production of the sum of N2O‐N and N2‐N without inhibition. If the rate of supply of electron acceptors (NO‐3 or NO‐2) is smaller than DNI, a parameter, gaseous nitrogen production rate (GNPR), the magnitude of which is unaffected by the inhibition of conversion of N2O to N2, characterizes the denitrification process.
Soil‐pore Orientation and Faults
Authors: Low Alison J. , Douglas Lowell A. , Platt David W.
Published: July 2010

The orientation of soil pores was studied in order to assess the effect of faulting on soil pores. The results from soil samples collected adjacent to, in a fault zone, and at some distance from a fault were portrayed as rose diagrams and indicated the following: the shortest pores in all samples tend not to show any strongly developed orientation pattern; therefore, the long and midsized pores should be studied. Also, the orientation of these pores were similar in different samples of undisturbed soil from the same horizon, suggesting that the soil‐pore distribution can be characterized. Details of sample size for this characterization are also given. This work indicates that pore orientation can be used to further substantiate some megascopic observations and may be useful in documenting faulting histories, even where horizon displacement is lacking. However, in such cases, pore data will not yield unqualified conclusions.

Pore orientation patterns may change very little with time.
Surface Soil Physical Properties after 36 Years of Cropping to Winter Wheat
Authors: Unger Paul W.
Published: July 2010

A dryland tillage and cropping system study for winter wheat (Triticum aestivum L.) was conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) from 1941 to 1977, a period much longer than most field studies. In 1977, soil samples were collected from the surface layer to evaluate effects of the long‐term tillage and cropping practices on dry and water‐stable aggregate distribution, organic matter (OM) concentration, modulus of rupture, penetrometer resistance, and bulk density of clods. Oneway disk tillage resulted in significantly fewer small dry aggregates than sweep tillage in the wheat‐fallow system, but had no significant effect in the continuous wheat system. Mean weight diameters (MWD) were similar for all tillage methods. Oneway tillage resulted in more < 0.25‐mm diameter water‐stable aggregates than sweep tillage in both cropping systems, resulting in lower MWD for oneway than for sweep tillage. Organic matter concentration was lower for oneway than for sweep tillage in both systems, while continuous wheat resulted in higher OM concentration than wheat‐fallow for comparable tillage methods. Slight changes from 1966 to 1977 indicated that soil OM concentration was at or nearly in equilibrium with prevailing management and climatic conditions. Modulus of rupture of briquettes and resistance of briquette fragments to fracture with a penetrometer were inversely related to OM concentration, but no tillage method or cropping system had an overriding influence on soil physical properties. Dry aggregate analyses indicated that the soil did not contain enough coarse aggregates to control wind erosion, indicating the need to maintain residues on the soil surface to aid wind erosion control.
Organic and Inorganic Sulfur Constituents of a Forest Soil and Their Relationship to Microbial Activity
Authors: David M. B. , Mitchell M. J. , Nakas J. P.
Published: July 2010

Sulfur (S) constituents, microbial biomass, and sulfohydrolase activity were determined for each soil horizon at both hardwood and conifer sites in a Becket soil (Adirondack Mountains, New York). Drying of soil before analysis altered the S constituents. There was a threefold increase (p < 0.05) in sulfate in the organic horizons. Total S was greatest in the O horizons with 2,010 and 1,690 µg S/g in conifer and hardwood solums, respectively. Mineral soil had a maximum S concentration in the B21h horizon. Sulfate concentrations were a small proportion (<15%) of total S in B horizons. Organic S was dominant (93% of total S) in all horizons. Carbon‐bonded S and ester sulfate were 74 and 18% of total S, respectively. Microbial biomass was greatest in the 01 horizon of both hardwood and conifer solums (59 and 70 mg biomass C · 100 g−1 dry mass, respectively). The B21h horizon contained the greatest biomass in the mineral soil. Sulfohydrolase activity exhibited the same distribution. Total S, carbon‐bonded S, and ester sulfate were all positively correlated (p < 0.05) to percent organic matter in the soil horizons. Correlations between microbial biomass and sulfohydrolase activity with organic S indicate the potential for microbial S transformations. Sulfate formation by mineralization may be more important than exogenous inputs. This has major implications for assessing the impact of atmospheric S deposition on soils.
Time, Rate, and Method of Phosphorus Application for Continuously Double‐cropped Wheat and Soybeans
Authors: Touchton J. T. , Hargrove W. L. , Sharpe R. R. , Boswell F. C.
Published: July 2010

Currently, phosphorus (P) fertilizer recommendations for double‐cropped wheat (Triticum aestivum L.) and soybeans (Glycine max L. Merr.) are based on data from monocropping conventional tillage systems. The purpose of this 3‐year study on an eroded Ultisol was to compare times (fall, spring, and fall plus spring) and rates (0, 32, 64, and 128 kg ha−1 year−1) of P applications for double‐cropped wheat and soybeans grown with disk tillage and no‐tillage production practices. Disk tillage was used to incorporate P; otherwise, tillage implements were not used. Although most of the applied P was concentrated in the surface 7.5 cm of soil, it did not affect extractable soil levels of K, Ca, Mg, Cu, Zn, and Mn. Applied P did, however, reduce Cu and Zn concentrations in both soybean and wheat tissue, but the reduction probably was not great enough to affect yields. Yield response to applied P was obtained, but this response was primarily with the lowest P rate; average yields for 0 and 32 kg ha−1 year−1 were 2,330 and 2,750 kg/ha, respectively, for wheat and 2,210 and 2,690 kg/ha, respectively, for soybeans.

Time of application did not affect yields or nutrient concentrations of either crop. Nutrient concentrations in soybean leaves did not differ among tillage systems, but soybean yields averaged 200 kg/ha higher with no‐tillage than disk tillage. With wheat, nutrient concentrations were lower and forage and grain yields were higher with disk‐ than no‐tillage. Yield differences between tillage systems were essentially the same for no P as for any rate of applied P, which suggests that these differences between tillage systems were due to tillage rather than method of application. The data suggest that current P recommendations for monocropping systems are suitable for double‐cropping systems but P recommendations for disk‐ and no‐tillage systems should be based on soil samples taken from the upper 7.5 cm of soil rather than the more common 0‐ to 20‐cm depth.
Comparison of Batch and Miscible Displacement Techniques to Describe Potassium Adsorption Kinetics in Delaware Soils
Authors: Sparks D. L. , Rechcigl J. E.
Published: July 2010

Kinetics of potassium (K) adsorption in three soils were compared using batch equilibrium and miscible displacement techniques. The batch method reached equilibrium sooner than miscible displacement in all cases. Greater clay content did not affect the equilibrium time using the batch technique but increased that time for miscible displacement.

The percent‐K adsorption was closely related to (time)1/2 indicating diffusion‐controlled exchange. Relative rate coefficients were significantly higher for batch than for miscible displacement.

Miscible displacement simulates solute movement in soils under field conditions, and since flow rate and leachate volume can easily be adjusted, miscible displacement has great advantages for rapid reactions. Batch techniques require separation of solid and solution by centrifugation and/or filtration in which the time of separation of solid from liquid phases is not precisely known.
An Improved Thermocouple Hygrometer for In‐situ Measurements of Soil Water Potential
Authors: Brunini O. , Thurtell G. W.
Published: July 2010

A new dewpoint hygrometer for in‐situ measurements of soil water potential was designed and its performance evaluated. A porous silver membrane serves as the hydraulic connection between the soil and the measuring cavity which encloses a four‐terminal thermojunction made by cross welding chromel and constantan wires 0.001 in. (0.00254 cm) in diameter. The membranes were screwed to the copper body of the hygrometer and such configuration minimized the temperature difference between the vapor source and the reference junctions. When a thermal gradient was imposed on a hygrometer placed horizontally in a soil column, the maximum voltage offset observed was 0.05µV, but the soil water potential values as indicated by the hygrometer readings remained constant at −0.56MPa.

This new device has a fast response for water flow with a time constant of approximately 5 min, and the time constant for salt diffusion in and out of the membranes is about 8 min. The results of soil water potential measurements under corn (Zea mays) plant hybrid United 108 grown in a growth chamber environment have shown that this new device is capable of following the changes in soil water potential very well. The difference in water potential observed between leaf and soil after the plant had been left several hours in the dark appeared to be related to uneven moisture distribution in the pot, and the plant was responding to the average soil water potential.
Crystallization of Iron(III) Phosphate at Room Temperature
Authors: Hsu Pa Ho
Published: July 2010

Ferric nitrate, sodium dihydrogen phosphate, and sodium hydroxide solutions were mixed in a variety of combinations and aged at room temperature. The results showed that, with solutions 0.001M in Fe, 0.0002 to 0.001M in phosphate, and NaOH/Fe molar ratios ranging from 0 to 3 (pH 2.6 to 7.8), all precipitates were amorphous basic iron(III) phosphates without any tendency to crystallize toward strengite‐type compounds for up to at least 66 months.

With 0.01M in Fe, metastrengite was observed from samples 0.03 to 0.06M in phosphate (pH 2.0 to 2.4) 24 months after preparation, but the reaction product was positively charged amorphous basic iron phosphate if the sample was dispersed in 0.01M in phosphate (pH 1.8) during the entire period of study. These positively charged particles were rapidly precipitable with sulfate. The sample 0.02M in phosphate was on the borderline for metastrengite formation.
Diurnal Variability in Rate of Emission of Nitrous Oxide from Soils
Authors: Blackmer A. M. , Robbins S. G. , Bremner J. M.
Published: July 2010

Diurnal variability in the rate of emission of nitrous oxide (N2O) from Iowa soils was studied by using a chamber technique to measure the N2O emission rates at sites on fertilized and unfertilized soils at 1‐ or 2‐h intervals for periods of from 1 to 5 d. The coefficients of variation for the rates of N2O emission observed at these sites within 24‐h periods ranged from 12 to 66% and averaged 38%. As much as 90% of the diurnal variability observed could be attributed to diurnal N2O emission patterns related to changes in soil temperature. Observations reported suggest that these patterns were caused largely by changes in the solubility of N2O in soil water induced by diurnal changes in soil temperature, that the amplitudes of these patterns were determined largely by the amounts of water and N2O in the surface soil, that the times of minima and maxima in these patterns were determined by the depth at which temperature‐induced changes in the solubility of N2O in water were significant, and that neither the amplitudes nor the times of minima and maxima in these patterns can be predicted solely from soil temperature. Data reported show that there is no short time during a 24‐h period that is always satisfactory for assessing the amount of N2O evolved during that period.
L‐Histidine Ammonia‐Lyase Activity in Soils
Authors: Frankenberger W. T. , Johanson J. B.
Published: July 2010

Approximately 20 to 40% of the total nitrogen (N) in most surface soils is in the form of amino acids. Because of the importance of amino acids as a N source for plant and microbial growth, this work was carried out to study the enzyme that catalyzes the deamination of L‐histidine in soils. A simple, precise, and sensitive method to assay L‐histidine ammonia‐lyase (EC 4.3.1.3) activity in soils is described. This enzyme catalyzes the deamination of L‐histidine and produces urocanate and ammonia. The method involves determination by steam distillation of the ammonium (NH4+) produced by L‐histidine NH3‐lyase activity when soil is incubated with buffered (0.1M Tris, pH 9.0) L‐histidine solution and toluene at 37°C for 48 h. Results show that the rate of NH4‐N released through soil L‐histidine NH3‐lyase activity exhibited a buffer pH optimum of 9.0. The reaction rate of this enzyme approached zero‐order kinetics when 50 mM of L‐histidine solution was added to soils. The D‐isomer of histidine was also deaminated in soils but was only 40% of the activity of the L‐isomer at saturating conditions of the substrate. The dependence of the reaction rate on the amount of enzyme present was linear up to 5 g of soil. Under the standard conditions, the accumulation of NH4‐N was linear with time for at least 168 h. However, in the absence of toluene the NH4‐N released with time followed an exponential relationship which might be due to induction of the enzyme by its substrate and a multienzyme system that degrades urocanate and its reaction products. The optimal temperature for soil L‐histidine NH3‐lyase activity occurred at 80°C and denaturation began at 85°C. Among the various pretreatments that affected L‐histidine NH3‐lyase activity in soils, 2‐mercaptoethanol, cysteine, CaCl2, and MgSO4 activated this enzyme by an average of 12, 16, 11, and 11%, respectively. Treatments with formaldehyde, phenyl mercuric acetate, NaF, and NaAsO2 inhibited the activity considerably.
Composition of a Conover‐Brookston Map Unit in Southeastern Michigan
Authors: Asady G. H. , Whiteside E. P.
Published: July 2010

A Conover‐Brookston soil mapping unit, named on the basis of point‐transect observations after its delineation, was reevaluated through laboratory characterization of the major components of this map unit. Eight Conover (fine‐loamy, mixed, mesic Udollic Ochraqualf) and eight Brookston (fine‐loamy, mixed, mesic Typic Argiaquoll) pedons, identified by the transect observations, were investigated by laboratory determinations.

The particle‐size distributions indicated some translocation of clay from the surface to the subsoil in each series. However, even in those pedons with other characteristics of an argillic horizon, the ratios of fine‐clay in total clay of B2/Ap horizons were insufficient for an argillic horizon as defined in Soil Taxonomy. Alternative criteria are proposed.

The 16 pedons covered the whole particle‐size range of the fineloamy family. The transects of the map unit after its delineation overestimated its homogeneity, judged by the laboratory analyses.
The Genesis of Certain Soil Profiles on an Archaeological Site in Southern Greece
Authors: Haidouti C. , Yassoglou N. J.
Published: July 2010

Genetic studies were conducted on soil profiles developed on an archaeological site in southwestern Greece. The parent materials of the profiles were unconsolidated Holocene and Pliocene deposits. Argillic horizons formed through the movement of montmorillonite developed in 2,000 to 3,000 years. Cambic horizons formed by the removal of carbonates developed in < 900 years. The depth of pedogenesis was influenced by the consolidation of the parent material and presence of limestone boulders.

Changes in the mineralogical composition during soil development were the leaching of carbonates, translocation of montmorillonite from the surface horizon to the Bt horizon, and changes in the proportion of iron oxides extracted by ammonium oxalate.
Time and Frequency of Irrigation Effects on Sunflower Production and Water Use
Authors: Unger Paul W.
Published: July 2010

Sunflower (Helianthus annuus L.) production has greatly increased in the U. S. in recent years, with some being produced under irrigation in the Southern Great Plains. However, because of limited water supplies in the Southern Great Plains, sunflower usually is not fully irrigated. The objective of this study was to determine the influence of limited irrigation on sunflower growth, seed yield and quality, oil percent and quality, and water use and use efficiency. Treatments providing one or two irrigations at readily identifiable growth stages were compared with treatments providing no, adequate, and full irrigation. Sunflower irrigated before flowering averaged 17 cm taller than those not irrigated between emergence and flowering. Seed yields averaged highest (2.49 t/ha) with full irrigation, but in individual years, differences between full irrigation and other treatments were not always significant. Usually, the highest seed yield resulted from flowering or late flowering irrigations. These irrigations usually also resulted in the highest seed test weight and weight/seed. Oil percent averaged highest (48.8%) for the emergence plus late flowering irrigation treatment and lowest (43.4%) with the emergence plus budding treatment. Irrigation treatments significantly affected linoleic and oleic acid concentrations of the oil, but the maximum difference among treatments was only four and five percentage units for linoleic and oleic acids, respectively.

Total water use increased with increased number of irrigations, but yield increases were not proportional to water use, especially for the adequate and full irrigation treatments. With these treatments, water‐use efficiency was less than for limited irrigation treatments that provided adequate water from flowering to late flowering.
Effect of Dry‐Season Soil Management of Water Conservation for the Succeeding Rice Crop in a Tropical Soil
Authors: Hundal S. S. , De Datta S. K.
Published: July 2010

In tropical Asia, soil water conservation during the dry‐season fallow is critical for early establishment of the first rice (Oryza sativa L.) crop and increases in sequential cropping intensity under rainfed conditions. Five dry‐season fallow soil water conservation techniques using shallow rotovation (soil mulch), deep plowing followed by rotovation, herbicide‐treated bare and straw mulched soil, and weedy control were evaluated on a clay soil. Soil water changes were monitored weekly to the 1.05‐m soil depth. Soil temperature at the 10‐cm depth, soil matric potential at the 15‐cm depth, and fluctuations in groundwater table were measured regularly.

Highest soil temperatures were obtained in the bare soil treatment. The straw mulch application maintained the lowest temperatures. By the end of the dry season, the soil had dried to the 1‐m depth in the weedy control compared to 15 cm in soil mulch, 30 cm in straw mulch, and 45 cm in the bare soil treatment. Starting with initial soil water contents close to field capacity, a maximum water depletion of 248, 86, 55, 35, and 58 mm occurred in the weedy control, bare soil, straw mulch, plowed and rotovated, and rotovated treatments, respectively, at the end of the dry season. Groundwater table during this period varied from about the 1.5‐ to 1.75‐m soil depth. Rainfall requirement was significantly reduced and early crop establishment was made possible when soil was kept weed‐free during the dry‐season fallow. Minor differences in water conservation occurred among soil mulch, straw mulch, and bare soil systems.
Separating Soil Iron‐ and Manganese‐Oxide Fractions for Microelement Analysis
Authors: Shuman L. M.
Published: July 2010

Since sodium dithionite (Na2S2O4) is often contaminated with zinc (Zn) and can form metal sulfide precipitates, it is not suitable for solubilizing iron (Fe) oxides in fractionation schemes for soil microelements. The objective was to find an alternate method to solubilize crystalline Fe oxides that would fit into a scheme including extractants for amorphous Fe and manganese (Mn) oxides. Three soils were extracted with seven reagents designed to remove amorphous and/or crystalline Fe or Mn oxides [0.1M Na4P2O7, pH 10.0; 0.2M (NH4)2C2O4 in 0.2M H2C2O4, pH 3.0 (oxalate); 0.1M NH2OH‐HCl, pH 2.0; 1.0M NH2OH‐HCl in 25% acetic acid; 0.1M ascorbic acid in the oxalate solution; 0.1 g SnCl2 per gram of soil in the oxalate solution; and 1.0 g dithionite per gram of soil in citrate buffer]. The Na4P2O7, an extractant for elements associated with the organic fraction, extracted amounts of Fe similar to that for the oxalate solution. The two NH2OH‐HCl extractants solubilized very little Fe (<1% total), but NH2OH‐HCl alone solubilized as much Mn as most of the other extractants indicating that it is specific for Mn oxides. The ascorbic acid‐oxalate and SnCl2‐oxalate experimental methods extracted amounts of Fe similar to the dithionite method and amounts of Al higher than the dithionite method. Of the amorphous Fe‐oxide extractants, the oxalate solution solubilized the most Zn and Cu, whereas of the crystalline Fe‐oxide extractants, the ascorbic acid‐oxalate solubilized the highest amounts of Zn and Cu. The extractants suggested for a fractionation scheme are NH2OH‐HCl for Mn oxides, oxalate solution shaken with the soil in the dark for amorphous Fe oxides, and ascorbic acid‐oxalate for crystalline Fe oxides.
Influence of Soil Moisture on Smectite Formation in Soils Derived from Serpentinite
Authors: Istok J. D. , Harward M. E.
Published: July 2010

X‐ray diffraction (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM) were used to characterize the phyllosilicates in a catena of soils derived from serpentinite in southwestern Oregon. Serpentine (variety chrysotile) and chlorite were the phyllosilicates in the bedrock and in the <2‐µm fraction of soil samples from the two well‐drained profiles. Samples from the two soils which were deeper, finer‐textured, and more poorly drained consisted of smectite, serpentine, and chlorite. The data indicate that smectite is forming from serpentine and/or chlorite in poorly drained landscape positions. The abundance of amorphous material, revealed by TEM, may suggest a mechanism for smectite formation in these soils.