bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Procedures for Reducing Cross‐contamination During Steam Distillations in Nitrogen‐15 Tracer Research
Authors: Mulvaney R. L.
Published: July 2010

A study was conducted to compare the effectiveness of various procedures for reduction of cross‐contamination errors when unenriched samples of (NH4)2SO4 containing 0.5 mg of N were steamdistilled in a glass distillation apparatus following samples enriched with 50 atom % 15N. Twelve procedures were compared in this study, including most of those previously proposed in the literature. None of the procedures completely eliminated cross‐contamination; however, some were considerably more effective than others. The results suggest that, when a glass distillation apparatus is used in 15N‐tracer research, the best way to reduce cross‐contamination error is to distill two aliquots of each sample whenever possible, discarding the first distillate and retaining the second for isotope‐ratio analysis. When this is not possible, it is recommended that 1 mL of 1M formic acid be distilled for 1 min and 25 mL of 16.4 M (95%) ethanol be distilled for 3 min between samples. This procedure can be made more effective by increasing the amount of formic acid used and extending distillation beyond 1 min.
Available Nitrogen and Nitrogen Cycling in Forest Soils Exposed to Simulated Acid Rain
Authors: Stroo H. F. , Alexander Martin
Published: July 2010

The formation of NO‐3 and NH+4 was measured in columns containing samples from the surface horizons of 12 forest soils both during and after exposure to simulated rain applied at three times the ambient deposition rates for 116 d. The relative responses to increased acidity were correlated with organic matter and N levels of the soils. The average inhibition for the 12 soils was linearly related to the amount of acidity added. The quantity of N mineralized was less in some soils after their exposure to simulated rain at pH 3.5 than at pH 5.6 and greater in other soils, but the average amount mineralized after exposure of the 12 soils was not significantly affected by the pH of the simulated rain during the treatment period. The mean percentage of the inorganic N produced in the 12 soils that was in the NO‐3 form was lower during but not after the exposure to simulated rain at pH 3.5 than at 5.6. The amount of inorganic N added in the simulated acid rain exceeded the diminished supply arising because of the inhibition of mineralization during the exposure. The suppression of N mineralization in Crary soil (Aquic Fragiorthods) containing white pine (Pinus strobus L.) seedlings and in Mardin soil containing red oak (Quercus rubra L.) seedlings was less than in unplanted soil. The simulated rain at pH 3.5 altered the amounts of K, Ca, Mg, Al, Fe, and Mn leached from the soil. It is suggested that the inhibition of inorganic N formation by microorganisms in short periods of acid precipitation may be compensated by the N added with the precipitation, but the impact on available N over long periods of exposure is unknown.
Effects of Phosphorus/Aluminum Molar Ratio and Calcium Concentration on Plant Response to Aluminum Toxicity
Authors: Alva A. K. , Edwards D. G. , Asher C. J. , Blamey F. P. C.
Published: July 2010

Total aluminum (Al) in solution often comprises both monomeric and polymeric Al species. Concentrations of total and monomeric Al and Σ activities of monomeric Al species (Σ aAl mono) were determined in nutrient solutions at 40 µM Al with varying P/Al molar ratios (0, 0.02, 0.2, 2.0 and 4.0) and calcium (Ca) concentrations (0.5, 1.5, 5.0, 15 mM). Effects of these treatments on root elongation of soybean [Glycine max (L.) Merr.], sunflower (Helianthus annuus L.), subterranean clover (Trifolium subterraneum L.), and alfalfa (Medicago sativa L.) were determined. Concentrations of total and monomeric Al in solution decreased with increasing P/Al molar ratio. Ca concentration had no significant effect on concentration of total or monomeric Al, but significantly affected the Σ aAl mono in solution. Root elongation of the plant species increased with increasing P/Al molar ratio and Ca concentration. The increase in root elongation with increase in P/Al molar ratio was associated with a decrease in monomeric Al in solution. The beneficial effect of Ca on root elongation was evident even when Al in the root environment was expressed as Σ aAl mono, which effectively removes the ionic strength effect of Ca. However, at Σ aAl mono ≥ 18 µM, increasing Ca concentration failed to improve root elongation. The range of critical Al values for a 50% reduction in root elongation with varying Ca concentration was much narrower if based on Σ aAl mono than on the concentration of monomeric Al in solution. The critical Σ aAl mono, with increasing Ca concentration from 0.5 to 15 mM, varied from 12 to 17 µM for soybean, <8 to 16 µM for sunflower, <7 to 15 µM for subterranean clover, and <5 to 10 µM for alfalfa.
Soils at Prehistoric Agricultural Terracing Sites in New Mexico: I. Site Placement, Soil Morphology, and Classification
Authors: Sandor J. A. , Gersper P. L. , Hawley J. W.
Published: July 2010

Soils and landscapes used for runoff terrace agriculture sometime between 1000 to 1150 A.D. in a semiarid area of New Mexico were studied in order to infer criteria for site selection, and to determine possible long‐term effects of the land use. Terracing involved construction of small rock dams across hillslopes and drainageways with subsequent sedimentation occurring upslope of each dam. Sites occur primarily within a narrow range of possible locations, implying deliberate placement with respect to climatic, topographic, and soil factors. Locational characteristics commonly include elevations of 1800 to 2000 m, 3 to 10% slopes, <1‐ to 8‐ha drainage areas, and soils with strongly developed argillic horizons (claypans). These soils, Paleustolls and Argiustolls, are developed in Pleistocene volcanic alluvium. The claypan probably served to confine moisture within the crop rooting zone. Terracing functioned to reduce runoff velocity, increase soil moisture, and thicken a naturally thin loamy A horizon overlying the claypan. Soil morphological changes continuing to the present are mainly limited to surface horizons. Although A horizon texture was not appreciably altered by terrace sedimentation, A horizons are usually 10 to 30 cm thicker in cultivated soils. Peds in cultivated A horizons are generally coarser, blockier, and compacted relative to the dominantly granular structure of their uncultivated counterparts, and are lighter in color value. The structure and color changes are attributed to decreased organic matter contents resulting from cultivation and persisting conditions of reduced grass cover and accelerated erosion.
Soils at Prehistoric Agricultural Terracing Sites in New Mexico: III. Phosphorus, Selected Micronutrients, and pH
Authors: Sandor J. A. , Gersper P. L. , Hawley J. W.
Published: July 2010

In this third paper examining long‐term effects of prehistoric cultivation on some New Mexico Mollisols about 900 yr after abandonment, data on total P, inorganic P fractions, Fe, Mn, Zn, Cu, and pH are presented. Cultivation‐induced soil changes, involving losses of total and moderately available P and total Cu but gains in total Mn, were inferred by comparing cultivated soils with nearby, similarly developed uncultivated soils (controls). Comparisons were also made between A horizons and sediment deposits accumulated upslope of recently fallen trees. These deposits are considered analogous to fresh agricultural terrace deposits just prior to cultivation. Total P losses in cultivated soils avg 15, 18, and 18% in the upper A, A, and BAt horizons, respectively, relative to control soils, and about 22% in the A horizon relative to recent sediment deposits. Below the BAt horizon, total P levels in cultivated and control soils converge. Moderately available P is not significantly lower (p <0.05) in cultivated upper A horizons but is about 40% lower in cultivated complete A horizons. Other inorganic P fractions have not changed much in cultivated soils. While total Fe and Zn levels are unchanged in cultivated soils, Cu is lower by about 20% and Mn is 20% higher in cultivated A horizons. Manganese increase is attributed to sedimentation under reducing conditions accompanying terracing in cultivated areas. There is a trend towards slightly higher pH in cultivated A horizons.
Properties, Classification, and Interpretations of Minesoils at Two Sites in West Virginia
Authors: Thurman N. C. , Sencindiver J. C.
Published: July 2010

Minesoils on two surface mines in Monongalia County, West Virginia, were classified using a proposed amendment to Soil Taxonomy. Minesoil properties and interpretations for selected nonagricultural uses were determined for both mine sites. The proposed amendment grouped minesoils into families based on differences in rock fragment lithology, soil reaction (pH), and particle size. The minesoils had a high rock fragment content (33–45%), high bulk density (1.55–1.86 Mg m−3), low porosity (26–38%), low water retention capacity (0.07–0.12 kg kg−1), moderately slow estimated hydraulic conductivity (0.1‐1 µm s−1), an irregular distribution of organic C with depth, and strongly acid pH (4.1‐5.1). Soil factors affecting the nonagricultural use of the mine sites were slow percolation, stoniness, acidity, and droughtiness. Site factors—slope, irregular topography, size of the site, and the presence of highwalls and steep outslopes—were more limiting to development than soil factors. Classification using the proposed amendment to Soil Taxonomy aided in separating minesoils according to differences in management‐related properties and can be useful for general planning purposes.
Soybean Growth and Yield Responses to Starter Fertilizers
Authors: Touchton J. T. , Rickerl D. H.
Published: July 2010

On highly fertile soils, increases in plant growth resulting from starter fertilizers, applications generally do not occur unless root growth is restricted or temperatures are cool. The use of some conservation‐tillage systems may result in restricted root growth and cooler soils at planting. The purpose of this 3‐yr field study was to determine if growth and yield of soybeans [Glycine max (L.) Merr.] planted in a conservation‐tillage system would be increased by starter fertilizers, and if interactions occurred between residual fertility levels and starter fertilizers. Treatments included residual fertility levels (low P and K, low P and high K, high P and low K, and high P and K) and starter fertilizers (no starter, N, P, K, N‐P, N‐K, and N‐P‐K). The N, P, and K starter fertilizer rates were 16, 19, and 44 kg ha−1, respectively. Raising both residual P and K to the high soil test rating improved soybean yields 43%. The N‐containing starter fertilizers, especially those also containing P, increased early season plant root and top weights, but the K starters did not. However, the P, K, N‐K, and P‐K starter fertilizers had the greatest effect on yields; when compared to the control, they increased yields 46% when residual P, K, or both were low, and 26% when the residual P and K were high. The N, N‐P, and N‐P‐K starter fertilizers increased yields 21% when residual P was low, but had no effect on yields when P was high. Seed quality did not vary among residual fertility levels, but was improved by the starter fertilizers, especially those containing K. The P and K concentrations in the leaves just prior to pod set corresponded to differences in yields among residual fertility levels, but not to differences among starter fertilizers.
A Centrifuge Method for Obtaining Soil Solution Using an Immiscible Liquid
Authors: Elkhatib E. A. , Bennett O. L. , Baligar V. C. , Wright R. J.
Published: July 2010

The low toxicity organic liquid ethyl benzoylacetate (EBA) was found to be an effective immiscible displacent for soil solution removal. The ionic composition of soil solution displaced by EBA was, in general, comparable to that removed by the toxic, immiscible displacent CCl4. Increasing the relative centrifugal force (RCF) from 4.8 × 105 to 49.4 × 105 m s−2 nearly doubled the volume of soil solution displaced but did not affect the ionic composition of the soil solution. The procedure provided an adequate volume of soil solution for chemical analysis when 120 g of moist soil were centrifuged for 0.5 h at an RCF of 49.4 × 105 m s−2.
Nitrogen Mineralization in Profiles of Differently Managed Soil Types
Authors: Hadas Aviva , Feigenbaum Sala , Feigin A. , Portnoy Rita
Published: July 2010

Nitrogen mineralization kinetics and relations between potentially mineralizable N and chemical availability indices have been studied mainly in surface soils. In this study, the rate of mineralization was measured, by incubation techniques, in various soil types and soil depths, in order to evaluate the contribution of different soil layers to mineral nitrogen (N) of the whole root zone and to relate the rate parameters obtained to various soil N fractions. Soil layers of 60 to 120 or 160 cm contributed about 30% of the N mineralized in the whole soil profile. Ammonium accumulated and its nitrification was delayed in deeper soil layers of several profiles. Several rate equations were fitted to the experimental data. The first order rate constant varied from 0.02 to 0.10 week−1, without any consistent trend. Similar random variations of rate parameters were observed in other models with two or more parameters. The potentially mineralizable N (No) of one‐parameter models was highly and better correlated with the amount actually mineralized in 32 weeks of incubation and with various N forms in soil than the No obtained from two‐parameter models. Total N weighted with respect to soil layer depth was the best estimate of N mineralized in soil profiles.
Soil Losses of Dinitrogen and Nitrous Oxide from Irrigated Crops in Northeastern Colorado
Authors: Mosier A. R. , Guenzi W. D. , Schweizer E. E.
Published: July 2010

Emissions of nitrous oxide (N20) and dinitrogen (N2) from irrigated fields were monitored during the 1982 and 1983 cropping season to assess the magnitude of N loss by denitrification. Miniplots were established within larger fields of corn (Zea mays L.) in 1982, and barley (Hordeum vulgare) in 1983. Soil inside the miniplots was amended at a rate of 200 kg N ha−1 as 99 atom % 15N ammonium sulfate, and the vertical N20 and N2 fluxes were measured periodically by sampling gases from a soil cover method, and analyzing the N20 by gas chromatography and the N2 by mass spectrometry. Maximum N20 emissions occurred in May for barley and in July for corn, and emissions for both crops increased with increasing soil‐water content. During 1982, total volatile N loss of N20 + N2 from the moderately well‐drained clay loam soil was about 2.5% of the applied fertilizer N, and about 70% of the total was N20. From the barley field in 1983, about 1% of the applied fertilizer N was emitted with about equal amounts of each gas. These data suggest that the role of denitrification as a N loss mechanism has been historically overemphasized for soils in this area.
Spectroscopic Investigations of Cultivation Effects on Organic Matter of Vertisols
Authors: Skjemstad J. O. , Dalal R. C. , Barron P. F.
Published: July 2010

Solid state carbon‐13 nuclear magnetic resonance (13C NMR) spectroscopy with cross polarization and magic angle spinning (CP/MAS) was used to study the effect of cultivation on the nature of organic matter in a Vertisol (mesic, mixed, clayey, Typic Chromusterts). Continuous cultivation for 20, 35, and 45 yr resulted in 50, 61, and 66% loss in organic matter, respectively, from the 0‐ to 0.1m layer. However, 13C NMR spectroscopy performed directly on samples from these cultivated soils (0–0.1 m depth) and on adjoining virgin soil under native, virgin brigalow (Acacia harpophylla) scrub showed only minor differences in the in situ organic matter. Resonance bands representing long‐chained alkyl groups were the dominant feature of all four spectra and represented >50% of the organic C. Fractions obtained from density separations (<1.6, 1.6–2.0, 2.0–2.4, >2.4 Mg m−3) made on the soil under native scrub and the soil that had been cultivated for 35 yr showed that the organic C content of the light fractions (<2.0 Mg m−3) was greatly reduced after cultivation, while the heaviest fraction remained unchanged. Carbon‐13 NMR spectra determined on the fractions with a density <2.4 Mg m−3 showed that the organic matter with the highest alkyl content occurred in the 2.0‐ to 2.4‐Mg m−3 fraction. Also, the relative amount of humic acid decreased after cultivation, while the relative amount of clay‐bound organic matter increased. Ultraviolet/visible and infrared spectroscopic analyses of the humic acid and humin fractions agreed well with the NMR data. It is concluded that the major mechanism responsible for the relative stability of the persistent soil organic matter is a physical association with the inorganic components of the soil, rather than an inherent chemical or biochemical inertness of the organic matter itself.
Long‐term Effects of Mesquite Removal on Soil Characteristics: I. Nutrients and Bulk Density
Authors: Tiedemann A. R. , Klemmedson J. O.
Published: July 2010

In 1981, we compared soil carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and bulk density (BD) for sites with three different mesquite (Prosopis juliflora) histories: (i) where mesquite had been removed 13 yr earlier (MR history), (ii) where mesquite was removed, but sprouted and regrew (MRS history), and (iii) where mesquite was left intact (MI history). Three soil depths from the surface to 19.5 cm were sampled in the canopy location (areas presently or once under the influence of mesquite canopy) and in adjacent open areas. Comparisons between canopy and open locations and among depths were similar to those we observed in 1968. In the surface soil layer of canopy soils, C and N concentrations were arrayed significantly among histories: MI > MRS > MR. There were no significant differences among histories for P, S, or BD, although reduced C following mesquite removal (MR history) was reflected in a tendency for increased BD, which will likely become significant in the future. The differential response of N to mesquite history compared to P and S is probably explained by differences in the amounts of organic and inorganic forms of these elements in soils, and by the differential rates of mineralization and ion mobility.
Reactions of Sechura Phosphate Rock and Single Superphosphate in Soil
Authors: Syers J. K. , Mackay A. D.
Published: July 2010

The reactions of Sechura phosphate rock (SPR) and single superphosphate (SSP) were investigated in an incubation study using contrasting soils over 90 d. The rate and extent of dissolution of SPR, measured by a single extraction with 0.5 M NaOH, increased as the phosphate (P)‐sorption capacity of the soils increased. In contrast, the initial dissolution of SSP was independent of soil type. Whereas the amounts of water‐ and Olsen‐extractable P in soils to which SSP was added declined from the time of application, the amounts of Olsen‐ and Bray‐extractable P in soils to which SPR was added initially increased. With both P sources, the amounts of extractable P decreased as P‐sorption capacity increased. In a glasshouse experiment a poor relationship (r = 0.051) was found between P uptake by ryegrass (Lolium perenne L. var. Nui) from soil to which SPR was added and the extent of dissolution at 90 d. In contrast a very good relationship (r = 0.954**) was found between P uptake by ryegrass and Bray‐extractable P in soil to which SPR was added. It is important to distinguish between those soil properties that promote the dissolution of a PR and those that control the subsequent amounts of plant‐available P in soil.
Temperature Dependence of Soil Water Retention Curves
Authors: Hopmans J. W. , Dane J. H.
Published: July 2010

Effects of entrapped air volume and surface tension of soil solution are often regarded as the primary cause of temperature effects on the water retention curve. A procedure was developed to determine simultaneously the water characteristic curves and the volume of entrapped air for a glass beads medium and a Norfolk sandy loam (Typic Paleudults) at two temperatures. The volume change of entrapped air was determined from the change in volume of the free gas phase and the volume of water outflow from or inflow into a pressure cell. The results indicate a decrease in entrapped air volume with increasing temperature and suction. Surface tension values, calculated from capillary height measurements, showed the temperature coefficient of surface tension of soil solution to be smaller in magnitude than that of pure water. It was concluded that neither changes in entrapped air volume nor the temperature coefficient of surface tension of soil solution could account for the temperature effect on experimentally determined water characteristic curves of the two porous media.
Estimating Macroporosity in a Forest Watershed by use of a Tension Infiltrometer
Authors: Watson K. W. , Luxmoore R. J.
Published: July 2010

The ability to obtain sufficient field hydrologic data at reasonable cost can be an important limiting factor in applying transport models. A procedure is described for using ponded‐flow‐ and tension‐infiltration measurements to calculate transport parameters in a forest watershed. Thirty infiltration measurements were taken under ponded‐flow conditions and at 3, 6, and 15 cm (H2O) tension. It was assumed from capillarity theory that pores >0.1‐, 0.05‐, and 0.02‐cm diam, respectively, were excluded from the transport process during the tension infiltration measurements. Under ponded flow, 73% of the flux was conducted through macropores (i.e., pores >0.1‐cm diam.). An estimated 96% of the water flux was transmitted through only 0.32% of the soil volume. In general the larger the total water flux the larger the macropore contribution to total water flux. The Shapiro‐Wilk normality test indicated that water flux through both matrix pore space and macropores was log‐normally distributed in space.
Chemical Kinetics from a Thin Disc Flow System: Theory
Authors: Skopp J. , McCallister D.
Published: July 2010

Chemical kinetics information is difficult to obtain. Interpretation of data sets are subject to ambiguity both in regard to existing theory as well as in regard to the intrinsic chemical and physical processes. Clarification of these problems would aid in the understanding of time‐dependent reactions such as K release from soil. This study was undertaken to analyze a miscible displacement technique for obtaining chemical kinetics data. Theory is developed within the context of multiple working hypotheses where it is necessary to for‐mulate alternative empirical rate laws. Each rate law represents an alternative hypothesis, the consequences of which are deduced for a flow system. The appropriate differential equations are presented, and where possible, solved analytically. Solutions are presented for zero‐order, first‐order, and fractional‐order reaction terms. The investigation of complete kinetic formulations suggests that graphs of logarithm of concentration vs. time must be interpreted with care. Multiple line segments in a semilog graph may raise suspicions that multiple reaction mechanisms, multiple transport mechanisms, or backwards reactions may be significant. However, multiple line segments by themselves are not sufficient evidence to prove any of the possibilities.
Aggregate Structure and Carbon, Nitrogen, and Phosphorus in Native and Cultivated Soils
Authors: Elliott E. T.
Published: July 2010

This work corroborates the hierarchical conceptual model for soil aggregate structure presented by Tisdall and Oades (1982), extends it to North American grassland soils, and elaborates on the aspects relating to the influence of cultivation upon losses of soil organic matter. Aggregate size distributions observed for our soils are very similar to those of Australian soils, indicating that the microaggregate‐macroaggregate model may hold for a wide array of grassland soils from around the world. The use of two wetting treatments prior to sieving demonstrated that the native sod soil had the same general structural characteristics as cultivated soil but the macroaggregates were more stable. When slaked, native and cultivated soil present in the microaggregate size classes had less organic C, N, and P than the soil remaining as macroaggregates, even when expressed on a sand‐free basis. Moreover, the C/N, C/P, and N/P ratios of microaggregates were narrower than those of macroaggregate size classes. Much more C and N was lost than P under the conditions of this study. Element‐specific differences in microbial catabolic processes vs. extracellular enzyme activity and its attendant feedback controls are postulated to account for this difference. When the macroaggregates were crushed to the size of microaggregates, mineralizable C as a percent of the total organic C was generally greater for macro‐ than microaggregates early in the incubation for the cultivated soil and throughout most of the incubation for the native sod soil. Mineralizable N as a percent of the total organic N was greatest in macroaggregates even when the macroaggregates were not crushed. The macroaggregate‐micraggregate conceptual model is applied to help explain accumulation of soil organic matter under native conditions and its loss upon cultivation.
Effect of Lime and Organic Matter on Soybean Seedlings Grown in Aluminum‐toxic Soil
Authors: Ahmad F. , Tan K. H.
Published: July 2010

Organic matter is believed to be able to reduce Al toxicity in Ultisols. Since little information is available to substantiate this hypothesis, a greenhouse experiment was conducted to compare the effects of organic matter and lime on soybean [Glycine max (L.) Merr.] plants grown under increasing Al stress in a Bradson (Typic Hapludults) soil. Treatments, replicated three times, were 0, 25, 50, and 100 mg Al kg−1 pot−1, 0, 5, and 10% wheat (Triticum aestivum L.) straw, and the equivalent of 0, 1, and 2 Mg CaCO3 ha−1. After thorough mixing and incubation of the growth medium at field capacity for 20 d, five soybean seeds were germinated per pot and the five seeds allowed to grow for 30 d. The results indicated that shoot and root growth were severely affected by increased Al treatments. Aluminum toxicity started to seriously affect plant growth at 50 mg Al kg−1, and plants were hardly growing at 100 mg Al kg−1. However, plant growth in the Al‐toxic soil was improved substantially by the application of wheat straw or lime. The data suggest that treatments with wheat straw produced taller plants and greater dry weight contents of roots than was found in plants grown only with lime. Lime alone yielded good results, but lime in the presence of organic matter was more effective in reducing the effect of Al toxicity. The plants receiving wheat straw still contained relatively high levels of Al (3.7–7.4 mmol kg−1) in their shoots, but little damage could be detected. A tendency toward a decrease in N content was noticed in shoots of plants grown in the presence of wheat straw, but this was believed to have been caused by a temporary immobilization of N because of the application of straw. It was concluded that organic matter was as effective as lime in reducing Al toxicity.
Pedogenesis on the Edwards Plateau, Texas: III. New Model for the Formation of Petrocalcic Horizons
Authors: Rabenhorst M. C. , Wilding L. P.
Published: July 2010

Petrocalcic horizons occur in a number of soils formed from Cretaceous limestone in central and west Texas (Edwards Plateau land resource area). Microfabric and stable C isotope analyses confirmed that the indurated carbonate zones are mostly of pedogenic origin. Multiple lines of evidence indicate that the petrocalcic horizons in these soils form through a process of limestone alteration by in situ dissolution and reprecipitation of carbonates. Evidence includes: (i) very low noncarbonate residue levels in petrocalcic horizons, which are comparable to levels in limestone bedrock; (ii) lithologic discontinuities between petrocalcic horizons and the overlying sola; (iii) presence, concentration, and particle size distribution of flourite in some petrocalcic horizons; (iv) presence of secondary silica within petrocalcic horizons indicating limited movement of components within this zone; and (v) microfabric analysis. This in situ process is in distinct contrast to commonly held models depicting translocation and accumulation of carbonates within a solum that was initially nonindurated. A model is proposed to describe the genesis of limestone‐derived petrocalcic horizons.
Goodness of Fit for Eight Water Infiltration Models
Authors: Davidoff B. , Selim H. M.
Published: July 2010

Eight infiltration models were investigated for their capability to describe water infiltration into soils. The models were; Philip's, Modified Philip's, Kostiakov's, Talsma and Parlange's, Horton's, and Lewis and Milne's. Field measurements of water infiltration were made using single ring infiltrometers on field plots established on a Norwood soil (Typic Udifluvents) with four long‐term (27 yr) winter cover crop treatments followed by cotton (Gossypium hirsutum L.) each year. The four treatments were; (i) common vetch (Vicia sativa), (ii) wheat (Triticum aestivum L.) + 60 kg/ha N; (iii) 60 kg/ha N, and (iv) check (no fertilizer or winter cover). Measured infiltration rates for the winter cover treatments were significantly higher than for the check plots. With the exception of Lewis and Milne's, all models showed good agreement with measured infiltration. Model parameters obtained by best fit of measured data, were significantly different among the winter cover treatments. Based on R2 values, Horton, Kostiakov and Philip equations provided best predictions over all other models. Soil bulk density and saturated hydraulic conductivity for two soil depths were not affected by the winter cover treatments.
Wheat Residue Management Effects on Soil Water Storage and Corn Production
Authors: Unger Paul W.
Published: July 2010

Corn (Zea mays L.) grown in the semiarid southern Great Plains usually is irrigated fully because yields decline if water stress occurs at any time during the growing season, but the groundwater supply for irrigation is being depleted. To decrease the dependence of corn production on the declining groundwater supply, practices must be developed to improve the storage and use of precipitation. This study was conducted to determine the effects of residue management practices after wheat (Triticum aestivum L.) on precipitation (and preplant irrigation) storage during fallow; corn growth, yield, and seed quality; and water use and use efficiency by corn. The soil was Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls). Because of high initial water contents at the start of fallow in 1982, relatively little water was stored from precipitation during the 1982 to 1983 fallow. For the 1983 to 1984 fallow, water storage was higher with disk and sweep tillage than with no‐tillage because the disk and sweep plots received a preplant irrigation to wet the tillage‐loosened soil. Water use by corn was not affected significantly by tillage in 1983, but was significantly lower with no‐tillage than with disk or sweep tillage in 1984. Corn grain yields were lowest with a no‐tillage standing residue treatment in 1983 due to N deficiency. In 1984, yields were not affected significantly by tillage, but avg 0.29 Mg/ha higher on fertilized than on nonfertilized low‐residue plots and 2.0 Mg/ha higher on fertilized than on nonfertilized high‐residue plots. Kernel weight (mg/kernel) and kernel test weight were affected significantly by tillage in 1983, but not in 1984. The study showed that crop residues can be managed to use a greater proportion of precipitation for producing corn, thus reducing the dependence on irrigation. However, soil fertility must be adequate for obtaining high yields, especially on high‐residue plots.
Effect of Soil Properties on Hydraulic Conductivity‐Moisture Relationships
Authors: Schuh W. M. , Bauder J. W.
Published: July 2010

A field study was initiated to examine relationships between in situ hydraulic conductivity, soil‐water suction, and soil physical and chemical properties. Data from the study were used to describe relationships between soil properties and slopes of hydraulic conductivity‐soil water suction curves, i.e., In K vs. In S curve slopes (N). Soil particle size distribution and soil moisture desorption slopes were also evaluated. Sand to silt ratio (SA/SI), geometric mean particle diameter (GMD), and an index of geometric mean standard deviation (GMSD) were strongly related to slope of the In K vs. In S curves. These same parameters were also functionally related to observed differences between slopes of In K vs. In S curves and slopes of soil moisture desorption curves. Particle statistical indices and sand to silt ratio (SA/SI) were better predictors of curve slopes than were particle size percentages alone. An attempt was made to determine any correlations between K(S) and these soil properties and to estimate K(S), using selected soil physical properties. Using “best fit” predictive models, estimated K(S) values varied from measured values by a factor of 2 to 3 at the 60% confidence interval and by a factor of 7 to 12 at the 95% confidence interval.
A Microlysimeter Field Study of Solute Transport through a Structured Sandy Loam Soil
Authors: Richter Goetz , Jury William A.
Published: July 2010

A 49‐d field experiment monitoring water and solute movement through a structured sandy loam is reported. Two field plots, each 15 by 30 m2 in area were instrumented with a 3 by 6 grid of small lysimeters containing undisturbed soil. Each lysimeter was weighed before and after irrigation and had effluent concentrations and drainage volumes recovered periodically. At the beginning of the experiment a pulse of KBr was added to the field and lysimeters with a mechanical lawn spreader and was leached into the soil with three water irrigations per week. Each plot received the same amount of water per irrigation but at intensities of 5.5 and 9.5 mm/h. Effluent breakthrough curves were constructed for each lysimeter. Substantial indication of preferential flow through part of the wetted pore space was observed in each lysimeter and the average breakthrough curves reflected substantial bypass. A statistical analysis of the drainage concentrations as a function of time showed the two fieldwide breakthrough curves to be identical. This not only showed that no intensity effect was apparent for solute movement on these plots but also indicated that the plot areas were large enough to incorporate all of the field scale variability within them. A calculation of solute flux from each lysimeter showed no correlation between instantaneous drainage and instantaneous solute concentration. As a consequence, we were able to show that the traditional method of estimating field scale solute flux as the product of average drainage and average concentration was adequate to describe solute leaching below the fields. Thirty‐six soil cores were taken in the two plots at the conclusion of the experiment. The average concentration depth patterns were similar for the two treatments and showed evidence of movement to at least 1.2 m during the lifetime of the experiment, implying that preferential flow continued to occur to greater depths.
Straw Decomposition in Irrigated Soil: Comparison of Twenty‐three Cereal Straws
Authors: Smith J. H. , Peckenpaugh R. E.
Published: July 2010

The objective of this research was to evaluate field decomposition of 23 cereal grain straws. Straw samples of ‘Fieldwin’ and ‘Owens’ soft white spring wheats (Triticum aestivum L.); ‘Borah’ and ‘McKay’ hard red spring wheat; ‘Nugaines’, ‘Daws’, ‘Lewjain’, ‘Stephens’, and ‘Hill 81’ soft white winter wheats; ‘Weston’, ‘Manning’, ‘Neeley’ hard red winter wheats; ‘Advance’, ‘Steptoe’, ‘Lud’, ‘Pirolene’, and ‘Klages’ spring barleys (Hordeum vulgare L.); ‘Kamiak’, ‘Boyer’, and ‘Schuyler’ winter barleys; Waid durham wheat (Triticum durum Desf.); and ‘Flora’ and ‘Palouse’ triticales (Triticale hexaploide Lart.); were buried in field plots. The straw bags were removed at intervals during 1 yr and analyzed for the amount of decomposition, and C and N contents. Final decomposition ranged from 54% for the Borah wheat straw to 75% for the Lud barley straw with about half of the straws decomposing 64 or 65%. The hard red spring wheat and triticale straws decomposed the slowest and two spring barley straws decomposed most rapidly, but no completely systematic differences were observed for different genera of straws. The original straw N concentrations ranged from 2.2 to 12.5 g/kg. Nine straws lost N during the incubation period from September to November while eight increased in N concentration during this time. In the next three incubation periods, from November to the following October, nearly every straw sample increased in N concentration. The total N weight in the straw increased to the May sampling and then decreased thereafter. This pattern indicates that the straw was releasing N as it was mineralized and became available for utilization by the growing corn crop. Carbon/N ratios ranged widely in the initial straw samples, becoming more nearly uniform as the decomposition process developed. The C/N ratios remained fairly high avg 41 for the final sampling even though the straw in every case had released N into the soil during the last sampling period. Regression analysis of total decomposition and change in weight of N in the wheat straw samples for the first 67‐d incubation in the field showed a linear relationship with decomposition during the year, decreasing with increasing N loss in the early stage.
Disposition of Fertilizer Phosphorus Applied to Winter Wheat
Authors: Sharpley A. N.
Published: July 2010

The disposition of fall‐applied fertilizer P (30 kg P ha−1) to winter wheat (Triticum aestivum L.) on four Southern Plains soils was investigated over a 4‐yr period under field conditions, using 32P as a tracer. Wheat was harvested 70 d after planting and P fertilization. An average increase in wheat dry‐matter yield (0.86‐1.94 Mg ha−1) and Bray‐1 P content of 0‐ 50‐mm surface soil (8.4‐34.4 mg kg−1) was observed following each fertilizer P application over the 4 yr. The major proportion of applied fertilizer P at wheat harvest remained in the soil as inorganic P (60‐76%) with little conversion to organic P (8‐15%). The proportion as Bray‐1 P ranged from 17 to 51%, decreasing with an increase in P sorption capacity of the soil. With consecutive fertilizer applications the proportion of fertilizer P as Bray‐1 P increased. Little movement of fertilizer P was observed below the 50‐mm depth (3‐7%). Recovery of fertilizer P by winter wheat decreased with consecutive fertilizer applications, ranging from 23 to 9% of that applied. The recovery was inversely related to the residual Bray‐1 P content of surface soil (Bray‐1 P content prior to each fertilizer application). Thus, although dry‐matter yield of winter wheat increased with consecutive fertilizer applications, fertilizer P recovery decreased as residual P made an increasing contribution to uptake of P by winter wheat. Consideration of residual soil P levels may, thus, reduce costly maintenance fertilizer P applications.
Ammonia Loss from Applications of Urea‐Ammonium Nitrate Solution to Straw Residue
Authors: McInnes K. J. , Ferguson R. B. , Kissel D. E. , Kanemasu E. T.
Published: July 2010

The increased use of urea and urea‐based N fertilizers along with an increase in crops under no‐ or reduced‐tillage practices may require changes in fertilizer management practices. Surface application of urea‐based fertilizer risks the loss of some N by volatilization of NH3. Our objectives were to assess the loss of NH3 and to simultaneously observe the associated N transformations and movements in the field following broadcast application of urea‐ammonium nitrate solution at a rate of 200 kg N ha−1 to soil with wheat (Triticum aestivum L.) straw residue cover. Also, we wanted to characterize the factors associated with the residue that might affect loss. A micrometeorological mass‐balance method was used to measure NH3 loss during two sequential field studies with different amounts of precipitation and irrigation. Volatilization losses showed diurnal patterns coinciding with fluctuations in residue temperature, residue water content, and wind speed. Cumulative NH3‐N losses were 7.6 and 16.6% of the N applied, respectively. The rate of urea hydrolysis and NH3 loss were quite sensitive to the availability of water. Simulated rainfalls with 2.5‐mm sprinkler irrigation increased NH3 loss. In both studies, peak volatilization rates came the 1st d after irrigation. The maximum measured rate of NH3 loss was 51 µg m−2 s−1 (1.5 kg N ha−1 h−1). Rainfalls of near 30 mm in both studies moved much of the remaining fertilizer below the 40‐mm soil depth. Wheat straw was found to have a urease activity of about 1830 mg urea kg−1 h−1, a pH near 8, and a H‐ion buffering capacity of 53 mmol kg−1 (pH unit)−1. These factors undoubtedly contributed to NH3 loss.
Phenolic Compounds in Soils of Hydrosequences and Developmental Sequences of Spodosols
Authors: Vance G. F. , Mokma D. L. , Boyd S. A.
Published: July 2010

The extraction of low molecular weight phenolic compounds from pedons of two hydrosequences and two developmental sequences was investigated. Seven phenolic compounds were identified in Na4P2O7 extracts: three benzoic acids—protocatechuic, p‐hydroxybenzoic, and vanillic acids; two aldehydes—p‐hydroxybenzaldehyde and vanillin; and two cinnamic acids—trans p‐coumaric and ferulic acids. Identification of the compounds was by cochromatography with authentic standards. In general, the total phenolic content increased going from the somewhat excessively drained to the somewhat poorlydrained members of the hydrosequences and from the least‐developed to the most‐developed members of the Spodosol developmental sequences. The substituted benzoic acids accounted for most of the phenolic compounds in all horizons. While p‐hydroxybenzoic and vanillic acids dominated in the surface horizons, protocatechuic acid was found in higher concentrations in the spodic horizons. Aluminum and Fe maxima also occurred within horizons that had protocatechuic acid as the prevalent phenolic compound. The results suggest that Al and Fe chelate complexes with protocatechuic acid may play a role in the formation of spodic horizons.
Manganese Oxide Analysis in Soils by Combined X‐ray Diffraction and Selective Dissolution Methods
Authors: Tokashiki Y. , Dixon J. B. , Golden D. C.
Published: July 2010

It is difficult to identify the Mn oxides in many soils due to their poor crystallinity, low concentration, the diffuse nature of the x‐ray diffraction patterns, and the coincidence of diagnostic peaks with those of associated minerals. A selective dissolution procedure is proposed to characterize Mn oxides and the associated minerals by using successive sodium hydroxide, hydroxylamine hydrochloride, and dithionite‐citrate‐bicarbonate (DCB) treatments. Mineral composition was determined by x‐ray diffraction analysis before and after each treatment. Three samples of soil Mn nodules from Okinawa Island, Japan, and synthetic sodium birnessite and lithiophorite ore were used as test materials. The NaOH treatment destroyed kaolinite and gibbsite but concentrated birnessite, lithiophorite, and goethite. Heat treatment followed by x‐ray diffraction analyses indicated that birnessite, lithiophorite, and goethite were destroyed at 200, 400, and 300°C, respectively. Birnessite was dissolved by hydroxylamine hydrochloride leaving lithiophorite and goethite unchanged. A DCB treatment following hydroxylamine hydrochloride dissolved lithiophorite and goethite leaving a layer silicate residue. The chemical separation and dissolution procedures were effective in characterizing the Mn oxides in soils.
Kinetics of Ion Exchange on Clay Minerals and Soil: II. Elucidation of Rate‐limiting Steps
Authors: Ogwada R. A. , Sparks D. L.
Published: July 2010

Kinetics of K+ adsorption were investigated on kaolinite, a Chester loam soil and vermiculite using static, stirred, and vortex batch techniques. The objective of this study was to elucidate the rate‐limiting steps for K+ adsorption on the clay minerals and soil. We hypothesized that it is possible under laboratory conditions to set up a system in which the global rate is limited by mass transfer (under static conditions), in which only the intraparticle diffusion step is rate‐limiting (stirred system), and a system in which the rates of film and intraparticle diffusion are both relatively rapid, presumably rendering the reaction step to be rate‐controlling (vortex batch). We derived and assigned additive resistance relations to the three proposed experimental methods according to the above stated assumptions. Observed rate coefficients obtained from static, stirred and vortex batch systems were combined and used to calculate rate coefficients for film diffusion (kf), intraparticle diffusion (kI), and reaction kinetics (kr) in a static system. Film diffusion and intraparticle diffusion rate coefficients were approximately the same in vermiculite, indicating that both steps were rate‐determining. In kaolinite and the Chester soil, film diffusion was the rate‐limiting step. These conclusions were also verified using the parabolic diffusion equation. The kI values were on the avg 8.7 times as great as kf values in the kaolinite system, indicating that intraparticle diffusion was not important for kaolinite. Higher energies of activation for adsorption (Eaa) were observed for the reaction step than for intraparticle diffusion or film diffusion steps. These findings were expected since chemical reactions are more sensitive to temperature changes than diffusion processes.
Sulfate Reduction and Calcium Carbonate Equilibria in a Central California Histosol
Authors: Deverel S. J. , Whittig L. D. , Tanji K. K.
Published: July 2010

Sulfate (SO2‐4) reduction and bicarbonate (HCO‐3) production were studied in three organic soil profiles removed intact from the California Delta area. The water table was maintained at approximately 0.75 m from the soil surface in columns 1.22 m in height. The partial pressure of carbon dioxide (PCO2) was monitored throughout the experiment. Extracted soil solutions were evaluated with respect to calcite solubility. Sulfate reduction was found to follow first‐order kinetics for three different initial SO2‐4 concentrations. Bicarbonate production followed approximately the stoichiometry of the organic matter oxidation‐SO2‐4 reduction reaction. Soil solutions extracted below the water table were found to be saturated with respect to calcite depending on the PCO2 and the initial SO2‐4 concentration.
Effect of Acidity on Denitrifcation and Nitrous Oxide Evolution from Atlantic Coastal Plain Soils
Authors: Weier K. L. , Gilliam J. W.
Published: July 2010

The effect of acidity on denitrification and nitrous oxide production in six soils from the Atlantic Coastal Plain was estimated using laboratory incubations of flooded soil for periods up to 21 d. Increased denitrification rates were associated with a decrease in acidity in all soils but most of the effect occurred above pH 6.5. Some accumulation of NH+4‐N occurred in all soils and was positively correlated to the NO‐3‐N lost from the system. Small quantities of NO‐2‐N were formed in all soils. Larger amounts of NO‐2‐N were found at pH 5.0 and 4.7 for two soils. Nitrite‐N accumulation corresponded to the release of large quantities of N2O suggesting a possible relationship between NO‐2‐N accumulation and N2O production. Nitrous oxide evolved, as a percentage of NO‐3‐N lost, increased with increasing acidity with maximum N2O being evolved at pH values ≤5.8. Above pH 5.8, evolution of N2O virtually ceased. Since all six Coastal Plain soils are generally <pH 5.8, a high percentage of nitrogen being lost from these soils through denitrification is as N2O.