bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil Adsorption Interactions of Band‐Injected Anhydrous Ammonia and Potassium Chloride Fertilizers
Authors: Stehouwer R. C. , Johnson J. W.
Published: July 2010

Fertilizer‐use efficiency of NH+4 and K+ can be low in soils that adsorb these ions in a nonexchangeable form. In a laboratory study, the soil adsorption interactions resulting from simultaneous proximal injection of anhydrous NH3 (AA) and KCl solution were investigated to determine if such interactions might have an effect on the availability of these nutrients. The fertilizers were injected separately and simultaneously into two soils, a Hoytville silty clay loam (fine, illitic, mesic Mollic Ochraqualf) and an Avonburg silt loam (fine‐silty, mixed, mesic Aeric Fragiaqualf). Following incubation for periods of 1, 7, 14, 28, and 84 d at 20 °C, soil in the injected‐fertilizer bands was sampled from four concentric zones of radii 0 to 2.0, 2.0 to 3.0, 3.0 to 4.5, and 4.5 to 6.0 cm around the injection point. In the Avonburg soil, very little interaction between the two fertilizer materials was observed. In the Hoytville soil, simultaneous injection of AA and KCl had little effect on NH+4 distribution, compared with AA injected alone. Relative to KCl injected alone, simultaneous injection of AA and KCl in the Hoytville soil increased exchangeable K+ and decreased fixed K+ within 3.0 cm of the injection point. The effect on fixed K+ persisted throughout 84 d of incubation, while the effect of exchangeable K+ was not apparent beyond 28 d of incubation. Decreased K+ fixation was attributed to preferential NH+4 fixation blocking K+ fixation. Increased exchangeable K+ was attributed to pH‐induced increases in cation‐exchange capacity (primarily in the organic fraction), and to decreased K+ fixation.
Effects of Root and Subirrigation Depth on Evaporation and Percolation Losses
Authors: Philip J. R.
Published: July 2010

Loss from surface evaporation and from percolation limit the efficiency of subirrigation. This study yields bounds on the relative magnitude of the two types of losses. Quasilinear results on evaporation from buried steady sources are used to investigate the effects of source depth and root sink depth on soil evaporation and deep‐percolation losses from subirrigated crops. The study quantifies the concept that the deeper the source relative to the roots the smaller the soil evaporation loss and the larger the deep‐percolation loss.
Stability Constants of Copper(II)‐Humate Complexes Determined by Modified Potentiometric Titration
Authors: Stevenson F. J. , Chen Y.
Published: July 2010

Humic substances form highly stable complexes with micronutrient cations. Little is known, however, regarding the nature of the complexes or of their stability constants. A ligand titration procedure using the Cu(II) ion‐selective electrode was investigated as a means of determining stability constants of the Cu(II) complexes with humic and fulvic acids. The procedure was superior to conventional titration (metal ion as titrant) because constants for binding at the strongest sites are measured. Furthermore, under the titration conditions employed (pH of 4 and 5; low ionic strength, 0.01 M; low Cu(II) concentration, 10−5 M), precipitation did not occur and thus did not adversely affect the binding measurements. A continuous‐distribution model showed promise for modeling the binding data. The binding affinity of some humates for Cu(II) followed the order: soil humic acid (SHA) > peat humic acid (PHA) > lignite humic acid (LHA) > soil fulvic acid (SFA) ≈ fungal melanin. Intrinsic stability constants (log Kint) at pH 4 and an ionic strength of 0.01 M for the five humate preparations were 8.3, 7.9, 7.4, 7.2, and 6.9, respectively; constants at pH 5 were 8.5, 8.4, 7.9, 7.6, and 7.6, respectively.
Modeling Magnesium Uptake from an Acid Soil: III. Determination of Root Magnesium Concentration
Authors: Rengel Z.
Published: July 2010

Research on the nutrient interactions in the rhizosphere of soil‐grown plants would benefit from a reliable estimate of root‐nutrient concentrations. Ryegrass plants (Lolium multiflorum Lam., ‘Wilo’) were grown for 35 d in a greenhouse on an acid Stough soil (coarse‐loamy, siliceous, thermic Fragiaquic Paleudult) amended with three rates of CaO and two rates of MgCl2. Careful washing of roots in water was followed by a digestion procedure involving HF. Root Mg concentration was corrected for soil contamination based on Ti content in the root tissue. Titanium‐corrected root Mg concentrations were lower than root Mg concentrations calculated by multiplying shoot Mg concentrations of soil‐grown plants by the ratio of root to shoot Mg concentrations of solution‐grown plants. Regression analysis showed that the Barber‐Cushman model overpredicted total Mg uptake when root Mg content was calculated either from Ti‐corrected root Mg concentrations (2.88 and 2.39 times for 0 and 36 mg Mg kg−1, respectively) or from root/shoot Mg concentration ratios in solution‐grown plants (1.98 and 1.66 times for 0 and 36 mg Mg kg−1, respectively). Partitioning of Mg between roots and shoots of ryegrass may be quite different in soil‐ and solution‐grown plants.
Spatial Pattern of Slash Pine Roots and Its Effect on Nutrient Uptake
Authors: Escamilla J. A. , Comerford N. B. , Neary D. G.
Published: July 2010

Nutrient‐uptake models generally assume that roots are uniformly arrayed throughout a soil volume. In high‐fertility soils, departure from this regular distribution is not thought to affect nutrient‐uptake predictions if the roots are randomly arranged, but has the potential to dramatically change nutrient‐uptake predictions if roots are clumped. This study was conducted to document root spatial patterns in a forest ecosystem and to determine if spatial patterns affect how we conceptualize nutrient uptake in low‐fertility soils. Roots were mapped on horizontal faces at 2‐cm depth intervals. Spatial patterns were measured using variance/mean ratio and nearest neighbor distance (R) indices. The spatial pattern of slash pine (Pinus elliottii Engelm.) roots, using either variance/mean or R index, was random and was not affected by either the understory plant community or planting microsite. However, 63% of the pine roots in the check plots were within 0 to 0.6 cm of another pine root, while a similar percentage of pine roots was within 0 to 1.0 cm of another pine root in the weed‐controlled area. At these interroot distances, little interroot competition for K was expected. In contrast, virtually all roots had P‐uptake efficiency of <30%, regardless of understory competition. When nutrient‐uptake efficiency is a function of interroot distance for a random root population in low‐fertility soils, average interroot distance cannot be considered typical of the root population.
Aspect and Species Influences on Nitrogen and Phosphorus Availability in Arizona Chaparral Soils
Authors: Klemmedson James O. , Wienhold Brian J.
Published: July 2010

Biota and topography are among the most important factors affecting nutrient status of wildland soils. Knowledge of these relations has a fundamental bearing on management of chaparral ecosystems. This study was conducted to determine the effect of shrub species and topographic aspect on availability of soil N and P in Arizona chaparral soils. Soil was collected under the canopy of 32 randomly selected shrubs, eight each of birchleaf mountain mahogany (Cercocarpus betuloides Nutt.) and shrub live oak (Quercus turbinella Greene) from both north and south aspects. A pot culture technique, using barley (Hordeum vulgare L. var. gustoe) and mountain mahogany (C. montanus Torr.) as test plants, was used to estimate availability of soil N. and P. Both test plants showed that shrub species and aspect influenced nutrient availability. Availability of P was very low, while that of N was quite high. Lower availability of P in soils from southerly aspects was associated with low amounts of total soil P, probably the result of long‐standing differential erosion between north and south aspects, aggravated by fire. High N availability was probably associated with inputs of N via symbiosis between actinomycetes and mountain mahogany. Higher fertility of soils from oak systems is associated with lower lignin content of litter from these shrubs.
Kinetics of Weathering in Soils from a Subalpine Watershed
Authors: Brown Aaron D. , Lund Lanny J.
Published: July 2010

Weathering reactions were studied in samples of two subalpine soils from the Emerald Lake Watershed in Sequoia National Park, California (36°35′N, 118°40′W). Rates of weathering were measured as a function of pH and ionic strength. Reaction kinetics were characterized by rapid H+ consumption, and Si, Al3+, Ca2+, and Mg2+ release in the first week. This was followed by a period in which H+ consumption and cation release were a linear function of time for up to 4 wk. Based on reaction stoichiometry and equilibrium calculations, rapid short‐term H+ consumption in these soils was related to Al solubility. The rate laws for long‐term acid consumption were approximately first order with respect to H+ concentration in the pH range 3 to 5. The consumption of H+ was independent of NaCl concentration. These results indicate that the long‐term acid‐consumption kinetics of these soils are consistent with a surface‐reaction‐controlled mechanism. Although the distribution of products was slightly different, the fractional orders of the rate laws for Ca, Si, and Mg release in response to acid addition were similar in these two contrasting soils. Based on reaction rates and solution composition, long‐term acid consumption was attributed to weathering of plagioclase or hornblende.
High‐Elevation Forest Soils of the Southern Appalachians: II. Geomorphology, Pedogenesis, and Clay Mineralogy
Authors: Feldman S. B. , Zelazny L. W. , Baker J. C.
Published: July 2010

We investigated soil mineral weathering sequences in three geologically distinct high‐elevation areas of southern Appalachian spruce‐fir (Picea rubens Sarg.‐Abies fraseri [Pursh.] Poir) forests in order to elucidate the pedogenic factors that distinguish these unique soils from their low‐elevation counterparts. Four pedons representing a developmental sequence ranging from soils having distinct spodic field morphology (E plus Bhs horizons) to those having either minimal (weak E horizons) or no spodic character (umbric epipedons/cambic horizons) were selected for further study from a total of 35 excavated pits. Whereas the mineralogy of sand and silt fractions reflected inheritance from parent materials, clay mineral suites of all soils were very similar, indicating biotic and climatic controls on weathering. Surface‐horizon clay fractions were dominated by regularly interstratified mica/vermiculite and high‐charge smectite, which decreased with depth in all profiles. Subsoil clay fractions were principally composed of gibbsite and hydroxy‐interlayered vermiculite. Genesis of secondary 2:1 layer silicates in these soils occurs initially by the pseudomorphic transformation of biotite to both hydrobiotite and vermiculite. However, direct conversion of biotite to kaolinite is of little importance in these soils. The demonstrated mobility of Al‐organic complexes out of surface horizons and the inability of hydroxy‐Al interlayers to form in vermiculite in the presence of organic acids suggest that these soils are undergoing early stages of podzolization and that they are more similar to northern Appalachian Spodosols than they are to adjacent low‐elevation soils of the southern mountains.
Potassium Accumulation and Corn Yield Related to Potassium Fertilizer Rate and Placement
Authors: Heckman J. R. , Kamprath E. J.
Published: July 2010

Sandy Coastal Plain soils have relatively low reserves of K and may not be able to supply adequate K for intensive corn (Zea mays L.) production. Field experiments were conducted on Dothan loamy sand (fine‐loamy, siliceous, thermic Plinthic Paleudult) for 3 y to determine K fertilizer rate and placement effects on corn growth and seasonal K accumulation. Treatments were 0, 56, 112, 168, and 224 kg K ha‐1 broadcast and 56 kg K ha‐1 banded plus 0, 56, 112, and 168 kg K ha‐1 broadcast. Total K accumulation was increased by K fertilization rate each year. Method of application had a significant effect in a relatively dry year when the broadcast‐plus‐banded treatments resulted in greater K accumulation. Stover dry matter was increased in two of three years with 56 kg K ha‐1, but grain yield was increased in only one year. Yield increased linearly with K rates up to 112 kg K ha‐1 when the initial exchangeable‐K level was 0.21 cmol L‐1. Critical exchangeable‐K level was 0.35 cmol L‐1 and the critical soil solution K concentration was 0.48 mmol L‐1 for dry‐matter yield. When corn is grown with intensive production practices, there is little benefit in applying banded K with broadcast K on sandy soils testing high in K.
Nitrogen Fertilizer and Dairy Manure Effects on Corn Yield and Soil Nitrate
Authors: Jokela William E.
Published: July 2010

Manure from livestock is an important source of N for crop production in many areas, but efficient management of manure is critical to improve the economics of manure use and to minimize the impact on water quality. A field study was conducted on an Enosburg fine sandy loam (sandy over loamy, mixed, nonacid, mesic Mollic Haplaquent) in northwestern Vermont to evaluate the effect of dairy‐manure and N‐fertilizer application on corn (Zea mays L.) yields and soil profile NO3 in a silage production system. Treatments consisted of a factorial arrangement of manure (0 and 9 Mg ha‐1, dry‐matter basis), N rate (56 and 112 kg ha‐1 as NH4NO3), and time of N application (planting or six‐leaf stage), as well as 0 and 168 kg N ha‐1 rate at planting (with and without manure). Yields and N uptake were increased by N fertilizer and by manure. Without manure, grain and silage yields were increased by fertilizer N to the 112 kg ha‐1 rate in all years; with manure, N fertilizer did not increase yields significantly. Time of application had little or no effect on yield. Plant uptake of N followed a similar pattern but with somewhat more pronounced effects. A presidedress NO3 soil test reflected N availability, as indicated by relative yields. Manure application rates were equivalent, in terms of yield response, to 73 to 122 kg fertilizer N ha‐1 in individual years, which represented 27 to 44% of the total manure N in the year of application. Sampling of the 1.5‐m soil profile before planting and after harvest showed increases in soil NO3 that were related to the amounts of manure and fertilizer N applied. Some decreases in NO3 were measured from fall to spring sampling times, but net losses were minimal where <60 kg ha‐1 NO3‐N was present in the fall. Application of manure resulted in similar or slightly lower soil profile NO3 than agronomincally equivalent rates of fertilizer N.
Organic Carbon Effects on Available Water Capacity of Three Soil Textural Groups
Authors: Bauer Armand , Black A. L.
Published: July 2010

A major cause of soil productivity loss through erosion is attributed to changes in soil water‐holding properties or a reduction in thickness of the plant rooting zone. The objective of this study was to measure the effect of management‐induced changes in soil organic carbon (OC) concentration on soil characteristics affecting the available water capacity. Four sites each of moderately coarse (sandy), medium, and moderately fine or fine (fine) soils were sampled in four increments to 0.457 m within each of two cropland management systems (conventionally cultivated and stubble mulched) and each of two virgin grassland management systems (grazed virgin and relict virgin). Measurements of the water concentration by weight (Pw) at field capacity (FC) and permanent wilting point (PWP) were made on disturbed soil samples. Bulk density decreased with increasing OC concentration. The magnitude of change was greatest in sandy and least in the medium‐textured soils. For all soils combined, a change in sand fraction accounted for about 75% of the change in Pw at both the FC and the PWP. The change in Pw was greater at FC than the PWP. A unit change in OC concentration in the sandy soils caused a greater change in Pw at FC than at the PWP, but in the medium and fine soils the change in Pw at FC essentially paralleled the change at the PWP. An increase in OC concentration did not change the available water capacity in the sandy group and decreased it in the medium and fine textural groups. Loss of soil productivity induced by erosion in the northern Great Plains is probably more closely associated with a decline in nutrients and biological activity than from a change in available water capacity.
Estimating Crop Residue Decomposition from Air Temperature, Initial Nitrogen Content, and Residue Placement
Authors: Douglas C. L. , Rickman R. W.
Published: July 2010

Managing cereal residues to control soil erosion by wind and water requires knowledge of residue decomposition. Four equations were developed to estimate decomposition of cereal residues based on cumulative degree days (CDD) calculated from daily maximum and minimum air temperature. Each is based on the general equation Rr = Ir exp(fN fW k CDD), where Rr = residue remaining, Ir = initial residue, fN is an N coefficient based on initial residue N content, fW is a water coefficient based on a combination of residue and field management, and k is a general decomposition coefficient. Projected decomposition was tested against data for different varieties of soft white and hard red spring and winter wheat (Triticum aestivum L.), durum wheat (T. durum Desf.), spring and winter barley (Hordeum vulgare L.), triticale (× triticosecale Wittm.) corn (Zea mays L.), and soybean [Glycine max (L.) Merr.] from Alaska, Idaho, Indiana, Missouri, Oregon, Texas, and Washington. The mean slope of the line relating observed to projected decomposition for all locations was 1.10 ± 0.543 with r2 values ranging from 0.76 to 0.99, with most > 0.95.
Overlaying Soil and Timber Inventories to Assess Aspen Productivity in Northern Minnesota
Authors: Bates P. C. , Robert P. C. , Blinn C. R.
Published: July 2010

Forest soil productivity is a difficult quantity to measure, yet it is an integral component of forest management decisions and an important interpretation of soil inventories conducted in forested areas. Soil‐site studies are time consuming and expensive, and often cannot identify productivity differences between soil units. Merging timber‐inventory data with soil‐survey data may provide an efficient means for evaluating forest productivity. In this study, timber‐inventory data were overlaid with soil‐survey data for Beltrami County, Minnesota. Soil map units were grouped into 10 soil classes based on drainage and parent material. Productivity of aspen (Populus tremuloides Michx. and P. grandidentata Michx.) was compared between soil classes using the estimates of volume, site index, and basal area collected during the timber inventory. Analysis of the volume data indicated that the soils formed in outwash deposits were significantly less productive (mean volume of stands between 40 and 55 yr = 126 m3 ha‐1) than soils formed in calcareous glacial till or calcareous deposits of stratified fine sands and silts (mean volume of stands between 40 and 55 yr = 155 m3 ha‐1). Very poorly drained soils were also in the higher productivity group, though aspen was a relatively minor cover type on these soils. The site‐index data was of minimal value in separating soils into productivity groups. Basal area was highly correlated with volume estimates and may be a useful stand attribute for assessing forest productivity during land‐resource inventories.
A pH‐Stat Procedure for Evaluating Reactivity of Agricultural Limestone
Authors: Hartwig R. C. , Loeppert R. H.
Published: July 2010

Limestone dissolution occurs as a surface reaction; therefore, the particle‐size distribution of the material influences its reactivity. Particle‐size distribution alone, however, may not provide a good comparative index of reactivity because of differences in mineralogy, surface composition, and morphology. A pH‐stat titration procedure was previously developed to determine the “effective” reactivity of soil carbonate. The objective of this study was to evaluate the pH‐stat procedure as a method for comparing the reactivities of liming materials. Eighteen liming materials, representing a wide range of physical and chemical properties, were analyzed. The relative reactivities of the materials are expressed as Iceland‐spar reactivity equivalent (ISRE), and reported as particle‐size distribution (ISRE‐PSD) or surface area (ISRE‐SA) of a standard Iceland‐spar calcite that has the equivalent quantity and reactivity as the sample. The ISRE‐PSD of the calcitic materials gave higher proportions of fine‐clay‐size particles than were obtained by sieving and sedimentation, indicating that the calcitic liming materials had greater surface reactivities than the Iceland‐spar calcite standard. The dolomitic materials, being less reactive than the calcitic materials, exhibited large proportions of ISRE fine‐sand‐size particles and small proportions of ISRE clay‐size particles. Calculations of surface area using ISRE‐PSD data provide a more explicit index of reactivity than the ISRE‐PSD. The ISRE‐SA values of the calcitic and dolomitic materials were not highly correlated with surface areas determined by the Brunauer‐Emmett‐Teller (BET) or sedimentation procedures, indicating the pH‐stat procedure provides a method for comparing the reactivities of liming materials not possible by BET, sieving, or sedimentation methods.
Oxalate Determination in Soils Using Ion Chromatography
Authors: Lilieholm B. C. , Dudley L. M. , Jurinak J. J.
Published: July 2010

A method was developed for determining oxalate in soils with variable levels of CaCO3. The soils were extracted with 1.0 M HCl for varying periods of time at 80 °C and room temperature, as well as being extracted as saturation pastes. Oxalate in the extracts was determined on and ion chromatograph, with special care taken in the cleaning of the column and suppressor. The eluant was 0.85 mM NaHCO3 and 0.90 mM Na2CO3. Recovery of oxalate from CaC2O4 spiked samples extracted with HCl ranged from 16 to 104%. Each soil required a different extraction time to obtain maximum release of oxalate. Soil with the greatest CaCO3 content yielded the lowest oxalate recovery. Oxalate content of unspiked samples was also determined. Recovery of oxalate as CaC2O4 from the saturation pastes ranged from 0.1 to 25.0%. Detection limits were 15 µg L‐1 in the HCl extracts and 22 µg L‐1 in the saturation‐paste extracts.
Apparent Solubility Products of Phosphorus Impurity Compounds in Commercial Monoammonium Phosphate Fertilizers
Authors: Sikora F. J. , Copeland J. P. , Mullins G. L.
Published: July 2010

Monoammonium phosphate (MAP) fertilizers contain P impurity compounds that have low solubility and bioavailability. Solubility products of fertilizer impurity compounds not currently documented would be useful data to predict the solubility and subsequent P bioavailability of the compounds in soil. Water‐insoluble MAP fractions from seven commercial MAP fertilizers were equilibrated with water and the filtrate was analyzed for total concentration of chemical components. Activities of individual elements were calculated using a chemical speciation program, MINEQL, and were used to determine apparent solubility products (Kosp) of P impurity compounds. The apparent log Kosp values were −16.33, −9.33, and −14.59 for Al‐NH4HPO4F2, FeNH4(HPO4)2, and MgAl(NH4)2H(PO4)2F2, respectively. The values were only considered estimates because they were determined from a heterogeneous mixture of compounds in the water‐in‐soluble MAP fractions rather than pure solid phases. The approximate log Kosp values were instructive for comparing solubilities of the impurity compounds with solubilities of variscite, strengite, monetite, brushite, struvite, and FePO4(c) in water and soil. At pH 6 in water, the general order of decreasing P solubility was struvite > brushite > monetite > MgAl(NH4)2(PO4)2F2 = AlNH4HPO4F2 > FeNH4(HPO4)2 > > FePO4(c) > variscite ≈ strengite. In soil, the P impurity compounds have a greater solubility than variscite, strengite, monetite, and brushite between pH 5.5 and 7. Therefore, the impurity compounds are not expected to remain intact in soil for long periods of time. Of the three impurity compounds, MgAl(NH4)2H(PO4)2F2 appears to be the least desirable because of lower calculated solubility in soil.
Desorption and Extraction of Selected Heavy Metals from Soils
Authors: Sheppard Marsha I. , Thibault Denis H.
Published: July 2010

The need for proper disposal of industrial wastes and for remediation methods for soils contaminated with heavy metals necessitates a better understanding of the processes involved in mobilizing, transporting, and retaining elements in surface soils. The objective of this study was to investigate the desorption in water and efficacy of several traditional extraction agents in removing Tc, Np, Mo, U, Cr, Pb, Cs, and Th. Selected slices were taken with depth in acidic sand (Dystrochrept) soil cores that were spiked for 4 yr. Similarly, Tc, Np, and U were desorbed and extracted from the clay subsoil of reed/sedge peat cores following a one‐season migration study. Technetium and Mo behaved as anions, and the small amount of Tc retained was attributed to insoluble organic complexes and oxides in the sandy soil and carbonates in the clay subsoil. The retention of Mo was attributed to colloidal Fe(III) oxides and organic colloids or complexes. Neptunium sorption appears to be dependent on the variable charge of the soil, making organic matter and pH important factors. Uranium and Pb were associated with the oxides. Cesium and Cr took part in inorganic reactions that fixed them rigorously to the soil solids or formed precipitates; Th formed organic complexes. Results suggest that remediation techniques for soils contaminated with Tc, Mo, and Np could be quite successful using intense leaching with acidified water. Soils containing U, Pb, and Th may be partially reclaimed by manipulation of the organic matter or leaching with organic acids; however, soils contaminated with Cs and Cr would require extensive chemical treatment.
Phosphorus Distribution in Calcareous Soil Profiles of the Central Plains
Authors: Bowman R. A. , Savory D. J.
Published: July 2010

Deep‐rooted crops benefit from high subsurface P content. While some documentation exists for high levels of available inorganic P well below the soil solum, very little information exists on organic‐P contents deep in the soil profile. This research was conducted to document the presence of large pools of available organic and inorganic P on top of a carbonate layer 2.2 m below the soil surface. Additionally, soil organic C, N, texture, and selected mineral concentrations were determined to assess their correlations with total P. Soil samples (Aridic Argiustolls) from two fields that have been out of cultivation for at least 10 yr were taken in 0.15‐m increments to a depth of =2.5 m. The surface soils (0.0–0.3 m) were high in nutrients (11.0 g C and 1.1 g N/kg soil) and negligible in carbonates; the middle soil layers (0.30–0.25 m) were low in nutrients (4.0 g C and 0.3 g N/kg) and intermediate in carbonates (90 g/kg); and the deep soil layers (2.25–2.55 m) were high in available inorganic and total organic P, and very high in carbonates (> 300 g/kg). The total P concentration in the profile was inversely correlated with the percentages of sand and Ca, and directly correlated with the total content of Fe and Al. Total organic C and N and, to a greater extent, total organic P accumulated near or on top of a carbonate layer. Most of the organic C and P below 0.45 m were soluble in 2 M HCl. For the surface soil (0.0–0.45 m), the bulk of the organic P was extracted only after 2 M HCl pretreatment. Alfalfa and similar deep‐rooted crops may benefit from this large reserve of available P near the water table.
Interaction of Nitrapyrin and Dicyandiamide with Soil Humic Compounds
Authors: Jacinthe P. A. , Pichtel J. R.
Published: July 2010

Sorption to organic matter is a primary factor influencing the effectiveness of nitrification inhibitors applied to soils. Interaction of the nitrification inhibitors nitrapyrin [2‐chloro‐6‐(trichloromethyl)‐pyridine] and dicyandiamide (DCD) with humic acid (HA) and fulvic acid (FA) was studied to compare the adsorptivity of the humic materials and elucidate adsorption mechanisms. Ten milligrams of HA or FA were suspended in aqueous solutions (10 mL) of either nitrapyrin (2, 4, 6, 8, and 12 mg L−1) or DCD (5, 10, 20, 40, and 80 mg L−1). The quantity of nitrification inhibitor adsorbed was measured after shaking the suspension of nitrapyrin for 24 h or DCD for 48 h. Results of adsorption experiments along with Freundlich K values indicate that FA adsorbed more DCD than HA, and HA was a better adsorbent for nitrapyrin. Infrared spectra provided evidence that adsorption occurred predominantly through an ionic‐bonding mechanism involving the protonated amino group of DCD or the N of the pyridine ring of nitrapyrin and the negatively charged functional groups of the humic materials. The contribution of hydrophobic forces in the adsorption of the nitrification inhibitors was minimal.
In Situ Measurement of the Effective Transport Volume for Solute Moving Through Soil
Authors: Clothier B. E. , Kirkham M. B. , McLean J. E.
Published: July 2010

A simple field method for measuring the soil's effectively mobile water fraction during near‐saturated flow is presented. Initial charging of the immobile fraction θim is achieved by first wetting the soil with a disk permeameter until steady conditions prevail. The disk is then removed and rapidly replaced, but now filled with a tracer solution. Subsequently after a period of infiltration with tracer (0.1 M KBr), the soil underneath is sampled. The ratio of the measured to applied concentration, c*/cm, in the samples will be the fraction of the soil's water that is effectively mobile. We assume that the antecedent tracer concentration is zero, and that the mobile fraction, θm, is at concentration cm. Disk permeameters, set at the slightly unsaturated potential head ψo = −20 mm, wetted Manawatu fine sandy loam to a water content of θo = 0.414 m3 m−3. From analysis of the tracer concentrations measured under the disk, we deduced θm to be just 0.203. This semimobility was in accord with the observed depthwise penetration of tracer, as well as other measures of mobility previously found by others from longer term leaching studies carried out nearby.
Mineralization of Nitrogen and Phosphorus from Soil Organic Matter in Southern Pine Plantations
Authors: Polglase P. J. , Comerford N. B. , Jokela E. J.
Published: July 2010

Sustained weed control and/or annual applications of fertilizer have accelerated stand development of young slash pine (Pinus elliottii Engelm. var. elliottii) and loblolly pine (P. taeda L.) growing on Spodosols in Florida. Productivity of these plantations will depend largely on the extent to which nutrients are recycled through soil organic matter derived from decomposition of fresh residues. We attempted to sample this newly formed soil organic matter and measured the effects of weed control and fertilizer treatments on N and P mineralization under laboratory conditions (42‐d aerobic incubation). Sequential in situ containments using interbed soil were used to provide information on field rates of mineralization. The laboratory study demonstrated that specific N mineralization was little affected by cultural treatment. In contrast, specific P mineralization was consistently increased by fertilizer application, both in the laboratory and in situ. This suggests that, in organic residues, the general composition of P substrates was altered by fertilizer application, while organic‐N substrates remained unaffected. The effect of weed control inhibited specific N and P mineralization in the laboratory, indicating that organic residues of understory vegetation are a better supply of available N and P than are organic residues of pine. In fertilized plots and for P, annual rates of in situ mineralization were large relative to demand (uptake) by vegetation. The recycling of P through organic residues of fertilized plots has the potential to enhance long‐term productivity beyond the immediate benefits derived from fertilizer uptake.
Predicting Removal of Major Soil Cations and Anions during Acid Infiltration: Model Evaluation
Authors: Gaston L. A. , Mansell R. S. , Selim H. M.
Published: July 2010

Models for the effects of acid deposition on soil acidification generally have not been adequately validated, especially under conditions of simultaneous water flow. The objective of this study was to assess the capability of a simple model for soil acidification and solute transport to describe changes in solution‐ and sorbed‐phase compositions of acid soil subjected to inputs of H ion. Columns of Cecil series (clayey; kaolinitic, thermic Typic Kanhapludult) and Candler series (hyperthermic, uncoated Typic Quartzipsamment) soils were leached with pH 3.0, 3.7, and 4.7 solutions. Effluent was collected in fractions and analyzed for ionic composition. Evaluation of model performance was based on a comparison of soil column leachate compositions to model predictions. The model adequately described effluent pH. However, it tended to overpredict concentrations of basic cations removed by infiltration of pH 3.0 and 3.7 solutions. Conversely, the model underpredicted concentrations of Al in the effluent from columns leached with pH 4.7 acid. These discrepancies may reflect an inadequacy of simple equilibrium models for cation exchange and Al solubility. Extension of the model to include exchange kinetics improved predictions of effluent Ca and Mg concentrations. An empirical model for Al solubility better described effluent Al concentrations than did the equilibrium dissolution of gibbsite.
Water‐Insoluble Impurity Effects on Phosphorus Availability in Monoammonium Phosphate Fertilizers
Authors: Bartos J. M. , Mullins G. L. , Williams J. C. , Sikora F. J. , Copeland J. P.
Published: July 2010

Water‐insoluble, P‐containing impurity compounds can form during the production of commercial monoammonium phosphate (MAP, NH4H2PO4) fertilizers. Increased reliance on lower grade phosphate rock (PR) could result in an increase in these water‐insoluble fertilizer impurity compounds, thus lowering the percentage of water‐soluble P in commercial P fertilizers. There is some concern regarding the effect that impurity compounds may be having on P‐fertilizer effectiveness. Therefore, a greenhouse study was initiated to determine the concentration at which water‐insoluble impurity compounds will reduce MAP‐fertilizer effectiveness. Five commercial MAP fertilizers, representing the major U.S. sources of PR (Florida, North Carolina, and Idaho), were selected for study. Fertilizer impurities were collected as water‐insoluble residues by washing the MAP fertilizers with deionized water. Mixtures of water‐soluble, reagent‐grade MAP and the water‐insoluble fertilizer residues were prepared to give a wide range in water‐soluble P. The fraction of water‐soluble P was controlled by supplying 0, 20, 40, 60, 80, and 100% of the total P as reagent‐grade MAP. Fertilizer mixtures were applied at a rate of 80 mg P kg−1 soil, and sorghum‐sudangrass [Sorghum bicolor (L.) Moench] was grown in the treated soil. Four harvests were taken at 21‐d intervals. Forage yields and P uptake were affected by the content of water‐soluble P and the source of fertilizer P. Statistical analysis of the data for the five sources produced two separate regression yield models. The two respective fertilizer groups required 57 and 68% water‐soluble P to obtain 90% of the maximum yield. Results from this study indicate that current impurity levels in MAP fertilizers are not a major agronomic problem.
Revised Quasiparticle Model of Protonation and Metal Complexation Reactions
Authors: Sposito Garrison , Blaser Peter
Published: July 2010

A Scatchard quasiparticle model was developed previously by the authors to account for protonation side reactions in trace metal complexation by organic ligands in an aqueous leaf litter extract. This model is inconsistent with the typical acid‐base behavior of organic acid mixtures expected at low pH. A detailed investigation of a mixture of monoprotic quasiparticles led to a new expression for the protonation side‐reaction coefficient that yields correct acid‐base chemistry at any pH. The new expression also requires quantitative revision of the reaction stoichiometries and pH‐independent conditional stability constants reported previously by the authors based on a Scatchard quasiparticle model of metal‐ organic complexes involving Cu or Al. Besides these quantitative effects, the revised results also emphasize the important conceptual point that quasiparticle models of protonation and metal complexation reactions are formulated and tested independently of one another.
Dynamics of Potassium Chloride Induced Manganese Release in Different Soil Orders
Authors: Krishnamurti G. S. R. , Huang P. M.
Published: July 2010

The salt‐induced Mn release from soils has been known for more than two decades; its kinetics and mechanism still remain obscure. Manganese release from selected soils of different taxonomic orders was studied as a function of the concentration of KCl (0, 0.01, 0.1, and 1.0 M), reaction period (0–216 h), and temperature (277, 298, and 317 K) to understand the influence of KCl on the dynamics of the release of soil Mn. The soils were sampled from six countries located in temperate and subtropical regions. Total Mn contents of the soils varied from 2.9 to 32.5 mmol kg−1; Mn was generally concentrated in the <2‐µm size fractions. At the end of a 24‐h reaction period at 298 K, Mn release increased consistently by 12 to 161 times as the concentration of KCl increased from 0 to 1.0 M. The amount of Mn released from the calcareous Vertisols by 1 M KCl was very low (12–20 µmol kg−1) during the reaction period of 0 to 24 h, even though the total Mn content was among the highest (25.1–32.5 mmol kg−1). Manganese release from selected soils, an Oxisol (Pakua), two Alfisols (Hyderabad and Waitville), and a Mollisol (Oxbow Orthic) by 1 M KCl followed parabolic diffusion kinetics. The activation energy of Mn release, calculated from the overall diffusion coefficients, varied from 10.9 to 16.5 kJ mol−1 among the soils, indicating diffusion as the predominant process in limiting the rate of Mn release. Ionic‐strength effect coupled with complexation was mainly responsible for the enhanced Mn release by KCl from the soils in the common soil pH range.
Seasonal Microbial Biomass Dynamics after Addition of Lentil and Wheat Residues
Authors: Bremer E. , van Kessel C.
Published: July 2010

The dynamics of soil microbial biomass after the addition of plant residues have a considerable influence on nutrient availability for plants, and can be quantified using the chloroform‐fumigation‐extraction method. The dynamics of microbial C and N following addition of 14C‐ and 15N‐labeled lentil (Lens culinaris Medik.) green manure, lentil straw, and wheat (Triticum aestivum L.) straw were investigated under field conditions at a site located at Outlook, Saskatchewan, on a Bradwell sandy loam (Typic Boroll). Plant residues were incorporated into microplots on 5 Oct. 1988, and the fraction of added 14C and 15N in microbial biomass was determined on four dates during the 1989 growing season. Maximum levels of labeled and unlabeled microbial biomass were observed at the time of planting (8 May) in 1989. Of added 14C, 26 and 15% was in the microbial biomass in the green manure and straw treatments, respectively, on 8 May; greater microbial accumulation of green‐manure 14C was due to a higher proportion of 14C being available rather than to a higher efficiency of 14C assimilation. Microbial 15N accounted for 65 to 81% of added residue 15N on 8 May. Plant‐residue 15N was readily available to decomposer microorganisms from all residue types, whereas 14C was more available from green manure than straw. During the 1989 growing season, microbial 14C declined by 51 and 40% in the green manure and straw treatments, respectively, while microbial 15N declined by 54% in all treatments. The decline in microbial 15N during the 1989 growing season was approximately five times greater than the amount of 15N mineralized in all sampling periods except the first for the green‐manure treatment. The highest levels of labeled and unlabeled microbial biomass observed at the time of planting indicates that microbial biomass may reduce losses of N and other nutrients during periods of low crop demand, and may act as a source of nutrients during active crop growth.
Automated Monitoring of Nitrous Oxide and Carbon Dioxide Flux from Forest Soils
Authors: Loftfield N. S. , Brumme R. , Beese F.
Published: July 2010

Gas flux determinations at the soil‐atmosphere interface are of value when modeling either soil or atmospheric chemistry. We describe a system for the automated analysis of N2O and CO2 flux from the soil surface. Fluxes are measured by monitoring increases in N2O and CO2 in double‐walled Plexiglas chambers at 30‐ and 60‐min intervals after the chamber lids are closed. Opening and closing of the chamber lids, gas sampling operations, and data collection and analyses are all controlled by a personal computer. In addition to gas fluxes, air and soil temperature as well as light intensity can be monitored. Using this system, up to 12 chambers can be continuously monitored within a 300‐m2 area.
Heterogeneity of Soil Mineral Nitrogen in Pasture Grazed by Cattle
Authors: Afzal M. , Adams W.A.
Published: July 2010

Herbage growth on grazed pasture is commonly limited by N availability. The availability of N in soils is affected by inputs of fertilizer N through N mineralization from soil organic matter and by the return of N on local areas in animal excreta. Our objective was to describe the spatial and vertical heterogeneity in soil mineral N caused by the deposition of excreta on pasture grazed by dairy cattle (Bos taurus). The persistence and change in pattern of heterogeneity was examined both during and between grazing seasons. The soil is a Dystric Eutrochrept and perennial ryegrass (Lolium perenne L.) was the dominant species in the sward. Intact soil cores were taken at 10‐cm intervals on randomly selected 5‐m transects during the grazing season in 1989 and immediately prior to grazing in 1990. Fresh cattle dung and simulated cattle urine were applied both during and at the end of the grazing season. Spatial variation in soil mineral N developed during the grazing season with differences in NO3‐N up to 66 mg N L−1 and total mineral N (TMN) up to 250 mg N L−1 occurring between sampling points at 10‐cm centers. Sites unaffected by excreta had TMN concentrations of ≈11 mg L−1 with less than one‐quarter of this as NO3‐N. Dung patches applied in summer increased TMN in the 0‐ to 2‐cm depth range only. Left over winter, they increased the soil TMN content significantly but did not increase mineralizable N. Urine patches caused a much greater increase in TMN than dung and the pattern of heterogeneity with depth changed with time. Soil NO3‐N remaining in spring beneath simulated urine patches applied in autumn was distributed throughout a depth of at least 1 m and vertical heterogeneity persisted into the summer.
Corn Responses to Ammonium‐ and Nitrate‐Nitrogen Fertilization
Authors: Barber K. L. , Maddux L. D. , Kissel D. E. , Pierzynski G. M. , Bock B. R.
Published: July 2010

Studies have indicated that, by maintaining relatively high solution culture or soil NH+4/NO‐3 ratios during the reproductive growth stage, certain corn (Zea mays L.) genotypes have a higher yield potential. Unfortunately, few data on soil NH+4 and NO‐3 levels have been reported. A 3‐yr field experiment was conducted in northeastern Kansas in 1987, 1988, and 1989 to evaluate the effects of time and form of applied N on fertilizer band NH+4/NO‐3 ratios and on the N nutrition, dry‐matter accumulation, and grain yield of two corn hybrids. Urea, urea‐NH4NO3, urea plus Ca(NO3)2, NH4NO3, and Ca(NO3)2 solutions having NH+4/NO‐3 ratios of 1:0, 3:1, 1:1, 1:1, and 0:1, respectively, were used at equivalent N rates. The nitrification inhibitors, nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine] and dicyandiamide, as well as two‐way and three‐way timing of application schemes were used to maintain N as NH+4. Split applications of ammoniacal N with a nitrification inhibitor were effective in maintaining elevated soil NH+4 concentrations from planting through early grain fill. In 1988 only, grain yield was increased slightly (3–9% higher) when corn was fertilized with ammoniacal N compared with NO‐3 only. Overall, manipulation of soil NH+4/NO‐3ratios had few effects on corn development or yield.
Automated Nitrogen‐15 Analysis of Ammonium in Diffusion Disks by the Rittenberg Technique
Authors: Liu Y. P. , Mulvaney R. L.
Published: July 2010

A recent development in 15N analysis of inorganic N in soil extracts involves diffusion of NH3 into acidified glass‐fiber disks in disposable specimen containers. A simple and convenient technique was developed for isotope‐ratio analysis of the NH4 in these disks using a mass spectrometer equipped with an automated Rittenberg apparatus (ARA‐MS). For collection of diffused NH3, the disks were treated with 10 µL of 1 M H2SO4. Following diffusion for 6 d, the disks, containing 50 to 150 µg of N, were transferred to a disposable plastic sample tray (96 wells per tray) and treated with 10 µL of 28.9 M (concentrated) HF, which digested the disks without affecting the tray. The tray was placed in a desiccator containing anhydrous CaSO4, for drying of the digested disks in 1 to 3 d. Good agreement was obtained between 15N analyses of diffused and nondiffused NH4‐N when correction was made for isotopic dilution by NH4 in the reagents used in diffusion. Trays containing the processed disks can be conveniently shipped to a service laboratory for analysis by ARA‐MS.
Chisel Tillage, Furrow Diking, and Surface Crust Effects on Infiltration
Authors: Baumhardt R. L. , Wendt C. W. , Keeling J. W.
Published: July 2010

Chisel tillage and furrow dikes (small earthen dams constructed in the furrow) are commonly used to increase infiltration and soil water storage in semiarid regions. Data quantifying the combined influences of these practices are limited. Our objective was to determine the effects of chisel tillage, furrow dikes (with and without ponding), and drop impact or surface crusts on infiltration. Infiltration rate (IR) and cumulative infiltration (CI) into an Olton clay loam (fine, mixed, thermic Aridic Paleustoll) were measured by applying water at 65 and 80 mm h−1 for 1 h using a rotating‐disk‐type rainfall simulator. Furrow dikes increased infiltration under both ponded and nonponded conditions. Cumulative infiltration was higher when raindrop impact energy was dissipated and, to some extent, when crusts were removed. Infiltration rate at the end of water application was lower with raindrop impact than when raindrop impact was eliminated; however, there were no differences in the final IR between the initially crusted and uncrusted soils. There were no differences in infiltration between chisel‐disk and disk tillage measured during the mid growing season. Furrow dikes not only detain water on the surface to provide more time for infiltration, but also increase infiltration through increased hydraulic head and additional tillage performed during dike installation or by moving loose soil from the furrow into the dikes. Our data do not support using the same hydraulic‐conductivity value for both diked and undiked field conditions, which may cause underestimation of water conservation in furrow‐diked fields.