Roberto R. Filgueira

Maximum compactibility of Argentine soils from the Proctor test;: The relationship with organic carbon and water content

Soil compaction is recognized as an increasingly challenging problem for the agricultural, horticultural and forest production in many climatic regions. The Proctor test provides a standardized method to study compactibility of disturbed soils over a range of soil water contents. The objectives of our study were: (a) to determine values of the critical water content for compaction and maximum bulk density from Proctor compaction curves for soils different in their properties; (b) to study the correlation between the maximum bulk density and readily available soil properties. Thirty soil samples were taken from six different locations in Argentina between 58 and 64°W and 34 and 38°S. The degree of saturation at maximum bulk density varied from 73.2 to 96.8%. Comparison of our data with data of two studies in USA showed that relationships between the maximum bulk density and the critical water content were similar to these studies. However, the slope of the relationship between the maximum bulk density and the organic carbon content was 50% less in our study as compared with the two others. The maximum bulk density was highly correlated with the organic carbon content and the silt content, the determination coefficient of the multiple linear regression, r2, was 0.88.

The microwave spectrum of pyrrolidine

Abstract The rotational spectra of the normal and N-D isotopic species of pyrrolidine have been measured. The molecule exists in an envelope conformation, with the nitrogen atom out of the plane containing the carbon atoms and with the imino hydrogen in the axial position. The analysis of the rotational spectra of two and three vibrationally excited states for the normal and N-D isotopic species, respectively, indicates that both barriers to pseudorotation and to the imino hydrogen inversion are relatively high. Additionally, the N(14) quadrupole coupling constants have been determined.

Sensitivity of fractal parameters of soil aggregates to different management practices in a Phaeozem in central Argentina

Abstract Changes in soil structure often accompany changes in management practices and may affect the effectiveness of these practices. Parameters are needed to quantify these changes. Our objective was to see if fractal dimensions derived from ‘aggregate bulk density–aggregate size’ and ‘aggregate number–aggregate size’ relationships could be applied to quantify such changes. The study was conducted at the Experimental Farm of the School of Agronomy and Forestry Engineering, National University of La Plata, Argentina. A Vertic Phaeozem soil was sampled at seven locations differing in long-term management practices. The ‘aggregate bulk density–aggregate size’ and ‘number of aggregates–aggregate size’ data were obtained for seven ranges of aggregate sizes. Differences in treatments were reflected by the fragmentation fractal dimension but not the mass fractal dimension. The lowest fragmentation fractal dimensions corresponded to plots under long-term no-tillage and the highest to plots with a history of cultivation of rice ( Oryza sativa L.) under water. The fragmentation fractal dimension reflected the differences in soil management whereas the mass fractal dimension appeared to be insensitive to those differences.

Contribution of macroporosity to water flux of a soil under different tillage systems

A importância da macroporosidade para o transporte de agua no solo faz a sua avaliacao de forma quantitativa uma tarefa desafiadora. Os valores da condutividade hidraulica (K) do solo em diferentes potenciais de retencao de agua no solo e a quantificacao de macroporos condutores de agua (θM) em diferentes sistemas de preparo do solo proporcionarao melhor compreensao dos efeitos no arranjo de poros e nas propriedades fisico-hidricas do solo. Dessa forma, o objetivo deste estudo foi avaliar os efeitos de um preparo convencional do solo com arado de aivecas (CT), com subsolador (CP) e utilizando um sistema com plantio direto (NT) sobre os atributos θM e K, bem como quantificar a contribuicao da macroporosidade para o fluxo total de agua em um solo franco. Um infiltrometro de tensao no solo foi utilizado para emitir duas pressoes ascendentes de agua (-5 cm e 0 cm) para inferir θM e K, durante o pousio. A macroporosidade foi determinada com base na contribuicao do fluxo entre os potenciais de agua de 0 e -5 cm (K0 e K5, respectivamente), de acordo com a equacao de Hagen-Poiseuille. Os valores da K0 obtidos foram estatisticamente superiores no preparo CT, quando comparados aos valores do NT e do CP. Os valores da K5 nao diferiram estatisticamente entre os tipos de preparo. Os valores medios da K variaram entre 0,20 e 3,70 cm/h. A quantificacao de macroporos condutores de agua (θM) foi significativamente superior para o preparo CT em relacao aos preparos CP e NT, seguindo a mesma tendencia da K0. Nao foram detectadas diferencas significativas dos valores de θM entre os preparos CP e NT. Utilizando o preparo CT, foi possivel a formacao de macroporos condutores de agua com persistencia ate a pos-colheita; ja no preparo CP, os macroporos condutores de agua nao foram persistentes. Os resultados apresentados sustentam a hipotese de que o sistema de preparo do solo escolhido altera o movimento da agua no solo, principalmente, devido a formacao de macroporos condutores de agua. Estudos futuros sobre o efeito do sistema de preparo relacionado ao movimento da agua no solo devem-se concentrar nas condicoes de formacao da macroporosidade do solo.

Using Tension Disc Infiltrometer to Determine Infiltration and Water-conducting Macroporosity and Mesoporosity Relationships in an Agricultural Silty Loam Soil

Measurement of soil hydraulic properties, such as hydraulic conductivity (K) and quantification of water-conducting macroporosity and mesoporosity (&thgr;ma, and &thgr;me), is important to improve the understanding of soil physical behavior. The aim of this study was to assess the effects of soil loosening on &thgr;ma and &thgr;me, as well as on K, and to relate the importance of &thgr;ma and &thgr;me to infiltration. The experimental design was completely randomized, with two treatments: (i) no tillage and (ii) conservation tillage (CnT). The soil was classified as a Typic Argiudoll, with a silty loam A horizon. A tension disc infiltrometer at three ascending soil-water pressure heads (−6 cm, −3 cm, and 0) was used to infer &thgr;ma, &thgr;me, and K at different water potentials (K6, K3, and K0, respectively), after harvest. The K values obtained for each tension were statistically greater for CnT than for no tillage. To summarize, mean values of K varied between 0.50 and 2.06 cm h−1. &thgr;ma and &thgr;me were statistically greater for CnT. Soil loosening created water-conducting macroporosity and mesoporosity that remained active after harvest. Saturated hydraulic conductivity, K0, was mainly influenced by &thgr;ma for both treatments. The influence of &thgr;ma on K0 was greater for CnT. This result indicates that the increment in K0 by soil loosening is mainly due to the creation of water-conducting macropores, supporting the idea that studies of effect of tillage on water movement should focus on macroporosity.

Stabilization of soil hydraulic properties under a long term no-till system

Nos ultimos anos, o sistema plantio direto (NT) tem aumentado. Alguns autores indicam que os atributos fisicos do solo ficam estaveis apos anos cultivando nesse sistema, sendo esse fato discutido por outros autores. O objetivo deste trabalho foi avaliar o efeito do ultimo cultivo apos a rotacao (1o ano: milho; 2o ano: soja; e 3o ano: trigo/soja) sobre a configuracao do sistema poroso do solo e das suas propriedades hidraulicas de diferentes tipos de textura (solo 1: franco; e solo 2: franco-arenoso) da regiao do pampa argentino, em NT por um longo prazo, para determinar se a estabilidade das propriedades fisicas do solo independe do momento da rotacao. Adicionalmente, foram comparados os procedimentos para avaliar a macroporosidade, bem como avaliada a eficiencia da funcao de pedotransferencia ROSETTA, para estimar os parâmetros do modelo de van Genuchten-Mualen (VGM) desses solos. A configuracao do sistema poroso do solo e as propriedades hidraulicas nao foram estaveis e se alteraram em razao da rotacao da cultura e do ultimo cultivo utilizado na rotacao em ambos os solos. Nos dois locais, a condutividade hidraulica do solo saturado (K0), a macroporosidade (ema) e o raio medio ponderado do poro por fluxo (R0ma) aumentaram do 1o para o 2o ano da rotacao de culturas e isso se atribuiu ao aumento de macroporos condutores de agua pra as raizes de milho. O modelo VGM descreveu adequadamente a curva de retencao de agua (WCR) nos dois solos, porem nao foi adequada para as curvas de condutividade hidraulica (K) vs tensao (h). A funcao ROSETTA nao foi eficiente para a estimativa dos parâmetros. Em resumo, os valores medios de K0 variaram entre 0,74 e 3,88 cm h-1. Com relacao as propriedades fisicas do solo no NT, o efeito do cultivo deve ser considerado.

Microwave spectrum and conformation of thiomorpholine

Abstract The microwave spectrum of normal thiomorpholine (CH 2 CH 2 SCH 2 CH 2 NH) was investigated within the region 8–40 GHz, and that of N -deuterothiomorpholine (CH 2 CH 2 SCH 2 CH 2 ND) within the region 26.5–40 GHz. The observed spectra are due to the chair equatorial conformers. The rotational constants of both isotopic species were determined for the ground states and for two vibrationally excited states. The dipole moment components and quadrupole coupling constants of normal thiomorpholine and the iminohydrogen r s coordinates were also determined.

Infrared and Raman matrix isolation spectra and molecular force field of disulfur dichloride

Abstract The infrared and Raman spectra of S2Cl2 isolated in Ar matrices have been investigated. In the SCl stretching region, three instead of two bands were observed. It was concluded that Fermi resonance is present between ν5 and (ν3+ν6). From the experimental band centers, 35Cl37Cl and 32S34S isotopic shifts and other additional data a molecular force field has been derived.

Sedimentación de partículas con distribución de tamaño fractal

Since several years the fractal fragmentation model has attracted the attention of researchers, as a logic way to describe and interprete observed particle size distributions. Textural analysis has shown to be very important because of its usefulness in the dignosis and inferences about soil functioning and use. Most popular methods of textural analysis employ sedimentation of particles in water using the hydrometer or the pipet. Both have the objective of determining the particle fraction remaining in suspension at predetermined time and to relate them with particle diameters. In the present work a new power law relationship between the mass fraction in suspension and the time was developed. Using this relationship it was possible to determine the fragmentation fractal dimension of a set of particles in sedimentation. The new equation has been checked with data obtained in this research by the Bouyoucoss hydrometer, and others published in the literature, using the Robinsons pipet method. The agreement between the model and the experimental data, using non linear regression, was excellent. Resulting fractal fragmentation dimensions ranged from 2.404 to 2.512, for samples from La Plata, Argentina, and between 2.434 and 2.819 for soils from California, USA. Determination coefficients, R2, were always higher than 0.9.

The centrifugal distortion constants for the molecule of thiane

Abstract The microwave spectrum of thiane has been studied in the 8- to 18-GHz region. Thirty five new rotational lines of the ground vibrational state with J up to 41 have been measured and assigned. These lines and a previous set reported by R. W. Kitchin, T. B. Malloy, Jr., and R. L. Cook [J. Mol. Spectrosc.57, 179–188 (1975)] have been used for the determination of the centrifugal distortion constants in Watsons model by means of a least-squares fitting method.