bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the Most Probable Number Method for Enumerating Denitrifying Bacteria
Authors: Davidson E. A. , Strand M. K. , Galloway L. F.
Published: July 2010

Most probable number (MPN) enumerations of denitrifying bacteria were conducted on an agricultural soil (pH 6.6) and a forest soil (pH 5.6), in both neutral (pH 6.8) and acid (pH 5.6) media. The neutral medium yielded higher enumerations for both soils and, therefore, appears to be optimal, even for denitrifiers present in acid soils. Enzyme activity assays and MPN enumerations of seven soil samples were weakly correlated (r = 0.71; p = 0.07). One soil exhibited a high MPN enumeration, but had no detectable denitrifying enzyme activity. While the enzyme assay indexes denitrification potential of soils under the environmental conditions at the time of sampling, the MPN enumeration indexes the denitrifying capability of the populations inhabiting soils. A population's denitrifying capability is related to its size, but other factors which might also influence MPN enumerations are discussed. Precise incubation time was critical in the MPN procedure. Delays of 2h affected the scoring results. Populations in some of the incubation tubes appeared to be in a dynamic growth phase at the end of the 14‐d incubation period. Inconsistencies in incubation duration could confound comparisons among soils. Despite inherent flaws and disadvantages, the MPN procedure may be appropriate for certain research objectives as an index of a population's denitrifying capacity. Recommendations and cautions are offered.
Thermoluminescence Dating of Loess from Western Iowa
Authors: Norton L. Darrell , Bradford Joe M.
Published: July 2010

This study was conducted to evaluate thermoluminescence as an alternative to radiocarbon dating to determine age of soil materials low in organic carbon from major loess units from western Iowa. Thermoluminescence (TL) ages were determined for Upper Wisconsinan (Peoria), Basal Wisconsinan (“Farmdale”) and Loveland loesses using the fine‐grained technique on the 4 to 11 µm particle size fraction. Corrections were made for soil moisture and cosmic radiation influences. Thermoluminescence dating was effective in separating the three major loess units studied. The dates for Upper Wisconsinan (Peoria) loess were comparable to published radiocarbon dates, ranging between 13 150 to 24 130; however, there was considerable variability in the dates. The Basal Wisconsinan (“Farmdale”) loess gave considerably older ages (45 960–46 720) than reported with radiocarbon dating. Illinoian age Loveland loess yielded a date of 89 200 yr and was somewhat younger than presumed for the Illinoian advance. Thermoluminescence dating appears to be a viable alternative to radiocarbon dating of loess when organic material is not present, but more work is needed to rectify the age discrepancies. Although TL dating does not give dates in stratigraphic or chronological agreement with radiocarbon dating, it does differentiate the loesses studied.
Length and Slope Effects on Runoff from Sodium Dispersed, Compacted Earth Microcatchments
Authors: Evett Steven R. , Dutt Gordon R.
Published: July 2010

The effects of microcatchment slope and length on runoff and erosion rates were studied under 18 rain storms to get information for design of water harvesting systems. Two replicates of a two‐factor experiment, including 1, 5, 10, and 15% slopes and 3‐and 6‐m lengths, were built on a gravelly sandy clay loam (mixed mineralogy) using 11.2 t ha−1 of NaCl mixed into the surface 2 to 5 cm of soil followed by compaction with a 6‐t roller after a heavy rain. Both slope and length had effects on runoff significant at the 0.1% probability level but the effect of rainfall intensity was not significant. The best fit linear model of runoff, Q, (cm) vs. rainfall, P, (cm) was Q = 0.858(P − 0.34) which explained about 98% of the variability in runoff on individual plots for individual storms but which explained no differences in runoff among treatments. A nonlinear model incorporating slope, s, (m/m) and length, x, (m) accounted for about 96% of the variability in average total runoff among treatments. This model, Q = (s0.0453 x−0.183 + 0.183)(P − 0.339), shows that the important differences in runoff among treatments can be explained by slope and length alone for our conditions. Water quality analyses indicated that only a minor salinity problem but slight to moderate permeability problems might be expected. However, no apparent problems have arisen in 12 yr of grape (Vitis vinifera) and fruit tree (Prunis sp.) cultivation in a water harvesting system using our catchment on the same soil.
Diffraction Patterns and Solubility Products of Several Divalent Manganese Phosphate Compounds
Authors: Boyle F. W. , Lindsay W. L.
Published: July 2010

Four divalent Mn phosphate compounds were prepared and identified. The compound, Mn3(PO4)2·3H2O slowly transformed to Mn5H2(PO4)4·4H2O, when the solid was left in contact with the mother liquor. Dissociation constants were determined for the following reactions:
urn:x-wiley:03615995:saj2sssaj198503615995004900030046x:equation:saj2sssaj198503615995004900030046x-math-0001 where log K· is the log of the equilibrium constant, (K·). The mineral Mn(H2PO4)2·2H2O (manganese [II] di‐[dihydrogen phosphate] dihydrate) was identified, but its solubility constant was not determined because of high ionic strength corrections. X‐ray diffraction patterns, densities, and refractive indices were determined for the four minerals.
Phosphate Rock Dissolution in Soil: Indications from Plant Growth Studies
Authors: Anderson D. L. , Kussow W. R. , Corey R. B.
Published: July 2010

Data from three plant growth studies conducted in controlled environments with seven phosphate rocks (PR) and 18 soils demonstrated how and to what degree selected PR and soil characteristics influence rock phosphate release. Rock phosphate release was calculated as the sum of the increase in plant P uptake and soil NaOH‐extractable P in treated soil as compared to untreated soil. The seven PR materials tested were carbonate apatites containing 0.4 to 7.1% CO2−3 substituted in the apatite lattices. Relative agronomic effectiveness of the rocks was directly related to their substituted CO2−3 contents. In a given soil, substituted CO2−3 content accounted for 71 to 84% of the variation in rock P released. For the group of 18 soils, substituted CO2−3 accounted for nearly 49% of the variation in rock phosphate release. Six selected soil characteristics accounted for 54 to 75% of the variation in phosphate release from a given PR. Across a group of four PR materials, no single soil characteristic appeared to have a consistent and predominate influence on phosphate release. Overlapping of soil spheres serving as a sink for dissolution products of adjacent PR particles decreases dissolution rates of individual particles. Within these spheres of influence are contained the elements (i.e., buffer powers, pH, solute concentration gradients, etc.) driving dissolution.
Fertilizer Phosphorus Recovery After Seventeen Years of Dryland Cropping
Authors: Halvorson A. D. , Black A. L.
Published: July 2010

Information on long‐term fertilizer P recovery by grain crops from a single broadcast application in the northern Great Plains is limited. Uptake of P by grain and straw was measured in 10 or 11 crops (1967 or 1968 to 1983) grown on a Williams loam (fine‐loamy, Typic Argiborolls) in a split‐plot, randomized complete block experiment. Fertilizer N, as main plots, was applied each crop year, except two, at rates of 0, 45, and 90 kg N/ha. Concentrated superphosphate P fertilizer (subplots) was applied only once, at study initiation, at rates of 0, 22, 45, 90, and 180 kg P/ha. The first six wheat crops (Triticum aestivum) were grown in a crop‐fallow system and the last four or five crops, including wheat, barley (Hordeum vulgare), and safflower (Carthamus tinctorius L.), in an annual cropping system. Average P uptake in the grain (21 crops) was 6.4, 7.2, 8.0, 9.1, and 10.0 kg P/ha per crop for the 0, 22, 45, 90, and 180 kg P/ha treatments, respectively, over all N levels. Average P uptake in straw (21 crops) was 0.6, 0.7, 0.9, 1.0, and 1.2 kg P/ha per crop for the same respective P rates. Nitrogen fertilization generally decreased P uptake at low P rates (0 and 22 kg P/ha) but increased P uptake at high P rates (90 and 180 kg P/ha). Average P uptake in grain (21 crops) was 7.6, 8.4, and 8.4 kg P/ha per crop for the 0, 45, and 90 kg N/ha treatments, respectively, over all P rates. Fertilizer P recovery in the grain for the 22, 45, 90, and 180 kg P/ha treatments averaged 32, 25, 23, and 13%, respectively, without N fertilization and 45, 38, 37, and 24% with 45 kg N/ha. The results of this study suggest that a one‐time broadcast application of P fertilizer at rates as high as 90 kg P/ha is an efficient way to meet crop needs and utilize P fertilizer resources.
Soil‐plant Diversity Relationships on a Disturbed Site in Northwestern Colorado
Authors: Stark John M. , Redente Edward F.
Published: July 2010

A 5‐yr‐old revegetation plot in the Piceance Basin of northwestern Colorado was used to study the relationship between several soil properties and plant species diversity. Soil properties, including coarse fragment content, topography, depth to bedrock, rooting depth, soil volume, fertility, and salt content, were quantified for 108 subplots. Using simple and multiple regression techniques, plant diversity on the subplots was correlated with the various soil properties. A seed mixture composed of introduced grasses and forbs was used most extensively to study diversity‐soil physical property relationships. For these plots, percent large coarse fragments (> 4.76 mm) within the rooting depth had a high positive correlation with the Shannon‐Weiner diversity index. Depth to bedrock, rooting depth, total soil volume, soil volume within the rooting depth, and a topographic index all exhibited negative correlations with the Shannon‐Weiner index. On plots seeded with a native grass‐forb seed mixture, where variation in salt content was greatest, SAR, ESP, and EC had positive correlations with species richness. When all seed mixtures were considered, rate of fertilizer application had a negative correlation with the Shannon‐Weiner index. In every case where a regression was significant, soil properties normally associated with high production resulted in low diversity and soil properties normally associated with low production resulted in high diversity. Mechanisms are proposed to explain the relationships between soil factors and diversity. Management techniques are also suggested which could be incorporated into the reclamation process to increase plant diversity.
Estimating Ammonia Volatilization From Flooded Rice Fields by Simplified Techniques
Authors: Freney J. R. , Leuning R. , Simpson J. R. , Denmead O. T. , Muirhead W. A.
Published: July 2010

Two simplified methods for assessing the emission of ammonia, from fertilized, flooded rice (Oryza sativa L. cv. Inga) fields without affecting the plant's environment, are described and compared with an established micrometeorological method. Method A requires a circular plot of a 25‐m radius over which wind speed and atmospheric ammonia concentrations are observed at 0.8 m above the floodwater. Method B requires measurements of ammoniacal nitrogen concentration, pH and temperature in the floodwater, and wind speed at a fixed height. Method A is the more accurate technique and requires fewer measurements. It appears that one calibration curve relating vertical flux of ammonia to these measurements can be applied in widely different environments. Method B is not only less accurate than Method A but appears to require different calibration curves to determine vertical flux for different environments. However, this method may be more useful for comparing ammonia losses from several different fertilizer treatments since only small plot areas are required for each treatment. Method B can be calibrated easily for each site by one set of simultaneous measurements on one treatment plot, using Method A.
Spatial Variability of a Cultivated Soil as Affected by Past and Present Microtopography
Authors: Kachanoski R. G. , Rolston D. E. , de Jong E.
Published: July 2010

The effects of 30 yr of cultivation on the magnitude and spatial variance relationships of selected soil properties are examined. Soil cores (76‐mm diam) were taken every 1 m in 46‐m long transects in a native and adjacent cultivated field. The soil is a mixture of Typic Haploborolls and Typic Argiborolls. Spatial relationships observed in the native soil were used to construct a moving average model for predicting the soil surface on the cultivated site that existed before cultivation. The model along with 137Cs distribution was used to separate the effects of tillage translocation and erosion on changes in solum mass and C. Tillage translocation during the initial years of cultivation resulted in considerable redistribution of soil. Spectral analysis indicated the redistribution was not random, but was related to the spatial distribution of the past surface curvature. The systematic redistribution resulted in higher overall variances for soil properties compared to the native site, but also resulted in significant increases in autocorrelation and the proportion of variance associated with deterministic cycling. A conceptual and mathematical filter model is presented for representing the effects of management, weathering, or other treatments on the soil. In profiles where no significant tillage translocation occurred, total C losses in the solum were 0.35% (of original C) per year. Soil erosion could account for 40% of the observed total C loss.
Model for the Soil Solution Composition of an Oasis
Authors: Elprince Adel M.
Published: July 2010

A static computer model based on the evaporative concentration of irrigation waters has been developed for the origin of soil solution compositions in the Al‐Hassa oasis in Saudi Arabia. The model successfully predicted the precipitation of calcite and the conversion of smectite to attapulgite when in equilibrium with atmospheric CO2 pressure. It also predicted precipitation of gypsum when irrigation water is concentrated by a factor of 3.7 and the precipitation of silica gel when water is concentrated by a factor of 7.5. Results from this study indicate that the model may be applicable to other oases in arid environments. Spring water discharges freely from the higher elevations and flows toward playas in the desert. Mineral fractionation follows the same natural slope within the oasis, as indicated by isoconcentration lines for salinity, carbonates, and gypsum in oasis soils. The calculated soil solution compositions at fixed electrolytic conductivity (EC) values were compared with the chemical analysis of 1:5 extracts having the same EC values. These comparisons showed that six primary processes are responsible for the formation of soil solutions from irrigation water under oases conditions. The processes are: (i) deaquation due to transpiration and evaporation, (ii) precipitation and dissolution of soil mineral phases, (iii) K fixation, (iv) Na and Cl retention, (v) MgSO04 formation, and (vi) biological formation of HCO3. Agricultural production of dates was absent in areas where the EC of 1:5 soil solution extracts exceeded 6 dS m−1 (i.e., in gypsum and silica gel precipitation areas).
Sodium‐Calcium‐Magnesium Exchange Reactions on a Montmorillonitic Soil: III. Calcium‐Magnesium Exchange Selectivity
Authors: Sposito Garrison , Fletcher Philip
Published: July 2010

The Vanselow selectivity coefficient was calculated for Mg → Ca exchange on a montmorillonitic soil separate containing organic matter. Seven sets of cation exchange data were analyzed numerically, encompassing pH values ranging from 5 to 7 in a 50 mol m−3 perchlorate medium and exchangeable sodium percentages ranging from 0 to 25%. The selectivity coefficient for Mg → Ca exchange was observed to decrease from a value near 1.5 at 0% Ca saturation to a value near 1.0 at 100% Ca saturation with no effect of pH on this trend in the range examined. At low Ca saturation of the soil, the selectivity coefficient increased by about 15% as the ESP increased from 0 to 25%. This behavior was shown through a model calculation to be consistent with a mechanism in which Na adsorbs preferentially on the montmorillonitic component of the exchange complex in the soil, leaving the nonmontmorillonitic portion of the exchange complex to adsorb Ca selectively over Mg.
Loess Deposits on a Pleistocene Age Terrace in Eastern Arkansas
Authors: Rutledge E. M. , West L. T. , Omakupt Manu
Published: July 2010

The area of eastern Arkansas between Crowley's Ridge and the Ozark Plateau, known as the Western Lowlands of Arkansas, was shaped by the ancestor of the Mississippi River. As this river responded to changes in glaciers upstream, a series of five braided stream terraces was formed within the lowlands. The second highest of these terraces was transected normal to its long axis to determine whether the silty materials capping this terrace were loess or silty alluvium and to determine the source area for any loess deposit(s). Two silty deposits were identified on the terrace by morphology, fine‐earth and clay‐free particle size distribution, and total Ca and K distribution. Relationships between clay‐free silt fractions and distance from a loess source, which are similar to relationships developed for other loess deposits, were utilized to locate source areas and to demonstrate the loessial nature of both deposits. The surface deposit, Peoria Loess, was correlated as a continuation of the Peoria Loess on Crowley's Ridge which had its source area in the lowlands east of Crowley's Ridge. The lower deposit, correlated as Loveland Silt, had a well‐developed paleosol in its upper part. The main source area for this loess was the lowlands west of the study terrace.
Conservation Tillage Systems for Cotton Production
Authors: Brown S. M. , Whitwell T. , Touchton J. T. , Burmester C. H.
Published: July 2010

Cotton (Gossypium hirsutum L.) production is intensive in many areas of the southeastern USA, and the common tillage system used is a highly erosive fall plow‐winter fallow‐spring disk. The primary purpose of this 3‐yr field study was to evaluate seeding systems for winter cover crops, effect of cover crop management on cotton production, and N fertilizer requirements for cotton following various winter cover crops. Treatments consisted of (i) winter cropping systems [fall plow‐winter fallow; winter fallow; and three cover crops, rye (Secale cereale L.), hairy vetch (Vicia villosa Roth.), and crimson clover (Trifolium incarnatum L.)]; (ii) cover crop seeding methods (broadcast interseeded prior to cotton defoliation or drill seeded after picking); (iii) spring tillage (disk or no tillage prior to cotton planting); and (iv) N rates for cotton (0, 34, 67, and 101 kg N ha−1). The soil was a Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults). Interseeding resulted in adequate cover crop stands for all covers each year, but drill seeded clover winter killed 2 out of 3 yr. Total N in the legume tissue at cotton planting was higher for interseeded (120–145 kg N ha−1) than drill seeded (33–86 kg N ha−1). In 1 of the 3 yr, cotton seedling mortality was higher with no tillage than disk tillage. None of the conservation‐tillage systems resulted in higher cotton yields than the fall plow system. Planting into killed rye resulted in yields equal to the fall plow system, but more fertilizer N (approximately 34 kg N ha−1) was required for cotton planted into rye. When cotton followed vetch, yields were equal to the fall plow system in 2 of the 3 yr, and N fertilizer requirements were reduced approximately 34 kg ha−1. When compared with fall plow, no tillage into clover or winter fallowed soils resulted in inferior cotton yields each year.
Effect of Electrolytic Concentration on the Hydraulic Properties of Depositional Crust
Authors: Shainberg I. , Singer M. J.
Published: July 2010

Depositional crusts form when turbid water infiltrates into soil. These crusts reduce the rate of water penetration. Hydraulic conductivity of two California soils was measured as a function of volume of suspension infiltrated and electrolytic concentration in the range ≤ 0.005 M. Whereas the hydraulic conductivity of the bulk soils was not affected by electrolytic concentration; the hydraulic conductivity of the soil columns with depositional crust increased by two orders of magnitude as the electrical conductivity (EC) of the suspension increased from 0.1 to 0.55 dS m−1. Saturated hydraulic conductivity of depositional crust made of flocculated particles was much higher than saturated hydraulic conductivity (HC) of crust made of dispersed clay and silt particles. Drying of the crusted soils destroyed the crust and restored the rate of water penetration. The curves of water penetration in consecutive irrigations were similar to that in the first irrigation. Phosphogypsum maintained high water penetration in three consecutive irrigations by increasing the electrolytic concentration in the solution above the clay flocculation values.
Factors Affecting the Mineralization of Nitrogen in Sewage Sludge Applied to Soils
Authors: Barbarika Alexander , Sikora Lawrence J. , Colacicco Daniel
Published: July 2010

An investigation to determine the factors affecting the rate of N mineralization in sewage sludge amended soils using multiple regression techniques was undertaken. Five published incubation studies involving 11 different sludges were analyzed. Both soil and sludge factors were considered in the statistical analyses. Factors positively affecting mineralization rate were total N content of the soil, and the duration and temperature of the incubation. Negatively affecting mineralization were the C/N ratios of the sludge and soil. Two of the estimated equations resulting from the statistical analyses were tested on the results of a sixth incubation study in which several different sludges were incubated under the same time, temperature, moisture, and amendment rate conditions and a 0.75 correlation coefficient was obtained. The resulting model equation using data from all six studies indicated that soil factors are important variables in predicting mineralization of N in sewage sludge amended soils.
Effects of Phenylphosphorodiamidate and Dicyandiamide on Nitrogen Loss from Flooded Rice
Authors: Simpson J. R. , Freney J. R. , Muirhead W. A. , Leuning R.
Published: July 2010

The effects of a urease inhibitor, phenylphosphorodiamidate (PPD), and a nitrification inhibitor, dicyandiamide (DCD), on the losses, tranformations, and recovery of nitrogen (N) were studied when urea was applied to a flooded rice field near Griffith, New South Wales (NSW). When PPD was applied with urea to the floodwater, urea hydrolysis was not prevented but merely delayed by ∼4 d. Consequently, the accumulation of ammoniacal N in the floodwater was also delayed. The maximum ammoniacal N concentration was reached after 3 d in the urea control, and after 9 d in the urea + PPD treatment. The relative losses of ammonia (NH3) from the treatments thus depended on the temperatures and pH of the floodwater and the windspeeds prevailing during the respective periods when the concentration of ammoniacal N was high. Low windspeeds at 8 to 10‐d after application caused NH3 loss on the PPD‐treated plots to be less than on urea‐only plots, but this was fortuitous and an opposite effect might have occurred. The 15N balance on microplots which received labelled urea showed that PPD addition increased recovery of urea N in the plant‐soil system from 60 to 82%. Plant uptake of labelled N was increased by 56%. After subtracting NH3 volatilization and any other potential losses, the resultant N balance suggested that PPD addition had allowed more urea N to be retained in the soil surface layer (0–10 mm) in such a way that nitrification‐denitrification loss was substantially reduced. The nitrification inhibitor (DCD) had no significant effect on nitrate concentrations in the floodwater, NH3 loss, or recovery of fertilizer N in plants and soil.
Nutritional Complexities Associated with pH Variables in Humid Tropical Soils
Authors: Fox R. L. , Yost R. S. , Saidy N. A. , Kang B. T.
Published: July 2010

Soil fertility problems associated with soil acidity in the humid tropics were identified by observing variations of some growth‐controlling factors along response curves. Data for these curves were generated by liming an Oxisol and an Ultisol of Hawaii so that pH increased progressively, from <5 to > 7. Legumes were grown across the pH gradients. Liming the Oxisol depressed Al concentration in the pH range 4.8 to 5.5 and Mn in the pH range 4.8 to 5.7. Liming did not change solution Ca until pH 5.7 was reached, after which, solution Ca contents of saturation extracts increased exponentially. The beneficial effects of liming Leucaena leucocephala were linear from pH 4.8 to 7.0. Soybean (Glycine max L.) yields increased abruptly at approximately pH 5.9 which corresponded to increased Ca concentration in soil saturation extracts. Indigenous soil microvariability in the humid tropics, although sometimes disastrous to conventional field plot experimentation, provides opportunities for investigating soil‐plant relations in ways that are difficult to duplicate by design. Such variability made possible an indigenous‐function investigation using soybeans growing on an Alfisol of Nigeria. Increasing yield with increasing soil pH of the Alfisol was associated with increased N fixation, and this with decreased Mn in the foliage. Predicted N yield was zero at approximately 600 mg Mn kg−1 leaf tissue. Vigorous soybean plants contained 1.5% leaf K, which was associated with at least 0.25 cmol K kg−1 soil. Exchangeable K was positively correlated with cation exchange capacity, and cation exchange capacity with soil pH. Results of this study demonstrate the complex relationships that exist between soil pH and crop nutrition in the humid tropics. It is unlikely that such complex relationships can be covered by simple unqualified statements about liming such soils.
Characteristics of Wisconsinan Glacial Tills in Indiana and Their Influence on Argillic Horizon Development
Authors: Franzmeier D. P. , Bryant R. B. , Steinhardt G. C.
Published: July 2010

In relatively young soil landscapes the parent material largely controls the properties of soils formed on it. Glaciers of the Tazewell subage (15 000–21 000 yr ago) covered the northern two‐thirds of Indiana and glaciers of the Cary subage (15 000–12 000 yr ago) covered the northern third. Particle size distribution, calcium carbonate equivalent (CCE), and calcite‐dolomite ratio were determined by standard soil characterization procedures on pedons sampled mainly during the course of the soil survey to represent till‐derived soils. These data were grouped into classes according to geographic areas defined by major end moraines and recognized ice‐margin positions and by new boundaries that separate areas shown to have different kinds of till in this study. Tazewell‐age till is mainly loam in texture and has a CCE between 200 and 300 g kg−1 (20 and 30%), but some in the eastern part of the state has CCE around 350 to 400 g kg−1. The Cary‐age till in the north‐central part of the state also has loam (to sandy loam) texture and CCE around 200 to 250 g kg−1. In a series of concentric Cary‐age moraines in the northeast, average clay content increases from 27 to 37% and CCE decreases from 310 to 170 g kg−1 northeastward, reflecting increasing lacustrine influence in the younger tills. The clay content of the B horizon of till‐derived soils is a function of the clay content, CCE, and age of the glacial till parent material.
Phosphorus Losses in Runoff As Affected by Tillage
Authors: Andraski B. J. , Mueller D. H. , Daniel T. C.
Published: July 2010

Little data are available on P losses in runoff from land under conservation tillage (CT) where the surface‐applied fertilizer variable has been eliminated. Thus, simulated rainfall was used to evaluate the comparative effects of four tillage systems on the losses of total P, dissolved molybdate‐reactive P (DMRP) and algal‐available P (AAP) where fertilizer was subsurface banded at planting. Tillage treatments included conventional (CN) and three CT systems: chisel plow (CH), till‐plant (TP) and no‐till (NT). Above‐ground portions of corn (Zea mays L.) plants were removed prior to simulation. Trials were conducted over a 4‐yr period, with individual trials being performed in June and July, September, or October of various years. The NT, CH, and TP treatments reduced total P losses by an average of 81, 70, and 59%, respectively, relative to CN. Concentrations and losses of total P among tillage treatments followed those for sediment concentrations and losses. Concentrations of DMRP were, in most cases, lowest for CN, although differences among treatments were generally small and not significant. With the exception of the first simulated rainfall trial (September 1980), no significant correlation was observed between DMRP concentrations and residue cover. Losses of DMRP for the CT treatments were similar to, or significantly lower than those for CN. Differences in AAP concentrations varied among treatments and sampling periods, although concentrations were usually lowest for NT. The relative percentage of AAP concentrations to total P concentrations increased over the course of this study. This increase was 6, 8, 26% higher for CH, TP, and NT, respectively, relative to CN. Relative to CN, the NT, CH, and TP treatments reduced AAP losses by an average of 63, 58, and 27%, respectively. These results indicate that CT systems can effectively reduce AAP losses in runoff relative to CN, especially at times when high sediment concentrations and losses occur from conventionally tilled land.
Referencing Water Content Effects on Soil Electrical Conductivity—Salinity Calibrations
Authors: Bottraud Jean‐Christophe , Rhoades J. D.
Published: July 2010

The effects of hysteresis on soil electrical conductivity (σa), matric potential (ψm), and σa‐volumetric water content (Θ) relations were evaluated for two matrix materials using laboratory column techniques. These σa‐Θ relations were found to be little dependent on whether changes in soil moisture occurred by drying or wetting. In contrast, σa‐Ψm relations displayed a strong hysteresis effect. It is concluded that Θ is a simpler and more accurate parameter to use for adjusting for soil moisture status when determining soil salinity from measurements of σa.
Field Aging of Transparent Polyethylene Mulches: I. Photometric Properties
Authors: Avissar R. , Mahrer Y. , Margulies L. , Katan J.
Published: July 2010

Field observation of the temperature regime of irrigated plots mulched with new and old (previously used during one solarization season) transparent polyethylene sheets, has shown that higher temperatures prevail under the old sheets. In order to explain this unexpected phenomenon, we measured the photometric properties (absorbance, transmittance, and reflectance in the ultraviolet‐visible and infrared regions of the radiation spectrum) of polyethylene mulches at four aging states encountered during prolonged field utilization. The measurements, carried out both in the field (with pyranometers) and in the laboratory (with spectrophotometers), show that the photometric properties change significantly during the aging process. Fine water droplets that condense on new polyethylene sheets reflect significantly more global radiation and better transmit infrared radiation than the soil deposits and water film found on polyethylene sheets after utilization during one solarization season. The thus increased incoming radiative flux at soil surface can explain the observed higher temperature.
Predicting Loblolly Pine Current Growth and Growth Response to Fertilization
Authors: Hart S. C. , Binkley Dan , Campbell R. G.
Published: July 2010

Various indices of N and P availability were tested for correlation with current stem volume growth and growth response to N + P fertilization of loblolly pine (Pinus taeda L.) plantations in the Coastal Plain of North Carolina. Although no single index or combination of indices significantly correlated with stem volume growth in unfertilized plots, several soil variables correlated well with growth in the fertilized plots (r = 0.79 for extractable soil Al, and r = 0.73 for NH+4‐N extracted by a boiling salt solution). Of the soil variables, only extractable soil Al correlated significantly with growth response to N + P fertilization. Volume growth in the unfertilized plots was the best predictor of growth response to fertilization (r = −0.82). Combining one of the P availability indices (double‐acid extractable or ion exchange resin PO4‐P) with growth in the unfertilized plots significantly increased the model's correlation with growth response (R = 0.88 and 0.93, respectively).
Introduction of Acetylene Into Soil for Measurement of Denitrification
Authors: McConnaughey P. K. , Duxbury J. M.
Published: July 2010

Gaseous N loss via denitrification can be measured with static flux chambers when acetylene (C2H2) is used to block nitrous oxide (N2) reduction. This paper describes a method for the introduction of C2H2 at low concentrations into the soil by diffusion. The method utilizes an above‐ground manifold connected to diffusion tubes inserted in the soil and C2H2 flows through the manifold at a rate of 0.33 mL s−1. Acetylene levels in the soil atmosphere within the flux chamber site ranged from 0.16 to 2.07 mol m−3, and the apparatus did not alter CO2 fluxes as measured by a static chamber method.
Estimating Soil Parameters and Sample Size by Bootstrapping
Authors: Dane J. H. , Reed R. B. , Hopmans J. W.
Published: July 2010

Collecting large numbers of soil samples (observations) to estimate parameters of certain soil properties is not always feasible, especially for undisturbed soil samples. If the number of soil samples is small, however, the usefulness of classical statistics is often limited and an alternative procedure is required to determine statistics of interest. A recently developed, computer‐intensive, statistical procedure; bootstrapping, is discussed for two bulk density applications for which relatively small numbers of observations were obtained. Bulk density was determined at 16 depths along 1.2‐m long soil cores taken at each of 60 locations in a 50‐ by 100‐m cultivated field (Norfolk sandy loam, Typic Paleudults). Initially, 16 locations were sampled. At a later date, the additional 44 locations were sampled at similar soil‐water conditions. For each core, bulk density was determined at 0.20‐, 0.40‐, 0.60‐, 0.80‐, and 1.00‐m depths by a paraffin technique and at 0.14‐, 0.26‐, 0.34‐, 0.46‐, 0.54‐, 0.66‐, 0.74‐, 0.86‐, 0.94‐, 1.06‐, and 1.14‐m depths by a direct method. Semivariograms, determined for each depth, generally showed no evidence of spatial interdependence between locations. Additional statistical tests indicated that the samples for the two dates came from different populations. Bootstrapping was used to determine confidence intervals for the population mean, variance, and range by sampling date without a priori assumptions as to the distribution of bulk density in the population. Bootstrapping was further used to develop a general method for determining the minimum sample size (minimum number of observations) that can be used to estimate the population mean with a selected degree of precision and level of confidence. Application of the bootstrap method indicated not only differences in bulk density on the two sampling dates but also differences in the precision of the bulk density measurement techniques.
A Simple Model to Describe the Dissolution of Phosphate Rock in Soils
Authors: Mackay A. D. , Syers J. K. , Tillman R. W. , Gregg P. E. H.
Published: July 2010

Dissolution of phosphate rock (PR) in contrasting soils was evaluated by extraction with 0.5 M NaOH following a prewash with 1 M NaCl to remove exchangeable Ca2+. This provides a simple and direct method for measuring the rate and extent of PR dissolution in soils. Dissolution of Sechura phosphate rock (SPR) in six soils was essentially complete at 90 d and the pattern of dissolution could be described by a modified Mitscherlich equation of the form y = A (1 − e‐ex), in which y = amount of SPR dissolved at time x; A = asymptote, and c = curvature coefficient. Whereas A varied markedly across soils, c was independent of soil type. This exponential equation formed the basis of a simple model which describes and predicts the dissolution of SPR in soils. By establishing the relationship between A and a range of properties for 30 contrasting soils it was possible to identify those soil parameters that controlled PR dissolution in soil. Percent Ca‐saturation, P‐sorption capacity, and Ca‐exchange capacity of the soil were the three most important parameters influencing SPR dissolution in soils. When a model incorporating these three parameters was tested on soils not used to construct the model, the variance accounted for ranged from 66 to 76%, depending on the population of soils selected. These parameters determine the concentrations of Ca2+ and H2PO‐4 in the soil solution.
Small Grain Response to Potassium Fertilizers as Related to Soil and Site Characteristics
Authors: Veeh R. H. , Skogley E. O.
Published: July 2010

The major objective of this study was to determine what environmental characteristics best related to increased small grain yield when fertilizer K was included in a balanced soil fertility management program. These results would help explain why contemporary soil test approaches for predicting crop response to applied K fertilizers do not work in this region, and help lead to alternative approaches to resolve this problem. Two hundred twenty‐two small grain experiments established over a 13 yr period on 127 site locations throughout the Great Plains of Montana were selected for this study. Two to five rates of K, ranging from 0 to 135 kg K/ha, had been applied in the field experiments. Both KCl and K2SO4 were included as fertilizer sources in most experiments. Adequate rates of N and P were constant within an experiment, but varied from one experiment to another. Originally a total of 47 independent variables in various combinations were used in 45 multiple linear regression analyses. The dependent variables were (i) maximum, and (ii) average percent grain yield response to applied K. The statistical analysis was confounded considerably because of missing data for certain independent variables at some sites and because of intercorrelations between variables; however, significant relationships (simple r) existed in many of the regression analyses between independent variables and the dependent variables. In the final analyses, 32 sites were examined using 27 independent variables with a universal data base. Variables with the highest correlation to percent yield response (in decreasing order) were: (i) dry consistence of the Bk horizon; (ii) textural family; (iii) average soil temperature in May; (iv) growing season rainfall; and (v) stored spring soil moisture from 0 to 90 cm. Together these five variables produced a significant R2 of 0.34 (P=0.05).
Soil‐landscape Relationships and Soil Variability in North Central Florida
Authors: Ovalles F. A. , Collins M. E.
Published: July 2010

Morphological and selected chemical and physical properties of 12 pedons on three landscape positions (summit, shoulder, and backslope) were determined to evaluate how soil properties and landscape positions are related in north central Florida. A multistage nested design was employed to compare the variance of selected soil properties within and between landscape positions. Soil properties in the study area were related to landscape position. Soil‐landscape relationships were enhanced by the nonuniformity of the parent material. The parent material of the soils studied on the backslope was the clayey‐phosphatic Hawthorn Formation. This geologic formation also influenced the genesis of the soils on the shoulder but to a lesser extent. The soils on the summit were developed from sandy marine sediments. Classification problems were encountered for some of the soils on the shoulder and all of the soils studied on the backslope. The principal differences and trends across the landscape were decreases in A horizon thickness, matrix colors with chroma >2, sand percentage, pH, and organic C content below the A horizon downslope. Mottles and matrix colors with chroma ≤2, silt and clay percentages, and total P contents increased downslope. Clay and total P depth distributions were genetically and statistically related and highly significant (0.01 level) when studied for the whole landscape (rs = 0.77) and for the soils (rs = 0.81) on the backslope. Substantial increases in total P and clay contents were associated with the Hawthorn Formation. Several statistical analyses were performed. Kolmogorov D test showed nonnormal distribution of the data. The x2 test indicated a highly significant (0.01 level) dependence between soil properties and landscape position. Several relationships were masked when the Spearman correlation (rs) analysis was performed using data for the whole landscape. When rs was low (<0.50) for the whole landscape, rs values computed according to landscape position increased. The results of the Kruskal‐Wallis test indicated significant differences (0.01 level) for each soil property, except organic C, in at least two of the three landscapes. In a nested design >50% of the variability for pH in KCl, total P, sand, silt, and clay was due to differences between landscapes. For organic C content, >70% of its variability was due to differences between horizons.
Effects of Soil Drying on Ammonia Volatilization from Surface‐applied Urea
Authors: Ferguson R. B. , Kissel D. E.
Published: July 2010

Two laboratory experiments were conducted to evaluate the effects of rapid soil drying on the potential for ammonia (NH3) volatilization from urea. Urea was applied to the surface of a sandy loam soil in acrylic chambers at a rate equivalent to 200 kg N ha−1. Static traps for NH3 and carbon dioxide (CO2) were added to the chambers and left in place for 48 h. Humid or relatively dry air was passed over the soil in the chambers between 48 and 72 h at rates sufficient to not inhibit NH3 volatilization. Concentrations of NH3 in the airstream leaving the chambers was monitored during this period. At 48 and 72 h, soil in selected chambers was sampled in 2‐mm depth increments and analyzed for pH, urea‐N, and ammonium‐nitrate (NH4+‐N). Rapid drying of the soil was found to rapidly decrease the rate of NH3 loss from the soil. Drying also reduced the amount of urea that hydrolyzed during the period from 48 to 72 h to practically zero. In the surface 2 mm, the urea concentration of the chambers receiving the dry air treatment increased substantially during the period of airflow. This increase was due to the mass flow of urea towards the soil surface as water evaporated from the soil. These data indicate that the potential for NH3 volatilization from urea applied to a soil that is initially moist but dries rapidly is low, if the soil water content/potential falls to a level at which urea hydrolysis is inhibited.
The Adsorption of o‐Phosphate on Alumina: A Solid Solution Model
Authors: Miller J. W. , Logan T. J. , Bigham J. M.
Published: July 2010

Alumina‐P interactions were examined over a range of PO4 concentrations (0.8 µM‐0.2 mM) and pH's (7–9) conducive to adsorption rather than precipitation. The equilibria established were interpreted using chemical thermodynamic concepts to distinguish adsorption from precipitation and to evaluate the nature of the surface interaction. The chemical speciation model GEOCHEM, supplied with selected thermodynamic values, was used to predict adsorption‐free equilibria for the aqueous PO4/alumina systems. Relative to these predictions, the adsorption of PO4 increased soluble Al levels, apparently as a result of increasing the solid alumina surface activity. The formation of a soluble Al‐PO4 complex did not appear to contribute significantly to total soluble Al. The total soluble Al and PO4 concentration product was pH and total P addition dependent, as expected for equilibria controlled by the presence of a solid solution. An estimate of the ratio of activity coefficients, calculated for differing total PO4, indicated that the activity coefficient of the Al‐OH‐PO4 surface component increased with increasing amount of PO4 added. It was concluded that adsorption of PO4 at the inorganic oxide surface could be viewed as the formation of a surface‐limited solid solution. An attempt to apply a solid solution quasithermodynamic model to soil PO4 adsorption appears warranted, with particular emphasis on Fe, Al, and Ca oxide and carbonate minerals as the primary matrix for adsorption/solid solution formation.
Alfalfa Stand Losses from Irrigation: Influence of Soil Temperature, Texture, and Aeration Status
Authors: Meek B. D. , Donovan T. J. , Graham L. E.
Published: July 2010

Losses of alfalfa (Medicago sativa L.) occur under the combination of high summer temperatures and clay soils. This paper examines the relationship between these losses and soil temperature, texture, and aeration. The study consisted of short tests (one irrigation) and long‐term experiments (2.5 yr) in the field, and gas exchange experiments in a greenhouse. The design for the field experiments was a randomized block with four replications for the short‐term experiments and three replications for the long‐term experiment. It was necessary to flood 56 h (silty clay soil under high temperatures) to damage alfalfa in the field. Root damage was only 1% in a clay loam soil compared to 10% in a silty clay soil (56‐h flooding time and high temperature). Sufficient water could not be applied in the long term experiment to the alfalfa to leach salts (84% Epan treatment) without severe losses in stand. Long flooding times (96 h) at medium temperatures (maximum air temperature 32°C) did not result in root damage to the alfalfa. Oxygen deficiency, not ethylene toxicity, seemed to be the problem when alfalfa was flooded. Ethylene levels in the field were low and symptoms of toxicity were not observed. In the greenhouse, no damage to alfalfa occurred until O2 fell to 0.01 L/L at high temperatures. Results of this experiment indicate that there is a high probability of damage to grower fields when O2 stress under high temperature extends over many irrigations.
Physical and Chemical Soil Properties of Three Big Sagebrush Subspecies
Authors: Swanson Sherman R. , Simonson Gerald H. , Buckhouse John C.
Published: July 2010

The three subspecies of Artemisia tridentata Nutt. typically occupy qualitatively different sites. Wyoming big sagebrush, A. t. ssp. wyomingensis, commonly grows in Aridisols; mountain big sagebrush, A. t. ssp. vaseyana, commonly lives in Mollisols at a higher average elevation; and basin big sagebrush, A. t. ssp. tridentata, occurs in deep soils of either order. This study evaluated some physical and chemical characteristics of surface and subsurface soil horizons of soils occupied by each subspecies in four widely spaced Oregon locations. Most soil chemical characteristics showed no significant differences between subspecies. Interaction between location and subspecies often indicated that analysis should proceed at each individual location. The Frenchglen location had the greatest elevational differences between sites and also had most statistically significant soil differences between subspecies. Many of the measured characteristics are interrelated and differences in them probably are influenced by elevation‐related variation in climate. Surface horizons of Frenchglen, A. t. ssp. vaseyana sites had lower pH, base saturation, and exchangeable Na+ and higher organic matter, cation exchange capacity, and water retention at −1.50 MPa than surface horizons of A. t. ssp. wyomingensis sites. Fewer surface soil characteristics of A. t. ssp. tridentata sites were significantly different. In deeper soil horizons at Frenchglen, A. t. ssp. vaseyana sites had lower pH and base saturation than A. t. ssp. tridentata sites.