bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen Mineralization from Citrus Tree Residues under Different Production Conditions
Authors: Dou H. , Alva A. K. , Khakural B. R. 
Published: July 2010

AbstractUnder most citrus production conditions, dry leaves and other vegetative parts are returned to the soil under the trees. These materials and fibrous roots decompose on a regular basis. The objective here was to measure annual N contribution to citrus trees from organic residue decomposition. Mineralization of N was measured during 2 yr under citrus trees of two age groups each on Tavares fine sand (hyperthermic, uncoated Typic Quartzipsamment) and Wabasso sand (sandy, siliceous, hyperthermic Alfic Haplaquod). Mineralization of N from tree residues under the canopy accounted for 58 to 84 and 126 to 153 kg N ha−1 yr−1 for the 4‐ and 20‐yr‐old trees, respectively, on the Tavares fine sand and 39 to 64 and 121 to 126 kg N ha−1 yr−1 for the 7‐ and 40‐yr‐old trees, respectively, on the Wabasso sand. The transformation of potentially mineralizable N (i.e., total N in dry crop residue and fibrous roots under the canopy) into inorganic forms (i.e., percentage mineralization) was greater in Wabasso sand (41–86%) compared with that in Tavares fine sand (17–71%). Significant correlations (r = 0.82 [significant at P = 0.05] and 0.84 [significant at P = 0.01]) were found between measured quantities of mineralized N and potentially mineralizable N. There were also significant correlations between mineralized N and either rainfall or average temperature during each incubation interval. This study demonstrated that the quantity of net N mineralized from organic residues under the tree accounts for a significant portion of annual N requirement.
Ability for In‐Season Correction of Nitrogen Deficiency in Corn Using Chlorophyll Meters
Authors: Varvel Gary E. , Schepers James S. , Francis Dennis D. 
Published: July 2010

AbstractNitrate‐nitrogen contamination of groundwater continues to be a major concern throughout the USA. These concerns are greatest in areas where groundwater is close to the soil surface and in areas that have irrigated crops with large N fertilizer requirements. Specific objectives of this work were to use the chlorophyll meter to determine in‐season crop N status and to correct in‐season N deficiencies in irrigated corn (Zea mays L.). Chlorophyll meter readings were used to calculate a sufficiency index [(as‐needed treatment/well‐fertilized treatment) × 100] and in‐season N fertilizer applications were made when index values were below 95%. Using this procedure, maximum yields were attained if early season N levels were adequate to maintain sufficiency indexes between 90 and 100% at the V8 growth stage. However, if the sufficiency index at V8 was below 90%, maximum yields were not achieved with in‐season N fertilizer applications because early season N was below that needed for optimum growth and yield potentials had already been reduced. Even in these causes, N applications did increase yields, but not to the maximum. These results did demonstrate that early N deficiencies could be corrected using chlorophyll meters and the sufficiency index approach when they were not severe. Although the objective was not tested in this study, less N fertilizer may be required when in‐season monitoring is used as the basis for N application. Use of the chlorophyll meter and sufficiency index should also result in greater N use efficiency and less N being available for leaching to the groundwater since these applications are made when N uptake by corn is greatest.
Automated Soil Monolith‐Flux Chamber System for the Study of Trace Gas Fluxes
Authors: Thomson Petra E. , Parker John P. , Arah Jonathan R. M. , Clayton Helen , Smith Keith A. 
Published: July 2010

AbstractSoils are the major source of atmospheric N2O, and better estimates of fluxes are needed to improve the input to climatic general circulation models. We developed a system in a semicontrolled environment to investigate relationships between fluxes of N2O and controlling variables. It consists of 12 soil monoliths (1‐m diam., ≈ 0.6 m deep) in glass fiber casings, the tops of which have been converted into gas flux chambers. These chambers are connected to a gas chromatograph for measurement of N2O and CO2. Gas sampling and analysis is computer controlled and can be done continuously. Temperatures and soil water potential are also recorded continuously. The system has performed reliably since continuous operation began in September 1993. We conducted three experiments, examining the effects of soil water potential, organic matter input, and diurnal temperature variation on N2O fluxes, to illustrate the capabilities of the system. In these experiments, the major emissions of N2O (>800 εg N2O‐N m−2 h−1) occurred when the water potential was above −5 kPa. When plant material was incorporated into the soil, a highly significant correlation was found between N2O and CO2 emissions; the N2O emissions showed pronounced diurnal cycles, with the maxima occurring at night, 4 h after the temperature maxima at 0.1‐m depth. Data interpretation was greatly aided by the frequency and continuity of measurement.
Modeling Nonwetting‐Phase Relative Permeability Accounting for a Discontinuous Nonwetting Phase
Authors: Fischer Ulrich , Dury Olivier , Flühler Hannes , van Genuchten Martinus Th. 
Published: July 2010

AbstractA model for the wetting‐ and nonwetting‐phase constitutive relationships is presented. The nonwetting‐phase relative permeability in the model is a function of the degree of continuous nonwetting‐phase saturation. Different formulations of the continuous nonwetting‐phase model were evaluated by comparison of calculated and measured air permeabilities as well as discontinuous air saturations. A Brooks and Corey‐Burdine type formulation of the nonwetting‐phase relative permeability was more accurate than the corresponding van Genuchten‐Mualem equation. Estimated discontinuous air saturations were higher for drying than for wetting, thus reflecting hysteresis in the water‐retention and relative air permeability functions. The continuous nonwetting‐phase model provided a much better prediction of relative air permeabilities than a formulation that neglects the presence of a discontinuous nonwetting phase. The emergence point model for the nonwetting‐phase relative permeability provided a good approximation of the continuous nonwetting‐phase model.
Winter Cover Cropping Influence on Nitrogen in Soil
Authors: Kuo S. , Sainju U. M. , Jellum E. J. 
Published: July 2010

AbstractWinter cover crops may affect the short‐ and long‐term N availability in soil depending on the quantity, quality, and degradation rate of biomass returned to the soil. We examined the effects of several cover crops on soil inorganic and organic N levels in a winter cover crop‐silage corn (Zea mays L.) double‐cropping system that was initiated in 1987. High biomass N concentrations (BMN) in the above‐ and belowground biomass of the leguminous cover crops corresponded to high levels of inorganic N and water‐soluble N, but low levels of water‐soluble C and carbohydrate compared with the nonleguminous cover crops. The BMN above which there was net N mineralization 4 wk after residue incorporation was 17.9 g N kg−1. The organic N from the aboveground biomass degraded rapidly. The first‐order rate constants for the degradation of organic N and C in the cover crops were significantly correlated. This, coupled with a significant correlation between the soil organic N (SON) levels and cumulative biomass C added, indicated the importance of biomass C inputs in organic N retention in the soil. The cover crops had variable short‐ and long‐term effects on soil N availability. Whereas rye (Secale cereale L. cv. Tetra Petkus) and annual ryegrass (Lolium multiflorum Lam. cv. Billion) were ineffective in increasing soil inorganic N levels, they were more effective than hairy vetch (Vicia villosa Roth subsp. villosa), Austrian winter pea (Lathryrus hirsutus L.), and canola (Brassica napus L. cv. Santana) in increasing SON accumulation because of a higher biomass potential and a larger input of biomass C.
Soil Characteristics that Regulate Soil Reduction and Methane Production in Wetland Rice Soils
Authors: Gaunt J. L. , Grant I. F. , Neue H. U. , Bragais J. , Giller K. E. 
Published: July 2010

AbstractMethane production in soil is a microbiological process that occurs under strict anaerobic conditions. A laboratory incubation study was conducted using 10 wetland rice (Oryza sativa L.) soils from the Philippines to establish soil characteristics that govern the redox characteristics and CH4 production of soils upon wetting. Labile soil organic matter in the Ap horizon was quantified as enrichment of C and N and non‐clay‐protected C and N fractions. The C/N ratio of the enriched fraction controlled the rate of reduction upon flooding, whereas the buffering capacity, measured as extractable Fe3+ content, controlled the reduction capacity for the soils. Methane production was influenced both by the reduction characteristics of the soils and labile organic substrates.
Reactive Solute Transport with a Variable Selectivity Coefficient in an Undisturbed Soil Column
Authors: Momii Kazuro , Hiroshiro Yoshinari , Jinno Kenji , Berndtsson Ronny 
Published: July 2010

AbstractThe spatial distribution of major ion concentrations limits the pre‐dictability of solute transport processes in field soils. Therefore, it is important to analyze solute transport with chemical reactions based on results obtained from field soils and numerical simulation. A simulation model with cation‐exchange reactions was developed and applied to solute‐transport analysis of an undisturbed field soil. Chemical reaction terms in the convective‐dispersive equation were estimated by the Levenberg‐Marquardt nonlinear least‐squares regression technique to satisfy physical and chemical processes simultaneously. The reliability of the model was tested with liquid‐phase and solid‐phase concentrations of measured spatial distributions of Ca2+, Mg2+, Na+, and K+ after continuous infiltration of KCl solution into an undisturbed soil column. The experimental results revealed that the selectivity coefficients for Ca‐Na and Ca‐Mg exchange could be kept constant, while those for Ca‐K exchange increased with the equivalent fraction of K+ in the solid phase. The effects of the exchange selectivity coefficient on reactive solute transport are discussed based on the simulation results. When a constant selectivity coefficient was used, the model failed to predict the spatial distributions of cation concentrations in the solid phase. Thus, model predictions can be improved by use of variable instead of constant selectivity coefficients.
Acoustic Radiation Analog for Steady Infiltration from Finite Buried and Surface Disk Sources
Authors: Joshi Bhaskar , Maule Charles 
Published: July 2010

AbstractThe movement of solutes by advection from sources of finite size may be predicted if the distribution of moisture potentials and flux around them is determined. We have developed a new analytical approach to the problem of steady‐state infiltration from oblate spheroidal sources of finite size and applied it to buried as well as surface disk sources. It is possible to calculate the distribution of matric flux potential and stream functions around these sources by using this method. The approach establishes an analogy with radiation of sound from vibrating circular pistons. Within the limit of small source size, the solutions approach the point‐source solutions already available in the literature. We derived relatively simple expressions to calculate the matric flux potential and stream function distributions around sources of finite size.
Preferential Movement of Oxygen in Soils?
Authors: Dziejowski Jerzy E. , Rimmer Alon , Steenhuis Tammo S. 
Published: July 2010

AbstractPlant roots and soil biota require O2 to function normally. When the soil O2 is depleted, it must be replaced by O2 from the atmosphere. The transport occurs primarily by gaseous diffusion. Although O2 diffusion has been researched in homogeneous soils, and in tight clay soils with cracks, little is known about the effects of macropores on O2 transport in typical agricultural soils. In this study we examined the impact of large pores on O2 concentration in a sandy loam soil. Experiments were carried out with homogeneous and simulated‐macropore columns with a steady‐state rainfall of 3 cm d‐1 in which the O2 concentration in the soil matrix and in the macropore was measured at 15‐cm vertical intervals. The diameter of each column was 20 cm and the height was 105 cm. Groundwater depth was systematically varied between 30 and 105 cm. Soil water content did not vary with distance above the water table for the 30‐, 60‐, and 90‐cm groundwater depths. While both the soil water for the entire column and the O2 concentration from the surface to the 30‐cm depth was the same for the homogeneous and macropore columns, the O2 penetrated deeper in the macropore column and was 4% greater below the 30‐cm depth in the macropore column than for the homogeneous column.
Optimal Solid‐to‐Solution Ratios for Organic Chemical Sorption Experiments
Authors: McDonald, Louis M. , Bill Evangelou V. P. 
Published: July 2010

AbstractThe presence of organic chemicals in natural systems requires an understanding of how these chemicals distribute themselves between the different phases of the environment. Partition coefficients (K) then are an important parameter for environmental fate studies. One experimentally critical parameter in the estimation of K for solid‐liquid systems is the solid‐to‐solution ratio. Recommendations for a solid‐to‐solution ratio have ranged widely. Our objective was to derive a relationship for the variance of K, based on the analytical precision of the experimental variables, that could be used to determine the optimal solid‐to‐solution ratio for linear and Freundlich‐type partitioning. The optimal solid‐to‐solution ratio occurred at 55% sorption for linear and Freundlich partitioning when the Freundlich constant was between 0.8 and 1.
Differentiation of Clover Rhizobium Isolated from Biosolids‐Amended Soils with Varying pH
Authors: Ibekwe A. M. , Angle J. S. , Chaney R. L. , van Berkum P. 
Published: July 2010

AbstractMetal contamination may alter the diversity of microbes residing in soil. The genetic structure and phenotypic characteristics of clover Rhizobium isolated from contaminated and control soils were compared. Plant infection and symbiotic competence tests were used for phenotypic characterization. Variation across isolates in fingerprint patterns determined with primers for repetitive extragenic palindromic (REP) sequences and the polymerase chain reaction (PCR) were used for genetic characterization. Two phenotypic groups of effective and ineffective isolates were identified using the symbiotic effectiveness test. Soil pH was the primary factor influencing this phenotypic characteristic. Effective isolates were associated with higher soil pH and ineffective isolates were associated with lower soil pH regardless of soil metal content. The isolates were genetically diverse. The variation of isolates from the different soils overlapped, indicating that neither the heavy metals nor the low soil pH resulted in the selection of a single genotype. Isolates from the most heavily contaminated soils were more variable than isolates from control soils. Soil pH, and not heavy metal content, was important in the selection of rhizobia that formed ineffective N2‐fixing symbioses.
Fate of Fertilizer Nitrogen as Affected by Time and Rate of Application on Corn
Authors: Jokela William E. , Randall Gyles W. 
Published: July 2010

AbstractManagement of fertilizer N on corn (Zea mays L.) can greatly affect the efficiency of N use and the potential for adverse environmental effects. Field studies were conducted on two nonirrigated southern Minnesota soils — a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) and a Mt. Carroll silt loam (fine‐silty, mixed, mesic Mollic Hapludalf) — to determine the effect of time and rate of N application on recovery of fertilizer‐derived N (FDN) in corn grain and stover and in the soil. Nitrogen rates of 75 and 150 kg ha‐1 on the Mt. Carroll soil and 100 and 200 kg ha‐1 on the Webster were applied at planting or at the eight‐leaf stage as (NH4)2SO4 to the same plots from 1982 to 1984. Enriched 15N was applied to separate microplots each of the first 2 yr to allow measurement of FDN. Grain yield responded to applied N in 5 of 6 site‐yr, but not to time of application. Uptake of FDN in grain was increased by higher N rate in all cases, but by delayed application in only one site‐year. Total plant FDN recovery ranged from 31 to 60% at the low N rate and from 24 to 45% at the high rate. Both yields and FDN recovery were affected by unusually dry midseason conditions. Fertilizer‐derived N recovery from the soil after harvest ranged from 25 to 56%, with a large proportion at the high N rate in inorganic forms, especially with the late application, which increased the potential for leaching losses. Residual uptake of FDN by grain ranged from 1 to 10% of the initial N rate. The difference method for estimating FDN recovery gave different results from the 15N method, emphasizing the importance of examining both labeled and nonlabeled N pools for complete inter‐pretation of 15N studies.
Wyoming Rocky Mountain Forest Soils: Mapping Using an ARC/INFO Geographic Information System
Authors: Rahman S. , Munn L. C. , Vance G. F. , Arneson C. 
Published: July 2010

AbstractIn the western USA, wildland soil survey areas are often large, and the resources of money, personnel, and time required for conventional soil survey techniques are in short supply. We evaluated an alternative methodology for producing soil maps through a process of transecting, model construction, and projection onto a map base using ARC/INFO geographic information system (GIS) technology. We conducted this study in the Libby Creek watershed in Wyoming where soil distribution (Cryoboralfs, Cryoborolls, Cryaquolls, Cryaquents, Cryochrepts, and Cryorthents) is a function of geology, slope stability, and vegetation. The GIS‐generated soils map was compared with existing general (Order 4) and detailed (Order 3) soils maps prepared for the U.S. Forest Service (USFS). Discrepancies noted between the GIS‐generated map and USFS maps included: Cryochrepts were the dominant soil on the GIS map (44%), but comprised only 15% on the USFS detailed soils map; Cryumbrepts occupied 19% of the USFS general soils map but only 2% on the GIS‐derived soils map; and no Cryumbrepts were delineated in the study area on the USFS detailed soils map. Only two of the eight Cryumbrepts sampled occurred within Cryumbrept delineations on the USFS general soils map. Of the 37 pedons sampled and classified along the five transects across Libby Creek watershed, 11 (30%) corresponded to named soils of mapping units in the USFS general soils map, and 20 (54%) coincided on the USFS detailed soils map. Results of this study suggest transecting and GIS‐based mapping can be an effective technique for producing general soils maps, and can aid in placing soil boundaries for detailed soils maps.
Water Movement and Solute Transport through Saprolite
Authors: Li K. , Amoozegar A. , Robarge W. P. , Buol S. W. 
Published: July 2010

AbstractMany soils are underlain by saprolite. The purpose of this study was to assess the potential for preferential movement of pollutants through one soil and two saprolites in the Piedmont region of North Carolina. At one site (Site 1), two 100 by 100 by 100 cm intact blocks were isolated in situ in the Bt horizon and underlying saprolite, and a solution containing KBr, NH4NO3, a blue dye, and a red dye was applied to the top of each block. At a second location (Site 2), a 120 by 120 by 100 cm intact block of saprolite was similarly prepared. Acid red dye powder (5 g) was placed in four small holes (3 cm deep) bored into the surface of the block, and the block was leached with a solution containing only KBr and NH4NO3. After drainage, each block was dissected layer by layer (5 or 10 cm thick), and the middle 80 by 80 by 100 cm volume was divided into 768 samples and analyzed for K+, Br‐, NH+4, and NO‐3, as well as dye content. The visible patterns of the dyes, and extracted solute concentrations, at Site 1 indicated that preferential movement was more pronounced in the Bt horizon than in the saprolite. At Site 2, the red dye and solutes moved vertically with little lateral deviation. Our results suggest that vertical water movement in the two saprolites occurs mainly through matrix pores with little preferential movement via the visible features inherited from respective parent rocks.
Axial‐Radial Influence of Porous Cup Soil Solution Samplers in a Sandy Soil
Authors: Hart G. L. , Lowery B. 
Published: July 2010

AbstractPorous cup soil solution samplers (PCS) have been extensively used to assess movement of solutes through the vadose zone. The ease of installation, simplicity of design, and low cost make PCS attractive and perhaps useful tools. Quality of PCS data is often suspect, and it is difficult to determine solute flux because the volume of soil sampled is unknown. We compared the performance of PCS constructed of ceramic and stainless steel porous cups in Sparta sand (mesic, uncoated Typic Quartzipsamment) to assess their axial‐radial influence under transient water flow conditions. Bromide tracer was used to mimic water transport. Replicated (two) samplers of each porous material were placed at 25‐, 60‐, and 140‐cm depths. A time domain reflectometry system was utilized to measure water content adjacent to the samplers at 15‐min intervals. Axial‐radial PCS influence estimates were obtained by three independent methods: (i) an analytical approach based on a soil hydraulic conductivity function and sample volume; (ii) a mass balance of estimated water flux and volume collected by each sampler; and (iii) a mass balance of collected vs. leached Br‐. Calculated axial‐radial spheres were lognormally distributed. Significant differences (P < 0.05; type 1 error) were observed for mean axial‐radius estimates obtained by the three analytical methods. The mean axial radius for the ceramic and stainless steel porous cup samplers within each depth of sampling was also significantly different (P < 0.05; type 1 error). Combining data from both ceramic and stainless steel samplers across all three methods of analysis and depth of sampling resulted in a mean axial radius of ≈ 24 mm.