bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Equilibration Method for Cation‐Exchange Capacity Measurement
Authors: Matsue Naoto , Wada Koji
Published: July 2010

A method is proposed for the measurement of cation‐exchange capacity (CEC) of leached soils carrying both variable and constant negative charges at conditions pertinent to the field. The method consists of equilibrating a soil with 0.01 M SrCl2 (five centrifuge washings), replacing the retained Sr with 0.5 M HCl (one centrifuge washing) and determining the replaced Sr by atomic absorption spectrophotometry. The equilibrium pH is measured with the final 0.01 M SrCl2 washing. If desired, exchangeable bases and Al can be determined by collecting the 0.01 M SrCl2 washings. This method was developed because we found that the Gillman's BaCl2‐MgSO4 CEC method has problems due to specific adsorption of SO2−4. For evaluation, the CEC obtained by the proposed method was compared with the sum of exchangeable bases and Al and with the CEC obtained by other methods including saturation‐equilibration with 1 M SrCl2‐0.01 M SrCl2 and 1 M NH4OAc‐0.05 M NH4OAc (pH 7.0), respectively.
Corn and Soybean Cropping Effects on Soil Losses and C Factors
Authors: Alberts E. E. , Wendt R. C. , Burwell R. E.
Published: July 2010

Greater soil losses are generally thought to occur with soybean (Glycine max. [L.] Merr.) cropping than with corn (Zea mays L.) cropping. However, runoff and soil losses from corn and soybean cropping systems have been measured simultaneously in only a few studies. The objectives of our study were to evaluate differences in soil and water losses between continuous corn and continuous soybean cropping for conventional, field cultivation, and no‐till methods of tillage; and to evaluate differences between measured cropping and management (C) factors and those in Agricultural Handbook 537, USDA that are currently used in soil conservation planning. These objectives were accomplished by analyzing soil and water loss data from a 7‐yr study conducted on a claypan soil in central Missouri. Cropping differences were evaluated for five seasonal periods based upon cultural operation dates and estimated amounts of canopy cover. Average annual soil loss from soybeans was significantly higher (p <0.01) than that of corn for the conventional and no‐till methods. Seasonal periods having the greatest cropping differences in soil loss were period F (rough fallow), period 12 (30 to 60 d after planting) and period 4 (fall harvest to spring tillage). Annual C factors for soybeans were about two times those of corn for all tillage methods. Measured C factors for all tillage methods were consistently lower than those presented in Agricultural Handbook 537, USDA.
Effects of Two Methods of Timber Harvesting on Microbial Processes in Forest Soil
Authors: Hendrickson O. Q. , Chatarpaul L. , Robinson J. B.
Published: July 2010

Microbial populations and activities in a mature, mixed conifer and hardwood stand were compared with those in similar adjacent stands harvested by conventional (CH) and whole‐tree (WTH) methods. Samples of forest soil (sandy, mixed, frigid Typic Haplorthods) were collected monthly during the first season after harvesting. The NH+4‐N production, measured over the course of 21‐d laboratory incubations, declined in the forest floor of the WTH plot, but increased significantly in mineral soil in both harvested areas. Less than 10% of the NH+4‐N produced was nitrified. Nitrifier and denitrifier populations did not increase during the first year following harvesting, and no significant changes in nitrification activity were noted. Forest floor respiration (measured as CO2 evolved in laboratory incubations) was significantly reduced on both harvested plots relative to the intact stand. Litter bag experiments indicated a reduction in nutrients (N, P, K, Mg) available for decomposer organisms on the WTH plot, and a corresponding reduction in litter decay rates. These effects correspond to reductions in forest floor moisture, water‐holding capacity, and organic matter content after harvesting. In the 0 to 5‐cm mineral soil depth, total bacteria increased on the CH plot but not on the WTH plot. Despite reduced forest floor moisture and nutrient availability, sprouting of trembling aspen (Populus tremuloides Michx.) on the whole tree‐harvested area was vigorous.
Isotopic Triple Labeling in Miscible Displacement Studies
Authors: Nkedi‐Kizza P. , Jackson R. K. , MacIntyre J. L.
Published: July 2010

A technique was developed to analyze three beta‐emitter isotopes (45Ca, 36Cl and 3H2O) in a sample, using a two channel liquid scintillation spectrometer. This technique was further successfully used to analyze the concentration of these isotopes in the effluent during miscible displacement studies through columns packed with an Oxisol soil. The isotopic triple labeling approach was used to investigate the effects of physical and chemical properties of the porous medium during solute transport. Tritium was used to study the effects of the physical properties of the porous medium (aggregate size and flux), while 45Ca (a cation) and 36Cl (an anion) were used to study the effects of the chemical properties (solution pH and concentration) of the same porous medium. This is a promising approach to determine how the physical and chemical properties of a soil interact to influence solute transport.
Steady Absorption from Spheroidal Cavities
Authors: Philip J. R.
Published: July 2010

Exact solutions are given for steady absorption from prolate and oblate spheroidal cavities (or bulbs of saturation). The solutions for the needle, sphere, and disc are special cases. Apart from their direct relevance to systems with gravity negligible, our results yield the leading terms of expansions describing steady infiltration for small and moderate values of the dimensionless cavity (or bulb) length.
Sorption of Copper(II) on Aluminum Hydroxide as Affected by Phosphate
Authors: McBride M. B.
Published: July 2010

The mechanisms of Cu2+ bonding on noncrystalline aluminum hydroxide with or without various levels of presorbed phosphate have been studied by the technique of electron spin resonance. Evidence for two separate chemisorption sites in the absence of phosphate is presented. At high levels of Cu2+ adsorption, discrete site chemisorption is replaced by nucleation or precipitation of hydroxy‐Cu species at the surface. High levels of sorbed phosphate suppress Cu2+ adsorption, blocking the coordination of Cu2+ to AIOH groups on aluminum hydroxide. It is proposed that the decreased adsorption of Cu2+ observed in this study was a result of the weaker coordination of Cu2+ to the phosphate‐coated surface than to the alumina surface in the absence of phosphate. The enhanced adsorption of metal ions on oxide and hydroxide surfaces following phosphate sorption observed in other studies is attributed to a different mechanism, involving the formation of a ternary complex in which Cu bonds simultaneously to phosphate and the surface.
The Occurrence of Extractable Elements in Soils from the Northern Great Plains
Authors: McNeal James M. , Severson R. C. , Gough Larry P.
Published: July 2010

The modes of occurrence of extractable elements from 21 A and C horizon samples of uncultivated soils were examined using R‐mode factor analysis. The extractants (DTPA, EDTA, HCl, hydroquinone, magnesium nitrate, and ammonium oxalate) cover a wide range of chemical attack. Four major elements (Ca, K, Mg, and Na) and eight trace elements (Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) were determined in each extractant solution. A variety of chemical, mineralogical, and physical variables were also determined on each sample. Four varimax factors (clay, organic, Fe and Mn oxides, and soluble‐Na) accounted for 74.2% of the total variance of the 90 variables for the A horizon. Seven varimax factors (Fe and Mn oxides, clay, CEC, soluble‐Na, organic, Fe and Mn, and plagioclase) accounted for 77.2% of the total variance of the 79 variables for the C horizon. A and C horizon extractable trace elements are most generally related to Fe and Mn oxides, as indicated by loadings on the Fe and Mn oxide factor for both the A and C horizons. Each extractant generally operates on different modes of occurrence of an element in soil. For example, substantial differences occur between the HCl‐, oxalate‐, and hydroquinone‐extractable trace elements. However, the modes of occurrence for trace elements removed by DTPA and EDTA were very similar, suggesting strong relationships between elements dissolved by these two extractants. The modes of occurrence for each individual major element are similar with each of the six extractants. A horizon Ca and Mg, and C horizon K and Mg are strongly related to a clay factor. C horizon Ca and A horizon K are strongly related to the CEC and organic factors, respectively. Both A and C horizon extractable Na are very strongly related to the soluble‐Na factor. These results suggest that extractable major elements are water‐soluble and are associated with the constituents that are responsible for that factor. Consequently, strong relationships should occur for any individual major element dissolved by any pair of extractants.
Long‐term Dryland Crop Responses to Residual Phosphorus Fertilizer
Authors: Halvorson A. D. , Black A. L.
Published: July 2010

Little information is available on the long‐term effects of a single P fertilizer application on grain yields of crops grown on dryland soils deficient in plant‐available P. Therefore, duplicate plots were established in 1967 and 1968 on a Williams loam (fine‐loamy mixed, Typic Argiborolls) with a NaHCO3−extractable P of 6 mg P/kg soil. A split‐plot, randomized complete block design was used with three levels of available N (generally 0, 45, and 90 kg N/ha each crop year) as main plots and a one time application of P fertilizer at rates of 0, 22, 45, 90, and 180 kg P/ha as subplots. During the first crop year, application of 22, 45, 90, and 180 kg P/ha raised the average soil test P levels to 9, 12, 26, and 40 mg P/kg soil, respectively. Soil test P levels 16 yr after P fertilization and 10 or 11 crops harvested avg 5, 6, 7, 9, and 13 mg P/kg soil in 1983 for these same respective P treatments. Soil test P levels declined progressively with each additional crop year until the eighth crop or 13 yr after P application, at which time a new soil P equilibrium level appeared to be developing. Grain yields generally increased with increasing residual soil P level when adequate levels of N, either residual or applied, were present. However, no response to increasing residual soil P level was observed under annual cropping without adequate N. Accumulated grain yields after 10 or 11 crops were about three times greater with both N and P fertilization than with P fertilization alone. The study verifies that adequate available N is required to derive benefit from residual P fertilizer. The long‐term (16 yr) residual benefits from P fertilization suggest a method for possibly satisfying the P needs for several crop years in reduced and notillage systems, if the P is applied and incorporated before initiation of these tillage systems.
Changes in Soil Properties Under Annual Applications of Feedlot Manure and Different Tillage Practices
Authors: Sommerfeldt T. G. , Chang C.
Published: July 2010

A long‐term manure study was set up in which cattle feedlot manure was applied annually at four rates to nonirrigated and irrigated land and was incorporated into the soil by plow, rototiller, or cultivator. The soil is a Dark Brown Chernozem (Typic Haploborolls) at the Lethbridge Research Station. The effects of the manure, incorporated by different methods, on the physical properties and organic matter content of the soil were determined. On both nonirrigated and irrigated land, the soil organic matter content of the surface 0 to 15 cm increased with increasing rates of manure application. Spring‐time soil temperatures, at 8‐cm depth, were coldest where the highest rate of manure had been incorporated. Drawbar draft decreased with increasing rates of manure application. Similarly, bulk density of the surface 0 to 15 cm of soil decreased with increasing rates of manure application, the greatest effect being where the manure had been incorporated by cultivator on irrigated land. But, at 15 to 30‐cm depth, the smallest bulk density was where the manure had been incorporated by plow. Increasing rates of manure on irrigated land tended to decrease the amount of aggregates < 1 mm and increase the amount > 1 mm in size, at the 15 to 30‐cm depth. These results indicate that manure, applied at the relatively low rates that are currently recommended, can maintain and increase the organic matter content of the soil and ameliorate the physical condition of southern Alberta soils.
Tillage Effects on Soil Water Retention and Pore Size Distribution of Two Mollisols
Authors: Hill R. L. , Horton R. , Cruse R. M.
Published: July 2010

A study was conducted to determine the effects of conservation and conventional tillage on soil water retention and pore size distribution of two mollisols. Two locations were used, each having randomized complete‐block designs with three replications of continuous‐corn (Zea mays L.) plots under no‐tillage, reduced tillage, and conventional tillage. One location, site 1, was in its 2nd yr of tillage experimentation on a Canisteo series soil (Typic Haplaquolls), and the other location, site 2, was in its 8th yr on a Nicollet series soil (Aquic Hapludolls). Undisturbed soil cores were obtained near the planted row at the 5.0‐ to 7.5‐cm and 10.0‐ to 12.5‐cm depths from the two sites. Soil water retention of the soil cores was measured at water matric potentials of 0 to −39.22 kPa. Pore size distribution was estimated by using a capillary model. Statistical differences in soil water retention due to tillage treatments appeared at site 1, with general means comparisons of reduced tillage > no tillage > conventional tillage in the amount of water retained at any matric potential. Reduced tilled soil generally retained a significantly (LSD 0.05) larger quantity of water than conventionally tilled soil. No‐tilled soil was not significantly different from reduced tilled or conventionally tilled soil in its water retention characteristics. Differences in water retention between tillage treatments were not significant at site 2, but trends in the means comparisons similar to those of site 1, were observed. Analysis of variance failed to show significant tillage effects for the pore size distribution regardless of pore radius interval partitioning. Trends indicated that soil under conventional tillage had a larger proportion of its pore volume in pores > 15 µm radii compared with soils under conservation tillage. Conservation tilled soils appeared to have a larger portion of pores in the 15‐ to 0.1‐µm pore radius interval. Implications are that conventionally tilled soils should drain more rapidly than conservation tilled soils and that conservation tilled soils should retain more plant available water than conventionally tilled soils. The data indicate that bulk density increases occurred at the expense of larger pores (>150‐µm radii). Because conventionally tilled soils have the greater proportion of large pores, these soils seem to be more susceptible to densification than the soils under the conservation tillage systems.
Tillage Effects on Bulk Density and Soil Strength of Two Mollisols
Authors: Hill R. L. , Cruse R. M.
Published: July 2010

Farmers in the Midwest are concerned that continuous no‐tillage cultivation may be causing soil compaction within their fields. A study was conducted to determine the effects of conservation and conventional tillage on soil bulk density and soil strength of two Mollisols. Two locations, each having randomized complete‐block designs with three replications of continuous corn plots under no‐tillage, reduced tillage, and conventional tillage were used. One location, site 1, was in its 2nd yr of tillage experimentation and the other location, site 2, was in its 8th yr of tillage experimentation. Gamma irradiation was used to determine bulk densities of undisturbed soil cores. Soil strength was determined by using a fall cone penetrometer at soil water matric potentials of 0, −20, and −40 kPa. Tillage treatments did not have a statistically significant effect on bulk density at either site. Bulk density increased significantly with depth for the three tillage treatments at both sites. Tillage treatments had significant effects on soil strength at site 2, but not at site 1. Strength of soil at site 2 under reduced tillage was not significantly different than for soils under no‐tillage, but the soils under both these tillage systems had significantly greater soil strengths than that observed for conventionally tilled soil. The pattern of differences in soil strength due to tillage treatment was the same at site 1, but the differences were not statistically significant. Soil strength increased with decreased matric potential for the three tillage treatments of both sites. Neither bulk density nor soil strength of the soils under any of the tillage systems for the 0 to −40 kPa matric potential range appeared to be large enough to have an appreciable inhibitory effect on plant root growth.
Effects of Tractor Logging on Soils and Vegetation in Eastern Oregon
Authors: Snider Michael D. , Miller Richard F.
Published: July 2010

Soil characteristics were investigated on a mixed conifer forest stand in Oregon's Blue Mountains. The most recent logging had occurred on the site 6 yr previously; 1 yr after harvest, slash was machine‐piled and burned. Five classes of ground disturbance including a control were identified, based on degree of soil and ground cover disruption. Bulk density of the disturbed classes was not significantly different from control areas. Infiltration and saturated hydraulic conductivity rates on both disturbed and control areas were high relative to projected storm intensities. Soil organic matter content in the upper 3 cm of disturbed areas was markedly below that of control areas. Understory vegetation production on seeded skid trails was 66% above that of control areas; however, below ground biomass of control areas, vegetated with native rhizomatous species, was three times that of skid trails.
Oxygen Uptake and Transport in Soils: Analysis of the Air‐water Interfacial Area
Authors: Skopp J.
Published: July 2010

Aeration of soil influences root activity, microbial processes, and chemical reactions. Descriptions of this process have relied on macroscopic concepts which do not allow the incorporation of detailed theories of gas movement. The present study presents a microscopic approach to this problem. Equations are presented to describe the movement of gas. The following parameters are of importance in this theory: gas phase diffusion coefficient, air‐water interfacial area, air‐water transfer coefficient, volumetric water content, gas solubility in water, and gas concentration in solution. These parameters are indirectly dependent on total porosity, air‐filled porosity, temperature, solute composition, or microbial activity. The solution to the governing equations suggests that air‐water interfacial area is an important soil physical property which has a controlling influence on oxygen transport. The dependence upon soil moisture of air‐water interfacial area and flux of gas through the soil surface is examined. The qualitative influence of soil texture on this dependence is also examined.
Determining Soil Hydraulic Properties from One‐step Outflow Experiments by Parameter Estimation: I. Theory and Numerical Studies
Authors: Kool J. B. , Parker J. C. , van Genuchten M. Th.
Published: July 2010

The numerical feasibility of determining water retention and hydraulic conductivity functions simultaneously from one‐step pressure outflow experiments on soil cores by a parameter estimation method is evaluated. Soil hydraulic properties are assumed to be represented by van Genuchten's closed‐form expressions involving three unknown parameters: residual moisture content θ, and coefficients α and n. These parameters are evaluated by nonlinear least‐squares fitting of predicted to observed cumulative outflow with time. Numerical experiments were performed for two hypothetical soils to evaluate limitations of the method imposed by constraints of uniqueness and sensitivity to error. Results indicate that an accurate solution of the parameter identification problem may be obtained when (i) input data include cumulative outflow volumes with time corresponding to at least half of the final outflow and additionally the final outflow volume; (ii) final cumulative outflow corresponds to a sufficiently large fraction (e.g., >0.5) of the total water between saturated and residual water contents; (iii) experimental error in outflow measurements is low; and (iv) initial parameter estimates are reasonably close to their true values.
Nitrification and Characteristics of Nitrifying Microorganisms in an Acid Forest Soil
Authors: Kreitinger J. P. , Klein T. M. , Novick N. J. , Alexander M.
Published: July 2010

A study was conducted of factors affecting nitrate (NO‐3) accumulation and characteristics of the nitrifying microflora in the O2 horizon of an acid forest soil (pH 3.6–4.0) from the Adirondacks region of New York. The addition of ammonium (NH+4 did not enhance NO‐3 formation in suspensions of soil, but such an enhancement occurred if the suspensions were amended with peptone or if the soil had been previously leached with distilled water. The effect of additions of NH+4 on NO‐3 production was correlated with the influence of NH+4 on N mineralization. Although levels of 47 µg NH+4‐N/mL stimulated NO‐3 formation in suspensions of leached soil, additions of 94 µg NH+4‐N/mL or more were toxic. The enhancement of nitrification by low concentrations of NH+4 was not accompanied by an increase in CO2 fixation. Nitrapyrin inhibited nitrification in NH+4‐amended but not in unamended suspensions of soil, but it suppressed CO2 fixation in suspensions with and without added NH+4. Nitrapyrin stimulated N and C mineralization. The results show that nitrification in this soil is not the result of classical autotrophic nitrifiers, and a possible role for methylotroph‐type organisms in nitrification is suggested.
Fallow Nitrate Accumulation in a Wheat‐fallow Rotation as Affected by Tillage System
Authors: Lamb J. A. , Peterson G. A. , Fenster C. R.
Published: July 2010

The objectives of this study were to compare NO‐3‐N levels for three tillage systems, and to measure seasonal variation in NO‐3‐N levels during the fallow period of a winter wheat (Triticum aestivum L.) crop‐fallow rotation. The study was conducted on two sites, Duroc loam (Pachic Haplustolls) which was broken from native sod in 1970, and Alliance silt loam (Aridic Argiustolls) which had been cultivated 30 to 40 yr prior to establishment of the experiment, at the High Plains Ag Lab, Sidney, NE.

No‐till, stubble mulch, and plow (bare fallow) treatments were established in 1970. In the first 2 yr at the Duroc site, the no‐till and stubble mulch tillage system soils accumulated 64 and 73% as much NO‐3‐N as the plow soil, respectively. Except 1975 and 1980, the NO‐3‐N accumulation from tillage systems from 1974 to 1980 was not different. From 1970 to 1975 NO‐3‐N accumulation in no‐till and stubble mulch soils at the Alliance site was different with no‐till and stubble mulch having 67 and 71%, respectively, as much NO‐3‐N as plowed soils. From 1976 to 1983, except 1981 and 1982, the NO‐3‐N accumulation under the different tillage systems was not different. The fallow portion of the experiments were sampled every 21 d between 1981 and 1983. Neither rate nor the beginning point of accumulation was affected at either site by tillage system. The date during fallow when a soil sample for N fertilizer recommendation was taken was important. A sample taken in July would only have 50 to 60% of the NO‐3‐N found at seeding time.
Tillage Effects on Soil Temperature, Soil Water, and Wheat Growth in South Australia
Authors: Radke J. K. , Dexter A. R. , Devine O. J.
Published: July 2010

Plots of an Urrbrae fine sandy loam (Rhodoxeralf) were tilled with either a scarifier (tine digger) or a rotary cultivator (rotovator), or left untilled as checks. Wheat (Triticum aestivum L. cv. Gabo) was planted 9 June 1981 on half of the tilled plots resulting in five treatments randomized over plots in each of three replicates. Soil temperatures at the 50‐mm depth and microclimate variables were measured every half hour in one replicate only. Soil water content in the surface 10 mm was measured at 0800 and 1600 h on work days in two replicates. Soil water profiles, plant heights, soil structure, and penetrometer resistances were determined at various times on selected plots and replicates during the growing season. June and July were unusually cool and wet and wheat growth was slow. After 12 August, wheat grown on rotovated plots was significantly taller and yielded more at harvest in December than wheat grown on scarified plots. Soil temperatures at 50 mm differed only slightly among treatments except for wheat vs. no‐crop where the wheat plots had lower daytime soil temperatures after 8 September. Soil water in the surface 10 mm tended to be greater for scarified treatments than for rotovated treatments until late August. It was concluded that differences in wheat plant height were related to soil structure and soil water but not to soil temperature.
Effect of Three Conservation Tillage Practices on Soil Temperature and Thermal Properties
Authors: Johnson M. D. , Lowery B.
Published: July 2010

Three conservation tillage systems, chisel (CH), till‐plant (TP), and no‐till (NT), were compared to conventional (moldboard) tillage (CN) for differences in depth zone (5 cm) and upper profile (5–15 cm) soil temperatures and related soil thermal properties. In‐row spring soil temperatures were highest in CN, slightly lower in TP and CH, and lowest in NT. The maximum difference in daily average temperature observed between tillage treatments occurred on 2 May 1982 when the NT, CH, and TP treatments were 5.9, 2.3, and 1.8°C cooler than CN, respectively. Soil thermal diffusivity (K') in the 5‐ to 15‐cm zone was 20 to 25% higher in the NT treatment than in the CN and CH treatments, which were not significantly different. In 1 of 2 yr, K' was significantly higher in the TP treatment than in the CN and CH treatments. The reduction in soil temperatures observed with conservation tillage was attributed to differences in thermal admittance (µ), heat flux to deeper depth, and total heat inputs to the soil profile. The higher thermal admittance and heat flux in the NT treatment produced lower upper profile soil temperature.
Point and Line Infiltration—Calculation of the Wetted Soil Surface
Authors: Warrick A. W.
Published: July 2010

For water introduced at a point on the soil surface a finite‐sized area becomes wetted which is not exceeded for large times. Similarly, a wetted strip develops parallel to a surface line source. In this paper, relationships are derived to provide the limiting (steady‐state) extent of these wetted areas. The quasi‐linear assumption necessary for solution is that the unsaturated conductivity K is Ko exp(αh) with h the pressure head (matric potential as a length) and Ko and α constants. Results for the area around a point is in near agreement with Wooding's (1968) approximation Ko/α2q = (πα2ro2 + 4αro)−1 for a slightly different surface boundary condition (ro is the wetted radius and q is the volume of discharge per unit time). For the strip the dimensionless quantity Ko/αqL = (3.96 αxo/2 + 0.721)−1 is a valid approximation for αxo/2 <5 where qL is the rate of discharge per unit length and 2xo the wetted width. For larger αxo/2 the simpler one‐dimensional relationship Ko/αqL = 1/(2αxo) suffices. The results are relevant with respect to trickle (drip) irrigation.
The Spectrophotometric Determination of Dissolved Organic Carbon in Peat Waters
Authors: Moore T. R.
Published: July 2010

Based on spectra of peat water samples representing a range of geochemical origin from minerotrophic fens to ombrotrophic bogs, dissolved organic carbon (DOC) was only weakly predicted (r2 = 0.710) by absorbance at 330 nm. Differences in molecular weight fractions in the dissolved organic matter apparently did not affect the correlation. Major improvement in the predictive power of absorbance at 330 nm was produced by inclusion of the Fe content of the peat water (r2 = 0.962), which can be determined simply as o‐phenanthroline reactive Fe. Dichromate‐oxidizable organic C was also predicted well from absorbance at 330 nm.
Effects of pH and Organic Acids on Orthophosphate Solubility in an Acidic, Montmorillonitic Soil
Authors: Traina Samuel J. , Sposito Garrison , Hesterberg Dean , Kafkafi U.
Published: July 2010

The effects of pH and organic acid addition on residual orthophosphate (o‐phosphate) solubility in an acidic, montmorillonitic soil separate suspended in 20 mol NaCl m−3 were investigated. In the absence of added organic acid, the solubility of residual o‐phosphate in the soil decreased as the pH value was increased from 4 to 7. With o‐phosphate additions that resulted in low aqueous‐solution o‐phosphate concentrations, the soil sorbed more o‐phosphate at pH 7 than at 5.5. The solubility data appeared consistent with the presence of an Al‐phosphate solid whose formation was initiated through the hydrolysis of exchangeable Al3+ and subsequent reaction of the hydrolytic product with o‐phosphate in aqueous solution. Additions of citric, tartaric, or formic acid at low concentrations (<0.1 mol m−3) produced a drop in residual o‐phosphate solubility at pH 5.5 and 7.0. In the case of citric acid, o‐phosphate solubility gradually returned to its value in the absence of organic ligand as the ligand concentration was increased to 0.6 mol m−3, whereas no such increase occurred in the case of tartaric or formic acid. This behavior was rationalized as the outcome principally of two competing reactions: (i) the reaction of adsorbed, polymeric hydroxy‐Al with organic ligand to form an exchangeable Al species that combined with o‐phosphate to reduce its solubility, and (ii) the complexation of adsorbed Al to form a soluble Al‐organic complex that did not subsequently combine with o‐phosphate. The latter reaction was important only for citric acid. The former reaction, favored by a large stability constant for Al‐organic acid adducts, produced o‐phosphate solubility decreases in the order citrate > tartrate > formate.
Ammonia Volatilization from Nitrogen Sources Applied to Rice Fields: I. Methodology, Ammonia Fluxes, and Nitrogen‐15 Loss
Authors: Fillery I. R. P. , De Datta S. K.
Published: July 2010

The extent of NH3 volatilization from (NH4)2SO4, urea, and urea amended with the urease inhibitor, phenyl phosphorodiamidate (PPD), was studied concurrently in flooded rice (Oryza sativa L.) by using nondisturbing micrometeorological techniques. Nitrogen‐15 balance techniques were used to estimate the total 15N loss and the relative contribution of NH3 volatilization and nitrification‐denitrification to the N loss. N sources were applied to the floodwater 18 d after the transplanting of rice seedlings (AT treatments). Ammonia volatilization proceeded rapidly after the application of (NH4)2SO4 and urea, although the pattern of NH3 loss differed between the N sources. Ammonia fluxes accounted for 38 and 36% of the N applied as (NH4)2SO4 or urea, respectively, in an 8‐d period. A lower rate of NH3 loss (22% N applied) occurred within the same period from a field amended with urea + PPD (1% wt/wt), primarily because NH3 fluxes were negligible for at least 3 d after urea was applied. The total 15N loss at the termination of the NH3 loss measurements accounted for 44 and 41% of the (NH4)2SO4 and urea N, respectively. A significantly (P ≦0.05) lower 15N loss (33% N applied) occurred when a nitrification inhibitor (nitrapyrin) was applied with urea. These results suggested that nitrification‐denitrification may have contributed slightly to the total N loss from urea. Nitrapyrin did not significantly (P <0.05) affect 15N loss from microplots amended with (NH4)2SO4. A simplified micrometeorological technique that used wind speed and atmospheric NH3 concentrations at a single predetermined height to measure NH3 fluxes accurately estimated fluxes (R2 = 0.99) that were determined by the horizontal flux or mass balance technique. An indirect estimate of NH3 loss based on the rate of 15N loss from nitrapyrin and urea amended microplots (33% N applied) was similar to the total NH3 loss computed with the mass balance micrometeorological technique (36% N applied). This finding confirms the reliability of the mass balance micrometeorological technique used in NH3 loss measurements.
Uptake of Nitrogen from Soil, Fertilizer, and Crop Residues by No‐till Corn and Soybean
Authors: Power J. F. , Doran J. W. , Wilhelm W. W.
Published: July 2010

The relative availability of nitrogen (N) from indigenous soil organic N, immobilized fertilizer N, currently applied fertilizer N, and crop residues is largely unknown. A nonirrigated experiment was conducted on a silty clay loam at Lincoln, NE, with both continuous soybean [Glycine max (L.) Merr.] and corn (Zea mays L.), in which crops were produced with no tillage after surface application of 0, 0.5, 1.0, or 1.5 times the quantity of aboveground crop residue produced the previous year. In 1980 and 1981, depleted 15N NH4NO3 (at 45 kg N ha−1) and crop residues were managed so that labeled isotope taken up in the 1981 crop could be separated into that from crop residues, from 1st‐yr fertilizer that had become immobilized, from fertilizer N applied the 2nd yr, and from indigenous soil N (plus fixed N for soybean).

Grain and straw (stover) production of both crops in 1981 were increased 2000 to 3000 kg ha−1 by increasing crop residue rate. Almost all the N in soybean residues was mineralized and taken up by the second crop, with most of this uptake occurring after mid‐July. Uptake by soybean of labeled N immobilized in soil organic matter the previous year increased from about 2 to 6 kg N ha−1 as residue rate increased, possibly originating mainly from N temporarily immobilized in microbial biomass. Uptake by soybean of current‐year fertilizer N also increased slightly with residue rate. The fraction of total N in soybean derived from indigenous soil (plus fixed) N decreased with increased residue rate from about 85% for no residues to 55% for the 1.5 residue rate. For corn, essentially none of the N immobilized in corn residues was recovered by the next crop at any residue rate. Uptake of labeled N immobilized in soil organic matter was not affected by residue rate, but uptake from 1981 fertilizer treatment increased about 6 kg ha−1 with increased residue rate. Over 80% of the total N uptake by corn in 1981 came from indigenous soil N, regardless of residue rate.
Coastal Plain Soils of Southeastern Nigeria: II. Forms of Extractable Iron, Aluminum, and Phosphorus
Authors: Lekwa G. , Whiteside E. P.
Published: July 2010

The distribution of citrate dithionite and ammonium‐oxalate extractable Fe2O3 and Al2O3 were determined in nine Coastal Plain pedons of southeastern Nigeria. Distribution of available, organic, and active inorganic forms of P, plus the P fixation and available water holding capacities of these soils were also studied. The dithionite extractable Fe2O3 and Al2O3 generally increased with depth and clay contents in each of the six, loamy, well drained pedons studied. The active Fe ratio usually decreased with depth, suggesting that higher proportions of Fe2O3 were generally present in more crystalline forms in the lower horizons of the well drained soils. The active Al ratio usually increased with depth, but it was high throughout in the more poorly drained, loamy aquic pedons. The well drained ustic pedons contained larger amounts of Fe2O3‐d than did the well drained udic pedons. They also contained more Fe2O3‐d than Al2O3‐d, and the active Fe ratios were higher (≧ 3). The loamy udic pedons and the loamy aquic pedons contained larger amounts of Al2O3‐d than Fe2O3‐d, particularly in the latter. The sandy Aquod was very low in dithionite and oxalate Fe2O3 and Al2O3, except that the spodic horizon had maxima of dithionite and oxalate Fe2O3. Available and total active P contents of the studied soils were generally low. The relative abundance of the extractable inorganic P forms was generally in the order of Fe‐P > Al‐P > Ca‐P in the well‐drained loamy pedons. Organic P in all the pedons was relatively high in the surface horizons and constitutes the most abundant form of P measured in these soils. Phosphorus fixation increased with depth and showed close positive correlations with free iron oxide and clay contents.
Formation of Ferrihydrite by Inhibition of Green Rust Structures in the Presence of Silicon
Authors: Karim Zahurul
Published: July 2010

The initial phase formed during neutralization and partial oxidation of ferrous chloride solutions, with XRD reflections at 0.258 and 0.155 nm, is a close‐packed oxygen/hydroxyl sheet. The presence or absence of Si determines, apparently, what happens to the initial phase as oxidation proceeds. In the absence of Si, the initial phase further reacts to form green rust, presumably a double hydroxide of ferrous and ferric Fe which ultimately forms lepidocrocite. In the presence of Si, the formation of green rust structure from the initial phase is inhibited, as evidenced by symmetrical basal and asymmetrical hk x‐ray diffraction (XRD) lines, and ferrihydrite is the ultimate oxidation product.
Soil Equilibration with Minimal Solution Loss
Authors: Hooper Ginger K. , Kittrick J.A.
Published: July 2010

Both gas exchange and moisture loss are important experimental variables influencing the attainment of equilibria in CO2‐dependent systems. The Kimble permeable membrane (PM) cap and perforated parafilm were tested for both CO2 flow across the membrane and moisture holding ability. Samples of calcite and calcite + soil were equilibrated in an open atmosphere (of known CO2 content). No significant difference in pH − 1/2pCa2+ − 1/2pCO2 was found between the PM cap and the parafilm, perforated to allow gas exchange. However, the moisture loss for perforated parafilm was 10 times greater than with the PM cap.
Calculation of Microbial Maintenance Rates and Net Nitrogen Mineralization in Soil at Steady‐state
Authors: Smith J. L. , McNeal B. L. , Cheng H. H. , Campbell G. S.
Published: July 2010

Product formation equations were used for the calculation of specific maintenance energy rates for soil microbial biomass and incorporated into a conceptual model for maintenance C flow. The model separates active and sustaining biomass and includes considerations for endogenous catabolism, cryptic growth, and microbial death. Coupling of the model with product formation equations enabled the calculation of specific maintenance rates for five soils, using data from a 60‐d incubation. Calculated maintenance rates were approximately half the values commonly reported for soils and used in ecosystem models. With the use of the calculated specific maintenance rates, the conceptual model and data from a 60‐d incubation, the net soil N mineralized during the steady‐state period could also be calculated. The resultant C/N ratio of the biomass formed during this period was 7.6. Calculations involving N provided verification of the maintenance rate calculations and of the validity of the conceptual model.
Organic Carbon and Nitrogen Changes in Soil Under Selected Cropping Systems
Authors: Zielke R. C. , Christenson D. R.
Published: July 2010

The use of different cropping systems is one means of conserving soil organic matter. This study was conducted to evaluate the effect of 9 yr of selected cropping systems on organic C (WBC), N levels (TKN), and N mineralization characteristics (BMN) of a Charity clay (Aeric Haplaquepts). The six cropping systems consisted of combinations of corn (Zea mays L.), oats (Avena sativa L.), alfalfa (Medicago sativa L.), sugarbeets (Beta vulgaris L.), and navy beans (Phaseolus vulgaris L.). Each crop in each system was fertilized at recommended rates. Cropping systems that contained corn had up to 10% more WBC and 7% more TKN at the time of sampling than systems that did not contain corn. Nitrogen mineralization characteristics correlated linearly with WBC and TKN using S81 soil samples but not with WBC, TKN, or N uptake in a greenhouse study using F81 soil samples. The uptake and response to applied N in the greenhouse indicated that 9 yr of cropping with a particular system had an effect on the N supplying capacity of the soil. Reduced uptake and larger responses to applied N were observed for systems that did not contain corn and that lost larger amounts of C and N over the 9‐yr cropping period.
Soil pH Effects on the Distribution and Plant Availability of Manganese, Copper, and Zinc
Authors: Sims J. Thomas
Published: July 2010

Crop response to micronutrient fertilization on the poorly buffered coastal plain soils of Delaware has received renewed interest in recent years. Specifically, given the susceptibility of these soils to overliming and the widespread use of manures, questions have been raised concerning the influence of soil pH and micronutrient source on the distribution and plant availability of Mn, Cu, and Zn, Four soils that varied widely in organic matter content (16‐100 g/kg), texture, and cation exchange capacity (CEC) were studied. A fractionation scheme was utilized that partitioned Mn, Cu, and Zn into the exchangeable, organic, Mn‐oxide bound, amorphous Fe‐oxide bound, and crystalline Fe‐oxide bound forms. Micronutrient distribution among these fractions was studied over a pH range of 4.0 to 7.7 in the soils alone, and in the same soils amended with poultry manure (PM) or (MnSO4 + CuSO4 + ZnSO4). The various fractions of each element were then correlated with Mn, Cu, and Zn uptake by wheat (Triticum aestivum L.) in a greenhouse experiment. Soil pH markedly altered the distribution of Mn and Zn but had little effect on Cu. Although soil type did have some influence, exchangeable Mn and Zn were generally the dominant species of the elements below pH 5.2, while at higher pH values organically complexed and Fe‐oxide bound forms were dominant. The majority of soil Cu was in the organic fraction, but considerable percentages were found in the amorphous Fe‐oxide fraction. Significant source by pH interactions were observed only for exchangeable Mn and Zn. Organic ligands in the manure retained more Zn in a nonexchangeable form under acidic conditions, but had only minor effects on exchangeable Mn. Plant uptake of Mn and Zn was primarily related to the exchangeable fractions; however, predictive models were significantly enhanced by the inclusion of soil pH. Inconsistent correlations and low r2 values for all models involving Cu illustrate the difficulty in predicting crop response to native or added Cu.
Using Ground‐penetrating Radar to Study Changes in Soil Map Unit Composition in Selected Histosols
Authors: Collins M. E. , Schellentrager G. W. , Doolittle J. A. , Shih S. F.
Published: July 2010

Intensive cultivation practices and subsidence of Histosols in Florida's Everglades Agricultural Area (EAA) has resulted in the need to reevaluate soils information gathered and published in the early 1970s as part of the National Cooperative Soil Survey Program. This study was initiated to determine the present range, thickness, distribution, and spatial variability of selected Histosol map units in the EAA using ground‐penetrating radar (GPR). Four consociations were selected for study. The thickness of the organic materials has decreased significantly when compared to the thickness in the published soil survey report. When compared with the GPR data, the proportions of areas mapped in the 1970s that have thick organic layers (>90 cm) had decreased with a corresponding increase of areas with thin organic layers (<90 cm). This shift represents approximately a 35% increase in lithic subgroups. Also, many areas previously mapped as consociations need to be recorrelated as complexes; only the Okeechobee muck map unit would remain a discrete consociation. Using the GPR increased sampling speed and enabled a continuous profile of organic thickness over bedrock to be obtained.
Effect of Periodic Burning on Soil Nitrogen Concentrations in Ponderosa Pine
Authors: Covington W. W. , Sackett S. S.
Published: July 2010

To determine the effects of different burning intervals on soil N status in substands of sapling‐, pole‐, and sawtimber‐sized ponderosa pine (Pinus ponderosa Laws.) we sampled plots burned at 1‐, 2‐, and 4‐yr intervals by three strata at two depths (0–5 and 5–15 cm). Generally, NH4+ and NO3‐ concentrations were higher on plots repeatedly burned than on unburned controls. However, plots not reburned for 4 to 5 yr had concentrations similar to controls. No significant difference in total (organically bound) N was found among treatments. We conclude that frequent periodic burning can be used to enhance N availability in southwestern ponderosa pine sites.
A Simple Barium Chloride Method for Determining Cation Exchange Capacity and Exchangeable Cations
Authors: Hendershot William H. , Duquette Martin
Published: July 2010

Seventeen soil samples from acidic forest soils (Typic and Pergelic Cryorthods) and near‐neutral agricultural soils (Typic Haplaquepts) were used in an experiment to compare three methods of determining cation exchange capacity (CEC). The methods tested are the sum of cations displaced with 0.1 M BaCl2, and exchangeable Ba after saturation with BaCl2 and replacement with either MgSO4 (compulsive exchange) or MgCl2. The results show that when Al, Mn, and Fe are included with Ca, Mg, Na, and K in the sum of cations, this method gives the same result as do the other methods. It is recommended that this simple one‐step method be used in routine analysis of acidic soils, especially when nonagricultural lands are under investigation.
Effects of Ionic Strength, Calcium, and Citrate on Orthophosphate Solubility in an Acidic, Montmorillonitic Soil
Authors: Traina Samuel J. , Sposito Garrison , Hesterberg Dean , Kafkafi U.
Published: July 2010

A recent study by the authors of the effects of pH and organic acids on residual orthophosphate solubility in an acidic, montmorillonitic soil (Typic Chromoxererts) was extended to include variations of ionic strength (NaCl background) and Ca2+ concentration at fixed ionic strength. The objective of the experiments was to elucidate further the mechanism of orthophosphate solubility in a montmorillonitic soil containing exchangeable Al(III) and added citric acid. At ionic strengths between 20 and 100 mol m−3 (NaCl) and Ca2+ concentrations between 1 and 5 mol m−3 at 20 mol m−3 ionic strength (NaCl background), additions of citric acid at low concentrations (<0.1 mol m−3) reduced orthophosphate solubility. The solubility then gradually returned to its value in the absence of added organic acid as the citric acid concentration was increased to 0.6 mol m−3. The only significant effect of increasing the ionic strength or the Ca2+ concentration was to decrease orthophosphate solubility at any level of citric acid addition. Orthophosphate‐citric acid interactions in the soil were influenced only quantitatively, probably through the displacement of exchangeable Al(III) by Na+ and/or Ca2+, by increasing the concentration of these two metal cations in the soil solution.
Fate of Fertilizer Nitrogen in the Rice Root Zone
Authors: Reddy K. R. , Patrick W. H.
Published: July 2010

Poor N use efficiency by rice (Oryza sativa L.) in many regions of the world is due to the intensity of loss mechanisms functioning in the system. A study was conducted to determine the maximum potential loss of fertilizer 15N in a Crowley (Typic Albaqualfs) silt loam soil where conditions are favorable for both nitrification and denitrification in the root zone of rice. Nitrogen losses were measured in the rhizosphere (soil core with rice plants) and nonrhizosphere (soil core without rice plants) soil systems. The potential N loss in the system with plants was found to be 193 mg N m−2 d−1, while N loss due to the rhizosphere effect alone was 143 mg N m−2 d−1 (18% of the applied 15N). About 5% of the applied 15N was found to be lost due to upward movement of 15NH+4 into overlying flood‐water.