bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen Mineralization from Citrus Tree Residues under Different Production Conditions
Authors: Dou H. , Alva A. K. , Khakural B. R.
Published: July 2010

Under 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

Nitrate‐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

Soils 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

A 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

Winter 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

Methane 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

The 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

The 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

Plant 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

The 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

Metal 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

Management 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

In 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

Many 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

Porous 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.
Simple Linear Model for Calibration of Time Domain Reflectometry Measurements on Solute Concentration
Authors: Kim D. J. , Vanclooster M. , Feyen J. , Vereecken H.
Published: July 2010

The lack of an adequate method for calibration of time domain reflectometry (TDR) measurement on bulk soil electrical conductivity is a limiting factor, especially for field‐scale solute transport study. This study investigated an appropriate calibration method that can be applied to horizontally positioned TDR probes in situ. A nonlinear model (RM) has been proposed assuming a two‐pathway conductance. Using the quadratic form, the RM equated electrical conductivity in the immobile phase of soil solution (ECws) in a series‐coupled pathway with electrical conductivity in the mobile phase of soil solution (ECwc) in a continuous pathway. We related bulk soil electrical conductivity (ECa) to electrical conductivity of soil water (ECw), assuming constant ECws during breakthrough. This resulted in a linear relationship between ECa and ECw. The linear relation, termed here simple linear model (SLM), was tested using experimental data obtained from soil columns. Laboratory breakthrough experiments were performed on short and large columns by applying a pulse input of solute. At the end of breakthrough, separate calibration experiments were performed using a step input of solute. Both RM and SLM were compared with the step input calibration method (SIM) as a reference method. Results show that the SLM is better than RM in terms of mass recovery. In addition, parameters of the solute transport model were not affected within 20% of uncertainty in the slope coefficient of the SLM when compared with the reference method. Advantages of the SLM are that it has an identical equation form to the SIM but less effort is required, especially for soil columns showing preferential flow, and it can be readily applied to field conditions.
Tillage and Crop Residue Effects on Carbon Dioxide Evolution and Carbon Storage in a Paleustoll
Authors: Dao Thanh H.
Published: July 2010

Cultivation, high temperatures, and a semiarid climate accelerate organic carbon (OC) loss and weaken soil structure in the Southern Plains. Our hypothesis was that differences in soil C storage attributable to tillage method are related to differences in soil respiration and microbial biomass dynamics. Carbon dioxide fluxes following wheat (Triticum aestivum L.) harvest were determined in Bethany silt loam (fine, mixed, thermic Pachic Paleustoll). Treatments were moldboard plowing (MP) and no‐till (NT) at two residue rates (0 and 4 Mg ha−1). Soil respiration was measured from 1 August to 30 September using closed chambers. Peak CO2‐C flux densities reached 1.3 g m−1 d−1 in NT for 2 d and stabilized at 0.4 g m−1d−1. The CO2‐C evolution peaked at 4.1 and 2.9 g m−1d−1 in MP with and without buried residues, respectively. After 3 d, they decreased to a steady state of 0.4 g m−1d−1. Daily average temperatures in the 0‐ to 0.2‐m depth were 0.5 to 3.4°C higher under MP than NT, increasing microbial adenosine triphosphate (ATP), biomass C, and CO2‐C fluxes. The proportion of soil OC respired in the 60‐d period was twice as great under MP than NT, accounting for 0.42 to 0.58% and 0.19 to 0.22%, respectively. After 11 yr, NT soil OC showed increases of 65, 17, and 7% over the MP for the 0‐ to 0.05‐m, 0.05‐ to 0.1‐m, and 0.1‐ to 0.2‐m depths, respectively. Tillage and residue incorporation enhanced C mineralization and atmospheric fluxes, suggesting that tillage intensity should be decreased to reduce C loss.
Controlled Environment Potentionstat to Study Solid‐Aqueous Systems
Authors: Peterie Robert A. , Sims Ronald C. , Grossl Paul R.
Published: July 2010

We designed a redox apparatus that controls electropotenial (Eh), pH, and temperature. The apparatus is fully automated and can be assembled from equipment found in most soil analytical laboratories. The reactor can maintain environmental conditions used to evaluate the chemical fate of contaminants under natural conditions (natural attenuation) or adjust them to a new steady state to evaluate the effect of engineered remediation on a subsurface system. It can operate within a wide range of redox potential values (−400 to 400 mV) and at any pH value. The stability and accuracy of the instrument was tested by performing Eh‐pH titrations on MnO2 suspensions. Results indicated that Eh could be controlled within 1 to 2 mV, pH within 0.05 to 0.1 unit, and temperature within 0.1°C for weeks or months.
Diffusion Methods for Automated Nitrogen‐15 Analysis using Acidified Disks
Authors: Khan S. A. , Mulvaney R. L. , Brooks P. D.
Published: July 2010

Diffusion methods are often employed to speciate inorganic N in soil extracts or water for N‐isotope analysis with automated mass spectrometers. Diffusion is usually carried out in a plastic specimen container with an acidified filter disk to collect the diffused NH3. Owing to the small size of the container and the limited surface area of the acidified disk, a diffusion period of 6 to 14 d is generally required, and even then recovery may be incomplete. Simple diffusion methods were developed that use two acidified disks in a 473‐mL (1‐pint) wide‐mouth Mason jar. Diffusions with MgO to recover NH4‐N, or with MgO plus Devarda's alloy to recover (NH4 + NO3)‐N or (NH4 + NO3 + NO2)‐N, were performed from 5 to 100 mL of either 2 or 4 M KCl. Quantitative recovery of 150 µg of N was achieved in 1 to 7 d at 20 to 25°C, and in 2 to 14 h by heating on a hot plate at 45 to 50°C. Isotopic analyses of labeled soil extracts were accurate to within 5%, as determined by isotope‐dilution calculations. Incomplete diffusion led to <2% error in analysis of NH4‐N, whereas serious error occurred in analysis of (NH4 + 15NO3)‐N.
Soil Organic Matter Dynamics after Addition of Nitrogen‐15‐Labeled Leucaena and Dactyladenia Residues
Authors: Vanlauwe B. , Sanginga N. , Merckx R.
Published: July 2010

Quantification of the movement of residue N through various biologically meaningful soil organic matter (SOM) fractions is essential in low‐input tropical cropping systems for the development of management practices aimed at optimizing N‐use efficiency. The flow of N derived from 15N‐labeled leucaena [Leucaena leucocephala (Lam.) de Wit] and dactyladenia [Dactyladenia barteri (Hook f ex Oliv.) Engl.] leaf residues was followed through the SOM of different particle‐size fractions during 858 d. A bioassay study with maize (Zea mays L.) was carried out to assess the availability of residue‐derived N (RDN) incorporated in the particle‐size fractions. At 53 d after residue application (DAA), most of the RDN was found in the fraction between 0.250 and 2 mm (O250) in the leucaena treatment and in the fraction >2 mm and the surface litter (O2000 + SL) in the dactyladenia treatment. The RDN content of all fractions <0.250 mm was significantly higher in the leucaena than in the dactyladenia treatment up to 471 DAA. The proportion of the total amount of RDN recovered in the fractions <2 mm shifted toward the smaller particle‐size classes near the end of the experiment. Highly significant (P < 0.001) relationships between RDN present in the particulate organic matter (POM) and uptake of RDN by maize indicated the relatively high availability of RDN in the POM. Fractionating the SOM pool into different particle‐size classes yielded useful information on the relative contributions of the different SOM fractions to N turnover and availability. This information is needed in identifying SOM pools with direct relevance to plant nutrition in low‐input cropping systems.
Improving the Berthelot Reaction for Determining Ammonium in Soil Extracts and Water
Authors: Rhine E. D. , Mulvaney R. L. , Pratt E. J. , Sims G. K.
Published: July 2010

Colorimetric methods based on the Berthelot reaction are used widely for quantitative determination of NH4‐N in biological and environmental samples. Studies to evaluate phenol and salicylate, the most commonly used chromogenic substrates, revealed minor interferences by metallic cations, whereas up to a threefold shift in absorbance was observed with 38 diverse N‐containing organic compounds. Interferences differed markedly between phenol and salicylate. The possibility of a simple correction was precluded by the fact that interferences were both positive and negative, and depended on the temperature during color development and the concentration of NH4‐N. Fourteen compounds were evaluated as alternatives to phenol and salicylate, of which the Na salt of 2‐phenylphenol (PPS) proved to be the most promising. Using PPS, macro‐ and microscale batch methods and an automated flow‐injection method were developed. These methods are simple, convenient, and sensitive. Using the PPS microscale method, for which the limit of detection is 0.17 mg NH4‐N L−1, recovery of NH4‐N added to soil extracts ranged from 98 to 104%, with a coefficient of variation of 1.4 to 2.7%. As with phenol and salicylate, precipitation of metal hydroxides was observed. Precipitation was controlled by chelation with citrate rather than ethylenediaminetetraacetic acid (EDTA), which suppressed color development by preventing monochloramine formation. Compared with Berthelot methods that use phenol or salicylate, interference by amino acids was decreased by up to 10‐fold. Interference by other organic N compounds was virtually eliminated.
Design of Porous Media for Optimal Gas and Liquid Fluxes to Plant Roots
Authors: Jones Scott B. , Or Dani
Published: July 2010

The selection of plant growth media remains an empirical endeavor often focusing on available materials rather than on the physical principles that govern water retention and flow. Apparent water‐ and O2‐induced stresses affecting plant growth experiments in microgravity (10−3–10−6 g0) have prompted the need for refinement of selection criteria for optimal growth media. The objective of this work was to develop a comprehensive approach for selecting the physical characteristics of plant growth media that optimize the dynamic availability of liquids and gases to plant roots. Physically based models describing the relationship between content and fluxes of liquids and gases were written in terms of media parameters and were used to cast a multi‐objective optimization problem. Plant physiological target values, growth container design, and other system considerations provided constraints for the optimization problem. The optimized media parameters designated a pore‐size distribution (psd) that is scaled to a corresponding particle‐size distribution (PSD) by inversion of the Arya and Paris model. The iterative process resulted in an average scaling of psd to PSD and led to the synthesis of an optimal medium. Sand and glass bead mixtures were well matched to the optimized media characteristics resulting from the optimization procedure. This methodology is amenable to horticultural, greenhouse, and research applications where optimal porous media design is of value.
Inexpensive Automated Paging System for Use at Remote Research Sites
Authors: Sargent S. L. , Dey W. S. , Keefer D. A.
Published: July 2010

The use of a flow‐activated automatic sampler at a remote research site required personnel to periodically visit the site to collect samples and reset the automatic sampler. To reduce site visits, a cellular telephone was modified for activation by a datalogger. The purpose of this study was to demonstrate the use and benefit of the modified telephone. Both the power switch and the speed‐dial button on the telephone were bypassed and wired to a relay driver. The datalogger was programmed to compare values of a monitored environmental parameter with a target value. When the target value was reached or exceeded, the datalogger pulsed a relay driver, activating power to the telephone. A separate relay activated the speed dial, dialing the number of a tone‐only pager. The use of this system has saved time and reduced travel costs by reducing the number of trips to the site, without the loss of any data.
Nitrous Oxide Emission From Long‐Term Manured Soils
Authors: Chang C. , Janzen H. H. , Cho C. M.
Published: July 2010

Land‐applied manure is a significant source of N2O, but current estimates of emission are based on laboratory studies or field measurements from short‐term application studies. Manure is often repeatedly applied to the same field for long periods, however. Our objectives were to determine annual N2O emission from a Typic Haploboroll soil that received 21 annual applications of solid feedlot manure at rates of 0, 60, 120, and 180 Mg ha−1 (wet weight), and to relate the emission rates to environmental conditions. Nitrous oxide fluxes from soil were measured weekly from 10 Nov. 1993 until 27 Oct. 1994. Annual N2O emission increased with manuring rate and reached 56 kg N ha−1 yr−1 at the highest manuring rate (<1 kg N ha−1 in the control). The N2O emission rate was not related to any single environmental factor, apparently because the N2O emission rate is not only controlled by rates of N2O production, but also by its rate of diffusion. The N2O emission rates were highest in early spring, but fluxes of N2O were also significant in winter, perhaps associated with freeze‐thaw events. The N2O emission rates observed in our study are similar to N‐fertilizer or combining N‐fertilizer and manure application, but they are higher than other short‐term studies with similar manure. These results probably reflect the accumulation of NO3 and organic matter from repeated manuring and suggest that the N2O emission from long‐term manured soils may be underestimated by quantifying fluxes from short‐term manuring studies.
A Volumetric Inorganic Carbon Analysis System
Authors: Wagner S. W. , Hanson J. D. , Olness Alan , Voorhees W. B.
Published: July 2010

Measurement of soil organic carbon (OC) is slow and expensive when inorganic carbon (IC) is present. Our objective was to develop an automated volumetric IC analysis system, thus allowing OC to be determined by difference. The system was developed by combining a pressure transducer with a personal computer (PC), data acquisition board, and appropriately developed software. The volumetric system was compared with combustion, neutralization, and sum of Ca + Mg techniques for samples containing up to 60 g kg−1 IC. Correlations between methods showed linear agreement (r2 ≥ 0.994). The volumetric system was more precise for relatively low IC amounts (2.0 g kg−1) and could process 20 samples h−1.
Subalpine Loamy Spodosols in Taiwan: Characteristics, Micromorphology, and Genesis
Authors: Li Shin‐Yi , Chen Zueng‐Sang , Liu Jen‐Chyi
Published: July 2010

Four subalpine loamy Spodosols with illuvial clay in the spodic horizons were selected for study to understand their characteristics, micromorphology, and genesis. These Spodosols, located in central Taiwan, are covered by coniferous vegetation, receive high levels of precipitation, and occupy gentle slope positions at elevations >2400 m. Soil textures, which range from loam to clay, are finer than those of Spodosols formed in temperate regions. The pedogenic products in the soils of the study area are mainly organo‐metallic complexes or illuvial clay mixed with organo‐metallic complexes in the spodic horizons. Typical micromorphological features in the spodic horizons of these Spodosols revealed infillings of organo‐Fe complexes, argillans, or argiferrans along the irregular voids. The four selected pedons have loose spodic horizons where illuvial clay also has accumulated. The large amounts of spodic materials and illuvial clays in the spodic horizons indicate that podzolization and clay accumulation were the two dominant pedogenic processes. Some of the illuvial clay translocated into the spodic horizons is mixed with organo‐Fe (or ‐Al) complexes along the irregular voids of the spodic horizons. This may also have resulted in a lack of well‐oriented clay in these horizons despite the occurrence of large amounts of illuviated clays.
Measuring Nutrient Depletion by Roots of Mature Trees in the Field
Authors: Escamilla J. A. , Comerford N. B.
Published: July 2010

The kinetics of ion uptake by roots is of fundamental importance to the study of the mineral nutrition of plants and the definition of an “effective” root system. Our understanding of ion uptake by roots comes from studies of transport phenomena using new, white roots of young plants. Much less is known about nutrient absorption by older roots of perennial plants, where these root may encompass >90% of the fine root system. However, studies of nutrient uptake in situ are complicated because of plant size, age, and access to the root system. This is also true when considering roots of mature trees. The objectives of this study were to: (i) present the design and construction of a system suitable for measuring nutrient uptake by lateral root systems of mature trees in the field, and (ii) test the system under laboratory and field conditions. We developed a system for root regeneration that allows easy access to roots while minimizing disturbance. The design includes: (i) a system for gas supply; (ii) a root chamber; and (iii) a Mariotte flask system. The system was tested under laboratory and field conditions. Laboratory results showed that all components of the nutrient uptake system were inert to P and K. Under field conditions when the chambers were aerated, P and K were absorbed from the nutrient solutions. In comparison, when roots were gassed with N2 (hypoxic conditions), P was still absorbed but K absorption was inhibited.
Recent and Long‐Term Organic Soil Accretion and Nutrient Accumulation in the Everglades
Authors: Craft C. B. , Richardson C. J.
Published: July 2010

Organic soil accretion and nutrient accumulation were measured in the northern, central, and southern Everglades to evaluate the effects of anthropogenic nutrient and hydroperiod alterations on organic C and nutrient storage during the past century. Six soil cores (euic, hyperthermic Typic Medisaprists) were collected from nutrient‐enriched (Water Conservation Area [WCA] 2A) and unenriched locations. Soil depth increments were analyzed for radionuclides (137Cs, 210Pb, 14C), bulk density, and nutrients (C, N, P, S) to estimate recent (30‐yr) and long‐term (100‐yr) organic soil accretion and nutrient accumulation. Since WCA 2A was completely impounded in the early 1960s, organic soil accretion in northern WCA 2A (5.8–6.7 mm yr−1) increased by three to five times compared with before 1960 (1.9 mm yr−1) or with unenriched areas within and outside of WCA 2A (1.4–1.6 mm yr−1). Nutrient accumulation in the enriched area of WCA 2A since 1960 was two (184–223 g C m−2 yr−1, 13.6–16.6 g N m−2 yr−1) to eight (0.40–0.46 g P m−2 yr−1) times higher than before 1960 (110 g C m−2 yr−1, 6.6 g N m−2 yr−1, 0.06 g P m−2 yr−1) or in unenriched areas (65–90 g C m−2 yr−1, 4.7–6.4 g N m−2 yr−1, 0.06 g P m−2 yr−1). Unenriched areas of the Everglades possess some of the lowest rates of P accumulation of peatlands in North America. Successful restoration of the Everglades will have to include the elimination of anthropogenic nutrient loadings to limit the P enrichment zone from expanding into existing unenriched interior areas and areas downstream of WCA 2A.
Dichromate Digestion and Simultaneous Colorimetry of Microbial Carbon and Nitrogen
Authors: Doyle Allen , Schimel Joshua P.
Published: July 2010

Dichromate digestion is used frequently for analysis of organic C and is followed by manual titration. We sought to automate C detection and to include N in the analysis. We optimized digestion parameters (duration, temperature, acids, and catalysts), compared detection methods [manual and automated titration, colorimetric absorbance of Cr(III) and Cr(VI) and automated colorimetry of Cr(VI)], adapted salicylate‐indophenol colorimetry for N detection, and compared N digestion efficiency with Kjeldahl digestion. Optimal digestion conditions were 144°C internal temperature for 3 h with 2:1 H2SO4/H3PO4 and Ag2SO4. Automated and manual titrations were reliable but the titrant (ferrous ammonium sulfate) precluded N detection. Colorimetric detection of Cr(VI) with s‐diphenylcarbazide was fast and precise, but high blanks and steady decomposition of Cr(VI) necessitated several internal standards. Colorimetric analysis of N was possible after precipitating Ag and it was stable, precise, and accurate. Digestion recovery of yeast extract and soil extract N from birch (Betula papyrifera Marsh.), alder (Alnus tenuifolia Nutt.), and poplar (Populus balsamifera L.) stands was low compared with Kjeldahl N (82, 79, 88, and 78%), but precision of the two digestions was the same. The detection limits were 25 µg C and 2 µg N per digestion (125 mg C and 10 mg N kg‐1 dry soil). While this method is not suitable for work demanding high accuracy, automated C detection combined with N detection provides data acceptable for studies comparing field or laboratory soil treatments.
Modified Iron‐Oxide‐Impregnated Paper Strip Test for Soils Treated with Phosphate Fertilizers
Authors: Habib L. , Chien S. H. , Menon R. G. , Carmona G.
Published: July 2010

The Fe‐oxide‐impregnated paper strip (Pi) test with 0.01 M CaCl2 has been proposed as an improved soil test for evaluating available P from soils treated with phosphate rock (PR) and triple superphosphate (TSP). However, conclusive evidence for this suggestion has not been reported. This study was conducted to evaluate the suitability of the Pi test for both PR and TSP. In a greenhouse study, two acid soils — Hartsells silt loam (fine‐loamy, siliceous, thermic Typic Hapludult) and Hiwassee clay loam (fine, kaolinitic, thermic Rhodic Kanhapludult) — were mixed with ground (0.15‐mm, 100‐mesh) North Carolina (NC) PR or commercial‐grade granular TSP at 0 to 300 mg P kg‐1 soil. The soil samples were preincubated for 2 wk before maize (Zea mays L.) was planted and grown for 5 wk. Prior to planting, soil samples were analyzed by three soil tests: Bray I, Pi test with 0.01 M CaCl2, and Pi test with 0.02 M KCl. The results showed that NC‐PR and TSP were equally effective in increasing dry‐matter yield and P uptake by maize in Hartsells soil. North Carolina phsophate rock was approximately 83 and 91% as effective as TSP in increasing drymatter yield and P uptake, respectively, in Hiwassee soil. When P uptake was plotted against soil test values, both the Bray I and Pi test with CaCl2 underestimated available P from NC‐PR for TSP‐treated soil. Available soil P estimated by the Pi test using KCl instead of CaCl2 was more closely related to P uptake with both NC‐PR and TSP. More P was extracted from NC‐PR by the Pi test with KCl than with CaCl2, whereas no effect was observed for TSP.
Solute Transport in Seasonal Perched Water Tables in Loess‐Derived Soilscapes
Authors: Reuter R. J. , McDaniel P. A. , Hammel J. E. , Falen A. L.
Published: July 2010

Hydraulically restrictive fragipans and argillic horizons are a common feature of loessial soils in the Palouse region of northern Idaho, resulting in perched water development during the winter and early spring. The high relief of the region may result in lateral flow of perched water and solutes. This study was initiated to quantify the rates of solute movement through perched water at three sites receiving 610, 700, and 830 mm of annual precipitation. Three transects, perpendicular to slope contours, consisting of seven, nine, and seven sampling wells, were installed at each site. Five kilograms of KBr tracer were applied in a trench upslope from the transects. Water samples were drawn biweekly to test for Br‐. Rate of Br‐ movement and saturated hydraulic conductivity (Ksat) of soil horizons were used to quantify flow of perched water. Results indicate that maximum observed Br‐ transport decreased with annual precipitation and was 86, 50, and 35 cm d‐1 at the 830, 700, and 610‐mm sites, respectively. Depth profiles for Ksat are similar among sites; values range from 63 to 129 cm d‐1 in the Ap horizons and decrease with depth to 0.10 to 0.21 cm d‐1 in the restrictive horizons. The E horizons immediately above the argillic‐fragipan horizons have Ksat values from 1.2 to 5.2 cm d‐1 suggesting that much of the rapid solute transport via perched water tables occurs in the more permeable horizons overlying the E horizons. Our results demonstrate that perched water flow through these landscapes may enhance agrichemical transport, thereby impacting both nutrient‐use efficiency and local water quality.