bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrate Leaching as Influenced by Cover Cropping and Nitrogen Source
Authors: McCracken Daniel V. , Smith M. Scott , Grove John H. , MacKown Charles T. , Blevins Robert L.
Published: July 2010

To minimize groundwater contamination by NO−3 and to maximize efficient crop N use, it is necessary to better characterize NO−3 leaching in various cropping systems. Our objectives were to compare the contributions of hairy vetch (Vicia villosa Roth) and NH+4 N sources to NO−3 leaching in corn (Zea mays L.) production, and to compare NO−3 leaching losses in a corn production system utilizing hairy vetch as a N source and winter cover crop with leaching losses in one utilizing an NH+4 N source and a rye (Secale cereale L.) cover crop. Nitrogen, sometimes enriched with 15N, was applied to corn grown on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) in lysimeters as vetch‐ or NH+4‐N at rates between 10.5 and 14.0 g N m−2 yr−1. Treatments (N source/cover crop) were: NH+4‐N/fallow, vetch‐N/fallow, NH+4‐N/rye, and vetch‐N/vetch; mean 3‐yr cumulative NO−3 leaching losses were 6.11, 4.85, 0.35, and 2.51 g N m−2, respectively. Total recovery of added 15N in leachate was <5% for all treatments, and the percentage of leached NO−3 derived from labeled N sources was generally <15%. In the winter‐fallow lysimeters, effects of N source on the fraction of water input discharged, concentration of NO−3, and quantity of NO−3 leached varied with year and time of year; differences in N‐source availability and mulch effects were sometimes indicated. Generally, cover crop effects were larger than N‐source effects. The NH+4 N source/rye cover system leached consistently less NO−3 than the vetch N source/vetch cover system, even though the fraction of water discharged was not consistently different.
Leaching and Water Flow Patterns in Every‐Furrow and Alternate‐Furrow Irrigation
Authors: Benjamin J. G. , Havis H. R. , Ahuja L. R. , Alonso C. V.
Published: July 2010

Deep water percolation and chemical leaching is a recognized environmental problem with furrow irrigation. Alternate‐furrow irrigation (AFI) was hypothesized as a method to increase water‐use efficiency and decrease chemical leaching compared with every‐furrow irrigation (EFI). The SWMS_2D finite‐element model was used to investigate water and CaCl2 movement in EFI and AFI with furrow‐placed or ridge‐placed fertilizer bands. Model simulations were conducted for a Crook loamy sand (mixed, mesic, Ustic Torripsamment) and a Nunn clay loam (fine, montmorillonitic, mesic Aridic Argiustoll). Water isolation zones occurred with AFI and EFI that contributed little to overall profile drainage. The soil water contents after infiltration and redistribution were more uniform for EFI than for AFI for both soils. Water distribution was more uniform with AFI in the clay loam than in the loamy sand. Chemical movement was least with AFI and CaCl2 placement under the nonirrigated furrow. The greatest chemical leaching was predicted with furrow placement of CaCl2 and EFI. Results with CaCl2 suggest soluble chemicals or fertilizers placed under the nonirrigated furrow in loamy sand may not be available for plant uptake because the soil did not wet during irrigation. With either form of furrow irrigation, placement of a fertilizer in the ridge rather than in the furrow would decrease leaching of the fertilizer and keep the fertilizer in the root zone.
Foliar Deficiencies of Mature Southern Appalachian Red Spruce Determined from Fertilizer Trials
Authors: Joslin J. D. , Wolfe M. H.
Published: July 2010

A field fertilization study employing additions of Ca, Mg, and N to a mature red spruce (Picea rubens Sarg.) stand was conducted at a high‐elevation site in southwestern Virginia. Statistically significant increases in needle weight (20% larger than controls) were observed after two growing seasons in treatments receiving Ca or Ca plus Mg. Significant foliar growth responses were accompanied by significant increases (20–60%) in foliar concentrations of Ca, Zn, Mg, and Mn in current‐year and 1‐yr‐old needles. Both Ca and Mg addition, alone or together, appear to have alleviated antagonisms by Al towards the uptake of these four cations. Both the foliar growth response (negative) and the foliar N concentration response to N addition were nonsignificant, a response consistent with the evidence for N saturation at this site. Vector analysis, correlation analyses, and literature evidence all provide support at this site for a foliar deficiency of Zn at a foliar concentration of 14 mg kg−1 and for a foliar and/or root deficiency of Ca at a current‐year needle concentration of 1700 mg kg−1. Foliar concentrations of Ca and Zn at or below these thresholds are common in southern Appalachian red spruce and may be related to its apparent growth decline in the higher elevations.
Nitrogen Losses and Lowland Rice Yield as Affected by Residue Nitrogen Release
Authors: Becker M. , Ladha J. K. , Ottow J. C. G.
Published: July 2010

Synchronizing N supply from incorporated plant residues with N demand of rice (Oryza sativa L.) may increase the plant's N use efficiency and reduce soil N losses. This hypothesis was tested under flooded lowland conditions in a three‐season field experiment. Leguminous green manures and rice straw with various lignin to N ratios (L/N) and urea were compared using N release, rice N uptake, N use efficiency, grain yield, and total 15N balance as criteria. Basally applied urea resulted in high initial soil NH+4. Where residues were applied, exchangeable NH+4‐N varied as a function of L/N. Daily N uptake by rice peaked at ≈4 wk. Matching of soil NH+4‐N with daily rice N uptake was less apparent in urea and Sesbania rostrata Brem. S. Oberm. treatments than in the S. rostrata‐rice straw mixture treatment. Nitrogen‐15 balances indicated that the mismatch between supply and demand may have caused the measured N losses of 35% from urea and 6 to 10% from S. rostrata applied at 60 kg N ha−1. Synchronized N supply and rice N uptake resulted in negligible N loss and increased the portion of applied N remaining in the soil, but it did not cause a yield increase. Sesbania rostrata‐rice straw mixture depressed yield and N use efficiency in the dry season when yield potential was high. A residual effect was observed in the S. rostrata‐rice straw treatment in the third unfertilized crop, resulting in a 10% increase in grain yield. Apparently, synchronizing soil N supply with N demand by incorporating residues with suitable chemical composition may not immediately increase rice grain yields, but it improves long‐term soil fertility.
Soil Microbial Respiration at Different Water Potentials and Temperatures: Theory and Mathematical Modeling
Authors: Grant R. F. , Rochette P.
Published: July 2010

If ecosystem simulation models are to be used to study changes in C distribution under proposed changes in climate, then they must represent the effects of soil physical conditions upon microbial activity. Hypotheses for the effects of soil water content (θ) and temperature (Ts) on microbial oxidation rates were formulated into mathematical algorithms as part of the ecosys modelling program. Access to organic substrates by heterotrophic microbial populations was represented from competitive enzyme kinetics, which were presumed to be sensitive to θ. Access to O2 by obligately aerobic or facultatively anaerobic microbial populations was represented from O2 diffusion gradients and active uptake rates controlled by θ and Ts. Sensitivity to Ts of substrate hydrolysis and oxidation by heterotrophic microbial populations was modelled from an Arrhenius function. Rates of simulated respiration were tested against rates measured under laboratory and field conditions at different θ and Ts. Simulated CO2 fluxes were largest when θ = 0.6 to 0.7 of total porosity and declined to <0.2 of their largest values when θ declined to 0.2 or rose above 0.9 of total porosity. The sensitivity of simulated CO2 fluxes to θ was consistent with that measured during laboratory incubations, except in the range of 0.65 to 0.80 of total porosity, where sensitivity of measured fluxes was greater than that simulated. When θ was >0.8 of total porosity, simulated respiratory quotients rose above 1.0 to values consistent with those recorded elsewhere at high θ. Model hypotheses allowed simulated CO2 evolution rates to reproduce those reported from wheat residue during a 30‐d incubation at Ts from 0 to 20°C and ψs from −0.033 to −5.0 MPa. These hypotheses also allowed simulated changes in CO2 evolution rates attributed to changes in Ts and θ to reproduce those measured in the field during 60 d under barley.
Phosphorus Release Kinetics and Extractable Phosphorus after Long‐term Fertilization
Authors: Steffens D.
Published: July 2010

If different P fertilizers have been applied for a long time, it is difficult to measure the P availability. The objectives of this study were to investigate (i) the kinetics of soil P release by electroultrafiltration (EUF), (ii) extractable P using different soil extractants, (iii) plant P uptake, and (iv) the importance of considering both the P release kinetics and extractable P for plant P uptake prediction. This study was conducted with 15 European Alfisol topsoils with different histories of P and lime applications. The soils had received P as basic slag phosphate (BSP), superphosphate (SP), partially acidulated phosphate rock (PAPR), and phosphate rock (PR) for a long period. Plant P availability was measured in a 4‐yr pot experiment with different plants. Phosphorus release kinetics analyzed by EUF were better described by the Elovich equation than by other diffusion functions. The Elovich b values, which can be used as an index of release rate, ranged from 53.5 to 140.0 mg P kg−1 soil min−1. These b values were more closely correlated to cumulative plant P uptake (r = 0.96) than P extracted with water (r = 0.90), calcium acetate‐calcium lactate‐acetic acid (CAL) (r = 0.89), Mehlich 3 (r = 0.81), and double lactate (r = 0.79). Only Elovich b values in the PAPR and PR treatments were significantly correlated to cumulative plant P uptake (r = 0.92). The cumulative plant P uptake of the 15 soils was well predicted with the fitted equation: y = 27.8 + (0.40 CAL P) + (0.83b), r = 0.99, where y denotes the plant P uptake and b is the Elovich b value (mg P kg−1 soil min−1) and CAL P is the adsorbed P. This indicates that considering the b value as a parameter for P release and the amount of CAL‐extractable P for determining P availability following different fertilizer applications is a better estimation of plant P uptake than consideration of only one index of P availability.
Statistical Characterization of Dry Aggregate Strength Using Rupture Energy
Authors: Perfect E. , Kay B. D.
Published: July 2010

Dry aggregate strength, s, is important in tillage studies. Weibull's brittle fracture model is a widely accepted statistical approach for analyzing variability in s. Tensile strength, T, is commonly used as the measure of s in Weibull's model. However, compression and shear also occur during tillage. Use of specific rupture energy, E, involves no assumptions regarding the mode of failure. Furthermore, E can be related to tillage draft energy. Information is lacking on the statistical characterization of s using E. Our objective was to compare the performance of E and T as measures of s in Weibull's model. We determined E and T simultaneously for 1400 air‐dry aggregates from five size classes and seven cropping‐tillage treatments on a loam soil. Weibull's model fit equally well using either T or E. Model parameters estimated using T (αT and βT) were significantly correlated with those estimated using E (αE and βE). A log‐log relationship was established between αE and αT, with an intercept of −5.01 and a slope of 1.16. The β values were related by the equation: βE = 0.69βT, indicating less variation in s as measured by T than as measured by E. The α parameter was more sensitive to size and cropping‐tillage effects than the β parameter. The αE resulted in a better discrimination between size classes and cropping‐tillage treatments than did the αT. The αE decreased with increasing aggregate size and decreasing tillage intensity. The use of E in Weibull's model is recommended for the statistical characterization of s in tillage studies.
Adsorption of Thiamin (Vitamin B1) on Soils and Clays
Authors: Schmidhalter U. , Kahr G. , Evéquoz M. , Studer C. , Oertli J. J.
Published: July 2010

Recent research suggests that thiamin applied to soils or coated onto seeds may stimulate plant growth. The behavior of thiamin in soils has not been investigated. Therefore, studies were carried out to determine how thiamin hydrochloride (3‐[(4‐amino‐2‐methyl‐pyrimidinyl)methyl]‐5‐(2‐hydroxyethyl)‐4‐methylthiazolium chloride hydrochloride) is adsorbed by 17 soils and three clays. The dominate mechanism in binding of thiamin is thought to be cation exchange with clay minerals and organic matter. In soils with low to medium organic matter content, thiamin adsorption occurred primarily on clay minerals and depended particularly on the amount and composition of the clay. Adsorption is species dependent (pKa1 [negative logarithm of the first dissociation constant] = 4.85) and takes place principally in the acidic pH range, probably with position 1′ of the pyrimidine ring. Adsorption equilibrium is attained in <30 min. Adsorption in all soils, and in kaolinite and illite clays, could be described by a one‐surface Langmuir isotherm at initial concentrations ranging from 16.3 to 995 µmol L−1. Adsorption by smectite in the same range was log‐linearly related to the equilibrium concentration. Extending the initial concentration range from 16.3 to 9890 µmol L−1 showed that a two‐surface Langmuir equation more adequately described adsorption in hydroxy‐interlayered vermiculitic and chloritic‐illitic soils, whereas a one‐surface Langmuir equation was found to be adequate in mixed layer‐smectitic soils. Only in the case of smectite clays is thiamin allowed to lie in a monolayer configuration parallel to the basal plane.
Nonequilibrium Transport of Atrazine through Large Intact Soil Cores
Authors: Gaber H. M. , Inskeep W. P. , Comfort S. D. , Wraith J. M.
Published: July 2010

Preferential flow in heterogeneous soils may result in more rapid leaching of pollutants through soils than would be predicted using transport models based on the local equilibrium assumption (LEA). Our objectives were to evaluate nonequilibrium processes important to the transport of tritiated water (3H2O) and atrazine under varying pore water velocities and soil water contents, and to distinguish between transport‐related nonequilibrium (TNE) and sorption‐related nonequilibrium (SNE). Column experiments were performed using a 3H2O‐14C‐labeled atrazine pulse through intact soil cores (15.24‐cm diam., 30‐cm length) at pore water velocities of 0.12, 0.69, and 2.16 cm h−1 (θv ≈ 0.39) and at 0.74 cm h−1 (θv ≈ 0.44). The asymmetrical shape and the left‐handed displacement of 3H2O breakthrough curves (BTCs) as a function of pore water velocity and soil water content (θv) indicated that 3H2O was subject to TNE at only the 0.74 (θv = 0.44) and 2.16 cm h−1 pore water velocities. The asymmetrical shape and increased tailing of atrazine BTCs at all pore water velocities indicated that atrazine was influenced primarily by SNE at pore water velocities of 0.12 and 0.69 cm h−1, and a combination of both TNE and SNE at pore water velocities of 0.74 (θv ≈ 0.44) and 2.16 cm h−1. The convection‐dispersion equation based on the LEA was unable to predict atrazine BTCs at any pore water velocity. Although the nonequilibrium bicontinuum (two‐site/two‐region) model provided excellent fit to all atrazine BTCs, fits to the model cannot be used to separate between TNE and SNE when both mechanisms are operative. Results of this study confirm that TNE and SNE are important transport processes in naturally structured soils under conditions of relatively high pore water velocities and volumetric water contents.
Ancient Agricultural Soils in the Andes of Southern Peru
Authors: Sandor J. A. , Eash N. S.
Published: July 2010

Knowledge about soil changes resulting from long‐term agriculture is important because agricultural influences on soil continue to increase in extent, intensity, and duration. Agricultural terraces in the Colca Valley, Peru, present an opportunity to study soils that have been cultivated for at least 15 centuries. Physical and chemical properties of soils were determined to explore possible effects of traditional agricultural practices on soils. Relative to nearby uncultivated Mollisols, agricultural A horizons are commonly 0.3 to 1.3 m thicker, contain buried organic‐matter‐enriched horizons, and are lower in bulk density. They also have more organic C and N and lower pH. Cultivated A horizons, particularly in agricultural terraces that have been abandoned for about four centuries, are enriched in P. Data suggest that P applied as fertilizer has been translocated deeply into soils during centuries of agriculture and accumulated in physically undisturbed B horizons. Agricultural practices inferred to be causal factors in changing these soils include terracing, tillage, fertilization, and irrigation. These ancient agricultural soils contain features characteristic of anthropic and plaggen epipedons and agric horizons.
Traffic Effects on Water Infiltration in Chisel‐Plow and No‐till Systems
Authors: Ankeny M. D. , Kaspar T. C. , Prieksat M. A.
Published: July 2010

Traffic effects on pore structure and hydraulic properties of soils may be affected by site‐specific factors. The objective of this study was to determine if the effects of wheel traffic on infiltration rates in chisel‐plow and no‐till tillage systems differed among five Midwestern locations. Ponded and unsaturated (30‐, 60‐, and 150‐mm water tension head) infiltration rates were measured sequentially using infiltrometers after removing surface residues and the upper 2 cm of soil. Wheel traffic reduced ponded infiltration rates in both tillage systems at all locations, ranging from 95% in the chisel‐plow system in Iowa to approximately 55% in the chisel‐plow system in Missouri. Tillage systems significantly affected ponded infiltration rates at only two of the locations. At the Minnesota and Nebraska locations, no‐till reduced ponded infiltration rates in untrafficked interrows by 33 and 64%, respectively, compared with those in the chisel‐plow system. Ponded infiltration rates of trafficked interrows did not differ between tillage systems at any location. At the Iowa and Nebraska locations, the decrease in infiltration rate with an increase in tension head was greater for untrafficked interrows than for trafficked interrows in the chisel‐plow system. The large pores that drain at 30 mm of tension head accounted for a lower percentage of the water flow with ponding in trafficked interrows (73%) than in untrafficked interrows (88%). Infiltration rate comparisons between tillage systems should consider wheel traffic patterns.
Interpreting Differences among Hydraulic Parameters for Different Soil Series by Functional Characterization
Authors: Leummens H. , Bouma J. , Booltink H. W. G.
Published: July 2010

Using soil survey data for simulation modeling of water regimes and crop growth requires characteristic expressions for hydraulic characteristics of major soil horizons and soil series. It is unclear at present whether: (i) hydraulic functions based on parameter estimation techniques are adequate for simulations in macroporous soils, and (ii) to what extent different soil horizons and series can be pooled to reduce input data in simulation models. These questions were examined using two methods of expressing measured hydraulic conductivity data in computer simulations with previously validated crop models. Both hydraulic conductivity expressions used parameterized equations derived from one‐step outflow data for the −5.0 to −60.0 kPa pressure range. For the 0 to −5.0 kPa range, one method used hydraulic conductivities estimated by extrapolating the parameterized functions, whereas the second method used actual crust test data to account for macropore flow. Differences between the two methods were functionally tested by simulating maize (Zea mays L.) yields and fluxes below the root zone in three Costa Rican soil series, using the SWACROP model. Yields were significantly higher when considering structural porosity (Method 2), while fluxes were significantly lower. Thus, extrapolation of one‐step outflow data to conditions near saturation seems to be questionable. Using Method 2, maize yields and fluxes below the root zone were compared for three representative soil series to test whether they could be considered as one functional group of soils. Yield data indicated that two rather than one functional group should be distinguished. Flux data were similar for all three series, indicating that only one functional group was necessary.
Solubility of Hydroxy‐Aluminum Interlayers and Imogolite in a Spodosol
Authors: Su Chunming , Harsh James B. , Boyle Jeffrey S.
Published: July 2010

Information on the thermodynamic stability of minerals is essential when describing dissolution‐precipitation reactions. The solubility of imogolite in the Bs and BC horizons of a Spodosol influenced by volcanic ash in the Cascade Range, Washington, was studied using batch chemical equilibrium modeling at 25°C and 0.1 MPa pressure. Imogolite was found to be a major component of the clay fraction in the Bs and BC horizons of these soils using transmission electron microscopy (TEM) and selective dissolution techniques. Soil solutions were collected in 60‐, 120‐, and 180‐d intervals from soils (<2 mm) equilibrated in 0.01 M NaCl at initial pH 5.7 or 3.5 under conditions of both under‐ and oversaturation. The pH, total and labile (inorganic monomeric) Al, and labile (monomeric) Si were determined. We used a computer speciation model to calculate the activities of Al, H4SiO4, F, SO4, and other species including a soluble aluminosilicate complex. Soil solutions appeared to be in equilibrium with interlayer Al(OH)3 of 2:1 phyllosilicates and natural imogolite in the Bs and BC horizon soils, based on the most recent free energy values for synthetic and natural imogolites. The equilibrium activity of H2SiO4 was 10−3.71±0.08. Soil solutions were oversaturated with respect to gibbsite (3pH + log Al3+ = 8.73 ± 0.16). Interlayer Al(OH)3 appeared to have a higher solubility than well‐crystallized gibbsite. Assuming equilibrium with the soil solution, imogolite in this Spodosol was more soluble (log K25C [equilibrium constant at 25°C and 0.1 MPa] = 13.76 ± 0.25) than its synthetic counterpart (log K25C = 13.04 ± 0.14), but not different from a Japanese natural imogolite (log K25C = 13.56 ± 0.18).
Boron Sorption by Soil in the Presence of Composted Organic Matter
Authors: Yermiyahu U. , Keren R. , Chen Y.
Published: July 2010

Although the organic matter content in cultivated soil is relatively low, its presence may have a significant effect on B distribution between the solid and liquid phases in soils. This study was conducted to determine the influence of organic matter in soil on B sorption and to test a B sorption model for soil in the presence of organic matter. The study was conducted on a loess soil (Calcic Haploxeralf). Mature compost, produced from the solid fraction of separated straw‐containing cattle manure, served as a simulation of organic matter. Boron sorption by soil‐composted organic matter mixtures increased as the organic matter content increased. At low pH levels (below pH 8), the sorption isotherms were linear regardless of the composted organic matter content. At the higher pH range, however, a deviation from linearity was observed. This deviation, which increased with pH, was related to the surface concentration of occupied sorption sites. Sorption B data from batch experiments were compared with results computed according to fitted adsorption coefficients (maximum B sorption and affinity coefficients that related to the binding energy). The B sorption capacity of the mixture increased with the composted organic matter content. The agreement between calculated values and experimental results indicates that the sorption model can be used to predict B sorption by soil‐organic matter mixtures.
Manganese and Iron Oxides as Reactants for Oxidation of Chlorophenols
Authors: Pizzigallo M. D. R. , Ruggiero P. , Crecchio C. , Mininni R.
Published: July 2010

Manganese and Fe oxides are capable of decreasing the concentration of chlorophenols, which are highly toxic pollutants in natural systems. Four di‐ and trichlorophenols were oxidized in oxide‐buffered solution suspensions at rates depending on the concentration of reactants, the number and position of the chloro substituents, the surface charge and point of zero charge of the metal oxides, and the environmental pH. Second‐order graphical plots were used to calculate the reaction constants and the half‐life times. The order of reactivity of the oxides was birnessite > pyrolusite > Fe(III) oxide in all systems. Their reactivity was maximum at pH 4.0. The 2,4,6‐trichlorophenol (TCP) was the substrate oxidized to the largest extent, whereas 2,3,5‐TCP showed the lowest reactivity. The quantity of chlorophenols removed per unit mass of birnessite increased as the concentrations increased, without any apparent saturation effect across a wide range of concentrations, whereas it tended to be constant at high equilibrium concentration when pyrolusite and particularly Fe(III) oxide were used as oxidants. From radioactivity measurements of the 14C recovered in liquid and solid phases after incubation of radiolabeled 2,4‐dichlorophenol and 2,4,5‐TCP with the metal oxides, the presence of less soluble oxidation products was shown. Oxidation products, such as quinones and traces of a dimeric compound, were detected by mass spectrometry. The effects observed support the general mechanism for a surface chemical reaction involving a metal oxide‐chlorophenol complex formation followed by a phenoxyl radical generation.
Soil Organic Carbon, Microbial Biomass, and Mineralizable Carbon and Nitrogen in Sorghum
Authors: Franzluebbers A. J. , Hons F. M. , Zuberer D. A.
Published: July 2010

Quantifying changes in soil microbial biomass and mineralizable C and N is important in understanding the dynamics of the active soil C and N pools. Our objectives were to quantify long‐term and seasonal changes in soil organic C (SOC), soil microbial biomass C (SMBC) and N (SMBN), and mineralizable C and N in continuous sorghum [Sorghum bicolor (L.) Moench] and sorghum‐wheat (Triticum aestivum L.)/soybean [Glycine max (L.) Merr.] sequences under conventional tillage (CT) and no tillage (NT) with and without N fertilization. A Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in south‐central Texas was sampled after planting in April, during flowering in June, and following sorghum harvest in August. More crop residue C input was retained as SOC and SMBC under NT than under CT. Soil organic C, SMBC, SMBN, and mineralizable C and N were greatest at a depth of 0 to 50 mm under NT. Mineralizable C and SMBC averaged 18% greater in rotation than in monoculture, probably due to greater C input via crop roots and residues in rotation and a shorter fallow. Mineralizable N with N fertilization was 36% greater in continuous sorghum but not different in rotated sorghum. Mineralizable C and SMBC increased an average of 5%, but mineralizable N decreased 41% from planting to flowering, probably due to rhizodeposition. From planting to post‐harvest, mineralizable C and SMBC increased 9% but mineralizable N decreased 15% due to crop residue addition. Soil N availability was reduced by plant additions in the short term but enhanced in the long term.
Soil pH and Copper Effects on Young ‘Hamlin’ Orange Trees
Authors: Alva A. K. , Graham J. H. , Anderson C. A.
Published: July 2010

Soil pH is an important factor affecting the forms of Cu in soils and, in turn, its effects on plants. A field experiment was conducted on a Candler fine sand (sandy, hyperthermic, uncoated Typic Quartzipsamment) to investigate the effects of high soil Cu (as a result of repeated spray applications of Cu on the soil surface in 14 doses, for a total of 120 kg Cu ha−1) on growth and mineral content in the foliage of young ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] trees on three different rootstocks at four soil pH regimes (pH 5.0–7.0 at 0.5‐unit increments). The recovery of Cu (15 mo after the last application), by Mehlich 3 (M3) extraction, in the top 15 cm of soil accounted for 22 to 80% of applied Cu depending on the soil pH. Stem diameter and canopy volume of the trees (3 and 5 yr old) were significantly influenced by soil pH, Cu, and rootstock. Effects of Cu on tree growth were more pronounced at pH 5.5 to 6.0 than at the lower or higher pH regimes. The concentration of Cu in mature spring flush foliage of the trees did not exceed the optimal concentration range. There was no significant relationship between M3 soil Cu and Cu concentrations in the foliage of the trees on all three rootstocks. A significant relationship was found between the concentrations of feeder root Cu and M3 soil, suggesting that the former can be used as an index of soil Cu status.
Pedogenic Carbonate in Soils of the Isaacks' Ranch Surface, Southern New Mexico
Authors: Gile Leland H.
Published: July 2010

Pedogenic carbonate has potential as a chronological tool for vast areas of arid and semiarid regions. However, much more work is needed on variations in carbonate accumulation in soils of the same age. A long gully and study trench in southern New Mexico provide continuous exposures of soils of a drainageway and ridge of Isaacks' Ranch age (8000–15 000 yr). A fine‐loamy Typic Haplargid in the drainageway has a Stage II carbonate horizon and 108 kg/m2 of carbonate. Two coarse‐loamy Typic Haplargids of the ridge side have Stage II carbonate horizons and 78 and 97 kg/m2 of carbonate, distinctly less than for the soil of the drainageway. The difference is attributed to finer texture (which would slow the wetting fronts) in the drainageway, and more water there for movement of carbonate into the soil. At the ridge crest, a facies change from coarse‐loamy to sandy materials caused a change from Stage II nodules to Stage I coatings on grains. In the sandy materials, a Typic Torripsamment has 22 kg/m2 of carbonate. In the coarse‐loamy materials, a Typic Torriorthent has 60 kg/m2 of carbonate; the coarse‐loamy materials must have captured carbonate that moved to greater depths in the Torripsamment. Although the totals obtained must be considered estimates, they indicate that the amount of pedogenic carbonate in Isaacks' Ranch soils may range up to fivefold, that landscape position is an important factor in this range, and that texture of the parent materials can have a major effect on the amount of carbonate in soils of a given age regardless of landscape position.
Surface Soil Degradation and Soil Productivity Restoration and Maintenance
Authors: Bruce R. R. , Langdale G. W. , West L. T. , Miller W. P.
Published: July 2010

In the Piedmont of the Southern Appalachian region, soil degradation is most often expressed by crop water deficit that limits crop yield in the warm season. To evaluate the nature of variability on these cropped lands, soybean [Glycine max (L.) Merr.] yield and associated soil characteristics were measured across the range of surface soil conditions in 40 farm fields. Factor analysis of the data permitted identification of variables responsible for most of the yield variability. Carbon in the surface soil was identified as the manageable soil variable that could significantly influence crop water availability and curtail soil erosion. Subsequently, selected crop cultures that supplied a range in quality and quantity of crop biomass to the soil surface were applied on three soil erosion classes for 5 yr. Large increases in rainfall infiltration and reduced soil erodibility were associated with no‐till planting of grain sorghum [Sorghum bicolor (L.) Moench] into crimson clover (Trifolium incarnatum L. ‘Tibbee’) in comparison to conventional tillage of grain sorghum and soybean. The maintenance of a decomposing mulch by crop residue additions of about 12 Mg ha−1 yr−1 generated high soil C levels in the 0‐ to 15‐mm depth and a high water stability of aggregates in the 0‐ to 80‐mm depth in comparison to incorporated crop residues. In the 6th yr, grain yield of conventionally tilled soybean was 30 to 100% greater on the previously no‐till crop culture than on the conventionally tilled. The restoration and maintenance of soil productivity commensurate with inherent site resources was associated with maintenance of a decomposing mulch on the soil surface derived from an appropriate quantity and quality of crop residue produced in situ.
Raindrop‐Induced Soil Detachment and Sediment Transport from Interrill Areas
Authors: Sharma P. P. , Gupta S. C. , Foster G. R.
Published: July 2010

Physically based soil erosion simulation models require input parameters of soil detachment and sediment transport due to the action and interactions of both raindrops and overland flow. In this study, we report on the soil detachability and transportability parameters for raindrop‐impact‐dominated interrill erosion processes. The detachability parameter is derived by integrating estimated soil detachment due to single raindrop impact over all the raindrops occurring in a storm. Using artificial rainfall characteristics and soil properties as inputs, we simulated raindrop‐induced soil detachment rates for 33 cropland soils used in the USDA‐ARS Water Erosion Prediction Project (WEPP) experiments in the USA. The magnitude of difference between the predicted detachment rates and the measured interrill sediment delivery rates decreased with clay content. This suggests that in coarse‐textured soils, most of the rain‐detached sediments are redistributed within the interrill area. Small differences between detachment rates and sediment delivery rates in clayey soils indicate that the interrill erosion is detachment limited. A raindrop‐induced interrill transportability parameter is derived by dividing the measured sediment delivery rates with the product of rainfall rate and unit effective kinetic energy. The derived transportability parameter increases linearly with an increase in clay content, thereby suggesting the predominant role of raindrop impact in the sediment delivery process, specifically on up‐slope areas with shallow overland flow. The raindrop‐induced soil detachment and sediment transport processes can be represented by incorporating intensity and effective kinetic energy of rainfall into the basic interrill erosion model.
A Multiregion Model Describing Water Flow and Solute Transport in Heterogeneous Soils
Authors: Hutson J. L. , Wagenet R. J.
Published: July 2010

Many different processes influence chemical breakthrough patterns from soil columns, including chemical kinetics, diffusion, matrix geometry, and flow heterogeneity. TRANSMIT, a multiregion model that reflects many of these features, was used to simulate a suite of solute breakthrough curves from soil columns subjected to both transient and steady‐state flow. When utilized as a two‐region model. TRANSMIT matched analytical solutions for steady‐state flow through two‐region soils. The TRANSMIT model is easily expanded to describe a wide range of multiregion and two‐dimensional geometries and is applicable to transient and steady‐state flow typical of both laboratory experiments and field situations. Sorption and degradation parameters can be varied, and nonuniform surface boundary conditions, resulting from irrigation method and banded chemical placement, can be described.
Spatio‐Temporal Variability of Soil Temperature within Three Land Areas Exposed to Different Tillage Systems
Authors: Mohanty B. P. , Klittich W. M. , Horton R. , van Genuchten M. Th.
Published: July 2010

The rational (lateral) spacing between soil temperature sensors to obtain spatial independence of measurements in the field under various tillage systems is not well studied. In particular, properly positioning sensors in a tillage plot requires knowledge of the spatial dependence of the measurements. This study was conducted to measure the horizontal spatial variability of soil temperature and its diurnal fluctuation in three different tillage systems. Soil temperature was measured with copper‐constantan thermocouples at 49 positions in each system at the 1‐ and 10‐cm depths. The thermocouples formed a 7 by 7 grid with a spacing of 3.0 (east‐west) by 1.5 m (north‐south). The three management systems were fall moldboard plowing followed by spring disking and planter operation (MP), fall chisel plowing followed by spring disking and planter operation (CP), and ridge tillage slot planting (RN). Each management system had been under continuous field corn (Zea mays L.) for 8 yr. A novel finding of the study is that a hysteresis within the diurnal cycle existed between the mean and the sample variance. This hysteresis was presumably due to differences in soil surface heating and cooling rates during the diurnal cycle. Although no definitive relationships could be determined, semivariograms appeared to show a time dependence and anisotropy during the 24‐h observation period. Correlation distances were ≈9 m in the E‐W direction along crop rows and tillage operations but <1.5 m in the N‐S direction across crop rows and tillage operations. These spatial correlation distances will be useful in deciding the minimum (lateral) spacing between adjacent soil temperature sensors in the field.
Kinetic Behavior of Synthetic Organo‐ and Organo‐Mineral‐Urease Complexes
Authors: Gianfreda Liliana , De Cristofaro Annunziata , Rao Maria A. , Violante Antonio
Published: July 2010

A study was conducted for characterizing the properties and the catalytic behavior of enzymatic complexes that are considered analogues of those usually present in soil. Active enzymatic complexes were formed at 10°C by interaction for 1 h of urease and tannic acid with and without Fe ions and OH‐Al polymers. The enzymatic complexes obtained in the presence of Fe3+ ions and OH‐Al species showed higher activity levels than urease‐tannate complexes. The pH optimum of immobilized urease did not differ significantly from that of free urease, except for the tannate complexes, which showed a pH optimum slightly shifted upwards by ≈0.5 units. Immobilized urease displayed the highest activity in a wider range of temperatures (60–80°C) compared with the free enzyme. The free enzyme showed a marked reduction in activity above 70°C. Higher values of energy of activation (Ea), enthalpy of activation (ΔHa), and the kinetic parameter (Km) were obtained for urease immobilized on tannate molecules. On the contrary, the complexes obtained with Fe3+ and OH‐Al species displayed kinetic and thermodynamic parameters similar to those of the free enzyme. Immobilized urease showed a catalytic behavior similar to the free enzyme, when the interaction with tannic acid occurred in the presence of Fe3+ ions and OH‐Al polymers. Evidently, both Fe ions and OH‐Al species favored the formation of enzymatic complexes in which conformational and catalytic features of the enzyme remained practically unchanged.
Chemical Structure and Biological Activity of A Siderophore Produced by Rhizopus arrhizus
Authors: Shenker M. , Chen Y. , Ghirlando R. , Oliver I. , Helmann M. , Hadar Y.
Published: July 2010

Rhizopus arrhizus grown on low‐Fe medium produces a siderophore, the chemical structure of which was determined by means of 1H nuclear magnetic resonance (NMR), 13C NMR, and circular dichroism spectroscopy. The siderophore was identified as N1,N4‐bis(1‐oxo‐3‐hydroxy‐3,4‐dicarboxybutyl)‐diaminobutane, chemically identical to rhizoferrin produced by Rhizopus microsporus. Growth promotion of R. arrhizus by several unferrated chelates in Fe‐limited medium was studied in microtitration plates. The impact of rhizoferrin was much more pronounced than the effect of other siderophores. This growth promotion was used as a bioassay for the detection of rhizoferrin. Purified Fe‐rhizoferrin was found to be a very efficient Fe source for tomato plants [Lycopersicon lycopersicon (L.) Karsten] in nutrient solutions. Uptake and translocation of 55Fe mediated by rhizoferrin in a short‐term (10‐h) experiment were at levels higher than those obtained by other microbial siderophores. Iron‐rhizoferrin acted similarly to the synthetic chelate FeEDDHA [ethylenediamine di(o‐hydroxyphenylacetic acid)] on remedy of chlorosis in a long‐term (14‐d) experiment.
Isotopic Labeling of Soil Nitrate Pools Using Nitrogen‐15‐Nitric Oxide Gas
Authors: Stark John M. , Firestone Mary K.
Published: July 2010

In N cycling studies, soil NO−3 pools are typically labeled by adding solutions containing 15NO−3. The associated increase in moisture may perturb the system and preclude measurement of N‐cycle processes in relatively dry soils. This study examined the feasibility of using 15N‐NO gas to label soil NO−3 pools without addition of water. Soil samples (ashed, oven dry, or with soil water potentials ranging from −3.7 to −0.2 kJ kg−1 [1 MPa = 1 kJ kg−1]) were exposed to various quantities of NO gas (0–600 mg NO‐N kg−1 soil). Maximum recovery of NO‐N in soil NO−2 and NO−3 pools occurred after <2 h of exposure to the gas and ranged from ≈ 40% for moist soil samples to >90% in ashed soil. Relative increases in either NO−2 or NO−3 depended on the initial NO concentration and the soil treatment. In general, higher soil moisture resulted in higher NO−2/NO−3 ratios. Within 20 h of addition of 15NO, almost all of the NO−2 was converted to NO−3; however, a small amount was also converted to NH+4 and organic N. These results demonstrate that 15NO can be used to label soil NO−3 pools without addition of water. Depending on the objectives of the study, however, it may be necessary to monitor the enrichment of a variety of other soil N pools as well.
Nitrate Leaching through Lysimeters in a Corn‐Soybean Rotation
Authors: Owens L. B. , Edwards W. M. , Shipitalo M. J.
Published: July 2010

Leaching of NO3‐N can be excessive under continuous corn (Zea mays L.) production. To reduce NO3‐N losses, corn might be rotated with soybean [Glycine max (L.) Merr.], which does not require fertilizer N. Six large, undisturbed monolith lysimeters (8.1‐m2 surface area, 2.4 m deep) were used to investigate NO3‐N leaching in a 6‐yr cornsoybean rotation study in eastern Ohio. Four lysimeters (Y103 A, B, C, and D) contained a moderately well‐drained Keene silt loam (fine‐silty, mixed, mesic Aquic Hapludalf) on a 6% slope, and two lysimeters (Y102 A and C) contained a well‐drained Rayne silt loam on a 13% slope (fine‐loamy, mixed, mesic Typic Hapludult). In the spring of each year, 224 kg N/ha as NH4NO3 was surface applied, and a rye (Secale cereale L.) winter cover crop was used following soybean. Nitrate‐N levels in lysimeter percolate varied seasonally from 1 to 20 mg/L and on a 2‐yr cycle, showing the influence of the crop rotation. The highest NO3‐N levels usually occurred during the dormant season following corn. During the 6 yr of the study, the flow‐weighted average NO3‐N concentration in the percolate was 10.5 and 14.3 mg/L from the Y103 and Y102 lysimeters, respectively. Mean annual NO3‐N losses in the percolate were 31.6 and 47.1 kg/ha, respectively. These NO3‐N losses are smaller than losses from continuous corn production previously measured with the same lysimeters. Thus, a corn‐soybean rotation may be one strategy for reducing NO3‐N loading to groundwater.
Hydraulic Conductivity of Saprolite as a Function of Sample Dimensions and Measurement Technique
Authors: Vepraskas M. J. , Williams J. P.
Published: July 2010

Accurate hydraulic conductivity (K) data are needed to evaluate soils for on‐site waste disposal, but such data are difficult to obtain where K values vary with sample dimensions. This study evaluated the K of a quartz‐diorite saprolite (Cl horizon) by comparing saturated hydraulic conductivities (Ksat) for sample volumes of 347, 6280, and 675000 cm3. Unsaturated hydraulic conductivities [K(h)] for sample volumes of 347 and 6280 cm3 were compared using a one‐step outflow procedure and the crust test. A dye was also applied to the largest samples to determine the depth distribution of water‐conducting macropores. The mean Ksat value found for samples with volumes of 347 cm3 (0.04 cm h−1) was significantly lower than the mean Ksat values found for larger samples (0.16–0.20 cm h−1); means for the latter samples were not significantly different (P = 0.10). Means for K(h) also differed between the two sample volumes for soil water pressure heads of −5 and −10 cm. Channels were the major kind of water‐conducting macropore observed. The results from both the pore studies and K measurements showed that the minimum sample size needed in situ for K measurements in this horizon was ≈ 5000 cm3 for soil water pressure heads between 0 and −10 cm. Detached cores with smaller cross‐sectional areas could be used for measuring K(h) at soil water pressure heads of ‐20 cm or less.
Dithionite‐Citrate‐Bicarbonate‐Extractable Organic Matter in Particle‐Size Fractions of a Haplaquoll
Authors: Schulten H.‐R. , Leinweber P.
Published: July 2010

The influence of the dithionite‐citrate‐bicarbonate (DCB) extraction on soil organic matter (SOM) in five particle‐size fractions of a Haplaquoll was studied by pyrolysis‐field ionization mass spectrometry. By treatment with DCB, 4 to 19 g kg−1 of organic C (Cdcb; 17.8–44.4% of total C), 2.2 to 20.3 g kg−1 of Fe (Fedcb; 13.6–29.7% of total Fe), and 0.4 to 8.4 g kg−1 of Al (Aldcb; 0.6–8.0% of total Al) were extracted from the size fractions. The pyrolysis‐field ionization mass spectra recorded before and after DCB extraction and the proportions of six important compound classes of SOM showed that lipids, alkylaromatics, and lignin dimers were preferentially extracted. In the extraction residues of clay, fine silt, and medium silt, increases in total ion intensities, weight‐averaged molecular weights of the pyrolysate, and characteristic shifts in the pyrolysis thermograms toward lower temperatures were observed. These properties indicated a general destabilization of the SOM structure due to DCB extraction. We explained these results by the solubility of these SOM constituents in alkali or by associations with pedogenic oxides that stabilized the SOM structure. The results pointed also to unknown, possibly selective, losses of C species when DCB extraction is used to improve the quality of solid‐state (cross polarization/magic angle spinning)‐13C nuclear magnetic resonance spectra.
Nitrogen Mineralization and Microbial Biomass Nitrogen Dynamics in Three Alpine Tundra Communities
Authors: Fisk Melany C. , Schmidt Steven K.
Published: July 2010

The alpine tundra of the Colorado Front Range supports a variety of plant communities whose distribution corresponds to their topographic position. Our objectives were to: (i) determine patterns in net N mineralization and microbial N pools among three communities, Kobresia, Acomastylis, and Carex meadows, that span a topographic gradient, and (ii) relate any patterns to soil microclimate differences among these communities. Average yearly net N mineralization rates, measured with an in situ core incubation technique, were 1.2 g N m−2 in 1991 and 1.0 g N m−2 in 1992. No differences were detected in yearly N mineralization rates among the three communities; however, net nitrification and other soil properties were found to differ among communities. Net N mineralization rates and microbial N showed strong temporal variation, and this variation was related to different variables for each community. Seasonal variation in N mineralization was related to soil water and microbial N in Kobresia meadows, to soil temperature and microbial N in Acomastylis meadows, and to soil water and temperature in Carex meadows. Seasonal changes in microbial N were related to soil water in Kobresia and Acomastylis meadows. Large fluctuations in microbial N indicate that periodic losses from the microbial pool may be important to N availability in this alpine tundra site.