Isaac Barshad

Bio: Isaac Barshad is an academic researcher from University of California, Berkeley. The author has contributed to research in topic(s): Vermiculite & Montmorillonite. The author has an hindex of 13, co-authored 18 publication(s) receiving 653 citation(s).

Oxidation of ferrous iron in vermiculite and biotite alters fixation and replaceability of potassium.

Abstract: Oxidation of octahedral ferrous to ferric iron in soil vermiculite clays and biotites increases the potassium-fixation capacity of vermiculites and increases the difficulty of replacing interlayer potassium in biotites. This unexpected effect is believed to be related to an increase in the attractive forces between potassium ions and oxygen ions of the surface layers which is brought about by a tilting of the dipole of the octahedral hydroxyl ions from a perpendicular position to an inclined position with respect to the cleavage plane.

On digital soil mapping

Abstract: We review various recent approaches to making digital soil maps based on geographic information systems (GIS) data layers, note some commonalities and propose a generic framework for the future We discuss the various methods that have been, or could be, used for fitting quantitative relationships between soil properties or classes and their ‘environment’ These include generalised linear models, classification and regression trees, neural networks, fuzzy systems and geostatistics We also review the data layers that have been, or could be, used to describe the ‘environment’ Terrain attributes derived from digital elevation models, and spectral reflectance bands from satellite imagery, have been the most commonly used, but there is a large potential for new data layers The generic framework, which we call the scorpanSSPFe (soil spatial prediction function with spatially autocorrelated errors) method, is particularly relevant for those places where soil resource information is limited It is based on the seven predictive scorpan factors, a generalisation of Jenny’s five factors, namely: (1) s: soil, other or previously measured attributes of the soil at a point; (2) c: climate, climatic properties of the environment at a point; (3) o: organisms, including land cover and natural vegetation; (4) r: topography, including terrain attributes and classes; (5) p: parent material, including lithology; (6) a: age, the time factor; (7) n: space, spatial or geographic position Interactions (*) between these factors are also considered The scorpan-SSPFe method essentially involves the following steps:

Selective sorption and fixation of cations by clay minerals : A review

Abstract: Investigations concerning selective sorption and fixation of K and similar cations by clay minerals and soil clays and the mechanisms of these reactions are reviewed. In particular, recent observations on selective sorption of these ions in dilute solutions by weathered micas and vermiculite in relation to the interlayer structures are discussed in detail. Also, implications of the resistance to weathering of small mica particles to cation selectivity by soils are described. Despite the increased understanding of sorption and fixation reactions, the following aspects remain unclear. First, the mechanism of the collapse of alternate layers in vermiculite on K or Cs sorption has not been unequivocally established. Second, factors that impart stability to the central core of mica particles so that K extraction becomes progressively difficult are not known. Third, inability of Ca or Mg ions to expand interlayers of Cs-saturated vermiculite in contrast to K-saturated vermiculite is not completely understood.

A critical review of the conventional SOC to SOM conversion factor

Abstract: Use of a single factor for converting soil organic carbon to soil organic matter is challenged. The basis for this challenge arises from four sources: the original papers published in the nineteenth century, empirical studies published throughout the twentieth century, theoretical considerations of organic matter composition, and a consideration of what led to the popularity and general acceptance of the conventional factor. The conventional factor of 1.724, based on the assumption that soil organic matter contains 58% carbon, applies only to some soils or only to particular components of soil organic matter. Studies published since the end of the nineteenth century have consistently shown that the factor of 1.724 is too low for most soils. In a review of previously published data, the median value for the conversion factor was found to be 1.9 from empirical studies and 2 from more theoretical considerations. A factor of 2, based on the assumption that organic matter is 50% carbon, would in almost all cases be more accurate than the conventional factor of 1.724. A consideration of the possible variation in organic matter composition predicts a range of factor values between 1.4 and 2.5, a range that is narrower than empirical results at least in part because of the interaction between the methods used to estimate organic matter and soil composition. Convenience, authority, and tradition rather than strength of evidence are in large part responsible for the widespread acceptance of the conventional factor.