Darrell G. Schulze

Purdue University West Lafayette

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U. Schwertmann

Technical University of Munich

Zamir Libohova

United States Department of Agriculture

João José Marques

Universidade Federal de Lavras

Nilton Curi

Universidade Federal de Lavras

Joshua Minai

Argonne National Laboratory

Phillip Owens

United States Department of Agriculture

Helge Stanjek

RWTH Aachen University

Don M. Huber

Texas A&M University

Mercy W. Ngunjiri

International Centre of Insect Physiology and Ecology

Terezinha Cássia de Brito Galvão

Spelman College

Cooperative Institutions

Purdue University West Lafayette

Technical University of Munich

State Street (United States)

Texas A&M University

University of Minnesota

Johnson Space Center

University of Molise

Universidade Federal de Lavras

The Ohio State University

Agricultural Research Service

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Book Reviews

Clays and Clay Minerals (2002)

Darrell G. Schulze

10.1346/000986002760832892

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Citations (8)

Correction of Mismatches in 2θ Scales During Differential X-ray Diffraction1

Clays and Clay Minerals (1986)

Darrell G. Schulze

10.1346/ccmn.1986.0340610

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Citations (17)

Spatial prediction of soil properties for the Busia area, Kenya using legacy soil data

Geoderma Regional (2021)

Joshua Minai Zamir Libohova Darrell G. Schulze

Digital Soil Mapping

Silt

Soil carbon

Soil test

10.1016/j.geodrs.2021.e00366

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Citations (9)

The influence of aluminium on iron oxides: XIII. Properties of goethites synthesised in 0·3 M KOH at 25°C

Clay Minerals (1987)

Darrell G. Schulze U. Schwertmann

Abstract Aluminium-substituted goethites were synthesised in 0·3 M KOH at either 25° or 70°C. The 25°C goethites had unit-cell a and c dimensions about 0·1–0·2% larger than the 70°C goethites of comparable Al substitution. Unit-cell b dimensions were similar regardless of synthesis temperature. The 25°C goethites contained larger amounts of Al in their structures than the 70°C goethites synthesised at the same initial Al/(Al + Fe) mole ratio in solution. The 25°C goethites had lower dehydroxylation temperatures and smaller differences between the two OH-bending bands than comparable 70°C goethites. These differences between the two sets of goethites are believed to be caused by the presence of more structural defects in the 25°C goethites than in the 70°C goethites. Goethites with the lowest Al substitutions consisted of crystals with several coherently diffracting domains, while at high Al substitutions the crystals were mainly monodomainic. Surface areas of the 25°C goethites varied in a complex manner as a function of thickness along [100], character of the domains, and physical size.

10.1180/claymin.1987.022.1.07

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Citations (81)

Reflectivity (visible and near IR), Mössbauer, static magnetic, and X ray diffraction properties of aluminum‐substituted hematites

Journal of Geophysical Research Atmospheres (1992)

R. V. Morris Darrell G. Schulze H. V. Lauer D. G. Agresti T. D. Shelfer

Because aluminum substitution for iron occurs in polymorphs of Fe 2 O 3 and FeOOH in terrestrial (and by inference Martian) environments, it is important for the mineralogical remote sensing of both planets at visible and near‐IR wavelengths to know the effects of Al substitution on their reflectivity spectra. Diffuse reflectivity (350–2200 nm), Mössbauer, static magnetic, and X ray diffraction data are reported for a series of aluminum‐substituted hematites α‐(Fe,Al) 2 O 3 for compositions having values of Al s . (mole ratio Al/(Al+Fe)) up to 0.61. Samples were prepared by oxidation of magnetite, dehydroxylation of goethite, and direct precipitation. Unit cell dimensions decrease with Al s but at a rate less than that predicted by the Vegard rule. At 293 K, Mössbauer spectra are sextets (negative quadrupole splitting, QS) for Al s up to ∼0.5 and doublets for larger Al s . At 21 K, all compositions are sextets; however, there is a discontinuity of ∼0.5 T in the magnetic hyperfine field (B hf ) and QS changes sign at Al s = 0.06(2) (Morin transition). Al‐poor compositions have positive QS and higher B hf . Negative and positive quadrupole splittings are indicative of the weakly ferromagnetic and antiferromagnetic states of hematites, respectively. The position of the least energetic crystal‐field transition ( 6 A 1 → 4 T 1g ) of ferric iron shifts to longer wavelengths with increasing Al s . The magnitude of the shift is a linear function of (1/a) 5 , where a is the hexagonal unit cell dimension. For geologically reasonable amounts of Al substitution (Al s < 0.33), the magnitude of the shift is small (∼20 nm), so that it is problematical (based on reflectivity data alone) to uniquely ascribe shifts in 4 T 1g band positions to different degrees of Al substitution. On the basis of Martian spectral data, the range in Al s for Martian hematites is 0 < Al s < 0.19.

Quadrupole splitting

Ferrimagnetism

10.1029/92je00455

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Citations (21)

Major element geochemistry and geomorphic relationships in Brazilian Cerrado soils

Geoderma (2003)

João José Marques Darrell G. Schulze Nilton Curi Stanley A. Mertzman

Trace element

Biogeochemical Cycle

10.1016/s0016-7061(03)00260-x

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Citations (114)

Predicting soil types and soil properties with limited data in the Uasin Gishu Plateau, Kenya

Geoderma Regional (2019)

Mercy W. Ngunjiri Zamir Libohova Joshua Minai C. Serrem Phillip Owens

Digital Soil Mapping

Topographic Wetness Index

10.1016/j.geodrs.2019.e00210

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Citations (13)

Evaluating the effect of tillage on soil structural properties using the pedostructure concept

Geoderma (2011)

Joseph Mallory Rabi H. Mohtar Gary C. Heathman Darrell G. Schulze Erik Braudeau

Soil structure

10.1016/j.geoderma.2011.01.018

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Citations (26)

Evidence for a naturally occurring post-glacial acid sulfate weathering event in northwestern Indiana, USA

Geoderma (2017)

Darrell G. Schulze Nils Charles Landin Phillip Owens James J. Camberato

Outwash plain

Bedrock

Jarosite

10.1016/j.geoderma.2017.06.006

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Citations (2)

Evidence of a Multicopper Oxidase in Mn Oxidation by Gaeumannomyces graminis var. tritici

Phytopathology (2006)

Ian A. Thompson Don M. Huber Darrell G. Schulze

ABSTRACT Manganese (Mn) oxidation by the plant-pathogenic fungus Gaeumannomyces graminis var. tritici has been correlated with virulence in take-all disease. The mechanism of Mn oxidation has not, however, been investigated adequately. Research on bacteria and other fungi indicates that Mn oxidation is most often the result of the activity of multicopper oxidases. To determine if G. graminis var. tritici oxidizes Mn by similar means, the Mn oxidizing factor (MOF) produced by G. graminis var. tritici was characterized by cultural, spectrophotometric, and cellulose acetate electrophoresis methods. Based on our results, the MOF is an extracellular enzyme with an estimated molecular weight of 50 to 100 kDa. Electrophoresis and spectrophotometry indicate that the MOF is a multicopper oxidase with laccase activity.

Multicopper oxidase

Take-all

10.1094/phyto-96-0130

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Citations (27)