Nitrogen transformations in a flooded soil in the presence and absence of rice plants: 2. Denitrification

Denitrification rates (d) in a flooded alkaline clay were measured following addition of either to the floodwater, by collecting evolved N₂ + N₂O in an enclosure in the absence or presence of rice plants. Similar estimates of d were obtained in the treatment when the isotopic composition of the enclosed atmosphere was determined using arc redistribution or direct mass spectrometric analysis. Approximately 90% of the gaseous products of denitrification were physically trapped in the soil five days after addition. Mechanical shaking of the soil-water system was an effective method for releasing entrapped gas. Denitrification showed a marked diurnal variation in both and treatments planted to rice, with higher rates during the day than at night. Measured rates of denitrification were higher in planted than in unplanted pots for both and treatments for normal gas sampling. However, evidence was obtained that this was not a real effect, but was due to release of entrapped gas. Denitrification losses corrected for gas entrapment were estimated at <5% of applied . The ¹⁵N mass balance indicated that a much larger amount of applied ammonium (15–25%) was lost by NH₃ volatilisation. The rate of denitrification corrected for gas entrapment was similar to the rate of nitrification estimated by inhibition of ammonium oxidation. Although the inhibitors 2-ethynylpyridine and acetylene prevented denitrification by effectively inhibiting nitrification of , the total recovery of ¹⁵N in the soil-plant system did not increase. The total recovery of was 7–9% higher in the presence than in the absence of rice.     

Polymer Complexes. XLIII. EPR, Spectra, and Stereochemical Versatility of Novel Copper(II)Polymer Complexes

Copper(II) polymer complexes of empirical formula [Cu(ligand)₂X₂] (where X = Cl, Br, I, NO₃, and SO₄) and [Cu(ligand)(CH₃COO)₂] have been prepared with poly(3-phenylacrylidine semicarbazone). All the polymer complexes prepared have been characterized by elemental analysis, magnetic moment, conductance, IR, electronic, ¹H-NMR, and electronic paramagnetic resonance spectral studies. The polymer complexes [Cu(ligand)₂X₂] and [Cu(ligand) (CH₃COO)₂] may have tetragonal symmetry while the [Cu(ligand)₂( SO₄)₂] may be five-coordinate trigonal bipyramidal in structure. All complexes exhibit normal magnetic moments corresponding to one unpaired electron except [Cu(ligand)(CH₃COO)₂] which shows a subnormal magnetic moment. EPR spectra of the polymer complexes have been studied with a view to assigning their stereochemistries. Various EPR parameters have been calculated. The g, A, G values for all the polymer complexes are consistent with a tetragonal 1–5 and trigonal bipyramidal 6 stereochemistry in the Cu(II) polymer complexes of homopolymer.     

Humic fertilizers by oxiammoniation of hydrolyzed olive pits residues

Hydrolyzed olive pit residues from the production of furfural were ammoniated to obtain a nitrogenenriched humic fertilizer. Samples had been previously oxidized with nitric acid. The oxidized samples were further ammoniated in a batch reactor in the following range of experimental conditions: T = 80–210°C, , solid/liquid ratio, S/L = 0.5–2.8 w/w and reaction time, t = 1–4 h.Planning of experiments was made by statistical design and results were fitted by multiple non-lineal regression polynomials. The product consists of two fractions: a water soluble fraction which contains most of the nitrogen (10–13 wt%) and a solid fraction with a very low nitrogen content (<4.0 wt%), which is likely to be fixed during the oxidation step. The soluble fraction can be used as a humic fertilizer and the solid product as a soil conditioner.     

Mass transfer at the electrodes of the ‘falling-film cell’

In the falling-film cell the electrolyte flows as a thin film in the channel between an inclined plane plate and a sheet of expanded metal which work as electrodes. The present work gives the mass transfer coefficients at both electrodes; the experimental variables are the electrolyte flow-rate, the angle of inclination of the channel and the interelectrode distance. The results allow three different flow regimes to be characterized. At low flow rates, there exists a particular regime where capillary effects are present; in this regime the mass transfer coefficient decreases with increasing flow rate, which is interesting from the point of view of possible industrial electrolytic applications.Nomenclature b width of the inclined channel - D diffusion coefficient - d interelectrode distance - e _m mean film thickness - Grashof number, based ond - Grashof number, based onL - ¯k overall mass transfer coefficient, defined by Equation 9 - L electrode length - Q _v volumetric flow rate - volumetric flow rate per unitQ _vl width of channel - Reynolds number - Schmidt number - Sherwood number, based ond - Sherwood number, based onL - mean velocity of the liquid film - inclination angle of the channel with respect to the horizontal - kinematic viscosity of them electrolyte     

Structure of Atomic and Molecular Adsorbates on Low-Miller-Index ZnO Surfaces Using X-ray Absorption Spectroscopy

We review our X-ray absorption spectroscopy studies of adsorbate geometries on the O-terminated (000 ) and Zn-terminated (0001) basel faces, as well as the non-polar (10 0) prism face of ZnO. Studies employing near-edge X-ray absorption fine-structure (NEXAFS) and surface X-ray absorption fine-structure (SEXAFS) are included.     

New Poly(Methacrylate)s Containing Benzylpiperazine and Methylpiperidine Moieties

The synthess of two new methacrylate esters containing 2-(4-benzyl piperazin-1-yl)-2-oksoethyl and 2-(4-methylpiperidin-1-yl)-2-oksoethyl group are described. The monomers produced from the reaction of corresponding 4-methylpiperidinechloroacetamide and 1-benzylpiperazinechloroacetamide with sodium methacrylate were polymerized in DMSO solution at 65°C using AIBN as an initiator. The monomers and their polymers were characterized by IR, ¹H- and ¹³C-NMR spectroscopy. The glass transition temperature of the polymers were investigated by DSC and the apparent thermal decomposition activation energies (E _d ) were calculated by Ozawa method using the SETARAM Labsys TGA thermobalance. By using gel permeation chromatography, weight average ( ) and number average ( ) molecular weights and polidispersity, indices of the polymers were determined.     

Spin Labels as the Instrument for Analysis of Topochemistry of Polymer-Immobilized Ziegler Catalytic Systems

A spin labeling technique was used to investigate the topochemical characteristics of polymer carriers and immobilized metal complexes. Functionalized polyethylenes (PE) such as PE–grafted-polyallylamine (1), PE–grafted-polydiallyl-amine (2), and PE–grafted-poly-4-vinylpyridine (3), obtained by grafting polymerization of the corresponding monomers, were used as polymer carriers. Metal-containing polymers were obtained by immobilization to 2 with either TiCl₄ (2/Ti) or Al(C₂H₅)₂ Cl (2/Al). The stable nitroxyl radical 2,2,6,6-tetramethyl-4-(2-oxy-4,6-dichlorotriazine)piperidine-1-oxyl was used for spin labeling 2 to give , while 2,2,5,5,tetramethyl-3-(N-acetoamidiiodine)-pyrrollidine-1-oxyl was used for spin labeling 3 to give . Radical 2,2,6,6-tetramethyl-4-hydroxy-pyperidine-1-oxyl was bonded to 2/Ti and 2/Al to give and , respectively. The accessibility of the functionalized polymers 1–3 to interact with the spin labels and the immobilized metal complexes was examined. Estimation of the effective distances between the spin labels and the dynamic behavior of nitroxyl radicals in the functionalized polymer matrixes and metal-containing polymers revealed several important features of spin-labeled systems. Metallation of a functional covering makes the polymer more accessible for spin labeling and has a considerable effect on the dynamic characteristics of polymer matrix. A change of the rotational activation energy of the spin labels from 15 kcal/mol in to 44 kcal/mol for in the temperature range 100–150°C was observed.     

The IR spectroscopy of methane and hydrogen adsorbed on α-chromia

The vibrational perturbations induced in the IR spectra of methane and of dihydrogen by the non-dissociative adsorption on the (01 2) and (11 0) faces of -chromia are illustrated and compared. It is concluded that both molecules are adsorbed on Cr³⁺ sites and that the involved forces are mainly of the electrostatic type. The resulting situation is compared with that found on the more basic MgO. The problems associated with the C–H and H–H bond activations on transition metal oxides are also discussed.     

Effect of turnover rate on the change of concentration of an unstable compound in a dip coating bath

The effect of turnover rate on the change of concentration of unstable (degradable) compounds in a dip coating bath during a continuous coating process was theoretically calculated as a function of the degradation rate of the compound. It is assumed that the bath is replenished by the same coating material as that in the original bath to maintain the volume of the material in the bath constant. The results show that the fraction of the unstable compound in the bath at the end of the nth day is given by where t is the number of days for one turnover and where P is the fraction of the compound remaining undegraded in the bath per day. The equilibrium fraction of the compound after infinite coating days is given by The concentration of the compound in the replenishing material (C_r) to maintain the original concentration in the bath (C_o) constant is given by.     

[CuL(H2O)2]{[CuL][Fe(CN)6]}2·2H2O (L=3,10-Bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane): A Novel Three-Dimensional Coordination Polymer via H-Bonded Linkages of One-Dimensional Zigzag Chain

A complex with the formula [CuL(H₂O)₂]{[CuL][Fe(CN)₆]}₂·2H₂O, where L=3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane, has been synthesized and crystallographically characterized. The structure is composed of a one-dimensional zigzag chain of units, and [CuL(H₂O)₂]²⁺ units. The one-dimensional zigzag chain extents through linkages. The adjacent two polymer chains are linked by the hydrogen bonding between [CuL(H₂O)₂]²⁺ and [Fe(CN)₆]^3–, forming a 3D supramolecular structure with inner hydrophilic channels. Magnetic susceptibility measurements show no exchange interaction between the Cu(II) and Fe(III) ions due to the longer (axial) bond length.     

Synthesis and characterization of polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide)

Summary Free radical copolymerization of acrylonitrile (AN, M₁) with poly(2,6-dimethyl-1,4-phenylene oxide)--vinylbenzyl ether (PPO-VBE, M₂, _n + 4200g/mol, _w/ _n + 1.04) was performed at 60°C in either a mixture of N,N-dimethylformamide/toluene or tetrahydrofuran, using 2,2-azoisobutyronitrile (AIBN) as initiator. The characterization of the resulting polyacrylonitrile grafted with poly(2,6-dimethyl-1,4-phenylene oxide) (PAN-g-PPO) was performed by 200 MHz ¹H-NMR spectroscopy and solubility.     

Macro and micro-nutrient effects on the yield and nutrient concentration of maize (Zea mays L.) in South Western Nigeria

Despite various fertilizer recommendations, maize (Zea mays L.) yields in tropical forest and savanna zones are very low. These low yields could be attributed in part to the exclusion of some secondary and all micro nutrients in fertilizer recommendations for maize, a condition which often leads to nutrient imbalance. The inclusion of some secondary and micro nutrients in fertilizer recommendation for successful maize cultivation in this zone has been suggested [2, 16] but no one has proposed a balanced nutrient program for this purpose. Field trials were therefore conducted to investigate the potential for improving maize yields by fertilizing soils of different parent materials with both macro and micro nutrients in three ecological zones of maize production in south western Nigeria.The study has indicated that in addition to NPK, Mg was necessary for high yield of maize on forest soils derived from sedimentary materials while on forest and savanna soils formed from basement complex rocks, inclusion of Mg, Fe, Cu and Zn to NPK was required. This was further confirmed with ear leaf tissue and soil analyses. High nutrient concentration in earleaf does not necessarily guarantee high yield of maize. It is therefore concluded that there is a need for soil testing program in this region.     

Kinetics of electroless copper deposition using cobalt(II)-ethylenediamine complex compounds as reducing agents

Electroless copper deposition using Co(II)-ethylenediamine (En) complexes as reducing agents was investigated in 0.4–1.2 M En solutions at 50 and 70 °C. There is a complicated dependence of the process rate on pH, En concentration and temperature. A copper deposition rate up to 6 m h^–1 (50–70 °C) in relatively stable solutions (pH 6) can be achieved. The stoichiometry of the Cu(II) reduction at pH 6–7 corresponds to the reaction:

The distribution of phosphorus fractions and desorption characteristics of some soils in the moist savanna zone of West Africa

The fractionation of soil P into various organic and inorganic pools with differing levels of bioavailability, coupled with knowledge of the P adsorption and desorption characteristics of the soils, provides insights into management strategies that enhance P availability to crops. Sequential soil P fractionation was conducted on samples from 11 soil profiles and different experimental fields selected from the derived savanna (DS) and northern Guinea savanna (NGS) zones of the West African moist savanna to assess the influence of soil characteristics and management on soil P pools. Phosphorus adsorption and desorption studies were conducted on samples from the surface horizon of the soil profiles. The total P content varied within and among the soil profiles and tended generally to decrease as depth increased. The total P content in topsoil varied from 90 to 198 mg kg^–1 of which about 30% was organically bound P. The resin P fraction was generally low (mean = 5 mg kg^–1, topsoil) and decreased with depth. These low resin P levels indicate low P availability. Within the DS, where the organic resource (OM) was Senna siamea residues, the effects on soil P fractions of OM and soluble P fertilizer (PF), whether sole or in combination, were site-specific. While resin P was significantly increased by OM in some sites, no significant differences were observed in others. In the NGS fields, farmyard manure (organic resource, OM) combined with PF and PF applied alone increased the inorganic P (Pi) fractions extractable with resin, bicarbonate, and NaOH by about 400% but had no significant effect on the organic P (Po) pools and the more stable Pi forms. The P sorption capacities were low, with the adsorption maximum deduced from the Langmuir equation ranging from 36 to 230 mg kg^–1. The amount of P sorbed to maintain 0.2 mg l^–1 in solution ranged between 0.6 and 16 mg kg^–1. Phosphorus desorption with anion exchange resin differed among the soils, with the recovery of added P ranging from 17 to 66% after 96 h. On average, more of the applied P was recovered in the DS soils than in the NGS soils. Because of the relatively low sorption capacity and the relatively high percentage recovery, small additions of P to most of the soils studied might be adequate for crop growth. In essence, quantities of P fertilizer needed in these soils might be estimated based on considerations of P uptake by crops rather than on sorption characteristics.     

Effect of electrolysis factors on crystal orientation and morphology of electrodeposited cobalt

Cobalt electrodeposition was carried out using sulfate and chloride baths to investigate the effects of electrolysis factors on the crystal orientation and morphology of the deposits. The preferred orientation of Co deposited from the sulfate baths changed from (0 0 0 2) to (1 1 0) plane with an increase in the deposition overpotential and the deposits showed the largest grain size with a smooth surface in the low overpotential region. On the other hand, no dependence of crystal orientation and morphology on deposition overpotential was found in chloride baths.     

A spatially explicit methodology to quantify soil nutrient balances and their uncertainties at the national level

A soil nutrient balance is a commonly used indicator to assess changes in soil fertility. In this paper, an earlier developed methodology by Stoorvogel and Smaling to assess the soil nutrient balance is given a major overhaul, based on growing insights and advances in data availability and modelling. The soil nutrient balance is treated as the net balance of five inflows (mineral fertilizer, organic inputs, atmospheric deposition, nitrogen fixation and sedimentation) and five outflows (crop products, crop residues, leaching, gaseous losses and erosion). This study aims to improve the existing methodology by making it spatially explicit, improving various transfer functions, and by modelling explicitly the uncertainties in the estimations. Spatially explicit modelling has become possible through a novel methodology to create a simulated land use map on the basis of the principles of traditional qualitative land evaluation. New literature data on the various inputs and outputs allowed improvement of the estimations of deposition, sedimentation, leaching, and erosion. Moreover, the uncertainty of the calculated soil nutrient balances was assessed. To illustrate the improved methodology, we applied it to Burkina Faso and revealed that nutrient depletion is occurring throughout the country at rates of , and . The resulting spatial soil nutrient balances at the national level can constitute the basis for targeting soil fertility policies at lower levels.     

The influence of total monomer concentration on the “reactivity” of ω-(p-vinylbenzyl ether) macromonomers of poly(2,6-dimethyl-1,4-phenylene oxide) determined from radiacal copolymerization experiments with butyl methacrylate

Summary The influence of the total monomer concentration on the radical reactivity ratio r₁ of butyl methacrylate (BMA) (M₁)--(p-vinylbenzyl ether) macromonomer of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-VBE) (M₂) monomer pair was investigated. For two different molecular weights of the PPO-VBE macromonomer ( , and ), the determined reactivity ratio r₁ decreases with the increase of the macromonomer concentration. Therefore, the reactivity of the macromonomer, 1/r₁, follows the opposite trend. This dependence is due to micelles formation during copolymerization. This microsegregation process partitionates the comonomer concentrations between the bulk of solvent and around the growing chain and therefore, the experimental r₁ is actually a product of the true reactivity ratio r₁ ⁰ and a partition coefficient k.     

Hydrogen half-cells in molten salts. A potentiometric investigation of the systems (Pt or Au) H2O/H2, OH− in fused alkali nitrates

The potentiometric behaviour of the hydrogen electrodes (Pt or Au) H₂O-H₂, OH_–has been investigated in molten (Na_0·5, K_0·5)NO₃ at 503 K. In both cases the potential of the indifferent electrode could be expressed by the general equation [H₂O]/[H₂] [OH^–] which is different from the one expected on the basis of a Nernstian behaviour of the theoretical overall system 2H₂O+2e=H₂+2OH^–.The experimental findings are discussed in terms of mechanistic models involving the actual electrode surface and the standard potential for the theoretical (reversible) hydrogen electrode is calculated: =–·0V(versus Ag/Ag⁺ 0·07 M).     

Effects of fertilizer and weeding in no-tillage and tilled maize

Field trials were carried out on Apomu soil (Psammentic usthorthent) and Egbeda soil (Oxic paleustalf) in southern Nigeria to investigate the effects of fertilizer and weeding on growth and yield of maize (Zea mays L.) under no-tillage and tilled land preparations.On the newly cleared Apomu soil, broadleaved weeds comprised the major portion of the weed flora, with the shrubs being more important under no-tillage. More grasses and sedges were present when the soil was tilled. Regardless of tillage method, there was a 38% yield reduction due to weeds in the unfertilized plots, with yield in tilled plots being almost double that in no-tillage plots. Effect of weed competition in maize can be partially overcome by fertilization as yield reductions due to weeds were 19% in the fertilized plots. Weeding was shown to be necessary even with a first crop following bush clearing especially when the soil fertility was low.On both soil types maize yield responded to fertilizer application. Yield of no-tillage maize was less than that of tilled maize with no or low rates of N application, but with adequate N fertilization yield from no-tillage maize equalled that of tilled maize. Lower yield of no-tillage maize may in part be attributed to severe N stress during early growth. Consequently on low fertility soil, no-tillage maize production is not recommended without adequate N fertilization.     

Blackening in yttria stabilized zirconia due to cathodic processes at solid platinum electrodes

The DC cathodic voltage current density (V-J) characteristics at the contact between a solid disc Pt-13% Rh electrode and yttria stabilized zirconia (YZr) electrolyte were investigated to evaluate the conditions under which blackening occurred in the anionic conductor. Polycrystalline and single crystal samples have been studied using oxygen-argon mixtures between 10⁰ and 10^–3 atm oxygen and at temperatures in the range 800 to 1450°C. It is shown that the rate determining step of the overall cathodic reaction, O₂(g)+2Vö+4ear2O _o ^x under low field, ohmic conditions is the first electronation step, but true activation polarization at higher fields is masked by mass transfer limitations. The limiting current density in the polycrystalline material was directly proportional to the oxygen partial pressure whereas at low temperatures, below 1000°C, in the single crystal.The former behaviour is attributed to a flux limit in the ambient oxygen gas, whereas the regime is believed to be a consequence of molecular dissociation, coupled with surface exchange, onto the mobile interfacial layer. It is further shown that blackening is a consequence of thermionic emission of electrons across the cathodic interface into anion vacancy traps and the cathodicV-J characteristics of the blackened material saturate to obey aJV ² law above about 2 V, indicative of a space charge limited current. A tentative model is proposed.