bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors Affecting Field‐Saturated Hydraulic Conductivity Measured by the Borehole Permeameter Technique
Authors: Campbell C. M. , Fritton D. D.
Published: July 2010

The borehole permeameter method for measuring field‐saturated hydraulic conductivity, Kfs, is prone to variability due to soil smearing during borehole excavation, and swelling that results from differences in initial soil‐water content. The effects of borehole preparation techniques and initial soil‐water pressure on Kfs were analyzed in this study. Eighty boreholes were studied in a strongly structured clayey soil (a fine, mixed, mesic Typic Hapludalf). A version of the borehole permeameter method was used to measure Kfs in soil that was initially at soil‐water pressures of 0, −0.016, −0.050 and −0.080 MPa. Three different borehole excavation techniques were also studied to determine the effect on Kfs of soil smearing during borehole preparation. The treatments consisted of removing a uniform thickness of soil from the sides of the borehole with an ice pick, scarifying the sides of the borehole with a wire brush, and no treatment. Field‐saturated hydraulic conductivity for the brushed treatments was similar to Kfs values obtained when no treatment was used. The ice pick method resulted in significantly higher Kfs. When Kfs values measured using the ice pick method were analyzed, no significant effect of initial soil‐water pressure was evident. This could possibly be due to soil variability.
Steady‐State Temperature Distribution in Nonisothermal, Unsaturated Closed Soil Cells
Authors: Prunty Lyle , Horton Robert
Published: July 2010

Ambient temperature interference (ATI) is a concern that has not been adequately addressed in studies of coupled water and heat transport in unsaturated soil. Our objectives were to detect ATI, minimize it, and obtain nonisothermal, steady‐state temperature and moisture profiles with minimum ATI. Two soils, a sand and a silty clay loam (sicl), were packed into cylindrical cells with uniform moisture. Temperature gradients were imposed by making one end warmer (40, 23, or 19°C) than the other end (1 or 9°C). Steady‐state temperature profile data were obtained for various cell configurations and ambient temperatures. The configuration showing least ATI was a 2.5‐cm‐diam., 5‐cm‐long cell, with 8 cm radial insulation. Longer cells of the same basic design or with less insulation had greater ATI, as did a larger diameter cell (4 cm diam. and 14 cm long). All tests (sand at 0.049 m3 m−3 moisture; sicl at 0.049 and 0.146 m3 m−3) using lowest ATI cells produced concave upward temperature profiles. In contrast, the larger diameter cell (sicl, high ATI) had concave downward profiles. Water redistribution into the cooler half of cells was more pronounced with sand (>90%) than sicl. Cells exhibiting low ATI appear to provide more consistent and meaningful soil temperature and moisture profiles than had previously been obtainable.
Cation Exchange Chemistry of Hexadecyltrimethylammonium in a Subsoil Containing Vermiculite
Authors: Xu Shihe , Boyd Stephen A.
Published: July 2010

Substituting native inorganic exchangeable cations of soil clays with cationic surfactants like hexadecyltrimethylammonium (HDTMA) greatly increases the sorption of organic contaminants, and hence reduces their transport potential. Both static and kinetic studies were conducted to probe the inorganic‐HDTMA exchange processes in a subsoil containing vermiculite and to determine the chemical stability of the resultant HDTMA‐soil complexes. The HDTMA generally had much higher affinity for the clay surface than inorganic cations native to soil and thus HDTMA saturation of soil resulted in a low residual HDTMA concentration in solution (≈ 10−6 to 10−5 M). Conditions leading to flocculation of soil clays (e.g., high ionic strength or divalent exchangeable cations) resulted in inorganic cation entrapment in the interlayers of clays and decreased cation selectivity coefficients of inorganic‐HDTMA exchange. Under these conditions, a portion of HDTMA was adsorbed via nonpolar interactions (hydrophobic bonding) resulting in a higher residual concentration of HDTMA in solution (≈ 10−4 M) and a greater tendency for HDTMA desorption. The change in electrophoretic mobility of soil clays and turbidity of soil suspensions as HDTMA loading increased suggested that HDTMA, if adsorbed via cation exchange mechanism, caused clay aggregation and tended to distribute on the internal sites of the aggregates, leaving inorganic cations on external surfaces. The kinetic study revealed that inorganic‐HDTMA exchange was fast on external surfaces but slow on internal sites of Al‐hydroxy‐interlayered vermiculites or flocculated vermiculites where the inorganic cation entrapment had been found. We concluded that the most stable HDTMA‐soil complexes form at HDTMA loading of 0.6 to 0.7 cation‐exchange capacity for nonsodic soils.
Release of Fixed Ammonium during Nitrification in Soils
Authors: Green C. J. , Blackmer A. M. , Yang N. C.
Published: July 2010

Ammonium added to soils can be fixed by clay minerals and subsequently released. There is, however, uncertainty concerning how rapidly this release occurs. We evaluated the possibility that relatively rapid release of recently fixed NH+4 may accompany nitrification of exchangeable NH+4 in soils. Labeled urea was added to four soils at rates of 0, 100, or 200 mg N/kg, and the soils were incubated anaerobically for 20 d to allow ample time for urea hydrolysis and NH+4 fixation to occur. Recovery of the labeled N as fixed NH+4 at 20 d averaged 1% in a Nicollet (fine‐loamy, mixed, mesic Aquic Hapludoll) soil, 3% in a Bremer (fine, montmorillonitic, mesic Typic Argiaquoll) soil, 10% in a Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) soil, and 23% in a Canisteo (fine‐loamy, mixed [calcareous], mesic Typic Haplaquoll) soil. Air was introduced after 20 d to promote nitrification of NH+4 and release of fixed NH+4. In the two soils with greatest fixation, a mean of 45% of the labeled N present as fixed NH+4 after 20 d was released in the next 15 d. These observations indicate relatively rapid release of fixed NH+4 during nitrification. Failure to recognize the importance of release of fixed NH+4 during nitrification in recently fertilized soils could result in underestimates of the amounts of N available to plants and microorganisms and in overestimates of mineralization‐immobilization turnover of N.
Multivariate Diagnosis of Nutrient Imbalance in Potato Crops
Authors: Parent L. E. , Cambouris A. N. , Muhawenimana A.
Published: July 2010

Compositional Nutrient Diagnosis (CND) involves a correction procedure for two constraints inherent to foliar analytical data, i.e., the bounded‐sum constraint to 100% of the components and the redundant information among interactive nutrients, which are addressed only partially by the Diagnosis and Recommendation Integrated System (DRIS) and not at all by the Critical Value Approach (CVA). The objective of this study was to extract the correlation structure among nutrients using principal component analysis, to test for correlation between DRIS and CND nutrient indices, and to diagnose independent samples. Yield and foliar analyses (N, P, K, Ca, and Mg) of late potato were collected in the St‐Lawrence Lowlands for 3 yr. The high‐yielding subpopulation (182 observations) produced >40 Mg ha−1. Three varimax‐rotated principal components (PC) explaining 93.5% of total variation in the high‐yielding subpopulation were designated as (N−P−Ca+), (P−Mg+) and (K+). A euclidian distance d computed from the PCs provided a nutrient imbalance index for the crop. DRIS and CND indices were highly correlated to each other (r = 0.956‐0.989) using 36 independent early potato samples. The CVA diagnosed correctly 66.7% of the cases. The CND classified the crops in two groups assuming χ2 distribution for d2 values (P ≤ 0.10). Nitrogen was the most limiting nutrient in the high‐yielding subgroup and K was extremely limiting in the low‐yielding subgroup. Defining critical CND nutrient indices empirically, CND produced correct diagnoses 87.5% of the time.
Temporal and Spatial Patterns of Episaturation in a Fragixeralf Landscape
Authors: McDaniel P. A. , Falen A. L.
Published: July 2010

Relatively low saturated hydraulic conductivities associated with fragipans result in seasonal perched zones of saturation (episaturation). This study was conducted to monitor seasonal episaturation in a Fragixeralf landscape of northern Idaho. Perched zones of saturation above a fragipan in a 1.4‐ha field were monitored during a 2‐yr period using 64 piezometers arranged on a 15‐m grid spacing. During the winter of 1991–1992, relatively mild temperatures and high rainfall resulted in development of perched zones of saturation lasting from early December into May. Average quantities of perched water present within the landscape during the winter and early spring months ranged from 8.4 to 15.4 cm, representing between 34 and 43% of the seasonal precipitation that had been received at the study site. During the 1992–1993 winter, colder temperatures and relatively large quantities of snow delayed development of episaturation. When the snow pack began to melt in early March, an average of >20 cm of water was present in the saturated zone above the fragipan. This water represented 58% of the seasonal precipitation that had been received. Soil morphological characteristics and elevation were correlated with quantities of perched water present on sampling dates when potential evapotranspiration was low. For all sites, quantity of perched water was most strongly correlated with the thickness of the zone above the fragipan exhibiting redoximorphic features; depth to the fragipan was less strongly correlated. Elevation was generally a poor indicator of episaturation. Results of this study indicate that significant periods of episaturation occur in fragipan‐dominated landscapes under xeric moisture regimes.
Comparison of Six Methods To Determine Unsaturated Soil Hydraulic Conductivity
Authors: Stolte J. , Freijer J. I. , Bouten W. , Dirksen C. , Halbertsma J. M. , Van Dam J. C. , Van den Berg J. A. , Veerman G. J. , Wösten J. H. M.
Published: July 2010

Knowledge of soil hydraulic properties is required for soil‐water flow models. Although many studies of individual methods exist, comparisons of methods are uncommon. Therefore, we compared application ranges and results for six laboratory methods for determining hydraulic conductivity or diffusivity on eolian sand, eolian silt loam, marine sandy loam, and fluviatile silt loam. The methods, hot air, sorptivity, crust, drip infiltrometer, Wind's evaporation, and one‐step outflow, fall into three groups: (i) those that only yield a conductivity curve; (ii) those that yield a simultaneous estimate of conductivity, diffusivity, water content, and pressure head; and (iii) those that yield a diffusivity curve. Diffusivities were converted to conductivities with a water retention curve. One main difference between the methods was the pressure head‐water content range. Despite the large differences between the methods, the results for the first two groups tended to be similar. The results of the third group did not match well with those of the first two. It proved difficult to compare these methods correctly due to hysteresis.
Gypsum Determination in Soils by Conversion to Water‐Soluble Sodium Sulfate
Authors: Berigari M. S. , Al‐Any F. M. S.
Published: July 2010

Precise and accurate determination of gypsum in soils has been difficult by the wet‐chemical methods, based on its solubility in water. In this work, 2‐g samples of three Typic Gypsiorthids were washed once with 25‐mL portions of 50% (v/v) ethanol to selectively remove nongypsic soluble sulfates. Soil gypsum was subsequently converted to CaCO3(s) and Na2SO4 by ultrasonic dispersion of the samples twice with 25‐mL increments of 0.5 M Na2CO3 solution. The SO2−4 in the supernatant solution was centrifuge separated and analyzed by the standard gravimetric BaSO4 (A) and turbidimetric (B) methods to obtain the gypsum content of the samples. The agreement between the data of Methods A and B was excellent where the best‐fitted regression line coincided with the 1:1 line in a scattergram. Soil gypsum was also extracted with water, then determined by turbidimetric SO2−4 (C) and the Bower‐Huss conductometric (D) methods for comparison. Statistical analyses of the data showed higher values (P = 0.05) of gypsum in soils obtained by the proposed method than by water extraction even when the same method of SO2−4 analysis was applied. The efficiency of the proposed method was 25 to 31 times greater than that achieved by water. The proposed method of gypsum extraction and its determination in soils from turbidimetric SO2−4 analysis was applied. The efficiency of the proposed method was 25 to 31 times greater than that acheived by water. The proposed method of gypsum extraction and its determination in soils from turibidimetric SO2−4 analysis is simple, rapid, and quite accurate for soil taxonomy, land reclamation, and other engineering purposes.
Atrazine Desorption from Smectites
Authors: Barriuso E. , Laird D. A. , Koskinen W. C. , Dowdy R. H.
Published: July 2010

In soils low in organic matter, pesticide adsorption and desorption by clay minerals may strongly influence the fate of pesticides in soil environments. Atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine) adsorption‐desorption was determined on 11 reference smectites (<2‐µm size fraction), and a soil smectite (<0.02‐µm size fraction from the Ap horizon of a fine‐loamy, mixed, mesic Typic Haplaquoll). For each clay sample, adsorption and desorption isotherms were determined using batch equilibration. Atrazine adsorption on the clays decreased with increasing surface change density (SCD) of the smectites. The desorption isotherms indicated that adsorption was generally reversible. This suggests that atrazine is primarily adsorbed on smectite surfaces through relatively weak van der Waals or H bonds. However, a small positive hysteresis was observed with some clays, and the magnitude of the hysteresis, evaluated using the ratio of the Freundlich isotherm coefficients for adsorption and desorption, increased with SCD. This suggests that atrazine is retained by stronger binding mechanisms on smectites with high SCD, in spite of its lower adsorption capacity. On clays with high atrazine adsorption coefficients, the amount of atrazine desorbed was larger than would be predicted from the adsorption isotherms, resulting in a “negative hysteresis” whereby the desorption isotherm slope was greater than the adsorption isotherm slope. “Negative hysteresis” can be explained if atrazine is assumed to be excluded from interlayer or intraquasi‐crystal water, where only external or interquasi‐crystal water would be available during the desorption process.
Spatial and Temporal Variability of Ammonium in Flooded Rice Fields
Authors: Dobermann A. , Gaunt J. L. , Neue H. U. , Grant I. F. , Adviento M. A. , Pampolino M. F.
Published: July 2010

Monitoring and modeling the dynamics of N in flooded rice fields require reliable methods for both sampling and analysis. Destructive soil sampling and centrifugation and in situ sampling of soil solution using microporous polymer tubes (rhizon soil solution samplers; RSSS) were used to study the dynamics and variability of NH+4 in two field experiments. Both methods gave similar results in unfertilized treatments, whereas significant differences were measured in treatments with N application. The RSSS were suited for measuring point dynamics or microvariation of nutrients in the root zone, whereas soil‐core sampling was a better method to obtain quantitative N data integrated across a particular depth range. We observed a highly significant linear relationship between the logs of soil exchangeable and solution NH+4 only until panicle initiation (PI). Microvariability accounted for a large proportion of the within‐field variation and was significantly reduced by bulking of soil cores. Coefficients of variation were higher in the fertilized field compared with an unfertilized field and were changing throughout the growth period of rice, with the highest variability between PI and flowering. Sampling to obtain representative mean values at the plot or field scale can be optimized with regard to temporal changes in the spatial distribution patterns of NH+4. Before transplanting (TP) and at the end of the growth period, less samples are needed and can be taken as composite samples of the whole puddled soil layer. Between TP and flowering, more samples are needed and should be taken in several depth ranges.
Effects of Bulldozer and Chain Clearing on Soil Properties and Crop Yields
Authors: Barber R. G. , Romero D.
Published: July 2010

The use of bulldozers and straight blades for clearing subtropical forests in eastern Bolivia is believed to result in serious soil degradation and low crop yields. It was hypothesized that chain felling with a tree pusher and rake windrowing would cause less soil degradation and give higher crop yields. An experiment established on a Typic Haplustalf compared the effects on soil degradation and subsequent crop yields of (i) conventional bulldozer felling and windrowing with a straight blade (land clearing control), (ii) bulldozer felling with a straight blade and tree pusher, and rake windrowing, (iii) chain felling with a tree pusher and straight blade windrowing, (iv) chain felling with a tree pusher and rake windrowing, and (v) undisturbed forest (control). All four methods caused significant soil physical degradation as manifest by 10 to 20% increases in bulk density and a 6.2% loss of total porosity at the 0‐ to 0.20‐m depth, a lowering of the soil surface by about 30 mm due to compaction, and a significantly lower 30‐min cumulative infiltration (4.36 cm) compared with the forest control (15.08 cm). All four land clearing methods gave significant increases in Ca (from 7.7 to 11.6 cmolc kg−1) in the 0‐ to 0.20‐m depth as a result of forest burning. Very few significant differences in soil properties, and no significant differences in subsequent yields of corn (Zea mays L.) or soybean (Glycine max. L.), were found among land clearing methods. Thus, under dry to slightly moist soil conditions and with skilled operators, the clearing of a low‐biomass, subtropical forest by bulldozer clearing with a straight blade was no more degrading to the soils than chain felling with a tree pusher and rake windrowing, and did not result in lower yields of subsequent crops.
Controlled Displacement Technique for Measuring Soil Friability
Authors: Snyder V. A. , Vázquez M. A. , Martínez G. , Ramírez L. , Hadas A.
Published: July 2010

An important physical property of agricultural soils is their friability or tendency to fracture into small fragments when tilled. Because friability varies greatly with soil water content, simple tests to determine the point of maximum friability are needed. Previous tests have failed to simulate a set of conditions that are necessary to achieve effective soil fragmentation in tillage. The most important of these conditions is a loading path that imposes a compression/shear ratio conducive to fracture and that also provides continuous energy for crack propagation after fracture initiation. Also, many tests do not directly measure the amount of soil fragmentation. The latter is a primary variable of interest when considering soil reaction to tillage. A new procedure is described that provides the necessary fracture conditions and gives a direct measure of the amount of soil fragmentation under any desired compression/shear ratio. Forces, displacements, and energy expenditures during the soil fragmentation process can be measured. The amount of soil fragmentation determined by the method was found to be very sensitive to compression/shear ratio, particularly in highly plastic soils. However, different soils always ranked the same for all ratios. Friability indices were measured with the technique on a set of soil cores sampled in the field at different soil water matric pressures. The matric pressure at which these indices indicated maximum soil friability agreed well with the point of maximum friability determined by tillage of the same soil.
Field and Undisturbed‐Column Measurements for Predicting Transport in Unsaturated Layered Soil
Authors: Ward A. L. , Kachanoski R. G. , von Bertoldi A. P. , Elrick D. E.
Published: July 2010

Transport properties vary considerably over small distances in most soils. The stochastic streamtube model offers one approach to incorporating heterogeneity into transport predictions. This study tested the ability of the streamtube concept to predict transport in heterogeneous fields using measurements from undisturbed columns. Fifty undisturbed columns (0.15‐m diam. by 1.5 m deep) were taken every 0.4 m from a 20‐m‐long transect in a loamy sand soil with variable horizon thickness. Each core was instrumented at 0.1‐m intervals with time domain reflectometry probes to measure resident fluid concentrations of a conservative (Cl−) tracer under steady flow conditions. Large‐scale concentration curves of Cl− from solution samplers and coring were obtained from field experiments conducted on the same soil under similar boundary conditions. Differences were observed in the solute spread and mass recovery, but not in the centers of mass. Horizontal scale dependence of transport was observed in the field but not in the columns. This suggests that a higher dimensionality of transport, probably along the horizon interfaces, may be responsible for the observed scale dependence in the field. Although the stochastic streamtube model gave good predictions of the center of mass, it does not appear to be a realistic physical analogue for describing solute dispersion in soils with spatially variable layer thickness.
Comparison of Diagnosis and Recommendation Integrated System and Nutrient Sufficiency Range for Corn
Authors: Soltanpour P. N. , Malakouti M. J. , Ronaghi A.
Published: July 2010

The diagnosis and recommendation integrated system (DRIS) is a potential method for interpreting plant foliar nutrient composition. The objective of our study was to compare DRIS with the nutrient sufficiency range (NSR) for corn (Zea mays L.). We used published standard DRIS norms and Colorado DRIS norms calculated from ear leaf composition at tasseling to silking of corn yielding 11 Mg grain ha−1 or higher. Our NSR values are based on the minimum and maximum nutrient concentration values found in the literature. We changed the minimum value of 21 g kg−1 for N to 26 g kg−1. For identifying nutrient needs of corn, the NSR was superior to DRIS regardless of the DRIS norms used. Identified flaws of DRIS are: (i) very high levels of one nutrient can cause false relative deficiency (imbalance) diagnosis of other nutrients, and (ii) an optimal ratio between two nutrients produces maximum yields only when both nutrients are in their respective sufficiency ranges. We recommend use of the NSR technique in combination with a soil test to avoid the misdiagnosis of Zn and Cu deficiencies in corn when N is extremely deficient.
Freeze‐Drying Effects on Wet and Dry Soil Aggregate Stability
Authors: Staricka J. A. , Benoit G. R.
Published: July 2010

Freeze‐drying of soil aggregates may reduce aggregate size and increase erosion potential. We investigated whether freeze‐thaw frequency, water content, and initial aggregate size influences the freeze‐drying disruption of soil aggregates, as measured by dry and water‐drop‐impacted wet sieving. Aggregates of two western Minnesota soils, Barnes loam (a fine‐loamy, mixed Udic Haploboroll) and Hamerly clay loam (a fine‐loamy, mixed, frigid Aeric Calciaquoll) were tested. Vulnerability to wet sieving was increased much more by freeze‐drying than was vulnerability to dry sieving. Freeze‐drying decreased wet aggregate stability in 85 of 96 cases and dry aggregate stability in 56 of 96 cases. Initial water content largely determined whether freeze‐drying decreased aggregate stability. For water contents of 0.05, 0.15, 0.25, and 0.35 kg kg−1, the mean weight diameters (water‐drop‐impacted wet sieving method) of freeze‐dried aggregates were 93, 64, 48, and 46%, respectively, of their non‐freeze‐dried values. For dry sieving, values for the same four water contents were 100, 103, 90, and 88%, respectively. The detrimental effects also generally increased as aggregate size increased. Freeze‐thaw frequency and soil type had less effect on freeze‐drying disruption than did water content and initial aggregate size. Thus soil surface resistance to breakdown by freeze‐drying and raindrop impact would be expected to decline as initial aggregate size and soil water content increases.
Multidimensional Infiltration: Points, Furrows, Basins, Wells, and Disks
Authors: Clothier Brent E. , Green Steven R. , Katou Hidetaka
Published: July 2010

Multidimensional infiltration theory continues to be an area of soil physics research dominated by the works of J.R. Philip. The point source of these endeavors was his landmark paper in 1966. Here in our contribution honoring John Philip, we first discuss the multidimensional, similarity‐solution antecedents that were queried by him nearly 30 yr ago. We then list the new theoretical developments contained in this comprehensive treatise on multidimensional flow into unsaturated soil. Next we comment on the three steady‐state sequels derived by J.R. Philip, P.A.C. Raats, and R.A. Wooding, especially in relation to the experimental studies they spawned. Experiments initially began with attempts to verify directly the various multidimensional flow theories. But experimental procedures soon came to use, in an inverse sense, these theories to permit measurements of the hydraulic properties of field soil. The disk permeameter, currently a widely used device, employs multidimensional theory. In a variety of ways, disks are used to infer the hydraulic properties of field soil in the pressure potential range close to saturation. However, here we propose a method by which the disk permeameter can be used to deduce in situ the nonlinear adsorption isotherm that holds for the transport of reactive chemicals through soil. We demonstrate this proposal by using in the inverse sense of parameter identification, not an analytical description, but rather a two‐dimensional numerical simulation of the flow of water and transport of solute away from a surface disk maintained at a given pressure potential, and some fixed concentration of reactive solute.
Desperately Seeking Darcy in Dijon
Authors: Philip J. R.
Published: July 2010

Henry Darcy (born 1803, died 1858) is known to soil physicists as the founding father of the science of fluid flow in soils. This illustrated account of a short visit to Dijon, his native town, reveals little‐known aspects of Darcy's character, life, and work. The central square and town gardens are named after Darcy, as are numerous commercial and public undertakings: a cinema, bus stop, a garage, a multistory car park, a pharmacy, and a shopping arcade. Inquiry revealed that Henry Darcy himself has been forgotten by the citizens of Dijon, and that his name persists only as a ubiquitous geographical label. It was not always thus. Darcy, with great vision and skill, designed and built a pure water supply system for Dijon, in place of previous squalor and filth. Dijon became a model for the rest of Europe. Darcy selflessly waived fees due to him from the town, corresponding to about $1.5 million today. Medals were struck recognizing his skill and selflessness; and a monument celebrates his great work. Dijon gave him a public funeral, the whole population lining the streets, and the council renamed the central square in his honor. His simple tomb is in good condition in Dijon cemetery. His letters to Henri‐Emile Bazin reveal him as intelligent, witty, and sceptical, and quite devoid of pretension.
Aluminum Transformations and Solution Equilibria Induced by Banded Phosphorus Fertilizer in Acid Soil
Authors: Sloan J. J. , Basta N. T. , Westerman R. L.
Published: July 2010

Banded P fertilizer may alleviate Al toxicity in strongly acid surface soils (pH < 5) and is a useful remediation management practice when liming is not possible. The objective of this study was to determine the effect of banded P fertilizer on Al transformations and soil solution composition in acid soils. Pond Creek silt loam (fine‐silty, mixed, thermic Pachic Argiustoll; pH = 4.0) was amended with five P fertilizer rates and incubated at 24°C for 70 d. Dissolved Al, Mn, Ca, Mg, K, PO4, SO4, Cl, and NO3, pH, electrical conductivity, and exchangeable cations were measured after 1, 5, 10, 15, 30, and 70 d of incubation. Soil solution Al, Ca, Mg, and Mn decreased but SO4 increased with P fertilizer rate. The concentration of dissolved metals increased and soil solution pH decreased with time. Soil solution Al3+ decreased and Al‐orthophosphate complexes increased with P fertilizer rate. Saturation indices derived using MINTEQA2 suggest possible precipitation of Al as gibbsite at low P rates (<175 mg P kg−1) and incubation times ≤15 d, K‐taranakite at high P rates (>262 mg P kg−1) and incubation times ≤30 d, and amorphous variscite analogs at all P rates. Soil solution was undersaturated with respect to Ca and Mg phosphates. Formation of MnPO4·1.5H2O was consistent with the well‐aerated conditions of this study. Significant (P < 0.05) reductions in exchangeable Al, Ca, and Mg were correlated with P fertilizer rate. Phosphorus additions did not affect exchangeable Fe or Mn. Banded P fertilizer is a viable alternative method to reduce toxic forms of Al in strongly acidic soils.
Design and Construction of a Personal‐Computer‐Based Automatic Titrator
Authors: Kinniburgh D. G. , Milne C. J. , Venema P.
Published: July 2010

We designed and constructed an automatic titrator that uses a personal computer (PC) and commercially available components. The titrator can be used for a wide variety of tasks including pH logging, titrations (including “salt titrations”), and two‐way pH stats. The titrator is programmed using a simple command language that enables it to carry out a timed sequence of commands. Examples are given that illustrate the titrator's use for: conventional acid‐base titration using dynamic dose sizing; the base‐acid‐base titration of an acid soil; and the automatic determination of Cd binding by humic acid at a fixed pH.
Kinetics of Potassium Fixation in Vermiculitic Soils under Different Moisture Regimes
Authors: Olk D. C. , Cassman K. G. , Carlson R. M.
Published: July 2010

Fixation of K in vermiculitic soil and the residual benefit from fertilizer‐K addition are influenced by soil moisture. The purpose of this study was to determine K fixation rates under simulated field moisture regimes. Fixation rates were measured during three consecutive wetting‐drying cycles and in long‐term aerobic incubations with soil moisture held constant at different matric pressures. In all studies, 12 mmol KCl kg−1 soil was applied before monitoring K fixation. All rates conformed to first‐order kinetics. Each wetting‐drying cycle had a rapid fixation phase lasting 2 d with slower fixation thereafter, and rate constants of fixation decreased in each successive cycle for both phases. Depending on the soil, rate constants of the rapid phase in the first cycle ranged from 0.064 to 0.143 d−1 and were 0.026 to 0.061 d−1 in the second cycle. Slow‐phase rate constants ranged from 0.030 to 0.058 d−1 in the first cycle and 0.005 to 0.021 d−1 in the second cycle. In samples maintained as saturated pastes, the rapid phase was extended to 5 d but the rate constant was smaller in magnitude than when soil was drying. The rapid phase represented an abiotic process that was controlled by K+ diffusion. When soil moisture was held constant in a long‐term aerobic incubation, K fixation rate constants increased at lower soil moisture levels. Rate constants of fixation were 0.00055 d−1 at −0.03 MPa and 0.00114 d−1 at −0.48 MPa, an increase of 107%. The measured fixation rates were sufficient to explain long‐term fixation measured in a related field study.
Tolerance of Clover Rhizobia to Heat and Desiccation Stresses in Soil
Authors: Trotman A. P. , Weaver R. W.
Published: July 2010

The ability to withstand desiccation and heat is an important attribute of Rhizobium leguminosarum bv. trifolii for inoculation of clover (Trifolium spp.). Desiccation and heat tolerances of 10 commercial strains of rhizobia and 150 isolates from 15 clover fields in Texas were determined by studying survival of rhizobia in soil incubated at 37°C and −30 J kg−1 water potential for heat stress and 28°C and −1.5 kJ kg−1 water potential for desiccation stress. Fewer commercial strains were tolerant to these environmental stresses than field isolates. Of 150 field isolates, 31 and 19 were able to maintain at least 1% of their initial populations for 1 wk under desiccation and temperature stresses, respectively. Six of the field isolates were tolerant to both stresses, and three of these were effective in N2 fixation. Only one of 10 commercial strains were tolerant to either stress, and none was tolerant to both stresses. Rhizobia in inoculants are usually selected on their ability to fix N2, but it appears that there is good genetic material in field populations for developing strains that have greater tolerance to environmental stresses.
Carbon and Nitrogen Mineralized from Leaves and Stems of Four Cover Crops
Authors: Quemada M. , Cabrera M. L.
Published: July 2010

Increased understanding of surface residue decomposition may improve cover crop management in no‐till systems. Most decomposition studies of cover crop residues have been conducted with samples composed of a mixture of leaves and stems. Because leaves and stems have different composition, however, they would be expected to show different mineralization kinetics. The objective of this work was to study C and N mineralization from isolated stems, isolated leaves, and a mix of leaves and stems of wheat (Triticum aestivum L.), rye (Secale cereale L.) oat (Avena sativa L.), and crimson clover (Trifolium incarnatum L.). Cecil loamy sand soil (clayey, kaolinitic, thermic Typic Kanhapludult) was packed into acrylic plastic cylinders, adjusted to 55% water‐filled porosity, treated with either leaves, stems, or a mix of both (1‐cm pieces) on the surface, and incubated at 35°C for 160 d. Air samples for CO2 and N2O determinations were taken periodically and NH3 evolved was trapped during the first 16 d. Soil columns were leached periodically and leachates were analyzed for N (total and inorganic) and total C. The dynamics of C and N mineralization of a mix of leaves and stems was different from the patterns predicted from isolated leaves and isolated stems. These results indicate a strong interaction between stems and leaves during early stages of decomposition, which may be relevant for predicting N mineralization from cover crop residues. The best predictors for N mineralization were residue C/N ratio and the reciprocal of residue N concentration.
Loess Toposequences in the Lower Mississippi River Valley: I. Fragipan Morphology and Identification
Authors: Lindbo D. L. , Rhoton F. E. , Bigham J. M. , Jones F. S. , Smeck N. E. , Hudnall W. H. , Tyler D. D.
Published: July 2010

Despite large acreages of agronomically important fragipan soils in the Lower Mississippi River Valley, relatively little information is available regarding their morphology, particularly in regard to fragipan definition and formation. This study was designed to evaluate morphological differences between nonfragipan (memphis [fine‐silty, mixed, thermic Typic Hapludalf]) and fragipan (Loring [fine‐silty, mixed, thermic Typic Fragiudalf] and Grenada [fine silty, mixed, thermic Glossic Fragiudalf]) soils occurring on the same landscape. A secondary objective was to determine if morphological characteristics of the Loring and Grenada pedons are consistent with taxonomic criteria. Five representative sites were selected based on published soil survey maps and landscape relations. Morphological characteristics associated with fragipans are present in all the Loring and Grenada pedons. The most obvious and consistent indicators of a fragipan are vertical gray seams and associated redoximorphic features. Because brittleness is subjective and a function of moisture content, it is not always a reliable indicator of fragipan occurrence. Likewise, root distribution is not particularly useful since deep‐rooted vegetation did not occur on these soils. Several Memphis pedons exhibit protofragipan development, but based primarily on the organization of gray seams, these should not be considered fragipan soils. Overall, the published criteria are adequate, with the notable exception of slaking, and the characteristics of the Loring and Grenada pedons are consistent with them. Greater relative root penetration and less brittleness also assist in differentiating between the nonfragipan horizons within the Memphis pedons and fragipan horizons of the other members of the toposequence, but these evaluations have to be made in detail from deep pits, particularly in borderline situations.
Influence of Soil Properties on the Statistical Characterization of Dry Aggregate Strength
Authors: Perfect E. , Kay B. D. , da Silva A. P.
Published: July 2010

Dry aggregate strength measurements, important in tillage and erosion studies, are often analyzed statistically using the Weibull model. The parameters of this model, α and β, characterize the absolute strength and the spread of strengths, respectively. Information is lacking on the influence of soil properties on values of α and β. We measured dry aggregate strength as the specific rupture energy (E in J g−1) of 40 aggregates in two size classes (4–8 and 8–16 mm) from 36 locations along a 500‐m transect across four soil types with a wide range of physical and chemical properties (e.g., 8.0–72.6% sand content). Estimates of α and β were obtained by fitting Weibull's model to these data using nonlinear regression. The α and β values were lognormally and normally distributed, respectively. The mean log(α) was ‐2.4 and the mean β was 1.3. Multiple regression analysis was used to relate log(α) and β to soil properties. The resulting regression equations explained 93% of the variation in log(α) and 60% of the variation in β. The log(α) increased with decreasing aggregate size and sand content and increasing organic matter content. The β increased (indicating a narrower range of strength values) with decreasing log(α) and aggregate size. The regression equations were validated by predicting the cumulative relative frequency distribution of E for aggregates from a different site where independent measurements of E were available for comparison. A good agreement (R2 ≥ 0.91) was obtained between predicted and observed values of E.
Spring Wheat Straw Production and Composition as Influenced by Topsoil Removal
Authors: Tanaka D. L.
Published: July 2010

Wind and water erosion have resulted in reduced crop productivity and created soil management problems. Management of crop residues can be effective for soil erosion control, but influences of soil erosion on crop residue production is unknown. The purpose of this study was to determine total residue production and residue N and P concentration and content for 8 yr as influenced by topsoil removal and additions of N and P fertilizer for a spring wheat (Triticum aestivum L.)‐fallow system. Total straw production for the first increment of P increased ≈ 14% for 0.00‐ and 0.06‐m soil removal treatments compared with ≈ 33% for 0.12‐ and 0.18‐m soil removal treatments. Total straw production was increased more than total grain production with the addition of N and P fertilizer. Total straw production for 0.12‐ and 0.18‐m soil removal treatments needed at least 20 kg P ha−1 and 35 kg N ha−1 to equal or exceed that for 0.00‐m soil removal treatment with no fertilizer additions. Total straw N content decreased 33% as soil removal increased from 0.00 to 0.18 m. While total straw P content was considerably less than total straw N content, both decreased about 32% for 0.18 m compared with 0.00‐m soil removal treatments. Greater total straw N and P content for the 0.00‐m soil removal treatment was due to greater total straw production as well as greater N and P concentrations. Consequently, cycling of N and P may be reduced for eroded soils due to low quantities of residue as well as low N and P concentrations in the residues.
Aboveground Net Primary Productivity and Nutrient Content of Fertilized Plantation Sweetgum
Authors: Nelson L. E. , Shelton M. G. , Switzer G. L.
Published: July 2010

Sweetgum (Liquidambar styraciflua L.) is a commercially desirable species that can be successfully established in plantations, and information is needed concerning its genotypic variation and response to fertilization. This study evaluates various aspects of productivity and nutrition for two half‐sib seed sources in a 9‐yr‐old sweetgum plantation that was refertilized in 1981 with a total of 0, 100, 200, or 400 kg N ha−1. Foliar and litter samples were collected in the year preceding and for 3 yr following N application, and tree diameter and height were measured annually. Aboveground net primary productivity (AGNPP) of the unfertilized controls averaged 6.7 Mg ha−1 from 1981 to 1983. By contrast, maximum AGNPP for treatments receiving N were 11, 16, and 16 Mg ha−1 in 1981, 1982, and 1983, respectively. Fertilization resulted in large increases in foliar biomass and leaf area index (LAI); values were highest in 1982, and then declined in 1983. Most responses peaked at the highest application rate, but differences between 200 and 400 kg N ha−1 were generally small. Estimated apparent recovery of applied N in aboveground tissues was 75% for the 100 kg N ha−1 rate in the first and second years; however, in the third year following fertilization only 47% was accounted for. The response of the two half‐sib seed sources differed, especially in terms of woody biomass.
Effects of Incubation and pH on Soil Solution and Exchangeable Cation Ratios
Authors: Curtin D. , Smillie G. W.
Published: July 2010

Bioavailability of nutrients is dependent on their concentration in the soil solution and on exchange equilibria between solution and adsorbed nutrient species. Elucidation of these nutrient supply relationships has been hampered by the fact that soil solution is not only difficult to extract, but its composition may change significantly during storage or incubation of field‐moist soil prior to solution extraction. The objectives of this study were to evaluate the effects of liming on the exchange relationships of the major cations (Ca, Mg, K, and Na) and to determine the causes of incubation‐induced changes in their solution concentrations. For periods of up to 1 yr, soil solution was extracted from soils treated in the laboratory with CaCO3 and incubated at approximately field capacity. Solution samples were also obtained from field‐limed soils (lime applied 17 yr previously) after 1 and 10 wk of incubation in field‐moist condition. The concentrations of cations in solution increased substantially during incubation. These increases were balanced by NO−3, indicating that the changes in cation solubility were microbially mediated. In contrast to cation concentrations, cation ratios (i.e., Mg/Ca, Na adsorption ratio, K adsorption ratio) were little affected by incubation. These ratios were directly related to the composition of the exchange phase and were strongly influenced by liming. Protons generated by mineralization of organic N during incubation displaced exchangeable Ca, Mg, K, and Na in ratios that maintained the equilibrium between solution and exchangeable phases. The results suggest that a reasonable approximation of soil solution cation ratios can be obtained from exchangeable cation data.
Maize Temporal Yield Variability under Long‐Term Manure and Fertilizer Application: Fractal Analysis
Authors: Eghball B. , Power J. F. , Binford G. D. , Baltensperger D. D. , Anderson F. N.
Published: July 2010

Long‐term experiments offer unique possibilities to study the effects of management practices on crops and soils with time. Characterizing temporal variability of grain yield provides an opportunity to distinguish between the effects of environment vs. management practices on grain yield, an important parameter. A long‐term study was established in 1912 in western Nebraska as part of a rotation study. In 1953, each plot was divided into manure (27 Mg ha−1 annually) and no‐manure sections to which fertilizer treatments of 0, 45, 90, 135, 180 kg N ha−1, and 135 kg N + 80 kg P ha−1 were applied annually. Grain yield data from 1953 to 1993 for these treatments were used for fractal analysis and determination of fractal dimension (D), which is an indication of pattern of variation. A D value close to 1 indicates dominance of long‐term variation (or trend), while a D value close to 2 indicates dominance of short‐term (year‐to‐year) variation. Grain yield increased with increasing N application rate without manure, but no response to fertilizer application was observed where manure had been applied. Fractal dimensions ranged from 1.942 to 1.996, indicating significant domination of short‐term variation of grain yield in the past 41 yr in all treatments. There was no significant difference between D values for manure or fertilizer treatments. Soil fertility amendments did not alleviate year‐to‐year variability observed in the corn (Zea mays L.) yield. Environmental factors like hail, fall freezing, and temperature variation during the growing season had a significant effect on the grain yield over the years. Although management practices can reduce temporal grain yield variability in some crops, variations in environmental factors in this study were great enough to dominate the yearly maize grain yield regardless of soil fertility amendments.
Tillage Effects on Thermal Conductivity of Two Soils in Northern British Columbia
Authors: Azooz R. H. , Arshad M. A.
Published: July 2010

Tillage management practices may affect crop growth, in part by altering soil thermal properties. Effects of long‐term conventional (CT), no tillage (NT), and modified no tillage (NTR: NT with surface residue pushed away from a 7.5‐cm zone over the seed rows) systems on soil thermal conductivity (K) and water content (θ) were evaluated on Donnelly silt loam and sandy loam (Typic Cryoboralfs). Measured K (M1) was compared with calculated K using the McInnes equation (M2) and a modified McInnes equation (M3, which included additional soil properties). The K in both soils increased with an increase in soil θ; the differences among the tillage systems decreased as the soil dried. Soil K for the silt loam was 0.81 (θ = 0.13 m3 m−3), 0.83 (θ = 0.14 m3 m−3), and 0.84 W m−1 K−1 (θ = 0.15 m3 m−3) in CT, NTR, and NT, respectively, at 25 d after planting in 1992 (a dry year). It was 1.13 (θ = 0.42 m3 m−3), 1.53 (θ = 0.50 m3 m−3) and 1.55 W m−1 K−1 (θ = 0.57 m3 m−3) in CT, NTR, and NT, respectively, at 47 d after planting in 1993 (a wet year). Soil K for sandy loam was significantly lower than for silt loam. Soil K measured by M1 and calculated by both the M2 and M3 methods were highly correlated. However, the calculated K values were somewhat improved, although not significantly, with the M3. Mean K was lower by 0.133 W m−1 K−1 in M2 and by 0.045 W m−1 K−1 in M3 than in M1 under CT on silt loam. Increased soil water storage under long‐term NT produced a greater thermal contact area and, consequently, a significantly greater K under NT and NTR than CT.