Phillip Barak

Effects of long-term soil acidification due to nitrogen fertilizer inputs in Wisconsin

Agroecosystems are domesticated ecosystems intermediate between natural ecosystems and fabricated ecosystems, and occupy nearly one-third of the land areas of the earth. Chemical perturbations as a result of human activity are particularly likely in agroecosystems because of the intensity of that activity, which include nutrient inputs intended to supplement native nutrient pools and to support greater biomass production and removal. At a long-term fertility trial in South-Central Wisconsin, USA, significant increases in exchangeable acidity were accompanied by decreases in cation exchange capacity (CEC), base saturation, and exchangeable Ca2+ and Mg2+ with application of ammoniacal N fertilizer. Plant analysis shows that a considerable portion of the alkalinity generated by assimilation of N (and to a lesser extent by S) is sequestered in the above-ground plant parts as organic anions and is not returned to the soil if harvested. Elemental analysis of Ca-saturated soil clays indicates an loss of 16% of the CEC of the soil clay and minor increases in Fe and Al. The reversibility of these changes due to prolonged acidification is doubtful if the changes are due to soil weathering.

Carbon, nitrogen and phosphorus mineralization of tree leaves and manure

Abstract Farmers in developing countries cannot afford inorganic fertilizers. Multipurpose tree leaves or livestock manure are major sources of nutrients for soil fertility replenishment. Nutrient release from these organic inputs depends on their chemical composition and on soil properties. This study determined the chemical composition of leaves of four African browse species and manure from goats fed leaves as protein supplements, and their mineralization of C, N and P. Cumulative evolved CO2 was significantly correlated with the initial N content of the organic inputs (r 0.83, P<0.05) and the C : N ratio (r 0.80, P<0.05), and was negatively correlated with the lignin : N ratio (r–0.71, P<0.05). Cumulative P released was negatively correlated with the C : P ratio (r 0.76, P<0.05) and positively correlated with initial P content of the organic amendments (r 0.76, P<0.05). Cumulative N mineralized was not significantly correlated with initial N, lignin or P concentrations of the organic inputs. Leaves from Acacia karro and Acacia nilotica had high concentrations of polyphenols, which may have caused immobilization of N in both leaves and manure. Gliricidia sepium leaves had low amounts of soluble polyphenols, a high N content and a high rate of N mineralization, but the manure from goats fed Gliricidia leaves immobilized N. The leaves of all browse species immobilized P, but the manure released P. The results suggested that some browse leaves cannot meet the N and P requirements of crops due to their low P content and prolonged N and P immobilization. However, the manures had higher P contents and rates of P mineralization, which suggested that manure is a good source of P for crops. The implications of these results for nutrient cycling in mixed farming systems is discussed.

Assimilation of nitrogen by soil microbial population: NH4 versus organic N

Abstract Nitrogen assimilation by microbial, biomass during the decay of organic material in soil may follow two patterns: (1) direct assimilation of low molecular weight organic N compounds (Direct hypothesis) or (2) immobilization of mineral N, while organic N is completely mineralized (MIT hypothesis). To test these hypotheses equal concentrations of NH 4 -N and alanine-N were added to soils, either one or the other labeled with 15 N, and incubated for 1.2 days. The K 2 SO 4 -extractable organic and mineral N and 15 N and CO 2 release were measured periodically. Experimental results were compared with data computed by two versions of the model NCSOIL, that simulates the C-N turnover and 15 N distribution among soil pools, and is structured to represent either the Direct or the MIT hypothesis. The fitted first order rate constant of mineralization of alanine was 3.2 d −1 , following a delay of 0.25 d. Evolution of CO 2 proceeded at a considerable rate after alanine was decomposed and net N mineralization had ceased, indicating a rapid decomposition of the microbial population that consumed alanine. The isotopic dilution of mineral N proceeded very rapidly and fitted the simulation by MIT better than by the Direct model. The rate of 15 N withdrawal from total extractable N was greater when alanine was labeled and fitted the prediction by the Direct model, but when NH 4 was the source of 15 N, the Direct model failed to predict 15 N consumption. It seemed that both pathways operated concurrently, with the Direct dominating N assimilation by the substrate specific population and the MIT operating at the level of the native soil population.

The Chemistry of Zinc

Zinc is a metallic element with atomic number 30 and stable isotopes of mass 66, 67, 68, and 70, averaging 65.38 a.m.u. The terrestrial chemistry of Zn is that of Zn (II) rather than Zn(0). The Zn (II) ion has an electron configuration of 1s 2, 2s 2, 2p 6, 3d 10, and therefore lacks unfilled d subshells in the well-known oxidation state, the requisite criterion for true transition metals. Zinc(II) has an ionic radius comparable with Mg(II) but a Lewis acidity more like that of the smaller Cu(II) ion.

Isocratic ion-pair high-performance liquid chromatographic method for the determination of various iron(III) chelates

Abstract The micronutrient iron, an essential element for plant growth, is usually added as fertilizer in chelated form. An isocratic ion-pair chromatographic method was developed to identify and determine the total amount of chelate in fertilizers. Iron(III) chelates containing ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA), also known as N,N′-ethylenebis-2-(o-hydroxyphenyl)glycine, ethylenediaminedi(o-hydroxy-p-methylphenylacetic) acid, N,N′-bis-(2-hydroxybenzyl)ethylenediamine-N,N′-dipropionic acid and N,N-bis(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid were well separated by this method. The mobile phase contained 0.03 M tetrabutylammonium chloride and 30% acetonitrile at pH 6.0. The stationary phase was a LiChrospher RP-18 column, the injection volume was 20 μl and the flow-rate was 1.5 ml/min. For the iron(III)-EDDHA chelate, linear range studies showed that the method is capable of determining Fe concentrations between 0.5 and 150 μg/ml, which permits the determination of the concentrations found in commercial fertilizers. With this method, separation and identification of the iron(III) complexes were obtained with good resolution and selectivity, including the separation of the geometric isomers of the complexes, in 15 min.

EQUIVALENT RADII OF HUMIC MACROMOLECULES FROM ACID-BASE TITRATION

The macromolecular nature of humic substances is well established, and cylindrical geometry appears most likely although molecular dimensions have not been published. Previous analyses of acid-base titrations of humic acids have largely ignored the macromolecular nature of the humic molecule and the effect of ionization of titrated groups on the hydronium ion concentration in the vicinity of untitrated groups. In this work, humic macromolecules are modeled as cylinders with surface potentials generated by the ionization of acidic groups. Based on data collected from titrations of two humic acids at ionic strengths between 0.001 and 0.100 M NaCl and numerical solutions of the Poisson-Boltzmann equation for surface potentials, the radii of ideal charged cylinders that would display the same titration behavior in response to humic charge density and ionic strength were calculated. The results of these calculations show that humic macromolecules have equivalent radii ranging from about 1.1 nm at 10% ionization to 0.24 nm at 90% ionization. This change in equivalent radius may be conceptualized as the quantitative expression of changes in configuration as a result of uncoiling and extension due to electrostatic repulsion among charged groups on the same molecule. The derived charge densities reach relatively constant values of 1.3 to 1.5 × 104 esu cm−2 at 50 to 90% ionization. The data also support the concept of at least two different weakly acidic groups with different acid strengths or a Gaussian distribution of acidic groups about a central pK value.

Chromatographic determination of commercial Fe(III) chelates of ethylenediaminetetraacetic acid, ethylenediaminedi(o-hydroxyphenylacetic) acid and ethylenediaminedi(o-hydroxy-p-methylphenylacetic) acid

Abstract The use of synthetic iron chelates is the most common and effective way to treat iron chlorosis in plants. Using an ion-pair HPLC method previously proposed by the authors, it was found that the older commercial products reached the percentage of Fe chelated indicated by the manufacturer, but in no case did the current products reach their nominal, or legal, composition. Moreover, the current products of Fe–ethylenediaminedi( o -hydroxyphenylacetic) acid (FeEDDHA) showed significant additional chromatographic peaks that, based on published synthesis pathways for these type of compounds, may correspond to para – para FeEDDHA or ortho – para FeEDDHA, sterically-hindered isomers of FeEDDHA which are of little or no value as an iron chelate for agricultural purposes.

Soil landscape models at different scales portrayed in virtual reality modeling language.

Most state-of-the-art manipulations and visualizations of soil data use geographic information systems to portray soil landscapes in two dimensions (2-D). Nevertheless, soil attributes are distributed continuously in three dimensions (3-D) across landscapes. The objective of this study was to investigate the use of Virtual Reality Modeling Language (VRML), a 3-D graphics language suitable for stand-alone or browser-based interactive viewing, to create 3-D soil landscape models at different scales. Four different locations in southern Wisconsin were selected to represent pedon, catena, catchment, and soil region scales. Soil data, including texture, cone index, and depth of soil layers, were used in conjunction with topographic attributes to create 3-D soil landscape models. Spatial modeling techniques comprised 2-D and 3-D ordinary kriging. We used Environmental Visualization Software (EVS) to export the geometry of 3-D objects, which were enhanced to include: (i) viewpoints, (ii) Munsell colors, (iii) texture maps, (iv) 3-D cross-section animation, (v) animations such as zooming and rotation, and (vi) primitive shapes to highlight areas of interest. Virtual reality modeling language is capable of describing and visualizing extremely complex shapes, such as complex soil layers or terrain. Visualization of Munsell soil colors was difficult to implement because there is no hardware or software independent color-management system available in VRML. Animation techniques were valuable to high-light specific characteristics of each model. The accessibility of interactive VRML models via the World Wide Web and the portability of these models across platforms facilitate the entry of soil science into the virtual world of cyberspace.

Optimization of an ecological model with the Marquardt algorithm

Abstract Optimization of parameters in ecological models can present many challenges, including multiple dependent variables on which to calculate fit, slowly converging search algorithms, nonanalytical derivatives, parameters constrained by their physical meaning in the model to a given sign or range, and excessively long run times for optimization calculations. The Marquardt algorithm has been restructured and an appropriate figure-of-merit function formulated to address these problems. As an example, a soil nitrogen and carbon transformation simulation model (NCSOIL) may be optimized for two and three unknown parameters within ten iterations or less, based on initial guesses of parameter values in error by an order of magnitude.

Measurement of pore size distribution in a lamellar Bt horizon using epifluorescence microscopy and image analysis

Abstract A staining technique suitable for epifluorescence microscopy of polished block surfaces was developed using proprietary dyes (Sanford Co.). The dyes greatly enhanced the contrast between particles and pores, thereby allowing, with only minimal processing, the production of images suitable for automated pore and particle size measurements. An algorithm, the “multi-directional minimum chord” (MDMC) method, was developed for measurement of pore size as it relates to the hydraulic properties of soils. Pore chord lengths were measured in two or more directions through a set of points on a grid. The smallest dimension was retained as being most representative of the effective capillary diameter, or hydraulic diameter, of the pore. Chord length distributions measured by the MDMC method were compared to those obtained by the unidirectional chord intercept method. These techniques were applied to a study of lamellar Bt horizon formation in sandy glacial outwash in the Anoka Sand Plain, Minnesota, U.S.A. The lamellae are nearly horizontal, occur from 0.6 to > 2 m depth, and vary in thickness from 0.5 to 6 cm. It was hypothesized that differences in pore size distribution initially present in the sands caused changes in soil hydraulic properties that may have been responsible for the initial formation of lamellae. Undisturbed samples containing lamellae and the underlying interlamellar horizons were collected using Kubiena boxes, oven-dried at low temperature, cast in resin, sawed in half, polished, and stained. Digitized images of lamellae and the uppermost part of the interlamellar horizons were taken using epifluorescence microscopy and then edited to remove clays to simulate conditions present before the formation of the lamellae. Pore and particle size distributions measured on the images by the MDMC method showed that significant differences existed between the lamellae and the uppermost part of the underlying interlamellar horizons. In all cases a coarser over finer pore size discontinuity existed at the bottom of the lamellar horizon, in support of the proposed mechanism for the initiation of lamellae formation.